MasterThesis_DarioMarić_final

RHEIN MAIN UNIVERSITY OF APPLIED SCIENCES
WIESBADEN
HOCHSCHULE RHEIN MAIN
JOSIP JURAJ STROSSMAYER UNIVERSITY OF OSIJEK
FACULTY OF CIVIL ENGINEERING
OSIJEK
MASTER THESIS
TOPIC: OPTIMIZATION OF HYDROTECHNICAL SYSTEM
Wiesbaden, 25.07.2016. Dario Marić

RHEIN MAIN UNIVERSITY OF APPLIED SCIENCES
WIESBADEN
JOSIP JURAJ STROSSMAYER UNIVERSITY OF OSIJEK
FACULTY OF CIVIL ENGINEERING
OSIJEK
MASTER THESIS
TOPIC: OPTIMIZATION OF HYDROTECHNICAL SYSTEM
STUDENT: DARIO MARIĆ
MENTORS: Prof.Dr.-Ing. FALK SCHÖNHERR
Izv.prof.dr.sc. MARIJA ŠPERAC, dipl.ing.građ.
TOPIC DESCRIPTION:
For the purposes of designing new hydrotechnical system by using methods of
optimization synthesis, determine optimal configuration and optimal physical
parameters of the system in order to obtain its optimal usage.
Mentor: Student:
Prof.Dr.-Ing. FALK SCHÖNHERR Dario Marić
__________________ __________________

CONTENT
LIST OF FIGURES WITH SOURCES
1. INTRODUCTION ........................................................................................................................ 1
2. THEORY OF HYDROTECHNICAL SYSTEMS ................................................................................... 2
2.1. THE TERM HYDROTECHNICAL SYSTEM..........................................................................................2
2.2. APPLICATION OF HYDROTECHNICAL SYSTEMS THROUGHOUT HYSTORY.....................................4
2.3. OPTIMIZATION OF HYDROTECHNICAL SYSTEMS...........................................................................9
2.3.1 OPTIMIZATION SYNTHESIS....................................................................................................9
3. WATER SEWAGE SYSTEMS .......................................................................................................11
3.1. DEFINITION AND TYPES OF WASTEWATER ................................................................................ 11
3.1.1. SANITARY WASTEWATER .................................................................................................. 12
3.1.2. INDUSTRIAL WASTEWATER............................................................................................... 13
3.1.3. STORMWATER................................................................................................................... 13
3.1.4. LEACHATE WATER ............................................................................................................. 14
3.2. HYSTORICAL DEVELOPMENT OF SEWAGE SYSTEMS .................................................................. 14
3.3. TYPES OF SEWERAGE SYSTEMS .................................................................................................. 15
3.3.1. COMBINED SEWER SYSTEM .............................................................................................. 16
3.3.2. SEPARATE SEWER SYSTEM................................................................................................ 18
3.3.3. PARTIALLY SEPARATE SEWER SYSTEM.............................................................................. 22
3.3.4. COMBINATION OF SEPARATE AND COMBINED SEWER SYSTEMS.................................... 23
3.3.5. PRESSURISED SEWER SYSTEM........................................................................................... 24
3.3.6. VACUUM SEWER SYSTEM ................................................................................................. 27
3.3.7. OPEN CHANNEL DRAINS.................................................................................................... 29
3.3.8. SETTLED SEWER SYSTEM................................................................................................... 32
3.3.9. SIMPLIFIED SEWER SYSTEM- CONDOMINIAL SEWERAGE................................................. 34
4. DESIGN OF SEWER SYSTEM ......................................................................................................38
4.1. LOCATION................................................................................................................................... 38
4.2. SELECTION OF AN OPTIMAL TYPE OF SYSTEM ........................................................................... 46
4.3. DESIGN OF SIMPLIFIED (CONDOMINIAL) SEWERAGE ................................................................ 49
4.4. OVERVIEW OF PROGRAM ˝SIMPLIFIED SEWERAGE˝................................................................. 54
4.5. DEVELOPMENT OF MODEL USING PROGRAM ˝SIMPLIFIED SEWERAGE˝ ................................. 60
5. CONCLUSION...........................................................................................................................67
6. LITERATURE.............................................................................................................................68
APPENDICES

LIST OF FIGURES WITH SOURCES
Figure 1 – Hidrotehnički sustavi, lessons- Faculty of Civil Engineering Zagreb
Figure 2 – Osnove hidrotehnile i vodogradnje- Živko Vuković
Figure 3 – http://www.hadashot-esi.org.il/report_detail_eng.aspx?id=2208 (20.04.2016.)
Figure 4 – Environmental History of Water: Global Views on Community Water Supply and
Sanitation (20.04.2016.)
Figure 5 – http://www.hydriaproject.net/en/egypt-sadd-al-kafara-dam (20.04.2016.)
Figure 6 – http://www.indiawaterportal.org/articles/persian-wheel-water-lifting-device-
kolar-karnataka (20.04.2016.)
Figure 7 – https://en.wikipedia.org/wiki/Qanat (21.04.2016.)
Figure 8 – http://www.touropia.com/ancient-aqueducts/ (21.04.2016.)
Figure 9 – Hidrotehnički sustavi- Marija Šperac, Faculty of Civil Engineering Osijek
Figure 10 – Tušar Božena, Pročišćavanje otpadnih voda; Kigen d.o.o.; Zagreb, 2009.
Figure 11 – Odvodnja, lessons- Faculty of Civil Engineering Zagreb
Figure 25 – http://www.sswm.info/content/ (14.05.2016.)
Figure 36 – Duncan Mara: PC-based Simplified Sewer Design (18.05.2016.)
Figure 37 – http://www.un.org/waterforlifedecade/africa.shtml (03.06.2016.)
Figure 38 - http://www.citylab.com/design/2015/02/the-bright-future-of-dar-es-salaam-an-unlikely-
african-megacity/385801/ (03.06.2016.)
Figure 39 – Rural water demand: The case of Eastern Africa - Lessons from the Drawers of
Water II study
Figure 40 – http://www.trainsafaris.com/rovos-rail-dar-es-salaam.html (18.06.2016.)
http://www.zoomtanzania.com/warehouses-for-rent/industrial-open-space-at-vingunguti-
industrial-area-114075 (18.06.2016.)
Figure 41 – http://www.humanitariancentre.org/2013/11/opinion-simplified-sewerage-and-
africas-sanitation-crisis/ (10.06.2016.)
Figure 42 – Google Maps (18.06.2016.)

Figure 47 – http://www.citypopulation.de/php/tanzania-coastal-admin.php?adm2id=070208
(24.06.2016)
Figure 49 – https://cadmapper.com/ (18.06.2016.)
Figure 50 – https://cadmapper.com/ (18.06.2016.)
Figure 51 – Autodesk AutoCAD
Figure 52 – www.altitude.nu (24.06.2016.)
Figure 53 – Jean-Marie Ily, programme Solidarité Eau- Choosing and implementing non-
conventional sewers for the provision of sanitation services
Figure 54 – https://cambridgedevelopment.wordpress.com/category/engineering/
(24.06.2016.)
Figure 55 – Duncan Mara: PC-based Simplified Sewer Design
Figure 59 – Simplified Sewerage – program (University of Leeds)

1
1. INTRODUCTION
Simple and free access to adequate sanitation and sufficient amounts of safe
water for drinking and hygiene at homes, schools and health care facilities is essential to
human health and should be a primary prerequisite in the 21st
century. ˝Today, 2.4 billion
people in the world do not have access to basic sanitation. This is mostly related to population
that abide in Southern Asia (953 million) and Sub-Saharan Africa (695 million). Access to
basic sanitation facilities close to home is critical to maintaining healthy and safe populations.
Worldwide, 1.1 billion people currently defecate in the open. Open defecation helps diseases
and parasites spread and can contaminate drinking water supplies. Almost 1,000 children
under five die each day from diarrhea caused by inadequate water, sanitation and hygiene.
Without sanitation girls are more likely to drop out of school or are vulnerable to attacks
while seeking privacy. Recent analysis shows that ending open defecation can save children’s
lives by reducing disease transmission, stunting, and under-nutrition, which are important for
childhood cognitive development and future economic productivity.˝ 1
It is hard to imagine that in the 21st
century world is facing such problems and it is
even harder to accept considering the significant development of technology and science. Just
providing any kind of sanitation in the above-mentioned areas would decrease the number of
deaths and greatly enhance the quality of life. One of the problems for weak development of
certain regions and corresponding lack of primary life conditions is weak awareness and lack
of information about such situations in developed parts of the world.
This thesis intends to introduce sanitation sites in such areas, address its problems and
needs, show possible options and offer feasible solutions from engineering point of view.
Thesis will present the process of optimization of hydrotechnical system within the
boundaries of such specific locations or sites. It consists of both theoretical and practical
parts. In the theoretical part the term hydrotechnical system is described, its development
throughout the history, the method of optimization and its application to the system design.
From all types of hydrotechnical systems the water sewerage system is chosen and different
types are introduced and described in detail. At the end the location design is introduced with
specific requirements and restrictions. The practical part deals with system design for
specified location, development of the model and its analysis.
The main aim of this thesis is to introduce problems in specific regions, offer possible
solutions, use method of system optimization, and emphasize importance of hydrotechnical
engineering in solving such and similar problems.
1
Humanitarian Information Unit; World Water Day 2016: Urban Access to Sanitation

2
2. THEORY OF HYDROTECHNICAL SYSTEMS
2.1. THE TERM ˝HYDROTECHNICAL SYSTEM˝
Hydrotechnical systems can be defined as a group of hydrotechnical
constructions interrelated in functional unit with main goal to ensure better human activity on
water in order to satisfy human needs (water usage, water protection, protection from water,
etc.). According to constant increment of human needs connected to water and limited
amounts and quality of water, nowadays are used multifunctional solutions which can provide
satisfaction of needs just with proper planning of these solutions.
Hydrotechnical systems can be classified in several groups. According to
occurrence, hydrotechnical systems can be natural and artificial; according to interaction with
environment they can be open and closed; according to determination they can be determined
and stochastic; according to completeness the systems can be complete and reduced;
according to existence, they can be realistic and abstract; according to operability, systems
can be operable and non-operable; according to dynamics, systems can be static and dynamic;
according to stability, systems can be stable and non-stable; according to connections,
systems can be with or without feedback, and according to the method of functioning, systems
can be physical, technical and cybernetic. When occurrence is considered, hydrotechnical
systems are consisted of natural systems (land, terrain, hydrology, etc.) and artificial systems
(hydrotechnical constructions). 2
Figure 1 Scheme of terms consisted in expression ˝Hydrotechnical system˝
Important tendency for every hydrotechnical system is to be open, because
interaction with environment is significant for system as well as for environment.
Hydrotechnical systems are mostly stochastic systems, but are frequently used with
deterministic approach in order to obtain simplification with possible probabilistic
interpretation of final results. Generally, systems are reduced because mathematical analysis
2
Hydrotechnical systems- lessons, Faculty of Civil Engineering Zagreb
HYDRO
TECHNICS
SYSTEM
≈ WATER
- IN COMPOUNDS DEFINES
RELATION BETWEEN OTHER
WORDS AND WATER
- TOOLS AND KNOWLEDGE
WHICH WERE DEVELOPED
THROUGH HISTORY AND WHICH
PROVIDE HUMAN INTERACTION
WITH ENVIRONMENT IN ORDER
TO SATISFY HUMAN NEEDS
- GROUP OF ELEMENTS AND
PROCESSES MUTUALLY
CONNECTED INTO FUNCTIONAL
UNIT
HYDROTECHNICS
- TOOLS AND KNOWLEDGE
WHICH ALLOWS HUMAN
INFLUENCE ON WATER IN
ORDER TO SATISFY HUMAN
NEEDS

3
of system is often performed on several reduced systems where each system has a different
purpose. Every system should be constructed as a real, dynamic and operable system with
high stability in order to resist at any kind of environmental disorder. Development of society
guided specific evolution in development of hydrotechnical systems. Accordingly, the
development of hydrotechnical systems can be described in three phases. First phase is
characterised by period of water abundance, where mostly single-purpose, uncomplicated
systems are used in order to satisfy needs of several users in most economical way. Second
phase is characterised with increment of water usage and progressively decrement of water
quality and water resources, in general. Multipurpose systems were mostly used in this phase
and they could satisfy water needs for more and more users. In third phase of development,
people started to use complex systems with significantly exposed role of accumulation
volume. At the same moment high security level is implemented water quality protection is
taken care of. Water usage is restricted by long-term plans of usage rationalisation and with
relinquishment of old systems and technologies.
Characteristics of all hydrotechnical systems are similar: complex assignment,
spatiality and ramification, opposition of interests, asynchronous, complex safety problems,
economical problems, environmental influence, social aspects and stochastic nature of the
system.
Every hydrotechnical system can be described by mathematical expression. At
the highest level of abstraction, hydrotechnical systems ˝V˝ can be described with these three
terms:
 , ,rV Q K L (1)
where ˝Q˝ is a matrix that defines location of water, ˝K˝ is a matrix of water quality (chemical
and biological quality, temperature, water deposits, etc.) and ˝L˝ is a matrix that defines
spatial position of water resources in environment with x, y and z coordinates. These
components present total possibilities of resource usage.
Total possibilities of water system can be considered as a number of several
partial possibilities ˝Ei˝ that can be expressed as:
1
n
ii
E E
  (2)
where ˝n˝ (n > 1) is number of partial possibilities of water system.
Efficient part of total (theoretical) possibilities of water resource application, ˝Ek˝
is given by expression:
1
n
k i ii
E E
  (3)
where ˝ i ˝, (0 < i < 1) presents coefficient of efficiency for each possibility of partial water
resource usage.
The main goal of water management is to ensure maximum possible efficiency of
hydrotechnical system:

4
1
max
n
i ii
E
 (4)
Water systems can generally be divided in four groups that present main water
source activity: water usage, waterways planning and flood management, water protection,
organization and water management.3
Each of listed group consists of several fields of water
system usage that is well shown at Figure 2.
Figure 2 Categorization of hydrotechnical systems and fields of usage
2.2. APPLICATION OF HYDROTECHNICAL SYSTEMS THROUGHOUT
HISTORY
Water supply and water management in general have been the main challenges
from the beginning of civilization. In areas with poor water quality or insufficient water
resources, people experienced droughts, diseases and even deaths. This was the primary
reason why all the large civilisations were based near big water resources.
Initially, civilisations could only develop in areas that had plenty of water, such
as areas near large rivers. The first civilisations were established near to Euphrates, Tigris,
Nile, Indus, Ganges, Huang He, Amazon and others. With the passage of time, technology has
3
Hydrotechnical systems- lessons, Faculty of Civil Engineering Zagreb
WATER SYSTEMS
WATER USAGE
WATERWAYS
PLANNING AND
FLOOD
MANAGMENT
WATER
PROTECTION
ORGANIZATION
AND WATER
MANAGEMENT
FIELDS OF WATER SYSTEMS USAGE
- WATER SUPPLY
AND WATER
INDUSTRY
- AGRICULTURAL
IRRIGATION
- WATER ENERGY
USAGE
(HYDROPOWER)
- WATERWAYS
MANAGEMENT
- AQUACULTURE
- EXPLOATATION
OF CONSTRUCTING
MATERIALS FROM
WATERWAYS
- TOURISM AND
RECREATION
- SPECIAL USERS
(MILITARY ETC.)
- CHANNEL
RESTAURATION
- TORRENT AND SOIL
EROSION PROTECTION
- REGULATION OF
NATURAL
WATERWAYS
- RIVER BANKS
PROTECTION
- FLOOD PROTECTION
- WATER DRAINAGE
FROM URBAN AREAS
- AGRICULTURAL
DRAINAGE
- WASTEWATER
SEWAGE FROM
URBAN AREAS
- WASTEWATER
TREATMENT
- REGULATION AND
MANAGMENT OF
LOW FLOW WATER
- PROTECTION OF
ECOSYSTEM IN ALL
NATURAL AND
ARTIFICIAL
AQUARIUMS
- LONG-TERM
WATER SUPPLY
MANAGEMENT
- PLANNING OF
LONG-TERM WATER
POLICY
-REGULATION OF
WATER USAGE
- LEGAL
PROTECTION OF
WATER AND
ENVIRONMENT
- REGULATION OF
WATER LAWS AND
RESTRICTION
- INTERNATIONAL
WATER POLICY AND
COOPERATION

