1. screening and grit removal before the water is treated
2. the water then stands in a settlement tank and undergoes sedimentation to produce sewage sludge (heavier suspended that solids sink to the bottom) and effluent (lighter and floats to the top)
3. the sludge from the bottom of the settlement tank is removed and transferred into large tanks where it undergoes anaerobic digestion, which involves bacteria breaking down the organic matter in the sludge, releasing methane in the process. the methane gas can be used as an energy source and the remaining digested water can be used as a fertiliser
4. effluent goes through aerobic biologic treatment, which uses oxygen and bacteria, to break down organic pollutants and nutrients in wastewater, converting them into stable forms like carbon dioxide and water
5. waster water containing toxic substances requires additional stages of treatment, such as adding chemicals (e.g. to precipitate metals), UV radiation or using membranes