Understanding Wastewater Treatment

Wastewater treatment is the process through which contaminants are removed from household, municipal, or industrial sewage and water is made safe for release into the environment. In natural settings water purification is accomplished through dilution and decomposition; wastewater treatment is an industrialized and standardized variation of natural processes that uses a combination of physical, chemical, and biological procedures. There are five components to wastewater treatment, though the extent of the processing in any given system will vary by location and government. The process of wastewater treatment includes: pretreatment, primary, secondary, and tertiary treatment, and polishing.

Pretreatment allows large debris like trash or tree limbs to be removed from wastewater prior to entering the more sensitive mechanized stages of processing.

The first stage of treatment is the physical removal of biological solid wastes from wastewater. Biological solids include such items as hair, food, or feces. This first stage of treatment collects wastewater for a regulated period of time during which solid materials will settle to the bottom; fats and oils rise to the top. Physical implements then physically separate the wastewater from both solids and oils.

Secondary treatment is typically a biological process and closely approximates what occurs in nature. Various native bacteria and microbes are cultivated to decompose the organic compounds in wastewater. This stage can be accomplished through the use of aerated basins, constructed wetlands, or soil biotechnology.

Tertiary treatment is most frequently used in areas where there is a concern of excess nutrients from treated wastewater entering the environment. This level of processing removes excess phosphorous and nitrogen from water through chemical or biological means. An excess of nutrients could result in eutrophication, i.e. algal bloom, and cause impaired environmental conditions for many oxygen-sensitive species.

Polishing is a fifth level of wastewater treatment. It is chemical disinfection, often via chlorination.