Study On The Effect Of Hydrothermal-Assisted CaO₂ Pretreatment On Anaerobic Digestion Of Wheat Straw

China is a large agricultural country,and a huge amount of biomass straw is burned or buried every year,which not only causes a waste of resources,but also pollutes the ecological environment.Biomass energy technology mainly refers to the use of lignocellulose and other waste to produce biofuels such as ethanol,hydrogen and methane.Due to the complex structure of lignocellulose cellulose,hemicellulose and lignin cross-linking with each other,resulting in the difficult degradation of straw,the straw needs to be pretreated to loosen the fiber raw materials and destroy its complex structure,reduce the degree of polymerization of cellulose.In this study,wheat straw was used as a raw material,and a combination of hydrothermal and Ca O₂chemical pretreatment was used to pretreat the wheat straw,to explore the promotion effect of this method on the hydrolysis and anaerobic digestion capacity of wheat straw.The main research contents are as follows:?1?The effect of hydrothermal coupled Ca O₂pretreatment on the hydrolysis of wheat straw was studied.By changing the solid-liquid ratio,hydrolysis temperature,and Ca O₂addition amount during the pretreatment,the determinations of COD and TOC of hydrolyzate were carried out to investigate the optimal conditions for hydrothermally coupled with Ca O₂pretreatment and hydrolysis of straw.It was found that the solid-liquid ratio,hydrolysis temperature and the amount of Ca O₂added have a great influence on the hydrolysis of straw.When the solid-liquid ratio was 1:8,the hydrolysis temperature was 121?,and the Ca O₂mass concentration was 8%,the hydrolysis effect was the best.The TOC value of hydrolysate increased by 173.09%compared with the control group.When the ratio of solid to liquid,the temperature of hydrolysis and the mass fraction of Ca O were 1:8,121?and 10%,respectively,the hydrolysis effect is the best,where the TOC of hydrolysate was 176.56%higher than that of the control group.?2?The effect of hydrothermal coupled Ca O₂pretreatment on the fermentation of wheat straw was studied.Under the conditions of 1:8 solid-liquid ratio and 121?hydrolysis temperature,different gradients of Ca O₂additives were set to pretreatment wheat straw.The control experiment of hydrothermally coupled with Ca O pretreatment of wheat straw was also done.The hydrolysate characteristics were measured,the hydrolysis residue was characterized by XRD and FT-IR,and the main characteristics of hydrogen production by subsequent fermentation were analyzed.It was found that hydrothermally coupled with Ca O₂/Ca O pretreatment could destroy the complex structure of straw and increase the biodegradability of straw.Both Ca O₂and Ca O pretreatment can improve the hydrogen production effect to a certain extent.With the increase of Ca O₂or Ca O content,from 0 to 6%,H₂output also increases.Ca O₂or Ca O is added at a concentration of 6%.The highest H₂yield in the treated wheat straw was71.8 m L/g TS and 114 m L/g TS,respectively,which were 66.20%and 163.88%higher than the control group?43.2 m L/g TS?.Appropriate amount of Ca O₂or Ca O has certain promotion effect on the hydrogen production process of wheat straw fermentation,and excessive amount will inhibit its biological hydrogen production.?3?The effect of hydrothermal Ca O₂pretreatment on the anaerobic digestion of wheat straw was studied.Under the conditions of 1:8 solid-liquid ratio and 121?hydrolysis temperature,different gradients of Ca O₂additives were set to pretreatment wheat straw.The control experiment of hydrothermally coupled with Ca O pretreatment of wheat straw was also done.Through the further analysis of the key features of anaerobic digestion,the study found that both Ca O₂and Ca O pretreatment can improve the anaerobic digestion production effect to a certain extent.With the increase of Ca O₂or Ca O content,from 0 to 6%,methane yield also increases.Ca O₂or Ca O added concentration of 6%under the condition of pretreatment of wheat straw methane yield the highest,166.7 m L and 163.6 m L/g/g TS,respectively,which were 37.09%and 34.54%increased by control group.However,excessive Ca O₂or Ca O can inhibit its bioanaerobic digestion.?4?The effect of hydrothermally coupled with Ca O₂and cellulase pretreatment on the anaerobic digestion of wheat straw was studied.Under the conditions of solid-liquid ratio of 1:12,Ca O₂mass concentration of 6%,hydrolysis temperature of121?,and enzymolysis temperature of 55?,different gradients of enzyme addition were used to pretreat wheat straw.In addition,hydrothermal coupled Ca O₂pretreatment,cellulase pretreatment and control group were performed.The main characteristics of subsequent anaerobic digestion were analyzed by measuring the hydrolysate characteristics and characterizing the hydrolysis residue with SEM,XRD and FT-IR.It was found that hydrothermal coupled Ca O₂and cellulase pretreatment could effectively degrade hemicellulose,lignin and cellulose,make straw hydrated and swell,and effectively destroy the complex connection among straw components,thus increasing the availability of cellulose and cellulase.Hydrothermally coupled with Ca O₂with cellulase pretreatment can effectively promote anaerobic digestion of straw.The methane production rate was 214 m L/g TS in the sample pretreated with 6%Ca O₂coupled with 15 mg enzyme/g cellulose,which was 64.81%higher than the control group.