This document provides information about ENVIS Energy and Environmental Systems Research and Development Ltd., including their areas of expertise and services provided. It then discusses sewage sludge pyrolysis in detail. Specifically, it describes how sewage sludge is dried using various technologies until it reaches 80-90% dryness. This dried sludge can then undergo pyrolysis to produce biochar, biodiesel and syngas. Pyrolysis has advantages over incineration such as lower emissions and production of usable products. The document provides examples of slow and fast pyrolysis processes and the typical product distributions of each.

1. ENVIS ENERGY AND ENVIRONMENTAL SYSTEMS
RESEARCH AND DEVELOPMENT LTD.
TRAINING REPORT
MARMARA UNIVERSITY
ENGINEERING FACULTY
DEPARTMENT OF ENVIRONMENTAL
ENGINEERING
DATE : 04.09.2015
STUDENT NAME : NİLGÜN KADAK

2. TABLE OF CONTENTS
ABOUT COMPANY.................................................................................................... 1
INTRODUCTION........................................................................................................ 5
SEWAGE SLUDGE PYROLYSIS............................................................................. 6
 Sewage Sludge ................................................................................................... 6
 Solar Drying Technology for Sewage Sludge........................................ 7
 Thermal Drying Technology for Sewage Sludge................................... 7
 Screw Press Technology for Sewage Sludge ......................................... 8
 Pyrolysis ............................................................................................................. 9
 Advantages of Pyrolysis Process............................................................ 9
 Pyrolysis vs. Inciniration...................................................................... 10
 Products of Pyrolysis and Their Features............................................. 10
 Types of Pyrolysis Technologies ......................................................... 11
 Basic Description of Pyrolysis Process................................................ 13
 Calculations about Drying and Pyrolysis Processes ............................ 13
CUMULATIVE ENVIRONMENTAL IMPACT ASSESSMENT (CEIA) .......... 15
 Cumulative Impacts.......................................................................................... 15
 Cumulative Environmental Impact Assessment (CEIA) and Management..... 16
 Cumulative Environmental Impact Assessment (CEIA) Process......... 17
WASTEWATER TREATMENT DESIGN ............................................................ 18
 Biological Nutrient Removal Activated Sludge (BNRAS) Systems................ 18
 The University of Cape Town (UCT) Method for Enhanced Biological
Phosphorus Removal ........................................................................... 19
 The Modified University of Cape Town (UCT) Process.......... 20
REFERENCES........................................................................................................... 21

3. ABOUT COMPANY
ENVIS has taken development and application of R&D projects aiming at providing solutions
in the area of environment and energy technologies as a mission in line with the clean
production technologies and sustainable waste management concepts [1].
ENVIS aims to establish cooperation between university and industry for research and training
purposes to develop tailor-made solutions to the problems in the area of environment and
energy; and using the outputs of such cooperation to provide solution oriented technological
support compliant to national and international standards [1].
 Area of Services
~ Resource Recycling and Re-use
~ Innovative Technologies
ENVIS contributed to the development of innovative technologies in the international
scale and has the scientific and technological infrastructure to provide all sorts of services
regarding innovative technologies in the design, application and operation phases [2].
~ Experimental Analysis and Treatability
ENVIS provides technical support on
realization of successful applications by
establishing resource recycle principles for different
types of wastes of both residential and industrial
origin. Recycle and re-use are the basic principles in
ENVIS’ project approach for all waste management
projects [2].
ENVIS has the privilege to exploit all laboratory
facilities of the Istanbul Technical University, Environmental
Engineering Department, which acquires equipment and
experience rarely found in universities in the international scale
[2].
The technical staff of ENVIS is an experienced group
which has conducted extensive studies on almost every type of
municipal and industrial wastes in these laboratories and the
published the results in international scientific arena [2].

