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

Abstract

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°C prior to mesophilic AD were studied through a series of batch experiments. Pretreatments at a lower temperature (50°C) and a shorter time (<12h) 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°C for 6-12h or a thermal pretreatment at 80°C for 1.5h. Thermophilic pretreatments at higher temperatures (>55°C) and longer operating times (>12h) 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.

Enhanced Anaerobic Digestion of Food Waste by Supplementing Trace Elements: Role of Selenium (VI) and Iron (II)

“…The net SBP of FW-A and FW-B were 421.2 (±14.6) mlCH 4 /gVS added and 412.5 (±12.0) mlCH 4 /gVS added , respectively, which is in a good agreement with the literature (Banks et al, 2012;De Vrieze et al, 2013;Ariunbaatar et al, 2014Ariunbaatar et al, , 2015. The effect of TE addition had nevertheless a different effect on FW-A and FW-B, due to their different TE background concentration ( Table 2).…”

“…To reduce experimental bias, the substrate used for this research was synthetically generated based on an average compositional analysis of FW in the EU, as it was used in previous research (Ariunbaatar et al, 2014(Ariunbaatar et al, , 2015. It contained 79% fruits and vegetables, 5% pasta and rice, 6% bread and bakery, 8% meat and fish, 2% dairy product (Ariunbaatar et al, 2014(Ariunbaatar et al, , 2015. A fresh substrate was prepared for each set of experiment using food bought from local supermarkets in Delft, The Netherlands (Albert Heijn) and Tampa, USA (Walmart).…”

“…The plant treats the buffalo dung together with the milk whey and sewage sludge generated from the mozzarella producing industry. It was used previously in studies of Ariunbaatar et al (2014Ariunbaatar et al ( , 2015 and Liotta et al (2015).…”

“…The biomethane potential (BMP) test of FW was conducted in duplicate serum bottles as described by Ariunbaatar et al (2014Ariunbaatar et al ( , 2015. The substrate to inoculum ratio was 0.5 gVS/gVS.…”

“…The daily biomethane production was measured with the liquid displacement method using sodium hydroxide (120 g/L) to absorb the carbon dioxide. The BMP test was continued for 20 days, as most (80-85%) of the organics are converted to biomethane and the AD process reaches a plateau (Ariunbaatar et al, 2014(Ariunbaatar et al, , 2015. The normalized specific biomethane production (SBP) was calculated using the net cumulative biomethane production (after deducting the biomethane production of the blank, i.e., the inoculum without substrate) and the initial VS added.…”