| As a high-quality cellulosic biomass,herbaceous biomass is one of the ideal ways to alleviate the shortage of fossil energy and improve the energy structure.Biological hydrogen production technology can use waste biomass to produce hydrogen,which can realize the resource utilization of waste and improve the environmental pollution at the same time.In this paper,Arundo donax,Phragmites communis(Cav.)Trin.ex Steud.,Pennisetum alopecuroides(L.)Spreng.,Medicago sativa L.,Miscanthus,Saccharum arundinaceum Retz.,Pennisetum purpureum Schum.,Panicum virgatum L.,Pennisetum giganteum z.x.lin and Triarrhena sacchariflora(Maxim.)Nakai were selected to study the biohydrogen production.(1)Among the ten selected herbaceous biomass,Arundo donax,Medicago sativa L.,Miscanthus and Pennisetum giganteum z.x.lin have higher cellulose content,and the hemicellulose content of Arundo donax is also higher.Therefore,in theory,the reducing sugar of these herbaceous biomass can be relatively higher through cellulase hydrolysis reaction,but the lignin content of Pennisetum giganteum z.x.lin is higher,and lignin will inhibit the effect of enzymatic hydrolysis reaction.Considering the element composition,hydrogen is the only source of herbaceous biomass as the raw material for biological hydrogen production,while sulfur can inhibit the growth of hydrogen producing bacteria,thus inhibiting the effect of biological hydrogen production.The carbon nitrogen ratio of Medicago sativa L.was lower than that of other herbaceous biomass,and the hydrogen content of Medicago sativa L.was the same as that of Triarrhena sacchariflora(Maxim.)Nakai,but higher than that of other herbaceous biomass.Therefore,the theoretical hydrogen production of Medicago sativa L.and Triarrhena sacchariflora(Maxim.)Nakai was the highest,and the sulfur content of Arundo donax was significantly higher than that of other herbaceous biomass,which had a certain inhibitory effect on the biological hydrogen production of Arundo donax.Compared with the lignocellulose content and element composition of herbaceous biomass,Medicago sativa L.has the strongest absorption peak at the main assigned wave number of cellulose,and its crystallinity is small.Theoretically,Medicago sativa L.should produce more hydrogen than other herbaceous biomass.(2)The effects of enzymolysis conditions on hydrogen production by dark fermentation of herbaceous biomass and the changes of physicochemical properties of fermentation broth were studied.The results showed that enzyme load and hydrolysis time had significant effects on hydrogen production process and hydrogen production,and there were significant differences in the effects on different herbaceous biomass.When the enzyme load was 10 FPU·g-1 TS,the hydrogen production of Medicago sativa L.was the highest,reaching 53.49 mL·g-1 TS(enzymatic hydrolysis time 0 h),and the material conversion rate was 44.06%,and the hydrogen conversion rate was 8.03%.When the enzyme loading was 20 FPU·g-1 TS,the maximum hydrogen production of Medicago sativa L.was 85.42 mL·g-1 TS(enzymolysis time 0 h),by-products yield was 42.65%,and the conversion of hydrogen was 12.59%.When the enzyme load was 30 FPU·g-1 TS,the time of enzymatic hydrolysis had the greatest effect on the hydrogen production of Medicago sativa L..At this time,the highest hydrogen production of Medicago saliva L.was 114.88 mL·g-1 TS(enzymatic hydrolysis time 0 h),byproducts yield was 36.81%,and the hydrogen conversion rate was 15.84%.When the enzyme load was 40 FPU·g-1 TS,the highest hydrogen production of Medicago sativa L.was 133.23 mL·g-1 TS(enzymatic hydrolysis time 0 h),by-products yield was 40.61%,and the hydrogen conversion rate was 18.49%.When the enzyme load was 50 FPU·g-1 TS,the highest hydrogen production of Medicago sativa L.was 143.01 mL·g-1 TS(enzymatic hydrolysis time 0 h),byproducts yield was 52.78%,and the hydrogen conversion rate was 21.46%.In the process of hydrogen production by dark fermentation,with the increase of enzyme load,the main metabolic pathway of dark fermentation bacteria changed from butyric acid fermentation to acetic acid fermentation.(3)The effects of enzymolysis conditions on hydrogen production by photolysis of herbaceous biomass and the changes of physicochemical properties of fermentation broth were studied.The results showed that there were significant differences in the effects on different herbaceous biomass.When the enzyme load was 10 FPU·g-1 TS,the hydrogen production of Triarrhena sacchariflora(Maxim.)Nakai was the highest,reaching 51.28 mL·g-1 TS(enzymatic hydrolysis time 12 h),by-products yield was 12.07%,and the hydrogen conversion rate was 7.70%.When the enzyme load was 20 FPU·g-1 TS,the highest hydrogen production of Medicago sativa L.was 83.24 mL·g-1 TS(enzymatic hydrolysis time 36 h),byproducts yield was 13.11%,and the hydrogen conversion rate was 16.03%.When the enzyme load was 30 FPU·g-1 TS,the highest hydrogen production of Medicago sativa L.was 132.43 mL·g-1 TS(enzymatic hydrolysis time 60 h),and by-products yield was 12.98%,and the hydrogen conversion rate was 19.87%.When the enzyme load was 40 FPU·g-1 TS,the highest hydrogen production of Medicago sativa L.was 147.64 mL·g-1 TS(enzymatic hydrolysis time 60 h),and by-products yield was 15.06%,and the hydrogen conversion rate was 22.16%.When the enzyme load was 50 FPU·g-1 TS,the highest hydrogen production of Medicago sativa L.reached 143.42 mL·g-1 TS(enzymatic hydrolysis time 0 h),by-products yield reached 13.52%,and the hydrogen conversion rate reached 21.52%.In the process of photofermentative hydrogen production,the main metabolites of photofermentative bacteria gradually changed from butyric acid and acetic acid to butyric acid with the increase of enzyme load.(4)From the aspects of energy consumption and environmental impact,10 processes of hydrogen production from herbaceous biomass were analyzed.The results showed that the energy consumption of dark fermentation for hydrogen production was significantly lower than that of photo fermentation for hydrogen production when the maximum hydrogen production of herbaceous biomass was obtained,and the energy consumption of dark fermentation for hydrogen production was the lowest when the enzyme load of Medicago sativa L.was 30 FPU·g-1 TS and the enzymatic hydrolysis time was 0 h.When the enzyme load of Medicago sativa L.was 30 FPU·g-1 TS and the enzymolysis time was 0 h,the impact of dark fermentation on the environment was the least.The results showed that the effect of hydrogen production by photo fermentation of Medicago sativa L.under enzyme loading of 30 FPU·g-1 TS and enzymolysis for 60 h was the least.Among the 10 biohydrogen production processes with the highest hydrogen production,the comprehensive evaluation results of dark fermentation were significantly better than that of photo fermentation.The best comprehensive evaluation results were Medicago sativa L.with 30 FPU·g-1 TS enzyme load and 0 h enzymolysis.Therefore,among the 10 kinds of herbaceous biomass selected in this study,Medicago sativa L.is the most suitable one for hydrogen production,which is more suitable for dark fermentation. |
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