Effect of Inoculum on Anaerobic Co-digestion of Vegetable Processing Wastes and Cattle Manure at High Solids Concentration

In this study, effect of inoculum percentage on anaerobic co-digestion of vegetable processing waste (VPW) with cattle manure (CM) at high solids concentration (TS%) (7%) was investigated. The results were satisfactory: the time for peak appearance of daily methane yield was reduced, the earliest appeared peak was obtained on conditions of 40% inoculum percentage and 25:75 of VPW:CM ratio; at all VPW:CM ratios, the process stability of daily methane yield was enhanced by increasing inoculum percentage; the methane yield on condition of 40% inoculum percentage and 50:50 of VPW:CM ratio was the maximum (179.2 L kg VS); technical digestion time (T 80) for the maximum methane yield was the shortest (22 days). However, from the view of practical application, the capacity of treating VPW on conditions of 30% inoculum percentage and 50:50 of VPW:CM ratio may be optimal, the methane yield was 169.7 L kg VS, which was only 5.3% less than the maximum methane yield (p > 0.05). These results indicate that the increase of inoculum percentage in an appropriate range is helpful for the process performance and the methane yield of anaerobic co-digestion of VPW and CM at the high TS%.