5
dramatically developed and thus has enabled to increase the distances water can cross in order
to satisfy human needs. Nevertheless, fresh and clean water that is usable is still dependent on
many factors, such as density and size of population or geographical location. In spite of high
technology, water conservation and protection needs to be on the highest level in order to
protect clean and proper quality water.
The human conscience about value and importance of water has gradually
increased during the history. People have thus moved from indirect activity to direct activity
with water. Because of natural impacts human race needed to learn how to overwhelm
problems connected with water protection and protection from water. The first great
inventions in water supply and sewerage (sanitation) were probably the wells and the toilets.
These two inventions needed to be applied in order to avoid many diseases to which people
were exposed. The main thing that makes these inventions very important is the fact that both
the wells and the toilets are still in use and will certainly be used throughout the future.
It is hard to point to the exact time and location of the first human-made well.
There are many remains of wells that still exist dating back to Neolithic era. For example, two
of them were found in Cyprus and Israel (Figure 3) and are assumed to be approximately
10,000 years old. The design of the first well was very simple. They were constructed with
dry-stone wall with diameter of 1.5 meters and depth of about 5.5 meters. Wells were
believed not to be mere water resource points. Wells were also used like gathering points,
border markers, places of worship and many other things.
Figure 3 Underwater remains of around 9500 years old well in ancient village of Atlit Yam,
Israel
Besides supply of fresh water, people needed to ensure dewatering of waste and
other used water. First demand was to ensure proper places for personal hygiene. That is well
shown in the example of the Bronze Age Minoan culture in Crete. In Knossos, capital city of
their former civilization, several different water systems for drainage, drinking water and
rainwater were discovered. Drinking water was transported from mountains 1.6 kilometres
away through clay pipes, which are the oldest existing ones and are approximately 4000 years
old. There were also many toilets that were using water to flush waste to the close river.
Besides toilets, this civilization had cisterns for collecting rainwater, and also separate
drainage systems that were sewing unnecessary rain water out from the town (Figure 4).

6
Figure 4 Minoan civilization toilet from Crete (left) and rain drainage (right)
First toilets were really simple and did not require particular construction; some
of them were just holes in the ground. Invention of toilets can be divided in two groups:
private toilets and public toilets. When mentioning public toilets it is important to say that
some of them were free of charge and some were not. Probably the best example for ancient
toilets is Rome. In Rome there were many public toilets; constructed as seats over running
water which took the wastes through the sewer network to the river Tiber. For private, home
toilets Romans used to have chamber pots that they emptied into the drain or in night soil
wagons that would carry the wastes to be used later for enrichment of the agricultural fields.
Besides first wells and sewerage systems, one of the first hydrotechnical systems
were simple dams constructed to protect people from adverse water impacts. One of the oldest
dams is ˝Sadd el-Kafara˝ dam in Egypt that dates around 2650 years B.C. It was never
completed because of devastation caused by the flood 10 years after the construction began. It
was an embankment, masonry dam with the purpose of flood control. The dam was 111
meters long, 14 meters high and 98 meters wide at the base and thus being the oldest dam of
this size in the world4
(Figure 5).
After development of wells, the first water transportation system involved hand
to hand or ‘human chain’ transportation from wells to the required place. Later people
invented systems that could mechanically transfer water from wells to the place of its need.
Example of such invention is ˝Sakia˝ or Persian wheel that was used for carrying water from
the wells in order to provide water for daily use and irrigation. The diameter of wheel was
around 5 meters and it dates back to 200 years B.C. First wheels were moved by human
power but gradually through the years people started to use the power of animals, wind and
water (Figure 6).
4
https://en.wikipedia.org/wiki/Sadd_el-Kafara

7
Figure 5 Sadd el-Kafara dam in Egypt, constructed around 2650 years B.C.
Figure 6 Example of Sakia wheel, simple water system for water transportation
When it is question of water supply systems, one of the oldest and most
interesting systems called Qanat was invented around 2500 years B.C. in Iran. It consisted of
wells and galleries mutually connected by tunnels with the main purpose of transporting water
from area with shallow water table to irrigated land. Persian people developed Qanats because
historically the Persians faced lack of water in many areas are were thus dependent on Qanats
for their daily water usage.5
Such systems were really hard to construct due to the high costs
and construction time but were necessary because of the afore-mentioned circumstances
(Figure 7).
5
https://en.wikipedia.org/wiki/Qanat

8
Figure 7 Schematic view of Qanat water supply systems developed during 2500 years BC
One of the most famous historical hydrotechnical systems ever invented were
aqueducts. The consistent provision of water has been one of the main tasks for areas that
experienced fast urbanisation. At the beginning of urbanization, people used water from
springs, lakes, creeks, rivers, wells or any other resource that was close to them. Later, towns
faced an explosion of the population growth that led to insufficiency of water and thus people
began to make a larger effort to secure enough water. For the problems of that time, aqueducts
were the perfect solutions because it was the first invention that could satisfy increasing
demand. The water could be taken from the source and transported to distant cities6
(Figure
8).
Figure 8 Aqueduct of Segovia, one of the best-preserved Roman monuments in Spain (50AD)
6
https://en.wikipedia.org/wiki/Roman_aqueduct

9
2.3. OPTIMIZATION OF HYDROTECHNICAL SYSTEMS
Optimization methods are formed to ensure the best values of system
configuration that will lead to the highest level of system performance. They can also be
defined as methods which provide explicit assessment of optimal operational decision, based
on clearly defined goals, in accordance with defined criteria and system restrictions.
Optimization model needs to have analytically defined objective function for validation of
every operational decision, and last decision should result in choosing of optimal solution for
that system. Optimal solution presents choice of most favourable option for system operation,
which does not mean that it needs to be optimal in every criterion. In the case of enormous
and complex tasks, method of sub-optimization can be taken. This method ensures gradual
improvement of final solution and all the processes in systems environment.
During the process of planning, complex hydrotechnical systems could reach
their optimum in just individual parts of that system. However, the optimization on that level
does not guarantee the achievement of the objectives for the system in global. It can even
undermine the realization of some of the main objectives for that system, so the optimization
of global system is not suggested just to sum up the optimums of sub-systems. Accordingly,
sub-optimization is a better method than sum of the sub-system optimums. To get the
acceptable solution it is important to follow the iterative process, with gradual correction of
sub-optimum.7
In the process of hydrotechnical system optimization, problem solving could be
divided in two main types of tasks:
- tasks of optimization analysis
- tasks of optimization synthesis.
Optimization analysis is used in situations when for the known system a
configuration is needed to find an optimal solution for system management. Mostly, this
method solves the problems of exploitation of existing systems. Optimization synthesis is an
operational method in case it is needed to find an optimal system configuration for optimal
system management, which means that it solves problems related with design of new
hydrotechnical systems.8
2.3.1. OPTIMIZATION SYNTHESIS
Tasks of optimization synthesis are significantly complex in comparison to
analysis tasks. It is mostly because for the optimal system management it is needed to
determine optimal system configuration and optimal system parameters, while tasks of
analysis are determining just optimal final system management.
For every optimal solution it is considered that answers on some questions are
known:
- What were the main objectives at the beginning of optimization?
- Under what criterion is the chosen solution optimal?
- Which system restrictions are taken into consideration in the process of optimization?
7
Water resources systems planning and management; Daniel P. Loucks, Eelco Van Beek
8
Hydrotechnical systems- lessons; Marija Šperac, Faculty of Civil Engineering Osijek

10
List of optimization synthesis tasks is presented in the diagram where the process of
choosing optimal solution with final affirmation of selected solution for that system is
described (Figure 9).
At the beginning of optimization for the new hydrotechnical system it is required to
identify problems related to that system. Considering the problems it is very important to set
the system objectives that will be followed throughout the whole optimization process. After
that it is possible to start with formulation of valuable system. The best way to accomplish
that is to create a mathematical model in which it will be easier to adjust all parameters until
optimal model is generated. If mathematical model shows that chosen solution is optimal, the
analysis of feasibility for chosen solution needs to be done.
At the end, the selected solution needs to be realistic and feasible under the systems’
local boundaries. If it is not, system goals need to be readjusted once again in order to form a
valuable system. And if mathematical model shows that chosen solution is realistic and
feasible, it is possible to start with realization of the chosen solution.9
IDENTIFICATION OF PROBLEMS
DEFINITION OF MAIN GOALS FOR THE SYSTEM
FORMULATION OF VALUABLE SYSTEM
IDENTIFICATION OF POSSIBILE SOLUTIONS OF
SYSTEM
CREATION OF MATEMATHICAL MODEL FOR CHOSEN SOLUTION
CREATION OF VALORIZATIONAL MODEL
OPTIMIZATION OF PARAMETERS FOR CHOSEN
SOLUTION
IS CHOSEN SOLUTION OPTIMAL?
ANALYSIS OF FEASIBILITY FOR CHOSEN SOLUTION
IS SOLUTION REALISTIC?
REALIZATION OF CHOSEN SOLUTION
Figure 9 Diagram of tasks and their correlation in optimization synthesis method
9
Hydrotechnical systems- lessons; Marija Šperac, Faculty of Civil Engineering Osijek
READJUSTMENTOFMAINGOALS
NO

11
3. WATER SEWAGE SYSTEMS
The words ˝sewage˝ and ˝sewer˝ are coming from Old French seuwiere that
means ˝channel to drain the overflow from a fish pond˝, or from Old North French sewiere
that means ˝sluice from a pond˝, or from Anglo-French sewere. The term ˝sewerage˝ also has
several meanings. It can mean a system of sewers, the removal of waste by using a sewer
system or sewage.10
Systems for drainage of wastewater are usually called sewerage systems, but
sewerage is also term for scientific-technical field that is related with proposing, designing,
constructing and using of sewerage network, wastewater treatment and water outlets into
environment. Sewerage network is mostly used for:
- collecting of wastewater in urban and industrial areas
- water drainage into water treatment facilities
- water treatment to the level that satisfies local conditions and law restrictions
- water outlet into convenient water receiver (Figure 10).11
Figure 10 Primary units of sewerage system
Sewerage network and objects on it need to be adjusted with water management
plans for certain watershed areas.
3.1 DEFINITION AND TYPES OF WASTEWATER
˝Sewage is the water that has been used by community and which contains all the
materials added to water during its use. It is thus composed of human body wastes (faeces and
urine) together with the water used for flushing toilets, and sullage, which is the wastewater
10
http://www.newworldencyclopedia.org/entry/Sewage
11
Tušar Božena, Pročišćavanje otpadnih voda; Kigen d.o.o.; Zagreb, 2009

12
resulting from personal washing, laundry, food preparation and the cleaning of kitchen
utensils˝.12
According to the definition, wastewater is a liquid waste consisting of everything
that somehow gets into sewage system. There are several types of wastewater. Fresh
wastewater is grey cloudy liquid that has earthy but harmless smell. Usually it consists of
large floating and suspended solids (faeces, pieces of clothes, plastic parts, etc.), smaller
suspended solids (partially dissolved faeces, paper, vegetable peel, etc.) and very small solids
in non-settleable suspension. An important fact to emphasize is that wastewater contains high
number of disease causing organisms called pathogens. Thus wastewater has to be transferred
from the settlements very early in order to prevent disease outbreaks or even deaths in some
cases. But transport of wastewater is not the only concern. Before wastewater is to be released
to the environment it should be treated up to level that is adequate for preserving natural water
resources. Urban wastewater can be classified in several groups depending on its occurrence.
3.1.1 SANITARY WASTEWATER
This group can be classified as a group that serves for supplying water to the
population. In the first instance, this is the wastewater that arises with the use of sanitary
devices in households, hotels, offices, restaurants, etc., and also in industrial and other
manufacturing objects where sanitary facilities exist.
Sanitary wastewaters are loaded with organic substance so their primary feature
is biodegradability – degradation by activity of microorganisms. Microorganisms are using
organic matter from wastewater as their nutriment, wherein oxygen is consumed. The
indicator of the amount of degradable organic matter in wastewater is biochemical oxygen
demand (BOD). For practical purposes, there is indicator of ‘five day biochemical oxygen
demand’ that occurs at 20 °C, and which is expressed in mg/lO2. In composition of sanitary
wastewater are also substances that interfere with biochemical substances and disorder
biochemical processes. Accordingly, the amount of organic matter in wastewater can be
expressed through indicator of ‘chemical oxygen demand’ (COD), in mg/lO2. The
composition and concentration of substances in water used in households, generally depends
on population lifestyle, climate change, amounts of available water in supply network,
development of system, etc.
Faecal wastewaters are nowadays very rare, and are mostly represented at
isolated objects that are poorly supplied with flushing water. In that case, ‘sanitary dry toilets’
are being built with main purpose to dispose only urine and faeces without using flushing
water. Sanitary wastewaters are different from industrial wastewaters, although are commonly
drained with the same channels. Sanitary wastewaters are full of organic matter and can be
classified in several conditions according to the level of biological degradation:
- fresh water – wastewater in which biodegradation is not progressed
- stayed water – water in which the level of oxygen is equal to zero. Oxygen is consumed
because of the biological degradation
- septic water – water in which biological degradation is in high progress and whole process is
anaerobic.
One should try to avoid appearance of septic water in channel system because of
its hazardous effects. Septic water can induce concrete corrosion and damages on sewage
system objects. With anaerobic degradation carbon dioxide (CO2) and hydrogen sulphide
12
Duncan Mara: Domestic wastewater treatment in developing countries

13
(H2S) are produced, which can later oxidize in water into sulphuric acid (H2SO4) and other
corrosive compounds. This can be avoided by bigger flow in channel, or higher velocities in
order to prevent sedimentation in sewage network.
The temperature of wastewaters is increased in comparison to supplying water
not only because of the usage of hot water in kitchens and bathrooms, but also because of
biodegradation process. Average wastewater temperature is 11.6 – 20.5 °C. By the increment
of temperature biodegradation processes are getting faster, leading to faster consumption of
oxygen and risk of water decomposition. This phenomenon is very important for summer
periods, especially in warmer climate areas. Besides chemical contamination, urban waters
are unpleasant in smell, taste and look, which cause additional contamination of network
aesthetically.13
3.1.2 INDUSTRIAL WASTEWATER
Industrial technological processes have mutually different characteristics, so
wastewaters from different processes are very different in their content. Generally, industrial
wastewaters can be divided into two main categories:
- Biological degradable or compatible waters (i.e. from food industry) that can be mixed
together with urban wastewaters from town, and drained with common sewage channels.
- Biological non-degradable or incompatible waters (i.e. from chemical or metal industry) that
need to be treated with some kind of wastewater treatment before being mixed with other
urban wastewater.
Industrial wastewaters need to be treated for several reasons. Firstly, the level of
toxic and persistent substances in water needs to be controlled because of biological
degradation. Secondly, to separate explosive, corrosive and flammable matters that can harm
sewage pipes and objects. Thirdly, to remove inhibitors those are disabling normal work of
devices for wastewater treatment. In practice, industrial wastewaters are commonly classified
in two groups – group of contaminated waters and group of conditionally clear waters.
Conditionally clear waters are the ones that did not sustain significant changes in chemical
and physical term.12
3.1.3. STORMWATER
Stormwater can conditionally be considered as clear water. By definition,
stormwater is the water that appears as a result of precipitation or snow melting. On its way,
storm water infiltrates atmosphere and collect all the substances that are somehow released in
the atmosphere or dispersed from distant areas by the wind. Examples of this appearance are
acid rains that destroy forests or red (bloody) and yellow rains that appear because of rinsing
of the desert dust, like in Africa. This problem can be regulated by controlled discharge of
pollutants.
Contamination of stormwater that drains from urban areas to public sewage
depends on many factors, such as: type of land cover, intensity and type of traffic, industry
influence, rainfall duration and intensity, air pollution, duration of drought periods before
rain, etc. Concentration of pollutants is changing significantly during the precipitation
13
Margeta J.: Kanalizacija naselja, Građevinski fakultet Split, 1998.

