Effects of Urea-biological Co-pretreatment of Wheat Straw on Its Characteristics of Anaerobic Digestion for Biogas Production

Wheat is one of the major crops in northern part of China, it accounts for18.31%of thetotal. To compare with the developed country, the utilization ratio of straw resourcesinChinawas just35%of it was in developed country. Due to the low utilization efficiency ofthese straws,the phenomenon that the straws were burnt in largetractsofland could be seeneverywhere in China. Because of the low calorific value of wheat straw, to burn the strawis a way of wasting resources and tremendous influenced the environmenta.How to solvethe reuse these resources has become an important topic of new rural construction.It is a key technology to pretreat the straw to break down the crystal structure which isconsist of lignin,hemicellucose and cellucose, thus for the efficient use by themicroorganisms. There are there methods for the pretreatment of straw, physics,biologicaland chemistry.This topic base onthe Shanghai major torch-plan projects (08DZ1900405)"the research and application demonstration of the key technology on agriculture wasterecycling utilization".Urea-microorganism co-pretreatment was applied to slove theobstacle of plant stalk anaerobic digestion and to optimize biogas production.It is expectedthat these tests will supply practical reference for biogas commercial production fromagricultural wastes. All the result that:1. Wheat straw was treated with urea solution. The effect of pretreatment time onanaerobic digestion of wheat straw for biogas production was investigated in a bench scaleanaerobic digester. The results showed that the total yield of biogas reached the maximumof8388ml when the concentration of urea was40g/L and the pretreatment time was25d atfermentation time of31d. The maximum CH4content at mesophilic fermentation was56.2%at the tenth day of anaerobic digestion which was8.91%higher than the control. Inaddition, the addition of urea had an accommodative effect on the process of anaerobicdigestion. This study provided a good reference for the research and development of the comprehensiveutilization of straw waste.2.Wheat straw was treated with urea solution. The effect of pretreatment time on anaerobicdigestion of wheat straw for biogas production was investigated. The results showed thatthe total yield of biogas reached the maximum of11115ml when the concentration of ureawas45g/L and the pretreatment time was25d at fermentation time of33d.The maximumCH4content at mesophilic fermentation was56.4%at the tenth day of anaerobic digestionwhich was9.09%higher than the control.3. Co-pretreatment of wheat straw by urea-microorganism was conducted. The effects ofsupplement dose of microorganism in biological pretreatment of wheat straw on itsanaerobic digestion for biogas production were investigated using a self-made anaerobicdigestion device with pretreated wheat straw as raw materials. Results showed that thetotal yield of biogas reached the maximum of7968mL, which was23.11%higher than thecontrol, when the urea concentration, pH of biological pretreatment and ratio ofPhanerochaete chrysosporium to Trichoderma reesei added into the wheat straw were35g/L，4and1×109:1×109，respectively. The values ofVFA,CH4and pH were located innormal range. The maximum CH4content was51.33%which is6.01%times higher thanthat of control. The fermentation time was shorten to23d during the whole experiment.4. Co-pretreatment of wheat straw by urea-fungi was carried out. The effects of fungipretreatment pH of wheat straw on anaerobic digestion for biogas production wereinvestigatedusing a self-made anaerobic digestion device with pretreated wheat straw asraw materials. Results showed that the total yield of biogas reached the maximum of9123ml when the ratio of Phanerochaete chrysosporium to Trichoderma reesei added intothe straw and fungi pretreatment pH were1×108:1×108and4, respectively. The maximumdaily biogas production was980ml when the fungi pretreatment pH of wheat straw was4at ninth day of anaerobic digestion. The values of VFA and pH were in normal range. Themaximum CH4content was54.64%which was3.62%higher than that of control. Besides,the fermentation time was shorten to22dduring the whole experiment.5. Three factors of the urea-microorganism co-pretreatment,urea treatment time, ureaconcentration and fungi pretreatment pH were investigated during the process the fermentation.The R2of the model of a second order quadratic equation was0.811.Theconstant of the model was not significant, while the quadratic termof urea treatment timewas significant.The experimental results show that the optimal conditions:ureaconcentration:45g/L, urea treatment time:27.13d, the pH of fungi treatment:4.82, themaximum predictive yield (Y):9775.5ml.