Fluorescence characteristics of dissolved organic matter during composting at low carbon/nitrogen ratios.

We investigated the composting of swine manure at low carbon/nitrogen (C/N) ratios (about 13). The purpose was to elucidate organic matter transformation during composting by means of chemical and spectral methods. Swine manure was composted with two bulking agents (rice straw and leaves) at a ratio of 2:1 (manure:bulking agent; v:v) respectively. Low initial C/N ratios (about 13) did not prevent the swine manure from composting, which would greatly decrease the usage of bulking agent. A high organic matter mineralization rate was observed in the co-composting of straw and manure paired with a high maximum temperature and long thermophilic phase. Fluorescence excitation-emission matrix spectra were also used to monitor the component changes in the dissolved organic matter. Fluorescence parameters, including peak location, peak intensity, the ratio of peak intensity and fluorescence regional integration, were displayed and discussed as the maturity index. The fluorescence regional integration, showing higher correlation coefficient than the fluorescence intensity peaks, could be used as a valuable tool for assessing compost maturity.