14
episode. For example, it is considered that just at the beginning of rain episode, concentration
of pollutants in that water is 10 times higher than in the last phase.
During long and intense rain episodes, that difference can be much bigger, even up to 20
times. According to level of BOD, first inflow is usually 2-5 times more burdened than the
last one.14
3.1.4. LEACHATE WATER
Leachate is water or a liquid that is produced when water percolates through any
permeable material. As a term connected with sewage, ‘leachate’ is considered as
underground, mostly clear water that is filtrated through layers of soil. It is a common
problem with objects located on hillsides or any kind of slopes and deep basements where
underground water drains to the objects. Approaching this problem is pretty simple. Leachate
need to be drained by special sewage system – drainage, and later dropped to the common
sewer system. The bigger issue can appear if leachate is filtrated through landfill that can
cause water contamination in sewage system if wastewater is not treated properly.13
3.2. HISTORICAL DEVELOPMENT OF SEWAGE SYSTEMS
Initially, rough sewage was dropped into a natural water resource, such as a creek, a
river or an ocean, where it would be rarefied and dissipated. The Indus civilization designed
sewage disposal system considerably impressive for that period by designing networks of
bricks where wastewater drains similar to the shape of the streets. The drains were two to
three meters wide, placed at 60 cm under the ground surface with U-shaped bottom made of
loose brick that could easily be removed for cleaning. At each intersection of two drains,
small underground tanks were installed with steps leading down for periodic cleaning. By
2700 B.C., these cities had standardized simplex plumbing pipes with wide flanges for easier
reparation in case of leakage.
In the prehistoric Middle East and the surrounding areas the first sanitation systems
ever made were found. Furthermore, in the palaces of Crete, Greece, first systems with
inverted siphons were found. They were covered with clay pipes that were still in working
condition, even after more than 3,000 years. In civilization of Ancient Minoans stone sewers
that were periodically flushed with clean water were used.15
Roman towns and settlements in the United Kingdom between 46 B.C. and 400 A.D.
had complex sewer networks. These systems were commonly constructed out of hollowed out
elm logs shaped in a way that they butted together with the downstream pipe providing a
socket for the upstream pipe. Areas with higher population densities and places that were
increasingly getting overpopulated needed more complex sewer collection and distribution
systems in order to ensure acceptable level of sanitary conditions for such cities. Furthermore,
the ancient cities of Harappa and Mohenjo-Daro of the Indus Valley civilization invented
complex networks of brick-lined sewage drains around 2600 B.C. These networks also had
outdoor flush toilets that were connected to the same network. The Indus Valley civilization
was the first that provided public and private baths. Their sewage system was constructed
with underground drains that were built with precisely placed bricks and had numerous
underground reservoirs. Drains from their houses were directly connected to wide public
14
According to: Margeta J.: Kanalizacija naselja, Građevinski fakultet Split, 1998
15

15
drains that can be related to present sewer systems. After that, current systems remained the
same without much progress until the 16th
century.
In England, Sir John Harrington invented a system that released wastes into cesspools
where they could easily be treated. For that and all further sewer developments and
inventions, significant discovery was the application of a network of sewers to collect
wastewater that began from the times of Indus Valley civilization. In some cities,
including Rome and Constantinople, initial networked sewer systems that remained from
ancient times continue to function today as supporting collection systems to modernized
sewer systems of those cities. But instead of flowing and disposing into a river or the sea, the
pipes have been redirected to the modern sewer treatment objects.
However, many cities throughout the history did not have any system to drain wastes
and relied on nearby rivers or occasional rain to wash away sewage. In some cities,
wastewater simply ran down the streets, where elevated stone bricks were installed to keep
pedestrians out of the mud and other sediments, which later resulted in appearance of many
serious diseases. This kind of drainage was satisfactory in early cities with few beneficiaries
but the increment of population and change of lifestyle quickly polluted streets and became a
main source of disease spread. Even in the 19th
century, consequences of inadequate sewer
systems could be seen. The sewerage systems in some parts of the highly industrialized
United Kingdom were so insufficient that water-borne diseases such
as cholera and typhoid were still common.16
In Merthyr Tydfil, a big town in South Wales, many houses had been discharging their
sewage into individual cesspits that constantly overflowed causing the pavements to be
flooded with dirty and smelly sewage. Afterwards, the usage of sewer beds helped to prevent
appearance of new diseases. A sewer bed is a piece of land typically used by a municipality
for the unloading of coarse wastes. In that period, raw sewage was transported by truck or
drawn by horses to be dumped into these beds, but the practice stopped back in the 1940s.
Latterly, sewage networks for collecting household sewage and transporting to the treatment
facilities was shown to be an optimal decision in prevention of diseases and solving problem
of pollution. This was the beginning of systems that can be seen nowadays.17
3.3. TYPES OF SEWERAGE SYSTEMS
Sewerage systems can be divided in several groups. By principle of collection,
sewerage systems can be classified as combined, separate, above ground/underground. By
principle of wastewater transport, sewerage systems can be classified as gravity, pressure or
vacuum. However, sewer systems in general can be categorised as:
- combined sewers
- separate sewers
- partially separated sewers
- combination of separate and combined sewers
- pressurised sewers
- vacuum sewers
- open channel drains
- solids free sewers (settled sewers)
- simplified sewers (condominial sewers).
16
Environmental History of Water - Global views on community water supply and sanitation; Petri D. Juuti,
Tapio S. Katko, Heikki S. Vuorinen
17

16
3.3.1. COMBINED SEWER SYSTEM
Combined sewer system collects all types of wastewater that appear at watershed
area and transport them together in same pipes to the water treatment plant after which water
is released to water recipient. This type of sewage system can also be described as a system
with large network of underground pipes that transmit domestic wastewater, industrial
wastewater and stormwater runoff in the same pipe to a centralised treatment facility. These
systems can be found mainly in urban areas and usually do not require on site pre-treatment or
storage of the wastewater. During the design of sewage network it is desirable to consider
location topography in order to ensure gravitational flow in sewage pipes. Likewise, it would
be beneficial to do the pre-validation of water to establish quality and composition of water in
order to avoid possible adverse effects to sewage network. In case of low quality water, it is
possible to do the pre-treatment of industrial wastewater.
Legend:
1. Secondary sewers
2. Main collecting sewer
3. Main discharge sewer
4. Wastewater treatment plant
5. Outlet
- - - - Borders of sewer system
A, B, C – Industrial facility
Figure 11 Schematic view of combined sewer system
Figure 12 Detail of wastewater acceptance in sewage pipes
STORMWATER HOUSEHOLD WASTEWATER INDUSTRIAL WASTEWATER
PRE-TREATMENT
WASTEWATER TREATMENT
PLANT

17
In Figures 11 and 12 is shown combined sewer system of urban sewage with
outlets of untreated wastewater and stormwater that drain together during precipitation.
According to designed capacity of water treatment plant, most of the combined wastewater is
released over the rain overflow during wet weather events (Figure 13). In period without
stormwater in projected system flows just sanitary wastewater with whole volume to the water
treatment plant.
Figure 13 Section of rain overflow during the drought and rainy season
In combined sewer system maximum hydraulic load is produced by stormwater.
Because of this, hydraulic dimensioning of sewage pipes is done according to relevant
precipitation. In dry period, flow in pipes is evidently decreased which can result in
sedimentation of solid particles. Therefore, channels with special shapes are used to ensure
critical velocities even in dry periods. Because the wastewater is not treated before it is
conveyed in the pipes, the sewer need to be designed in way to ensure self-cleansing velocity
which is generally obtained with a minimal flow of 0.6 to 0.75 m/s. Likewise, along the whole
length of sewer should be ensured constant downhill gradient in order to keep self-cleansing
velocity on proper level. In case of insufficient slope gradient, sewer should have installed
pumping station. About the network design, minimal depths of the primary pipes that are laid
beneath roads should be from 1.5 to 3 m to avoid damages that can appear because of traffic
loads (Figure 14).18
Figure 14 Detail of typical sewer position in road profile
18
Sustainable Sanitation and Water Management Toolbox
SANITARY WASTES
STORMWATER
DROUGHT SEASON RAINY SEASON
ROAD ROAD

18
Manholes as main access points on network should be installed at pipe
intersections, at changes of direction and diameter, at drops and at regular intervals along the
network.
As combined sewer system conveys stormwater and sanitary water in same pipe
network it is needed to take care about water level in pipes. If stormwater overflow is not
ensured, it can easily come to profile fulfilment which can result in later network blockage,
appearance of road floods and many further problems on whole system. Possible water levels
are shown in Figure 15.
Figure 15 Level of wastewater in sewage channel in droughts (left) and hard rain season
(right)
From economic aspect, initial cost of combined systems is quite high.
Maintenance costs are also extreme compared to decentralised systems because frequently
inspections, unblocking and repair of network damages are pretty common and even
extension of the system can be difficult and expensive (Table 1).
Table 1 Advantages and disadvantages of combined sewer systems
ADVANTAGES DISADVANTAGES
Low health risk High capital costs
Stormwater and wastewater can be managed at
the same time
Need a reliable supply of piped water
No problems related to discharging industrial
wastewater
Difficulties with constructing in high-density
areas, difficult and costly to maintain
Moderate operation and maintenance costs Difficulties with recycling of nutrients and energy
Convenience- minimal intervention by users
Unsuitability for self-help, requires skilled
engineers and operators
No problems with smells, mosquitoes or flies Frequently problems with blockages and
breakdown of pumping equipment
Adequate treatment and/or disposal required
According to: Sustainable Sanitation and Water Management Toolbox
3.3.2. SEPARATE SEWER SYSTEM
Separate sewer systems are designed to convey mostly two separate channel
sewers, but it is also possible to convey more of them. One network usually conveys sanitary
wastewater (wastes from households and industry), while another network is used for
transportation of stormwater. In view of the fact that stormwater was, until recently,
considered as just slightly contaminated or almost clear water, sewers for stormwater were
usually designed to transfer water by shortest possible route to recipient. Nowadays, it is well
known that stormwater from the first rain includes significant pollution so it is necessary to

19
remediate the quality of water at some receivers. Figures 16 and 17 show one separate
sanitary and stormwater sewer system.
Legend:
1. Secondary sewers
2. Main sewers
3. Main discharge channel
4. Stormwater outlet
6. Purified wastewater outlet
_______ Wastewater sewers
- - - - - - Stormwater sewers
Figure 16 Schematic view of separate sanitary and stormwater sewer system
Figure 17 Detail of wastewater flow in separate sewage system
Sanitary wastewater and stormwater flow in separated pipe networks, where
stormwater is mostly discharged without any pre-treatment while household sanitary
wastewater is treated together with industrial water. One part of industrial wastewater can be
transferred to stormwater sewage network over rain overflows during the rainy season but it is
not mandatory. As it is already mentioned, in such systems stormwater is usually drained in
receiver without any pre-treatment. But because of cognition about quality of stormwater
nowadays, it is desirable to ensure stormwater treatment before its discharge. Sanitary
wastewater is completely transferred to water treatment facilities. In these facilities it is
possible to adjust water flow in order to achieve better results of water purification. Besides
other advantages, one of the most significant advantages is better possibility in view of
dimensioning and operation of sewer system. Separate sewage systems are usually designed
with two separate networks, one for stormwater and one for sanitary wastewater. But in some
INDUSTRIAL WASTEWATER
WASTEWATER TREATMENT PLANT
STORMWATER HOUSEHOLD WASTEWATER

20
cases it is possible to construct separate system with more networks. For example, in urban
areas with highly developed industry that produces big amounts of industrial wastewater
daily, it is possible to construct separate network for just industrial wastewater with its own
treatment facility (Figure 18).
Figure 18 Detail of separate sewage system with three separated network; (1) stormwater, (2)
sanitary wastewater and (3) industrial wastewater
Certainly, industries can also have their own separated pre-treatment facility that
purifies wastewater until certain level and after that discharges it to sewer network so it could
easily be treated in common facility afterwards. Also, big industries can perform
redistribution of industrial wastewater which can result in reuse of wastewater that is not very
polluted for industrial purposes and after that discharge to specific sewer network (Figure 19).
Legend:
1. Stormwater
2. Household sanitary wastewater
3. Polluted industrial wastewater
4. Conditionally clear industrial
wastewater
5. Water pumping station
6. Cooling water facility
7. Drainage of excess water
8. Industrial wastewater treatment plant
9. Household wastewater treatment plant
Figure 19 Detail of separate sewage system with three separated networks and partial
redistribution of industrial wastewater
Separate sewage systems can be complete or incomplete. Complete separate
sewage system is the one that drains every kind of wastewater that is formed on watershed
with two or more channel networks. Incomplete separate sewage system is a system where
stormwater is drained by open channels (gutters or side ditches). Mostly, it is just first phase
of constructing sewage system which will later become separate sewage system.
Design approach is similar to combined sewer systems, sewers under the road
need to be laid on the depth of 1.5 to 3 meters in order to avoid damages from traffic load.

