Synergistic Improvement Of Methane Production In Anaerobic Wastewater Treatment By PANI/Carbon/Iron Conductive Materials

In this study,polyaniline（PANI）-based materials were used as conductive medium to improve the rate of direct interspecies electron transfer（DIET）in the anaerobic biological system,and then the rate of conversion of organic matter into methane（CH₄）in the anaerobic biological treatment of wastewater was improved.The synergistic improvement of CH₄ production by carbon,iron and PANI was investigated.On this basis,the core-shell structure suitable for anaerobic biological system was designed and prepared.Based on the performance of CH₄ production,the thickness of carbon layer and the structure of PANI layer in the core-shell structure were optimized.PANI hydrogel was prepared by chemical oxidation polymerization method.The conductivity of PANI hydrogel was 0.42 S/cm.PANI hydrogel had good biological affinity and higher electric point（p H=10）,which was conducive to rapid microbial enrichment.Under the optimal dosage（3000 mg/L）,the COD removal rate and CH₄yield rate of the system with PANI hydrogel material were improved by 33.2%and 28.95%respectively compared with the control group.The addition of PANI hydrogel was beneficial to the enrichment of Syntrophus bacteria and Methanosaeta archaea communities with DIET ability,which was the main reason to promote the production of CH₄ by anaerobic organisms.Zero-valent iron（ZVI）was prepared by liquid phase reduction method,and carbon microsphere（CMB）was prepared by hydrothermal carbonization method.ZVI,CMB and PANI were selected as the objects to investigate the performance of promoting the production of CH₄ by anaerobic organisms when each of them was added to the anaerobic biological system.The experimental results showed that when ZVI and PANI presented,the yield of CH₄ was 13.38%higher than that of ZVI and PANI alone;when ZVI,C and PANI presented,the yield of CH₄ was 52.72%higher than that of ZVI,C and PANI alone.The addition of ZVI conducive to increase the production of hydrogen（H₂）,and the addition of CMB conducive to increase the production of carbon dioxide（CO₂）.The combination of H₂ and CO₂ was promoted to produce CH₄,and the co-cultured acetic acid bacteria metabolized CO₂ to produce acetic acid and then produced CH₄.The DIET process of Geobacter bacteria,Methanosaeta and Methanobacterium communities occupies a dominant position in the CH₄ production path,which is the main reason for the increase of CH₄ production.Based on the above results,the core-shell structure suitable for anaerobic biological system was designed in this study,and the core-shell structure material was obtained by hydrothermal carbonization and in-situ polymerization.First,the structure of ZVI@C was optimized.When C/Fe was 30,the carbon layer of ZVI@C emerging graphite-like structure with good ordering（I_D/I_G=1.53）,large specific surface area（134.62 m²/g）and micropore structure（pore size=4.36 nm）.When this material was added,the yield of CH₄ could be increased by 53.8%.Then,the conductivity of the PANI layer was optimized.When p-toluenesulfonic acid（PTSA）was used as the doping acid（0.36 m M）and ammonium persulfate（APS）was used as the oxidant（0.02 m M）,the conductivity of ZVI@C@PANI achieved the highest,reaching 4.89 S/cm.When the conductivity was greater than 2.4 S/cm,the material can promote the production of CH₄ by anaerobic organisms.The optimum dosage of material was 2 g/L,which could increase the yield of CH₄ by 71.36%.In the anaerobic biological system with ZVI@C@PANI added,the activity of acid-forming enzymes such as NNLD,PTA and ACK were improved,Desulfovibrio,Mesotoga and Smithella had established a good symbiotic relationship with Methanosaeta and Methanobacterium,and the abundance of Geobacter,Syntrophus,Dechlorobacter,Methanosaeta with DIET capacity increased from 0.12%,0.39%,0.15%,48.17%to 0.31%,0.47%,1.42%,74.13%respectively.