Prediction and optimization of the performance in an osmotic microbial fuel cell for water purification and bioelectricity production using a developed process model

Abstract

To better understand and mathematically express the process of osmotic microbial fuel cells (OsMFCs), a model describing the integration of electrogen growth kinetics and osmotic mass transfer was developed and validated in this study. Low root mean square error (RMSE) and mean relative error (MRE) were obtained for simulated water flux, voltage generation, and chemical oxygen demand (COD) removal, which revealed a reasonable accuracy of the developed model. The local sensitivity analysis indicated that operating parameters such as draw solution concentration, anode hydraulic retention time (HRT) and influent COD concentration played important roles in influencing the key performance of OsMFCs. At the benchmark settings of anode HRT (4 h), influent COD (880 mg L−1), and external resistance (3000 Ω), a voltage increment of approximately 9.4% was predicted with an increased draw solution concentration from ∼0 to 3.0 mol L−1 (sodium chloride, NaCl), revealing the merit brought by the combined effects of water flux-facilitated proton advection and the high conductivities of electrolytes in OsMFCs. Shortening the anode HRT from 14 to 0.5 h at a fixed draw solution concentration of 0.5 mol L−1 was able to achieve approximately 9.3% increment in voltage output, whereas, the COD removal compromised from 99.2% to less than 20%. High COD removal rate of over 95% was obtained when the examined influent COD was as low as approximately 300 mg L−1. The optimization of combined parameters indicated that the optimized operation was at a draw solution concentration of ∼1.0 mol L−1 (NaCl), anode HRT ranging between 4 and 8 h, and a low influent COD of ∼300 mg L−1 at the model settings.