Mixotrophic Chlorella pyrenoidosa as cell factory for ultrahigh-efficient removal of ammonium from catalyzer wastewater with valuable algal biomass coproduction through short-time acclimation

Abstract To achieve ultrahigh-efficient ammonium removal and valuable biomass coproduction, Chlorella-mediated short-time acclimation was implemented in photo-fermentation. The results demonstrated short-time acclimation of mixotrophic Chlorella pyrenoidosa could significantly improve NH4+ removal and biomass production in shake flasks. After acclimation through two batch cultures in 5-L photo-fermenter, the maximum NH4+ removal rate (1,400 mg L-1 d-1) were achieved under high NH4+ level (4,750 mg L-1) in batch 3. In 50-L photo-fermenter, through one batch acclimated culture, the maximum NH4+ removal rate (2,212 mg L-1 d-1) and biomass concentration (58.4 g L-1) were achieved in batch 2, with the highest productivities of protein (5.56 g L-1 d-1) and total lipids (5.66 g L-1 d-1). The hypothetical pathway of nutrients assimilation in mixotrophic cells as cell factory was proposed with detailed discussion. This study provided a novel strategy for high-ammonium wastewater treatment without dilution, facilitating the algae-based “waste-to-treasure” bioconversion process for green manufacturing.