Seasonal influence of waste stabilisation pond effluent on DAF/F (dissolved air flotation/filtration) process operation

The Bolivar wastewater treatment plant (WWTP), North of Adelaide, South Australia encompasses the largest waste stabilisation pond (WSP) system in the Southern hemisphere. The wastewater effluent will ultimately be fully reused for agriculture irrigation. A dissolved air flotation/filtration (DAF/F) plant was installed for tertiary treatment downstream of the stabilisation lagoons for supply to the irrigation scheme. Chemical treatment in the form of coagulation and flocculation is required to assist the separation process. The DAF/F plant operation is highly dependent on the raw water algal population. Seasonal variations seem to be the main abiotic factors affecting the algal population growth. Significant doses of chemical can be required to respond to rapid changes of water quality. United Water International is currently assessing the appropriate chemical treatment for short term response, and is also working with Flinders University of South Australia on determining ways to manage the lagoons and to control the water quality feeding the DAF/F plant in the long term. This paper outlines the effect of seasonal variations of WSP effluent quality on the DAF/F process operation, the findings for an adapted chemical treatment, and the eventual possibilities for lagoon management.