we use water for a lot of things - the waste goes into sewers
agricultural systems also produce a lot of waste water including nutrient run off from fields and slurry from animal farms
sewage from domestic or agricultural sources has to be treated to remove any organic matter and harmful microbes before it can be collected and treated
as well as organic matter industrial waste water can also contain harmful chemicals so it has bto undergo additional stages of treatment before it is safe to release into the environment
Sewage Treatment Happens in several stages
Before being treated the sewage is screened - this involves removing any large bits of material as well as any grit
then it stands in a settlement tank and undergoes sedimentation - the heavier suspended solids sink to the bottom to produce sludge while the lighter effluent floats on top
the effulent in the settlement tank is removed and treated by biological aerobic aerobic digestion - air is pumped through the water to encourage aerobic bacteria to break down any organic matter - including other microbes in the water