Improving phosphorus removal efficiency and Chlorella vulgaris growth in high-phosphate MFC wastewater by frequent addition of small amounts of nitrate

Microalgae coupled with the wastewater treatment and CO2 biofixation becoming a promising biomass feedstock for fermentative hydrogen production. Microbial fuel cells wastewater (MFCW) contained high phosphorus but low nitrogen (N/P is 1:73) due to phosphate buffer. To keep a high microalgae growth rate in MFCW and P removal efficiency, some extra NaNO3 was added into MFCW to balance N/P. With 0.5 g L−1 NaNO3 adding, Chlorella vulgaris showed the highest biomass yield of 4.7 g L−1 and highest lipid productivity of 61.29 mg L−1 d−1. In order to avoid the inhibition of excess nitrate that added one-time on microalgae growth, NaNO3 was added frequently with small amounts during cultivation. The biomass yield of microalgae by adding NaNO3 twice increased by 13.4% compared to that cultivated by adding the same amount of NaNO3 one-time. Moreover, with a NaNO3 adding frequency of 0.5 g L−1 3 d−1, the maximum R=(S0−St)/(t0−tt) removal rate was up to 45.16 mg L−1 d−1.