Sewage treatment


It is the process in which contaminants from domestically used water or municipal water is removed by using physical, chemical, biological means. After the removal of waste, the by-product of sewage treatment is called sludge. Sewage treatment involves a scientific and sequential operations explained as under.

Table of Contents

1. Introduction

2. Phases of Sewage treatment 

   2.1. Collecting wastewater

   2.2. Odour management

   2.3. Screening and separation

3. Primary Treatment

4. Secondary treatment


Phases of Sewage treatment 

1. Collecting wastewater

This is a civil responsibility apart from the department of water management because people should cooperate on flushing water out of their premises by managing their pipelines properly. This water is then directed to a treatment plant through a safe underground drainage systems or by exhauster tracks

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.

3. Screening and separation

This means the removal and separation of different types of objects. The objects and materials like nappies, cotton buds, scissors, glass pieces, and biological products, plastics, diapers, rags, sanitary items, face wipes, broken bottles or bottle top that in one way or another may damage the equipment. After collecting they must be separated and also leave the sewage free from clogging by these objects by completely separating them. If this step is not carried out then it results in constant machine and equipment problems. The solid wastes removed from the wastewater will be shifted to landfills.


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 that is 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.


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 becasue many aerobic organisms have already died as a result of lack of oxygen. At this stage, water flows into a tank with paddles. Paddles create a mechanical force for the slow and gradual mixing of the effluent, thereby combining the small particles together to form 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.





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