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| What is Common Effluent Treatment Plant? |
Many of the Small Scale Industries are unable to put up the treatment systems individually, the concept of CETP's (Common Effluent Treatment Plants) is envisaged to benefit such industries in treating its effluent before disposal whether it is in stream, land, sewerage system or in rivers and seas. CETP’s are set up in the industrial estates where there are clusters of small scale industrial units (Sis’s) and where many polluting industries are located.
The Ministry of Environment & Forest, Govt. of India has launched the centrally sponsored scheme, namely, Common Effluent Treatment Plant (CETP) in order to make a cooperative movement of pollution control especially to treat the effluent, emanating from the clusters of compatible Small-Scale Industries (Sis’s). The major objective of the CETP is therefore, to reduce the treatment cost to be borne by an individual member unit to a maximum while protecting the water environment to a maximum.
The proposal for setting up of CETP’s by such industries is to be submitted by the CETP Association to the respective State Pollution Control Board, which after examining the proposal and obtaining commitment from the concerned State Government regarding its contribution will give their recommendation to the Ministry of Environment and Forests for consideration , the Ministry examines the proposal and takes the decision through a Screening Committee constituted in this regard for providing support from the Central Government.
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| The pattern of financial subsidy for construction of the CETP is as follows: |
| State Subsidy |
25% of the total project cost |
| Central Subsidy |
25% of the total project cost |
| Entrepreneurs contribution |
20% of the total project cost |
| Loan from financial institutes like (IDBI, ICICI, any nationalized Banks, State Industrial Financial Corp, etc.) |
30% of the total project cost |
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The Ministry releases the funds for the approved projects which is the matching grant to the amount released by the concerned State Government, subject to the bank guarantee to be taken from the CETP associations for the amount released by the Central Government, The CETP Company should meet the remaining cost by equity contribution by the industries and loans from financial institutions. Funds released for the CETP’s should be utilized for the CETP only and not for payment for any debts/bank loans, etc. |
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| Need to Install a CETP |
There are various industries like Textiles, Electroplating, Vehicle servicing, Oil Processing, Refineries etc.
All these industries do not have enough facility or space to install effluent treatment plant boundary further, it is not economical to treat effluent in individual units.
Hence, some environmental concerned & conscious agencies installed some combined effluent treatment plants which win receive effluent from various industries. The combined effluent shall be treated in these plants to bring the discharge water quality as per the norms given by State Pollution control Committees. |
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| Treatment Process in a CETP |
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| 1. Collection |
2. Receiving Chamber |
3. Course Screening |
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| 4. Oil & Grease removal |
5. Grit Removal |
6. Fine Screening |
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| 7. Equalization Chamber |
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8. Pre Clorination
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| 9. Flash Mixture |
10. Tube Settlers |
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| 11. Sludge Thickner |
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| 12. Drum Filter |
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| 13. Pre Tertiary Tank |
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| 14. Tertiary Pump House |
15. Treated Water |
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| 16. DMF (Dual Media Filter) |
17. ACF (Active Carbon Filter) |
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| Screening |
| Raw effluent is initially passed through screen to trap all the floating material like wooden plank, plastic bags, paper etc. Initially its passed through coarse screen and later on through fine screens .all the material trapped in the screen are removed manually with the help of racks .The screened material are disposed off suitably. |
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| Oil & Grease Removal |
Many of industrial units discharge oil in waste water due to leakage of oil from the system .Grease also comes in water from lubricating system. The oil I & Grease are required to be removed in oil\Grease removing chamber effluent enters and due to availability of more cross sectional area, velocity of effluent suddenly drops down. Since the specific gravity of oil & Grease is lower than water, it floats on the top surface. From top surface oil & Grease are removed by manual skimmer. |
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| Equalization |
The flow of effluent varies from time to time .At the same time quality of effluent changes during different periods of the day. Since the treatment plant is designed for a particular flow rate and quality, it is essential to have an equalization tank prior to main treatment units. In this equalization tank a detention period for effluent is given to take care of surge load and also the Flow during lean period. The effluent in the equalization tank is pumped at constant flow rate to treatment plant. |
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| Pre Chlorination |
Effluent contains lot of organic matter, which gets oxidized later on by the reaction with dissolved oxygen in water. Normally oxygen is not available in effluent and hence it ultimately consumes oxygen from the river water or in any other natural source of water. The purpose of Pre Chlorination is to oxidize these organic and inorganic materials by chlorine.
