Spectroscopic-Electrochemical-Mass Spectrometric Study On The Structure Of Dissolved Organic Matter During Vermicomposting Of Dairy Manure

With the rapid development of economy in our country,a great deal of livestock manure has been produced with the increasing demand of animal products.Livestock manure not only contains a lot of nutrient element like N and P,but includes lots of pathogens.It will cause serious pollution to the environment without timely treatment.Vermicomposting has gradually developed into the main current technology for efficient treatment of livestock manure in recent years.It is characterized by the joint action for earthworms and microorganisms,which helps to accelerate the stabilization of organic matter.In this paper,dairy manure was used as raw material,with vermicomposting and non-worm control.In this research,organic matter content,seed germination rate?GI?,water-soluble organic carbon content and other related physical and chemical index in vermicomposting and control treatment were analyzed,respectively.Results here showed that there was an obvious difference in the composting process of the two treatments.For the vermicomposting treatment,the organic matter content and C/N decreased by 27.26%and 6.64%after 40 days,respectively.While the control,organic matter content and C/N decreased just by 10.07%and4.45%,respectively.In addition,germination index?GI?of the vermicomposting reached to 120.89%,but for the control treatment,it was only 85.29%.The results showed that the degradation rate of organic matter and compost maturity could be significantly improved,moreover the compost cycle could be dramatically shortened after vermicomposting.Then high-throughput sequencing of vermicomposting and control treatment was carried out on the IonS5TMXL platform,and the CCA was performed to study the effects of compost parameters on microbial community structure.The result showed that microbial community structure of the two treatments showed obvious difference.In comparison of the control,the dominant colonies of the level were the Xanthomonadaceae and Flavobacteriaceae,while the vermicomposting was dominated by the Microscillaceae and Gammaproteobacteria??-Deformation bacteria families?.The CCA analysis found that the change was small compared with the control group if microbiome structure of vermicomposting at maturity stage,that was to say,the microbiome tended to be stable.On the other hand,the significant correlation between the composition of microbial community and C/N and NH₄⁺confirmed that vermicomposting could promote compost maturity,and these dominant microorganisms could be used as biological indicators to evaluate compost maturity.Modern spectroscopy techniques,such as UV-Vis and Fourier-transform infrared spectroscopy?FTIR?would be adopted to analyze the structural changes of DOM in dairy manure after vermicomposting and control treatment.It also combined the electrochemical analysis techniques,such as cyclic voltammetry and electrochemical in-situ infrared spectroscopy which could be used to characterize the electron transfer capacity of DOM.The result showed that the spectral indexes such as E₂₅₃/E₂₀₃ and SUVA₂₈₀ had changed significantly within 0 to 40days during the process of vermicomposting.These observations revealed that the DOM aromatization and composting humus levels in the process of vermicomposting were increasing.FTIR assay showed that the decrease of fat compounds in vermicomposting was significantly higher than that in the control treatment at the end of composting,while the increase of aromatic structure could be higher than that one in the latter.According to research on FRI and parallel factors,the protein substances in vermicomposting and control treatment were mainly degraded to humic acid and fulvic acid respectively.Electrochemical technique analysis showed that the capacitance and current density of DOM in vermicomposting could be significantly enhanced.Based on the analysis of the above results,it could be seen that vermicomposting has obvious advantages over the control treatment,and the corresponding decomposition process is obviously accelerated to improve the quality of compost and to improve the redox activity.The structure of DOM in the composting process was characterized by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry?ESI FT-ICR MS?.The results showed that the vermicomposting was different from the control,which proved that the analytical technique could effectively characterize the molecular transformation of DOM during the treatment.After the dairy manure was treated by vermicomposting and control,the fomer produced more tanins and the latter produced more aromatic compounds.In addition,most of them were compounds with high O/C and low H/C,indicating that more carboxyl groups,carbonyl groups or compounds with double bonds in vermicomposting.All of these findings showed that the treatment of dairy manure with vermicomposting could significantly promote the humification and stabilization.Furthermore,it has great application potential in the field of livestock and poultry manure resource utilization.