Study On Decomposing Process Control And Nitrogen Conversion Mechanism In Green Waste Vermicomposting

Green waste is mainly lignocellulosic polymer as carbon source,and the C/N ratio is high,resulting in low organic matter decomposition rate and poor maturity during the composting process.N₂O and N₂ are significantly released during the process of waste disposal by earthworms,resulting in a high rate of nitrogen loss.Therefore,for high C/N ratio raw materials,how to control the vermicompost maturity process,reduce nitrogen loss and improve the quality of composted products,is a composting process problem that needs to be solved.In this study,nitrogen source was used to regulate C/N,inorganic additives and mircrobial inoculum to effectively control nitrogen loss during vermicomposting and improve product quality.Respectively through 1)urea and organic waste with higher total nitrogen content（cow manure,soybean meal and thermal hydrolysis sludge）to adjust the raw material C/N to 25:1 for vermicomposting;2)5%inorganic additives（zeolite,bentonite and superphosphate）added to vermicomposting;optimized combination of lignin degrading bacteria used in vermicomposting.Investigate the effects of different treatments on nitrogen loss and improve the quality of compost products to obtain the optimal exogenous nitrogen,inorganic additives and bacterial agents for vermicomposting process control;explore how the interaction of the three conditions affects the conversion of organic carbon and nitrogen,maturity and product quality;and metagenomics technology is used to reveal the microbial structure and function of the vermicomposting process and its influence on carbon and nitrogen metabolism.The main conclusions are as follows:（1）Compared with the control urea,the nitrogen-rich organic waste treatment has a significant increase in CO₂ release and a significant reduction in the nitrogen loss rate.The cattle manure treatment has the best nitrogen retention effect,and this treatment can significantly increase the total the content of humus and humic acid and the number of earthworms in the final vermicompost.The results of principal component analysis of the maturity and quality indicators of the final compost of different treatments showed that the cow manure adjusted the raw material C/N to obtain the best quality vermicompost product.（2）5%superphosphate treatment significantly reduces the organic matter content by 34%; increases the total nitrogen content by 178%.And superphosphate treatment significantly increased the content of NH₄⁺-N and NO₃^--N,GI value,growth quality and reproduction number of earthworms,reduced the ratio of E4/E6,and had the best effects of nitrogen retention and decomposing effects.（3）Optimized composite strain:No.A:No.2:No:11:No.5=1:2:2:1 secreted the largest lignin-degrading enzyme activity on the 18th and 35th days,which were 5380 and 731 IU/g respectively;the degradation rates of lignin and cellulose are significantly the largest,40.1%and 55.8%,respectively.After inoculating the optimized compound inoculum to green waste compost at 5%,the degradation rate of lignin and cellulose of the vermicompost was significantly reduced,and the number of earthworm cocoon,nutrients and humic acid content were significantly increased,and the quality of the vermicompost produced was the best.（4）At the end of vermicomposting,the combined treatment of cow dung and inoculants significantly increased the content of NH₄⁺-N and NO₃^--N,respectively 39.89 and 422.85 mg kg^-1;significantly increased the amount of CO₂ released to 1980 ml kg-1,and significantly reduced nitrogen loss rate,79%;significantly increase the enzyme activity of lignocellulose degrading enzymes（cellulase,Lip,Mnp and Lac）,total humus acid and humic acid content,CEC value.The main component analysis results of the maturity and quality indicators of the final vermicompost showed that the quality of the vermicompost produced by the combined treatment of cow dung and inoculants was the best.（5）In different treatments,the fungal and bacterial community structure changed significantly after vermicomposting.The composition of microorganisms at the phylum and genus levels was the same,but the relative abundance was quite different;the most abundant carbohydrate enzymes were all glycoside hydrolase（GH）family.Additive combination treatment can increase the sequence of pathway genes related to carbon cycle and has a greater impact on nitrogen metabolism oxidoreductase.The combined treatment of cow dung and bacteria agent promoted the nitrification,denitrification and nitrogen fixation of compost by increasing nir G,nir K and nif K genes,respectively.The accumulation of NH₄⁺-N is mainly caused by the dissimilatory reduction of nitrate.The combined treatment of cow manure and additives complicates the nitrogen conversion in the vermicomposting process,and the cellulase activity has a significant impact on the nitrogen cycle.In this study,the C/N ratio and additives were adjusted to promote the decomposing process of green waste vermicompost and reduce the loss of nitrogen.In the vermicomposting treatment of green waste,consideration should be given to the use of cow manure for raw material C/N adjustment,5%superphosphate application and compound lignin inoculant addition to promote vermicompost maturity,reduce nitrogen loss and improve product quality.It is added with compound lignin bacteria to promote compost maturity,reduce nitrogen loss and improve product quality.The combined treatment of cow dung and inoculants promotes nitrification,denitrification and nitrogen fixation in the vermicomposting process,and produces compost products with the highest maturity and quality.This research has certain significance for controlling nitrogen loss during vermicompost maturity and improving the efficient resource utilization of green waste.