Study On Spectral Characterization In Frass From Bioconversion Different Organic Wastes By Black Soldier Fly Larvae

Black soldier fly larvae（BSFL）effectively digest and convert the organic wastes into biomass and frass ultimately achieving waste reduction and resource recovery.However,the converted frass has been poorly explored and researched,which is detrimental to the subsequent utilization and promotion of frass.Dissolved organic matter（DOM）is a mixture of several organic substances with a complex structure,supporting microbial growth and reproduction.The analysis of DOM in frass enables characterize the stability and maturity.The current study explores the properties of DOM and microbial community changes in frass after BSFL bioconvert different organic wastes by analysing physicochemical properties,DOM chemical composition and bacterial structure.Our data will provide the theoretical basis for the efficient resource utilization of organic wastes.The conclusions are as follows:（1）Bioconversion of food waste substrates with different straw additions（0%,2%,4%and 6%）resulted in 15 times the initial weight of larval biomass,bioconversion rate was 31.2%-33.9%and waste reduction ratio was 61.3%-69.9%;bioconversion of meat and bone meal substrates with different straw additions（0%,1%,2%and 3%）resulted in 24 times the initial weight of larval biomass,bioconversion rate was 16.8%-19.0%and waste reduction ratio was 43.6%-58.6%;bioconversion of sludge-wheat bran substrate resulted in 25 times the initial weight of larval biomass,bioconversion rate was 10.7%-17.0%and waste reduction ratio was 75.8%-79.5%;bioconversion of pig manure-exogenous additives（biochar,zeolite）substrate resulted in 9 times the initial weight of larval biomass,bioconversion rate was 7.4%-10.2%and waste reduction ratio was 31.7%-46.3%.（2）The physicochemical properties of the BSFL frass obtained by bioconverting food waste-straw substrates were as follows:p H was 5.0-6.5,EC was 11.7-16.9ms/cm,OM was 59.8%-85.4%and NPK content was 4.3%-5.7%;the physicochemical properties of the BSFL frass obtained by bioconverting meat and bone meal-straw substrates were as follows:p H was 6.9-7.4,EC was 3.0-3.3 ms/cm,OM was 81.1%-91.2%and NPK content was 4.3%-5.5%;the physicochemical properties of the BSFL frass obtained by bioconverting sludge-wheat bran substrates were as follows:p H was8.3-9.2,EC was 0.5-1.1 ms/cm,OM was 55.3%-65.8%and NPK content was 11.0%-12.0%;the physicochemical properties of the BSFL frass obtained by bioconverting pig manure-exogenous additives（biochar,zeolite）substrates were as follows:p H was 8.8-9.4,EC was 2.2-2.4 ms/cm,OM was 48.3%-74.1%and NPK content was 7.4%-8.5%.The content of OM and NPK in different frass were in accordance with the national standard for organic fertilizers（NY525-2021）.（3）According to the FT-IR absorption spectrum,the carbohydrates and aromatic compounds were abundant substances in frass.Further analysis of the concentrations and spectral characteristics of DOM showed that the DOM concentrations of frass from food waste-straw substrates were 21.5-55.8 mg/g,those from meat and bone meal-straw substrate were 30.2-40.8 mg/g,those from sludge-wheat bran substrate were 8.9-10.0mg/g,and those from pig manure-exogenous additives were 9.5-12.9 mg/g.UV–vis spectra showed that for food waste,straw addition increased the molecular weight and humification of DOM in frass,with the best effect of 4%straw addition;for chicken MBM,a small amount of straw addition could obtain frass with more benzene rings and molecular weight;while for fish MBM,straw addition had a negative effect on DOM in frass.For sludge-wheat bran substrate,the higher sludge content reduced the molecular weight and aromatization of frass.For the pig manure substrate,biochar addition had a negative effect on DOM,while zeolite was not significantly different from the control.The results of EEM spectra showed that the main substances in the DOM of frass were humic substances（fulvic and humic acids）.The fluorescence area integration of DOM results showed P_i,n values of 29%-63%for humic substances in frass.（4）Straw addition changed the structure of the microbial community in frass.The phylum with the highest abundance of BFSL frass microorganisms in the different treatments was Actinobacteria,Bacteroidetes,Firmicutes and Proteobacteria.The dominant genera of the food waste-straw substrate were Lactobacillus;the dominant genera of the chicken MBM-straw substrate were Oblitimonas and Gammaproteobacteria＿unclassified;the dominant genera of the fish MBM-straw substrate were Myroides,Acinetobacter and Paenochrobactrum.For food waste-straw substrate,straw addition significantly increased the level of Firmicutes;2%straw addition significantly increased the relative abundance of Actinobacteria;for chicken MBM-straw substrate,1%straw addition significantly enriched Bacteroidetes and Fusobacteria,while 3%straw addition caused a significant enrichment of Firmicutes;for fish MBM-straw substrate,1%straw treatment significantly increased the level of Actinobacteria than the other groups.The results of KEGG analysis showed that the metabolism pathway was the most active group under different treatments;at level 2,the most predominant metabolism function was amino acid metabolism,carbohydrate metabolism and energy metabolism.（5）The correlation analysis showed that DOM spectra indexes and environmental factors were significant correlated between microbial community diversity.For food waste-straw substrate,there were significant correlations between DOM spectra indexes,SUVA₂₅₄,SUVA₂₈₀ and environmental factors,OM,NPK,and microbial community,Chao1 index;for chicken MBM-straw substrate,DOM spectra indexes(SUVA₂₅₄,SUVA₂₈₀,E₂₅₃/E₂₀₃and A_226-400)were significantly correlated with environmental factors（DOM and OM）and Shannon index of microbial diversity;for fish MBM-straw substrate,the spectra indexes(SUVA₂₅₄,SUVA₂₈₀ and S_280-400)were significantly correlated with environmental factors（EC,TP and OM）.