Life Cycle Assessment for Small-scale Anaerobic Digestion System - Case study in Small municipality - = Life Cycle Assessment for Small-scale Anaerobic Digestion System - Case study in Small municipality -

다국어 초록 (Multilingual Abstract)

Food waste is significant in Japan. For example, 17.4 million tons, including 11 million tons from households, was generated in 2010 alone (MAFF, MOE 2013). Of this, 10 million tons of food waste from households is currently incinerated. To develop cleaner production cycles, waste-to-energy should be considered. On-site small-scale anaerobic digestion (AD) facility can be applied for small municipalities where they have demand of not only electricity but also heating. This study evaluates the environmental impacts of on-site AD of food waste in small-scale municipality using a life cycle assessment (LCA).
Small municipality with 27,000 of population was selected as case study. The functional unit is the “treatment of 4 ton/day household food waste generated in the municipality.” The system boundary is considered to include the collection to the treatment of food waste. Totally 8 scenarios consist of 6 sub-scenarios considering treatment methods of AD residue and wastewater were developed. For AD residue treatment, treatment in the excreta treatment facility within the municipality, composting outside the municipality, and incineration outside the municipality, were considered. Incineration and composting were also included as reference treatment methods. For small AD, biogas is used as a source of electricity and heat through a combined heat and power (CHP) system. Global warming, fossil fuel consumption, urban air pollution, and acidification were considered as environmental impacts. After the characterization of each impact category, a damage assessment for the four different dimensions including human health, social assets, biodiversity, and primary production, was considered. Then, the results of these individual dimensions were integrated by conversion into a single index with units of value in Japanese yen (JPY). The calculation utilized characterization, damage, and integration factors are identified by the LIME2 model (JLCA 2012). Concerning global warming, CO₂ emissions derived from biomass are considered to be carbon-neutral and thus have been excluded from the calculation.
The results of the integration in Fig. 1 revealed that the small-scale AD system (Scenarios 3 and 4) showed environmental benefit (negative values). Regarding the comparison with the treatment methods of AD residue and wastewater, S4-3 (composting of AD residue) was the most desirable while S4-4 (incineration of AD residue) was the worst. Among the environmental impacts, global warming tended to be the dominant in scenarios 4-1 to 4-4.