The aim of this study was to investigate the influence of residual glycerine (5 and 10% w/w) from the biodiesel industry, used as a co-substrate, on biogas production from maize silage. The experiments were conducted in a laboratory-scale, single-stage anaerobic digester at 39ºC and hydraulic retention time (HRT) of 60 d. Addition of 5% residual glycerine caused organic load rate (OLR) to increase to 1.82 compared with 1.31 g organic dry matter (ODM) L-1d-1 for maize silage alone. The specific biogas production rate and biogas yield were 1.34 L L-1d-1 and 0.71 L g ODM-1 respectively, i.e. 86% and 30% higher than for maize alone. Increasing the residual glycerine content to 10% increased OLR (2.01 g ODM L-1d-1), but clearly decreased the specific biogas production rate and biogas yield to 0.50 L L-1d-1 and 0.13 L g ODM-1 respectively. This suggested that 10% glycerine content inhibited methanogenic bacteria and organics conversion into biogas. As a result, there was accumulation of propionic and valeric acids throughout the experiment.
The aim of this study was to implement ADM1xp model to simulate behavior of anaerobic co-digestion of maize silage and cattle manure. The accuracy of ADM1xp has been assessed against experimental data of anaerobic digestion, performed at OLR = 2.1 gVS dm-3·d-1 and HRT = 45d. Due to the high number of parameters in ADM1xp, it was necessary to develop a customized procedure limiting the range of parameters to be estimated. The best fitting of experimental to simulated data was obtained after verification of 9 among 105 stoichiometric and kinetic parameters. The values of objective function (Jc) ranged between 0.003 (for valerate) and 211 (for biogas production).