21
Difference is in fact that stormwater and sanitary water is conveyed with separated networks
so pipes for sanitary water should be laid even on greater depth under the stormwater pipes
(Figure 20).
Figure 20 Detail of typical separate sewer position in road profile
The construction costs are usually higher than for the combined sewer system
because separate systems require at least two separated networks. Another positive
characteristic of this system is high level of hygiene and comfort what is nowadays an
important item. The applicability of separate system is mostly same as applicability of
combined sewer system that means that system is suitable for urban areas with resources to
implement, operate and maintain the system. This kind of system is appropriate when a
centralised treatment facility is available and especially suitable in areas where irregular and
heavy precipitation is expected in order to avoid common overflows that may appear in
combined sewer systems (Table 2).
Greywater, blackwater and surface runoff can be
managed separately
Needs a reliable supply of piped water
No risk of sewage overflow Difficult to construct in high density areas
Minimal intervention by users Difficult and costly to maintain
Low health risk
High capital costs, more expensive than
combined sewer system
No problems with smells, mosquitoes or flies Requires skilled engineers and operators
No problems with discharging industrial
wastewater
Problems associated with blockages and
breakdown of pumping equipment
Reasonable operation costs Need for pumping on flat ground
Surface runoff and rainwater can be reused
Adequate treatment and/or disposal required for a
large point source discharge
SANITARY WASTES
STORMWATER

22
3.3.3. PARTIALLY SEPARATE SEWER SYSTEM
The same like separate, partially separate sewage system is composed of
individual sewer networks for stormwater and wastewater. However, for stormwater special
objects transferring first flows of stormwater directly to wastewater network are installed on
network. Then this water is taken to wastewater treatment facility and rest of the stormwater
is directly discharged to the recipient (Figure 21).
Legend:
1- Pipe for stormwater 2- Pipe for sanitary wastewater
Figure 21 Objects – manholes on partially separate sewage systems
This kind of system is designed to take stormwater and sanitary water with
different sewers and selectively convey stormwater to water treatment facility. From the view
of water protection in recipient, this kind of system is preferable than classic separate sewage
system, because water from road cleaning and first rain runoff is directly comprised of
wastewater and directed to municipal wastewater treatment plant. The complete schematic
view with water flow detail is shown in Figures 22 and 23.
Legend:
1. Secondary channels
2. Main collecting sewers
3. Main discharge sewage
4. Rain overflow
7. Purified wastewater outlet
_____ Channels for sanitary wastewater
- - - - - Channels for stormwater
Figure 22 Schematic view of partially separate sewer system
LAYOUT CROSS SECTION CROSS SECTION

23
Legend:
Q1- Stormwater transported to water treatment plant
Q2- Stormwater without any treatment
Figure 23 Detail of water flow in typical partially separate sewer system
Partially separate sewage systems have many advantages in the view of sewer
system maintenance, because at the moment of stormwater inflow into the pipes, large amount
of stormwater with greater velocity is formed that ensures sewer pipes purification. In this
kind of system it is necessary to construct both networks at the same time, in a way that
network for sanitary wastewater is constructed beneath the stormwater network and thus
basement rooms could be easily connected to the same network.
3.3.4. COMBINATION OF SEPARATE AND COMBINED SEWER SYSTEMS
Sewer system that is combination of separate and combined sewer system is
mostly a result of settlement expansion in which combined sewage was already constructed.
In that case, combined sewage will be retained for the old part of settlement and separate
sewage will be designed for the new part. For stormwater special channels with direct outlet
into recipient (with conditional treatment) are usually constructed. In large cities it is possible
to form several of these areas with described sewage system.
Some of the possible reasons for combination of these systems are lack of usable
space for installation of desired system and total costs for that system. Also, during the
extension of existed system, important item is requirements and consent of system users. If
they are not satisfied with existed system or if that system turns out to be not a good decision,
system extension can be designed by following user’s requests what is one of the another
reasons for usage of combination of separate and combined sewer systems.
This kind of system is well described in Figure 24 where two different areas are
shown, Area A with already existing combined sewage system and area B with newly
designed separate sewage system. This kind of system is usually never designed completely
like combination of systems. It is always a result of upgrade or extension of an already
existing system.19
19
Tušar Božena, Pročišćavanje otpadnih voda; Kigen d.o.o.; Zagreb, 2009
SANITARY WASTESSTORMWATER INDUSTRIAL WASTEWATER
WASTEWATER TREATMENT PLANT

24
Legend:
A- Area with combined sewer system
B- Area with separate sewer system
───── Combined sewer channels
─ · ─ · ─ Sanitary wastewater channels
─ ─ ─ ─ Stormwater channels
2. Rain overflow
3. Waste water treatment plant
4. Outlet to recipient
Figure 24 Detail of water flow in typical partially separate sewer system
3.3.5. PRESSURISED SEWER SYSTEMS
If new sewer system needs to be designed for small settlements or even parts of
settlements that are dealing with small amounts of wastewater, it is suggestible to construct
pressurised sewer system. Because of economic and construction conditions, design of such
system is favourable in specific local boundaries:
- in plain areas where installing pumping stations to ensure proper velocities or pipe gradient
is required
- in areas with high groundwater level
- in unstable soil areas (landslides)
- in hilly, rocky or densely populated areas
- in water protection areas.20
System of pressurised sewage is most similar to separate sewage system and first
usage of such system dates to early 1970-s. Primary sanitary effluent is gravitationally
conveyed to the collection tank where it is grinded and transported into pressurised system by
pumps. Accordingly, pressurised system is consisted of house collection tank with pump,
house pressure connection port, common pressure network and proper pumping stations on
network. Usually, items for pressurised sewage for one household are placed in a pit. That pit
contains of a grinder and a pump or a settling unit (septic tank) connected to a holding tank
with a pump that is installed close to the user (Figure 25). Because of the fact that
conventional sewer systems transport wastewater and sludge by traditional gravity way, it is
required to ensure a slope and pumping station. This can lead to high construction costs in flat
20

25
or hilly terrains. In some cases, a conventional system is almost impossible to construct,
because of previously listed conditions.
Pressurised sewage does not depend on gravity to transport effluent, thus there is
almost no concern about the local topography. Moreover the whole sewer network can be
constructed with relatively small diameter pipes that can also be laid in shallow ditches.
However, this type of sewage requires many pumps relying on electricity supply and that
makes the system more inclined to failure. Also, important thing is that pressurised systems
are affordable only if they are ordered by local topography. In other cases, simplified or
conventional systems may be preferable. The operation principle of pressurised system is
shown in Figure 25. A principal item for a network of pressurised sewers is that each
connection has a special tank that receives wastewater from every household. At the point
when tank fills to a set mark, a pump placed in the tank basin injects the wastewater beyond
into the sewer network. This transfer of wastewater pressurises the sewer. As various pumps
along the complete length of the network inject wastewater into the line, that water is
progressively moved to the wastewater treatment facility.
Figure 25 Schematic view of pressurised sewage system
From the economic point of view, pressurised sewage results in high capital
costs, which are still lower than gravity sewer system. These costs include the pump, basin,
controls, electrical service and system installation (Figure 26). According to SWPA,
operational costs for a typical residential station can be less than $3.00 per month.
Figure 26 Detail of prefabricated pressure sewer made for outside placement

26
All mentioned system components should be regularly serviced and electricity
should be available all the time. The pumps in network should be frequently checked and the
pipe connections need to be controlled for leakages. How frequently system should be
checked is determined by wastewater volume, relative risk to public health, influence to
environment and complexity of installed components.
The alternative for the described unit where all components are inside one tank is
to first install septic tank that can be placed in the basement of a building or outside in the
yard (Figure 27). Thus effluent flows in an underground septic tank from where it is delivered
by pumps into the pressurised sewer system ant further transferred to treatment facility.
Positive item is that pump in this system does not need to be as powerful as grinder pumps,
since it pumps just liquid and not solids.
Figure 27 Detail of underground septic tank with installed effluent pump
The total cost of a pressure sewage system can be divided in two main groups.
First group includes the pump, basin, control system, building sewer, lateral pipes, electrical
service and installation. Second group includes all the piping in the network that directs the
wastewater to the treatment facility. Another positive thing for this system is that to improve
efficiency the system can be installed in previously existing sewage systems of different
types. Preview of summarised system advantages and disadvantages is shown in Table 3.
Independent from land topography Needs an expert design
Effective wastewater transportation at minimum
depth, minimising excavation for piping system
Needs a permanent energy source for the grinder
pumps
Less costs compared to a conventional systems High capital costs
Requires small amounts of water only for
transporting the excreta
Requires skilled engineers and operators

27
3.3.6. VACUUM SEWER SYSTEM
Vacuum sewer systems showed up from the same reasons like pressurised
sewage systems. For low density population areas and settlements which are dealing with
small amounts of wastewater and which are also restricted with topography conditions,
pressurised and vacuum sewage systems found their optimal usage. Unlike gravity sewage,
vacuum sewers use differential air pressure that is also known as negative pressure for
transporting wastes. However, in vacuum sewage, wastewater is also conveyed gravitationally
to the collecting tank. The main source of power that is needed for operating vacuum pumps
is required to preserve proper level of negative pressure on the collection system. This kind of
system requires closed vacuum/gravity interface valve at every entry point to fasten the
network line so that the same level of negative pressure can be preserved. Usually, these
valves that are placed in special valve pits open up when a predetermined amount of
wastewater is accumulated in collecting tanks. The resulting differential pressure between
vacuum and atmosphere is the main force that transports the wastewater to the vacuum
station.21
Figure 28 Detail of underground septic tank with installed effluent pump
The whole process of vacuum sewage transportation is described in Figure 28.
As already mentioned, traditional gravity line carries wastewater down to the collection
chamber and as soon as the wastewater reaches predetermined level, the vacuum interface
valve opens and the negative pressure sucks the wastewater into the vacuum sewer main. At
the end of the pipe system, water is discharged in the collection tank. Furthermore, when the
tank fills to its predetermined level, sewage pumps transfer the wastes beyond to a water
treatment facilities by a conventional or separate sewer system. Important thing to mention is
that the collection system needs to be held on permanent level of vacuum all the time. The
important component of vacuum sewage for every household is collection chamber. The
household wastes are deposited in collection chambers that are placed together with
pneumatic valves close to houses. When particular level of water is provided, a hydrostatic
pressure activates pneumatic controller.
21

28
This controller then opens an interface valve for a predetermined time period.
The wastewater together with certain amount of air (10-50 litres of water and 20-60 litres of
air) is sent through the open valve further to the vacuum sewer line. The pressure gradient
between the atmospheric pressure at the collection pits and the vacuum station is responsible
for the movement of wastewater to the vacuum tank. All the vacuum sewage pipes are
connected to the vacuum collection vessel. Usually, this vessel is placed inside the central
vacuum station, but in some cases it can also be buried outside the station. Dimensions and
capacity of such vacuum station are directed by the requirements of corresponding sewer
system where they are installed. Vacuum pumps inside of central station create negative
pressure that is around -0.6 bars, and are usually controlled by software.22
In comparison to traditional gravity sewer pipes, piping for vacuum sewage is
cheaper and less complicated to construct. Due to the fact that effluent is conveyed by the
power of vacuum, no pumping stations or manholes are needed. Instead of manholes, this
kind of network requires just service or inspection points for pressure testing. Because of the
vacuum, there is no settling of mud that enables usage of smaller diameter and also trenches
are shallow and narrow. Usual diameter for vacuum sewers is from 80 to 250 mm and the
trenches are placed at a depth of 1.0 to 1.2 m, which is also an advantage for areas with high
groundwater level. Velocity of wastewater flow in such sewers is about 3 to 5 m/s. In the case
of pipe damage, the risk of the wastewater infiltration is low because of negative pressure in
the network. For designing this system professional knowledge is required but installation and
construction work can be done by local constructors and pipe suppliers. Because of low depth
of pipes placing, no heavy machinery is mandatory which in turn also reduces the total costs.
System cost depends on the size of the networks and the installed components.
Considering high-tech components used in this system it is costly. But if it is compared to
conventional sewer systems it is still much cheaper. Because of small diameters, piping costs
are lower. Furthermore, low depth of ditches results in avoidance of heavy machinery and low
excavation costs. At the end, great amounts of water for flushing can be saved which is
ecologically and economically reasonable. On the other side, constant electrical energy
requirement increases the total system costs.
Another positive characteristic of this system is that the risk of network blockage
is really low and there is no need for cleaning or emptying any parts of network. From the
view of system maintenance, vacuum pressure in sewers should be frequently checked.
Complex and technical problems are the responsibility of the manufacturer so that the system
can be maintained only by instructed workers without the constant help of experts. Due to the
fact that this is a closed system, there is almost no contact between operators and effluent.
Also, risk of environment contamination, damages or leakages is very low. As long as the
system is designed, constructed and maintained properly, it enables high level of hygiene and
comfort. However, wastewater treatment at the end of the network needs to be ensured.
Generally, this kind of sewer system is most acceptable in areas where water
drainage is needed but other options are too expensive or not realizable. For example, in areas
where poverty is highly expressed or in areas with short supply of potable water, gravity
systems are often not applicable. Because vacuum system relies on the negative pressure,
flushing velocities does not depend of the volumes of used water, which is optimal for such
areas. Other advantages and disadvantages are listed in Table 4.
22

29
Table 4 Advantages and disadvantages of vacuum sewer systems
Requires less water to sewage transport Needs expert design
Shorter construction period and savings in
construction costs
Needs energy to create the permanent vacuum
Shallow and narrow trenches, small diameter
pipes with flexible pipeline construction
Relatively high capital costs
Sewer and water supply network can be placed in
a common trench
Difficult possibility of nutrients and energy
recycling
Closed systems with no leakage or smell Treatment plant required at the end of network
No manholes along the network It depends on centralised system
One central vacuum station replaces several
pumping stations
3.3.7. OPEN CHANNEL DRAINS
Open channel drains are generally used for transportation of stormwater and
often exist in most urbanised areas. The recipient for such systems in many cases is river or
even agricultural irrigation channel. In a lot of middle to low-income countries unauthorised
discharge of domestic wastes in the system happens which leads to surface water pollution
and appearance of diseases. However, in areas without any sewage infrastructure, drainage of
wastewater into such systems can be optimal temporary solution. To avoid blockages and
uncontrolled discharge of litter and solids into the system, concrete slabs can be used to cover
open drains. The most simple and basic way to drain stormwater is by using open channel
drains. Collected stormwater has the possibility to increase agricultural production in rural
areas. It can also be very helpful in urban areas where it can refill freshwater resources after
natural pre-treatment. For example, treated stormwater is discharged into sea, lake, river or
any another water body. That water is clear enough to be discharged and mixed with existing
water and at the same moment it replenishes this water resource that is helpful for water
management of that area.
Network of open channel drains is mostly consisted of secondary drainage
system with attached network of small drains (micro drainage). Each of them is
predetermined for a small catchment area that can range from single house property to several
blocks of houses. These small drains (as secondary drains) convey the water to the primary
drainage system, which is composed of main drains. These drains usually serve large areas
and mostly are connected with natural drainage channels like streams or rivers. The design of
channel for this system differs from area to area, depending on many factors. On a steep
terrain it is needed to take care about possible erosion. Therefore, there are several types of
constructions or associated objects that impede water flow. Some of the solutions are
presented in Figure 29. Baffles and steps are objects constructed on channel network to slow
down the water flow and in that way they prevent drain erosion. They are built only within the
lined channels. Similar objects are checkwalls but they are constructed only for unlined
drains. Main purpose of checkwalls is to deposit silt behind them, gradually forming a natural
stepped drain.

