(393e) A Closed Loop Case Study of Food Waste Management in Singapore | AIChE

(393e) A Closed Loop Case Study of Food Waste Management in Singapore


Tong, Y. W. - Presenter, National University of Singapore
Tian, H., National University of Singapore
Food waste (FW) shows an increasing trend worldwide in recent years. If not treated properly, it causes other problems such as water and air pollutions. In Singapore, FW is an outstanding issue due to the large population residing in a limited island and the considerable yearly increasing FW quantity with low recycling rates (<20%). Singapore has a unique food culture that more than 100 food courts are distributed in the island for residents’ daily meal consumption (Tong et al., 2018). Hence, food waste onsite treatment to save the transportation cost and emissions has become a consensus. Anaerobic digestion (AD), as a widely used technology to recover energy and resources from different waste, has been used to treat food waste in large scale in many countries. However, small-scale decentralized AD system in urban area to specifically treat food waste onsite is seldom reported. A comparative life cycle assessment study performed by Tian et al. (2021) showed the environmental benefits of deploying decentralized system, but the actual operational performance and cost analysis are yet to be further explored. Moreover, in most of the food waste treatment studies, the organic loading is normally fixed during certain experimental periods. As for the actual situation of a food court, it is difficult to ensure the same daily organic loading, particularly the different waste quantity during weekdays and weekends, thus a robustness testing of a decentralized system fed with real and varying food waste quantity from a food court needs to be validated. Therefore, the aim of this study is to 1) customize a decentralized AD system to treat food waste for a representative food court in Singapore, i.e., East Coast Lagoon Food Village (ECLFV), and 2) discuss the robustness, energy balance, carbon emission profile, and cost benefits, of the system.

The electricity consumption by the system and the electricity generation by the biogas engine were recorded. The operation results showed that the electricity consumption that is not related to the organic loading but keeps the system running was about 9kwh per day, including circulation pump, control system, ventilation fans, etc., while the electricity consumption that is related closely to the organic loading was about 0.09kwh/kg FW, including the feeding pump, blender, digestate discharge pump, biogas compressor, etc. The engine converts the biogas into electricity at a rate of 1.78m3 biogas/kwh (STP), i.e., the electricity efficiency was around 10.5%. The efficiency is lower compared to other studies, which might be due to the small scale of the engine. At this stage with dine-in restriction, the low FW collection resulted in low electricity generation, which the recovered energy only contributed 12% of the system consumption. With the release of the restriction, the FW collection is expected to be close to the waste audit results. Hence, based on the waste audit results and the current system performance, the recovered energy is estimated to reach at around 16kwh/day, while the electricity consumption is also estimated to reach at 28kwh due to the high FW collection and feeding, which the recovered energy contribution can increase from 12% to 59%. Therefore, to have the system as electricity self-sustaining system, more effects should be spent on the improvement of the biogas engine efficiency to at least 18%.