Enhanced mesophilic anaerobic digestion of food waste by thermal pretreatment: Substrate versus digestate heating

Food waste (FW) represents a source of high potential renewable energy if properly treated with anaerobic digestion (AD). Pretreating the substrates could yield a higher biomethane production in a shorter time. In this study, the effects of thermal (heating the FW in a separate chamber) and thermophilic (heating the full reactor content containing both FW and inoculum) pretreatments at 50, 60, 70 and 80 degrees C prior to mesophilic AD were studied through a series of batch experiments. Pretreatments at a. lower temperature (50 degrees C) and a shorter time (<12 h) had a positive effect on the AD process. The highest enhancement of the biomethane production with an increase by 44-46% was achieved with a thermophilic pretreatment at 50 degrees C for 6-12 h or a thermal pretreatment at 80 degrees C for 1.5 h. Thermophilic pretreatments at higher temperatures (>55 degrees C) and longer operating times (>12 h) yielded higher soluble chemical oxygen demand (CODs), but had a negative effect on the methanogenic activity. The thermal pretreatments at the same conditions resulted in a lower solubilization of COD. Based on net energy calculations, the enhanced biomethane production is sufficient to heat up the FW for the thermal, but not for the thermophilic pretreatment. (C) 2015 Elsevier Ltd. All rights reserved.