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|The wastewater treatment plants are often complex facilities that use modern technology and reflect advancements in engineering principles and practices, chemistry and microbiology. The wastewater field has a language of its own.
The initial step in the wastewater treatment process is called preliminary treatment and begins as all raw sewage from domestic and commercial sources enters the treatment plant at the plant’s “headworks.” Wastewater flows through bar screens. Large objects — ranging from trash and toys to rocks and branches that could clog or damage plant machinery — are mechanically raked and screened out from the sewage.
After screening, the wastewater enters a grit removal chamber where objects small enough to get through the influent screens such as sand, coffee grounds, eggshells, jewelry and coins sink to the bottom by gravity.
After leaving the grit chamber, wastewater is ready for primary treatment. During this mostly physical process, wastewater is piped into primary settling or sedimentation tanks where heavy particles sink and light particles float. With very few exceptions, wastewater is further treated beyond the primary treatment stage.
During secondary treatment, biological processes are incorporated to remove contaminants dissolved in wastewater with the use of naturally occurring microorganisms that feed on organic materials. After the microorganisms have absorbed and digested the organic materials, the wastewater is sent into secondary sedimentation tanks.