If the problem of direct urban sewage discharge becomes increasingly prominent, it will not only threaten the safe operation of related facilities but also pose potential risks to the water environment and public safety. This paper, in collaboration with a manufacturer of online water quality monitoring instruments, explores the hazards of direct sewage discharge and identifies its primary pollution sources.
Direct discharge of urban sewage into water bodies not only triggers severe water pollution and eutrophication—endangering aquatic organisms such as fish and shrimp—but also compromises human health. Two typical types of such sewage are elaborated below:
Fecal sewage
Fecal sewage contains various parasites and pathogens. Upon entering water bodies, it causes rivers to turn black and emit foul odors, directly degrading environmental sanitation and urban aesthetics. More critically, it endangers human health. For instance, untreated fecal discharge from public toilets may introduce hundreds of pathogens into groundwater or soil, leading to multi-dimensional pollution and posing tangible threats to human health.
Medical wastewater
Medical wastewater also demands high attention due to its complex composition, which includes large quantities of bacteria, viruses, parasites, and other hazardous substances. Direct discharge without disinfection will result in severe water pollution and the spread of infectious diseases.
Therefore, strict control over the discharge of urban and industrial sewage is imperative. Wastewater must undergo disinfection; subsequently, online water quality monitoring instruments should be employed to conduct real-time monitoring of key water quality indicators. Discharge is only permitted when all indicators meet the specified standards.
Primary pollution sources contributing to water body contamination are analyzed from four dimensions:
1.Pathogen-related pollutants
These primarily originate from domestic sewage and wastewater discharged by tanneries, wool-washing facilities, and hospitals. Such wastewater contains diverse pathogens that directly induce water pollution.
2.Oxygen-consuming pollutants
Certain industrial wastewaters contain organic substances such as carbohydrates and proteins. These substances consume dissolved oxygen in water during decomposition, disrupting the aquatic ecological balance and causing water pollution.
3.Plant nutrients
Nitrogen and phosphorus are the main plant nutrients affecting water quality. They stimulate the overgrowth of algae and aquatic plants, interfering with the natural water purification process and elevating the Biochemical Oxygen Demand (BOD) of water bodies.
4.Toxic substances
Once toxic substances (e.g., heavy metals and refractory organic pollutants) enter organisms and accumulate to a threshold concentration, they trigger biochemical or physiological alterations in body fluids and tissues, leading to temporary or persistent pathological conditions. In severe cases, they may even be life-threatening.