Chlorine is a powerful oxidizing agent, which oxidizes Ammonia, Hydrogen Sulphate and many organic compounds.
By chlorination COD & BOD of effluent are reduced. In this plant solution of bleaching powder is dozed. Hypo chloride supplies free chlorine in effluent. |
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| Clarification |
Raw effluent contains suspended solids besides grit and floating material. Floating material and grit are removed in screen and grit chamber respectively. Rest 6fthe suspended solids are removed in clarification process. Any suspended solids generated due to Pre chlorination are also removed in clarifier. The clarifier is provided with tube packing to enhance the settling of suspended solids. Since clarifier is designed with tube packing it has been designated as Tube settler.
After pre chlorination, effluent goes to tube settler via flash mixer. In flash mixer Alum solution is dosed as coagulant. This coagulant aids in flocculation. The flocculated water flows upwards through tube settler. The suspended solids settle due to higher specific gravity of floes. Due to presence of PVC tubes, the settling height of particles reduces substantially resulting in higher surface overflow rates. Alum solution is used as coagulant. |
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| Sludge Thickening |
The sludge settled at the bottom of tube settler has a consistency of 1-2% W\ V and it is not possible to handle such sludge for disposal. This sludge is further filtered in rotary vacuum. After filtration, sludge is in the form of rake: and disposed off suitably.
The rotary vacuum drum filter is a rotary filter, cylindrical in shape and covered with filter cloth. Sludge is sucked by vacuum through the cloth. Solid remain on the surface of screen and filtrate is recycle back to the system. |
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| Process scheme at CETP JHILMIL & FRIENDS colony Indl. Area |
In the-installed effluent treatment plant there is only one stream of process units with certain stand by arrangement. The treatment plant consists of mainly receiving chamber, screen chamber, Grit chamber, Equalization Tank. Pre Chlorination contact tanks, flash mixer, Tube settler and final treated effluent tank. Besides main treatment units, there are sludge conditioning thickener and rotary vacuum drum filters have been provided.
Raw effluent is collected in wet well sumps of friend’s colony Ind. Area and Jhilmil industrial Area. From wet wells, effluent is pumped to receive chamber and from receiving chamber it goes to inlet chamber of equalization tank it passes Through screen chamber, oil & grease removing chamber and grit chamber.
From inlet chamber of equalization tank, it enters in equalization tank, which is in two compartments. There is isolating gate in inlet chamber to facilitate diverting effluent in any compartment of equalization tank. Normat1y in one compartment effluent is received for mixing and homogenizing. From other compartment effluent is pumped to up stream processing unit. In equalization tank agitator mechanism are provided for proper mixing. From equalization tank effluent is pumped to distribution chamber. In distribution chamber bleaching powder solution is dozed for pre chlorination from distribution chamber effluent flow by gravity to tube settlers of quall capacity. Isolation gate and valves have been provided, so that any of the flash mixer and tube settlers can be isolated for maintenance.
Over flow from tube settlers flow by gravity in to the receiving chamber of final treated effluent storage tank. Water from receiving chamber overflows in to final treated effluent storage tank. From final treated effluent sump, treated effluent is pumped I to the nallah for disposal.
Sludge is taken from the bottom of tube settler in to sludge thickener by gravity. Over flow from thickener goes to waste water sump. From waste water sump, it is pumped in to inlet chamber of equalization tank.
Sludge from bottom of sludge thickener is gone to sludge sump. Sludge from sludge sump is pumped in to vacuum filters. Cake formed in the vacuum filter is disposed of manually. Filtrate from vacuum filter is recycled by pumps to inlet chamber. |
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| Process Chemistry |
Various chemicals are used in waste water treatment to reduce soluble
Chemicals in the form of insoluble chemicals as sludge. |
| Chemical Precipitation |
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Chemical precipitation in waste water treatment involves the addition of chemicals to alter the physical state of dissolved and suspended solids and to facilitate their removal by sedimentation.
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In some cases the alteration is slight, and removal is effected by entrapment within a voluminous precipitate consisting primarily of the coagulants itself.
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Result of chemical addition is a net increase in the dissolved constituents in the water waste.
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Chemical process is developed in a conjunction with various physical operations to remove nutrients and heavy metals.
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Chemical process is saldomly used to improve ETP performances.
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Chemicals Used in the treatment of Waste Water: |
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Alum
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Bleaching Powder
- Poly Electrolite
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