| This study took residues from anaerobic digestion of agricultural waste rice straw and pig manure as the research object.By separating key functional microorganisms from the natural world and the natural composting process of biogas residue,a group of composite microbial agent that enhanced biogas residue composting was artificially constructed,and the composting effects of natural composting and bio-enhanced composting(maximum temperature,thermophilic duration,total nitrogen,GI,etc.)were compared.By investigating the main factors affecting the biogas residue composting process(moisture content,ventilation intensity,carbon-nitrogen ratio),this research analyzed the changes of key parameters in biogas residue composting under different process conditions,and discussed the efficiency and nutrient content of biogas residue composting under each conditions.In addition,high-throughput sequencing technology was used to analyze the diversity of the bacterial communities in biogas residue composting under different moisture content,and the reasons for the differentiation of biogas residue composting under different moisture content in the perspective of bacterial communities were explored.Besides,based on the best technological conditions for composting biogas residue obtained from previous work,and combining metagenomics methods and spectroscopy techniques(FT-IR,UV-Visible light scanning,and 1H-NMR),the composition and changes of the soluble organic matter in the biogas residues and the differences in the functional composition of the microbial genes before and after the bio-enhancement by composite microbial agents were analyzed and compared,which preliminarily explored the principle of the composite microbial agent to enhance the composting of biogas residues.Moreover,by combining different proportions of inorganic substrates(vermiculite and perlite),using unfertilized garden soil(CK)and two commercial substrates(S1,S2)as references,the physicochemical properties of compound seedling substrates under different ratios were investigated.Tomatoes and cabbages were used as research objects,and the appearance indexes(fresh weight,dry weight,stem thickness,seedling length,etc.)and physiological indexes(chlorophyll content,polyphenols oxidase,peroxidase,and superoxide dismutase,etc.)of these two plants in different seedling substrates were compared and analyzed,and the optimal compound ratio of biogas residue composting that can be developed into a compound seedling substrate was also discussed in this study.The results of the study are as follows:(1)7 strains of cellulose degrading bacteria,3 strains of phosphorus solubilizing bacteria,1 strain of nitrogen fixing,and 1 strain of potassium dissolving bacteria were isolated from the natural world and composting.When the ratio of cellulose degrading bacteria stain F3 and X3 was 3:1,it had better degradation ability for straw waste.A self-made composite microbial agent was obtained by combining with phosphorus,nitrogen fixing and potassium dissolving bacteria.When it was applied to biogas residue composting,the maximum temperature of the compost was 57 ℃,which was 28.09%higher than that of the control group.and the duration of the thermophilic period was 9days,while the maximum temperature of natural composting under the same conditions cannot exceed 50 ℃.Besides,the content of available phosphorus,available potassium and total nitrogen in the composting increased by 5.83%,6.69% and 11.44% respectively compared with the control group.It shows that the compound microbial agent greatly improves the efficiency and fertilizer efficiency of biogas residue composting.(2)When the moisture content of the biogas residue composting was 60%,the maximum temperature in the biogas residue composting can reach 64 ℃,the duration of the thermophilic period was 7 days,and the GI reached 110.37%.When the carbon to nitrogen ratio of biogas residue composting was 30:1,the maximum temperature in biogas residue composting reached 64 ℃,the duration of the thermophilic period was 8 days,and the T value was 0.524.When the ventilation intensity of biogas residue composting was0.48 L·kg-OM-1·min-1,the maximum temperature of biogas residue composting reached66.5 ℃,the duration of the thermophilic period was 7 days,and the TN in the compost was2.41%.(3)After being bio-enhanced by the composite microbial agent,the activities of CMC enzyme,filter paper enzyme,and xylanase in the experimental group reached the peak on the 7th(24.8 U),4th(17.7 U),and 7th(20.21 U)day of composting,respectively,which increased by 34.78%,71.84%,and 98.14% compared with the control group.Besides,the activities of catalase and urease were also higher than those of the control group.Spectroscopic analysis of DOM in composting showed that the initial stage of composting mainly carried out the metabolism of polysaccharides,aliphatic compounds,and simple amino acids,while the biosynthesis of stable compounds such as humus mainly took place in the latter stage of the composting.Further analysis of the changes in microbial and functional genes in biogas residue composting under bio-enhancement by metagenomics techniques found that bio-enhancement effectively improved the diversity of microorganisms and gene functions in composting.Among above,Proteobacteria(35.38%-64.19%),Actinobacteria(11.24%-28.93%),and Bacteroidetes(3.65%-9.57%)were the dominant microorganisms at the phylum level of biogas residue composting,and the relative abundance of Luteimonas in the experimental group was 2.84 times that of the control group.After comparing all the sequenced functional genes through KEGG and CAZy databases,it was found that the functional genes involved in carbohydrate metabolism in the biogas residue composting were very active.Besides,further statistics on the differences at the level 2 through KEGG and CAZy databases showed that the relative abundances of amino acid metabolism,carbohydrate metabolism,nucleotide metabolism,energy metabolism,cofactors,and vitamin metabolism,and lipid metabolism in the experimental group were indeed significantly higher than that in control group(p<0.05),and glycoside hydrolase and glycosyltransferase were the two types of enzymes with the biggest difference between the experimental group and the control group.In addition,after comparing with the CARD database,it was found that the relative abundance of Sul1,AAC6-Ib7,aad A3,Mycobacterium tuberculosis,mec I,and APH6-Id and other 6 drug resistance genes,as well as the tetracycline resistance gene tet Z and chloramphenicol resistance gene cmx in the experimental group were lower than that in the control group,which greatly improves the harmlessness of the composting.(4)Mixed with inorganic substrate vermiculite and perlite in a certain ratio,when the ratio of compost: vermiculite: perlite was 1:1:1,physical-chemical properties of the fermented composting whose bulk density was 0.43 g·cm-3,the total porosity was 75.37%,the capillary porosity was 21.72%,and the EC was 1367 μS·cm-1was very close to the commercial matrix.When the composite substrate was used for tomato seedlings,the fresh weight of tomato seedlings was 0.503 g,the average seedling length was 10.43 cm,and the chlorophyll content(SPAD)was 17.97,which were increased by 174.86%,93.15%,and11.61% respectively compared with the CK group.When the substrate was applied to cabbage seedlings,the fresh weight was 1.095 g,the average seedling length was 6.76 cm,and the chlorophyll content(SPAD)was 21.27,which increased by 134.48%,58.31%,and14.54% respectively compared with the CK group.The above results fully indicate that the self-made microbial compound agent has great potential in promoting the rapid decomposition of biogas residue composting and improving the efficiency of composting.The fully fermented composting product compounded with a certain proportion of inorganic substrates(vermiculite,perlite)has very broad application prospects in the soilless culture of tomatoes and cabbages. |
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