Optimizing microalgae cultivation and wastewater treatment in large-scale offshore photobioreactors

Algae Systems LLC has designed and implemented a novel approach to wastewater treatment in which municipal wastewater is used to cultivate microalgae in modular, offshore photobioreactors (PBRs). At the Algae Systems plant in Daphne AL, this process was used to treat up to 50,000 gal/day of incoming raw wastewater. A combination of algae nutrient uptake, aeration by photosynthetically produced oxygen, and dewatering via suspended air flotation removed 75% of total nitrogen, 93% of total phosphorus and 92% BOD from influent wastewater. Offshore PBRs contained evolving polycultures of microalgae and associated heterotrophs, with community composition shifting based on the dynamic external and internal environment. During one year of operation, microalgae composition shifted from dominance of Scenedesmus dimorphus to a diverse polyculture dominated by genus Chlorella, Cryptomonas and Scenedesmus. "The more, the merrier" approach to species richness produced resilient communities, enabling efficient nutrient uptake due to niche complementarity and eliminating process downtime due to biological disruptions. The resulting biomass was suitable for fuel conversion via hydrothermal liquefaction due to consistent lipid content, low ash content, and consistent elemental composition. Biomass production rates ranged from 3.5 to 22.7 g/m(2)/day during continuous operation, with productivity predominantly driven by temperature and frequency of harvest. (C) 2016 Elsevier B.V. All rights reserved.