The Effects Of Composting Conditions On Carbon Losses And Humus Formation During The Composting Process

The objective of this research is to explore the carbon loss and humification process during composting under different composting conditions and bulking agents. This study chose pig manures as the materials and selected several representative organic matters as bulking agents, they were composted at different C/N (18,24 and 30) and aeration rate (0.1,0.2 and 0.4 L/kg·min). This study investigated the physical and chemical properties changes, gases emissions and humification process during composting. Elemental analysis, Fourier infrared spectrum (FTIR), three-dimensional fluorescence (3DEEM) and other chemical analysis methods were used to monitor humic substance structure changes during composting. The main results are as follows:(1) The temperature of all treatments began to rise rapidly, thereafter started to decrease continually to reach a constant level as ambient temperature. The temperature of treatments which was set under high C/N and aeration rate met the hygienic standards for non-hazardous disposal. Because of the initial properties of bulking agents, the ability to keep high temperature was worse in middle C/N and aeration rate. The indexes such as GI values and DOC contents showed the composting reached mature and stable.(2) The variation of CO2 and CH4 emission rate was subjected to the temperature profile of nine treatments. The gases emissions were mainly concentrated in the heating period and high temperature period. Most carbon lost via CO2 emission during composting, accounting for 12.79-62.75%,14.30-34.84% and 33.81-51.79% of the total C losses in high, low and middle C/N and aeration rate, respectively. The carbon losses were significantly correlated with aeration rate and C/N. Under the same compost conditions, the highest CO2 losses were observed in treatments that added garden waste as bulking agents, the lowest CO2 losses were found in treatments using Chinese medicine residue and mushroom residue as bulking agents. With the same bulking agents, the highest CO2 losses were observed in middle C/N and aeration rate treatments, the CO2 emissions were lowest in the low C/N and aeration rate treatments.(3) The synthesis and decomposition of humic substance simultaneously occurred in composting followed with the dynamic change of its content. The change trend of humic acid and fulvic acid contents was contrary, and FA content showed a decreasing trend while HA content increased during composting, and the final productions were given priority to with humic acid. The DP values increased gradually of all treatments, so that humification degree enhanced unceasingly, and the compost reached mature and stable. Humification process influenced by parameter conditions and the physical and chemical properties of bulking agents, the correlations were different. Low C/N and aeration rate was not beneficial to the humus aromatization and humus composition of complex structure. A transformation relationship was observed between carbonaceous organic matters and humic.(4) 3DEEM and FTIR were applied to quantify the structure changes of humic substance with different composting conditions. The fluorescence intensity of three treatments under low C/N and aeration rate was stronger than other compostig treatments. While the level of aromatization in products was lower which added garden waste as bulking agents, the main products had aliphatic structure. The fluorescence intensity changes of two kinds of humic-like peaks in fulvic acid components showed that garden waste as bulking agent was not in favor of humification process during composting. FTIR analysis showed the degree of aromatization enhanced of humic acid in compost materials along with the composting. The degree of aromatization in fulvic acid was lower than humic acid, and the humification products were given priority to humic acid, and a transformation relationship was observed between humic acid and fulvic acid.