Pathogen Inactivation And Comprehensive Evaluation Of Kitchen Waste Treatment By Black Soldier Fly Larvae

The conversion of black soldier fly larvae?BSFL?into organic solid waste such as kitchen waste is a new method of resource utilization.In order to evaluate the efficiency and safety of BSFL in the treatment of kitchen waste,this study focused on the environmental treatment conditions and the characteristics of microbial flora in vitro and in vivo,and explored the inactivation rule,mechanism and environmental factors of high concentration pathogens in the transformation process of BSFL.The main findings are as follows:?1?In the treatment of kitchen waste with water content of 50%,55%,60%,65%,70%?M50,M55,M60,M65,M70?using BSFL,It was found that the growth rate of larvae in M60and M65 groups was faster,the insect yield and garbage reduction rate were higher,reaching18%²0%and 58%⁶7%,respectively.The results of 16S rRNA sequencing showed that the clustering results of bacterial community structure in vivo and in vitro were consistent with the significant differences of resource utilization rate of each water content group.The main bacteria in M60 and M65 groups were lactobacillus,Morganella and vagococcus,which had significant positive correlation with the growth and garbage reduction of the BSFL.The above shows that the water content of food waste can affect the transformation process of BSFL resources.Adjusting the water content in the range of 60%-65%is helpful to get the optimal reduction rate and resource utilization rate of waste.The water content condition may be through improving the composition of Lactobacillus in the external environment,promoting the transformation efficiency of BSFL.?2?E.coli O157:H7?EC?,Salmonella typhimurium?ST?and Staphylococcus aureus?SA?were inoculated into kitchen waste at the concentration of 6.4-7.1 log₁₀0 CFU·g^-11 on the 0 and6 days respectively.EC was inactivated in 4-6 days,ST in 3-4 days.After 6 days treatment,the concentration of SA decreased to 1.9-2.6 log₁₀0 CFU·g^-1,but it could not be completely inactivated.The inactivation efficiency of pathogenic bacteria showed the trend of EC=ST>SA,and there was no EC,ST or SA residues in the body of the BSFL.During the degradation of kitchen waste,the environmental pH changed to acid condition?4.0-5.3?at the early and middle stage of the treatment,which enhanced the pathogen inactivation.The BSFL did develop antimicrobial molecules against EC and ST,with the antimicrobial effects ranked as ST>EC,however,the BSFL did not develop antimicrobial molecules against SA.The inactivation effects against SA mainly provided by the larval intestinal bacterial flora associated with the microbial competition effects.After 18 days,the reduction rate of food waste in EC group,ST group and SA group reached 74.0%,79.1%and 78.5%respectively,and the biotransformation rate reached 13.0%,13.2%and 19.4%respectively,which was not affected by EC,ST or SA.?3?Adjust the initial pH value of the kitchen?5.3,6.0,8.0,10.0 and 12.0?to explore the potential of inactivation of EC in the treatment of BSFL.It was found that EC was removed within 2-6 days after treatment and the larvae were not contaminated by pathogens.Larvae lived in all pH conditions have developed humoral antibacterial activity against E.coli O157:H7,intestinal microflora enhancing the effects,and the pH8 condition showed the highest larval immune activity.After 18 d,the kitchen wastes were reduced 52%-80%,while high alkaline condition inhibited the waste decomposition.The results showed that the larvae of the BSFL could quickly kill EC in the kitchen waste treatment.Considering the degradation of kitchen waste and the inactivation effect of pathogenic bacteria,the initial pH8.0 may be better than other conditions.