Study On Physical Characteristics Of Rice Straw With Different Size And Its Effect On Anaerobic Digestion Performance

China's crop yield ranks the top in the world and is still growing,and a large a,nount of crop straw has become an extremely abundant biomass resource.These straw resources are often not effective use of the disposal,and even threaten the ecological envirorunent.In order to utilize these biomass resources effectively and turn waste into treasure,biogas can be produced by anaerobic fermentation.The polymer structure of biomass straw is not conducive to the direct utilization of microorganisms.In practical engineering,crushing straw will bring huge energy consurrjption,and the smaller the crushing particle size is,the greater the energy consumption will be,so it is necessary to find a suitable crushing particle size.However,in engineering applications,the phenomenon of floatation in anaerobic fermenters hinders the normal process of fermentation.Based on the above problems,this study mainly studied the anaerobic fermentation performance of straw with different grain sizes(40 mesh,20 mesh,10 mesh,5 mesh and 1cm),as well as the floating characteristics and energy consumption in the processFirstly,in batch anaerobic fermentation,the floating phenomenon of materials in the tank is obvious throughout the fermentation process,especially during the peak period of gas production,the material volume expansion rate is higher,and the final volume expansion rate of materials is 8.4%,10.0%,14.1%,10.4%and 14.8%(particle size from small to large),respectively.The content of lignocellulose and organic matter in the floating layer is higher than that in the bottom layer,so the floating phenomenon will hinder the anaerobic fermentation process.In terms of methane production performance and economic benefits,5-mesh straw was the best.A.fter digestion for 50d under 50g TS/L load,the methane production per unit TS was 188mL/g,which was 0.7%,1.1%,3.8%and 15.1%higher than the groups of 40,20,10 and Icm,respectively.The removal rate of volatile solid(VS)and cellulose degradation rate of 5-mesh straw were 68.7%and 59.8%respectively,both better than those of other grain sizes.The power consumption of 5 mesh straw is 42kW h/t,which is 81.7%,61.8%and 40.0%lower than that of 40 mesh,20 mesh and 10 mesh straw respectively.The net methane yield per ton of 5-mesh straw was 259.1 yuan,228.9%,66.4%and 23.3%higher than that of 40-mesh,20-mesh and 10-mesh straw respectively.Secondly,in the sequential batch anaerobic fermentation process,the volume expansion rate of materials under high load is much higher than that under low load,and the thickness of floating layer is basically positively correlated with particle size.When the system was stable,the average daily gas production of each group under low load was 4.06L,3.87L,4.25L,4.83L and 5.60L,respectively.The average daily gas production of 1cm straw was 37.9%,44.7%,31.8%and 15.9%higher than that of the other groups,respectively.Under high load,the daily gas output of the Icm straw group was significantly lower than that of the other groups in stable state,and the daily gas output of the groups of 40 mesh,20 mesh,10 mesh and 5 mesh was 20.0%,22.3%,15.3%and 21.1%higher than that of the 1cm straw group,respectively.lt can be seen that the floatation phenomenon is serious when the load is high,thus inhibiting the process of fermentation and gas production.Lastly,through SEM observation,it was found that potassium hydroxide pretreatment for three days had a certain effect on destroying the surface structure of straw,and debris shedding and pits appeared in the surface layer,which would improve the anaerobic fennentation efficiency.However,when the grain size of straw increases obviously,the effect of pretreatment is not so obvious.Through the analysis of XRD diffraction pattern,it is concluded that in the pretreatment process,the degradation rate of the non-crystallization zone material is higher than that of the crystallization zone,and more non-crystallization zone material is hydrolyzed.However,in the process of anaerobic femientation,the larger the particle size is,the more difficult it is to utilize the amorphous cellulose in the floating layer,and the larger the particle size will deepen the adverse effect brought by the floating phenomenon.Through the analysis of biological characteristics,the following conclusions are drawn:straw with different particle sizes has a certain impact on the richness and diversity of bacterial colonies;the finer the particle size is,the higher the richness and diversity of bacteria is;while the opposite is true for archaea,but the overall sample difference is small.In the 40-order and Icn straw groups,the overlap of bacterial species was about 85%,and the overlap of archaea species was slightly lower,so there was a certain difference between the two species.To sum up,this study provides a straw grain size with better economic performance,which provides certain data support for rational arrangement of stirring frequency and reduction of energy consumption cost.However,the increase of particle size is bound to aggravate the floating phenomenon.Particle size has certain influence on the abundance and species of bacteria and archaea in samples,and there are some functional differences,but the community structure is generally similar.