Stp project

Sewage Treatment Plant
A Dissertation Submitted
in partial fulfilment
For the award of Degree of
Bachelor of Technology
in Department of Civil Engineering.
HOD: Dr. Kuldeep Singh
Associate Professor: Mr. Javed Ul Islam
Submitted By:
Saiyam Kumar Singh: 18EVJCE201
Vivek Firoda: 17EVJCE064 Akash:
17EVJCE003
Uttkarsh Saini: 17EVJCE062
Deepak Sharma: 17EVJCE010
Department of Civil Engineering
Vivekananda Institute of Technology
Jaipur (303012)
“May 2021”

Small Scale Wastewater Treatment Project, Phase 1 2
1: Introduction
1.1 General
In general, the sanitation field seems to live the life of an orphan in many Pacific Island
Countries. In many cases this important sector of public health has been left alone when
major upgrading projects improved the water supply systems in many countries and
provinces. This basically ignored the downstream effect of improved water supply, that of
increased discharges into rivers or aquifers. Two reasons appear to be the major cause
for that: firstly, wastewater collection and treatment is costly and their benefit often hard
to show; and secondly, even if low-cost solutions are being implemented many projects
fail to deliver the expected outcome.
Without pretending to reflect the complexity of sanitation projects three principal reasons
may be held accountable for the non-delivery problems:
• The technology was not appropriate,
• The beneficiary was not involved and consulted sufficiently, and
• The responsibilities within government were not resolved to ensure the necessary
support.
During the last years many rural areas were provided with some kind of water supply
system. The availability of water leads to wider spread use of flush toilet systems. These
systems mainly use simple toilets to discard the waste water either directly into the
porous underground or into simple holes. At the same time many villages still supplement
their water supply from shallow wells which are often located in the direct neighbourhood
of the toilets. Even if landowners consider the possible contamination of their well
through their own toilet and locate them far apart they can not avoid the location of their
neighbour’s toilet close to their well. A similar risk of water body contamination occurs
where villages situated on the banks of a small estuary/lagoon discharge their
wastewater without treatment. It is expected that Small Scale Wastewater Treatment
Plants (SSWTP), under certain circumstances, are the solution for these problems. More
specifically the SSWTP technology could be applied where,
• conventional sewage is simply too costly,
• environmental conditions require a high effluent quality,
• conventional on-site treatment proved to be of low community acceptance,
• low technology solution, such as composting toilets seem to be inappropriate.

In July 1998 the New Zealand Ministry of Foreign Affairs approved a regional project that
aimed at introducing SSWTP into three Pacific Countries. NZ$ 20,000 was allocated to
investigate the implications of implementing this important sanitation technology in Fiji,
Marshall Islands and Tonga. During the SOPAC 27th
Annual Session Niue specially
requested to be included in the project.
While it is hard to resolve the problem of government responsibilities for practitioners in
the sanitation engineering field, the first and the second problem of non-delivery may be
relieved through ensuring certain procedures during project planning and
implementation. However, the aim of the SSWTP Project in its first phase is to contribute
to technological discussion and provide insight into government structures and
procedures within the relevant countries. The method used to achieve this challenging
goal was to involve as many experts as possible experts, be they scientists or
practitioners, in the early phases of the project. The use of Internet and Email facilities
allowed for an extensive technology research and valuable feedback from virtually
anywhere in the world. Along with good contacts with government officials at national and
district level, project is ensured to reach its addressee during this phase.
1.2 Purpose Of The Project
The main purpose of the project is to identify:
• current wastewater disposal and treatment techniques,
• ongoing sanitation initiatives and projects,
• stakeholders in the sanitation sector,
• the administration structures related to sanitation projects,
• a possible project implementation agency,
• sites for future pilot projects.

