Effects of Fe2+ concentration on biomass accumulation and energy metabolism in photosynthetic bacteria wastewater treatment

Photosynthetic bacteria (PSB) wastewater treatment has the advantage of biomass recovery in together with pollutant removal. The effects of different Fe2+ concentrations on the biomass accumulation through regulating energy metabolism were investigated in PSB wastewater treatment. Results showed that the optimal Fe2+ dosage was 20 mg/L. Optimal Fe2+ content could significantly increase the biomass production (4800.9 mg/L) and COD removal (93.4%). Addition of 10–30 mg/L Fe2+ could shorten the hydraulic retention time of wastewater. Mechanism analyses revealed that different Fe2+ concentrations had different impacting mechanisms on biomass accumulation. Fe2+ constituted the dehydrogenase active center, and therefore proper addition of Fe2+ could improve energy production by up-regulating dehydrogenase activity, which was beneficial for biomass accumulation. With 20 mg/L Fe2+, the dehydrogenase activity and ATP production of PSB were improved by 48.1% and 42.4%, respectively. However, excessive addition of Fe2+ was harmful for biomass accumulation since the ions inhibited the dehydrogenase activity.