Study On The Properties And Components Of Dissolved Organic Matter During Composting Of Food Waste And Sugarcane Leaves

Two organic solid wastes of food waste and sugarcane leaves were compost 40 d to monitor the changes of physical and chemical parameters and evaluate the maturity of composted.Humic acid(HA),fulvic acid(FA),hydrophilic substance(Hi)and hydrophobic neutral substance(HoN)were obtained by fractionating dissolved organic matter(DOM).The dynamic changes of DOM subfractions were analyzed during the composting process.The thermophilic phase(>50 ℃)of the pile maintained 20 d and the C/N ratio was less than 15 at the end of composting,which indicated that the compost had reached the standard of maturity.During the composting process,Hi had the highest proportion in DOM.The content of HA continued to increase,while the content of FA and Hi continued to decrease during the composting process.The proportion of 29.94%HA,30.01%FA,and 38.64%Hi existed at the end of composting,while the content of HoN was 1.36%.The spectroscopic characteristics of HA,FA,Hi and HoN were investigated by using UV-vis、FTIR and fluorescence spectrum.The highest value of SUV264 was observed in HA,indicating that the HA pool played a dominant role in aromaticity of DOM.HA and FA had the maximum and minimum molecular weight,respectively.HA had higher level aromatic compounds during cooling and maturity phase of the composting process.FA had abundant carboxyl groups.There are fewer aliphatic and aromatic compounds with C-H structure in Hi.With the composting process,the number and intensity of peaks in HA,FA,Hi and HoN gradually become less and weaker,indicating that the structure of DOM tends to be simpler and more stable.With the composting process,the material composition of HA transformed from polycyclic aromatic hydrocarbons to polycarboxylic humic acids,while FA substance transformed from amino protein to humic-like.Compared with HA,Hi and HoN,FA contained more abundant material components.Hi and HoN were mainly composed of soluble microbial products.DOM subfractions played different roles in the composting process.Hi and FA can be used as effective energy materials directly used by microbes to promote microbial activities.Microbial degradation of lignocellulosic and protein substances into Hi.Pyrolysis-GC/MS and ICP-MS were employed to detect the molecular composition and distribution of heavy metals of HA,FA,Hi,and HoN,respectively.A large number of alkanes and lignocellulose degraded during the thermophilic stage of composting,resulting in the rapid increase of aromatic compounds.Alcohols and aldehydes are likely to be transitional by-products and participate in the formation of ketones during the composting process.During the thermophilic phase of composting,the concentrations of 8 heavy metals in HA,FA,Hi and HoN were at the same level.The quantitative information of heavy metal content in the DOM subfractions shows that Hi had the highest content of As,Cr,Cu,Ni,Pb and Zn in DOM subcomponents.Hi can be used as a priority energy source for microbes,indicating that Hi was the main carrier of microbial transformation of heavy metals.At the end of composting,the concentration of Cu and Ni was the highest in HA,while 1te concentration of Cd in FA was the highest.The effects of different concentrations of DOM and its subcomponents on the growth of seed seedlings of Chinese cabbage(Brassica rapachinensis L.)were investigated by taking 40 d samples.DOM,HA,FA and Hi had no inhibitory effect on the growth of Chinese cabbage in 50,100,300,600 and 1000 mg·L-1.The accumulation of biomass in Chinese cabbage seedlings was increased in varying degrees.The concentrations of DOM,HA,FA and Hi at 50,100,300,600 and 1000 mg·L-1 significantly increased the accumulation of biomass in Chinese cabbage seedlings(p<0.05),indicating that there was no inhibitory effect on the growth of Chinese cabbage.DOM group significantly promoted the growth of Chinese cabbage root and shoot(P<0.05).However,the high concentration of DOM,HA,FA and Hi were not beneficial to the root growth of Chinese cabbage,especially the root length of FA and Hi in 1000 mg·L-1 was significantly lower than that in the control treatment(P<0.05),indicating that the root growth was inhibited.DOM and Hi are more conducive to the healthy growth of Chinese cabbage seedlings than HA and FA.