Experimental Study On The Efficiency Enhancement Of Biogenic Methane From Coal By Adding Electric Field

To satisfy the increasing demand of energy and reduce the impact of greenhouse gases on the environment,it is more and more important to develop and utilize coalbed methane(CBM).As an important part of coalbed methane,biogenic CBM is generated by coal biodegradation.The microbially enhanced CBM(MECBM)which is proposed based on the formation of biogenic CBM have shown a good prospect,but the related research is still in an exploratory stage.The significant increase of biomethane production is still a big bottleneck.Therefore,it is urgent to enhance methane production.Application of the electric field is an efficiency method to assist such anaerobic fermentation system as wastewater treatment and soil remediation to improve substrate degradation rate.It has been proved that the applied electric field is an effective method to degrade various substrates,increase methane production.However,the study on enhancement of biomethane production from coal by application of an electric field has just started with only the stimulation effect has been confirmed.In this paper,the effects of different electrode materials and voltages on biomethane production from coal were studied to optimize the stimulation conditions.Pyrosequencing,GC-MS and Fourier infrared spectroscopy(FTIR)were used to determine the effects of application of an electric field on the succession of microbial communities and intermediate products during methane generation,and the changes of coal structure after degradation,to analyze the enhancement mechanism of methane production from coal by application of an electric field.The main results of the study are as follows:(1)To explore the influence of different electrode combination on methane production,an orthogonal experiment was established by using carbon felt and graphite rod as the anode,carbon felt and stainless steel as the cathode.The results showed that the highest methane yield of 78.3 ?mol/g coal was observed in the reactor with carbon felt as the anode and stainless steel as the cathode(CS),which was 91% higher than the control group(41 ?mol/g coal).(2)The results of the voltage optimization experiment showed that the highest methane production of 96.9 ?mol/g coal was observed at 1.2 V with lignite as substrate,which was 155% higher than that at 0 V.Meanwhile,the methane productions at 0.6 V and 1.8 V also increased by 128% and 59.2% respectively compared with that at 0V.Therefore,the optimal voltage value was 1.2 V.(3)High-throughput sequencing results revealed that the structure and succession of microflora changed due to the application of an electric field.The relative abundances of the bacteria related to coal degradation,such as Pseudomonas and Desulfovibrio,were basically higher than those in the control group during the whole experiment period after application of an electric field.These bacteria play an important role in promoting the degradation and transformation of organic matter in coal.The structure of fungal community changed significantly,especially that the relative abundances of the dominant genera,such as Debaryomyces and Fusarium,were higher than those in control group.These fungi have good biodegradability and they are excellent degraders of macromolecular complex compounds in coal.The application of an electric field can optimize the community structure,to improve the cooperation among the functional microorganisms in the whole anaerobic fermentation system,which may be an important reason for the increase of methane production.(4)GC-MS analysis results revealed that the relative abundances of esters and acids in the experimental group were lower than those in control group,while the relative abundances of aromatic and ketones were higher than those of the control group at all stages,which might be due to the changes of biodegradation metabolic pathway of coal as suggested by the shifts of bacterial and fungal communities caused by application of an electric field.Organic compounds in coal are further degraded or transformed by application of an electric field to facilitate the subsequent methanogenesis.(5)The results of FTIR revealed that the tensile vibration intensity of aromatic functional groups in the residual coal after application of an electric field was weaker than that in control group.The ether oxygen bond,carboxyl,and carbonyl groups in the oxygen-containing functional group of residual coal reduced significantly.The intensity of each peak in aliphatic functional group was significantly lower than that of raw coal and residual coal in control group.These results showed that under the application of an electric field,the aromatic structure,oxygen-containing structure and aliphatic structure of coal were destroyed by biodegradation.In summary,the application of an electric field changed the succession of microbial community and metabolism of organic matters in coal,promoted the biodegradation of coal,thus increased the biomethane production significantly.