Study On The Properties Of Dissolved Organic Matter And Bacterial Structure During Composting Of Dairy Manure And Chinese Herb Residues

Composting,as an eco-friendly technology,has been widely used in the recycling of solid organic wastes.Composting is a biochemical process to convert degradable organic matter into humus like product while dissolved organic matter(DOM)is also produced.DOM is a small and reactive fraction of total organic matter(OM),which plays a crucial role in the biochemistry of carbon and nitrogen cycles and in the nutrients transformation.Moreover,DOM represents a class of heterogenous substances which microbes can utilize directly in composting process.Composting is also a biodegradation process using innate microbes.The composting efficiency depends on microbial activity and microbial structure is affected by composting conditions.Above all,study on the DOM and microbial structure is an effective way to gain a better understanding of composting.Thus,the studies were conducted as follows.In this study,DOM was studied using elemental analysis,spectroscopic analysis(UV-Vis,FTIR and pyrolysis-GC/MS)and colloidal analysis during a 120-days composting of dairy manure and Chinese herb residues.The lipid and polysaccharide fractions of DOM are labile and continuously decreased,which represent the active substances in the participation of OM transformation and microbial activity.Conversely,as the main component of compost DOM,the contents of the aromatic and nitrogenous compounds showed a trend of continuous increase.With the development of aromaticity and humification,the absolute increase of N and the relative increase of aromaticity occurred,while other classes of alkanes,alcohols and fatty acids gradually decreased.Moreover,DOM was more stable with an accumulation of low weight and small size molecules with the course of composting.Taken together,these results shed a good insight into the properties and evolution of DOM during a composting process.Dissolved organic matter is a crucial indicator of compost maturity and stability.Different pools of DOM fractions may function distinctly from one another and show unique properties in the transformation of organic matter and microbial activity.In this work,compost DOM was fractionated and the properties of individual DOM fractions including humic acids(HA),fulvic acids(FA)and hydrophilic compounds(Hi)were analyzed.The pools of HA,FA and Hi were studied via elemental analysis,FTIR and UV-Vis spectroscopy,and colloidal properties like particle size and zeta potential were characterized as well.Compared to HA or FA,Hi pool had a higher content of nitrogenous compound,higher saturated degree and more easily oxidized capacity.As composting proceeded,the aromaticity of HA and FA was higher and higher while Hi exhibited only a very slight change.The colloidal analysis indicated that the particle size of DOM subfractions gradually decreased.Hi compounds from matured compost had a good application potential in cations absorption.Taken together,these results provide valuable insights into the evolution and characteristics of DOM fractions during a composting process of dairy manure and Chinese herbal residues.Illumina MiSeq technology was useful to study the microbial composition and abundance,and the biological differences in composting process.With composting proceed,an increment of microbial species and diversities were shown.Bacteroidetes,Firmicutes and Proteobacteria are dominant in the whole composting.The abundance of Firmicutes,as well as Proteobacteria was less and less,while Bacteroidetes and Actinobacteria become more and more as composting proceed.Gemmatimonadetes,Chlorroflexi and Deinococcus-Thermus warmed up in the final compost Samples represent the 0,4 d,respectively,and 4,30 d,respectively,of composting own the significant differences from one another attribute to the remarkable changes of microbial community by thermophilic phase of composting.Moreover,samples represent the 30 and 120 d,respectively,have indistinctive difference with each other by PCA analysis.