Dry semi-continuous anaerobic digestion of food waste in the mesophilic and thermophilic modes: New aspects of sustainable management and energy recovery in South Korea

Abstract

In this study, parallel, bench-scale, mesophilic and thermophilic, dry, semi-continuous anaerobic digestion (DScAD) of Korea food waste (FW, containing 22% total solids (TS) and 20% volatile solids (VS)) was investigated thoroughly under varying operational conditions, including hydraulic retention times (HRTs) and organic loading rates (OLRs). The aim was to evaluate the start-up, stability, overall removal efficiency, and inhibitory effects of toxic compounds on process performance over a long-term operation lasting 100 days. The results from both digesters indicate that the simultaneous reduction of VS and the production of gas improved as the HRT decreased or the OLR increased. The highest average rates of VS reduction (79.67%) and biogas production (162.14 m 3 biogas/ton of FW, 61.89% CH 4), at an OLR of 8.62 ± 0.34 kg VS/m 3 day (25 days of HRT), were achieved under thermophilic DScAD. In addition, the average rates of reduction of VS and the production of biogas in thermophilic DScAD were higher by 6.88% and 16.4%, respectively, than were those in mesophilic DScAD. The inhibitory effects of ammonia, H 2 S, and volatile fatty acids (VFAs) on methane production was not clear from either of the digesters, although, apparently, their concentrations did fluctuate. This fluctuation could be attributed to the self-adaptation of the microbial well. However, digestion that was more stable and faster was observed under thermophilic conditions compared with that under mesophilic conditions. Based on our results, the optimum operational parameters to improve FW treatment and achieve higher energy yields could be determined, expanding the application of DScAD in treating organic wastes.

Evaluation of Anaerobic Co-Digestion to Enhance the Efficiency of Livestock Manure Anaerobic Digestion

“…This increase in energy consumption has, in turn, led to an increase in the demand for fossil fuel, such as coal, oil, and natural gas, which are used as primary energy sources, thereby resulting in higher costs of fossil fuels [1]. Since fossil fuels are known to be one of the sources of environmental pollution, such as greenhouse gas emissions, it is necessary to develop environmentally friendly and renewable energy sources that can replace fossil fuels worldwide [2,3]. Accordingly, research has been conducted for the production of new and renewable energy using biomass that is low in cost [4].…”

A new approach for concurrently improving performance of South Korean food waste valorization and renewable energy recovery via dry anaerobic digestion under mesophilic and thermophilic conditions

“…The main characteristics of TS, VS, VS/TS ratio, total chemical oxygen demand (TCOD), total nitrogen (TN), NH 4 -N, and C/N ratio of the FW and inoculum are outlined in Table 1 and described in our previous work (Nguyen et al, 2017 ;Nguyen et al, 2016).…”

“…The circulating pump was integrated into a hot water jacket system to ensure uniform hot water in the system and eliminate dead zones. All the electrical equipment (pumps, sensors, and agitator) used in each AD system was able to operate and record in two modes: automatic and manual (Nguyen et al, 2017). Initially, 10 L of inoculum was added into each dry anaerobic digester for quick startup with the anaerobic microorganisms.…”

“…Initially, 10 L of inoculum was added into each dry anaerobic digester for quick startup with the anaerobic microorganisms. The digesters were operated under solids loading rates (SLRs) that increased stepwise from 2.3 to 9.21 kg TS/m 3 day at a fixed TS content of 22%, corresponding to hydraulic retention times (HRTs) from 100 days to 25 days, respectively (Nguyen et al, 2017). Operational details are summarized in Table 2.…”

“…Subsequently, the TheDA digester was gradually shifted from the mesophilic condition (38 °C) to the thermophilic condition (55 °C) at a rate of 1 °C per two days until it reached 55 °C. This was done to minimize the shock due to rising temperatures during transient conditions (Nguyen et al, 2017).…”