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 CH 4 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 CH 4 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 y m, 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 y m can be obtained from curve fitting or a simple batch test and k results from plotting y/( y m− y) against 1/OLR from long-term experiments. In the present study values for y m 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.