30
Figure 29 Different designs of channels: a) baffles, b) steps and c) checkwalls
Besides steep terrain areas, problems can appear in flat low-lying areas where
high level of receiving water causes flooding. Because of the limited slope to which drains
need to be laid, flow of wastewater is often slow and inefficient. Thus, there is another design
approach for open channels. Channels can be built with sloping sides and narrow bottom to
maintain a steady flow speed of wastewater. The central channel for low flow built with
narrow bottom is called ˝cunette˝. The main purpose of cunette is to carry the flow in dry
weather and moderate rain, while the outer part of the channel prevents the occasional heavy
flood flow (Figure 30).
Figure 30 Detail of channel design with ‘canette’
As it is already mentioned, this kind of system could be a temporary solution to
transport wastewater. But it is not a pleasing technology for transportation of effluent even if
solids have been removed from wastewater.
a)
c)
b)

31
There are two main reasons to prove why open channel drains are not satisfactory
for sewage transport:
- residents can easily get into contact with the wastewater which potentially contains
pathogens
- there is a possibility for illegal discharge of household sewers to open drain systems.
In comparison to underground sewer systems, open channels are a solution that is
less costly. Of course, total system cost depends on local factors. For example, if the terrain is
flat, it is needed to have deep excavations because of minimal slope gradient. Also, in areas
with high groundwater level, excavations need to be wide. Furthermore, in steep areas system
should contain extra objects for slowing water flow such as baffles, steps or checkwalls.23
In open channels, built for transport of stormwater, household wastes are often
discharged. During the time solid particles are settling to the bottom of channel and these
channels are becoming desirable place for development of many diseases. Additionally, it is
needed to remove settled sludge frequently. The main responsibilities for maintenance of open
channels are:
- routine drain cleaning
- reporting of defects and blockages
- semi-annual inspection
- repairs
- payment for maintenance
- passing of by-lows regarding the use of drains
- enforcement of by-lows.
However, open channels are easy to design and build. This kind of system is
applicable in almost all types of settlements but before constructing thorough case study is
required to be sure if such construction is reasonable for that area. Even though this system is
simple and cheap solution for stormwater transportation, because of illegal wastes discharge,
open drains system bear many risks for public health. Therefore, open drains should be
applied only if proper wastewater treatment system is provided. List of all advantages and
disadvantages is presented in Table 5.
Table 5 Advantages and disadvantages of open channel drains
Low cost drain solution if drains already exist
High health risk due to illegal discharge of
wastewater and solid wastes
Simple to construct Blockages can cause spill-over and flooding
Construction materials are often locally available Foul odour source establishment
Creates employment (construction and
maintenance)
Regular cleaning service required to remove the
solids
Breeding ground for insects and pests
23
http://water.worldbank.org/shw-resource-guide/infrastructure/menu-technical-options/open-drains

32
3.3.8. SETTLED SEWER SYSTEM
Settled sewer system is also known as ˝solids-free system˝, and it was developed
over 40 years ago. Generally, this system is similar to conventional sewer system, with main
difference that the wastewater is pre-settled and solid particles are removed. The solids-free
approach allows only the liquid part of the wastewater to be transferred to centralised local
wastewater treatment plant, while the solids are kept in a septic (interceptor) tank located
close to household. Besides solid-free sewers, settled sewer systems are also referred to as
small-bore, small-diameter, variable-grade gravity or septic tank effluent gravity sewers.
Schematic view of the settled sewer system is shown at Figure 31.
Figure 31 Schematic of the settled sewer system in a small neighbourhood
If the whole network with all components is designed and constructed correctly,
this type of system does not require self-cleansing velocities or minimum slope. Only required
condition is that wastewater should be properly treated at the household level before being
discharged to the network. Considering settlement of solids before releasing wastewater to the
sewers, shape and alignment of pipes can curve and easily avoid obstacles allowing greater
design tolerance. If pipe alignment is following ground contours roughly, water flow can vary
between pressure flow and open channel flow. However, care should be taken to ensure that
sewers do not have negative slope, which can result in blockages and system damage.
Another important thing is that settled effluent or sludge from interceptor tank requires
secondary treatment and proper discharge. For example, sludge can be treated through several
processes: settling and thickening, drying and mineralization, non-planted filters, mechanical
dewatering, composting, further anaerobic digestion at large scale. During the designing of
the system, inspection points should be installed at major connection spots or in places where
diameter of the pipe is changing. Also, objects for ventilation of the pipe need to be provided
at high points with pressure flow. Minimum diameter for this system is 75 mm and it is
related with water level in pipes during the peak flow. The water depth in pipes during peak
flow needs to be less than full pipe diameter. Furthermore, in sections with pressure flow, the
invert of inceptor tank outlet should be higher than the water level in sewer to avoid liquid
backflow in the tank.24
24

33
Access for the network cleaning is not necessary costly as manholes are not
needed in this system. Cleanouts need to be ensured at upstream ends, at high points, at
intersections or at major changes in pipes size, but compared to manholes they can be tightly
sealed to avoid stormwater leaking.
In comparison with conventional sewerage, solids-free sewer system can be 20%
to 50% cheaper because of its simplified design. But expert design and constructing
supervision is mandatory. Even repairs and fixing blockages are more frequent and with the
emptying settling unit it can raise the costs significantly.
Typical solids interceptor tank is the main object on settled sewage network.
Generally, it has four main functions: sedimentation, storage, digestion of sludge and
reduction of peak flow (Figure 32).25
Figure 32 Detail of interceptor tank with components and dimensions
Settled system is optimal for medium-density urban and peri-urban areas but not
much applicable in low density and rural regions. It is appropriate for this system to be
installed in situations where effluent cannot be disposed due to low infiltration capacity or
high groundwater. It is also suggestible for rocky and corrugated soil because of flexible
alignment design. A solids-free system can be connected to existing septic tanks where
infiltration is no longer effective. Another positive characteristic is that this system can easily
be extended in case of sudden population growth with considerably lower costs than a
conventional gravity system.
It is recommendable to apply such systems in areas with high preparedness of
community to pay for the operation and maintenance costs and with locally available
professionals and resources. Moreover, system users should go through some kind of basic
training in order to prevent illegal connections to network and harmful discharges. Also,
responsibilities and obligations of a private contractor or users committee for control,
management and maintenance of system should be clearly set. Advantages and disadvantages
of this system are listed in Table 6.
25

34
Table 6 Advantages and disadvantages of settled sewer system
No requirement for minimum gradient or flow
velocity
Space for interceptors is required
Can be used in areas with limited water supply Interceptors need regular desludging
Can be build and repaired with locally available
materials
Requires repairs and removals of blockages
frequently compared to a conventional gravity
sewer
Lower capital costs than conventional systems
Requires training and acceptance for correct
usage
Construction can provide short-term employment
to local labourers
Leakages pose a risk of wastewater exfiltration
and groundwater infiltration
Can be extended as community grows Requires expert design and construction
Appropriate for densely populated areas with
sensitive groundwater or no space for a soak pit
or leaching field
Effluent from interceptors needs secondary
treatment or appropriate discharge
3.3.9. SIMPLIFIED SEWER SYSTEM – CONDOMINIAL SEWERAGE
Simplified sewerage is an important sanitation solution in peri-urban areas of
developing countries, especially as it is often the only technically possible option in high-
density areas. Principally, this system is similar to conventional sewerage but conscious
efforts are made to avoid unnecessarily conservative design features and to fit into design
standards according to the local social and economical conditions. The term ‘simplified
sewer’ describes a sewerage network that is constructed using smaller diameter pipes that are
laid in shallower depth and a flatter gradient than conventional sewers with the main goal to
reduce the total costs. Several approaches to reduced-cost sewerage have been invented and
developed all around the world, but one of the most significant is the approach of simplified
sewerage developed in Brazil in 1980s, called condominial system. The name ‘condominial’
comes from Portuguese term ‘condominio’ that means housing block. The main reason for it
is the fact that condominial system is designed as an in-block system, rather than an in-road
system. This means that the system is placed in private land laid either in back or front
yards.26
Considering the fact that simplified sewers are laid in or around the private
property of the users, better connection possibilities can be ensured, fewer and shorter pipes
can be used and shallower excavation would be required because the pipes will not be under
the influence of heavy traffic loads. Still, this type of system requires careful negotiation
between stakeholders because design and construction process need to be mutually
coordinated, which can sometimes be really challenging, as this system is applicable in areas
with low education rate and expressed poverty. Interesting fact is that the beginnings of back-
yard systems were recommended in the United Kingdom 150 years ago, but the first country
that developed condominial system was Brazil at the beginning of 1980s.
26
Duncan Mara: PC-based Simplified Sewer Design

35
Condominial sewerage is now highly developed and used in many states in
Brazil. Besides Brazil, within the borders of Latin and Central America, this system is used in
simplified sewerage has been successfully applied in countries like Bolivia, Columbia,
Honduras Nicaragua, Paraguay and Peru. In Africa it has been applied in several parts of
South Africa, and in Asia it is successfully implemented in Sri Lanka, Pakistan and city of
Malang, Indonesia.
Design approach of sewers alignment is very flexible in comparison to
conventional system. Schematic view of network design is well shown in Figure 33.
Figure 33 Comparison of schematic layouts between a) conventional and b) condominial
sewerage
Before designing such system several factors need to be satisfied. Simplified
sewerage is feasible only if water supply is ensured, so that total water use per person is at
least 60 litres per day. If this criterion cannot be satisfied, other possible options should be
taken into consideration. For example, if the water usage per person is about 30 litres per day,
settlement tanks could be installed and network can be reassigned to solids-free sewer
network. Other conditions that this system relays on are population density, volume of
effluent, sludge disposal management and the preferences of the local users. View of the
system is shown in Figure 34.
Figure 34 Schematic of simplified system installed in one neighbourhood
a) b)
FRONTYARD BACKYARD SIDEWALK

36
Nowadays, condominial sewerage system is considered as standard option to
poor and rich areas alike. Only in example of Brasilia – Brazil, this system is installed in poor
and also rich part of the town, which shows that this system can be applied also in other rich
parts of the world if main conditions are satisfied.
Another positive thing about condominial system is that it can be easily installed
in irregular urban area. One of the solutions is to lead the pipes inside of the lots which is
called ‘design of a garden branch’. It is suggestible for housing blocks where buildings are
slightly set back from the public road. Because of possibility to lay pipes in more flexible
lines, this type of system is optimal for overpopulated, irregular, already constructed areas as
a way of new system in settlements without any system or as a extension to already existed
sewer system (Figure 35).
Figure 35 Application of condominial system in irregular areas; design of garden branch
The main components of such system are the sewage pipes and inspection boxes,
which are in this system called ‘passage boxes’. Pipes from the housing block to the main
network will have hydraulically determined depth. The cover above pipes needs to be
minimally 25 cm in the internal or garden branches and 40 cm in the sidewalk branches. In
the case of road crossing, pipes should be laid at least on the depth of 100 cm. The pipe
diameter is also hydraulically determined and starts from 100 mm.
The inspection boxes should be designed and constructed to the way to satisfy
three main system tasks:
- access for the effluent from houses on the branch
- access to the branch for cleaning, unblocking and checking
- allowing direction changes in the course of the branch.
Dimensions and shape of these boxes are determined by their function and depth;
vary from a minimum section of 40 cm. Also, on the basic and public network, this kind of
system allows substitution of usual manholes with such inspection boxes, which is reducing
costs even more. All mentioned rules and restrictions are related to Brazilian standard ABNT,
1986; which is Brazilian representative standard in the international organisation for norms
ISO and IEC and in the regional entities COPANT and AMN.27
27

37
Figure 36 Comparison of conventional and simplified sewerage and on site sanitation on the
example of project in Natal in northeast Brazil in 1983.
As it is previously mentioned, this kind of system can significantly reduce the
costs. Just one example shows that in 1980 total costs of conventional system in Natal were
about 1500$ per household, while simplified sewerage reduced costs down to 325$ per
household. Similar range of cost savings have been recorded also on such systems all around
the world. But this fact that simplified systems are low-cost systems does not mean that they
are applicable only in low-income areas. On the example of project in Natal, results are
showing that, as the population density increases, simplified sewerage is becoming cheaper
than on-site sanitation systems (Figure 36). The system advantages and disadvantages are
listed in Table 7.28
Table 7 Advantages and disadvantages of settled sewer system
Greywater can be managed concurrently Requires enough water for flushing
Construction can provide short-term employment
and local workers
Requires repairs and removals of blockages more
frequently than a conventional gravity sewer
Can be extended as a community grows Requires expert design and construction
Lower capital costs than conventional systems
with low operating costs
The interception tanks can overflow when they
are not desludged in time
Can be laid at shallower depth and flatter gradient
than conventional sewers
Leakages pose a risk of water exfiltration and
groundwater infiltration and are difficult to
identify
Can be built and repaired with locally available
materials
Effluent requires secondary treatment and
appropriate discharge
Does not require onsite primary treatment units
The need to desludge the tank regularly requires
the involvement of a well-organised department
28

38
4. DESIGN OF SEWER SYSTEM
At the beginning of sewer system design, it is mandatory to choose system which
fulfils location area restrictions. Therefore, location needs to be precisely described in order to
obtain enough parameters for development of a quality mathematical model. Several factors
are important for choosing optimal type of system. In order to reach perfect solution, other
than topography and situational factors for a given location, social, economic and political
factors also need to be taken into account.
4.1. LOCATION
According to the United Nations, there are approximately 2.5 billion people in
the world who still do not use an improved sanitation facility and around 1 billion people who
practice open defecation. Current research shows that sub-Saharan Africa and Southern Asia
still struggle with low sanitation coverage. Just with the example of Africa, it can be seen that
in 18 countries, less than a quarter of the population uses proper sanitation facility (Figure
37). As a result of this, regions of West and Central Africa have the highest under-five
mortality rate amongst all developing regions. In numbers, this means that there are 191 child
deaths per 1000 live births. Furthermore, 115 people in Africa die every hour from diseases
linked to poor sanitation, poor hygiene or water contamination. (According to UN project
‘Water for life’ 2005-2015)
Figure 37 Use of improved sanitation facilities in Africa in 2010
Problems with overpopulation and poverty make the whole situation even worse.
Because of the lack of space and funds, installation of sanitation systems in regions of West,
Central or Eastern Africa sometimes presents almost an impossible mission. One of the
world’s poorest countries that is located in mentioned area is the United Republic of
Tanzania. Country with an area of around 970,000 square kilometres and a population of 40
million is facing lack of sanitation in measure that causes occurrence of diseases and human
deaths.
Dar es Salaam is the largest city and commercial centre of the country, with a
population of 4.2 million people (2015). Even though it is not capital city of the country, lot
of people arrive in Dar es Salaam seeking a prosperous future. The average poverty ratio of
the town is just 4.1%, compared to 33% in rural Tanzania, but because of constant stream of
the people, there is enormous expansion of informal settlements (Figure 38). According to the

