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

The production of Scenedesmus sp. using wastewater was validated with pilot-scale raceway photobioreactors during a complete annual cycle in Almeria (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 (R-2 = 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.

Automated summary

The study demonstrated the potential of using pilot-scale raceway photobioreactors to produce Scenedesmus sp. from wastewater with high levels of nutrients. Validation of the ABACO model showed robust and accurate prediction of biomass productivity throughout the year under different seasonal and temperature conditions in outdoor open raceways.