Study on the Anaerobic Co-Digestion of Wasted Fruits and Vegetables

Abstract : The paper deals with anaerobic co-digestion of wasted fruits and vegetables (WFV) with activated sludge (AS), cattle manure (CM) and swine manure (SM) in continuously stirred tank laboratory bioreactors at mesophilic and thermophilic conditions. As WFV, cucumbers (WC), tomatoes (WT), potatoes (WP) and apples (WA) from the markets in Sofia have been selected. AS, CM and SM as cosubstrates have been supplied from the Sofia wastewater treatment plant and a little farm nearby Sofia. Laboratory studies of continuous processes have been done in bioreactors with full volumes of: 5 L in mesophilic conditions (34 ± 0.5°C) and 20 L in thermophilic conditions (54 ± 0.5°C). To start the process, WFV have been added stepwise to both bioreactors treating AS or CM, respectively, in order to avoid problems during the start-up period. Finally, the anaerobic digestion of WFV only, at the ratio of: 40% WP:20% WT:20% WC:20% WA, has been studied in mesophilic and thermophilic conditions. As a supplement, an assessment of the digestate as a biological fertilizer has been made.