Construction And Performance Optimization Of Bioelectrochemical System Based On Reverse Electrodialysis Technology

In this study,reverse electrodialysis system and reverse electrodialysis bioelectrochemical system were constructed and improved.Extraction and utilization of salinity-gradient energy widely existing in nature can reduce the energy consumption of water treatment,and the double-chamber reactor structure can directly provide the electrons that were lost from the oxidation of anode organic materials to the reduction of heavy metal ions at the cathode.The reversed electrodialysis membrane stack raised the potential difference,so that the system can better strengthen the heavy metal ion reduction of the cathode compared to the traditional microbial fuel cells,and at the same time isolated the heavy metal ions of the cathode from the anodic microbial environment,avoiding the phenomenon that the metal ions of the common microbial fuel cells inhibit the growth of the anodic microbial communities through the ion exchange membrane,and was favorable for the stable and continuous removal of pollutants in the system.The influence of different parameters on the operating efficiency of the reverse electrodialysis system was explored.The results showed that there was a positive correlation between the selective permeability coefficient of the membrane materials and the efficiency of the reversed electrodialysis system.In the case of no external resistance,a large difference in concentration can produce a greater voltage.0.911 V,the highest average voltage,could be reached when 7 pairs of membranes were used,with the concentration of fresh water being 0.35g/L,and the flow rate being 3.2m L/min.,however,this would reduce the exchange between salt water and fresh water and lower the maximum power density.And the maximum power density was 0.221 W/m2,which could be reached at 3 pairs of membranes,fresh water 0.7g/L,and a flow rate of 3.2 m L/min.In the flow rate ranging from 0.8m L/min to 3.2m L/min,and the average external voltage increases with the increased of the flow rate,the degree of water exchange was weakened and the maximum output power of the system was increased.However,the amount of output power improved by the increasing flow rate was much lower than that required to increase the flow rate,and the ratio between the two was about 0.01-0.15.In the case of 1-7 pairs of membranes,the average external voltage and the internal resistance of the membrane presented a linear positive correlation with the pairs of membranes,and the correlation coefficient R2 was 0.9798-0.9993.The ion exchange in effluent could be more and more thorough as the pairs of membranes increased.The influence of different parameters on the operating efficiency of the reverse electrodialysis bioelectrochemical system was explored.The results show that for a reverse electrodialysis bioelectrochemical system with an external resistance of 1000 ohms,when the pair of membranes was 1,the high concentration gradient output voltage,anode COD removal rate,and cathode copper ion removal rate are higher than those in low concentration condition,to be specific,the highest increase could be 3%,2% and 5% respectively compared to the low concentration gradient.When the pairs of membranes was above 5,the above conclusion was opposite.As the flow rate increased,the average external voltage increased slightly,which had limited effect on improving the COD removal efficiency of the anolyte and the copper ion removal efficiency of the catholyte.The p H of the anolyte was basically stable and was maintained between 6.71-7.19.The average external voltage of the system exhibited a linear positive correlation with the pairs of membranes,and the correlation coefficient R2 was between 0.9621 and 0.996.With the pair number of membranes increasing,the ion exchange between the salt water and the fresh water was more complete,and the final anode conductivity and COD decreased continuously.The COD removal rate was highest at 7 pairs of membranes,freshwater 0.35 g/L,and flow rate of 3.2 m L/min,reaching 89.1%,effluent COD was 74mg/L.The final catholyte copper ion concentration decreased,and the copper ion reduction efficiency was improved,and could reach to 58.5%,the highest level,in the 7 pairs of membranes,fresh water 0.35g/L,the flow rate of 3.2m L/min,and the effluent copper ion concentration of 154.65 mg/L.The final catholyte conductivity decreased gradually with the increase of the pairs of membranes,the lowest reaches 0.50 m S/cm,and the final p H of the catholyte continuously increased with the increase of the pairs of membranes,and the maximum value reaches 5.72.The effect of different electrode materials on the operating efficiency of reverse electrodialysis bioelectrochemical system was explored.By replacing the carbon cloth of the reverse electrodialysis bioelectrochemical system with carbon felt,the catholyte removal rate increased by 4.6%,7.3%,4.9%,and 4.2% under different pairs of membranes.The maximum removal rate reached 62.7% in 7 pairs of membranes,freshwater 0.35g/L,and flow rate 3.2m L/min,the final p H of the catholyte solution increased to some extent,and there was no significant change in other parameters.