Study On Degradation Characteristics Of Corn Straw Pretreated By Composite Microbes

China is a country with abundant biomass resources,which are not reasonably utilized.It is a waste of resources and will cause serious environmental pollution.The production of biogas by anaerobic fermentation of crops straw is an effective way for the utilization of straw resources.However,the straw mainly consists of cellulose,hemicellulose and lignin.Lignin is difficult to hydrolyze.Due to the protective effect of lignin,it is also difficult to digest and utilize cellulose.Therefore,it is necessary to pretreat the straw before anaerobic fermentation,which can greatly improve the conversion and utilization efficiency of the wood cellulose.Microbial pretreatment is an effective way to degrade straw,but the complete degradation of lignin requires a variety of microorganisms.Nowadays,pretreatment with composite microbes has become a trend in the present study.In this paper,8 kinds of microorganisms were selected to construct efficient composite microbes for corn straw degradation.Firstly,the degradation ability of single strain on corn stalk were compared and analyzed.Then,the antagonistic relationships between single strain and mixed microbeswere analyzed.A group of wood cellulose degradation composite microbes were constructed.The degradation characteristics of corn straw material and the effect of composite microbes pretreatment on the degradation of the materials were also analyzed.The determination of the heat rule in the pretreatment process of corn straw by composite microbes was completed in the self-made straw aerobic pretreatment reactor.At the same time,the change of the degradation characteristics of material in the process of temperature dynamic change was studied.Based on the heat balance analysis and temperature fitting of the heat source in the center of the fermentation tank,the empirical formula of the inner heat source in the process of pretreatment of corn straw by composite microbes was derived.Finally,the anaerobic fermentation of hydrogen and biogas production with the corn straw pretreated with composite microbes was carried out.The effect of different pretreatment ways on the gas content and the change of gas content during the anaerobic fermentation process were analyzed.The main conclusions of this study are as follows:1.During the pretreatment of the whole 35 d,Aspergillus niger and Trichoderma viride had higher degradation ability to the cellulose in corn straw.The degradation rate of hemicellulose in corn straw pretreated by Aspergillus niger and Trichoderma viride was 47.81% and 37.53% respectively,and the degradation rate of cellulose in corn straw was 38.96% and 46.32% respectively.Phanerochaete chrysosporium and Coriolus versicolor were better in the degradation of lignin in corn straw,the degradation rate of lignin was 43.56% and 39.17% respectively.All the selected 8 kinds of microorganismswere difficult to achieve fully degradation of corn straws in the single strain pretreatment process.The results of antagonistic reaction showed that there was no antagonism between the 8 strains selected in this study.The contents of lignin,cellulose and hemicellulose were gradually decreased in the whole pretreatment process.After 15 days,the degradation rate of hemicellulose,cellulose and lignin in corn straw were 48.53%,36.38% and 40.11%,respectively.Meanwhile the degradation rate of lignin was improved,and the consumption of cellulose was decreased.The results of scanning electron microscopy(SEM)showed that the composite microbes had a destructive effect on the structure of lignin,which improved the accessibility of cellulose.2.Pretreatmentsbycomposite microbes and by natural accumulation can both promote the degradation efficient of corn straw.After pretreatment process,the structure of lignin changedin various degrees.The p H value of straw was relatively more stable and the organic matter content in the material is higherafter the pretreatment of corn straw by composite microbes,which is beneficial to the subsequent anaerobic fermentation to produce biogas.After 14 d’s pretreatment by composite microbes,the degradation rate of hemicellulose,cellulose and lignin were 44.43%,34.90%,38.03%,respectively.Composite microbes showed a stronger ability to degrade lignin.By changing the structure of the lignin,the pretreatment by composite microbes increased the exposure area of the cellulose and the hemicellulose,thus improved the accessibility of the cellulose.On the 8th day in the pretreatment by composite microbes,the microbial biomass reached to the maximum OD6001.521,p H reverted to a neutral level 7.07,and organic matter content reached to maximum 12865 mg·L-1.3.The corn straws were pretreated by composite microbes ina self-made aerobic pretreatment reactor.The result showed that composite microbes had a strong ability to degrade lignin.By changing the structure of the lignin,the pretreatment by composite microbes increased the exposure area of the cellulose and the hemicellulose,and improved the accessibility of the cellulose.After 14 d’s pretreatment by composite microbes,the degradation rate of hemicellulose,cellulose and lignin were47.08%,33.25%,39.21%,respectively.During the pretreatment process,the microbes compound accelerated the heating up,and the high temperature periodwas prolonged,which promoted the decomposition of organic matter in the material.The change of temperature parameters in the pretreatment process was detected by the data acquisition system.The results showed that temperature of the materials pretreatedby composite microbesrose faster,and could reach to the highest temperature(56.2 ℃)in advance.Pretreatment bycomposite microbes promoted the rapid initiation of fermentation as well as the decomposition and transformation of organic matter.The distribution of temperature field in the pretreatment reactor was studied.The fitting of the temperature curve of the material in the center of the reactor was carried out.The changing of temperature curve with time in the central part of the material was obtained.According to the law of conservation of energy,heat conduction differential equation under cylindrical coordinate element was analyzed.The empirical formula of the internal heat source in the corn straw pretreatment process was derived.4.Pretreatment can increase the content of hydrogen and the hydrogen yieldingper unit mass of straw in the anaerobic hydrogen production of corn straw.The hydrogen production efficiency of corn straw pretreated by composite microbes was higher.In the process of anaerobic fermentation,the hydrogen reached up to 42.82%.The cumulative hydrogen production increased by 21.14%.During the biogas fermentation,the gas production peak can be reached in advanceand the content of methane was higherafter pretreated,especially pretreated by composite microbes.The content of methane was more than 50%in the biogas production peak.