Variation of biomass energy yield in wastewater treatment high rate algal ponds

Wastewater treatment high rate algal ponds (WWT HRAPs) have been recently highlighted as a potential system for low-cost algal energy production since the algal biomass is essentially a free by-product of the wastewater treatment process. This paper investigates the biomass energy yield potential of WWT HRAP (calculated by multiplying biomass productivity and biomass energy content). We address experimentally, for the first time, the influence of algal species dynamics, zooplankton grazing, environmental conditions, biomass chemical composition and biomass algal proportion on overall biomass energy yield. Two parallel identical pilot-scale HRAPs (8m3 volume, 0.3m depth and 31.8m2 surface area) were operated for one year and monitored each week for biomass productivity and energy content. Pond effluent nutrient concentration, microalgal relative abundance, biomass chemical composition and chlorophyll-a content were all measured and their effect on biomass productivity and energy content was assessed. The algal species composition and algal proportion in the HRAP effluent varied with season and grazing pressure. The highest biomass lipid content (45wt%) was achieved when effluent ammonia concentration was lowest (