How Water Is Treated In Sewage Treatment Plant? All You Should Know

Sewage water process human and industrial waste so that it don’t pose a threat to humans or environment. Usually, treatment plants use physical, chemical and biological process to remove solid contamination and debris. Sewage treatments are step by step process where they are divided into stages.

Here we have collected information from a Greeley sewage treatment plant about what happens in every stage.

Primary Treatment

It is the first stage of treatment where solids are removed through screening, sedimentation, and skimming. In this stage, coarse solids are removed through screening. This stage also attempts to remove grit. During preliminary stage, sewage flow and velocity are kept high so that solids cannot settle at the bottom. At the end of primary treatment, flow is reduced so that sedimentation can occur. Settled solids are then scraped from the bottom, and floating material is skimmed. A considerable amount of oil, grease, and soap is eliminated at this stage.

Secondary treatment

The secondary process includes aerobic biological process that helps degrading the remaining organic matter including soap, oils, human wastes, food remnants. Some of the solid matter is decomposed by microorganisms, as a result of which coagulated masses are formed which can be removed easily. Subsequently, microorganisms can be removed from the effluent through sedimentation or filtration. Though most solids are removed during secondary treatment, still it contains dissolved nutrients like nitrogen and phosphorous.

Advanced treatment

Advanced treatment is done in order to eliminate solid remains which are left after regular secondary treatment. In this process, phosphorus and heavy metals are removed through chemical processes. To remove nitrogen, biological process are employed. Additional steps may remove specific industrial or agricultural chemicals from effluent. Advanced treatment also includes filtration stage where the remaining solid is removed.


Disinfection helps removal of microorganisms from the effluent that could be released back to environment and cause harm. Disinfection includes use of chlorine, ozone, UV rays and other chemical disinfectants. Though chlorination is most common method of disinfection, residual chlorine may cause damage to ecosystem after release. Ozone and UV process makes the effluent cleaner and ready to release back. It is why at present, they are one of the most used methods in sewage treatment.

Hope this quick guide would help you understanding the complete process involved in sewage treatment.


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