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 CH 4 ) , specific methanogenic activity (SMA) and a kinetic parameter (k0) were determined. A second feeding was also performed to examine the recovery of bacterial activity after exhaustion. e ratios of 1:1:1:1 and 1:3:4:0.5 (w/w) showed the best performance, with Y CH 4 of 664; 582 NmL CH4/gVSsubstrate, as well as SMA of 0.12; 0.13 g COD NmLCH 4 / g VS inoculum / d , respectively, during the digestion of the first feed. It was possible to relate synergetic effects with enhancement in Y CH 4 by up to 43%, compared with values calculated from Y CH 4 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.