5: Wastewater Treatment
5.1 Introduction - what is wastewater and what is it made up of?
Human waste or more technically referred to as ‘excreta’ is defined by
Chamber’s Concise 20th
Century Dictionary as “useless matter discharged by
animal alimentary”, animals being humans in this context. Excreta is made up of a
solid matter, faeces, and a liquid matter, urine and is essentially an organic compound.
The constituents making up
The compound are carbon, nitrogen, phosphorous, sulphur and hydrogen. Also present
are fats, carbohydrates, enzymes, proteins, trace elements, pathogens and many
different bacteria.
5.2 Why is it necessary to treat human waste or excreta?
It is necessary to treat human waste or excreta for many reasons, but the most important
reason is to preserve health. Untreated human excrement contains a variety of
pathogenic organisms, which include protozoa, bacteria, viruses and eggs of helminthes
that are disease-causing organisms. The presence of these in the environment transmits
various types of diseases. They could be:
• Water borne where pathogens are present in water supplies
• Soil–based where the excreted organism is spread through the soil
• Insect-vector borne where the pathogen is spread by insects that feed or breed in
water e.g. flies and mosquitoes.
• Faecal-oral transmission routes by which pathogens from faeces reach the mouth by
either hand, clothes food etc.
Figure 1: Faecal-oral transmission.
Source: Pickford J., 1991

5.3 Deciding which treatment option to use.
Once excrements have been produced, it is necessary to decide what to do with the
waste and determine the wastewater treatment option. There is a general distinction :
Waste being treated on-site via various treatment options e.g. VIP latrines, water seal
toilets, composting toilets etc. or by the use of water to carry the waste off-site to be
treated some place else either not too far from the compound as with septic tanks or to
specialised treatment plants through sewer lines. This form of waste often is reffered to
as wastewater or sewerage.
The total management of wastewater can be separated into four categories:
• wastewater collection,
• wastewater treatment,
• treated wastewater disposal and,
• sludge management.
Waste only becomes non-hazardous to human health after treatment.
5.4 What is Wastewater Treatment?
“The term treatment means separation of solids and stabilisation of pollutants. In turn
stabilisation means the degradation of organic matter until the point at which chemical or
biological reactions stop. Treatment can also mean the removal of toxic or otherwise
dangerous substances (for e.g. heavy metals or phosphorous) which are likely to distort
sustainable biological cycles, even after stabilisation of the organic matter.”(Sasse, 1998)
General Parameters to measure organic pollution.
COD (Chemical Oxygen Demand) is said to be the most general parameter to measure
organic pollution. COD describes how much oxygen is required to oxidise all organic and
inorganic matter found in the wastewater sample.
BOD (Biological Oxygen Demand) describes what can be oxidised biologically, with the
help of bacteria and is always a fraction of COD. Usually BOD is measured as BOD5
meaning that it describes the amount of oxygen consumed over a five-day measurement
period. It is a direct measurement of the amount of oxygen consumed by organisms
removing the organic matter in the waste. SS (Suspended Solids) describes how much of
the organic or inorganic matter is not dissolved in water and contains settleable solids
that sink to the bottom in a short time and non-settleable suspended solids.
It is an important parameter because SS causes turbidity in the water causing clogging of
filters etc. The mentioned parameters are measured in 'mg/l'.

Figure 2 Composition of solids in raw wastewater. Source: Small Wastewater System Operation
and Maintenance Vol. 1
5.5 Levels of Wastewater Treatment
Wastewater treatment options may be classified into groups of processes according to
the function they perform and their complexity:
Preliminary Treatment – includes simple processes that deal with debris and solid
material. The purpose of preliminary treatment is to remove those easily separable
components. This is usually performed by screening (usually by bar screens) and grit
removal. Their removal is important in order to increase the effectiveness of the later
treatment processes and prevent damages to the pipes, pumps and fittings.
Primary Treatment – is mainly the removal of solids by settlement. Simple settlement of
the solid material in sewage can reduce the polluting load by significant amounts. It can
reduce BOD by up to 40%. Some examples of primary treatment is septic tanks, septic
tanks with upflow filters, Imhoff tanks.
Secondary Treatment – In secondary treatment the organic material that remains in the
wastewater is reduced biologically. Secondary treatment actually involves harnessing
and accelerating the natural process of waste disposal whereby bacteria convert organic
matter to stable forms. Both aerobic and anaerobic processes are employed in
secondary treatment. Some examples of secondary treatment are UASB, reed bed
systems, trickling filters and stabilisation ponds.

