Sewage discharge is the release of untreated or inadequately treated wastewater into natural environments. This wastewater originates from domestic sources like homes, commercial establishments, and industrial facilities. Its uncontrolled release poses a significant environmental challenge, impacting water quality and ecosystem health. Understanding this discharge is crucial for addressing its widespread implications.
Where Sewage Discharge Comes From
Wastewater comes from several sources. Municipal wastewater collects from homes, businesses, and institutions like schools and hospitals, containing human waste, cleaning products, and other household effluents. Industrial discharges from factories and processing plants release wastewater with byproducts specific to their manufacturing processes, including chemicals and pollutants. Agricultural runoff carries animal waste, fertilizers, and pesticides from farms into waterways, especially during rainfall. Combined sewer overflows (CSOs) are another source, occurring when heavy precipitation overwhelms older sewer systems designed for both stormwater and sewage, leading to the direct release of this mixture into rivers or coastal waters.
Environmental and Health Consequences
Untreated or partially treated sewage degrades aquatic environments. Nutrient loading, mainly from nitrogen and phosphorus in wastewater, causes eutrophication, an over-enrichment of water bodies that fuels rapid algal growth, known as algal blooms. These blooms block sunlight and deplete oxygen as they decompose, creating “dead zones” where aquatic organisms cannot survive. Sewage also contains pathogens like Escherichia coli (E. coli), norovirus, Giardia lamblia, and Cryptosporidium parvum; exposure to these microorganisms through swimming or contaminated drinking water can cause gastrointestinal illnesses, respiratory problems, and skin infections.
Beyond biological threats, sewage introduces toxic substances into ecosystems. Heavy metals like lead and mercury, pharmaceutical compounds, and microplastics are often present. These contaminants persist, bioaccumulating in aquatic organisms and moving up the food chain, potentially affecting wildlife and human consumers. For instance, some pharmaceutical residues disrupt endocrine systems in fish, altering their reproduction. These pollutants compromise recreational water safety and threaten drinking water sources.
How Sewage is Treated
Wastewater undergoes treatment stages to remove pollutants before discharge. Primary treatment is a physical process removing large solids, grease, and grit from raw sewage. This stage uses screens and settling tanks, allowing heavier particles to sink and lighter materials to float for collection. Secondary treatment then biologically removes dissolved organic matter. Microorganisms consume organic pollutants in controlled conditions, often in aeration basins, significantly reducing the water’s biochemical oxygen demand (BOD).
After primary and secondary stages, some facilities use tertiary treatment, involving advanced processes to remove specific remaining pollutants. This includes filtration through sand or activated carbon for fine suspended solids and organic compounds. Disinfection, using chlorine, ultraviolet (UV) light, or ozone, eliminates harmful bacteria, viruses, and other pathogens. These combined treatments are important for minimizing environmental and public health risks from wastewater discharge.
What You Can Do
Individual actions can reduce the burden on wastewater treatment systems and minimize sewage discharge. Proper disposal of fats, oils, and grease is important; these substances should be collected and discarded in the trash rather than poured down drains, as they can solidify and cause blockages in sewer pipes. Avoid flushing non-biodegradable items like wet wipes, paper towels, dental floss, and certain medications, which can clog pipes and interfere with treatment. Reducing water usage at home, through shorter showers or fixing leaky faucets, lessens the volume of wastewater managed by the sewer system.
For properties with septic tanks, regular maintenance is necessary, including inspections every one to three years and pumping every three to five years, to prevent system failures and overflows. Beyond individual efforts, community involvement addresses larger issues. Report suspected illegal sewage discharges to local environmental authorities or public works departments to help identify and resolve pollution sources. Supporting community initiatives and advocating for investment in modern wastewater infrastructure can improve sewage management.