Wastewater Treatment Pond Algal Production for Biofuel

Wastewater treatment high rate algal ponds fertilised with CO2 (HRAP + C system) provide a niche opportunity for algal biofuel production in combination with energy-efficient and cost-effective tertiary-level wastewater treatment. Wastewaters are excellent media (water, nutrients, alkalinity buffering) for the growth of naturally occurring algae that could be harvested by bioflocculation and low-cost gravity settling, especially when fertilised with CO2 obtained from biogas produced and used for power generation at the treatment plant. The harvested algal biomass is converted to biofuels, preferably by processes that use the entire biomass with little or no dewatering. Anaerobic digestion of the algal biomass along with settled primary sludge is the most readily available and economic technology. The wastewater treatment function can essentially cover the entire capital and operation costs of biofuel production. Additional environmental and financial incentives are due to GHG abatement and nutrient fertiliser recovery. Since wastewater treatment systems using facultative ponds are already a widely used technology for secondary-level wastewater treatment, upgrading these ponds provides an opportunity to develop and refine algal production and harvest from HRAP systems and algal biofuel conversion technologies. The HRAP + C system can produce biogas for power generation at essentially no additional cost to that incurred for wastewater treatment alone. Additional research, in particular, on selection and cultivation of superior algal strains, grazer control and cost-effective algal harvest is still required before widespread adoption of this technology is possible.