39
U.N., 70% of city residents today live in informal communities, which face lack of basic
facilities and public services, and where many of the inhabitants cannot find jobs.
Figure 38 Map of Tanzania with marked city of Dar es Salaam(left) and Dar es Salaam with
expansion of population in last 40 years (right)
Although Dar es Salaam represents a comparably developed city in the whole
bigger area, it still deals with an undeveloped quarter which is the total opposite of developed
centre of the town (Figure 40). The so called ‘slums’ are neighbourhoods where inhabitants
face lack of water supply and normal sanitation conditions. For the sake of comparison
through numbers, water consumption per person per day in the region of Eastern Africa is
merely 38 litres. In the case of The Republic of Tanzania, water consumption highly depends
on the type of provided water supply. For example, in Tanzanian’s settlements that are
provided with piped water network, water consumption is 65.3 litres per day per capita, while
in the unpiped settlements water consumption is 26.2 litres per day per capita (Figure 39).
Figure 39 Differences in per capita water use for Dar es Salaam (Rural water demand: The
case of Eastern Africa)

40
It can be seen how numbers vary depending on region development and available
services and infrastructure. Besides average of 65.3 litres per day per capita for the piped
provided areas in Tanzania, in the town of Dar es Salaam, current water consumption per
person per day is 187 (according to DAWASCO), which is higher than the water usage even
in countries like Germany or Croatia.
However, water consumption in slums cannot be equal to that in the developed
areas of the city. Reasons for this are several, but at the beginning it is important to define
type and condition of water supply network for the researched area. It has already been
mentioned that the difference between city centre and informal settlements is enormous
(Figure 40). From 20 authorities in Tanzania, 3 can supply water continuously, in 11 others
there is supply of 19 hours per day and lowest water receiving areas are supplied just 5 hours
per day. The Dar es Salaam Water and Sewerage Authority (DAWASA) manages city water
and its distribution.29
Figure 40 Difference between developed (left) and not developed part of the Dar es Salaam
(right)
During the day, water is provided in the town for just 9 hours, which limits
normal sanitation. Furthermore, installed sewerage network in this town is estimated to be at
188 km, but just 4% of households have access to it. About 30% of people of Dar es Salaam
draw water from wells, 17% from surface water sources. Only 8 % people claim usage of
water from public taps.30
It can easily be deduced that inhabitants in slums still do not have
regular access to public sewerage and the level of their sanitation stays on usage of public
latrines and primitive methods of waste treatment.
The public sewerage network installed in Dar es Salaam connects the disposal to
the stabilization ponds which represent water treatment facility with sufficient efficiency for
described area (Figure 41). The biggest problem is lack of local sewerage network for each
part of the slum because while the public sewers are provided by the state, price of connection
to main network is relatively high for residents of this area. Accordingly, several
organizations and associations are helping to provide proper sanitation conditions in such
areas. One such project is ‘Cambridge Development Initiative’, where volunteering students
of University of Cambridge design and install sewerage systems all around the city of Dar es
Salaam. Results of such projects have shown that one household toilet can be installed just for
150£ and household can be connected to sewerage network for 30£. Therefore, several pilot
projects were initiated with the main goal to connect informal settlements of the town with the
29
UN-HABITAT; Tanzania:DAR ES SALAAM CITY PROFILE, 2009
30
Mwandosya & Meena, 1998

41
stabilization ponds. One of the most crowded and less developed slums of the city is
Vingunguti with around 110 000 residents (Figure 42).
Figure 41 Sanitation crisis in Vingunguti (left) and constructed stabilization pond (right)
˝Vingunguti settlement is located in Ilala Municipality in Dar es Salaam,
distanced six kilometres from the city centre. On the eastern side it borders the Buguruni area
and on the northern side the Msimbazi river valley. On the southern side it borders the central
railway and the industrial area along Nyerere road. On the western side is the Kipawa area.
Vingunguti settlement covers an area of about 32 hectares. It originated as a coconut
plantation owned by Arab settlers under freehold ownership system until the independence
1963 when the freehold system was abolished. A section of the people who originally settled
in this area was former plantation labourers. The urbanisation trends in the 1980s led to rapid
development of informal housing in the area. According to census in 2002 the total population
was close to 70,000, with a high increasing rate.31
Vingunguti is one of the fastest growing
informal settlements in Dar es Salaam and today it is one of the most densely populated
settlements. The area is relatively sloping, although most of its streets are flat with a slope
between 15 and 20 %.˝32
Lowest temperature for this region is measured in August and is around 12.8°C, while
the maximum is measured in February and is around 35.2°C. Average life expectancy for
people in Tanzania is 59.5 years and it is heavily influenced by insufficient sanitation
conditions. According to ˝The World Bank˝, in Dar es Salaam, population densities in some
parts of the town reach 1,500 persons/hectare, with an overall average of approximately 150
persons/hectare. All these parameters have influence on decision for the optimal system, so it
is very important to describe the area in as much detail as possible. Due to the crisis caused by
low sanitation conditions in the mentioned informal settlement Vingunguti, location for
design of sewerage system is carefully chosen in this slum (Figure 41). Noteworthy
characteristic of this area is that public sewerage network is installed on the main road with
the goal to conduct wastewater from distanced parts of Dar es Salaam to the water treatment
facility. However, because of the high level of poverty, residents of this quarter cannot afford
connection to the main sewer. There is a need to design network of sewers for affordable price
which will collect wastewater from households and dispose it to the main sewer. Vingunguti
is chosen because similar projects have occurred in this part of the town and due to the fact
that there are still many people who deal with lack of proper sanitation. Since Dar es Salaam
31
Kiunsi & Mchome, 2006
32
Research project report study on access to services in peoples settlements – Interdisciplinary perspectives on
infrastructure issues in Kenya and Tanzania; Elisabeth Ilskog and Eva-Lotta Thunqvist

42
is considered as one of the Africa’s fastest growing urban centre and is expected to expand
more than 85% through 2025, Vingunguti is the perfect area to design sewer system and solve
one of the greatest problems in this town resulting from informal settlement of the newly
arrived inhabitants. Chosen neighbourhood is shown in Figures 43 and 44.
Figure 42 Dar es Salaam with red marked area of Vingunguti
Figure 43 District of Vingunguti with chosen neighbourhood for sewer system design
Figure 44 Satellite footage of chosen housing block in Vingunguti

43
The view from above shows how overcrowded is the area of Vingunguti (Figure
45). Besides lack of proper sewerage in this part of town, people used to dispose their wastes
in closest possible natural water resource such as rivers, creeks or channels (Figure 46). As
these paths were not properly regulated, people from Vingunguti often faced problems with
channel blockages and even floods. In the case of flood, water from channels that was already
contaminated with wastewater used to reach housing blocks causing occurrence of diseases
and deaths. Figures 45 and 46 show the situation in the area of Vingunguti, close to the
chosen location for the system design.
Figure 45 View of Vingunguti from the air
Figure 46 Waste disposal in natural resource (Vingunguti, Dar es Salaam)
Location for design of drainage system is chosen at the north-western part of the slum
of Vingunguti behind the property of factory for chemical fertilizers Premium AgroChemical
LTD. Housing block is located between two main roads and is formed in triangular shape.
Inside the housing block, 24 objects are situated within the area of 0.59 hectares in an
irregular form. From these 24 objects, 23 are considered as objects with need for connection

44
to sewerage network while 1 object is considered as a storage object without any need for the
connection to network. Described location is presented in Figures 47 and 48.
Figure 47 Map of Vingunguti with red marked location for system design
Figure 48 Location for sewerage system design with presented roads, objects and property
borders
By using web portal CAD Mapper, chosen location was transformed from satellite
map view to Auto Cad file which in turn was used to design the sewerage network. CAD
Mapper transforms data from public sources such as OpenStreetMap and NASA into properly
organized CAD files. It allows downloading (.dxf) file with 2D or 3D axonometric view of
desired location including objects, roads and topography up to 1 km2
. Transformed view of
housing block is presented in Figures 49, 50 and 51.

45
Figure 49 Chosen housing block with main roads (blue), secondary roads (green) and objects
Figure 50 Chosen housing block in 3D view
Figure 51 Location for system design imported in Auto Cad

46
On the web portal Altitude.nu, it is possible to receive information about terrain
elevations of any place on the earth. It is possible to find the height above sea level of cities,
mountains, roads, seabed or any other place. Therefore, this service represents good
replacement for elevation and topographic maps. By using Altitude.nu, it was possible to get
information about terrain elevations which were further useful for the design (Figure 52).
Figure 52 Ground elevations for sewerage design location
4.2. SELECTION OF AN OPTIMAL TYPE OF SYSTEM
Optimal type of system needs to be chosen using methods of optimization synthesis.
The chosen type of system needs to satisfy conditions and limitations of specified location
boundaries. By following requests and restrictions of the design location, several options were
taken into account and optimal solution was used for the system design and development.
Specified location characteristics are described in detail in chapter 3.1. Main requirements
have also been summed up.
Chosen location is situated in the area of Eastern Africa, in one of the poorest parts of
the world. Although faced with overpopulation and poverty, the town of Dar es Salaam is still
one of the fastest growing towns in Africa, which results in occurrence of informal
settlements. Due to lack of proper sanitation, the design system needs to be the one that is
cheap, simple and sufficient for residents’ needs. In households which have been connected to
the water supply network, water is supplied just 9 hours per day and the average water
consumption for this area is 65.3 litres per capita per day.33
Chosen system needs to deal with
problems of less water which will be conducted in pipes. For this purpose, pipes with smaller
diameter can be used. Furthermore, as system is supposed to be as simple as possible, it is
optimal to design a system which will drain just sanitary wastewater while the stormwater is
conducted via open channels. Accordingly, costs can be reduced significantly. Design
location is situated in close proximity of equator and it experiences tropical climatic
conditions. Lowest temperature reaches 12.8° C which means that it is not mandatory to
secure pipes lying depth under freezing zone, which in Europe mostly amounts 80 cm. Small
33
Triche Thelma: Public-private and public-public partnerships in water supply and sewerage services in Dar es
Salaam; Case study

47
diameters and shallow trenches are also in the favour of total system costs. Besides that,
system location lies on mostly flat terrain with slight slope, which is suitable for many
solutions.
Following optimization synthesis identified are problems of the given location.
Considering these problems, main goals are set and system design is focused to achieve main
goals for the system. When model of the system is precisely described and requirements and
goals are formed, the system is called valuable system. With valuable systems, it is possible to
identify all possible solutions for each type of system following which the appropriate system
is chosen.
As the main goal is to design less costly system, expensive variants are eliminated at
the beginning. Gravitational systems require proper gradient in order to conduct water in the
gravitational way, which will increase excavation costs because of flat area. Furthermore,
designed pipes will need a bigger diameter and manholes will need to be installed. Because of
economical situation, system costs are the main design criteria. Decision about optimal
system needs to be related to low cost sewerage solutions. Drainage of wastewater with open
channels is not the appropriate solution because of climatic conditions of the locations.
During the year there are two rainy seasons: ˝the long rains˝ in April and May and ˝the short
rains˝ in November and December. Because of non-adequate infrastructure and regional
underdevelopment, in abovementioned months Dar-es-Salaam often faces enormous floods.
An example of this is the great flood in 2011 where 654 families lost their houses due to high
water level.34
Accordingly, it is pointless to design waste water network with open drains
when hard rain can overflow channels and cause wider contamination. The remaining options
are systems of settled sewerage and condominial sewerage.
On one hand, settled sewerage is a good solution because it requires less water
consumption and smaller diameters. Besides it can reduce costs by 20 - 50% in comparison to
conventional systems. Disadvantage is that settled sewerage requires enough space for
installation of interceptor tanks. Also, tanks need to be desludged very often and professional
experts are mandatory for system design and construction.
On the other hand, condominial sewerage is type of the system that was mostly used in
similar, poor and overpopulated, regions of South and Central America. It is designed as a
system that would collect and dispose waste water of one or more housing blocks. With very
shallow trenches and small diameters, this type of sewerage reduces costs by 65% or even
more in comparison to the conventional systems. The results of CDI project have shown that
the cost of household connection to simplified sewerage in Dar es Salaam is just 30£, which is
incomparable with other systems.35
34
According to: Thomson Reuters Foundation
35
https://cambridgedevelopment.wordpress.com/category/engineering/

48
Figure 53 Countries in which non conventional systems have been implemented
In Figure 53, it can be seen how widely non-conventional systems are implemented all around
the world. It is interesting how this kind of sewerage found its purpose the most in the zone
around equator, even though it can be applicable in other regions. It can be noticed that such
systems were already implemented in Tanzania and neighbouring countries which is all the
more the reason to use this approach. Moreover, recent projects of ˝Cambridge Development
Initiative˝ have shown the need for installation of sewerage systems in the area of Vingunguti,
and as a solution, mostly used condominial systems were used (Figure 54). It is demonstrated
that condominial type of sewerage system is satisfactory for location requirements. Next step
is to check availability of location for this system and to prove that system requirements are
also satisfied for this location.
Figure 54 Cambridge Development Initiative: Student Volunteers installing simplified
sewerage in Vingunguti, Tanzania

49
Every type of sewerage system has its own design rules and restrictions. Condominial
or simplified sewerage system can be used in areas with minimum water consumption of 60
litres per capita per day.36
In the case of housing block in Vingunguti, the average water
consumption that is taken into consideration is 65.3 per capita per day. Condominial system
can be considered as an option in areas with more than 150 people per hectare. In the case of
this housing block, 23 houses are placed on property of 0.59 hectare where every household is
considered as a house of a 5-member family. That makes 115 persons on 0.59 hectare or
approximately 190 people per hectare. Another restriction is that condominial system is
usually designed only for wastewater and not stormwater. This constraint is also suitable for
the location because of the already mentioned financial and climatic conditions. As a result of
the sewerage type analysis, it is rational to choose condominial system as an optimal solution
and form a model of such system.
In order to get optimal solution for every system, it is desirable to form model for
chosen option on which further analyses would be conducted. If such formed and analysed
model is optimal, there is no need for adjustment to the parameters and system can be
constructed by following the model. In case the model is feasible but not optimal, parameters
need to be adjusted. However, if the model is not feasible another solution should be chosen
and whole process should be conducted from the beginning.
4.3. DESIGN OF SIMPLIFIED (CONDOMINIAL) SEWERAGE
Every system is designed in accordance with some rules and standards. Main
reason for that is the uniform design and construction of the system for the wider use. As
condominial system is invented and implemented in Brazil, it was regulated by Brazilian
standards. Simplified or condominial sewerage was developed by the R&D Division of
CAERN, the water and sewerage company of the north-eastern State of Rio Grande in Brazil.
Another key feature in development of this system design was the research of Brazilian
sanitary engineer Eugênio Macedo, who imported simplified system into the 1975 Brazilian
national sewerage design code. After years of system development, rules and restrictions for
this system were incorporated into Brazilian standard ABNT, 1986; which is Brazilian
representative standard in the international organisation for norms ISO and IEC and in the
regional entities COPANT and AMN. In Brazil and in every location where this system is
used, design and construction still follows the standard ABNT 1986.
As this type of system is invented principally for overpopulated and poor areas
with the main goal to provide decent primary life conditions with the minimum costs, system
components and construction rules are not complicated. Some of the rules and restrictions
were already mentioned in previous chapter while choosing optimal type of system. At the
beginning of the design, it is important to choose the period of system usage. Usually,
condominial systems are designed for a period of 30 years and therefore, for this project same
period is considered. The idea of this system is to design a network that will not be on public
property, the so called in-block or back-yard sewerage that can significantly reduce the length
of sewer required, thus reducing costs.
The value of the wastewater flow used for sewer design is the daily peak flow.
This can be estimated as follows:
1 2 / 86400q k k Pw (5)
where:
36

