Year-long evaluation of microalgae production in wastewater using pilot-scale raceway photobioreactors: Assessment of biomass productivity and nutrient recovery capacity

Abstract

The production of Scenedesmus sp. using wastewater was validated with pilot-scale raceway photobioreactors during a complete annual cycle in Almería (Spain). Three different dilution rates (0.1, 0.2, or 0.3 day-1) were evaluated. Biomass productivity was significantly affected by season (temperature and solar radiation) achieving a maximum value of 25.1 g·m-2·day-1 when operating at a dilution rate of 0.2 day-1 in summer. Up to 96% of the N-NH4+ present in the media was either assimilated by microalgae to produce biomass, converted to N-NO3+ by the action of nitrifying bacteria, or desorbed (stripping). Maximum nitrogen removal rates reached 4286.6 mg·m-2·day-1 in summer. In terms of P-PO43+, up to 75% was removed, with removal rates ranging from 147.5 mg·m-2·day-1 in winter to 227.2 mg·m-2·day-1 in summer. Data reported herein was used to validate the ABACO model, which demonstrated to be robust enough to accurately predict biomass productivity in pilot-scale outdoor open raceways throughout the year (R2=0.929; 0.05). The current study demonstrates the potential of raceway reactors and Scenedesmus sp. to recover nutrients from unprocessed wastewater with an exceptionally high content of N-NH4+ at pre-industrial scale. Keywords: Bioremediation, microalgae, biomass, photobioreactor