Construction And Optimization Of CO₂ Reduction System Based On Microbial Reverse Electrodialysis

The continuous consumption of fossil fuels has led to the depletion of source of energy.Fuel combustion and exhaust emission especially the huge amount of CO₂ have caused serve global warming.At the same time,a large amount of swage is directly discharged into natural water without treatment due to the rapid population growth and fast development of industry,resulting in serious water pollution.Therefore,it's urgent to develop novel technologies that integrated pollutant treatment and energy recovery.Microbial electrochemical technology,as an emerging mode of wastewater treatment,converts potential chemical energy in wastewater into electrical energy and obtain different types of products?such as methane,hydrogen,hydrogen peroxide,etc?simultaneously,with high efficiency of pollutant degradation and easy coupling of clean energy to participate in electro-synthesis,which is of great significance in solving water pollution,CO₂ fixation and energy recovery.In this work,a Microbial reverse electrodialysis system?MRC?was constructed to realize the CO₂ conversion and valuable substances synthesis by taking advantage of the potential chemical energy in wastewater and osmotic energy.It is crucial to optimize the system operating parameters and develop high-efficiency catalysts to improve performance.The MRC system was constructed using carbon brush anode pre-acclimatized with electrochemically active bacteria,the rolling-press air electrode cathode,and the salt differential energy recovery module which built by perforated grill with thickness of 0.5mm and mesh size of 16,and anion-cation exchange membranes.When the fresh water and concentrated brine concentration were 0.7 g-NaCl/L and 36.0 g-NaCl/L,and the flow rate was 5 mL/min,the power density of the MRC system was 2.03 W/m²,and the current reached to 4.04±0.14 mA/m².Bi-based catalyst with high catalytic activity for CO₂ electroreduction was prepared by electrodeposition method.When the deposition current was 15 mA/cm² and the deposition time 1200 s,the prepared Bi?1200?had abundant dendritic structure which showed high catalytic activity.The overpotential of Bi?1200?was only 390 mV,and the faradaic efficiency of CO₂ reduction for formate reached to 99%at-1.5 V vs Ag/AgCl.In addition,the Bi?1200?had a superior stability and maintained faradaic efficiency for formate over 100 hours.A coupled system combining MRC with CO₂ electroreduction process was constructed,this system could remove organic pollutants in the anode chamber while CO₂was electrochemically reduced in the cathode chamber.The operation parameters of the coupling system was further optimized:with 20 pairs of stack chambers for salt-containing water and the thickness of the chamber 0.5 mm,and the COD concentration in anode chamber 2 g-NaAc/L,the COD removal reached to 60%,the maximum faradaic efficiency for CO₂-to-formate was 70%,and the cumulative production of formate was190 mg/L at the end of the batch cycle.