Industrial waste treatment should be handled in a systematic and planned way. The following steps are necessary:
1. The analysis of each effluent with its rate of flow should be carried out to determine the daily, monthly and yearly average. Any proposed expansion of the plant should also be considered. While finalizing the capacity of the waste (treatment plant), average volume over a period of 24 hours should be taken. It is also essential to know the variation in concentration by repeated analysis of the waste.
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2. Identification of pollutants, total pollution load with the assistance of flow rate and quantity should be determined.
3. The concentrated effluents should be separated and treatment programmers should be separately planned for concentrated as well as dilute effluents.
4. Material balance with regard to raw materials, intermediates and finished products should be used to verify the position.
The treatment methods can be classified into three main categories:
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1. Physical treatment
2. Chemical treatment
3. Biological treatment
Physical treatment:
This includes devices like
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1. Coarse or fine screens as well as bar screens to remove bricks, wood pieces, paper, cloth, rags, etc.
2. Communicating devices like grinders, cutters or shredders which are employed to break up solid material.
3. Grit chambers are employed as the name suggests, arresting sand, dust, stones, cinders and other heavy inorganic settle able material.
4. Grease traps are used to remove unemulsified oil and grease from the effluents.
5. Plain sedimentation tanks are employed to primarily remove suspended organic solids from the waste waters, prior to biological treatment. These tanks could be either rectangular or circular.
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Chemical Treatment:
This includes processes like neutralization, coagulation and flocculation, and chemical destruction of toxic substances like cyanides.
Biological Treatment:
As the name indicate, this process harnesses natural fauna and flora, both micro and macro, for the treatment of waste waters. Since most of the industrial effluents are deficient in one or the other essential nutrient, it is always advantageous to biologically treat them in conjunction with sewage, which provides not only the nutrients but also a heterogeneous population of bacterial flora, required for the breakdown of the pollutants.
A variety of operations, either singly or in combination, may be employed for the treatment of effluent. Various methods of treatment the choice of the method of treatment is determined by the conditions of each situation such as
1. The character of waste
2 circumstances pertaining to the body of the water being used for final disposal
3. State Health Department requirement
4. The cost of the plant and its operation.
While selecting the final method, it is also essential to determine techno-economic feasibility. For instance, the anaerobic treatment process has proved to be very effective for high-organic wastes like distillery wastes, tannery wastes, slaughter-house wastes, etc.
The aerobic process is particularly useful for waste waters, which are not very rich in organic content, like municipal water, dairy wastes, etc. Quite often, the anaerobic process has to be followed by the aerobic process for complete or near-complete treatment of waste waters.