Sewage

Sewage is wastewater that originates from households, businesses, and institutions and typically contains human waste, urine, greywater, detergents, and various chemicals. It is collected through an underground network of pipes and pumped or allowed to flow to wastewater treatment facilities. In many cities, combined sewer systems carry both sewage and stormwater, which can lead to overflows during heavy rain, releasing untreated material into the environment.

Treatment plants are designed to remove solids, reduce organic matter, and attenuate nutrients and pathogens to protect public health and water quality. Primary treatment uses physical processes to settle and remove larger solids, producing clarified liquid and primary sludge. Secondary treatment employs biological processes, such as activated sludge or biofilm reactors, to degrade remaining organic matter and reduce suspended solids. Tertiary or advanced treatment may include nutrient removal for nitrogen and phosphorus and disinfection by chlorine, ultraviolet light, or ozone before discharge. Some facilities recover energy from wastewater through anaerobic digestion, producing biogas, and generate biosolids for regulated beneficial reuse as soil amendments or dispose of them according to guidelines.

Discharge standards regulate the quality of treated effluent and the management of residuals to minimize environmental and health risks. Treated wastewater is typically released to rivers, lakes, or coastal waters, or reused for irrigation and industrial applications where permitted. Effective sewage management supports water quality, ecosystem health, and public sanitation, and requires ongoing investment in infrastructure, operation, and regulatory compliance.