Wastewater from your home comes from human waste, soaps and detergents. It goes through many stages before it is clean and safe to discharge into the sea, rivers or lakes.
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This preliminary treatment stage removes materials which can be easily removed from the raw wastewater before they damage or clog the pumps or downstream treatment processes. Preliminary treatment involves screening to remove papers and plastics as well as fats, oils, grease and grit removal.
In this stage wastewater flows through large primary sedimentation tanks with mechanical scrapers. They are used to settle solids by gravity, which are then transferred to the sludge treatment facilities.
The wastewater then passes through aeration tanks, where organic matter is reduced through a biological process. Chemicals may also be added during this secondary treatment stage to reduce unwanted nutrients like phosphates. These are turned into solids that later settle.
Following biological treatment in the aeration tanks, the wastewater is then passed through final settlement tanks equipped with mechanical scrapers where the particles settled by gravity are removed.
Various process checks and laboratory analysis is undertaken on the final effluent to ensure it has no detrimental effects on the aquatic life or other water users.