4. ~ Industrial Pollution Control and Treatment Plant Rehabilitation
Industrial wastes have significantly different characteristics depending on the industrial
activity. All studies within the scope of industrial pollution control are ENVIS’ field of
specialization [2].
Technical staff of ENVIS has implemented numerous studies on almost all industries
and in different organized industrial districts. Technical staff of ENVIS realizes the
rehabilitation of wastewater treatment plant, which are not being well operated or employing
an old technology, by implementing on-site diagnosis/treatment/remediation applications. In
this way, it becomes possible to make significant savings on operation costs as well as to meet
required conditions imposed by the stricter regulations [2].
~ Management of Wastes and Wastewater Treatment Plant Sludges
ENVIS is one of the companies having the level of expertise and experience found very
rare in Turkey, able to conduct both scientific research and applications in the field of waste
management and wastewater treatment plant sludge management [2].
~ Environmental Impact Assessment and Risk Assessment
ENVIS, provides scientific and technical support on assessment of environmental
impacts, definition of mitigation measures and design of systems for the investments within the
framework of scope defined by national and international legislation. ENVIS conducts
environmental impact assessment studies with its experienced staff within the framework of
Equator Principles, which is a requirement for the investor in his crediting applications [2].
ENVIS, identifies all possible environmental hazards and risks in all plants, establishes
and organizes plant-specific risk management application plans which include risk reduction,
risk control, reduction of harm, intervention and restoration processes [2].

5. ~ Wastewater Management and Wastewater Treatment Plant Design
ENVIS, with its experienced technical team, is among the exceptional companies who
are able to offer services in both residential and industrial areas. The long list of design and
feasibility studies concluded by ENVIS in both fields is the result of research and development
studies which are recognized as leading examples [2].
~ Treatment Plant Management, Operation and Maintenance
~ Carbon Inventory and Energy Management
ENVIS implements studies on greenhouse gas (GHG) inventories and footprints
defining sector-specific methods and technologies by identifying process modifications which
can be employed towards achieving GHG emission reductions. ENVIS provides consultancy
services on verification of GHG emissions and certification under ISO 14064, which forms the
basis for emission trading [2].
ENVIS determines energy management tools, targets and programs and defines an
effective energy management system which minimizes the energy costs and reduces GHG
emissions through identification of high energy consumption areas [2].
ENVIS has the expertise and experience
required by plant management approach towards
operation and maintenance services. ENVIS has
the privilege to exploit both the laboratory
facilities and applied training and documentation
potential required for the operation of the Istanbul
Technical University, Environmental Engineering
Department [2].

6. ~ Environmental Audit and Management
ENVIS determines the basis of environmental management by making use of scientific
data and in relation to that investigates and evaluates the industrial plants on-site considering
all environmental data with its expert team having extensive know-how. ENVIS re-organizes
the existing environmental management systems in accordance with the changing conditions
and determines the measures to be taken in order to fulfill the requirements of environmental
audits [2].
ENVIS determines possible improvement measures by evaluating
resource/energy/waste relation at all plants, defines saving opportunities and within the
framework of the investigations and evaluations. ENVIS prepares a new environmental
management plan and environmental action plan compatible with the legislation [2].
 Certificates Possessed by ENVIS Energy and Environmental Systems
Research&Development LTD.
Figure [1]: ISO 9001 certification Figure [2]: ISO 14001 certification
possessed by ENVIS [1] possessed by ENVIS [1]
 ISO 9001: 2008  ISO 14001: 2004

7. INTRODUCTION
ENVIS is a multi-functional company that has well-experienced instructors and highly
qualified staff. Therefore, my training in the office of ENVIS is considerably efficient from
every angle.
The main points I have learnt throughout my training;
 What sewage sludge is and which drying processes of sewage sludges must be applied
to meet the regulations in Turkey.
 How to obtain energy from sewage sludge by using pyrolysis method and how to make
the basic calculations of drying and pyrolysis process.
 How to write Cumulative Environmental Impact Assessment (CEIA) and which
parameters are to be considered while writing CEIA.
 How the University of Cape Town Process works and what happens during the
biochemical process of each unit.

8. SEWAGE SLUDGE PYROLYSIS
 Sewage Sludge
Sewage sludge is a by-product of the municipal and industrial wastewater treatment
plants. It is the residual slurry of settleable solids. In recent years, environmental issues have
increasingly focused on sewage sludge treatment because wastewater treatment standards have
become more stringent [3].
Figure [3] : Sewage sludge [4]
According to the related regulation in Turkey, dryness ratio of treatment sludge must
provide a ratio of 30%. [5].
Within the scope of the recent regulations in Turkey,
~ The sewage sludges that have the dryness ratio of 30 % are landfilled, or
~ The sewage sludges that have the dryness ratio of 30 % are dried untill the dryness ratio
reaches to 80-90 % and then energy is obtained by applying pyrolysis process. [5]
Figure [4]: Sludge phases according to the dryness ratio [6]
1000 kg 160 kg 44 kg 20 kg
Wet Sludge Dewatered Sludge Dried Sludge Ash
4 % DS 25 % DS > 90 % DS > 99 % DS
40-80 % organic
in DS
40-80 % organic
in DS
40-80 % organic
in DS
0-3 % organic

