Co-composting Kitchen Biogas Residue With Black Soldier Fly Larval Frass And Enhancing Maturation By Microorganism

Kitchen waste（KW）could be separated into three main substances after pretreatment:crude oil,kitchen wastewater and organic solid residue.At present,kitchen wastewater is mainly discharged after meeting national standard via anaerobic fermentation and aerobic biochemical treatment.Organic solid residue is mainly used for feeding black soldier fly larval and transformed into high-value protein insects.During the anaerobic fermentation process,a lot of kitchen biogas residue（KBR）would be discharged from the reator regularly,which presented the characteristics of high moisture content and low carbon/nitrogen ratio.Moreover,in the process of feeding black soldier fly larval with organic soild residue,a large amount of black soldier fly larval frass（LF）would be produced,which contented high salinity,odor and high moisture content.If the KBR and LF were discharged directly without any treatment,it would cause serious harm to the ecological environment.Therefore,it is necessary to treat KBR and LF safely and effectively.Composting is an effective method to treat organic solid waste such as KBR and LF,which can decompose organic solid waste into stable humus substances and form nutritious organic fertilizer.Compared with the traditional single composting,co-composting can use a variety of organic solid wastes to optimize the composting process.In addition,sinc thermophliic phase could significantly reduce the microbial richness and diversity,inoculating thermophilic inoculum in the thermophliic phase can further improved the quality and fertilizer efficiency of composting products.In this study,co-composting of KBR and LF were investigated,and thermophilic strains were screened and purified from samples in the thermophilic phase to prepare thermophilic inoculum.The thermophilic inoculum was inoculated to further strengthen the maturity of co-composting.The main conclusions were as follows:（1）Five mixing ratios（KBR:LF）were designed:T1（4:0）,T2（3:1）,T3（1:1）,T4（1:3）and T5（0:4）.The composting experiments lasted for 30 days.The results showed that compared with the content of nitrate nitrogen in T1,it increased by 72.63%,77.93%,88.69%and 85.99%,respectively in T2～T5.In addition,the highest organic matter degradation efficiency,humic substance content,humic acid content and HA/FA were obtained in T2 treatment with values of 13.80%,107.55 g·kg^-1,79.2 g·kg^-1 and 2.79,respectively.After composting,the germination index of each treatment group exceeded 80%,of which T1～T4 exceeded 100%.In addition,the Chao and Shannon indexes showed that adding BSFF could enhance the richness and diversity of bacterial community and increase the relative abundances of Proteobacteria and Actinobacteria.There were significant differences in biomarkers of microbial communities during different composting phases.However,the electrical conductivity of the composting product rose significantly with the increase of LF.The results indicated that the optimal composting group was obtained when BR:LF was 3:1.（2）Eight strains were screened from the samples of co-composting of KBR and LF in the thermophilic phase.Two strains of thermophilic bacteria and two strains of thermophilic fungi were optimized by comparing enzyme activity and growth characteristics.The identification results were Bacillus licheniformis,Bacillus aerius,Thermomyces lanuginosus and Aspergillus fumigatus.The activities of glucoamylase,cellulase,laccase,urease,protease and xylanase in Bacillus licheniformis were 22.00,67.15,46.30,29.86,15.26,32.57 U·mL^-1 respectively,while that of Bacillus aerius were 32.31,64.00,74.08,17.02,17.75,22.40 U·mL^-1 respectively.The activities of glucoamylase,cellulase and laccase in Thermomyces lanuginosus were 13.29,376.59,268.54 U·mL^-1 respectively,and those of Aspergillus fumigatus were 15.03,250.82,416.70 U·mL^-1,respectively.Finally,the optimized four thermophilic strains were prepared into thermophilic inoculum in equal proportion.（3）The thermophilic inoculum was inoculated on the second and eighth days of co-composting of BR and LF.The results showed that inoculating thermophilic inoculum prolonged the duration of thermophilic phase by two days and increased organic matter degradation efficiency,nitrate nitrogen content,germination index,humic substance content and HA/FA（humic acid/fulvic acid）by 20.25%,5.24%,5.57%,8.75%and 12.88%,respectively.Via three-dimensional fluorescence spectrum analysis and Fourier transform infrared spectrum analysis,it was proved that inoculating thermophilic inoculum could promote the formation of humic substances in the process of co-composting and accelerate the transformation of easily degradable organics and the degradation of aliphatic compounds.In addition,the thermophilic inoculum increased the relative abundance of Firmicutes and Actinobacteria and improved the diversity of fungal community in the thermophilic phase.The results indicated that inoculating thermophilic inoculum could strengthen the maturity of co-composting of KBR and LF,optimize microbial community structure,improve the fertilizer efficiency and stability of composting products.