Study On The Performance And Mechanism Of Conductive Polyaniline In Promoting Methane Production From Anaerobic Wastewater Treatment

Methane production through anaerobic organisms is one of the main ways to realize the resource utilization of organic pollutants in sewage.In terms of the issue that low efficiency of traditional anaerobic biological methane production,P-conjugated polyaniline（PANI）was used as the conductive medium to enhance the extracellular electrons transfer in the wastewater anaerobic biological treatment system,so as to improve the efficiency of wastewater methane production in the study.PANI material was synthesized by interface chemical oxidation method,which has relative high conductivity（0.74 S/cm）,high hydrophilic,high isoelectric point（p H=7.3）and stable chemical structure.These physical and chemical characteristics of PANI make it as a good electron transfer medium.By investigating the effect of PANI on methane production performance of anaerobic system,it could be found that methane production rate could be promoted by 1.8 times by adding 600 mg/L PANI.In the PANI anaerobic microbial system,the maximum accumulation of acetic acid can be increased to 4.25mmol/L,but all can be effectively degraded.The abundance of Clostridium sensu stricto bacteria and Methanosaeta archaea which could participate in the direct intermediate electron transfer process in anaerobic sludge increased from 12.8%and 17.3%to 51.6%and 36.2%respectively.The above results indicate that PANI has the ability to promote direct interspecies electron transfer and strengthen the acetic acid methanogenesis pathway,which is the main reason why PANI could promote the methane production by anaerobic organisms.This paper confirms that the conductivity of PANI is the main faster affecting the methane production.In order to clarify the relationship between the conductivity of PANI and the promotion of methane production by anaerobic microorganisms,a series of related studies have been carried out.The conductivity of PANI is controlled within the range of 5×10^-4～21.2 S/cm by chemical method and template method by means of material design.It was found that the conductivity of PANI is not positively correlated with the promotion of methane production by anaerobic microorganisms by detecting the rate of methane production promotion of PANI with different electrical conductivity.When the conductivity of PANI is between 5×10^-4and 3.1 S/cm,the rate of anaerobic methane production increases with the increase of conductivity,but when the conductivity exceeds 3.1 S/cm,adding PANI will reduce anaerobic methane production rate.Within the appropriate conductivity range,PANI has good biocompatibility to microorganisms in anaerobic system.The higher electrical conductivity is beneficial to the transfer of extracellular electrons by microorganisms in anaerobic sludge which is conducive to the enrichment of Clostridium sensu stricto bacteria and Methanosaeta archaea.Their abundance gradually increased from4%and 31.9%of the blank control group to 28.4%and 51.7%with the increase of PANI conductivity.However,when the conductivity is higher than 3.1 S/cm,adding the PANI will cause the microorganisms to secrete a large amount of extracellular polymers,which will increase the effective contact distance between the microorganisms and the material and reduce the efficiency of electron transfer.PANI was further surface-modified by iron oxide to improve the electron transfer efficiency between the composite material and the microbial interface.The experimental results show that the methane production of the anaerobic system with iron oxide/PANI composite is 1.5 times that of the anaerobic system with iron oxide or PANI which demonstrated that the Fe₂O₃/PANI composite have the effect of synergistic promotion on methane production.According to molecular dynamics simulation calculation,the binding energy between F420 enzyme and PANI composite modified by the introduction of iron oxide decreased by 2 k J/mol compared with that of simple PANI,which shows that the composite material has a higher interface electron transfer efficiency.At last,UASB system based on conductive PANI enhanced anaerobic biomethane has been constructed,the long-term operation effect of the system has been investigated,and the influence of the influent COD concentration and COD shock load on the system operation has been examined.The results showed that when the COD concentration is lower than 15000 mg/L,the methanogenesis rate of UASB increases steadily as the conductivity of PANI increases,and the electron utilization rate in UASB can increase to 95.5%.The impact of UASB instantaneous high-concentration organic wastewater were carried out at the condition of 60,00 mg/L COD influent concentration.The results show that adding PANI with appropriate conductivity can help UASB resist the impact load and quickly restore to maintain stable operation.Adding PANI strengthens the activity of biological enzymes related to metabolizing organic substances to produce acetic acid,promoting the intergrowth of Anaerolinea,Trichococcus and Proteiniphilum in UASB,so as to rapidly degrade the organic product-acetic acid,decreasing the accumulation of propionic acid and butyric acid to maintain the stable operation of the reactor.In addition,the functional bacteria Clostridium sensu stricto and Methanosaeta archaea,which can participate in direct inter-species electron transfer in UASB could quickly transfer electrons to enhance the direct inter-species electron transfer process and promote the efficiency of methane production through PANI as an electronic channel.