Methods to measure and enhance the circularity of wastewater resources

Abstract

The need for an alternative to the linear economy and a practical method to operationalise sustainable development has led to a surge in popularity of the circular economy (CE) concept. Europe’s CE Action Plan establishes the importance of circular wastewater treatment and resource utilisation, however, a lack of standardised CE definitions and assessment methods are hindering this transition. Therefore, the first step of this research reviewed the indicatorbased decision support systems (DSS) developed for wastewater treatment plant (WWTPs). It found that technology selection DSS aims are ill-defined and the scope of indicators used for process optimisation is narrow, meaning the sector is far from standardised assessments and decision making. This led to the development of a structured approach that generates shared CE strategies at a regional level, by adapting a multi-criteria analysis tool to select resource recovery technologies. A UK wastewater sector example demonstrated the approach’s decision-making capabilities, identifying five priority resources and quantifying the expected benefits in terms of nutrient recovery. However, it was concluded that a holistic assessment is required for further analysis of impacts to circularity and sustainability when implementing the selected technologies. Reviewing circularity assessments, and definitions of waste, showed a paradox exists when applied to WWTPs, as wastewater, regardless of its production, is nonvirgin so is currently considered a circular input. To overcome this, the CE principle of resource traceability was combined with their degree of environmental harm, to define the circularity of water, carbon, nitrogen, and phosphorus. This method showed how actions of water users impact upstream and downstream circularity of a conventional WWTP. Following this, it was seen that material circularity is commonly used as a proxy for environmental performance, revealing a large disconnect between circularity and sustainability during assessments. Therefore, the assessment method was expanded to investigate how changes to physical resource circularity directly impacts value creation. By defining several principles from sustainability science literature, a method that systematically selects resource, action, and sustainability indicators using participatory approaches was developed. Additionally, it showed how appropriate benchmarks are defined for direct quantification of impacts to resource circularity and sustainable value creation. This was validated by comparing extended aeration and novel photobioreactor (PBR) WWTPs, highlighting multi-dimensional benefits of the PBR compared with the conventional process. Lastly, it is believed the developed method can act as the basis for standardising the holistic circularity assessment of wastewater resources.