The Performance Of Microbial Desalination Cell Removes Organic Substances And Recovers Ammonium And Phosphate From Flowback Water

Shale gas development is China's major energy development strategy.The widely used hydraulic fracturing technology produces a large amount of flowback/produced water,which is complex in composition and contains high salinity?including ammonium salts and phosphates?,which is difficult to handle with existing water treatment technologies.Microbial desalination cell?MDC?is a device that emerged at the beginning of this century to remove both organic matter and desalination.In view of the defects of noble metal catalysts for MDC cathodes,this paper designs and prepares metal heteropolyacid/carbon black instead of platinum catalysts,carries out MDC removal of organic matter,and simultaneously recovers ammonium and phosphate experiments for the development of flowback water treatment.This experiment also provides a reference for the development of alternative technologies for flowback water treatment.?1?A novel H₃PMo₁₂O₄₀/carbon black?PMo/CB?material was prepared as an oxygen reduction reaction?ORR?catalyst.The structure and chemical composition of the catalyst were characterized by XRD,XPS,FT-IR and BET.The results showed that PMo was immobilized on carbon black and formed a specific structure.The electrochemical properties of PMo/CB were evaluated by LSV and rotating disk electrode?RDE?.The results show that the catalytic activity of PMo/CB is related to the mass ratio of PMo and CB.The sample with PMo and CB mass ratio of 10%?PMo/CB-10?has the best ORR activity,and the electron transfer number and transfer mechanism of PMo/CB-10 in the ORR process are basically the same as those of the platinum carbon catalyst.The air cathode microbial fuel cell?MFC?was constructed by using PMo/CB-10 as the cathode catalyst,and the high-salt?10 g/L NaCl?wastewater was prepared by using sodium acetate?CH₃COONa?.The results showed that the maximum power density of PMo/CB-10-MFC is 1195.1±41.7mW/m²,which is 21.4%higher than Pt/C-MFC?984.2±62.2 mW/m²?.The power density of PMo/CB-10-MFC continues for four consecutive months.Which is even higher than the power output of Pt/C,and always maintain a high power output,indicating that PMo/CB-10 as an MFC air-cathode electrocatalyst can maintain long-term stable ORR activity.?2?The performance of PMo/CB-MFC?PMo/CB-10-MFC?in the treatment of fracturing flowback water?with guar gum,polyacrylamide,etc.as the main organic pollutant?was studied.When the NaCl concentration in the flowback water is 10 g/L,the output power density of PMo/CB-MFC is 347.2±23.0 mW/m²,which is 44.4%higher than that of Pt/C-MFC?192.9±34.0 mW/m²?.In the 10 cycles of stable reactor operation,the average COD removal rate of PMo/CB-MFC is 71.2±2.4%higher than that of Pt/C-MFC?68.9±5.4%?.With the increase of NaCl concentration,the electricity production performance of PMo/CB-MFC gradually decreases.When the NaCl concentration is 120g/L in the flowback water,the output voltage of MFC is 0.32±0.1V,the power density is 67.4±26.0 mW/m²,the removal rate of COD was 50.8±15.0%,indicating that MFC has a high processing capacity for high salt flowback water.?3?The PMo/CB-MDC was constructed.Optimize MDC performance by changing applied resistance and circulating flow rate.The results show that when the applied resistance is 5?,the output currents of PMo/CB-MDC and Pt/C-MDC are up to 9.0mA and 8.0mA,respectively,and the system effluent increases with the circulating flow rate of the cathode and anode chambers.The COD removal rate and desalination efficiency increased continuously.When the flow rate was 1.6 mL/min,the COD removal rates of PMo/CB-MDC and Pt/C-MDC were 72.4%and 69.8%,respectively,and the salt rejection rates were 22.8%and 21.9%,respectively.The desalting rates were 190.0mg/h and 188.0 mg/h,respectively.The constructed MDC had higher COD removal and was able to remove and recover part of the salt in flowback water.?4?The NaCl concentration was increased to 60g/L,and PO₄^3-was set to 100mg/L and different NH₄⁺concentrations?100mg/L,300mg/L,600mg/L and 1000mg/L?in simulated flowback water.The effects of different NH₄⁺concentrations in the flowback water on COD removal,NH₄⁺and PO₄^3-removal and recovery performance were investigated.These results show that the NH₄⁺and PO₄^3-removal rates are the highest?58.6±19.0%and 75.8±32.0%?when the NH₄⁺concentration is 300 mg/L,and the NH₄⁺and PO₄^3-recovery rates are 42.1%and 59.1%,respectively.The COD removal rate reached the maximum?90.7±5.0%?at 600 mg/L.Therefore,it can be explained that the higher NH₄⁺concentration has a promoting effect on the metabolism of electroactive microorganisms,and the MDC can be used to remove COD and recover part of the nutrient salt in flowback water.