2.1.1.1 Septic SystemsSeptic systems are small-scale, biological treatment systems intended to handleresidential wastewater (Figure 2.1). Household wastewater originates fromresidential toilets, sinks, washing machines, and dishwashers. The wastewaterincludes a wide variety of contaminants; among them are bacteria and viruses,grease, synthetic organic chemicals, suspended solids, solid waste, organismsthat increase biological oxygen demand (BOD), and nutrients. Wastewater iscollected in a tank, acted upon and broken down by microorganisms, then isflushed through a leach field that filters pollutants in the wastewater. Thesesystems are intended to treat septic tank effluent through filtration andbiochemical reduction and transformation of the pollutants (Winkler 1998).When septic systems are properly designed and maintained through regularpumping of the accumulated waste products, they pose minimal problems towater quality. Septic system malfunctions may result from system overload, alow population of microorganisms, overflow of solids into the leach field, andclogging of the system. These overflows can pollute surface and groundwaterresources of a watershed. The location of septic systems is also a critical factorinfluencing the level of contaminants in a watershed system, especially thosesystems located in sensitive areas associated with the lake fronts, riparian areas,coastal waters, and wetlands. Failing septic systems can pollute groundwatertài nguyên. Ô nhiễm nước ngầm giếng và tầng ngậm nước có thể có nghiêm trọngtác động về y tế công cộng và làm suy giảm nguồn cung cấp nước ngọt trong một lưu vực.Bị ô nhiễm nước ngầm là khó khăn và tốn kém để điều trị, và trong một số trường hợpcó thể được infeasible để khôi phục lại.
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