Small Scale Wastewater Treatment Project, Phase 1
7.
require a safe place to be disposed of. Below is a diagram of waste stabilisation ponds
showing screening as the first stage.
Figure 4: Schematic drawing of a stabilisation ponds system, Source: Pickord J., 1991
Sedimentation
Separation of solids happens primarily by gravity, predominantly through sedimentation.
Coarse and heavy particles settle within a few hours or minutes while smaller and lighter
particles may need days and weeks to sink to the bottom.
Flotation
Flotation is the predominant method to remove fat, grease and oil. Unwanted flotation
occurs in septic tanks and other anaerobic systems where floating layers of scum are
easily formed. Accumulated scum could be removed manually or left purposedly to seal
the surface of anaerobic ponds to prevent bad odour. Below is a diagram of a septic tank
showing scum floating on the surface.
Figure 5: Wastewater separation in a septic tank. Source: Sasse L. 1998

Filtration
Filtration becomes necessary when suspended solid particles are to be removed that
cannot be forced to settle or float within a reasonable time. Most filters have a double
function, they provide a fixed surface for treatment of bacteria and they form a physical
obstacle for the smaller solid particles by creating adhesion of particles to their surfaces.
Filtration can be both on the upstream and the downstream. E.g. Upstream Anaerobic
Sludge Blanket. Anaerobic filters direct flow upwards through the filter material. Trickling
filters allow the wastewater to descend in a downward direction through the filter
material. The speed at which filtration occurs depends on the type of filter material used.
Smaller grain sizes and fine mesh sizes would cause filtration to be slower than larger,
wider-spaced material, but would cause the retention of many more solids and clog
faster.
7. What are aerobic and anaerobic processes?
With aerobic processes, bacteria use oxygen to feed on the organic material (which is a
food source) to produce carbondioxide and water, with the production of quantities of
extra bacterial mass (sludge). Most aerobic processes require the mechanical addition of
oxygen and that can be expensive.
Anaerobic processes take place in the absence of oxygen and bacteria break down the
organic wastes to produce carbondioxide and methane. This mixture of gases, called
Biogas, can potentially be harnessed as an energy source. Anaerobic process produces
much less excess sludge than aerobic processes however the treatment efficiency is not
as high as it is for aerobic processes.
The aerobic process happens much faster than anaerobic digestion and for that reason
always dominates when free oxygen is available. The high speed at which decomposition
occurs is caused by the shorter reproduction cycles of aerobic bacteria as compared to
anaerobic bacteria. Anaerobic bacteria leave some of the energy unused and it is this
unused energy which is released in the form of biogas. Aerobic bacteria use a larger
portion of the pollution load for production of their own bacterial mass compared to
anaerobic bacteria, which is why the aerobic process produces twice as much sludge as
the anaerobic process. Aerobic treatment is highly efficient when there is enough oxygen
available.
8. Sludge accumulation
Sedimentation and particles that escape filtration lead to sludge accumulation at the
bottom of vessels. This sludge gets compacted over time, consequently older sludge
occupies less volume than fresh sludge. Sludge removal is important and removal should
be performed as specified for each technology.
9. Elimination of Nitrogen
Nitrogen is a nutrient that causes algal growth in receiving waters and needs to be
removed from wastewater before discharge. It is also poisonous to fish in the form of

ammonia gases and also may become poisonous in the form of nitrite. The basic process
of nitrogen removal occurs in two steps, namely, nitrification (aerobic conditions) followed
by denitrification (anaerobic conditions) with the result that pure nitrogen diffuses into the
atmosphere. Nitrate is the most stable form of nitrogen and its’ presence indicates
complete oxidation
Figure 6: Simplified illustration of Nitrogen cycle. Source: Small Wastewater System Operation
and Maintenance Vol. 1
10. Elimination of Phosphorus
Phosphorus is a nutrient that is water soluble, often recycled and is required to support
living plants and organisms. Bacteria cannot transform phosphorus into a form in which it
loses its fertiliser quality permanently. This implies that no appropriate biological process
either aerobic or anaerobic can remove phosphorous from wastewater. Phosphorus
removal from water normally takes place by removal of bacterial mass (active sludge) or
by removal of phosphate fixing solids via sedimentation or flocculation. This process is
normally performed in the tertiary stage of treatment.
11. Elimination of toxic substances
Most heavy metals are toxic or carcinogenic and therefore should not remain in the
wastewater because they harm the aquatic life of the receiving water or could enter the
human nutritious cycle when wastewater or sludge is used in agriculture. Since heavy
metals settle easy their removal is not difficult however soluble toxic substances may be
difficult to remove. There are numerous methods for converting toxins into non-toxic
substances for e.g. ion exchange procedures.

