Small Waste Water Treatment Plant Report
Small Waste Water Treatment Plant Report
Small Waste Water Treatment Plant Report
Page 2
Table of Contents
1: INTRODUCTION
1.1 GENERAL
1.2 PURPOSE OF THE PROJECT
2: ACKNOWLEDGEMENT
3: SCOPE OF THE PROJ ECT
4: SCOPE OF THIS REPORT
5: WASTEWATER TREATMENT
5.1 INTRODUCTION - WHAT IS WASTEWATER AND WHAT IS IT MADE UP OF?
5.2 WHY IS IT NECESSARY TO TREAT HUMAN WASTE OR EXCRETA?
5.3 DECIDING WHICH TREATMENT OPTION TO USE
5.4 WHAT IS WASTEWATER TREATMENT?
LEVELS OF WASTEWATER TREATMENT
5.6 SEPARATION OF SOLIDS
5.7 WHAT ARE AEROBIC AND ANAEROBIC PROCESSES?
5.8 SLUDGE ACCUMULATION
5.9 ELIMINATION OF NITROGEN
5.10 ELIMINATION OF PHOSPHORUS
5.11 ELIMINATION OF TOXIC SUBSTANCES
5.12 REMOVAL
OF PATHOGENS
5.13CONCLUSION
e
.
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.
2:
Page 5
Page 6
3: Scope of the project
Traditionally, sanitation work in developing countries concentrates on research on
very rudimentary sanitation facilities such as stand-alone septic tanks, composting
toilets or pit toilets. Little is known about the viability of SSWTP. Therefore this
project has been designed to provide a comprehensive study to establish guidelines
for their application. It is anticipated that on completion of this project, money will be
available to implement pilot projects in theparticipating countries. Consequently the
objectives of the project can be summarised as follows:
Page 8
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 nonsettleable 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'.
Page 9
Biological treatment processes can themselves be divided into two general subdivisions aerobic and anaerobic processes.
are applicable only to industrial wastes to
Advanced or quartiairy treatment remove specific contaminants.
Figure 3 gives an overview on technologies and their categorisation
Primary
treatment
Secondary
Treatment
Tertiary
Treatment
Advanced
Treatment
Bar or Bow
Activated
Chemical treatment
Sludge
Screen
reverse Osmosis
Nitrification
Grit removal Extended
Electrodialysis
Denitrification Carbon
adsorption
Sedimentation aeration
Oil/ fat removal Aerated lagoon Chem.
Selective
ion
Trickling filter Precipitation
Flow
exchange
Disinfection
Rotation bioHyperfiltration
equalisation
Filtration
discs
pH
Chemical
neutralisation unaerobic
oxidation
Imhoff tank Sequence
batch reactor Biological P
Anaerobic filter reomval
Constructed wetlands
Aquaculture
Screening
Page 11
For the larger pieces of solids for e.g. diapers, cloth, etc. in wastewater treatment.
Screens require cleaning at very short intervals. Materials captured through
screening 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.
(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
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
[TR288 Schlzel & Bower]
Small Scale Wastewater Treatment Project, Phase 1
Page 14
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).
5.13 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.
Page 15
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
6.4 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
Page 16
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 cant be overcome.
In terms of land space the ratings are as follows:
Low land requirement, moderate land requirement, high land requirement
6.6 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
6.7 Cost
Financial support may be supplied by many sources. On a village level, funding
may be
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.
Page 18
Criteria
Technology
PROCESS TYPES
Effluent Water
Quality
Land
O&M
Cost
Electrici
ty
Low
No
Low
Low
Low
No
Low
No
Low
Low
Low
Yes
Low
Yes
Low
(Primary Treatment)
Composting Toilets,
Composti Enviroloo,
ng
Soltran II.
