2. Concept of ETP
Effluent treatment Plant covers the mechanisms and processes used
to treat such waters that have been contaminated in some way by
anthropogenic industrial or commercial activities prior to its release
into the environment or its re-use.
This effluent contains several pollutants, which can be removed
with the help of an effluent treatment plant.
ETP treat water and make free from all objectionable impurities
present in suspension, colloidal or dissolved form.
3. Need to Treat Effluent
To prevent groundwater pollution.
To prevent sea shore.
To prevent soil.
To prevent marine life.
Protection of public health.
To reuse the treated effluent.
For agriculture.
For groundwater recharge.
For industrial recycle.
Solving social problems caused by the accumulation of wastewater
4. Major Treatment units in ETP
1.Preliminary Treatment
2.Primary Treatment
3.Secondary Treatment
4.Tertiary Treatment
5. Preliminary Treatment
Preliminary treatment removes gross solids and materials that can be
easily collected from the effluent and can damage or clog the pumps and
skimmers of primary treatment clarifiers.
These are in-organic materials and insoluble organic pollutants (i.e. large
floating and suspended solid matter, grit, oil & grease) which are inert and
cause problems to further chemical and biological treatments.
The presence and sequence of preliminary treatment units are totally
depend upon the characteristic of effluent that is to be treated.
All preliminary treatment consist of physical separation techniques by
controlling flow rate of effluent.
7. SCREENS
Screens are used for removal of large floating and sub-merged material
such as plastic, paper pieces, rubber, etc. from effluent.
Major objectives are:
They prevent clogging in pump, pipes and valves, etc.
Prevent to interfere large material in primary and secondary treatment units.
Screens are classified in number of ways as follows:
Based on the size of opening- such as coarse, medium and fine screens.
Depending upon shape- such as disc, drum, band, etc.
Based on method of cleaning- such as mechanical ormanual.
8. Detritor /scrapers
Detritors are shallow circular ponds used in pre-treatment
plants with the purpose of grit removal.
Chain or blade type Detritors/scrappers are utilised in an
adjacent channel into which the collected grit istransferred.
Used when the soft and sticky substance, Grits with a 6 m
diameter are removed in the detritor.
9. Grit Chamber
Grit Chamber is used for removal of inert inorganic material consist of
sand, ash, cinder, silt, clay, glass pieces, etc.
It provides safeguard against damage to pumps, pipes and other
equipments by avoiding settling in pipe bends and channels.
The eliminated material is collected from chamber and used for land
filling, road making and on sludge drying beds.
10. Skimming Tank
Skimming Tank is used for removal of oil and grease consist of fats, waxes,
fatty acids, soaps, mineral oils, etc. present in emulsified condition in
effluent.
These materials have low solubility in water, therefore not readily available
for biological treatment and often accumulate on surface in form of scum
causing foul odors.
Objectives: Removal of scum (oil & grease) which can otherwise create
problem in biological treatment units.
11. Primary Treatment
Primary treatment consists of temporarily holding the sewage in a inert basin
where heavy solids can settle to the bottom while oil, grease and lighter solids
float to the surface.
The settled material go for sludge treatment and floating materials are
skimmed off. The remaining liquid is passed to secondary treatment.
Tanks are usually equipped with mechanically driven scrapers that continually
drive the collected sludge towards a hopper in the base of the tank where it is
pumped to sludge treatment facilities.
At this stage, over 70% of the suspended solids and 40% of the BOD is
removed from effluent.
13. Sedimentation Tank(Clarifier)
Sedimentation Tank are designed to remove suspended particles that are heavier
than water through gravitational force by reducing water velocity.
So it’s a solid liquid separation process in which a suspension is separated into
two phases –
1. Clarified supernatant leaving the top of the sedimentation tank(underflow).
2. Concentrated sludge leaving the bottom of the sedimentation tank(overflow).
An efficient sedimentation tank can remove about 90% of suspended particle
and 40% organic matter with two hour of detention time.
14. Clarifloculator
Clarifloculator consist of coagulation (chemical) and
flocculation (mechanical) process.
The chemical used for coagulation are called coagulants.
The most common coagulants are Alum, hydrated lime, ferric
chloride, ferrous sulfate and PAC (Poly aluminum Chloride).
15. Equalization Tank
Some industries produce different types of wastes, having different
characteristics at different intervals of time.
Hence, equalization tank is used to mixed different type of effluent
thoroughly to produce homogenous and equalized effluent for uniform
treatment.
This are large holding tanks with aeration or mechanical agitation with
paddles manually to give better mixing of the different unit volumes of
effluents.
The effluent is hold and mixed for specified period of time.
