Introduction
Wastewaters obtained from industries are generally much more polluted than the domestic or even commercial wastewaters. Still, however, several industrialists try to discharge their effluents into natural river streams, through unauthorized direct discharges. Such a tendency, on the part of industries may pollute the entire river water to a grave extent, thereby making its purification almost an impossible task. Sometimes, the industries discharge their polluted wastewaters into municipal sewers, thereby making the task of treating that municipal sewage, a very difficult and costly exercise. The industries are, therefore, generally prevented by laws, from discharging their untreated effluents. It, therefore, becomes, necessary, for the industry to treat their wastewaters in their individual treatment plants, before discharging their effluents either on land or lakes or rivers, or in municipal sewers, as the case may be. The characteristics of the produced wastewater will usually vary from industry to industry, and also vary from process to process even in the same industry. Such industrial wastewaters cannot always be treated easily by the normal methods of treating domestic wastewaters, and certain specially designed methods or sequence of methods may be necessary. In order to achieve this aim, it is generally always necessary, and advantageous to isolate and remove the troubling pollutants from the wastewaters, before subjecting them to usual treatment processes. The sequence of treatment processes adopted should also be such as to help generate useful bi-products. This will help economize the pollution control measures, and will encourage the industries to develop treatment plants
Industrial Wastewater Treatment Processes
Depending upon the quantum, concentration, toxicity, and presence of non-biodegradable organics in an industrial waste, the treatment may consist of any one or more of the following processes: preliminary treatment, physical treatment, chemical treatment and biological treatment
Primary and secondary treatment processes handle most of the nontoxic wastewaters; other waters have to be pretreated before being added to this flow. These processes are basically the same in an industrial plant as in a publicly owned treatment works – POTW
Primary treatment prepares the wastewaters for biological treatment. Large solids are removed by screening, and grit is allowed to settle out. Equalization, in a mixing basin, levels out the hour-to-hour variations in flows and concentrations. There should be a spill pond, to retain slugs of concentrated wastes that could upset the downstream processes. Neutralization, where required, follows equalization because streams of different pH partly neutralize each other when mixed. Oils, greases, and suspended solids are removed by flotation, sedimentation, or filtration