Optimization of electron donors to improve CO2 fixation efficiency by a non-photosynthetic microbial community under aerobic condition using statistical experimental design

To improve the CO2 fixation efficiency of non-photosynthetic microbial community (NPMC) isolated from sea water under aerobic conditions without hydrogen, the concentration of inorganic compounds as electron donors and their ratios were optimized using response surface methodology design (RSMD). These results indicated that Na2S, followed by Na2S2O3 and NaNO2 enhanced the CO2 fixation by NPMC and the efficiency was increased about 100%, 200% and 200%, respectively. Some interaction between NaNO2 and Na2S2O3, as well as between Na2S2O3 and Na2S was observed. Central composite RSMD experimentation predicted that the optimal concentration of these inorganic compounds and their ratios was 0.457% NaNO2, 0.50% Na2S2O3 and 1.25% Na2S. Under these conditions, the fixed CO2 was 105.76 mg/L, which obviously exceeded the amount before optimization, as well as that obtained using hydrogen as the electron donor. This indicates that the NPMC using the established electron donors system can effectively fix CO2 without light and hydrogen gas under aerobic condition.