12. Removal of pathogens
Pathogens are present in many forms in excreta e.g. bacteria, viruses and protozoa and
accumulate in the sediment sludge and are largely retained inside the treatment system
where they stay alive for several weeks. Most bacteria and viruses caught in the sludge
die after shorter periods. Those bacteria, which are not caught in the sludge but remain
suspended in the liquid portion, are hardly affected, meaning, these bacteria and viruses
exit the plant fully alive. Exposure to UV rays has a substantial hygienic effect. High
pathogen removal can also be experienced in shallow ponds with long retention times.
Constructed wetlands with their multifunctional bacterial life in the root zones can also be
very effective. Using chlorination to kill pathogens is only advisable for hospitals in the
case of epidemics and other such special circumstances as chlorine kills all forms of
bacteria both beneficial and non-beneficial. Apart from this chlorine has an adverse
impact on the environment. Water is made unstable as chlorine itself has a high chemical
oxygen demand (COD).
13. Conclusion
Wastewater treatment involves a variety of processes performed at different levels of
treatment. The basic form of treatment is the breaking down of organic waste by bacteria
either aerobically or anaerobically or a combination of both which occurs in secondary
treatment. Primary treatment offers the settlement of solids. Tertiary treatment involves
the removal of phosphorus, nitrogen and toxic substances. Pathogen removal occurs
throughout treatment but becomes more effective mostly at tertiary levels through the
use of UV rays and chlorination. The higher the treatment efficiency the better the quality
of effluent produced.

6: SMALL-SCALE WASTEWATER TREATMENT PLANTS CRITERIA
EVALUATION
1. Introduction:
The preliminary criteria of the small-scale wastewater project, given its objectives, were
determined by careful consideration of what was important when making wastewater
technological choices. Criteria were then prioritised, after which a table was set up rating
each technology against these criteria for better evaluation.
2. General Assumptions
General assumptions need to be made to keep a clear focus on the project objectives. If
these assumptions were not made then the choice of technology would be restricted to a
selected few. The assumption is that there is enough sustainable water supply for the
use of waste disposal
3. Effluent Quality
The technology chosen should produce effluent quality that is up to standard with regards
to the various quality measurements: BOD, suspended solids, nitrogen, phosphates etc.
Different technologies provide different levels of waste treatment, removing contaminants
by various methods. All options must be carefully considered with respect to the
treatment quality that is provided for by the different technologies. This is an important
criterion and is the determining factor in the effectiveness of the different technologies
chosen
In terms of effluent quality produced the ratings are as follows:
Low Effluent Quality, Moderate Effluent Quality, High Effluent Quality
4. Water Supply
Water is used in waste disposal mainly for the transportation of sewage from one place to
the next although it is used in the biological degradation of organic matter to a certain
degree as well. The assumption made by us is that there is enough water supplied for
this use as well as sustained for continuing future use for either purpose. Water is placed
here in the criteria because it is a key aspect in differentiating technologies. Without
water, it would be difficult to transport the sewerage to another site to be treated. This
allows only one option for on-site treatment, by the use of composting toilets. Locations
that are not capable of providing this water requirement would then be limited to on-site
treatment options.
To sustain water supply, a moderate amount must be used for this.
The water supply ratings are as follows:
Water Supply: Yes
Water Supply: No

