Two-phases anaerobic digestion of fruit and vegetable wastes: bioreactors performance

The two-phase anaerobic digestion of a mixture of fruit and vegetable wastes (FVW) was studied, using two coupled anaerobic sequencing batch reactors (ASBR) operated at mesophilic temperature. The effect of increasing loading rates on the acidification step was investigated. Results indicated that the hydrolysis yield (81%) stabilized at an OLR of 7.5 g COD/L.d. The volatile fatty acids concentration increased when the loading rate was increased and reached its maximum value (13.3 g/L) at higher loading rate tested (10.1 g COD/L.d). Methanogenic fermentation of the liquefaction acidification products was efficiently performed in the ASBR reactor and high methane productivity was obtained (320 L CH4 per kg of input COD). Total COD in the final effluent from the methanizer was usually below 1500 mg/L, and soluble COD below 400 mg/L. Overall COD removal in the treatment system was 96%. Phase separation with conventional ASBR reactors resulted in high process stability, significant biogas productivity and better effluent quality from fruit and vegetable wastes anaerobic digestion. (C) 2004 Elsevier B.V. All rights reserved.