Sewage Treatment refers to the process of removing contaminants, microorganisms and other types of pollutants from wastewater.Wastewater, or raw sewage, is water that drains from toilets, sinks, showers, baths, dishwashers, washing machines and liquid industrial waste.  It is treated in a multi-stage process by the Water Companies that make it safe to return to the environment.The wastewater undergoes several stages in its municipal treatment process for Environmental Protection:Pre-TreatmentThis involves the screening and removal of large debris, including sanitary towels, tampons, sticks, leaves, rags, wet-wipes, etc. from the raw sewage as these are not readily biodegradable by the process bacteria.  They are then dried and sent to landfill sites or incinerated.It also involves the removal of sand and grit which is settled out in tanks and also removed to landfill sites.Primary Sewage TreatmentThis is another settlement stage, during which mainly organic solids sink to the bottom and form a sludge and fats rise to the surface and form a scum or crust.  This crust is colonized by aerobic bacteria (they breathe oxygen) and partially digested. The liquid between these two layers drains off for processing in the Secondary treatment stage and the sludge and crust are removed periodically for further treatment.Secondary Sewage Treatment