12
6.5 Land Space
The reason for a limited land space requirement is that land issues are always a problem
and must be handled carefully. In a village, land may be owned by many families each
claiming their own piece. This family ownership does not only include the immediate
family, but encompasses the extended family as well, resulting in many people owning a
piece of land. Land secured for waste treatment would be difficult to obtain. This is also
placed high on the list because often there is limited land available and this needs to be
taken into account when choosing a technology. Although this would restrict our options,
limited land availability most often can’t be overcome.
In terms of land space the ratings are as follows:
Low land requirement, moderate land requirement, high land requirement
6. Maintenance and Operation
It is assumed that a certain degree of maintenance is required and also a skilled
workforce to perform maintenance and operational duties when needed. The
maintenance of a wastewater treatment system is then left up to the villagers themselves
after implementation where it is assumed that at least one villager has the capability to
oversee the operation and maintenance of the system. Although the operation and
maintenance of the system may be reviewed from time to time by the relevant parties it is
most often left to the villagers themselves in the long run. The proper maintenance of the
chosen system would be a limiting factor in terms of the sustainability of the project at the
village level, as it has been seen from past experiences that most often maintenance has
not been satisfactory. To overcome this, proper maintenance and operation training
should be made available to certain people who are responsible for this duty. Sometimes
mechanical equipment is imported and when parts need repair or replacement they are
not available locally so the system becomes non-operational for a period of time.
This criteria is placed here because maintenance and operation are important and need
to be considered when making a technological choice because the sustainability of
chosen technology rely on the proper workings of the two. Some skill would be required
for any technology, choice made as there is no technology that does not require
maintenance at all. Choices should perhaps be directed towards relatively low
maintenance systems.
In terms of maintenance and operation the ratings are as follows:
Low O & M, Moderate O & M, and High O & M
7. Cost
Financial support may be supplied by many sources. On a village level, funding may be
provided by the villagers themselves with the assistance of local government
departments e.g. Department of Health etc. Apart from this, financial service may also be
provided from other sources like foreign aid programs and so forth. Initially there would
be cost of construction after which the running costs may come into effect e.g. cost of
maintenance etc.Cost is not to be placed first on the list because within the scope of this

project it should not be the determining factor in the type of treatment system chosen.
However, people sometimes take the option of a less-than-adequate system that does
not perform satisfactorily giving out poor quality effluent for the sake of cutting costs. The
financial resources of the local area under consideration may not be much, but there may
often be foreign donor support for well-presented projects etc.
In terms of the ratings are: Low
Cost , Medium Cost, High Cost
6.8 Electrical requirement:
Electrical power may be used in many different ways in the waste treatment system for
e.g. it may be used for pumps to transport the sewerage from one place to the next and
also may be used in technologies involving aeration etc. Those technologies that are
dependent on electrical power for operation can sometimes become non-operational due
to power cuts. The assumption made is that the requirement of electrical power for
operation is not essential because there are technologies that can be chosen which do
not need electricity to operate. If electricity can be provided this just broadens the options
of technological choices.
This criteria is not placed high on the list as there are technological options available that
don’t require electricity and it is often not essential in the choices made. It is included in
the list of criteria because often the use of package plant type options requires electrical
power for operation.
The ratings for electrical requirement are:
Electrical Requirement – Yes
Electrical Requirement – No
6.9 Topography
Topographic conditions e.g. the slope of an area etc. have an influence over the type of
technology chosen and these conditions change from one site to the next. Some areas
have a topography that allows easier implementation of wastewater technologies then
others. The types of wastewater technologies chosen with consideration of topographic
conditions work more efficiently as with these technical considerations in mind they
become more effective, producing better quality effluent. Topographic conditions should
be considered as a criterion however is not included in the rating sheet as it is very site
specific.

7: Small-Scale Technologies
7.1 General
The following pages provide an overview of the identified small-scale wastewater
treatment technologies. The list does not claim to be complete but comprehensive. The
outline follows the complexity of the different systems as well as the effluent quality that
can be achieved by the respective treatment technology.
The sheets do not contain designing criteria. A separate software will be designed and
distributed once this report has been approved by the NZODA and the participating
Pacific Island Countries.
7.2 Identified technologies
7.2.1 Primary Processes

15
Moderate land requirements for both ponds with short HRT and l ong HRT as in comparison with other technologies
presented in this report however ponds with long HRT require sig ificantly more land than short HRT ponds.
No electrical requirement
Moderate Costs
ADVANTAGES DISADVANTAGES
• No electrical requirements
• Low operational and maintenance requirements
• Construction material locally available
• High effluent quality for low loaded ponds with long HRT
• Poor effluent quality for low loaded ponds
with short HRT or domestic water.
• Low effluent quality for small ponds treating
domestic wastewater
Important Sources of Information –
Sasse, L. 1998. DEWATS Decentralised Wastewater Treatment in Developing Countries
Mann, H.T., Williamson, D., 1982. Water Treatment and Sanitation
PRIMARY PROCESS TREATMENT INFORMATION
Ponds/Tanks
Sedimentation Tanks
Source: Horizontal Flow Type after Mann, H.T.,Williamson,D.,
1982
Raw sewage contains a lot of insoluble suspended
matter which can be settled in properly designed
sedimentation tanks of which there are two types
upward flow and horizontal flow. The tank has a
sloping floor to assist sludge removal that is done
by gravity through a valve at the lowest point of
the tank. The main action that occurs here is the
settling of the insoluble suspended particles and a
properly designed sedimentation tank can remove
about half of this polluting matter. Effluent
leaving here can be further treated in stabilization
ponds, percolating filters etc.