Toilets
Composting Toilets,
Composti Nature-Loo,
ng
Rota-Loo, Biolet
Toilets
Septic
Tank
Usage
Septic
Tank to
disposal
field
Low
Low
No
Septic Tank with up -flow filter Moderate
Yes
Low
Low
Moderate
Low
Low
Low
Yes
Low
Yes
Moderate
Imhoff Tanks
Yes
High loaded Anaerobic Moderate
Moderate
Ponds
with long HRT
Low loaded Anaerobic
Ponds
with short HRT
Low loaded Anaerobic
Ponds
with long HRT
Low loaded
Sedimentation Tanks
short HRT
No
No
LowModerate
No
Moderate
No
Low
Low
Yes
Moderate
LowModerate
No
High
Yes
Moderate
LowModerate
No
Low
Yes
Moderate
LowModerate
No
High
Yes
Moderate
LowModerate
No
Low loaded
Sedimentation Tanks
with long HRT
Secondary Treatment
UASB
Activated
Sludge Upflow Anaerobic
Sludge
Blanket
Septic
Baffled Septic Tanks
Tanks
Moderate
Yes
Low
Moderate
Yes
Low
Moderate
Low No
Moderate
Low No
Moderate
Yes
High
Low
Moderate
No
Technology
Criteria
Page 19
PROCESS TYPES
Effluent Water
Quality
Land
O&M
Cost
Electrici
ty
Moderate
Yes
High
Low
Moderate
No
Low
Moderate
No
High
High
Yes
Moderate
No
Moderate
High
Yes
High
Low
Moderate
No
High
Yes
High
Low
Moderate
No
High
High
Yes
High
Yes
High
Yes
Moderate
Yes
Low
Trickling
Filters/Percolating
Filter
High
Moderate
Yes
Moderate
High
Yes
Low
High
No
Low
Moderate
Yes
Moderate
Low
High
High
Yes
High
Yes
Low
Yes
Tertiary Treatment
Hybrid Hybrid Toilet Systems
(HTS)
Systems
Package
Plant
Types
Yes
Anaerobic Filters
Package
Plant
Types
High
High
High
d Extended
Plant
System Aeration
System.
(IDEA)
Package
Plant
Types
Cromagl
ass Unit
Package
Plant
Intermitt
ent
Decante
High
Yes
High
Low
Low
High
High
High
High
Tertiary Lagoons
Banks Clarifiers
Yes
High
High
Yes
Yes
High
Yes
High
Low
Moderate
No
High
Yes
High
Low
Moderate
No
Page 20
Technology
PROCESS TYPES
Grass Plots
Effluent Water
Quality
Land
O&M
Cost
High
Low
Moderate
Yes
High
Electrici
ty
No
6.11 Conclusion
The table ratings were done from the available information. It can be seen from the
different
ratings that each technology has its strong and weak points and therefore an
effective
combination of these treatment technologies together would maximise treatment
options.
Due to the fact that not all information is presented in the table a conclusive result
cannot be
made to totally represent all technologies present.
Page 21
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
Page 22
Primary Process
Composting Toilets
Some composting toilet systems do not require electricity however a few systems do to
power ventilation fans.
Low land requirement
Does not require water for use.
Finished Compost can still be contaminated with pathogens and should always be handled
with care.
ADVANTAGES
DISADVANTAGES
Low land space requirement
Finished compost still contaminated
No electrical requirements
with
Low operational and maintenance
pathogens
requirements
Low cost
No water required
Problems with acceptability
Important Sources of Information
Del Porto, D. The Soltran II Non-Polluting Biological Toilet and Wastewater Garden
Environment Equipment, Rotaloo Composting Toilet Brochure
Environment Equipment, Biolet Composting Toilet Brochure
[TR288 - Schlzel & Bower]
Small Scale Wastewater Treatment
Project, Phase 1
PRIMARY PROCESS
Septic Tank
Septic Tank, Longitudinal Section
Page 23
TREATMENT
INFORMATION
Page 24
Primary Process
This is essentially a septic tank with an
Upflow
Filter that is incorporated directly after the
second chamber of the septic tank. Effluent
after
leaving the second chamber of the septic
tank is
directed upwards through the bottom of the
filter before exiting to be disposed of either
in
leach fields etc. It is also mainly designed
for
on-site treatment of domestic sewage. In
the
upflow filter the effluent enters at the base
and
flows up through the layer of coarse
aggregate
F Filter, W Effluent Weir,
which is then discharged over a weir at the
C Effluent Channel
top.
Source: Septic tank with upflow filter after
Anaerobic bacteria grow on the surface of
Mara, D
the
filter material and oxidise the effluent as it
GENERAL INFORMATION
flows past. Disposal of the effluent may be
Effluent quality:
into
a stream or into soakage pits etc.
Can affect 70% reduction in BOD
Changes a malodorous highly turbid, grey to yellow influent to an odourless clear light
yellow effluent.
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.
O&M
Construction of septic tank and upflow filter requires skilled labor
Filter may be expected to operate without maintenance for 18-24 months. Need to then
drain filter and wash it
with freshwater.
Septic tank needs regular desludging. Filter and the septic tank can be cleaned together.
