Kinetic study of thermophilic anaerobic digestion of solid wastes from potato processing

Anaerobic treatment of solid wastes from potato processing was studied in completely stirred tank reactors (CSTR) at 55 °C. Special attention was paid to the effect of increased organic loading rate (OLR) on the biogas yield in long-term experiments. Both biogas yield and CH4 in the biogas decreased with the increase in OLR. For OLR in the range of 0.8 gl−1 d−1–3.4 gl−1 d−1, biogas yield and CH4 obtained were 0.85 l g−1–0.65 l g−1 and 58%–50%, respectively. Biogas yield y as a function of maximum biogas yield ym, reaction rate constant k and HRT are described on the basis of a mass balance in a CSTR and a first order kinetic. The value of ym can be obtained from curve fitting or a simple batch test and k results from plotting y/(ym−y) against 1/OLR from long-term experiments. In the present study values for ym and k were obtained as 0.88 l g−1 and 0.089 d−1, respectively. The simple model equations can apply for dimensioning completely stirred tank reactors (CSTR) digesting organic wastes from food processing industries, animal waste slurries or biogas crops.