To what extent do geopolitical conditions affect the environmental sustainability of the circular economy? A comparative LCA study of lactic acid production in Denmark and Iran

Transitioning to a circular economy is inevitable in well-developed and developing economies. Biowaste valorization into value-added products has shown a promising sustainable solution compared to its fossil-based counterparts. However, it has yet to be scientifically analyzed to what extent geopolitical conditions affect the environmental sustainability of the circular economy. To fill this gap, we conducted a consequential life cycle assessment of biorefining biowaste into lactic acid and bioenergy in Denmark and Iran as representative examples of developed and developing economies, respectively. Despite the notable environmental impacts associated with fossil-based energy consumption and infrastructural limitations, Iran could benefit more environmentally from transitioning to a circular economy by 2030 than Denmark. This contrast arises from the fact that the existing dominant waste management solution in Iran consists of sanitized and unsanitized landfills, which appear likely to continue through 2030. Therefore, any alternative waste management scenario would help avoid the environmental impacts arising from landfills. In contrast, Denmark already has a well-established and sustainable waste management practice for biowaste, namely anaerobic digestion. Accordingly, the environmental impacts of the investigated scenarios in Denmark were, on average, 85 %, 855 %, 177 %, and 130 % higher than those in Iran regarding resource scarcity, ecosystem quality, human health, and climate change, respectively. In both countries, incineration, the culture medium, ion exchange, vacuum distillation, transportation, emissions from digestate applications on farmlands, and the inorganic waste landfilling process contributed most to the overall environmental impacts. Besides impacts arising from geological conditions, our study revealed that abiotic augmentation and P. acidilactici bioaugmentation demonstrated superior environmental performance compared to other methods. The results also highlight the importance of international collaboration to implement circular economy approaches in developing countries, accelerating global environmental mitigation efforts. To comprehensively evaluate environmental sustainability, it is recommended to examine scenarios aligned with socio-economic pathways and various representative concentration pathways.