Septic Tank
Septic Tank With Upflow Filter
Longitudinal Section
No electrical requirement
Low land requirement
ADVANTAGES
Low cost and low land space required
No electrical requirements
Low operational and
maintenance requirements
DISADVANTAGES
Needs skilled construction
[TR288 - Schlzel
& Bower]
Small Scale Wastewater Treatment Project,
Phase 1
TREATMENT
INFORMATION
PRIMARY PROCESS
Imhoff Tanks
Imhoff Tank
Page 25
Page 26
Page 27
TREATMENT
INFORMATION
Page 28
TREATMENT
INFORMATION
No electrical requirement
Low land requirement
ADVANTAGES
DISADVANTAGES
Low cost
Needs skilled contractors for
No electrical requirements
construction
Construction material locally available
Low land space required
Important Sources of Information
Sasse, L. 1998. DEWATS Decentralised Wastewater Treatment in Developing Countries
SECONDARY PROCESS
Page 29
TREATMENT
INFORMATION
or unreliable.
Low land requirement
Moderate operation and maintenance required
ADVANTAGES
Low cost
Low land space required
Important Sources of Information
DISADVANTAGES
Needs time to stabilise process
Requires operator intervention from
time to
time to control and adjust treatment
process
Sasse, L., 1998. DEW ATS Decentralised Wastewater Treatment in Developing Countries
SECONDARY PROCESS
Activated Sludge Treatment
Activated Sludge Treatment
GENERAL INFORMATION
Effluent quality:
Treatment efficiency 95% BOD removed
90% Suspended Solids removed
Water Information
Page 30
TREATMENT
INFORMATION
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.
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.
Both greywater and blackwater can be flushed through the system
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
ADVANTAGES
DISADVANTAGES
Low land requirement
Needs skilled contractors for
High Effluent quality.
construction
Importation of some construction
material
Needs trained operator
High cost.
Important Sources of Information
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:
Page 31
TREATMENT
INFORMATION
No information available
Water Requirement
DISADVANTAGES
High land space required
Khan, A.R. 1995. Appropriate Wastewater Treatment Processes for N-WFP, Pakistan
Page 32
TREATMENT
INFORMATION
Land Treatment
Overland Flow Process
(No Diagram Available)
GENERAL INFORMATION
Effluent quality:
No information available
Water Requirement
Page 33
TREATMENT
INFORMATION
DISADVANTAGES
High land requirement
Phase 1
Page 34
SECONDARY PROCESS
TREATMENT
INFORMATION
Reed bed systems are suitable for domestic
Ponds/Beds/Lagoons
Reed Bed System/(SSF) Subsurface Flow
and
industrial wastewater that has undergone
/Wetlands/Root Zone
preliminary treatment and that has a COD
Treatment Plants/Horizontal Gravel Filter
content not higher than 500mg/l. The reed
bed
Horizontal Gravel Filter
system is 1m deep basin sealed with clay
or
some other form of lining to prevent
percolation
into groundwater with the basin itself
being
filled with soil in which reeds are then
planted.
Oxygen is transported through the pores of
the
plant down to the roots whereby the
oxygen
content increases the biological activity of
Source: Principle of the Horizontal Filter after the
soil. When wastewater runs through the
Ludwig, S. 1998
root
GENERAL INFORMATION
zone soil organic compounds and other
impurities are eliminated by microEffluent quality:
organisms in
84% COD removal rates
the soil.
86% BOD removal rate
Water Information
Since only receive liquid waste not suitable where water scarce or unreliable.
Requires high volumes of water for transportation to treatment site
O&M
Low operation and maintenance required.
Regular maintenance of erosion trenches
No electrical requirement.
Moderate land requirement
Moderate Costs
ADVANTAGES
DISADVANTAGES
Low operation and maintenance
No electrical requirement
Construction material locally available.
High effluent quality
Important Sources of Information
Sasse, L. 1998. DEWATS Decentralised Wastewater Treatment in Developing Countries
Khan, A.R. 1995. Appropriate Wastewater Treatment Processes for N-WFP, Pakistan
Page 35
TREATMENT
INFORMATION
O&M
Low operation and maintenance required
Regular desludging in defined intervals and start up needs special arrangement.
Ponds/Beds/ Lagoons
Aerobic Stabilisation Ponds/Algal
Ponds/Oxidation Ponds
No electrical requirement
Moderate land requirement, although if aeration provided land required even less.
Moderate Costs
ADVANTAGES
DISADVANTAGES
Low operation and maintenance
No electrical requirement
Construction material locally available.
High Effluent quality
Important Sources of Information
Sasse, L. 1998. DEWATS Decentralised Wastewater Treatment in Developing Countries
Mann,H.T., Williamson, D., 1982. Water Treatment and Sanitation
Page 36
TREATMENT
INFORMATION
Page 37
TREATMENT
INFORMATION
DISADVANTAGES
High cost
High operation and maintenance
requirements
Requires electricity
Page 38
TREATMENT
INFORMATION
and
fully utilize the media in filter.
air to enter the reactor. Wastewater also needs to
be equally distributed over entire surface to
80% BOD removal with organic loading rates of 1kg BOD/m3x d
Water Requirement
Since only receive liquid waste not suitable where water scarce or unreliable.
