Study On The Effect Of Exogenous Additives On Vermicomposting Of Green Waste

With the rapid development of landscape greening,the improper disposal of green wastes will not only bring serious environmental pollution problems,but also cause great waste of resources.Vemicomposting technology is one of the most promising technologies for organic solid waste treatment However,there are relatively fewer studies on the application of vemicomposting technology to the treatment of green wastes.In this study,the effect of Eisenia fetida on green wastes was firstly studied.Then,this study evaluated the potential of addition of different inoculants,including biosurfactant alkyl polyglycoside(APG),rhamnolipids,microbial inoculants(P.chrysosporium and A.chrococcum),biochar,spent mushroom substrate(SMS)and cow dung(CD)individually or in combination to enhancing the composting process.The main results of this study are as follows:(1)Compared with the control treatment using aerobic composting,vemicomposting can significantly increase the TN and available P content of final compost(P<0.05),while significantly reduce the TOC,lignin and cellulose content of compost.Vemicomposting can also improve the maturity of compost.Vemicomposting can significantly increase the richness and diversity of microbial populations.The dominant bacterial phylum was Proteobacteria,followed by Chloroflexi,Actinobacteria,Bacteroidetes,Acidobacteria,and Saccharibacteria.These phyla accounted for 88.3-90.9%of the sequences in the aerobic compost and for 90.1-93.5%of the sequences in the vermicompost.The relative abundances of the following phyla were<1%in all samples:Planctomycetes,Firmicutes,Verrucomicro b ia,Parcubacteria,Gemmatimonadetes,Candidate_division_WS6,and Spirochaetae.The fungal phyla Ascomycota,Basidiomycota,Chytridiomycota,Zygomycota,and Cryptomycota were detected in all compost samples and accounted for 71.3-98.7%of the sequences in the aerobic compost and for 79.1-97.6%of the sequences in the vermicompost.The remaining phyla belonged to the kingdoms Protozoa,Chromista,and Animalia.(2)Addition of APG and E.fetida significantly increased total bacteria,cellulolytic fungi,phosphate solubilizing bacteria and nitrogen fixing bacteria populations,and the activities of cellulase,urease and alkaline phosphatase in composts as compared with the control.The APG and earthworm treatments also increased surface roughness and porosity of the green waste;Compared with control,APG and earthworm addition increased the degradation rate of TOC,lignin and cellulose by 5.9-17.9,10.3-32.0 and 10.8-18.8%,respectively,and resulted in better compost quality,as was reflected in the neutral pH,higher cation exchange capacity(CEC)and nutrient concentrations(N,P,K,Ca,Mg,Fe,Cu,Zn,Mn).Final germination percentage and growth rate of tomato,eggplant and pepper seedlings were higher(P<0.05)or similar in all composts produced with the addition of APG and earthworm,while plant growth was lower(P<0.05)in the compost produced with the control than in peat substrate.The combination of APG+E.fetida enhanced the decomposition of green waste and improved final compost quality the most.(3)In general,treatments with the addition of spent mushroom(SMS)and/or cow dung(CD)increased the survival rate,biomass,cocoon and juvenile numbers of E.fetida as compared with the control.The addition of SMS and/or CD also significantly increased the activities of dehydrogenase,cellulase,urease,and alkaline phosphatase as compared to the control.Furthermore,the addition of SMS and/or CD facilitated the decomposition of organic matter,cellulose and lignin,and increased nutrient(N,P and K)concentrations and nitrification as compared to the control.The addition of SMS and CD led to greater morphological changes of the substrate as compared to control.Metal concentrations were increased in the final vermicomposts comparatively to the initial materials,but they were within the permissible limits in all treatments.The germination index achieved maturity after 10 weeks of vermicomposting in all treatments except for the control.Overall,the 2:1:1 GW:SMS:CD treatment had the highest growth and reproduction rates of E.fetida,percentage degradation of organic matter,cellulose and lignin,as well as the best quality of the final vermicompost.(4)Biochar addition increased(P<0.05)earthworm biomass,juvenile and cocoon numbers of Eisenia fetida,as well as the activities of dehydrogenase,cellulase,urease and alkaline phosphatase.Compared to the control,lignin degradation rate was enhanced up to 13.89%by biochar addition.Biochar addition also improved the vermicompost quality in terms of cation exchange capacity(CEC),dissolved organic carbon(DOC)degradation,humification,nitrogen transformation,toxicity to germinating seeds(Brassica rapa L.,Chinensis group)and heavy metals concentrations.The 6%bamboo biochar addition rate achieved maturity after 60 days of vermicomposting and resulted in the highest quality vermicompost based on parameters such as CEC,DOC,NH4+-N/NO,-N ratio,germination index and heavy metal concentration.We conclude that 6%biochar addition promoted earthworm growth and the vermicomposting of green waste.(5)The addition of rhamnolipid and/or either microorganism alone or in all combinations significantly increased E.fetida growth rate,the number of E.fetida juveniles and cocoons,the population densities of cellulolytic fungi and Azotobacter bacteria,and cellulase and urease activities in the vermicomposts.The quality of the final vermicompost(in terms of electrical conductivity,nutrient content,C/N ratio,humic acid content,lignin and cellulose contents,and phytotoxicity to germinating seeds)was enhanced by addition of rhamnolipid and/or microorganisms.The physical characteristics of vermicomposts produced with rhamnolipid and/or microorganisms were acceptable for agricultural application.The best quality vermicompost was obtained with the combined addition of P.chrysosporium,A.chrococcum,and rhamnolipid.