7.2.2 Secondary Processes
GENERAL INFORMATION
Effluent quality:
• Treatment Efficiency of low loaded tanks with short Hydraulic Retention Times 57% BOD removal, 53% COD
removal
• Treatment efficiency of low loaded tanks with long Hydraulic Retention Times 98% BOD removal, 96% COD
removal
Water Information
• Both greywater and blackwater can be flushed through the system
• Since they only accept liquid waste must be connected to a flush toilet. Not suitable where water supply scarce or
unreliable.
• Requires high volumes of water for transportation to treatment site. O & M
• Sludge removal is important and must be done regularly • Other then desludging no significant
maintenance required.
Moderate land requirements for both ponds with short HRT and long HRT as in comparison with some technologies
presented in this report however ponds with long HRT require significantly more land than short HRT ponds.
Moderate Costs
• High effluent quality for low loaded tanks with long HRT
• Low effluent quality for low loaded tanks
with short HRT
Mann, H.T., Williamson, D., 1982. Water Treatment and Sanitation
SECONDARY PROCESS TREATMENT INFORMATION
Reactors
Baffled Septic Tanks
Source: Flow Principle of baffled septic tank after Ludwig, S.
1998.
This process is suitable for all kinds of wastewater
including domestic. The baffled septic tank consists of
an initial settler compartment and a second section of a
series baffled reactors. Sludge settles at the bottom and
the active sludge that is washed out of one chamber
becomes trapped in the next. The reason for the tanks
in series is to assist in the digestion of difficult
degradable substances especially towards the end part
of the process. For the purpose of quicker digestion
influent upon entering the process is mixed with active
sludge present in the reactor. Wastewater flows from
bottom to top causing sludge particles to settle on the
upflow of the liquid wastewater allowing contact
between sludge already present with incoming flow. A
settler can be used for treatment after effluent has left
the tank. Hydraulic and organic shock loads have little
effect on treatment efficiency.

GENERAL INFORMATION
Effluent quality:
• Treatment Efficiency 70-95% BOD removal, 65-95% COD re
moval.
•Moderate Effluent Quality Water
Information
• Both greywater and blackwater can be
flushed through the sys em
• Since they only accept liquid waste must be connected to aflush toilet. Not suitable where water supply scarce or
unreliable.
O & M
• Requires skilled labor for construction.
• Sludge removal is important and must be done regularly
• Flow regulation is also important as up-flow velocity should not exceed 2m/h.
• Moderate operation and maintenance requirements
Low land requirement
• Low cost
• Low land space required
• Needs skilled contractors for construction

SECONDARY PROCESS TREATMENT INFORMATION
Activated Sludge Treatment
Activated Sludge Treatment
Source: After Loetscher T., 1998
Activated sludge treatment is a train of
processes designed to treat wastewater collected
from a sewer network. The preliminary
treatment removes coarse solids and grease and
primary settling allows further removal of
solids. It is in the Aeration tank that
microorganisms use oxygen to breakdown
organic pollutants. Flocs are formed which
settle in clarifier forming a sludge layer that is
then disposed in drying beds etc. at a sludge
disposal site. The clear liquid left in the clarifier
can either be further treated or discharged.
Suitable for blackwater as well as greywater.
GENERAL INFORMATION
Effluent quality:
• Treatment efficiency 95% BOD removed
• 90% Suspended Solids removed Water Information
• Since they only accept liquid waste must be connected to a
fl ush toilet. Not suitable where water supply scarce
or unreliable.
• Requires high volumes of water for transportation to treatment site.
•Both greywater and blackwater can be flushed through the em sys O
& M
• Implementation requires skilled labour and contractors •
Require expert staff for operation and maintenance.
• Process needs constant monitoring and control.
Use of pumps and control equipment needs electrical energy.
•Low land
requirement • High
Effluent quality.
•Needs skilled contractors for construction
•Importation of some construction
material • Needs trained operator
• High cost.
• Requires electricity
• High operation and maintenance
Khan, A.R. 1995. Appropriate Wastewater Treatment Processes for N-WFP, Pakistan Loetscher
T., 1998. SANEX Sanitation Expert Systems

