Modelization of anaerobic processes during co-digestion of slowly biodegradable substrates

The influence of the soluble substrates over the anaerobic processes has been extensively investigated, but little is known about the effects of particulate substrate. The biodegradation of these substrates starts with the hydrolytic step, this process is slower than the other ones involved in the biodegradation of particulate substrates and usually becomes the rate-limiting step. This study investigate the effect of the initial total solids (TS) concentration on the anaerobic co-digestion of two slowly biodegradable organic substrates. The wastes mixtures were prepared at different dilutions in the range from 10% to 28% TS. From these experiments it was observed that as TS concentration increased, the methane production decreased. These results were modelled and it was observed that neither hydrolysis nor fermentation stages controlled the methane production rate. Being a substrate inhibition event experienced at the methanogenic stage the responsible of the lower methane production when operating at high TS concentrations. •Anaerobic digestion stages at different solid concentrations were studied.•Hydrolysis presented the lower rate, 0.70 d−1.•Methanogenic rate was slightly higher than that of the hydrolysis, 0.75 d−1.•High solids concentrations inhibit methanogenic stage, becoming the limiting stage.