50
q = daily peak flow, l/s
k1 = peak factor (daily peak flow divided by average daily flow)
k2 = return factor (wastewater flow divided by water consumption)
P = population served by length of sewer under consideration
w = average water consumption in litres per person per day
86 400 is the number of seconds in a day.
A suitable design value for k1 for simplified sewerage is 1.8 and k2 may be taken as
0.85. Thus equation (5) becomes:
5
1.8 10q Pw
  (6)
The design values given above for the peak flow factor, k1 and the return factor,
k2 (1.8 and 0.85 respectively) have been found to be suitable in Brazil, but they may differ in
other regions. Parameters would be different in case of greater amount of stormwater which
also needs to be conducted together with wastewater or in case of bigger water consumption
for regions where residents use water for lawn-watering and car-washing. These parameters
were used in designing of sewerage for Brazilian slums called ˝favelas˝. Because of same
tropical climatic zone and similar conditions as those in Brazil, these parameters are accepted
for design in this project as well.
In simplified sewer design equations (5) and (6) are used to calculate the daily peak
flow in the length of sewer under consideration, but subject to a minimum value of 1.5 l/s.
This minimum flow is not justifiable in theory but, as it is approximately equal to the peak
flow resulting from flushing a WC, it gives reasonable results in practice, and it is the value
recommended in the current Brazilian sewer design code ABNT, 1986. For this project, the
minimum daily peak flow used the value of q=1.5 l/s. Gauckler-Manning equation relates to
velocity of flow in a sewer to the sewer gradient and the hydraulic radius:
  2/3 1/2
1/v n R I (7)
where:
v = velocity of flow at d/D, m/s
n = Ganguillet-Kutter roughness coefficient, dimensionless
R = hydraulic radius at d/D, m
I = sewer gradient, m/m (i.e. dimensionless)
Since flow is used as a result of multiplying area and velocity, equation for the
flow in sewer at d/D in m3
/s is changed:
  2/3 1/2
1/q n AR I (8)
The usual design value of the Ganguillet-Kutter roughness coefficient, n is 0.013.
This value is used for any relatively smooth sewer pipe material (concrete, PVC or vitrified
clay) as it depends not so much on the roughness of the material itself, but on the roughness of
the bacterial slime layer which grows on the sewer wall.37
For this project, Ganguillet-Kutter
roughness coefficient used is also 0.013 due to PVC material of installed pipes.
The ratio d/D is termed the proportional depth of flow (which is dimensionless). In
simplified sewerage the usual limits for d/D are as follows:
37

51
0.2 / 0.8d D  (9)
Tractive tension (or boundary shear stress) is the tangential force exerted by the flow
of wastewater per unit of wetted boundary area. It is denoted by the symbol τ and has units of
N/m2
(i.e. Pascals, Pa). As shown in Figure 55, considering a mass of wastewater of length l
m and cross-sectional area a (m2
), which has a wetted perimeter of p (m), the tractive tension
is given by the component of the weight (W, Newtons) of this mass of wastewater in the
direction of flow divided by its corresponding wetted boundary area (i.e. the area in which it
is in contact with the sewer = pl):
sin /W pl  (10)
The weight W is given by expression:
W gal (11)
where:
ρ= density of wastewater, kg/m3
g = acceleration due to gravity, m/s2
So that, since a/p is the hydraulic radius, r :
singr   (12)
When φ is small, sin φ = tan φ and tan φ is the sewer gradient, denoted as i (m/m).
Thus, equation 12 can be rewritten as:
gri  (13)
Figure 55 Definition of parameters for tractive tension in a circular sewer 38
38
Source: Barnes et al. (1981)

52
The minimum sewer gradient, Imin is closely related to minimum tractive tension
τmin. Yao (1974) recommends values of τmin for sanitary sewers to be 1-2 Pa, and 3-4 Pa for
stormwater or combined sewers. Designers must make an appropriate choice for τmin. Values
of τmin > 1 Pa have a large influence on the value of Imin. For the different values of τmin,
different minimum values of sewer gradient are suggested (Table 8).
Table 8 Minimum sewer gradient suggested in accordance to minimum tractive tension
τmin (Pa) Imin
1 1 in 213 (0.005)
1.5 1 in 130 (0.008)
2 1 in 91 (0.01)
If sewer can be constructed on a high standard and most stormwater can be excluded
from the sewer, a value of 1 Pa can be used. CAESB, the water and sewerage company of
Brasília and the Federal District, uses in practise a τmin of 1 Pa and a minimum value of Imin of
0.5% (1 in 200). In low-income areas, this has not resulted in any significant operational
problems (Luduvice, 2000).
Inspection box in this kind of system is usually provided at every connection to the
sewer, and inspection chambers are provided at changes in direction of sewers and at intervals
of no more than 30 m for condominial sewers and 100 m for public collector sewers.
Dimensions and shape of inspection boxes are determined by their function and depth but
most commonly boxes in rectangular and circular shape are used. For this project, circular
inspection boxes with accepted minimal dimension of 40 cm are used.
The cover above pipes varies from project to project. For example, in design of
simplified sewerage in Pakistan, engineers used a minimal cover of 25 cm for the concrete
pipes. In the case of Great Britain, minimal covers of 35 cm were used for the clay pipes. The
smallest cover was used in Brazil where for the in-block network, cover of 20 cm was used
and for the pavement, cover of 40 cm was used.
Following the design rules and restrictions, network scheme of simplified sewers was
designed in software Autodesk AutoCAD. Network of condominial sewers is planned to be
installed as an in-block system on the private property following shortest path in order to
reduce total costs. From the map with location elevations, it can be noticed that terrain slightly
tilts in the direction of East at the bottom of chosen housing block and tilts in the direction of
West at the top of chosen section it (Figure 52). Accordingly, sewers of simplified sewerage
were laid by following slope of terrain until they were connected to the already existing
conventional sewer placed under the main road on the both sides of the housing block.
The sewerage system for the project location is designed as a system of two networks
where each has connection to different line of conventional sewers (Figure 56). One network
has one branch which joins at drop junction, while second network is consisted of main sewer
with two sub-nets where each of them is joined at drop junctions (Figure 57). Network with
one branch serves 17 houses while network with 2 branches serves 6 houses.39
After disposal
into conventional sewerage, wastewater is conducted to the stabilization ponds which
represent wastewater facility, located also in Vingunguti in the direction of East from the
chosen housing block. Inspection boxes are presented with black circles and are located at
every connection to the sewer or change of sewer direction. Details of network design are
shown in Figures 57 and 58.
39
for detailed view see Appendix 2

53
Figure 56 Clip from AutoCAD drawing of simplified sewerage for the housing block in
Vingunguti slum
Figure 57 Detail of designed sewer networks for project location

54
Figure 58 Detail of sewer network with two sub-nets which serves residents of 6 houses
After sewerage network was designed in Autodesk AutoCAD, next step was to form
model in a program which would analyze all the parameters and give positive or negative
results for the initial model. For the system model design, software ˝Simplified Sewerage˝ is
chosen. It is a free program conceived solely for designing these type of sewerage systems.
After input of elementary parameters, program calculates data and analyses the suitability of
the model and suggests possible solutions. As this type of system is one of the simplest
systems, computer program was designed accordingly.
4.4. OVERVIEW OF PROGRAM ˝SIMPLIFIED SEWERAGE˝
Program ”Simplified Sewerage’’ along with user manual ’’PC-Based Simplified
Sewerage Design’’ was published by the School of Civil Engineering, University of Leeds,
UK, in January 2001. Package consisted of a manual and a Windows based program for
designing the simplified sewerage system. It was published with the aim of promoting the use
of simplified sewerage throughout the developing world.
The program is designed to outline the sewer network as a series of linked sewer
pipes. The sewers are only supposed to be linked in a tree form, meaning that the network
expands from the most downstream point furcating at junctions to several upstream ends. The
network is not supposed to have any loops within itself. In case there is any error in the model
design, the program has built-in automatic checks that warn the user if the network cannot be
calculated. In order to serve large amount of houses, the network may be split into sub-
networks. Sub-nets may join other sub-nets at “drop” junctions – i.e. places at which the
sewers are not necessarily at the same level. When system of network is complete, it needs to
be linked to a main street/collector sewer that could be at a much lower level. To begin the
design, there is information which is essential at bare minimum for starting a model.
Important information to know is the length of the sewer and number of people connected to
it. It can be achieved in two different ways. According to the first way, information about
number of people who live in one house can be input in the program. In the second approach,
the program can take information about total number of people connected to each sewer.

55
In order to get results for depths of pipe laying, program requires ground levels at
the end of each sewer length.40
Figure 59 Simplified Sewerage program: Visual Editor screen
The program interface has a simple design with four main buttons which allow
you to switch between the four main screens of the program: Visual Editor, Data Entry/Edit,
Results Table, and Calculator (Figure 59). The first button of the interface is Visual Editor
screen. This is the screen that is shown when program starts. Here it is possible to draw the
sewer network on-screen and also edit all the network description parameters. It provides the
normal means of entering all the necessary design data. An alternative to this method of
entering data is to use the Data Entry/Edit screen. The second button presents table-based
method for editing the sewer network description. The third button changes to the Results
Table screen, which is a table of the detailed design results for the sewer network. On this
screen, it is also possible to change some of the design calculations and recalculate to show
new changes. The fourth button displays the Calculator screen. On this screen, details of
calculations performed for each sewer in the network are shown and it is possible to adjust the
parameters to examine possible design changes. Besides four main buttons, there are two
additional buttons: Costing and Exit. With the Costing button, it is possible to import file with
information about material, equipment and labour costs if this information for selected
location are provided. Last button, Exit, ensures properly termination of the program after the
conformation that closing is not accidental.
With regard to this project, sewer network was designed by using Data Entry/Edit
button and it was just additionally edited in Visual Editor. With Data Editor/Edit screen, it is
possible to form network by entering requested data about each sewer. A sewer network is
made up of named sewers that join at named junctions. Thus each sewer has an upstream and
40

56
a downstream junction. Sewers and junctions have their own separate properties which
perfectly describe the network layout and the wastewater flows for which the model is made.
At the window List of Sewers it is possible to name each sewer. After naming the particular
sewer, it is mandatory to input information about the sewer length, initial infiltration
(l/m/day), downstream and upstream junction and number of people who will use that sewer.
41
Figure 60 Simplified Sewerage program: Data Entry/Edit screen
After all sewers are entered in the program, junctions can be formed in the window
List of Junctions. Junctions need to be entered with junction name and ground level (m). Next,
junctions can be assigned to each previously entered sewer with the role of upstream or
downstream junction. If sewers are designed in the ‘tree form’, consisting of several sub-
networks, each sub-net needs to have drop junction into the main sewer. For junctions that are
at the downstream level of sub-net sewer, it is mandatory to label them with D/S Drop
junction mark in the Data Entry/Edit screen. Likewise, each network needs to be denoted with
a datum junction, since a datum junction is considered the upstream junction of the first sewer
from where network starts. When all parameters are specified, system needs to check network
in order to warn user in case of errors. For checking accuracy of the model, Check Network
button at the bottom of the window should be pressed (Figure 60).
If system check shows that network has passed accuracy analysis, results will be
showed in Results Table. After all sewers and junctions are entered by parameters in table-
based form, view of the network is presented in Visual Editor screen. As junctions and sewers
are not specified with exact position in the space, Visual Editor displays all of them at the
same position. To get clearer view, network needs to be edited by clicking and dragging each
junction inside of the Visual Editor screen. Junctions and sewers can be positioned optionally
because length of the sewers is determined by parameters entered in Data Entry/Edit screen
and repositioning in Visual Editor will not change them (Figure 61).42
41
Duncan Mara: PC-based Simplified Sewerage Design
42

57
Figure 61 Sewer network entered in Data Entry/Edit screen before (left) and after
repositioning in Visual Editor (right)
By this step, system network will be formed in the program as just a visual. Analyses
cannot be performed because of the lack of information. Further parameters will then be
needed to be entered in Results Table. Inside the Results Table screen several parameters need
to be entered: initial water usage per person (litres/day), final water usage per person
(litres/day), initial and final mean number of people per house, minimum self-cleansing
velocity (m/s), minimum tractive tension (N/m2
, Pa), G-Manning’s coefficient, minimum
sewer cover (m), return factor (%), peak flow factor, minimum flow (l/s) and minimum pipe
diameter (mm). After all parameters are entered, it is required to choose in which form the
results should be presented: Min Vel is based at minimum self-cleansing velocity and Min Tau
is based at minimum tractive tension. In the example shown in Figure 62, it can be seen that
the results are shown in table with several columns. The parameters that should be presented
in columns of the result table can be chosen optionally from the suggested list in option View,
according to program user’s preferences (Figure 63).

58
Figure 62 Simplified Sewerage program: example showed in Results Table screen
Figure 63 List of parameters that can be shown in results table
On the Calculation screen, it is possible to check system suitability. This screen
presents the details of the calculation for an individual sewer. Opening the screen
automatically displays the design parameters of the current sewer in the Results Table. This
screen allows the calculation to be performed with new demand data or new calculation
parameters, so that changes in the design can be investigated.

59
Any changes made to this screen are not transferred to the Results Table of sewer data,
so this screen is used just as a help for checking the system suitability (Figure 64). Important
condition that needs to be checked in Calculator is that d/D ratio should always be greater
than 0.2 and the minimum velocity should be greater than that is previously set.
Figure 64 Simplified Sewerage program: example showed in Results Table screen
Another possibility of the program is to calculate maximum number of houses that can
be connected to a sewer of given diameter laid at minimum gradient. This option enables
program users to find out how many houses can be connected to designed network, which is
useful in areas with predicted increment of population in the near future. Because this kind of
sewerage system is designed for a period of 30 years, it needs to predict maximum number of
houses that can be served with this network in that period. As an input, program requires
information about population per house, water use (l/c/d), return factor (%), peak flow factor,
d/D ratio, minimal tractive tension (N/m2
, Pa), G-Manning’s coefficient and pipe diameter.
Withal, program can do the calculation of hydraulic properties inside the pipes for the
designed network. In drop down menu Tools, right next to option ˝Max. no. of houses˝ is
another option called ˝Section properties˝. In ˝Section properties˝, a screen is displayed which
allows quick calculation of the hydraulic properties of circular channels. After entering
information about the pipe diameter, depth of flow, G-Manning’s number and slope, program
can calculate flow section properties (Figure 65).

