Using fluorescence excitation-emission matrix spectroscopy to monitor the conversion of organic matter during anaerobic co-digestion of cattle dung and duck manure

In this study, the removal of volatile solids (VSs) and soluble chemical oxygen demand (SCOD) by co-digesting cattle dung (CD) and duck manure (DM) was determined and compared with the reduction achieved with CD or DM digestion alone. Moreover, fluorescence excitation-emission matrix spectroscopy was utilised to characterise the conversion mechanisms of organic nitrogen. It was found that the co-digestion provided 71% VS reduction compared with 58% for CD and 61% for DM. The amounts of COD removed were 28%, 23% and 31% for CD, DM and the mixture, respectively. Tyrosine-like/fulvic-like fluorescence intensity (FI) ratios increased during the initial 15 days of co-digestion and were associated with an increase in total nitrogen in the supernatant. After 15 days, CD and DM exhibited a lower tryptophan-like/fulvic-like FI ratio (0.8-1.6), whereas the co-digestion remained stable at a high level (3.0-3.6), rendering an improved microbial population and biochemical activity. (C) 2012 Published by Elsevier Ltd.