9. The methods mentioned below can use to dry the sewage sludges that have the dryness
ratio of 30 % ;
 Solar Drying Technology for Sewage Sludge
Solar drying is a process for sludge drying by convection: under the effect of solar
radiation, water evaporates from the sludge. When the solar system is completely covered with
a transparent roof and walls (glasshouse), the greenhouse effect accelerates sludge drying. Solar
drying of sludge has low operating costs for energy [7].
Figure [5]: Solar drying of sewage sludge [7]
 Thermal Drying Technology for Sewage Sludge
The pinnacle technology utilizing waste heat for thermal drying. Various heat sources
and heat transfer media starting with a temperature level of approximately 100°C (212°F) can
be utilized [8].
It's a technology that limits greenhouse gas emissions and insures control of odor
problems. Furthermore, the recovery of low calories present on the site (cogeneration, heating
and air conditioning systems, residual energy etc.) allows a decrease in energy consumption
[9].
 Solar drying technologies can be more preferable than thermal drying systems
considering the initial investment cost, operating cost, field conditions and
meteorological conditions [5].
In summer months, the sludge that has dryness ratio of 80-90 % due to the drying
processes can be more than at the other months. Because evaporation is much more than in
the other months depending on the weather temperature [5].

10.  Screw Press Technology for Sewage Sludge
Screw Press is one of the dewatering equipment for sewage sludge. It increases the dry
matter of sludge from 1 % to 30 % . For this reason, this technology is more advantageous than
the other known drying technologies like filter press, belt press etc [5].
Figure [6]: Screw press technology [10]
Figure [7]: A screw press while working [11]

11.  Pyrolysis
Pyrolysis is one of the methods of thermal utilization of wastes. It is a distillation process
affected by the application of heat in an insufficiency of air. Pyrolysis gases (syngas), untreated
oils (biodiesel), and solid matter in a form of char (bio-char) are the main products of the
process. The low-temperature pyrolysis runs at the temperatures between 350-400 °C, and
above 600 °C runs high-temperature pyrolysis [3].
 Advantages of Pyrolysis Process
The advantage of the pyrolysis process is the effective reduction of volume and mass of
the dewatered sludge and vaporization of organic toxic agents from the sludge into harmless
substances in the combustion chamber. Mercury and its compounds are thermo decomposed
and vaporized as well. Pyrolysis also performs energy recycling [12]. The other advantages of
pyrolysis process are mentioned below as main topics;
~ Reduces greenhouse gas emissions and waste going to landfill
~ Produces electricity
~ Low risk of water pollution
~ Low risk of odours
~ High recovery rate of resources
~ Minimal risk of health consequences
~ Commercially proven technology [13]
Pyrolysis is a method which is used to produce energy from 80 % dry sludge [5]. Not
only sludge but also other kind of wastes can be used in this process.
Table [1]: Inputs and outputs of pyrolysis process [14]
Application Feedstock to Pyrolysis System Products of Pyrolysis
Waste-to-
Energy
Municipal Solid Waste (MSW)
Waste plastics Electrical energy
Medical waste Steam
Rubber and tyres Black carbon
E-waste Oil
Biomass/wood Non-oxidized metals
Organic sludge (sewage/oil/paper
sludge)

12.  Pyrolysis vs. Incineration
Pyrolysis has a number of important advantages over incineration. The pyrolysis system
for treatment of MSW and other wastes demonstrates excellent practical performance in
controlling the emission of harmful substances such as dioxins with levels dramatically lower
than regulation values [14].
The pyrolysis facility is self-sustainable. Steam and/or electricity generated during
operation is further supplied outside of the facility to the customers. The pyrolysis plant does
not produce waste water effluent from the gas cleaning system. Along with this obvious
environmental advantage it also makes the system less expensive [14].
Another environmental aspect is the reduction of the residuals to be sent for landfill
disposal. Some remaining non-toxic ashes can also be used in the building industry. Recovered
Metals are non-oxidized and can be further used. Pyrolysis system can treat both low calorific
and high calorific waste [14].
 Products of Pyrolysis and Their Features
The main products of pyrolysis process are;
Biochar Biodiesel Syngas
~ Biochars are created by pyrolysis of biomass. They have the potential to help reduce
the climate change effects, via carbon sequestration. Independently, biochar can
increase soil fertility of acidic soils, increase agricultural productivity, Furthermore,
biochars reduce pressure on forests. They are stable solids, rich in carbon, and can
endure in soil for thousands of years [15].
Figure [8]: Biochar produced as a result of pyrolysis process [15]

