Pilot microalgae cultivation using food waste digestate with minimal resource inputs

Microalgae (Chlorella sorokiniana UTEX 1230) was cultivated in a pilot-scale outdoor system of four 100 L raceway ponds, using diluted ultrafiltered food waste digestate. The system was operated for 400 days using a repeated-batch strategy in Davis, CA with extensive water recycling. Supernatant liquid from FeCl₃-assisted algae harvesting was recycled successively five times and resulted in little impact on algae growth, eliminated liquid non-product discharge and freshwater inputs, and decreased coagulant loading requirements for algae harvest. High removals (>70 %) of ammoniacal-N were achieved but water recycling resulted in ion accumulation within the bioreactors. The maximum average algae production was 122 ± 61 g VS m⁻² with a maximum average productivity of 17.7 ± 1.8 mg VS L⁻¹ d⁻¹. The results indicate promise for the application of microalgae cultivation on anaerobic digestate and demonstrate an operating strategy with reduced freshwater inputs and water discharge.