16. Neutralization Tank
Neutralization tank is used to provide treatment to highly acidicor highly
alkaline effluent through neutralizing pH by addition of chemicals.
Industry require neutralization of discharged effluent when it has as highly
acidic and/or highly alkaline effluent.
Acidic effluent is usually treated with lime stone or lime-slurry or caustic
soda, depending upon the type and quantity of effluent.
Alkaline effluent is neutralized by sulphuric acid or CO2 or waste boiler flue
gas.
17. Secondary treatment
Secondary treatment is a biological treatment of effluent which is typically
performed by indigenous, water-borne micro-organisms in a managed
habitat.
Secondary treatment removes dissolved and suspended organic
(biodegradable) matter by consuming it as a food and convert it into new
cell mass, energy and CO2 .
The most common micro-organisms are bacteria (aerobic or anaerobic),
protozoa and rotifers; least common are fungi and algae.
After secondary treatment almost 70-90% of BOD and 80-90% of dissolved
solids are removed from effluent.
19. Trickling Filter
In trickling filter treatment, wastewater is sprayed through sprinkling
rotating arm on circular beds consist of 3-10 ft deep coarse media (of
crushed stones, gravels or synthetic material).
Microorganisms get attach and grows on the media and resultsin
formation of film of microorganisms called zoogloeal film.
This zoogloeal film consist of millions of micro-organisms breakdowns
organic material of effluent into simple and soluble matter. Treated
effluent is drain at bottom from where it is collected then undergoesfor
sedimentation.
It is simple to operate and give almost 80-90% of BOD removal with high
quality effluent
20. Activated Sludge Process(ASP)
This is most versatile biological oxidation method employed for the
treatment of effluent containing of dissolved solids, coarse and colloidal
organic matter.
In this method, effluent is aerated in a reaction tank consist of microbial
population in suspension form. Aerobic bacteria degrades effluent into
CO2 and H2O for which oxygen is supplied through mechanical aeration or
by diffused aeration system.
The bacterial flora grows and remains suspended in the form of a floc
called activated sludge. A part of sludge is recycled for the same tank to
provide an effective microbial population for a fresh treatment cycle.
Industrial ww require 6 to 24 hours of aeration through which almost 90-
95% of BOD can be removed.
21. Tertiary Treatment
Tertiary treatment is the final treatment, meant for ‘polishing’ the effluent
and removal of pollutants not removed in primary and secondary treatment.
These pollutants may include soluble inorganic compounds such as
phosphorous or nitrogen which may support algal growth in receiving water.
Also removes organic materials contributing BOD, COD, color, taste, odor;
bacteria, viruses, colloidal solids contributing turbidity; or soluble minerals
which may interfere with subsequent re-use of the wastewater.
Preferred when treated water is need to be reuse or discharge is into a
highly sensitive or fragile ecosystem (estuaries, rivers, coral reefs, etc).
23. Filtration
Filtration is process of removing particulates and bacterial impurities that
could not be removed in earlier treatment, from water by passing it through a
porous medium.
It is used to remove colloidal and other impurities which impart turbidity to
water. Also for disinfection of water by reducing 90% of bacterial load.
It is also used to reduce odor and color by arresting them in filter media.
There are various type of filter available to treat certain type of wastewater.
Selection is totally depend upon characteristics of ww, efficiency of absorbent,
flow rate and pollutant to be removed from ww.
24. Activated Carbon Filters
ACF consist of activated carbon granules supported by very fine quartz
filter media. Various grades of carbon are available for specialized
treatment of wastewater.
ACF are used to remove free chlorine, organic residues, toxic heavy metal
ions and color from ww
Most common adsorbents used are activated carbon, peat moss, brown
coal and other cellulose materials.
This treatment not only improves taste of water but also protects other
water treatment units such as reverse osmosis membranes and ion
exchange resins from possible damage due to oxidation or organic fouling.
25. Treatment Process
The following flow diagram shows the processes followed in
the existing ETP of Gonoshasthaya Antibiotic Limited and it
represents more or less the current scenario of waste water
treatment in the pharmaceutical industries of Bangladesh.
26. Process FLOW DIAGRAM
SCREENING EQUALIZATION
FLOCCULATION&
CLARIFICATION
NEUTRALIZATION
ANAEROBIC
DIGESTION AND
CLARIFICATION
AEROBIC
DIGESTION AND
CLARIFICATION
CHLORINATION
FILTRATION &
ADSORPTION ON
ACTIVATED
CARBON
SLUDGE
MANAGEMENT
27. Screening
It has the goal to separate coarse and fine matter at the inlet
of the plant, avoiding sedimentation and clogging in the
successive stages.
Raw effluent from the source is usually received into the bar
screen chamber by gravity.
