Performance of a high rate algal pond treating septic tank effluent from a community wastewater management scheme in rural South Australia

Abstract

A high rate algal pond (HRAP) incorporated into a community wastewater management scheme was operated over two years in the Mediterranean climate of Kingston on Murray, South Australia. Uniquely, the study evaluated the performance of the HRAP when fed (12m³ day⁻¹) either treated effluent from on-site septic tanks or a facultative pond further treating the septic tank effluent from within the community (population 300). The influence of depth and season on wastewater treatment and biomass production were determined for both configurations. Generally, wastewater treatment (> 90% BOD₅ removed) and biomass production (31.7 gm⁻² day⁻¹) was improved when the HRAP was fed septic tank effluent. PO₄-P removal was low and effected by biomass uptake rather than precipitation. Inorganic nitrogen removal was independent of depth in the warmer months and inversely related to depth in the colder months. The mean log₁₀ removal values for Escherichia coli were 1.75 and 2.75 for the HRAP when fed septic and facultative pond effluent respectively. In the prevailing Mediterranean climate, adequate BOD₅ and nitrogen removal, and disinfection assessed using E. coli as the faecal indicator organism was achieved at 0.32m depth at a retention time of 4 days.