GENERAL INFORMATION
Effluent quality:
• Produce very clear effluent equivalent to activated sludge treatment.
•95% BOD removal
•90% Suspended Solids removal
Water Requirement
• Since only receive liquid waste not suitable where water scarc or unreliable.
•Requires high volumes of water for transportation to site.
treatment O & M
•Low operation and maintenance required • Grass around ponds
need to cut regularly.
• Regular desludging is required
No electrical requirement.
High Land requirement
Moderate Costs
• Low operation and maintenance
• No electrical requirement
• Construction material locally available.
• High effluent quality
• High land space required
Khan, A.R. 1995. Appropriate Wastewater Treatment Processes for N-WFP,
Pakistan Pickford, J., 1991. The Worth of Water. Southampton Row, London, UK.
Loetscher T., 1998. SANEX Sanitation Expert Systems

7.2.3 Tertiary Processes
TERTIARY PROCESS TREATMENT INFORMATION
Lagoons/Plots
Tertiary Lagoons
(No Diagram Available)
The treatment process of Tertiary Lagoons is
similar to that of sedimentation tanks except on
a much larger scale. The area of the lagoon at
which the point of discharge is placed should be
deeper than the rest of the pond to avoid algae
being present in effluent, as algae flourish in
depths of upto 1m. The effluent from the
lagoons should be taken from the middle
portion. Suspended matter may accumulate in
lagoons, however if depths are adequate this
does not prove offence.
GENERAL INFORMATION
Effluent quality:
•Treatment quality performed on secondary treated effluent
• 40% BOD removed
•40% Suspended solids removed Water
Requirement
• Since only receive liquid waste not suitable where water scarce or unreliable.
• High volume of water required O & M
• Requires maintenance of lagoon banks and control of mosquito breeding.
High land requirement
Moderate Cost
• Construction material available locally
• No electrical requirement
• High Effluent Quality
Mann, H. T., Williamson, D., 1982. Water Treatment and Sanitation

TERTIARY PROCESS TREATMENT INFORMATION
Lagoons/Plots
Grass Plots
Source: After Mann, H. T., Williamson, D., 1982
Grass plots are simple to construct with high
rates of removal. Plots should be even and
sloped towards collection areas. Basically
effluent passes through the mesh of the grass
blades which then filter out solids in a
wellaerated environment. The possibility of
contamination of groundwater should be
considered, as some effluent will percolate into
porous ground. Coarse natural grass is
satisfactory. Surplus grass needs to be removed
and cuttings should be disposed of properly as
there could be danger of further pollution as
they decompose.
GENERAL INFORMATION
Effluent quality:
•Treatment quality performed on secondary treated effluent
• 50% BOD removed
• 70% Suspended solids removed
• 90% E. Coli removed Water Requirement
• Since only receive liquid waste not suitable where water
scarc or unreliable.
• High volumes of water required O & M sically prevent the flow
• Simple to construct.
•Requires removal of solids but only when they are seen to phy
• Surplus grass needs to be removed
High land requirement
Moderate Costs
•Low operation and maintenance • Construction material
available locally
• No electrical requirement.
Mann, H. T., Williamson, D., 1982. Water Treatment and Sanitation

