ABSTRACT
Urban wastewater is carried by sewers and constitutes the bulk of a city’s liquid waste. It contains an abundance of microorganisms, organic compounds, certain inorganic salts, mainly salts of ammonium, nitrogen and phosphorus as well as small quantities of other compounds. Urban activities also pollute rainwater, which when it runs off city streets is loaded with a wide variety of pollutants such as lead and cadmium, generally in small concentrations. Pollution with inorganic salts containing either nitrogen in the form of nitrates or ammonium salts or phosphorus in the form of phosphates may also have adverse effects on surface water. Groundwater is very susceptible to pollution because of its limited ability to self-purify. Dissolved oxygen is generally not abundant in water; therefore, organic matter can cause serious pollution, since it can lead to oxygen depletion of water and thus to a severe degradation of an aquatic ecosystem.
