Co-digestion of different waste mixtures from agro-industrial activities: Kinetic evaluation and synergetic effects

Several wastes from agro-industrial activities were mixed in different ratios to evaluate the co-digestion process. Methane yield (Y-CH4), specific methanogenic activity (SMA) and a kinetic parameter (k(0)) were determined. A second feeding was also performed to examine the recovery of bacterial activity after exhaustion. Mixture ratios of 1:1:1:1 and 1:3:4:0.5 (w/w) showed the best performance, with Y-CH4 of 664; 582 NmL CH4/gVS(substrate), as well as SMA of 0.12: 0.13 gCOD(NmLCH4)/gVS(inoculum)/d, respectively, during the digestion of the first feed. It was possible to relate synergetic effects with enhancement in Y-CH4 by up to 43%, compared with values calculated from Y-CH4 of the individual substrates. All batches started up the biogas production after an exhaustion period, when a second feed was added. However, long lag phases (up to 21 days) were observed due to stressed conditions caused by the substrate limitation prior to the second feed. (C) 2011 Elsevier Ltd. All rights reserved.