A wastewater treatment plant (WWTP) or wastewater treatment works is an industrial structure designed to remove biological or chemical waste products from water, thereby permitting the treated water to be used for other purposes. Functions of wastewater treatment plants include:
Agricultural wastewater treatment - treatment and disposal of liquid animal waste, pesticide residues etc. from agriculture. Sewage treatment - treatment and disposal of human waste, and other household waste liquid from toilets, baths, showers, kitchens, and sinks.
Industrial wastewater treatment - the treatment of wet wastes from manufacturing industry and commerce including mining, quarrying and heavy industries.
It is increasingly likely that a single facility will serve to treat water for all kinds of waste products. However, certain methods, such as biodegradation, has been found to be less effective for wastewater that includes toxic chemicals found in industrial wastewater.
Although the wastewater treatment process is a complex arrangement of pipes, pumps and tanks, it is designed to do two basic things. First, it speeds up the natural process by which water purifies itself. Second, it removes the contaminants that may harm the environment. Essentially the treatment process harnesses and enhances -- in a relatively short amount of time -- the cleansing process that would occur naturally in a lake or stream.
Treatment is accomplished through a three-stage process: Primary, Secondary and Tertiary. In Primary Treatment, water passes through screens to remove plastics, wood, sand, grit, floating objects and other heavy solids.
During Secondary Treatment, any remaining solid material in the water is removed by supplying air (O2) in an Aeration Tank. This stimulates the growth of helpful microorganisms, which consume organic matter in the wastewater. The Nutrient Removal Process uses bacteria to remove nutrients (like Nitrogen and Phosphorus) that are harmful to aquatic life. The water then moves to a Secondary Clarification Tank that allows the microorganisms and solid wastes to form clumps and settle to the bottom. Some of this residue is mixed with air again and reused in the Aeration Tank.
In Tertiary Treatment, the water passes through a deep-bed sand filter before it is disinfected as is passes through an Ultraviolet Disinfection System. The light inactivates bacteria in the water so it cannot reproduce. The purified water is then returned to the aquatic environment of the Stream / River.