Factors affecting the performance and risks to human health of on-site wastewater treatment systems

摘要

Aerobic wastewater treatment systems (aerobic systems) are the preferred choice in a regionnoverlying a karstic aquifer used for drinking water supplies, as they are thought to provide betternprotection to groundwater and human health than standard septic systems. However, aerobicnsystems in operation do not always perform to design standard; while this is often blamed onnlack of maintenance, few studies have investigated the link directly. This study investigates thenperformance of domestic on-site wastewater treatment systems in South Australia, andncompares effluent quality to maintenance records. Effluent from 29 septic tanks and 31 aerobicnsystems was analysed for nutrients, physico-chemical parameters and microbiological indicators.nAerobic systems generally provided greater treatment than septic tanks, yet most aerobicnsystems did not meet regulatory guidelines with high levels of indicator bacteria in 71%nof samples. The effect of system size, number of household occupants and maintenance onnaerobic system treatment performance was analysed: chlorine levels were positively correlatednwith time of last service, and nutrient concentrations were positively correlated with the numbernof occupants. A microbial risk assessment revealed the observed irrigation practices to be highnrisk; and sufficient residence time in the aquifer cannot be guaranteed for protectionnof groundwater used for drinking. Additional preventive measures such as irrigation managementnor post treatment of drinking water supply (such as UV disinfection) are required to meetnpublic health targets.