| Solid-state anaerobic digestion is an effective method to convert low energy density corn stalk into biogas.Furthermore,solid-state anaerobic digestion has advantages of less water consumption,lower heating cost and less biogas slurry compared to liquid-state anaerobic digestion.Biogas residue contains much hemicellulose and cellulose,so it is available to get much biogas potential via secondary fermentation after proper pretreatment.This study selected corn stalk as the experimental material,and the optimized thermo-chemical pretreatment was adopted to improve the ability of degradation of corn stalk.Then,this research focused on the characteristics of corn stalk solid-state anaerobic digestion and the secondary fermentation of biogas residue.The main research contents are as followed:(1)Corn stalk was pretreated by the bubbling fluidized bed reactor at 150?,170?,190?,210? with carrier gas flow of 3m3/h.The pretreated corn stalk was analyzed by SEM,crude fiber tester and XRD.The results showed that thermo-chemical pretreatment could change the fibrous-network structure of lignocellulose and reduce the content of hemicellulose and lignin.It resulted 15.74%,9.37% and 17.17% decrease on hemicellulose,cellulose and lignin at 190? pretreatment.The highest cumulative methane production was obtained at 190? pretreatment,which was 16.30% higher than the untreated.Furthermore,the 190? pretreatment got the shortest start-up time than others.(2)In solid-state anaerobic digestion experiments,20%,25%,and 30% TS contents were selected to study the effects of TS contents on biogas production.The results showed that inhibition to methane yield occurred when TS content was 30%.In the respect of cumulative methane yield,the 20% test performed better,which was 5.89%-26.39% higher than the 25% test.Furthermore,the 190? pretreatment in 20% and 25% tests performed better in each test,which were 14.68% and 36.88% higher than the untreated,respectively.Among all the tests,the 190? pretreatment in 20% was optimal for thermo-chemical pretreatment of the corn stalk for solid-state anaerobic digestion.Hence,treating it as case,and taking out some samples for analysis every 6 days until the test was terminated.The results showed that the synergetic correlation of changes of pH,COD,composition content,crystallinity and physical structure during fermentation process made the digestion environment more suitable for it.(3)In order to study the pretreatment effects of oxalic acid on corn stalk using 0.025mol/L Fe2(SO4)3 as catalytic agent on anaerobic digestion.The corn stalk samples with1%(w/w),3%(w/w),5%(w/w),7%(w/w)of oxalic acid and a control group,with Fe2(SO4)3alone.The results showed that the oxalic acid pretreatment could decrease lignin up to7.57%.It obtained methane yield of 200.31,222.92,272.35,249.91,206.14 L/kg VS,respectively.Among all tests,the 3% oxalic acid pretreatment got the highest methane yield,which was 35.96% higher than the control group.When the oxalic acid concentration became high,the methane yield decreased in turn.It was due to high oxalic acid could result acid inhibition and high organic composition consumption.(4)The biogas residue was pretreated by 3% oxalic acid with 0.025 mol/L Fe2(SO4)3 as catalytic agent.The solid-state anaerobic digestion was conducted with the pretreated biogas residue at 20% TS content for 50 days.The results showed that it had a stable daily biogas production and methane concentration,obtained 4826.08 mL cumulative methane production and per unit TS load of 158.75 L during secondary fermentation.It illustrated that secondary fermentation was a effective method to obtain biogas potential of biogas residue. |
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