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
HOCHSCHULE RHEIN MAIN
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

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