13. ~ Biodiesels are produced from the condensation of vapour of a pyrolysis reaction. The
biodiesels have heating values of 40%–50% of that of hydrocarbon fuels. The main
advantages of biodiesels are: clearly positive CO2 balance, possibility of utilisation in
small-scale power generation systems as well as use in large power stations, storability
and transportability, high-energy density compared to biomass gasification fuel, and
potential of using pyrolysis liquid in existing power plants [16].
Figure [9]: Biodiesels and biochars produced as a result of pyrolysis process [17]
~ Syngases, or synthesis gases, are a fuel gas mixture consisting primarily of hydrogen,
carbon monoxide, and very often some carbon dioxide.They are usually product of
pyrolysis and the main application is electricity generation [18]. There are lots of
benefits of syngas utilization like generation of renewable power, conversion of
problematic wastes to useful fuels, economical onsite power production and reduced
transmission losses, reduction in carbon emissions [19].
 Types of Pyrolysis Technologies
Pyrolysis processes can occur as slowly or rapidly. Slow Pyrolysis occurs during a much
longer reaction time span than fast pyrolysis and the main usable product is the solid char.
During fast pyrolysis process , the biomass must be heated very quickly with a large amount
of heat. The time period for the reaction must be very short and the vapor products must be
condensed immediately [20].
Although the main product types of slow and fast pyrolysis are the same as “biochar,
biodiesel and syngas”, the percentages of the product distribution are generally different. Slow
pyrolysis creates much less liquid products than fast pyrolysis [20].

14. The differences between the product distributions of slow and fast pyrolysis
technologies are shown in the graphs below;
Graph [1]: Slow pyrolysis product distribution pie chart [20]
Graph [2]: Fast pyrolysis product distribution pie chart [20]
35%
30%
35%
SLOW PYROLYSIS PRODUCT
DISTRIBUTION
Biochar
Biodiesel
Syngas
12%
75%
13%
FAST PYROLYSIS PRODUCT
DISTRIBUTION
Biochar
Biodiesel
Syngas

15.  Basic Description of Pyrolysis Process
Drying is essential to avoid adverse effects of water on stability, viscosity, pH,
corrosiveness and other liquid properties in the pyrolysis product [16]. For this reason, the
treatment sludge that has dry content of 30 % ratio is dried with drying systems untill dryness
of the sludge reaches 80-90 %. After drying process, the dewatered sludge is fed into the
pyrolysis reactor and the pyrolysis process takes place. During the pyrolysis process, only dry
content of the dewatered sludge is used. At the end of the process, approximately 60 % of dry
content is converted into syngas. The rest of dry content (ash,dirt etc.) is sent to landfills.
Diagram [1]: Drying and pyrolysis processes diagram [5]
 Calculations about Drying and Pyrolysis Processes
As an example, it is assumed that the sewage sludge (has 25 % dry solid) is dried in a
solar drying system untill dryness of the sludge reaches 80 %. After drying process, pyrolysis
process occurs. To calculate the vaporized water amount;
Assumption: The plant discharges 50 tons of sewage sludge per day. It means that this plant
discharges 18250 tons of sewage sludge per year.
For the sludge before drying process (25% dry content - 75% water content)
𝐴𝑛𝑛𝑢𝑎𝑙 𝑠𝑒𝑤𝑎𝑔𝑒 𝑠𝑙𝑢𝑑𝑔𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 = 50
𝑡𝑜𝑛𝑠
𝑑𝑎𝑦
∗ 365
𝑑𝑎𝑦𝑠
𝑦𝑒𝑎𝑟
= 18250 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
𝐴𝑛𝑛𝑢𝑎𝑙 𝑑𝑟𝑦 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑙𝑢𝑑𝑔𝑒 = 18250
𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟
∗
25
100
= 4562,5 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
𝐴𝑛𝑛𝑢𝑎𝑙 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑙𝑢𝑑𝑔𝑒 = 18250 − 4562,5 = 13687,5 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄

