Digestion of pre‐treated food waste in a hybrid anaerobic solid–liquid (HASL) system

Abstract

The hybrid anaerobic solid-liquid (HASL) system was developed to be used in industrial-scale operations to minimize the amount of food waste for disposal in Singapore. Thermal pre-treatment of food waste at 70• C for 2 h (experiment E1) or at 150• C for 1 h (experiment E2) facilitated the hydrolytic and acidogenic processes in the acidogenic reactor and methanogenesis in the methanogenic reactor in the HASL system. The highest dissolved chemical oxygen demands in the effluents from the acidogenic reactors were 17 575, 19 980 and 24 235 mg dm −3 in the control with food waste without thermal pretreatment and experiments E1 and E2, respectively. The maximum concentrations of methanogens in the methanogenic reactor were 2.3 × 10 7 , 3.8 × 10 7 , 4.3 × 10 7 cells cm −3 for the control and experiments E1 and E2, respectively. However, the performances of the methanogenic phase in terms of specific activity of methanogens did not differ significantly for the control and experiments E1 and E2. Use of thermally pretreated food waste halved the time to produce the same quantity of methane in comparison with anaerobic digestion of fresh food waste. The fluorescent measurements of co-enzyme F 420 and oligonucleotide probe Arc915 specifically bound (hybridized) with 16S rRNA were used for monitoring of methanogens during anaerobic digestion of food waste. There was a linear correlation between these parameters and the concentration of methanogens in the effluent from the methanogenic reactor.

Digestion of frozen/thawed food waste in the hybrid anaerobic solid–liquid system

“…Yield of methane production, in terms of l/g VS removed, increased by 6.7% in the experiment in comparison with the control. The similar increase by 7.1% was observed when food waste pre-treated at 150°C for 1 h was used for anaerobic digestion instead of fresh food waste (Wang et al, 2006). Therefore, successive freezing and thawing of food waste has not much changed the stoichiometric parameters in the HASL system, but significantly changed the maxima of the parameters, as well as kinetic parameters.…”

“…Use of frozen/thawed food waste instead of fresh one gave the opportunity to diminish operational time of the batch process by 42%. The effect of freezing/thawing of food waste as a pre-treatment step for its anaerobic digestion in the HASL system was comparable with thermal pre-treatment of food waste at 150°C for 1 h, which helped to diminish time needed to produce the same quantity of methane twice in comparison with the anaerobic digestion of fresh food waste due to speed up of organic matter hydrolysis (Wang et al, 2006). Therefore, freezing and thawing of food waste can be considered as alternative method for thermal pre-treatment of food waste before its anaerobic digestion.…”

Importance of storage time in mesophilic anaerobic digestion of food waste

“…Therefore, optimum environmental and operational parameters influencing acid-phase digestion of food waste, including pH (Jiang et al, 2013;Lim et al, 2008;Wang et al, 2014), temperature (Jiang et al, 2013;Komemoto et al, 2009;Lim et al, 2008;Vanwonterghem et al, 2015), hydraulic retention time (HRT) (Lim et al, 2008;Wang et al, 2015a), inoculum-to-substrate ratio (Forster-Carneiro et al, 2008;Xu et al, 2012), and organic loading rate (Jiang et al, 2013;Lim et al, 2008), have been intensively investigated. Some studies have focused on the physical or chemical pretreatment of food waste in order to enhance the hydrolysis or to alter the properties of food waste and thus to facilitate subsequent methanization through processes such as microwave treatment (Marin et al, 2010;Shahriari et al, 2013), ultrasonication (Cho et al, 2013;Elbeshbishy and Nakhla 2011), mechanical grinding (Izumi et al, 2010), alkali treatment (Lin et al, 2013), thermal treatment (Li and Li and Jin, 2015;Wang et al, 2006), ozonation (Ariunbaatar et al, 2014), and enzyme treatment (Kim et al, 2006).…”

Mixing Performance of a Suspended Stirrer for Homogenizing Biodegradable Food Waste from Eatery Centers

“…In an organic waste biodegradability [6] homogenized a waste mixture (85% food waste) with a mechanical mixer for two and a half hours at 60 °C before it was subjected to pasteurization and thermal hydrolysis. Wang et al [7] also exposed food waste meant for digestion to two types of thermal pre-treatment: 70 °C for two hours or 150 °C for one hour. An efficient storage or holding tank is required to ensure the food waste is properly pre-conditioned.…”