Enhancements of lipid productivity and phosphorus utilization efficiency of Chlorella pyrenoidosa by iron and acetate supplements in actual municipal wastewater

Wastewater with rich nutrients has been considered as a promising resource to replace artificial culture media in the production of low-cost microalgae biofuels. However, to compete with the traditional fossil energy, the corresponding algal lipid productivity needs to be improved. In this study, iron and acetate supplements were used to improve the lipid productivity of Chlorella pyrenoidosa in actual municipal wastewater (MW). The results showed that, simultaneously adding proper amounts of iron and acetate remarkably increased the microalga dry cell weight (DCW), lipid content and lipid productivity, respectively by 185%, 248% and 671%. Moreover, the addition of acetate increased the saturation degree of the alga based fatty acid methyl esters (P < 0.05), thus improved the quality of the algal lipid with better oxidative stability. Besides, the algal phosphorus utilization efficiency (PUE) was also greatly enhanced by the acetate supplement (P < 0.05), with the conversion efficiencies of phosphorus to algal DCW and lipid in mixotrophic cultures being more than twice of those in the corresponding phototrophic cultures. Finally, a bio-formation of β-tricalcium phosphate (β-TCP) by the microalga was reported, indicating potential phosphorus recovery by microalgae-driven bio-production of phosphorus-containing products combined with phosphorus removal in wastewaters.