16. For the sludge after drying process (80% dry content – 20% water content)
The annual dry content of the sludge was calculated as 4562,5 tons/year. After drying
process, the amount of solid content is the same but the percentage of it is changed from 25%
to 80%. So;
𝐴𝑛𝑛𝑢𝑎𝑙 𝑑𝑟𝑦 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑙𝑢𝑑𝑔𝑒 = 4562,5 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
𝐴𝑛𝑛𝑢𝑎𝑙 𝑠𝑙𝑢𝑑𝑔𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 =
4562,5 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
80
100⁄
= 5703,1 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
𝐴𝑛𝑛𝑢𝑎𝑙 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑙𝑢𝑑𝑔𝑒 = 5703,1 − 4562,5 = 1140,6 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
According to these calculations;
𝑇ℎ𝑒 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑒𝑑 𝑤𝑎𝑡𝑒𝑟 𝑎𝑚𝑜𝑢𝑛𝑡 𝑑𝑢𝑟𝑖𝑛𝑔 𝑑𝑟𝑦𝑖𝑛𝑔 𝑝𝑟𝑜𝑐𝑒𝑠𝑠
= 𝑇ℎ𝑒 𝑎𝑛𝑛𝑢𝑎𝑙 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑏𝑒𝑓𝑜𝑟𝑒 𝑑𝑟𝑦𝑖𝑛𝑔
− 𝑇ℎ𝑒 𝑎𝑛𝑛𝑢𝑎𝑙 𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑎𝑓𝑡𝑒𝑟 𝑑𝑟𝑦𝑖𝑛𝑔
𝑇ℎ𝑒 𝑣𝑎𝑝𝑜𝑟𝑖𝑧𝑒𝑑 𝑤𝑎𝑡𝑒𝑟 𝑎𝑚𝑜𝑢𝑛𝑡 = 13687,5 − 1140,6 = 𝟏𝟐𝟓𝟒𝟔, 𝟗 𝒕𝒐𝒏𝒔
𝒚𝒆𝒂𝒓⁄
Assumption: Average solar vaporization amount is assumed as 1000 L/m2
*year. It means that
1 m3
/m2
of water vaporizes in each year. So;
𝐴𝑟𝑒𝑎 𝑜𝑓 𝐷𝑟𝑦𝑖𝑛𝑔 𝐵𝑒𝑑 =
12546,9 𝑡𝑜𝑛𝑠
𝑦𝑒𝑎𝑟⁄
1 𝑚3
𝑚2 ∗ 𝑦𝑒𝑎𝑟⁄
= 12546,9 𝑚2
As a result of these calculations, 6 drying beds are sufficient and each of them has length
of 140 m and width of 15 m.
 Length = 140 m
 Width = 15 m
 Number of bed = 6

17. CUMULATIVE ENVIRONMENTAL IMPACT ASSESSMENT
 Cumulative Impacts
Cumulative impacts are the combined impacts of a single activity or multiple activities.
The individual impacts from a single development may not be significant on their own but when
combined with other impacts, those effects could become significant [21].
Cumulative effects have been defined as “the net result of environmental impact from a
number of projects and activities” [21].
Cumulative effects can occur from the following situations:
~ Combined impacts of a plan with impacts of another plan, affecting the same
receptor.
Diagram [2]: Diagram of cumulative impacts of plans [21]
~ Interaction of policies within a plan on the same receptor.
~ Interaction of impacts from proposals within a plan affecting the same receptor.
[21]
Cumulative effects occur when there is:
~ Spatial crowding or temporal overlap between plans, proposals and
actions
~ Repeated removal or addition of resources due to proposals and actions
~ Repeated alteration of the landscape in the plan area
[21]

