# The Life-Cycle Environmental Impact of Recycling of Restaurant Food Waste in Lanzhou, China
## 1 Introduction  
Food waste (FW) creates environmental and food security problems in society due to the impacts associated with both the production and treatment (or reusing) of FW in China. According to the current studies, the amount of FW from the restaurant industry occupied 50% of the total amount of FW [1] and is expected to grow continuously along with an increase in the scale of restaurant industry in the context of persistent urbanization and improvement of the residential living level in China. Restaurant FW has a high water content, high salt content, high organic matter content, and significant temporal and spatial differences in components; it can be harmful but also useful [2]. Traditional treatment techniques, such as landfills and incineration, involve considerable environmental hazards and high costs, and they produce less pronounced economic benefits [3]. Importantly, food wasteis not fully used as a resource. This made the treatment of restaurant food waste a popular topic in the associated research fields. An environmental impact analysis of restaurant food waste treatment, in particular, a life-cycle assessment of the treatment process, would facilitate appropriate selection of treatment techniques and optimization of existing techniques [4; 5]. Unlike other municipal solid waste, such as waste paper, waste metal, or construction waste, the recycling of food waste is complex and difficult due to the biological treatment process not only resulting in emissions with negative environmental impacts but also affecting the potential for nutrient and energy recovery through different treatment alternatives [6; 7]. Thus, the life-cycle assessment (LCA) of food waste recycling or treatment is full of complexity and uncertainty. The current studies mainly focused on the resource usage, environmental impacts [8; 9; 10], and human health impact [11; 12] of various recycling or treatment methods, such as feed and fertilizer, composing and landfill disposal [13], incineration, anaerobic digestion, and biodiesel [14]. Anaerobic digestion and incineration are the two most common ways to recycle food waste; however, the former seems to be preferable to incineration for biogenic substrates [15], due to its low cost and convenience [16; 17; 18; 19]. Previous studies concentrated on the environmental impact and economic feasibility of the process of obtaining energy (i.e., biogas) from food waste via anaerobic digestion [20; 21; 22], and attempted to explore a way to optimize the digestion process [23; 24], in an effort to recycle the most food waste while minimizing resource consumption and impact on the environment (e.g., optimization of the pre-treatment stage). LCA is extensively applied in the context of food waste management. However, the LCA of FW is still a complex and emerging field as it includes both technical and biological processes [25]. As [PERSON] et al. argued, the system boundaries should be explicitly defined since the biological process of food waste treatment can be highly dependent on factors of the local climate and environment, as well as the LCA of the process, including urban and forest environments, agriculture, landfills, and emissions to the external environmental system [26]. [PERSON] et al. also demonstrated the inconsistency of environmental impact produced by two kinds of boundaries: from waste to products and from waste to product use [27]. Furthermore, the treatment process and parameter selection of LCA could result in profound differences in the results of LCA [6; 7]. LCA of FW treatment is regarded as a potential hotspot in the research field of FW management. The environmental impact of food waste recycling was studied extensively by applying the LCA method, aimed at optimizing the current technology or identifying the best way to recycle food waste [28]. However, Chinese case studies and evaluation of the anaerobic digestion-aerobic composting technique are rare. Restaurant food waste in China differs from that in other countries.