Energy recovery in high rate algal pond used for domestic wastewater treatment.

High rate algal pond (HRAP) was evaluated according to its energy potential and productivity by two rates, net energy ratio (NER) and specific biomass productivity. All energy inputs were calculated according to one HRAP with pre-ultraviolet disinfection treating anaerobic domestic sewage. The outputs were calculated for two energetic pathways: lipid and biogas production for the raw biomass (RB) and biomass after lipid extraction. The non-polar lipid content in dry biomass was 7.6%, reaching a daily lipid productivity of 0.2 g/m·day and the biogas production potential was 0.20 m/kg solids. For the biomass after lipid extraction, the biogas production reached 2.6 m/kg solids. NER values of 10 for the RB were similar for lipids and biogas routes. The specific biomass productivity was 0.7 mg/kJ. For the residual biomass, after lipid extraction, NER value was 10 for the integrated route (lipids + biogas) and the specific biomass productivity of the extracted biomass was 0.4 mg/kJ. The best energetic pathway was to integrate both lipids and biogas route.