Research On The Influence Of Alkaline Pretreatment On Anaerobic Digestion Of Lignocellulosic Biomass

Converting lignocellulosic biomass, the most abundant bio-renewable resource and one of the effective substitute materials of traditional fossil fuels, into methane via anaerobic digestion route will get good environmental and economic benefits. However, the inherent properties of native lignocellulosic materials make them resistant to fungi, bacteria, and enzymatic attack, which results in poor performance of direct anaerobic digestion. In this study, the influence of NaOH、KOH、Ca(OH)2pretreatment under ambient temperature on mesophilic anaerobic digestion of corn stover was studied. Moreover, two novel methods, two-step NaOH pretreatment and NaOH combined Ca(OH)2pretreatment, were also carried out to improve the performance of anaerobic digestion of lignocellulosic biomass.Different concentrations (2%-14%g alkali/g dry weight of corn stover) of NaOH, KOH, and Ca(OH)2were used to pretreat corn stover at20±2℃. The results showed that NaOH pretreatment obtained the greatest improvement of the anaerobic digestion performance compared with the untreated corn stover. The optimal NaOH loading was6%, which moved up the methane production peak for4days and increased the cumulative methane yield by47.1%.The influence of different concentrations (2%-14%g alkali/g dry weight of corn stover) of two-step NaOH pretreatment under ambient temperature on mesophilic anaerobic digestion of corn stover was studied. It was found that the cumulative methane yields of two-step NaOH pretreatment group were6.8%-9.7%lower than that of the one-step NaOH pretreatment group under the same alkali loading. So the two-step NaOH pretreatment is not an effective alkaline pretreatment method.The influence of different concentrations of NaOH (2%-6%) combined Ca(OH)2(2%-4%) pretreatment under ambient temperature on mesophilic anaerobic digestion of corn stover was studied. The results showed that NaOH combined Ca(OH)2pretreatment could effectively move up the methane production peak and increase the methane yield.4%NaOH combined2%Ca(OH)2pretreatment was the optimal method which increased the cumulative methane yield by50.8%. Mesophilic anaerobic digestion of different particle sizes of corn stover was also studied. It was found that the highest and the lowest methane production performance was performed from>0.25-1.0mm and>5.0-20.0mm particle size, respectively. Then4%NaOH combined2%Ca(OH)2and6%NaOH were both used to pretreat these two particle sizes of corn stover. The results showed that both of the combined alkaline and single alkaline pretreatment significantly increased the cumulative methane yield of>0.25-1.0mm (15.0%and15.1%) and>5.0-20.0mm (45.6%and47.8%) of corn stover. Considering the methane yield, reagents and energy cost,4%NaOH combined2%Ca(OH)2pretreatment method and the particle size of>5.0-20.0mm were determined as the optimum pretreatment conditions of corn stover.The influence of4%NaOH combined2%Ca(OH)2pretreatment under ambient temperature on mesophilic anaerobic digestion of switchgrass and rice husk was also studied. The results showed that the cumulative methane yields of combined alkaline pretreated switchgrass and rice husk increased by59.0%and174.4%, respectively, compared with the untreated samples.It was proven in this study that pretreatment with the combination of sodium hydroxide and lime is a promising alternative to improve anaerobic digestion of lignocellulosic biomass at a lower cost and can be used to substitute sodium hydroxide pretreatment in the coming future.