ULTIMATE ANAEROBIC BIODEGRADABILITY OF SOME AGROINDUSTRIAL RESIDUES

Anaerobic mesophilic batch fermentations of the agro-industrial residues sugarbeet pulp, potato pulp and brewery grain were carried out to evaluate their ultimate biodegradability and first-order decay rates. Each 5-liter batch reactor was operated for 37-85 days, at substrate-to-inoculum ratios (S/I) ranging from 0.5 to 1.3 on initial total volatile solid (TVS) mass basis. Ultimate biodegradabilities of 92-94% for sugarbeet pulp, 86-91 % for potato pulp and 76-78% for brewery grain were obtained at the S/I of 0-8. There was no big difference in the ultimate biodegradability based on two independent methods. biogas production or mass loss. The substrate degradation was described by two distinct first-order decay rates (k1 and k2) which could be separated by a simple visual fitting. At the S/I of 0.8, most initial decay reactions accelerated within 4-7 days with an average k1 of 0.26 day-1 for sugarbeet pulp, 0.19 day-1 for potato pulp, and 0.18 day-1 for brewery grain. The mean values for the long-term, batch, first-order decay coefficients (k2) were 0.071 day-1 for sugarbeet pulp during days 7-37, 0.016 day-1 for potato pulp during days 15-85 and 0.063 day-1 for brewery grain during days 7-24.