Effects Of White Rot Fungus Pretreatment On Methane Production During Anaerobic Digestion Of Straw

Anaerobic digestion of straw can not only produce clean methane,but also avoid environmental pollution caused by the burning of straw,which is an efficient clean biomass energy utilization technology.However,the complex structure of lignocellulose in straw limited the methane conversion efficiency of anaerobic digestion.The white rot fungus pretreatment technology can effectively reduce lignin content in straw,change cellulose structure and improve biomass utilization efficiency.At present,the research of white rot fungus pretreatment technology mainly focuses on the selection of excellent bacteria,but the optimization of pretreatment process is seldom studied.In this paper,the typical white rot fungus species Phanerochaete chrysosporium and wheat straw were studied,and the white rot fungus pretreatment effects on biological methane potential in anaerobic digestion were studied by single factor experiment,Plackett-Burman experiment and Box-Behnken experiment.The results provide guidance for the selection of the optimal conditions for the pretreatment of white rot fungus and its industrial application.By using single factor experiment,the effects of different factors on pretreatment were studied.A model of lignocellulosic substrates and biological methane potential of the straw was established based on the literature data,i.e.BMP=360.148-481.252lig+2016.066hemi-299.981cell.The R-squared of the model R²=0.912.The error between the predicted and experimental values of the model is within 5%and the reliability of the model is high.The results show that the increase of spore inoculation amount and pretreatment time can promote the degradation of lignocellulose in straw and increase the biological methane potential,but the increase ratio of biological methane potential also decreases gradually with the increase of inoculation amount and pretreatment time.Biological methane potential increases with the straw moisture content,reaction p H value,reaction temperature,exogenous carbon source concentration and exogenous nitrogen source concentration.In the single-factor experiment,the conditions with the highest biological methane potential were:spore inoculation amount 1×10⁷,pretreatment time 30 d,water content 75%,reaction p H value 4,reaction temperature 30?,additional carbon source concentration 20 mg g^-1TS,additional nitrogen source concentration 10 mg g^-1TS,and Mn²⁺concentration 0.01 m M g^-1TS.Based on the results of single factor experiment,Plackett-Burman experiment was carried out to judge the significance of each influence factor.Experiment results show that among the 8 factors studied by the single factor experiments,the four factors including spore inoculation amount,pretreatment time,straw moisture content and reaction p H were significant.The order of influence of these four factors on straw was as follows:spores inoculation amount>pretreatment time>straw moisture content>reaction p H.The response surface optimization method was used to optimize four significant factors in the Plackett-Burman experiment.Experiment results show that the optimized parameters of the variable combinations:spore quantity of 8×10⁵,pretreatment time 20 d,moisture content 65.91%and reaction p H 5.58.Under this condition,the response value of biological methane potential model and the experimental value are 330.4487 m L·g^-1VS and 355.97m L·g^-1VS respectively,which are 23.49%and 34.53%higher than the untreated wheat straw.The study on the mechanism of pretreatment of white rot fungus straw shows that the crystallinity of wheat straw decreased from 0.659 before pretreatment to 0.589 after pretreatment,and the contact angle between straw press sheet and water in air decreased from 69.2°before pretreatment to 46.6°after pretreatment which indicate pretreatment reduced the crystallinity of straw and increased the hydrophilicity of straw.Moreover,the enzymatic adsorption and enzymatic hydrolysis of wheat straw treated by white rot fungus increased significantly.When the cellulase concentration was 1.2 mg/m L,the adsorption rate of cellulase increased by 51.9%.The amount of reducing sugar produced by enzymatic hydrolysis of unpretreated and pretreated wheat straw was 153.46 mg/g and 261.17 mg/g,respectively,and the amount of reducing sugar produced by enzymatic hydrolysis increased by 70.19%.