Performance analysis of established advanced onsite wastewater treatment systems in a subarctic environment: Recirculating trickling filters, suspended growth aeration tanks, and intermittent dosing sand filters

Household onsite septic systems with secondary wastewater treatment in Anchorage, Alaska, were sampled and analyzed for performance parameters during winter and spring months. System types included intermittent dosing sand filters, three types of recirculating trickling filters, and suspended growth aeration tanks. Mean total nitrogen (TN) from the trickling filter and aeration tank effluents was fairly uniform at about 30 mg/l. Total suspended solids (TSS) means were mostly less than 15 mg/l. Biochemical oxygen demand (BOD5) showed considerable variability, with means ranging from 9.2 mg/l for sand filters up to 39.5 mg/l for one type of trickling filter. Local wastewater treatment system certification limits for BOD5 and TN were not met by a large proportion of samples and sites. The data suggested that effluent temperature within the sample range had almost no effect on effluent concentrations of BOD5 or TSS, and only a small effect on removal of total nitrogen.