Requires a high volume of water.
O&M
High operation and maintenance
Bacterial film has to be flushed away regularly to prevent clogging and to remove dead
sludge.
Needs electrical power
Moderate land requirement
ADVANTAGES
High effluent quality
DISADVANTAGES
High cost
High operation and maintenance
requirements
Needs electrical power
GENERAL INFORMATION
Effluent quality:
Treatment quality performed on secondary
treated effluent
40% BOD removed
40% Suspended solids removed
Page 39
TREATMENT
INFORMATION
Water Requirement
No electrical requirement.
High land requirement
Moderate Cost
ADVANTAGES
DISADVANTAGES
Low operation and maintenance
High land space required
Construction material available locally
No electrical requirement
High Effluent Quality
Important Sources of Information
Mann, H. T., Williamson, D., 1982. Water Treatment and Sanitation
Page 40
TREATMENT
INFORMATION
Banks Clarifiers are a
compact tertiary
Banks Clarifiers
No electrical requirement.
High land requirement
Moderate Costs
ADVANTAGES
DISADVANTAGES
Low operation and maintenance
High land space required
Construction material available locally
No electrical requirement.
High Effluent Quality
Important Sources of Information
Mann, H. T., Williamson, D., 1982. Water Treatment and Sanitation
Page 41
TREATMENT
INFORMATION
Lagoons/Plots
Grass Plots
Source: After Mann, H. T.,
Williamson, D., 1982
GENERAL INFORMATION
Effluent quality:
Page 42
Treatment Information
Tertiary Process
Requires electricity
Low land requirement
ADVANTAGES
DISADVANTAGES
Low cost and low land space requirement. Accommodates blackwater only
Low operational and ma intenance
Electricity required
requirements
High Effluent Quality
Important Sources of Information
Gough Plastics, The Hybrid Toilet System
Brochure
Gough I., Langford M., Gough A., The Hybrid Toilet System: General Princip les And
System Design Drivers
[TR288 - Schlzel & Bower]
Small Scale Wastewater Treatment Project,
Phase 1
7.2.4 Package Plant Types
PACKAGE PLANT TYPES
Page 43
TREATMENT
INFORMATION
DISADVANTAGES
High operation and maintenance
required.
Requires electricity
High cost
[TR288 - Schlzel
& Bower]
Small Scale Wastewater Treatment Project,
Phase 1
Page 44
TREATMENT
INFORMATION
Total Nitrogen 15-25 g/m3
DISADVANTAGES
High maintenance.
Requires electricity
High cost
Page 45
TREATMENT
INFORMATION
Plant Type
Intermittent Decanted Extended Aeration
System. (IDEA)
(No Diagram Available)
GENERAL INFORMATION
Effluent quality:
ADVANTAGES
High effluent quality
Page 46
TREATMENT
INFORMATION
The Cromaglass
Systems
are
essentially
Source: After Cromaglass Wastewater Treatment Sequencing Batch Reactors where
System
treatment is by
timed sequences within a single vessel.
The unit
consists of 3 sections each performing a
different
task. In the first section (A) in which fill
and
aeration occurs is the Solids Retention
GENERAL INFORMATION
Section.
Effluent quality:
This section is separated from the rest of
Over 90-95% reduction of BOD and
the unit
Suspended Solids.
by a non-corrosive screen, which retains
BOD5 30mg/L, Total Suspendable Solids inorganic solids. Organic solids are broken
up by
30mg/L
Water Requirement
turbulence created with mixed liquor being
forced
through the screen by submersible aeration
pump
Section (B) is the continuing Aeration
section
where air and mixing are provided by
pumps.
Denitrification which is optional and is
performed
by creating anoxic conditions by closing
off air to
air intake pumps stopping aeration but
allowing
continual mixing. The liquid is then
transferred to
section (C) the Clarification Section. When
the
clarification section is overfilled excess is
spilled
back into the aeration section. When this
stops the
clarifier is then isolated, solids settle and
separate
after which effluent is pumped out of the
Clarifier
for discharge. Sludge is removed to a
sludge
processing unit.
Since only receive liquid waste not suitable where water scarce or unreliable.
High volumes of water required because it is a continuously fed activated sludge
process.
O&M
High maintenance and Operation
High technology requiring Skilled operation and Maintenance.
Needs electrical power.
Low land requirement
ADVANTAGES
Low land space required
High effluent quality
Important Sources of Information
DISADVANTAGES
High operation and maintenance.
Requires electricity
High cost
Page 47
2. Del Porto D., SPC Workshop on The Soltran II Non Polluting Biological Toilet and
Wastewater
garden, Suva, Fiji, 25 November 1996.
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