wastewater treatment

Wastewater is the polluted form of water generated from rainwater runoff and human activities. It is also called sewage. It is typically categorized by the manner in which it is generated—specifically, as domestic sewage, industrial sewage, or storm sewage (stormwater).

• Domestic wastewater results from water use in residences, businesses, and restaurants.
• Industrial wastewater comes from discharges by manufacturing and chemical industries.
• Rainwater in urban and agricultural areas picks up debris, grit, nutrients, and various chemicals, thus contaminating surface runoff water.

Wastewater contains a wide range of contaminants. The quantities and concentrations of these substances depend upon their source. Pollutants are typically categorized as physical, chemical, and biological. Common pollutants include complex organic materials, nitrogen- and phosphorus-rich compounds, and pathogenic organisms (bacteria, viruses, and protozoa). Synthetic organic chemicals, inorganic chemicals, microplastics, sediments, radioactive substances, oil, heat, and many other pollutants may also be present in wastewater.

Sewage treatment facilities use physical, chemical, and biological processes for water purification. The processes used in these facilities are also categorized as preliminary, primary, secondary, and tertiary. Preliminary and primary stages remove rags and suspended solids. Secondary processes mainly remove suspended and dissolved organics. Tertiary methods achieve nutrient removal and further polishing of wastewater. Disinfection, the final step, destroys remaining pathogens. The waste sludge generated during treatment is separately stabilized, dewatered, and sent to landfills or used in land applications.

Wastewater is a complex blend of metals, nutrients, and specialized chemicals. Recovery of these valuable materials can help to offset a community’s growing demands for natural resources. Resource recovery concepts are evolving, and researchers are investigating and developing numerous technologies. Reclamation and reuse of treated water for irrigation, groundwater recharge, or recreational purposes are particular areas of focus.