H.J.Fallowfield1, M.Taylor1, K.Baxter2, J. Lewis2 and N. Buchanan1ⱡ
1Health and Environment Group, School of the Environment, Flinders University, GPO Box 2100, Adelaide 5001, South Australia 2Melbourne Water Corporation, 990 La Trobe Street, Docklands, Victoria, 3008, Australia
Two, 223m2, single pass, HDPE lined, paddlewheel mixed high rate algal ponds (HRAPs) were constructed and operated adjacent to an Australian Gas and Light (AGL) power station at Melbourne Water Corporation’s Western Treatment Plant at Werribee, Victoria. The AGL power station utilises biogas generated from incoming raw wastewater during treatment in a covered anaerobic lagoon. Prior to combustion wastewater from a facultative pond is utilised in gas scrubbers to remove contaminating H2S and concurrently CO2 from the biogas. This enabled research on the effect of CO2 addition to wastewater on wastewater treatment and biomass production in HRAPs. The facility also enabled conduct of a study to determine the influence of depth of HRAP operation and theoretical hydraulic retention time (THRT) on HRAP wastewater treatment and biomass production. The performance of a 0.3m deep HRAP operated at a 4 d THRT over an annual cycle was also evaluated. Soluble total nitrogen (STN) removal, although higher in HRAPs operated at a depth of 0.3m compared with 0.4m, appeared to be independent of the THRTs employed in the study (2, 4 or 8d). There was no significant difference in E.coli removal between ponds operated at 0.3m or 0.4m depth. Although not significant longer THRT may increase E.coli removal in the 0.3m deep HRAP. Similarly, longer THRT increased particulate organic carbon production. STN removal by the HRAP operated at 0.3m with 4d THRT was consistent throughout spring to autumn but decreased significantly in winter. Dry matter production similarly reduced in winter and also in autumn. The E.coli removal by the same HRAP was also remarkably consistent over the year delivering 1000 MPN E.coli/100mL. Overall the study suggests that HRAPs be operated at 0.3m depth at a 4d THRT for both dry matter production and wastewater treatment. Furthermore, there seems little benefit to changing operational conditions in response to season.