Sewage production is going at an alarming pace in India. it is one of the major cause of water pollution. Everyday tones of domestic sewage is released unfortunately, it is not being properly processed. Sewage treatment is the process in which contaminants from the domestically used water or municipal water is being separated through a series of physical, chemical, and biological means. After the removal of waste, the by-product of sewage treatment, sludge should be again separated. Sewage treatment involves a scientific and sequential operations explained as under.
Phases of Sewage treatment
1. Collecting wastewater
This is the responsibility of every individual but not just of the department of waste management. The domestically used water as a result of bathing, cooking, washing vessels, as well as latrine wastes, must be directed to a deep septic tank in a systematic manner. The waste must be collected by placing the collection tank far away from the living area to avoid the risk of odour and infections. This wastes from the septic tank is then directed to a treatment plant through a safe underground drainage systems or by exhauster paths.
2. Odour management
Dirty substances present in the sewage causes a foul smell over time, certain chemicals will neutralize these odours so that it is easy to work for the next stage of processing. Odour control technologies help in physically, chemically or biologically suppress the unpleasant odours from treatment plants. Odour control may be required where wastewater treatment plants release sulphur compounds, ammonia and volatile organic compounds (VOCs).
3. Screening and separation
Screening helps in the removal and separation of different types of objects separately. The objects and materials like nappies, cotton buds, scissors, glass pieces, biological products, plastics, diapers, rags, sanitary items, face wipes, broken bottles or bottle and many other wastes must be carefully collected. After collecting, the sewage must be separated to prevent logging, this will also help in avoiding the mechanical problems of equipment while processing the sewage. The solid wastes removed from the wastewater should be shifted to the landfills but making sure that different wastes must be classified separately.
4. Primary Treatment
It involves the separation of macrobiotic solid matter by pouring the wastewater into big tanks which will allow the solid matter to settle at the bottom surface of the tanks. The resulting sludge at the lowest layer is removed by large machinery scrappers and the same will be pushed to the centre of the cylindrical tanks and later pumped out of the tanks for further treatment. After removing the sludge, the water is called primary effluent and this will be pumped for secondary treatment.
5. Secondary treatment
Secondary treatment is the combination of mechanical and biological treatment of the primary effluent. The primary effluent is being pushed to a large aeration tank. The agitators in the aeration tank create a mechanical agitation force against the primary effluent. This helps in dispersing the compact molecules found in the waste. Agitation will eventually help the aerobic microbes to grow and cultivate. Microbial growth aid in reducing the biological oxygen demand ( BOD) because most of the oxygen is being utilized by organic matter. BOD is a parameter defined as the amount of dissolved oxygen required by aerobic organisms to break down the organic material present in a given water sample at a certain temperature over a specific time period. Greater the BOD, higher the pollution. As the BOD rises, the wastes are being accumulated without conversion. At this stage, water flows into a tank with paddles. Paddles create a mechanical force during the slow and gradual mixing of the effluent, thereby consolidating the small particles together to produce larger flocs. In the next stage, the aerobically processed effluent is passed through the settling tank where the heavy flocs get settled down (sedimentation) along with the formation of an ‘activated sludge‘. Finally, inoculation of the activated sludge will be done by allowing the sludge to an aeration tank. The anaerobic sludge digestion will digest the bacteria and other microbes to release methane, and carbon dioxide gas. The resulting gas can be used as biogas. The final effluent after anaerobic processing is released into rivers and streams.