Change of three-dimentional excitation emission matrix fluorescence spectroscopic characterization of manure dissolved organic matter after composting and influence on its complexation with Cu

Dissolved organic matter (DOM) in animal manure may complex with Cu and facilitate its transmission to the soil solution and groundwater. The aim was to investigate the spectroscopic characterization of DOM isolated from pig, cattle manure and their composts using 3DEEM technology (the three-dimentional excitation emission matrix fluorescence), and to reveal the influence of composting process on DOM complexation with Cu by fluorescence quenching titration. The results showed that protein-like fluorescence peaks, including tyrosine-like and tryptophan-like peaks, were present in all DOM of pig and cattle manure. In addition to protein-like fluorescence peaks, humic-like fluorescence peak was also observed in cattle manure DOM. The fluorescence of tyrosine-like and tryptophan-like peak in DOM extracted from pig manure declined significantly after composting, at the same time, the humic-like fluorescence peak was observed in the compost although it did not exist in fresh pig manure. Similar to the pig manure, tyrosine-like and tryptophan-like peaks of cattle manure were not distinguishable after composting, meanwhile, the intensity of humic-like fluorescence peak stimulated by UV excitation had significantly increased. Moreover, subtle decrease in fluorescence of humic-like peak stimulated by visible excitation and a red shift of peak position were observed in comparison with the fresh cattle manure. Fluorescence quenching experiment indicated that the manure composts were characterized by the smaller binding capacities compared to the fresh manure. It was suggested that composting process may change compositions of manure DOM, with an elevated concentration of humic acid and fulvic acid, therefore may decrease the mobility and availability of DOM-Cu in animal manure.