Anaerobic Co-Digestion of Wasted Vegetables and Activated Sludge

Abstract : Anaerobic co-digestion of activated sludge (AS) and wasted vegetables (wasted cucumbers (WC) and wasted tomatoes (WT)) was carried out at mesophilic conditions (34 ± 0.5 0C). A continuously stirred bioreactor with volume of 5 dm3 (3 dm3 working volume) was used. The digestion was examined in semi-continuous mode and 30 days hydraulic retention time. Total solids, volatile solids, COD and volatile fatty acids (VFA) were determined according to the standard methods. Daily the total biogas production as well as CH4 and CO2 content were determined using a graduated gasholder and an infrared sensor, respectively. pH was measured with Seibold pH-meter. The initial AS/WC ratio of the mixture used was 90/10. The average biogas production was 0.150 dm3 dm-3 d-1. The VFA concentrations were low during the process. After 127 days WT was added to the mixture. The AS/WC/WT ratio was 80/10/10. The CH4 and CO2 content in the biogas varied in the range of 64 - 72 % and 13 - 25 %, respectively. The data obtained during this study confirm that the co-digestion of the vegetables with AS is more favourable compared to the single digestion of the vegetables.