Reusing shell waste as a soil conditioner alternative? A comparative study of eggshell and oyster shell using a life cycle assessment approach

Abstract

Shell waste is a valuable natural material that is rich in calcium carbonate and can be directly used as limestone or as lime in a variety of applications. This study investigated the environmental impacts and tradeoffs associated with eggshell waste recycling treatment and reuse for land application, as well as performed a comparative analysis with oyster shell waste systems, using a life cycle assessment (LCA) approach. Our results confirmed that recycling treatment and reuse of eggshells may potentially generate more environmental impacts than conventional end-of-life disposal. It was estimated that the recycling and reuse of an average eggshell amount of 60 g accounted for nearly 0.187 kg CO2 eq of climate change impact and had other remarkable environmental impacts, such as marine ecotoxicity, freshwater ecotoxicity, freshwater eutrophication and human toxicity. This result could be mainly attributed to the involvement of energy-intensive conversion processes, such as calcination at 800 °C, in the treatment process. Similar trends in the impact results were obtained in the oyster shell system, although these were found at a larger extent. Furthermore, our results revealed that the processing capacity and energy sources were the two key influential factors affecting the overall impacts of shell waste processing and reuse. Thus, it is recommended that future efforts for mitigating the associated impacts should be focused on technological advancement and the implementation of environmentally friendly energy sources, with the goal of improving both economic and environmental sustainability.