Coupling the Wastewater Treatment Process with an Algal Photobioreactor for Nutrient Removal and Renewable Resource Production

To address the growing need for renewable energy and high quality water, the concept of industrial symbiosis may be applied to a wastewater treatment system coupled with an algal photobioreactor (PBR). The coupled system is capable of removing nitrogen and phosphorus from wastewater while producing algal biomass containing precursors to renewable resources such as biofuels, electricity, plastics, and fertilizers.A laboratory experiment was performed to determine the feasibility of coupling a conventional wastewater treatment system with an algal PBR for the simultaneous removal of nutrients from wastewater and production of renewable resources. An activated sludge batch reactor was set up in series with an algal PBR to feed wastewater to the algae. The nutrient concentration in the water as well as lipid content, carbohydrate content, and growth rate of the algal biomass were tested over 10 cycles to determine the capabilities of the coupled system. The study revealed complete nutrient removal in some cycles, with the average final nutrient content of 2 mg-P/L and 3 mg-N/L in effluent of the PBR. The algae biomass contained 24±3% lipids and 26±7% carbohydrates by dry weight. A life cycle assessment of algae cultivation and harvesting revealed the highest energy demand of the coupled system occurred during harvesting of the algal mixture through centrifugation or filtration, but the highest global warming and eutrophication impacts were due to CO&sub2 use and PBR construction material production, respectively. Although the use of wastewater in place of fertilizers resulted in a smaller environmental impact of an algae cultivation system, the life cycle environmental impacts could be reduced more effectively by coupling the system with waste CO&sub2. It is feasible for the system to treat wastewater while generating renewable resources, but the system must be optimized to reduce life cycle environmental impacts and result in a net energy gain before large-scale implementation is possible