24-08-2013, 04:52 PM
“CETP” Common Effluent Treatment Plant :Working, Design, Benefits & Limitations
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WHY CETP IS ESSENTIAL
Small and medium scale industries are relieved of the problem of treating their effluents.
Waste water treatment is assured , thereby helping pollution control.
The pollution controlling authorities have to monitor only one outlet to check the performance of the CETP.
Participating industries have a commitment to generate only waste waters acceptable for treatment in the CETP.
Industries can concentrate on finding ways and means of reducing pollution at source, reduce water and power consumption to the extent possible.
SPECIAL REQUIREMENTS OF COMMON EFFLUENT TREATMENT PLANTS
A CETP serving several industries is only a special case of an ETP for a single industry. A CETP servers many industries, mostly small & medium scale industries together with sewage generated by its workers and adjoining house facilities , if any. The inclusion of domestic sewage is, in fact, welcome as it provides “Seeding” material for biological treatment.
Avg. flow of CETP varies from 200 to 55000 Cum /day ( 0.2 to 55 MLD), however to put thing in perspective, on a country wide basis, all industrial wastewater constitute only 10-15 per cent of the total wastewater generated in the country, the rest being municipal/domestic wastewater. As the CETP servers only small and medium sized industries, they take care of just 5-7 % of the total wastewater flow in India. However, CETPs are important for controlling industrial pollution locally in their own vicinity.
GENERAL ADVANTAGES OF CETP
Dilution is offered to the toxic constituents and inorganic dissolved solids in the industrial wastes.
Continuous seeding of microorganisms is possible when the mixture is subjected to biological treatment.
Better control over treatment plant is possible than if sewage is treated in a separate plant.
Sewage provides nitrogen and phosphorus as nutrients to the microorganisms which treat industrial wastes deficient in these elements. This reduces running cost of adding chemicals to some extent.
CETP CATAGORIES/ GROUPS
Homogeneous, in which industries producing similar goods are located in one area, for instance, tanneries or engineering goods, or pulp and paper, etc.
Heterogeneous, in which industries producing widely divergent goods are placed together, such as chemical, dairy, food and fruit processing , tanneries , pulp and paper, pharmaceuticals, etc.
WORKING CONCETP OF CETP
Liquid effluents from a group of pharmaceutical or chemical industries (located at one place in an industrial estate) can be collected and treated in combination in one treatment plant. This CETP can be managed effectively and efficiently by a separate team of experts in the field. Industries contribute finances to the functioning of CETP on the basis of pollution load (waste quantity and characteristics) , after treatment waste water may be disposed into municipal sewer or into water bodies.
In case sewers are not available ,liquid effluents may be transported from the industries to CETP, by means of tankers. It is always better if industries have primary units of treatment or even some specific units of treatment within their premises and send waste to CETP afterwards only.
Waste should have similar characteristics and be homogeneous in nature. Addition of domestic sewage from neighboring residential colonies (if any) enhances biological activity in the mixture of industrial wastes and sewage besides dilution. It is possible that COD and TDS may vary from industry to industry.
An Equalization tank is essentially the first unit in any CETP .
Air floating process is useful to collect floating matter and supply oxygen to the mixture.
Biological treatment may include anaerobic units or aerobic units or a combination of both.
Finally, sludge is removed for further treatment and disposal, whereas liquid effluents are sent to oxidation ponds for final disposal.