Characteristics Of Gas Production By Combined Anaerobic Fermentation Of Straw And Manure

Corn stalks and livestock manure are the main agricultural waste in China,with wide sources and high production,but some of them have not been effectively used.Their unreasonable utilization,such as straw burning and indiscriminate discharge of livestock manure,has brought serious environmental problems and waste of resources,and accidents are frequent.The use of straw or livestock manure for anaerobic fermentation to produce biogas has the advantages of being environmentally friendly and producing clean energy,and is considered to be the main means of resource utilization of agricultural waste.However,the complex structure of corn stover,consisting of a stable structure of cellulose,lignin and hemicellulose,is not easily degraded,leading to low conversion rates,poor gas production and crusting in anaerobic systems.For such problems,they are often solved by pretreating straw or mixing fermentation with livestock manure and improving fermentation conditions.For this reason,this paper strengthens the process research on the pretreatment of corn straw raw materials and the mixed anaerobic fermentation of straw and livestock manure,which is essential to improve the overall economic benefits of anaerobic fermentation biogas projects,improve the ecological environment and promote the development of low-carbon circular agriculture.In this thesis,a single-factor experiment was conducted to optimize the hydrothermal conditions using corn stover with hydrothermal pretreatment to increase the lignocellulose degradation rate of straw and improve sugar production.On this basis,anaerobic fermentation experiments were conducted by combining pig manure with corn stover to optimize the anaerobic fermentation process and to investigate the effect of hydrothermal pretreatment on the gas production of anaerobic fermentation mixed with pig manure under the optimized process conditions.The main research contents and results of this paper are as follows:(1)Using corn straw as raw material,the pretreatment conditions were optimized with lignocellulose content and reducing sugar content as indicators,and the effects of different hydrothermal pretreatment conditions(hydrothermal temperature,time,solid-liquid ratio,and added acid/alkali concentration)on the structure and enzymatic sugar production of straw were investigated.The experimental results showed that the hydrothermal temperature and hydrothermal time largely influenced the pretreatment effect of straw,and the solid-liquid ratio had a relatively weak effect.The cellulose degradation rate of straw lignocellulose reached 7.63%under the optimal pretreatment conditions of 160℃,30 min and 8%,and 3.26mg/ml reducing sugar was generated during the enzymatic digestion at 12 h.(2)Combined anaerobic fermentation of corn stalk and pig manure was carried out.The influence factors of total solid concentration(TS),ratio of manure to straw and inoculation amount were studied by single factor experiment.It was found that the cumulative gas production and methane production were the highest when TS=10%,manure-straw ratio=2:1and inoculation ratio=30%,which were 33092ml and 17175.6ml respectively.By monitoring the dynamic changes of p H,ammonia nitrogen,alkalinity and VFA indexes of fermentation broth,it is found that p H and ammonia nitrogen have similar trends with gas production,while VFA and alkalinity have opposite trends.(3)Response surface experiments were designed using the Box-Behnken Design(BBD)method,and the results were analyzed by ANOVA using Design Expert software,and the degree of influence of the three conditions of corn stover and pig manure on methane production was obtained as manure-straw ratio>inoculum ratio>TS concentration,and the fitted equation for methane production from anaerobic fermentation of corn stover mixed with pig manure was:Y=16292.4+20.00A-2156.25B-608.50C-91.25AB+94.25AC-312.75BC-1724.83A~2-1856.83B~2-3278.83C~2(p<0.0001),Where A is the TS concentration,B is the manure-straw ratio,and C is the inoculation ratio.(4)The optimal biogas production conditions for corn stover and pig manure were predicted by Design Expert software as the maximum cumulative methane production at a coding level of-0.62 for TS concentration,0.83 for manure-straw ratio,and-0.81 for inoculum ratio,at which time the predicted methane production was 11216.9 ml.The anaerobic experiment under optimal conditions yielded a value of methane production was11205.3 ml,which differed from the value predicted by the model by 1%,indicating that the model is reliable for predicting the cumulative methane production from anaerobic fermentation.(5)Straw and pig manure were treated under optimal hydrothermal pretreatment conditions and optimized anaerobic fermentation conditions,with the original straw as the control,and it was found that straw pretreated and then fermented with pig manure produced significantly more gas,with more advanced peak gas production and more stable fermentation.This study provides some reference for the optimization of pretreatment conditions of corn straw and the initial conditions of cooperative anaerobic of straw and pig manure.