Insights into the environmental performance of nature-based wastewater technologies towards water and carbon neutrality

Water reuse has become a promising strategy to address water scarcity and reduce pressure on natural water resources, particularly for irrigation practices. However, the implementation of water reuse for irrigation requires careful planning to address potential challenges, such as water quality concerns, public acceptance and the environmental impacts of treatment processes. To support informed decision-making, Life Cycle Assessment (LCA) serves as a powerful tool for evaluating the environmental implications of different water reuse strategies. This study presents a comparative analysis of several biological treatment systems across different regions of the Iberian Peninsula, including membrane bioreactors, filtration systems, constructed wetlands, and advanced oxidation processes. In addition to assessing the environmental performance of these technologies, this research work also links the LCA outcomes with the concepts of water and carbon neutrality in wastewater treatment plants. The results indicate that, among the four processes, only one achieves a positive water balance: the bio-filter system, which is also the best performing technology in most LCA categories. In contrast, the membrane bioreactor combined with integrated fixed film activated sludge shows worse performance, largely due to its high energy consumption. Regarding carbon neutrality, operating constructed wetlands requires approximately 0.79 ha of cropland to offset greenhouse gas emissions. This is significantly lower than the estimated 16.7-566 ha needed for non-nature-based solutions, which are not designed for carbon capture.