Assessing circularity of wastewater treatment systems: A critical review of indicators

Global energy demand, water demand, and raw materials extraction are major challenges for society as population grows. While a traditional linear economy approach leads to depletion of finite resources, damage to the Earth's ecosystems, and adverse impacts on human health, a paradigm shift toward implementation of circular economy principles is paramount to the reversal of world resources' exhaustion. The wastewater, or “used water,” sector can contribute to offsetting resource scarcity challenges by adopting circular economy principles to recover and reintroduce recovered resources into the economy. Transitioning to a circular economy model requires monitoring and tracking progress via metrics in the form of indicators. In this paper, a bibliometric analysis followed by a systematic literature review was conducted on available circular economy indicators in the used water treatment sector. Over 200 indicators were categorized into three impact categories: environmental, social, and economic to identify gaps in the existing literature. Results showed that less than 50% of the available circularity indicators are applied in the used water sector and environmental indicators represent the highest percentage among the potential applicable indicators. Research gaps in the circular economy literature in relation to used water treatment systems were identified and future research directions discussed.