Study Of Mustard Tuber Wastewater Treatment Efficacy In Microbial Desalination Cell(MDC)

The Mustard Tuber Wastewater(MTWW)was a high-salt,high-concentration wastewater from the food industry,which was difficult to treat with conventional biological or physical and chemical techniques.Microbial Desalination Cell(MDC)as an emerging electrochemical technology was used to remove the salinity of seawater or simulating saline wastewater,and at the same time could harvest electricity.However,few studies had used MDC for the treatment of actual high-salt wastewater.At the same time,the anode COD concentration of MDC was not suitable and the cost of air-cathode catalyst was too high when using Pt/C,which issues would limit its operating performance.Therefore,it was of theoretical significance and practical value to use MDC for MTWW treatment,and to optimize the anode COD concentration and air-cathode catalyst of MDC.In this paper,traditional MDC was used to treat high-salt MTWW,and three-chamber air-cathode MDC was constructed.The simulating saline wastewater of the traditional MDC desalination chamber was replaced with MTWW.The effects of anode COD concentrations and cathode catalysts on the electricity generation and desalination performance of MDC in the treatment of MTWW were studied,respectively;Exploring the better level of anode COD concentration;The low-cost Mn-Edible Fungus residue Activated Carbon(Mn-EFAC)was successfully prepared,which replaced commercial Pt/C as a cathode catalyst for MDC;The removal of pollutants(high NH₄⁺-N and high COD)in MTWW were investigated,and the removal path of high NH₄⁺-N was analyzed;The microbial community structure of MDC was analyzed by high-throughput sequencing,which further illustrated the change in MDC system performance from a microbiological perspective.This paper analyzed the effects of two experimental factors,anode COD concentration and cathode catalyst,on the efficiency of MDC in the treatment of MTWW,which basically realized the resource treatment of MTWW and provided a practical basis for MDC in the treatment of actual high-salt wastewater.The main conclusions of the study were as follows:(1)The efficacy of MDC in the treatment of MTWW under anode different COD concentrations were different.When the anode COD concentrations were 400 mg/L,900mg/L and 1400 mg/L,the maximum power densities of MDC were 1.93 W/m³,2.91 W/m³and 2.82 W/m³,respectively;Coulombic efficiencies were(19.5±0.7)%,(25.7±0.7)%and(23.6±0.8)%,respectively;When the TDS of MTWW was reduced to 1 g/L to complete the desalination goal,the desalination rates of MDC were(4.93±0.15)mg/h,(5.06±0.16)mg/h and(4.09±0.21)mg/h,respectively;The removal rate of high NH₄⁺-N in MTWW by MDC under the three COD concentrations of the anode were more than 99%,and the path of NH₄⁺-N removal were the same.In the early stage of MDC operation,part of NH₄⁺-N in MTWW was converted into NO₃^--N,most of which NO₃^--N gradually migrated to the anode chamber in the form of NO₃^-and was removed by denitrification.The remaining NO₃^--N was removed in the later stage by denitrification in the desalination chamber.The remaining NH₄⁺-N in MTWW was gradually transferred to the cathode chamber in the form of NH₄⁺and then converted to NH₃ in an alkaline state and discharged;The high COD in MTWW could be removed in the anode chamber of the dual-chamber MFC,the COD removal rate of MTWW were(85.8±2.5)%,(83.1±2.0)%and(84.3±2.4)%,respectively.To sum up,the efficacy of MDC was better when the anode COD concentration was 900 mg/L,which could be used as a better level of anode COD concentration when MDC in the treatment of MTWW.(2)The efficacy of MDC in the treatment of MTWW under cathode different catalysts were different.Characterization of the three catalysts,commercial Pt/C,prepared Mn-EFAC and Fe/Mn-EFAC,showed that Mn-EFAC was superior to Fe/Mn-EFAC in terms of oxygen content,surface wrinkles,and specific surface area,etc.When the cathode catalysts were Pt/C,Mn-EFAC and Fe/Mn-EFAC,the maximum power densities of MDC were 2.75 W/m³,2.52 W/m³ and 1.49 W/m³,respectively;Coulombic efficiencies were(28.7±0.5)%,(26.2±0.7)%and(23.9±0.8)%,respectively;The desalination rates of MDC were(5.60±0.21)mg/h,(5.42±0.18)mg/h and(4.50±0.20)mg/h,respectively;The removal rate of high NH₄⁺-N in MTWW by MDC under the three cathode catalysts were more than 99%,and the path of NH₄⁺-N removal were the same as factor 1;The high COD in MTWW could be removed in the anode chamber of the dual-chamber MFC,the COD removal rates of MTWW were(82.9±3.3)%,(81.7±2.8)%and(78.2±2.5)%,respectively.The efficacy differences of MDC were smaller when the cathode catalyst were Pt/C and Mn-EFAC,but the differences between Fe/Mn-EFAC and the other two were larger.The prepared Mn-EFAC was close to commercial Pt/C in efficacy of MDC,but its cost was greatly reduced compared to Pt/C,which proved that the prepared low-cost Mn-EFAC could replace expensive commercial Pt/C as MDC cathode catalyst and be used in the treatment of MTWW.(3)The microbial community of the anodic biofilm of MDC and MTWW under different COD concentrations of the anode were analyzed.A total of 9 kinds of main phylums were found in the three sets of MDC systems.Most of the electrochemically active microorganisms were concentrated in Proteobacteria,Firmicutes and Bacteroidetes,and the total abundance of the three kinds of phylums in the three sets of anodic biofilms were 59.19%(400 mg/LCOD),63.77%(900 mg/LCOD)and 62.98%(1400 mg/LCOD),respectively.In three sets of MDC anodic biofilms,8 kinds of hydrolytic fermentative bacterias(Lentimicrobium,Hyd24-12?norank,etc.)were found,2 kinds of electrochemically active bacterias(Pseudomonas and Desulfovibrio)were found,and 2 kinds of Methanogen(Methanosaeta and Methanobacterium)were found.In three sets of MDC anodic biofilms,hydrolytic fermentative bacterias total relative abundances were 35.02%(400 mg/LCOD),39.69%(900 mg/LCOD)and 35.70%(1400mg/LCOD),respectively,which could be considered that the hydrolytic fermentative bacteria were the core microorganisms of the anodic biofilm in MDC;and electrochemically active bacterias total relative abundances were 11.50%,13.16%and12.68%,respectively,which explained the higher electricity generation performance of MDC when the anode COD was 900 mg/L at genus level;and Methanogen total relative abundances were 12.21%,12.15%and 13.38%,respectively,which proved that the anode of MDC might produce methane.In three sets of MDC anodic biofilms and MTWW,6kinds of denitrification bacterias(Pseudomonas,Thauera,etc.)were found.In three sets of MDC anodic biofilms and MTWW,denitrification bacterias total relative abundances were 13.78%,15.53%,14.43%and 15.33%(MTWW),respectively;In MTWW,2 kinds of nitrification bacterias(SM1A02 and Nitrosomonas)were also found,with a total relative abundance of 6.53%.The existence of denitrification bacteria in anodic biofilm,denitrification bacteria in MTWW,and nitrification bacteria in MTWW verified the discussion of NH₄⁺-N removal path during MDC treating the MTWW.