What are the different types of inorganic and organic impurities generally present in sewage?
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes. The organic impurities include human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste. The inorganic impurities include nitrates, phosphates and metals. The nutrients include phosphorous and nitrogen. The improper treatment and disposal of sewage cause diseases like cholera, typhoid and dysentery.