Definition of Sewage and Sewage Treatment

Sewage is generated by residential, institutional and commercial establishments. It includes household waste liquid from toilets, baths, showers, kitchens, and sinks draining into sewers. Sewage treatment is sometimes also referred to as wastewater treatment. However, the latter is a broader term that can also refer to industrial wastewater. Sewage Treatment Plants either treat the sewage before dumping the water into rivers and similar water bodies or pass it to a Water Treatment Plant which would make the water Potable again. The extracted waste then needs to be managed as Solid Waste. Lack of application of Technology and Efficiency oriented Protocols leads to wastage, causing Scarcity. BMRV Engineering Consultancy stays on top of the latest technological developments, reducing wastages and increasing the efficiency of Water Treatment solutions, whether they be for drinking water or industrial purposes.

Waste-Water includes a mixture of Domestic Sewerage waste, Industrial Effluents, Commercial or Agricultural Activities, essentially any water that has been contaminated by human use, plus Storm water and Surface Run off. There are numerous processes that can be used to clean up wastewaters depending on the type and extent of contamination. Wastewater can be treated in wastewater treatment plants which include physical, chemical and biological treatment processes. Municipal wastewater is treated in sewage treatment plants (which may also be referred to as wastewater treatment plants). Agricultural wastewater may be treated in agricultural wastewater treatment processes, whereas industrial wastewater is treated in industrial wastewater treatment processes.

Current water availablity scenario

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163 Million Citizens do not have access to Potable Water

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~70% of surface water is Contaminated due to Biological, Toxic pollutants

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73 Million Work Days are lost due to Water Borne Diseases & Sanitation

For water that is known to be only contaminated by a particular type of waste, terms such as Sewage and Effluent are used and the corresponding treatment plants are known as Sewage Treatment Plants and Effluent Treatment Plants. The processes involved in waste-water treatment include physical processes such as settlement or flotation and biological processes such as aerated lagoons, activated sludge, or bio-films in trickling filters. Other physical methods such as filtration through sieves may be used in specialised circumstances such as de-watering waste-water sludge. At the simplest level, treatment of most wastewaters is carried out through separation of solids from liquids, usually by sedimentation. By progressively converting dissolved material into solids, usually a biological floc, which is then settled out, an effluent stream of increasing purity is produced.

Phase separation

Phase separation transfers impurities into a non-aqueous phase. It may occur at intermediate points in a treatment sequence to remove solids generated during oxidation or polishing. Grease and oil may be recovered for fuel or saponification. Solids often require dewatering of sludge in a wastewater treatment plant. Disposal options for dried solids vary with the type and concentration of impurities removed from water.

Sedimentation: Solids such as stones, grit, and sand may be removed from wastewater by gravity when density differences are sufficient to overcome dispersion by turbulence. This is typically achieved using a grit channel designed to produce an optimum flow rate that allows grit to settle and other less-dense solids to be carried forward to the next treatment stage. Gravity separation of solids is the primary treatment of sewage, the processing units being the Primary Separation Tanks (also called Primary Sedimentation Tanks). Solids that are denser than water will accumulate at the bottom of quiescent settling basins. More complex clarifiers also have skimmers to simultaneously remove floating grease such as soap scum and solids such as feathers, wood chips, or condoms. Containers like the API oil-water separator are specifically designed to separate non-polar liquids.


Oxidation reduces the biochemical oxygen demand of wastewater and may reduce the toxicity of some impurities. Secondary treatment converts organic compounds into carbon dioxide, water, and biosolids. Chemical oxidation is widely used for disinfection.

Biochemical oxidation

Secondary treatment by biochemical oxidation of dissolved and colloidal organic compounds is widely used in sewage treatment and applies to some agricultural and industrial wastewaters. Biological oxidation will preferentially remove organic compounds useful as a food supply for the treatment ecosystem. Concentration of some less digestible compounds may be reduced by co-metabolism. Removal efficiency is limited by the minimum food concentration required to sustain the treatment ecosystem.

Chemical oxidation

Chemical (including electrochemical) oxidation is used to remove some persistent organic pollutants and concentrations remaining after biochemical oxidation. Disinfection by chemical oxidation kills bacteria and microbial pathogens by adding ozone, chlorine or hypochlorite to wastewater.


Many wastewater treatment phases leave certain reactive chemicals in the water. Polishing is the phase in which we reduce the effects of those, down to standards. Chemical reduction or pH adjustment minimizes the chemical reactivity of wastewater following chemical oxidation. Carbon filtering removes remaining contaminants and impurities by chemical adsorption onto activated carbon. Filtration through sand (calcium carbonate) or fabric filters is the most common method used in municipal wastewater treatment.

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