18. Some examples of cumulative impacts include the following:
 Effects on ambient conditions such as the incremental contribution of
pollutant emissions in an airshed.
 Increases in pollutant concentrations in a water body or in the soil or
sediments, or their bioaccumulation.
 Reduction of water flow in a watershed due to multiple withdrawals.
 Increases in sediment loads on a watershed or increased erosion
[22]
Multiple and successive environmental and social impacts from existing developments,
combined with the potential incremental impacts resulting from proposed and/or anticipated
future developments, may result in significant cumulative impacts that would not be expected
in the case of a stand-alone development [22].
 Cumulative Environmental Impact Assessment (CEIA) and Management
CEIA is the process of (a) analyzing the potential impacts and risks of proposed
developments in the context of the potential effects of other human activities and natural
environmental and social external drivers on the chosen VECs (Valued Environmental and
Social Components) over time, and (b) proposing concrete measures to avoid, reduce, or
mitigate such cumulative impacts and risk to the extent possible [22].
The key analytical task is to discern how the potential impacts of a proposed
development might combine, cumulatively, with the potential impacts of the other human
activities and other natural stressors such as droughts or extreme climatic events. VECs are
immersed in a natural ever-changing environment that affects their condition and resilience.
VECs are integrators of the stressors that affect them [22].
VECs are environmental and social attributes that are considered to be important in
assessing risks; they may be:
~ physical features, habitats, wildlife populations (e.g., biodiversity),
~ ecosystem services,
~ natural processes (e.g., water and nutrient cycles, microclimate),
~ social conditions (e.g., health, economics), or
~ cultural aspects (e.g., traditional spiritual ceremonies). [22]

19. Good CEIA focuses on understanding whether cumulative impacts will affect the
sustainability or viability of a VEC as indicated by the predicted condition of the VEC.
Consequently, the significance of cumulative impacts is judged in the context of thresholds or
limits of acceptable change, within which the VEC condition is considered to be acceptable but
beyond which further change in condition is not acceptable [22].
 Cumulative Environmental Impact Assessment (CEIA) Process
The main stages of CEIA is shown in the diagram below;
Diagram [3]: Steps of Cumulative Environmental Impact Assessment [21]

20. WASTEWATER TREATMENT DESIGN
 Biological Nutrient Removal Activated Sludge (BNRAS) Systems
Nitrogen and phosphorus are limiting nutrients in most freshwater systems and cause
eutrophication. Recently, interest has been developed in the use of biological, rather than
chemical processes for phosphorus and nitrogen removal from wastewater [23].
Biological nitrogen removal is a two step process including ammonia oxidation by
nitrification, followed by reduction of nitrogen oxides to nitrogen gaseous compounds by
denitrification. In other words, a sequence of oxic and anoxic conditions is required for
nitrogen removal [23].
Biological phosphorus removal from wastewaters exploits the potential of some
microorganisms, known as Phosphate Accumulating Organisms (PAOs), to accumulate
phosphate in excess of their normal metabolic requirements under aerobic conditions.
In metabolism of PAO under anaerobic condition, PAO uptakes excess phosphorus and
stores it as polyphosphate in the cell mass using the energy from the heterotrophic oxidation of
organic materials (BOD/COD). If PAO is exposed to anaerobic condition, where little
molecular and combined oxygen molecules are available, it obtains energy from the hydrolysis
of the accumulated polyphosphate to uptake volatile fatty acids (VFA) as poly-
hydroxyalkanoates (PHA) and poly-hydroxybutyrates (PHB) [24].
Diagram [4]: Metabolism of PAO under anaerobic conditions [24]

21. Diagram [5]: Metabolism of PAO under aerobic conditions [24]
 The University od Capetown (UCT) Method for Enhanced Biological
Phosphorus Removal
One of the most commonly applied BNRAS methods for urban wastewater treatment
relies on the University of Cape Town (UCT) concept [23].
The UCT process was designed to minimize the effect of nitrate to the anaerobic contact
zone, which is crucial for maintaining truly anaerobic conditions and thus, allowing biological
phosphorus release. In fact, the higher the phosphorus concentration released in the anaerobic
tank, the higher is the phosphorus concentration taken up under aerobic conditions [23].
Diagram [6]: UCT process diagram [25]

22.  The Modified University of Capetown (Modified UCT) Process
It modifies the UCT process with the first anoxic zone designed to reduce only the
nitrate nitrogen in the return activated sludge. The second anoxic zone is designed for a much
higher quantity of nitrate nitrogen removal as mixed liquor is recycled to it from the nitrification
zone [26].
Diagram [7]: Modified UCT process diagram [25]

23. REFERENCES
1. http://www.envis.com.tr/en/index.html (05.10.2015)
2. http://www.envis.com.tr/en/services.html (05.10.2015)
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