| In the process of stalks as digestion raw material to produce biogas,stalks floats and collects in the upper part of the digestion reactor to form a scum layer,which seriously affects the stability and gas production efficiency of the digestion system.Moreover,once the scum layer encrusts,digestion fails,which has become a bottleneck problem for the development of stalks biogas.Generally,the way of stirring is used to destroy the scum layer and prevent crusting.However,when the stalks does not have sedimentation,stirring can only promote the release of biogas to a certain extent.Once the stirring is stopped,the scum still exists,and it is difficult to fundamentally remove the influence of the scum layer.Due to the complex pore structure features of corn stalks,the overall bulk density of stalks is far less than the specific gravity of water,which makes it difficult for water molecules to enter the microstructure during digestion,poor water absorption and low sedimentation,resulting in stalks floating in water,if the pores of stalks are filled with water,it will sink.Therefore,the key to reduce the scum layer and improve digestion performance is to quickly crack the shielding effect of lignin,increase the porosity of stalks on the microstructure,and improve the water absorption capacity and sedimentation.In order to solve the problem of scum crusting caused by corn stalks digestion,directional conditioning treatment was carried out to improve the sedimentation of stalks particles,Effectively destroy the wood fiber structure of stalks,analyze the water absorption kinetics and thermodynamic features of corn stalks before and after conditioning,and the influence mechanism of conditioning methods on the absorption and precipitation of substances in stalks,Explore the internal mass transfer law,and fundamentally solve the problem of autonomous sedimentation of stalks in digestion liquid.At the same time,combined with microbial treatment,further accelerate the internal damage degree of stalks,and improve the water absorption capacity and sedimentation performance of stalks,Explore the kinetic features of organic matter degradation and gas release features,so as to effectively improve the conversion and utilization rate of raw materials and methane yield in the process of corn stalks digestion,and provide technical support and theoretical basis for breaking through the bottleneck restricting the development of stalks biogas.The main results and conclusions are as follows:(1)The moisture content of corn stalks(The water contents were 71.26%,65.27%,57.39%,47.79%,38.05%and 16.84%respectively)in different air drying degrees from high to low were not easily flow water,combined water and free water respectively.The degree of freedom decreased with the decrease of water content of corn stalks;The combined water content of corn stalks with water content of 47.79%was the highest,and the signal amplitude reached 184.118 AU;In the process of water absorption for 0-6 h,the water content of 16.84%corn stalks has the fastest rate in the initial stage of water absorption,is not easy to flow,the water content increases rapidly,and the degree of freedom of bound water increases.The effect of radial compression on pith was more obvious than axial compression,and the effect was more obvious with lower water content.(2)After conditioning treatment,the physical and chemical properties of corn stalks were changed.The moisture absorption reached the maximum value of 4.42%after 6 hours,which was1.48%higher than that of untreated stalks.The water absorption rate increases,and The water absorption was 120%higher than that of untreated stalks,and the fitting effect of kinetic equation was better;The existing state and migration of water in stalks during water absorption were observed.It was found that the content of bound water and free water in conditioned stalks reached the maximum in 6 hours,and the signal amplitudes were 78.454 AU and 48341.522 AU respectively.The combination of water and substance was closer than that of untreated stalks,and gradually migrated to the"combined"state.The total content signal amplitude of the whole water absorption process was 12841.07 AU higher than that of untreated stalks.(3)The aerobic hydrolysis p H of conditioned corn stalks was lower than that of untreated stalks,and the accumulation of volatile fatty acids(VFAs)was higher.The content of acetic acid in VFAs was the highest at 35℃for 12 h.The degradation rate of lignocellulose hydrolyzed at 25℃,35℃and 45℃for 16 hours was 23.21%,27.67%and 27.19%higher than that of untreated stalks,respectively.(4)Bio enhanced hydrolysis can change the wood fiber structure of conditioned stalks,increase water absorption and improve sedimentation.The effect was better when the amount of bacterial solution was 8%.The p H value of the hydrolysate was 3.51 and the content of acetic acid reached 259.56 mmo L/L.The degradation rates of hemicellulose,cellulose and lignin were 45.48%,31.38%and 17.66%respectively.The concentration of reducing sugar was 67.86%lower than the initial value.The maximum content of acetic acid was 245.49 mmo L/L and the concentration of reducing sugar decreased by 79.03%.Therefore,it is the key to quickly crack the shielding effect of lignin,promote the full contact between the extracellular enzymes of hydrolyzed microorganisms and cellulose and hemicellulose,and increase the porosity of stalks in microstructure,so as to improve the water absorption capacity and sedimentation performance of stalks.(5)The mathematical models of hydrolysis time,temperature and compound bacteria concentration were established by regression analysis.The selected models were significantly reliable.Based on the regression model,the optimal hydrolysis process parameters are finally determined as follows:time,13.57 h,temperature,30.05℃,compound bacteria concentration,8.38%.Under the optimal conditions,the experimental results are consistent with the predicted values.The average sedimentation ratios of compound bacteria and compound bacteria+biogas slurry are 94.96%and 64.10%respectively.(6)Corn stalks conditioning treatment can effectively reduce the volume of scum layer in anaerobic digestion process and improve methane production.The optimal hydrolysis time is 12 h,the density of scum layer after digestion is 0.126 g/cm~3,and the volume of scum layer is 13%lower than that of untreated stalks;The highest cumulative methane yield was 319.64 m L/g·VS,which was 26.59%higher than that of untreated stalks;The VS degradation rate was 4.46%higher than that of untreated stalks.(7)Biologically enhanced hydrolysis adjustment corn stalks can effectively reduce the volume ratio of scum layer,improve the digestion efficiency and methane production,and shorten the digestion time.The appropriate amount of bacterial solution and hydrolysis time can provide a good environment for microbial reproduction and growth,so as to improve the utilization rate of substrate and inhibit the formation of scum layer.The cumulative methane yield of corn stalks treated by compound bacteria reached the maximum value of 367.92 m L/g·VS when the amount of bacterial solution was 8%,and the volume ratio of scum layer decreased by 43.9%;Under the treatment of the same bacterial solution concentration,the scum layer density of anaerobic digestion after the treatment of compound bacteria alone was higher than that of the treatment of compound bacteria solution+biogas slurry;The volumetric methane yield of compound bacteria and compound bacterial liquid+biogas slurry reached the maximum of 5.23 m L/m L·d and 4.97m L/m L·d when the amount of bacterial liquid was 4%and 8%respectively. |
PDF Full Text Request