Waste water is any water that has been adversely affected in quality by anthropogenic influence. The waters that are used for drinking, farming, manufacturing and other purposes are degraded in quality as a result of the introduction of contaminating constituents such as organic wastes, bacteria, nitrates, phosphates and suspended solids.
As the World’s population nears 10 billion, the worldwide shortages of fresh water will be one of the most pressing environmental concerns in the next 50 years, as expected by environmental scientists.
In order to make waste water acceptable for reuse or for returning to the environment, the concentration of the contaminants must be reduced to a nonharmful level.
Wastewater treatment is a process which is used to convert wastewater into an effluent that can be either returned to the water cycle with minimal environmental issues or reused.
There are basically two types of waste water collection systems:
A combined sewer
A separate sewer system
The combined sewer systems combine both the sanitary sewage (generated from homes, businesses, industries and institutions) and stormwater (generated from rain or melting snow that drains off rooftops, lawns etc.) collection. On the other hand, separate sewer systems have isolated the sanitary sewage collection from that of stormwater collection.
The municipal waste water, which is also known as sewage is usually conveyed in a combined sewer or sanitary sewer, and treated at a waste water treatment plant. The treated waste water is then discharged into receiving water via an effluent pipe.
Some of the processes which are commonly used to treat wastewater include the following:
Phase separation: This process of treating waste water involves transferring impurities into a non-aqueous phase. The phase separation may occur at intermediate points in a treatment sequence to remove solids generated during oxidation or polishing. Grease and oil may be recovered for fuel or saponification.
Oxidation: The process of oxidation reduces the biochemical oxygen demand of waste water, and may reduce the toxicity of some impurities. Secondary treatment converts some impurities to carbon dioxide, water and biosolids. Chemical oxidation is widely used for disinfection.
Polishing: Polishing refers to the treatments made following the above methods. These treatments may also be used independently for some industrial waste water. Chemical reduction or pH adjustment minimizes chemical reactivity of wastewater following chemical oxidation. Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon. Filtration through sand or fabric filters is the most common method used in municipal waste water treatment.