Tertiary Process Treatment Information
Hybrid Toilet Systems (HTS)
Source: Hybrid Toilet Systems, Gough Plastics Brochure
The Hybrid Toilet System consists of a non-flushing,
drop toilet which feeds directly into a septic tank filled
with water (primary tank), which then delivers via
displacement, clarified effluent to the secondary
treatment unit. On completion of treatment the effluent
is then dispersed to the ground via a gravel bed. Due to
the small volumes entering the primary tank there is a
long detention period which allows for effective
breakdown of solids and efficient settling and
clarification to occur with the remaining of the
undigested solids settling to the bottom of the unit
forming a sludge layer. In the secondary tank the
effluent entering from the primary tank is directed
along very specific ascending and descending flow
paths. The majority of the secondary tank and its in
built baffling system are filled with a polyethylene
media. As the effluent flows up and down through
these zones it is subjected to aerobic, facultative, and
anaerobic treatment on four separate occasions which
continues to kill pathogens. The treated effluent then
exits the system and is sent to ground via a gravel bed.
GENERAL INFORMATION
Effluent quality:
• BOD5 1mg/m2
, Non-Filtrable Residue (NFR) ,<1mg/l,
• Total N 1.2mg/l, Total P 0.89 mg/l. (Depending on primary loads)
• Faecal Colifrom<2 organisms/100ml.
• The holding time in the system was increased to include the life period of most pathogens, and decrease water
borne diseases by using the Hybrid as a sanitation barrier in more remote communities.
Water Information
• The system is a wet system, whereby upon installation the tanks are filled with water. The system works through
displacement where if 10L went into the system, approximately 10L would be displaced through the unit.
• The system is designed to operate around volumes generated by the population using the system as a toilet only.
Waste from hand washing facilities may be introduced at the at the effluent exit point of the system.
O & M
• Construction of septic tank and upflow filter requires skilled labor
• Requires sludge removal on a regular basis, and disposal at a proper disposal site.
Requires electricity
• Low cost and low land space requirement.
• Accommodates blackwater only
• Electricity required
Gough Plastics, The Hybrid Toilet System Brochure
Gough I., Langford M., Gough A., The Hybrid Toilet System: General Principles And System Design Drivers

7.2.4 Package Plant Types
PACKAGE PLANT TYPES TREATMENT INFORMATION
Plant Type
EnviroflowBiofilter Treatment Plant System
Source: After Enviroflow Wastewater Treatment Brochure
Enviroflow Plants treat both black and
greywater through a two-stage bacterial
digestion process followed by clarification and
disinfection. Essentially wastewater is run from
kitchens, toilets etc. through two treatment
stages before clarification and disinfection. The
first stage is carried out using anaerobic and
aerobic bacteria inside a primary tank. Solids
undergo digestion by bacteria and liquids
containing soluble organic matter then passes to
the second stage. The second stage has a
biological trickling filter in which selected
bacteria grow on a medium where wastes flow
in contact with the air. Any bacterial cell matter
that is separated in this step is kept in the
effluent stream and allowed to settle out in the
clarifying chamber. Following this the then
clear effluent is passed to a disinfecting step
where Chlorine is used to disinfect the effluent.
The plants are capable of servicing from just 10
people to communities of 20,000 people as
plants can be modified to suit such varying
populations.
GENERAL INFORMATION or unreliable.
Effluent quality:
•Effluent quality contains BOD5<20mg/l
• Suspended Solids <30mg/l Water Requirement
•Since only receive liquid waste not suitable where water scarc
• High volumes of water requirement O & M
• High operation and maintenance
• Manual provided for operation and maintenance
• Small pill kit tester for effluent monitoring
Needs electrical power.
Low land requirement.
• Low land space required
• High effluent quality
• High operation and maintenance required.
• High cost
Enviroflow Wastewater Treatment Brochure

PACKAGE PLANT TYPES TREATMENT INFORMATION
Plant Type
Intermittent Decanted Extended Aeration System. (IDEA)
(No Diagram Available)
The IDEA plant consists of two reaction tanks
and is operated with sewage being continuously
introduced into the first reaction tank. Aerators
are provided in the process for mixing as well as
to allow air into the biochemical reactions.
Sewage then overflows into the second tank that
operates on a fill and draw basis that is then
intermittently decanted. Contents of the tank are
left to settle for 30mins or so leaving the treated
effluent on the surface. A special decanting
device is used where effluent is drawn through.
Flow is temporarily placed in a flow balance
tank. Effluent is then disinfected in a UV unit
after which it is drained into a wet well for
pumping to irrigation. Sludge removal is done
daily and placed into a sludge storage tank.
GENERAL INFORMATION
Effluent quality:
• Expected effluent quality Total Nitrogen less than 10mg/l and often as low as 5mg/l.
• Normal sewage has 8-10mg/l of phosphorus. Effluent Contains 6-8mg/l. Water Requirement
• Since only receive liquid waste not suitable where water scarce or unreliable.
• High volumes of water required because the IDEA plant operates with wastewater being continually being
introduced into first reaction tank.
O & M
• High maintenance and Operation
• High technology requiring Skilled operation and Maintenance.
• Daily removal of sludge.
Needs electrical power.
No land requirements information available
• High effluent quality • High operation and maintenance.
• High cost
Sinclair, Knight, Merz, 1997 Review of Effluent Management Systems Castaway Resort

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