Screen provided will remove all floating and big size matter
such as plastic bottles, polythene bags, glasses, stones, etc.,
which may otherwise choke the pipeline and pumps.
28. Equalization Tank
Effluent is collected for equalization, which is designed for a normal storage
minimum 8 hours.
civil water is mixed with primary treated water. Coarse bubble aeration is
provided by means of an air blower and distribution system to achieve a
uniform and homogenous mixture of concentration of the discharge.
The raw waste from the main plant is first collected in the equalization tank
through a bar screen.
The equalization tank is designed for a hydraulic retention time of around 10
hours and is provided with air grids connected to air blowers for maintaining
the solids in suspension.
29. Flocculation and Clarification
The equalized effluent water is then pumped into the flocculation tank, where
coagulant and polymer is dosed in the flocculation compartment to air in the
process of settling.
Alum, Lime and Polyelectrolyte are added by means of dosing with pumping
or gravity force to reaction tank for sludge formation. The chemicals are
injected in the pipeline feeding and controlled by valve.
Prepared chemical solution and its dosing depend on Effluent properties BOD,
COD, and suspended solids reduce in this stage by nearly 50%.
The overflow from the LAMELLA clarifier is taken for further treatment for
removal of BOD, COD etc., while the underflow is taken for sludge treatment.
30. Neutralization
The waste water will have acidic pH and base dosing will be required for
bringing up pH to level (6-9).
The raw effluent contains average pH 3.3. The suitable pH of Anaerobic
Microorganisms is 8 to 9 and the suitable pH of Aerobic Microorganism is
7 to 8.
The biochemical reactions of the Anaerobic Microorganisms reduce pH
minimum by 0.5-1.5 by producing organic acids, so when the effluent pH
9.0 then for plant safety neutralize pH to 8.0 by controlled Alkali dosing.
31. Anaerobic Digestion and Clarification
Effluent from the high polluted equalization tank is pumped to anaerobic
digester for Bio-Chemical reaction.
Normally some Cow dung can be used as nutrient of anaerobic
microorganism at primary stage (up to 5 days). COD & BOD will be
reduced & pH also reduced by biochemical reaction at this area and
formed CH4 gas, organic acids, N2 and CO2.
Aerobic bio mass are used for nutrient as Nitrogen and Phosphorous
source. This digestion process ultimately reduces the total sludge quantity.
32. Aerobic Digestion and Clarification
To reduce pollution load (BOD, COD, TDS, TSS etc.) and decolorization reaction
is occurred by microbial action, in the oxidation process neutral effluent is
oxidized aerobic bacteria and microorganism.
These bacteria are very sensitive about pH, temperature, dissolved oxygen and
nutrients.
Aeration provides oxygen by means of air diffuser in the form of fine air bubble
which will oxidize the organic compound and oxidizable inorganic compound
by Biochemical reaction. Some sulfate reducing bacteria plays an important
role to removal of heavy metals in the effluent.
33. CONT….
This tank is divided into two parts, Oxygen will be provided in tank by air diffuser. In this
reduction process resulting in the formation of Biogenic Sulfide, these Sulfides form highly
insoluble precipitate with heavy metals such as Cd, Cu, Zn, Cr, etc. and be removed.
After oxidation effluent comes to clarifier with suspended sludge & for new cell settled at
the bottom of the clarifier unit. There is also a provision to return the activated sludge in to
the distribution tank and a part of it to carry at sludge drying bed or filter press & a part to
carry at anaerobic pond as nutrients.
To maintain a certain level of MLSS (3500-3800ppm) in oxidation tank as good efficiency,
clear water is overflowed from clarifier drain and collected in Clear water tank/ Post
Oxidation tank.
34. Chlorination
The overflow from the secondary lamella clarifier is collected
in the clear water tank where chlorine in the form of sodium
hypochlorite is dosed to aid in the process of disinfection.
The disinfected water is then treated through filtration to
achieve desired treated water quality.
35. Filtration & adsorption on activated carbon
The chlorinated waste water is then pumped into the Multi grade filter for
removal of suspended solids.
The filtered water is then passed through Activated carbon filter for further
polishing and removal of excess chlorine.
The ACF treated water is collected in the treated water tank from where it
is pumped for backwash of the filters. The dirty backwash water is taken
back to the equalization tank.
The filtered water can be used for low end applications like toilet flushing,
gardening etc.
36. Sludge Management
The concentrated sludge is then taken to sludge bed or filter
press.
The dried up sludge is manually cleared for disposal as land
filling.
Very minimum sludge will be produced from aerobic digester
as dry form and anaerobic sludge will be cleaned from
anaerobic digester once a year and these will be disinfected
by Sodium hypo Chloride. It can be used as fertilizer or as land
filling.
