The Sanitation And Resource Of Livestock Manure During Black Soldier Fly Larvae Conversion Combined With Composting

The black soldier fly larvae（BSFL）application for conversion of livestock manure into protein and frass is providing a new developing method for circular ecological agriculture.Most of previous investigation usually pay attention to the value of BSFL pupae after the livestock manure conversion and ignoring the environmental safety and resource utilization of frass.Thus,hampering the development of the industry for the transforming livestock manure in to valuable end products employing black soldier fly.To overcome all these environmental and nutrients loss issues during the traditional composing process.The present study design,7 days old BSFL were inoculated into manure[chicken manure（CM）,pig manure（PM）and cow manure（COM）]to convert high quality end product under controlled environmental conditions,and mainly focused on the better humification,nutrient conservation,and removal of pathogenic bacteria.Subsequently,another experiment was conducted by the amendment of cornstalk as bulking agents to adjust the optimum 25:1 C/N ratio for a 28-day simulated aerobic composting in 3-L biochemical incubator.Above this study,mainly focused on understand the microbiological mechanism of carbon and nitrogen transformation,and mitigation of greenhouse gases,heavy metals,as well as pathogenic bacteria to improve the end product quality.Finally,the plant growth experiment was performed to evaluate the compost quality and maturity,and provided another way of composting methods as well as theoretical basis for the resource recovery and manure recycling,and the details are as followed:The transforming of livestock manure with black soldier fly larvae was studied.Compared with control group,the addition of BSFL reduced total Kjeldahl nitrogen（TKN）loses,but enhanced the concentration of total phosphorus and total potassium.The total nutrient（N+P₂O₅+K₂O）value was 6.91%-10.89%,which increased 14.78%-26.19%compared to control group.It showed that frass had the potential for resource utilization.The addition of BSFL decreased the content of organic matter（OM）and dissolved organic carbon（DOC）,as well as the activities of dehydrogenase and urease enzymes,but increased the content of humic acid（HA）of frass.The addition of BSFL reduced the pathogenic bacteria population by 1.76-4.23 folds as compared to control group,and indicating that the application of black soldier fly larvae could better reduce the relative abundance of pathogenic bacteria in compost.At the end of the transformation,the mortality of ascarid egg in frass was 100%,but the number of fecal coliforms was higher than the standard value of 100 MPN g^-1.The value of germination index,NH₄⁺-N,DOC and HA/FA were 19.81-105.21%,0.5997-1.600 g kg^-1、20.68-24.86 g kg^-1、1.01-1.23,respectively,which indicating the frass was immature compost.Therefore,it is necessary to further utilize aerobic composting technology for sanitation and resource of frass.Furthermore,the amendment of cornstalk on the frass composting was studied.Compared with the initial materials,the content of total organic carbon（TOC）and DOC in all treatments was decreased by 14.65%-32.46%and 54.54%-66.38%during the end of composting,and the amendment of cornstalk could promote the degradation of organic carbon.Meanwhile,the value of HA and HA/FA among the all treatments was increased33.84%-74.36%and 73.65%-142.15%,and the additive of cornstalk could enhance the rate of humification,and the cornstalk amendment frass from chicken manure got the largest value.The spectroscopic characteristics also provided evidence for humification and the addition of cornstalk could enhanced the aromatics in the product.The cumulative NH₃emission was 3.39-4.88 g among the all treatments,adding cornstalk could promote the conversion of NH₄⁺-N to amino acid nitrogen and acid hydrolysis undefined nitrogen,and thus reduced NH₃emission by 13.00%-19.58%and the cornstalk amendment frass from pig manure had the maximum reduction than other treatments.The relative abundance of pathogenic bacteria and the mobilization of Cu and Zn were decreased with composting time.Compared with control,the concentration of DTPA-Cu and Zn was decreased by0.38%-10.18%and 2.80%-19.39%,respectively.The cornstalk amendment reduced the CH₄,N₂O,and greenhouse gas emission equivalent（GHGE）by 10.60%-23.22%,6.39%-24.68 and 9.20%-23.27%as compared with the control,respectively.However,least GHGE value was noticed in T4 treatment.Thus present study results confirm that cornstalk application has significant impact to reduce the on global warming potential by mitigation of heavy metals mobilization,NH₃emission and greenhouse gases emission.Finally,the compost maturity parameters confirmed that all composts reached the maturity level and within the standard limit.The bacterial population result was confirm that abundance of Firmicutes,Bacteroidota,Proteobacteria and Acidobacteriota relatively greater among the all treatment during the composting.The addition of cornstalk could increase the relative abundance of Firmicutes in the frass from pig manure at the thermophilic stage and the frass from chicken manure at the mature stage,resulting in a higher degree of humification.Proteobacteria was connected with nitrogen fixation and the cornstalk amendment frass from cow manure got the largest relative abundance at the mature stage,resulting in a smallest cumulative of NH₃.The bacterial community has a higher explanation rate for temperature（15%）and CH₄（13.6%）.Beside this,the dominant of fungi were Ascomycota,Basidiomycota and Neocallimastigomycota.The addition of cornstalk increased the relative abundance of Ascomycota 2-6-fold during the thermophilic phase,which promoted the degradation of cellulose and hemicellulose and increased the content of HA.The fungi community has a higher explanation rate for temperature（26.9%）and OM（9.4%）.The addition of cornstalk reduced the dehydrogenase and urease activities of the compost product,which made the carbon and nitrogen of the compost product more stable.The PICRUST function prediction analysis of the bacteria showed that carbohydrate metabolism was the main metabolic pathway.The fungal community FUNGuild nutritional type predictions found nutritional types in saprotroph and pathotroph,addition of cornstalk inhibited the associated fungal populations.The co-occurrence network analysis found that the bacteria was more complex than fungi,and the complementary effect of core bacteria is strengthen,and the addition of cornstalk could promote the ability of complementary and compost efficiency.The application of frass compost significantly increased the content of soil organic matter and available nutrients,and finally provided greater bioavailable nutrients for the growth of lettuce.The biomass and chlorophyll content of lettuce were increased by6.39-14.69 folds and 1.94-2.66 folds by amendment of frass compost,and observed greater lettuce biomass by the application cornstalk amendment pig manure frass compost.Interestingly,the application of the cornstalk amendment frass compost could decrease the concentration of DTPA-Cu and Zn,and thus less bio-available form of DTPA-Cu and Zn present in compost for the absorption of lettuce plant root.In summary,BSFL transformed the livestock manure into frass which could not meet the compost standard of sanitation and mature.Using stalk to adjust the moisture and C/N ratio performed the aerobic fermentation,which could effectively kill pathogenic bacteria and improve the maturity and humification,so that the frass reached the compost standard.The addition of cornstalk could not only reduce the nitrogen loss and the mobilization of heavy metals,but also mitigate the greenhouse gases emission.The results of this study provided the theoretical and practical guidelines for the development BSFL application toward resource recycling and conversion of high-value end product,can be further explore in industrial level.