Study On The Degradation Mechanism Of Straw Pretreated By UV-B Radiation And Its Effect On Aerobic Composting

Aerobic composting is an important means to realize the fertilization of straw.Lignin,one of the main components of straw,has a complex structure and is difficult to be degraded and utilized by microorganisms,which affects pile maturation and compost product quality.Pretreatment to degrade lignin is an important method to promote the process of aerobic compost humification of straw.In this study,we used the characteristic of photodegradability of lignin and selected UV-B,a medium-wave ultraviolet light that has an important effect on the decomposition of plant residues,to conduct a laboratory study to investigate the effect and mechanism of UV-B radiation on the degradation of corn stover.On this basis,the effect of UV-B radiation pretreatment on aerobic composting of corn stover was investigated.In order to provide technical support for the use of UV-B radiation pretreatment of straw to improve the level of aerobic straw composting humification in the northwest region with high UV radiation intensity and arid climate.The main research results are as follows:（1）To investigate the effect of UV-B radiation on corn stover components,three groups of UV-B radiation intensity of 0.4 W/m²,0.6 W/m² and 0.8 W/m² were set and corn stover was treated with radiation for 72 days.The results showed that the corn stover mass,carbon,nitrogen,phosphorus,cellulose,hemicellulose and lignin contents showed a decreasing trend after UV-B radiation treatment,and the changes of mass loss rate and degradation rate of each component of corn stover were more obvious in the pre-radiation period.In particular,the phosphorus content of corn stover decreased rapidly in the early stage of radiation treatment,and basically remained stable in the later stage.The phosphorus degradation rate was 20.44%,22.07%and 22.77%at 12days of treatment under the three radiation intensities.UV-B radiation mainly affected the degradation of lignin,and the lignin degradation rate increased with the increase of radiation time,and the lignin degradation rate of corn stover was 16.49%,18.06%and20.26%at 72 days of treatment under the three radiation intensities.（2）The degradation mechanism of UV-B radiation on corn stover was investigated by analyzing the changes of surface color,microstructure,oxygen-carbon elements,relative crystallinity,functional groups and thermal stability of corn stover before and after UV-B radiation.The results showed that the color of corn stover changed to yellow after UV-B radiation,porous structure appeared on the surface and thermal stability was improved.At the same time,the oxidation state of carbon and the oxygen-to-carbon ratio（O/C）increased,indicating that the lignin in corn stover underwent photooxidation and its relative content decreased.the characteristic absorption peak of guaiacyl units（G）at 830 cm^-1 basically disappeared,while the characteristic peak of lilacyl units（S）at1253 cm^-1 was still absorbed,indicating that the basic structural unit of lignin,guaiacyl units（G）,was more easily degraded than lilacyl units（S）.The contraction vibration of the non-conjugated carbonyl group at 1743 cm^-1 was enhanced,indicating that there was carbonyl group formation during the radiation process,which was the main reason for the discoloration of the corn stover surface.However,UV-B radiation only increased the relative crystallinity of the corn stover and had no effect on the corn stover crystalline structure and cellulose type.（3）The effect of UV-B radiation pretreatment of corn stover on aerobic composting was investigated by conducting a 21-day experiment of mixed corn stover-goat manure aerobic composting.The results showed that the temperature in the high temperature period of the pretreatment group was always higher than that of the control group,and the composting cycle was shortened by 2 days.At the end of composting,the total N and total P contents increased by 17.79%and 50.55%,respectively,in the control group,and by 32.69%and 70.15%,respectively,in the pretreatment group.Meanwhile,C/N and E4/E6 of the pretreatment group were lower than those of the control group,and the biological index GI reached 96.28%,which was higher than87.47%of the control group.It showed that UV-B radiation pretreatment of corn stover helped to shorten composting cycle and improve composting efficiency and humification.