Carbon-dependent alleviation of ammonia toxicity for algae cultivation and associated mechanisms exploration

•Ammonia toxicity was observed when the concentration of ammonia reached 28.03mM.•Carbon-dependent alleviation of ammonia toxicity was applied for algae cultivation.•Organic carbon generating more ATP and NADH is critical to NH3-N assimilation.•Nitrogen starvation treatment increased NH3-N removal efficiency and cell viability. Ammonia toxicity in wastewater is one of the factors that limit the application of algae technology in wastewater treatment. This work explored the correlation between carbon sources and ammonia assimilation and applied a glucose-assisted nitrogen starvation method to alleviate ammonia toxicity. In this study, ammonia toxicity to Chlorella sp. was observed when NH3-N concentration reached 28.03mM in artificial wastewater. Addition of alpha-ketoglutarate in wastewater promoted ammonia assimilation, but low utilization efficiency and high cost of alpha-ketoglutarate limits its application in wastewater treatment. Comparison of three common carbon sources, glucose, citric acid, and sodium bicarbonate, indicates that in terms of ammonia assimilation, glucose is the best carbon source. Experimental results suggest that organic carbon with good ability of generating energy and hydride donor may be critical to ammonia assimilation. Nitrogen starvation treatment assisted by glucose increased ammonia removal efficiencies and algal viabilities.