Effect And Mechanism Of Five Pretreatment Methods On Anaerobic Digestion Of Straw

Crop straw is mainly composed of lignin,cellulose and hemicellulose.Its efficient utilization by anaerobic digestion(AD)can produce biogas.However,the amorphous hemicellulose of lignocellulosic structure is wrapped around the crystal microfibrils of cellulose and all embedded in the lignin matrix,which limits the utilization of cellulose by microorganisms and enzymes.NaOH pretreatment method,which based on alkali dissolution and saponification,and H2O2 pretreatment method,which based on high oxidizability,can destroy lignin structure,while the reaction rate is slow.NaOH and H2O2 are combined to pretreat straw to further improve gas production performance and shorten digestion time.However,H2O2 has security problems in transportation and storage,and its instability in transportation and storage affects the stability of straw pretreatment effect.This paper mainly studied the pretreatment methods by the electrochemically produced NaOH-H2O2(eNaOH-H2O2)by real-time preparation and direct electrolysis pretreatment with the methods by NaOH and NaOH-H2O2 mixture solution.In addition,the pretreatment of AlMgCu alloy material with certain oxidation-reduction properties was also studied.The main research contents and results are as follows:(1)Gradient AlMgCu alloy powder concentration of 2%to 5%for the influence of anaerobic digestion of rice straw,and effect of five pretreatment methods,including the AlMgCu alloy powders,NaOH,NaOH-H2O2,eNaOH-H2O2 and direct electrolysis,was investigated and also explored the influence of storage time on eNaOH-H2O2 pretreatment,the results showed that anaerobic digestion performance of rice straw after the 2%AlMgCu alloy powders pretreatment was the best,and the cumulative production was 12%higher than that of untreated group;Among the five pretreatments,eNaOH-H2O2 had the best effect.Compared with AlMgCu alloy powder,NaOH,NaOH-H2O2 and direct electrolysis pretreatment,the peak gas production of eNaOH-H2O2 was shortened by 9 days,1 day,7 days and 0 day,respectively,and T80 was shortened by 9 days,5 days,9 days and 2 days,respectively.The cumulative methane production was increased by 27%,15%,5%and 0%,respectively.The three groups of electrolytes for which storage time was 0,1 and 2 days could effectively improve the gas production of rice straw and shorten the fermentation cycle.The cumulative methane production in the 1-d group was the highest with the value of 3652 mL,and was 7%and 5%higher than that in the 0-day and 2-day groups respectively,and T80 was 22 d.In addition,the effects of eNaOH-H2O2 pretreatment on the anaerobic digestion performance of corn straw and wheat straw were studied.The results showed that the total methane production of corn straw and wheat straw pretreated by eNaOH-H2O2 was 25%and 14%higher than that of the untreated group,respectively.(2)The composition changes of rice straw by NaOH,NaOH-H2O2,eNaOH-H2O2 and direct electrolysis pretreatment were studied through decomposition rate at the end of the anaerobic digestion,TS,VS removal rate and the content of lignin,cellulose,and hemicellulose,and the extract content changes of before and after the pretreatment of rice straw.SEM and XRD technology were used to analyze the rice straw structure change before and after the pretreatment.The results showed that,after anaerobic digestion straw degradation rate of eNaOH-H2O2 group is highest with the value of 41%.The direct electrolysis group showed the highest removal rate of TS and VS and the highest degradation ability of lignin,cellulose and hemicellulose.After several kinds of pretreatment,the content of cold water,hot water and 2%NaOH extract of straw increased,while the content of phenyl alcohol extract decreased.There was no obvious fiber bundle structure in SEM image,indicating that pretreatment could effectively destroy the entanglement of lignin to cellulose.(3)Based on the Gompertz model,the potential methane production of rice straw by anaerobic digestion after different pretreatments was studied.The results showed that the methane production potential of the raw materials by the eNaOH-H2O2 group was the highest after pretreatment,which was 191.86 mL CH4/g VSadd,and the highest daily methane production rate which was 15.41 mL CH4/g(VSadd·d),16.7%and 16.6%higher than that in the NaOH group,respectively.Stasis time by eNaOH-H2O2 was the shortest(11.44 days)which was 4.6 days shorter than NaOH group.The electrochemical and AlMgCu alloy powders pretreatment methods provided new ways for the efficient utilization of crop straw.