| Aerobic composting is a cheap, efficient and sustainable treatment for agricultural organic solid wastes, since it not only solves the pollution problem of agricultural organic solid wastes but also applies organic solid wastes as a resource. The key issue of rapid composting is to understand the degradation of organic matters and selection of composting inoculation. In this paper, the three piles were build by rapeseed meal mixed with blue algae and microbial agent, including rapeseed meal pile (CK treatment), rapeseed meal+microbial agent (AA treatment), and rapeseed meal+blue algae+microbial agent (LA treatment). The purposes of this study were1) to investigate the dynamic evolution of physical, chemical and biological indices as well as spectroscopy in order to explore the fate of organic matters during the fermentation;2) to identify the influence of microbial agent and blue algae in the spectroscopic characteristics of rapeseed meal composting;3) to explore the feasibility of two dimensional FTIR correlation spectroscopy on the mechanism of the degradation of rapeseed meal during compositng and assessment of compost maturity by fluorescence excitation-emmision matrix combined with fluorescence regional integrity (EEM-FRI) technique;4) to study the distribution of macromolecules and cells by multiple fluorescence labeling-confocal laser scanning microscopy (CLSM) method during the fermentation in order to reveal the mechanism of compost maturity. The main orginal conclusions of this work are drawn.1) Addition of microbial agent during the fermentation could significantly shorten the duration of start-up (i.e.5day), improve the maximum temperature (about10℃), and speed up composting. At the end of composting, pH and electricity conductivity (EC) had no markedly differences among the three piles. Meanwhile, the quality of compost products was compliant to the provisions of the relevant national standards. Moreover, the degradation of organic carbon was enhanced after the addition of microbial agent. Specifically, the total carbon content decreased and the dissolved carbon content enhanced with the addition of compost inoculation. More importantly, no cyanobacterial toxin was detected in the compost at the end of LA treatment, suggesting that blue algae being treated to harmless extent during the fermentation.2) The results of one dimensional FTIR of compost showed that for the compost from the three piles, the peak position of FTIR was similar but the intensity of peak was slightly distinct. The results of two dimensional FTIR correlation spectroscopy revealed the marked difference among the peak intensity among the three piles. Through2D FTIR correlation spectroscopy in the range of1800-900cm-1, the following trend in the ease of the degradation of organic compounds was observed:proteins, heteropolysaccharides and cellulose co-vary in theirdegradation during the fermentation; heteropolysaccharides> amide Ⅰ in proteins> amide Ⅱ in proteins> cellulose in proteins in the CK treatment; cellulose> heteropolysaccharides> amide Ⅱ in proteins> amide Ⅰ in the AA and LA treatment. The above-mentioned results revealed that addition of microbial agent could speed up the degradation of heteropolysaccharides. As a result, heteropolysaccharides play an important role in the priming effect which speeds up the degradation of other organic matters. Howevetr, blue algae could slow down the degradation of heteropolysaccharides and restain the role of compost inoculation. The2D FTIR correlation spectroscopy in the range of3600-3100cm-1further demonstrated that addition of microbial agent could change the degradation sequencing of OH bond. However, the role of compost inoculation was impressed in LA treatment but the performance of LA treatment was better than that of CK treatment. Therefore, the2D FTIR correlation spectroscopy can be applied as a tool to explore the mechanism of speeding up of the compost maturity with the addition of inoculant.3) Fluorescence EEM spectroscopy was applied to assess the maturity of compost. The results showed that during the three piles, proteins-like substances decreased but humic-and fulvic-like substances increased during the fermentation, revealing the increase of humification process. The fluorescence intensity of humic-like substances was enhanced in the pile with the addition of inoculation. Pearson correlation analysis between fluorescence indices and physical, chemical and biological indices demonstrated that the peak intensity of humic-like substances and fluorescence integrity indices of proteins-like substances were more suitable to assess the maturity of compost.4) Both the microbial agent and blue algae could influence the degradation and the crystallinity of lignocellulose. Specifically, the addition of microbial agent could significantly improve the degradation of hemicellulose and lignin and increase the content of cellulose. However, the addition of blue algae to composting affected the role of microbial agent to some extent. X-ray diffraction peak intensity of SiO2and CaCO3increased with the duration of composting. The crystallinity of lignocellulose for all the three piles increased first and then decreased. Among the three piles, the crystallinity of lignocellulose in AA pile decreased the most.5) DGGE profiles showed that bacterial communities were rich during compost start-up period and dominant communities were not obvious. In the thermophilic period bacterial communities decreased and dominant communities were significant. In the cooling period the structure of the bacterial population remained stable. Therefore, temperature played an important screening role in the composition of bacteria population. Multiple fluorescent labeling combined with CLSM observation clearly demonstrate that cellulose protects other biopolymers (i.e. proteins, a-polysccharides and lipids) from enzymatic attack and its successive aerobic fermentation by forming a network structure not accessible to enzymes. In the end of the fermentation, proteins, a-polysaccharides, lipids and eDNA were degraded and fluorescence intensity of those decreased significantly while the fluorescence intensity of cellulose increased markedly. |
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