Wastewaters

Wastewaters refers to used water from households, businesses, industry, and agriculture, as well as stormwater runoff and drainage that carries contaminants to treatment plants or natural receiving waters. In practice, wastewaters are categorized into municipal (domestic and some industrial effluent), industrial wastewater (specific to processes), greywater (from sinks, showers, laundry), blackwater (human waste), and agricultural or urban runoff.

Composition varies by source but commonly includes organic matter, nutrients, suspended solids, pathogens, salts, and chemicals. Key indicators include biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), nitrogen and phosphorus compounds, and a range of metals and synthetic organics. Wastewaters may also contain pharmaceuticals and micro-pollutants whose removal requires advanced processes.

Treatment generally proceeds in stages. Primary treatment removes settleable solids and floating debris. Secondary treatment uses biological processes, such as activated sludge or biofilm systems, to degrade dissolved organic matter. Tertiary or advanced treatment further reduces nutrients and contaminants through filtration, disinfection, and sometimes chemical precipitation or membrane processes. Sludge generated is stabilized, digested anaerobically, and dewatered for disposal or beneficial use. Treated effluent can be discharged to natural waters or repurposed for nonpotable uses; in some systems, advanced treatment enables limited potable reuse.

Wastewater management protects public health and aquatic ecosystems, supports water reuse, and can recover energy and nutrients. It is regulated by permits and standards that specify discharge limits and treatment requirements. Global challenges include aging infrastructure, funding constraints, and the emergence of micro-pollutants, requiring ongoing investment and technological development.