EFFECTS OF PRETREATMENT ON ANAEROBIC CO-DIGESTION OF GARDEN WASTE AND OTHER SUBSTRATES

Ultrasound, microwave and alkali-thermal pretreatment were applied for enhancing biogas production by anaerobic co-digestion of garden waste, kitchen waste and fruit and vegetable waste. The experiment without pretreatment served as the control. The results showed that pH values of the four experiments rapidly decreased to 7.24~7.45 within 2 days and then increased to 7.7~8.0 at the end of reactions, indicating that anaerobic digestion systems were relatively stable. The concentrations of VFA reached the maximum within 2~4 days, of which acetic acid and propionic acid were the main components, accounting for more than 70%. After 13 days, VFA concentrations decreased to below 500 mg/L, and mainly acetic acid remained. There were some fluctuations of TAN concentrations during the first 4 days, which then gradually increased to 2190~2410 mg/L at the end. While the concentrations of FAN firstly decreased, then increased and stabilized to 144~209 mg/L after 13 days. The proportion of methane in biogas all exceeded 50% after the 2nd day and reached the maximum value of 61.4%~63.8% on the 11th~12th day. According to simulation results of the modified Gomperts model, pretreatments could shorten the adaption period and enhance gas production at early stage. Ultrasonic pretreatment and alkali-thermal pretreatment could significantly increase the methane yield, from 396 mL CH₄/g VS to 601 mL CH₄/g VS, 536 mL CH₄/g VS, respectively, while microwave pretreatment slightly decreased the methane yield.