The major sources of water pollution can be classified as municipal, industrial and agricultural.
Municipal water pollution
Municipal water pollution consists of waste water from homes and commercial establishments. For many years, the main goal of treating municipal wastewater was simply to reduce its content of suspended solids, oxygen-demanding materials, dissolved inorganic compounds and harmful bacteria. In recent years, however, more stress has been placed on improving means of disposal of the solid residues from the municipal treatment processes.
Industrial waste waters
Industrial waste waters have different characteristics both within and among industries. The impact of industrial discharges depends not only on their collective characteristics, such as biochemical oxygen demand and the amount of suspended solids, but also on their content of specific inorganic and organic substances. Three options are available in controlling industrial wastewater:
Control can take place at the point of generation in the plant.
Wastewater can be pre-treated for discharge to municipal treatment sources.
Wastewater can be treated completely at the plant and either reused or discharged directly into receiving waters.
Agricultural pollution
Agriculture, including commercial livestock and poultry farming, is the source of many organic and inorganic pollutants in surface waters and groundwater. These contaminants include both sediment from erosion of cropland and compounds of phosphorus and nitrogen that partly originate in animal wastes and commercial fertilisers. Animal wastes are high in oxygen demanding material, nitrogen and phosphorus, and they often harbour pathogenic organisms. Wastes from commercial feeders are contained and disposed of on land so their main threat to natural waters is from runoff and leaching (percolating down). Control may involve settling basins for liquids, limited biological treatment in aerobic or anaerobic lagoons and a variety of other methods.
