Dynamic Features On Spectrum Of Dissolved Organic Matter And Microbial Community In Black Soldier Fly Larvae (Hermetia Illucens) Vermicompost During Secondary Composting

In the field of food waste treatment,vermicomposting using black solider fly larvae(Hermetia illucens)(BSFL)has attracted a large number of attention due to its extraordinary advantages of waste reduction and value-added resource regeneration.But in full-scale operation,the features of residues(or called as BSFL vermicompost)discharged from the BSFL bioconversion of food waste has not been fully understood.Moreover,the BSFL vermicompost is technically needed to be futher composted,i.e.,secondary composting.However,the physichmical and biochemical characteristics of BSFL vermicompost during the secondary composting process are not well understood,which is not conducive to the down-stream reuse in agri-ecosystem.Dissolved organic matter(DOM),as the energy source of microbial metabolism and the main component of organic fertilizer,is well regarded as an important cacrbon source for understanding the characteristics of metarial changes in composting process.Therefore,in this study,traditional biochemical experiments,spectroscopic analysis and modern molecular biology methods were combined to analyze and discuss the dynamic changes of physichemical proporties,nutrient composition and microbial communities during secondary composting process under the operational model of traditional strip-stacked composting.The conclusions are as follows:(1)The temperature and pH of BSFL vermicompost were gradually reaching the suitable conditions during the secondary composting,while the final compost products reached the harmless standard.Compared with raw materials beforing secondary composting,the contents of DOM,total nitrogen(TN),ammonium nitrogen(NH4+-N)and available phosphorus(Oslen-P)were decreased by 69.13%,11.87%,22.67%and 41.72%,respectively.The content of nitrate nitrogen(NO3--N)was increased by 18.73 times.It shows that the organic matter such as nitrogen-containing components had been decomposed and transformed in large quantities during the secondary composting.In addition,catalase activity was changed slightly during the composting process,which was 2.71%higher than that of the raw material.The urease activity was increased first and then decreased,ranging from 56.23 ug/(g.d)to 229.72 ug/(g.d).The activity of alkaline protease in compost was relatively higher,and then decreased to a stable level during composting,but it still maintained a higher activity in the range of 125±25 mg/(g d).(2)The analysis of three-dimensional fluorescence spectra(3D-EEM),Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance hydrogen perfusion(1H-NMR)showed that over the time of secondary composting,the diversity of DOM components was increased,the complexity of DOM structure was decreased,and the stability and aromaticity of DOM components were improved.During the secondary composting,humus-like substances,albuminoid substances,and multi-branched aliphatic organic compounds with complex structure in BSFL vermicompost were degraded and transformed by microorganisms to form soluble,simple amino acids,monosaccharides and other small molecular organic substances.At the end of secondary composting,the degree of humification of BSFL compost was deepened,and the quality of compost products was improved.(3)The 16S rRNA high-throughput sequencing technique was used to analyze the diversity of microbial communities.It was found that the activity,quantity and abundance of microbial communities were increased significantly with the increase of composting time.Meanwhile,date of the bacterial community at phylum,family and genus levels showed that the bacteria with significant differences in the compost mainly concentrated in Actinobacteria,Firmicutes,P.Roeobacteria,Tenericutes,Bacteroidetes and Deinococcus-Thermus.Furthermore,the relative abundance of metabolic function groups in the premetaphase of BSFL vermicompost consisted of amino acid metabolism,carbon cycle and nitrogen metabolism were changed into that of biotin and fatty acid biosynthesis in the later of BSFL vermicompost.After secondary composting,the BSFL vermicompost reaches the standards of harmlessness and humification of biological organic fertilizer,which further promotes the reduction and resource utilization of food waste.