60
Figure 65 ‘Maximum number of houses’ window and ‘Section Properties’ window (example)
If all required conditions in program are satisfied and the program analysis shows that
the model is valid, system can be constructed.
4.5. DEVELOPMENT OF MODEL USING PROGRAM ˝SIMPLIFIED SEWERAGE˝
For the purpose of this project, model was developed in program ˝Simplified
Sewerage˝. Program was downloaded together with user manual PC-based Simplified Sewer
Design from webpage of University of Leeds, where it is available for free to all visitors. To
promote the use of simplified sewerage throughout developing world, program is provided to
everybody online but it is also possible to receive CD with printed manual, on request.43
At the beginning, simplified sewerage network that was designed in AutoCAD was
introduced in the ˝Simplified Sewerage˝ program. Table-based approach – Data Entry/Edit
screen, was then used for entering network in the program. Sewers from longer sewerage
network were labelled as ‘sewer’ along with a corresponding number, while sewers from
shorter sewer line was named with letter ‘S’ with a corresponding number, as assigned in
AutoCAD design (Figure 66). For each sewer, information about sewer length and initial and
final number of houses was entered. It was also defined that each house is a residence of 5
persons. After all junctions were entered and properly named, upstream and downstream
junction for each sewer was determined. Junctions were characterised with ground level and
ending junction of every sub-net was labelled as a drop junction. First junction for each of
both main networks was set as a datum, which determines wastewater flow direction.
System was designed with two separated networks, in which one consisted of 11 sewers and
12 junctions and the other consisted of 5 sewers and 6 junctions. In Figure 66, a clip of Data
Entry/Edit screen for this project is shown. It can be seen that ‘sewer11’ and junction ‘j12’ are
marked. Chosen sewer in this example is specified with sewer length of 12.33 m, upstream
junction ‘j12’, downstream junction ‘j11’ and initial number of 3 houses connected on sewer.
Chosen junction ‘j12’ has set ground level at 38.00 m and it is marked as an upstream
junction for marked sewer. After data was entered and set, network successfully passed
system check.
43

61
Figure 66 Table-based input of sewerage network in program Simplified Sewerage
Figure 67 Designed network in Visual Editor screen after junction and sewer repositioning
After designed network was introduced into the program, design factors and design
limits were set in order to check available pipes for system suitability. According to location
analysis and detailed area description, initial and final population per house used in this

62
project is 5 persons, initial water use per person is 65 litres per day and final predicted water
usage per person is 120 litres per day. Onwards, following minimum suggested parameters for
this kind of system, simplified network was characterised with next parameters:
Return factor (80%), Peak flow factor (1.80), Minimal self-cleansing velocity (0.50 m/s), G-
Manning’s number (0.0130) and Minimal tractive tension (1.50 N/m2
, Pa). As a minimum
flow is selected flow of 1.50 l/s and minimum diameter of 100 mm.
Although, Yao (1974) recommends value for minimum tractive tension in the range of
1-2 Pa (Table 8), CAESB uses in practise a minimum value of 1 Pa for the whole area of
Brazil. Initially, for this project a minimum tractive tension of 1 Pa and corresponding
gradient of 0.005 (1 in 213) was selected on screen Calculator, which resulted in initial
velocities lower than minimum required (Figure 68). After increasing minimum tractive
tension factor to 1.5 Pa and corresponding gradient to 0.008 (1 in 129), system passed check
for pipe sizes of 100 mm (Figure 69). It is important to mention that design limits were
applied according to G-Manning’s coefficient and choice of pipe diameters was directed by
criteria of minimum velocity.
Figure 68 Calculator screen of Simplified Sewerage for minimum tractive tension with
unsatisfactory results
After suitability of chosen pipes was successfully passed on Calculator screen, total
results were presented on the Results Table screen. As the analysis on Calculator screen is
just informative and cannot be automatically transferred to the results, crucial parameters are
required to be entered again on the Results Table screen, as shown in Figure 71.

63
Figure 69 Calculator screen of Simplified Sewerage for minimum tractive tension with
satisfactory results
On the Results Table screen, following parameters were entered: initial water use per
person per day, final water use per person per day, initial mean number of people per house,
final mean number of people per house, minimum self-cleansing velocity, minimum tractive
tension, G-Manning’s coefficient, minimum sewer cover, return factor, peak flow factor,
minimum flow and minimum pipe diameter. All the values were already defined and
described in Calculator screen procedure. Besides listed parameters, it was necessary to
decide by which criteria (minimum velocity or minimum tractive tension) and by which
approach (G-Manning’s coefficient, Colebrook White - CW or Escritt) the results need to be
presented. For the purposes of this project, analysis and results were relied on minimum
velocity method and G-Manning’s coefficient. Furthermore, ground slope limiting was
marked which means that the minimum slope of the sewer will not be less than the ground
slope.
Parameters which will be presented in Results Table can be checked from the list that
can be found on the drop-down menu View by choosing option Select columns to view.
Parameters besides ‘sewer name’, ‘sewer length’, ‘initial infiltration’ and ‘initial flow’ that
were selected are shown in Figure 70. In Figure 71, a part of the results is shown. The detailed
list is given in appendix.
To justify the quality of the model, all parameters in the Result Table must comply
with the system and location requirements. If further analysis shows that the model designed
in Simplified Sewerage program is not in accordance with the system restrictions and
requirements, it needs to be adjusted or designed from the beginning. To prove that model is
correct, interpretation of results needs to be done.

64
Figure 70 Checked columns for the Results Table screen
Figure 71 Results Table screen for design location (all results see in Appendix)

65
Interpretation of results can be easily followed in the appendix. To begin, all listed
sewers that were used in this system have a length of less than 30 meters. This means that
inspection boxes do not need to be installed on the network because of exceeded suggested
length of the sewers. For the sewers, PVC pipes with diameter of 100 mm were used. Due to
this type of pipe material and shallow depths of placement, initial and final infiltration is
considered as non-existent. Infiltration should be considered where some sewers are laid
below the groundwater table. Initial wastewater flow should be greater than 1.5 l/s, which was
set as a minimum value for that parameter. It is important that results listed in the table show
values only for each specific sewer because some sewers are marked with flow of 0.00 l/s if
there is no house connected to that sewer. Ground levels are listed for the upstream and
downstream point of each sewer. They serve as an input data for calculating depth of pipe
placement. The minimum gradient entered was 0.008. In the results, it can be seen that
gradients for all the sewers are 0.008 or higher, which shows that restrictions were respected.
Minimum diameter for sewers is 100 mm and for the whole system pipes of minimum
diameter were used in order to achieve cost savings.
Another important restriction is that d/D ratio needs to be respected, as given in
equation 9. Depth of flow (d/D) should be greater than 0.2 and less than 0.8. In the Results
Table in the columns of initial and final d/D flow, it can be seen that from all listed sewers,
minimum value is 0.24 and maximum value is 0.40. At the beginning of the design, the
minimum self-cleansing velocity was of value 0.5 m/s. In the obtained results, lowest value
shown is 0.511 l/s which indicates that self-cleansing velocity restriction was also respected.
In chapter 3.3, soil covers used in different countries were described. Minimum soil cover
used in this kind of system is in Brazil where 20 cm of cover was used for in-block sewers
and 40 cm for the pavement sewers. As this system is designed as an in-block system in total,
cover of 25 cm is used for the whole sewer system. Accordingly, sewer depths should be
greater than 25 cm. In the last columns of the result table (see appendix), upstream and
downstream sewer depths are listed based on terrain ground levels and system restrictions. It
can be seen that the shallowest sewer was placed at 0.35 m while deepest sewer was at 0.98
m. Depth of sewer placing did not exceed 1 meter at any point which will significantly reduce
construction costs.
Figure 72 Maximum number of houses that can be connected to designed network

66
For designed model of sewerage system, program can calculate maximum number of
houses that can possibly be connected in projected time of system. For the population of 5
persons per house, water consumption of 65 litres per person per day, return factor of 85%
and peak factor of 1.80, minimum d/D ratio of 0.24, minimum tractive tension of 1.50 Pa, G-
Manning’s coefficient of 0.013 and minimum pipe diameters of 100 mm, system analysis
released that this system could serve 117 houses in total.
Considering all obtained parameters listed in results, it can be concluded that designed
model is perfectly correct and feasible in practice. Following method of optimization
synthesis (Figure 9), it was decided that simplified sewerage system is optimal solution for
specified location and accordingly was started formation of the model for this system. After
model was taken under several analyses in program Simplified Sewerage described in
previous chapters, results showed that system is feasible in practice. After model is proven as
a realistic solution for location requirements, it can be realised on site, which is the last step of
optimization synthesis.

67
5. CONCLUSION
In selection of the optimal hydrotechnical system for some specified area, three main
questions need to be answered. Analysis before selection should define the main problem that
needs to be solved, determine what actions and possible solutions are available, and from
existing solutions, choose the one that is the optimal. To define the problem, study needs to be
conducted, location needs to be described in detail and all parameters need to be analyzed.
Accordingly, several solutions should be taken into consideration but final decision should be
obtained with the method of optimization. As this project deals with design of a new system,
optimization synthesis is the method that was used. Task of optimization synthesis is to find
optimal system configuration and optimal physical system parameters for optimal system
operation. Optimization synthesis mostly analyzes several similar options with respect to
different criteria, such as economical, social, political, technical, etc.
For the selection of optimal sewerage system in slum Vingunguti, Dar es Salaam;
there was just one main criterion for optimal selection – economical. For the residents of slum
settlement, it was indispensable to construct the simplest possible system which will provide
proper sanitation and prevent diseases. The simplest solution should at the same time be the
cheapest solution, which was the main goal of system selection. After analysis of all possible
sewerage systems, selection was based on low-cost sewerage systems. Within the low-cost
sewerage systems, simplified (condominial) system was selected as an optimal type of system
for the specified location. As this kind of system is the cheapest one, it is also the simplest
system and does not require complicated construction or maintenance. Solution that is chosen
as optimal is also the most rational solution. This type of system is invented and developed
just for areas like the selected one, with purpose of enabling poor residents in low-income
regions to have a decent sanitation conditions.
Designed network was introduced in the program Simplified Sewerage, which was
later used for the formation of the model. Model analysis proved availability and feasibility of
the system for selected area which demonstrated that optimal solution can be implemented in
practise. Main goal of this thesis is to raise awareness about low sanitation conditions that is
still prevalent in many countries and to show how existing problems can be solved with
simple and economically feasible solutions.

68
6. LITERATURE
[1] Bakalian Alexander, Wright Albert, Otis Richard, Netto de Azevedo Jose: Simplified
Sewerage: Design Guidelines
[2] Duncan Mara: PC-based Simplified Sewer Design
[3] Margeta J.: Kanalizacija naselja, Građevinski fakultet Split, 1998.
[4] Petri D. Juuti, Tapio S. Katko, Heikki S. Vuorinen : Environmental History of Water -
Global views on community water supply and sanitation
[5] Tušar Božena, Pročišćavanje otpadnih voda; Kigen d.o.o.; Zagreb, 2009
[6] UN-HABITAT; Tanzania: DAR ES SALAAM CITY PROFILE, 2009
[7] Conception and Installation of the Condominial Sewerage System in the town of Santa
Maria – Case study
[8] Elisabeth Ilskog and Eva-Lotta Thunqvist : Research project report study on access to
services in peoples settlements – Interdisciplinary perspectives on infrastructure issues in
Kenya and Tanzania
[9] Hidrotehnički sustavi, lessons; Marija Šperac, Faculty of Civil Engineering Osijek
[10] Hidrotehnički sustavi, lessons- Faculty of Civil Engineering Zagreb
[11] Rural water demand: The case of Eastern Africa – Lessons from the Drawers of Water II
study
[12] Strengthening the capacity of water utilities to deliver water and sanitation services,
environmental health and hygiene education to low income urban communities: Dar es
Salaam Water and Sewerage Authority - Engr. Bill Wandera
[13] Triche Thelma: Public-private and public-public partnerships in water supply and
sewerage services in Dar es Salaam; Case study
[14] http://water.worldbank.org/shw-resource-guide/infrastructure/menu-technical-
options/open-drains (14.05.2016.)
[15] http://e-gfos.gfos.hr/index.php/arhiva/broj-2/rjesenje-kanalizacije-naselja (18.04.2016.)
[16] http://www.pseau.org/sites/default/files/fichiers/r_d/non-
convetional_sewers_analysis_report.pdf (18.04.2016.)
[17] http://www.humanitariancentre.org/2013/11/opinion-simplified-sewerage-and-africas-
sanitation-crisis/ (10.06.2016.)
[18] https://cadmapper.com/ (28.05.2016.)

69
[19] https://www.cam.ac.uk/news/cambridge-students-launch-development-initiative-in-dar-
es-salaam (24.06.2016.)
[20] http://dawasa.go.tz/facilities/sewerage-system/ (24.05.2016.)
[21] https://en.wikipedia.org/wiki/History_of_water_supply_and_sanitation (21.04.2016.)
[22] http://water.worldbank.org/shw-resource-guide/infrastructure/menu-technical-
options/open-drains (17.05.2016.)
[23] http://www.sswm.info/ (13.05.2016.)
[24] http://pubs.usgs.gov/chapter11/chapter11C.html (11.07.2016.)
[25] http://www.newworldencyclopedia.org/entry/Sewage (19.04.2016.)
[26] https://cambridgedevelopment.wordpress.com/category/engineering/ (19.07.2016.)

ELEVATION
ROAD LINE
HOUSING BLOCK BORDER
BUILDING
HOUSING BLOCK FOR SYSTEM DESIGN
HOUSING BLOCK WITH TERRAIN ELEVATIONS
UNIVERSITY OF APPLIED SCIENCES WIESBADEN
MASTER THESIS: OPTIMIZATION OF HYDROTECHNICAL SYSTEM
Appendix:
Scale: Appendix no.:
Student:
Date:
Mentor:
25.07.2016.
Prof.Dr.-Ing.
HOUSING BLOCK FOR SYSTEM
DESIGN
1:1000 1

14.77
4.64
19.99
24.46
25.59
13.08
4.32
6.33
14.93
3.87
21.94
18.35
2.79
9.00
6.36
ELEVATION
CONVENTIONAL MAIN SEWER
CONDOMINIAL SEWER
ROAD LINE
HOUSING BLOCK BORDER
MANHOLE
CHECKING POINT
6.54
6.54
14.16
12.33
3.84
18.10
HOUSEHOLD CONNECTION
HOUSING BLOCK WITH DESIGNED NETWORK
Appendix:
Student:
Date:
Mentor:
25.07.2016.
Prof.Dr.-Ing.
HOUSING BLOCK WITH
DESIGNED NETWORK
1:1000 2

14.77
4.64
19.99
24.46
25.59
13.08
4.32
6.33
14.93
3.87
21.94
18.35
2.79
9.00
6.36
6.54
6.54
14.16
12.33
3.84
18.10
DESIGNED SEWER NETWORK
Appendix:
Student:
Date:
Mentor:
25.07.2016.
Prof.Dr.-Ing.
HOUSING BLOCK FOR
SYSTEM DESIGN
1:500 3

21.94
18.35
2.79
8.85
3.84
18.10

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