Enhancing Fermentative Hydrogen And Methane Production From Biomass With Conductive Carbon Cloth And Ionic Liquid

Hydrogen production from cellulosic biomass by microorganisms has the advantages of environmentally friendly,renewable and energy-saving.It is vitally important for developing energy system that is clean,low-carbon,safe and efficient.In this study,the mechanisms of hydrogen production from genetically modified Enterobacter aerogenes enhanced by conductive carbon cloth were investigated.Mixed bacteria used carbon cloth to promote cogeneration of hydrogen and methane.Ionic liquid pretreatment of cassava residues was investigated to improve energy conversion efficiency.The application of carbon cloth on genetically modified Enterobacter aerogenes was first proposed to enhance hydrogen production efficiency.Scanning electron microscopy(SEM)images showed that the nanowires between bacteria were possibly replaced by conductive carbon cloth.The 59.1%microorganisms concentrated in biofilms of carbon cloth which promoted electron transfer.Fourier transform infrared spectra(FTIR)and Excitation Emission Matrix Spectra(EEM)indicated that soluble metabolic products(SMP)of biofilms were composed of polysaccharide,protein and etc,the fluorophore of biofilms(88.1%)was much higher than that of fermentation liquid(11.9%).The particle sizes of biofilms SMP were basically less than 1.2μm.Analysis of soluable metabolite products indicated that carbon cloth enhanced acetate pathway(C6H12O6 + 2H2O→ 2CH3COOH+2CO2 + 4H2),but weakend ethanol pathway(C6H12O6→2C2H5OH + 2C02).With the addition of 1.0 g/L conductive carbon cloth,hydrogen yields of glucose increased by 27.9%to 242 mL/g,the peak hydrogen production rates increased by 38.0%to 14.9 mL/g/h,accordingly.Cogeneration of hydrogen and methane from mixed hydrogen-producing bacteria and methanogens were enhanced by conductive carbon cloth.Conductive carbon cloth stimulated acetate and butyrate pathway.With addition of 1.2 g/L carbon cloth,hydrogen yields increased from 198.4 to 261.5 mL/g,correspondingly,the peak hydrogen production rates increased from 8.9 to 12.2 mL/g/h.In the presence of carbon cloth,fermentation efficiency of methanogens was accelerated.As a result,methane yields increased by 22.6%to 275.3 mL/g from hydrogen effluent,coorespondingly,the peak methane production rates increased by 18.2%to 55.1mL/g/d.Ionic liquid pretreated cassava residues to enhance the energy efficiency of cogeneration of fermentative hydrogen and methane.Deep grooves and numerous pores(4～5μm)formed in the cassava residues pretreated with NMMO.The crystallinity coefficient of NMMO-pretreated cassava residues decreased from 40 to 34.The reducing sugar yield of enzymolysed cassava residues with NMMO pretreatment improved by 16.7%to 42 g/100 g cassava residues.Hydrogen yield from the enzymolysed cassava residues pretreated with NMMO increased from 92.3 to 126 mL/g TVS,and the sequential methane yield correspondingly increased from 79.4 to 101.6 mL/g TVS.Thus,the total energy conversion efficiency improved from 7.6%to 27.9%.