Electricity Generation From Cellulose And Corn Straw By Cellulose Degrading Bacteria

Microbial fuel cell is an emerging technology that can generate electricity by utilizing organic waste.In microbial fuel cells,microorganisms act like catalysts,releasing electrons by degrading organic matters during their growth.The micro-organisms characteristics will decide the performance of microbial fuel cells.Generally,microorganisms can easily utilize carbon sources with low molecular weight such as sodium formate and sodium acetate.By contrast,it is more difficult for them to metabolize carbon sources with high molecular weight such as glucose,cellulose and starch.Especially,as one of the most abundant sources of biomass in nature,cellulose is one of the most accessible organic substances.The microbial fuel cells utilizing cellulose to produce electricity showed good advantages on both economic and environmental sides.In this study,the three-electrode system and microbial fuel cells system have been applied to study the electricity generation ability of microbial fuel cells by using cellulose.Meanwhile,growth conditions of the enriched and selected microorganisms with the ability to degrade cellulose have been optimized.Due to the cellulose is hard to be directly consumed by most microorganisms,the related cellulase from microorganisms possessed the ability to degrade cellulose,which made the cellulose be metabolized by microorganisms.Therefore,the main contents in this study includes that a mixed culture sampled from wastewater was firstly enriched on electrode surface using carboxymethyl cellulose as a substrate.As-enriched culture is then used to extract cellulase.Then the extracted cellulase was applied to enhance electricity generation performance of the mixed culture.On the other hand,three strains with cellulose degrading ability,named n1,n2 and n3 were isolated and purified from the mixed culture.The enzyme activities of strains n1,n2 and n3 were also analyzed.In addition,the strong acid and alkali were adopted to degrade the corn straw using strain n4.The degraded corn straw was used as carbon source of strain n4 in microbial fuel cells.The main results in this study are listed as below.In three-electrode system,the mixed culture in presence of cellulase produced a relatively higher current density(360μA cm^-2)than that without additional enzymes(307μA cm^-2).Similarly,in dual-chamber MFC,the maximum power density(866±16.6 m W m^-2)in the presence of enzyme was also higher than that in absence of enzyme(737±2.0 m W m^-2).On the other hand,the microbial biodiversity was then analyzed using high-throughput sequencing.In addition,the cellulase activities of the strains of n1,n2 and n3 were analyzed and corresponding values of 0.67 IU m L^-1 min^-1,0.46 IU m L^-1 min^-1,and 0.46 IU m L^-1 min^-1were obtained,respectively.Furthermore,the phylogenetic analysis of the strain n4 indicated that n4 belonged to Tolumonas,which accounts for a very large proportion（50%）in the mixed culture.Our study further confirmed that strain n4 showed good electrochemical activity and thus belongs to exoelectrogenic microorganisms.Due to it is difficult for cellulose to be used directly by microorganisms,enzymatic hydrolysis in combination with other pretreatment methods such as acid or alkali hydrolysis can be adopted.These pretreatments help degrade the cellulose to glucose that can be utilized by microorganisms.In this study,sulfuric acid and sodium hydroxide pretreated corn straw were used as carbon sources of strain n4.The results showed that the maximum current densities with three types of substrates including glucose,acid pretreated and alkali pretreated corn straw as carbon sources are 372μA cm^-2,658μA cm^-2 and 380μA cm^-2,respectively.Correspondingly,in dual-chamber MFC,the maximum power densities obtained by using these carbon sources are 308±8.0 m W m^-2,577±5.8 m W m^-2 and 430±6.8 m W m^-2,respectively.Since the corn straw after acid or alkaline hydrolysis treatment as carbon sources of strain n4 has stronger electricity production capacity than glucose,it is feasible to use corn straw by acid or alkali hydrolysis as carbon source of strain n4 in MFCs.