Algal production in wastewater treatment high rate algal ponds for potential biofuel use

Wastewater treatment High Rate Algal Ponds with CO(2) addition could provide cost-effective and efficient tertiary-level wastewater treatment with the co-benefit of algal biomass production for biofuel use. Wastewater grown algal biomass can have a lipid content of 10-30% of dry weight, which could be used to make biodiesel. This research investigated algal biomass and total lipid production by two pilot-scale wastewater treatment HRAPs (4-day HRT) with and without CO(2) addition under New Zealand mid summer (Nov-Jan) conditions. The influence of CO(2) addition on wastewater treatment performance was also determined. CO(2) was added to one of the HRAPs (the HRAP(E)) by maintaining the maximum pH of the pond below 8. Measurements of HRAP influent and effluent water qualities, total lipid content and algal biomass production were made twice a week over the experimental period. Both HRAPs achieved high levels of organic compound and nutrient removal, with >85% SBOD(5), >92 NH(4)(+)-N and >70% DRP removal. Algal/bacterial biomass production in the HRAP(E) (15.2 g/m(2)/d) was improved by CO(2) addition by similar to 30% compared with that of the control HRAP(W) (10.6 g/m(2)/d). Total lipid content of the biomass grown on both HRAPs was slightly reduced (from 25% to 20%) with CO(2) addition and the maximum total lipid content of similar to 40% was observed in the HRAP(W) when low NH(4)(+)-N concentration (<0.5 mg/L) and high maximum pH (>10.0) occurred. Total lipid content of the biomass increased by similar to 15% under nitrogen limiting conditions, however, overall algal/bacterial biomass production was reduced by half during the period of nitrogen limitation. More research is required to maintain algal production under near nitrogen-limiting conditions.