From Efficiency to Circularity in the Wastewater Sector: A Review of Performance Indicators in Regulated Countries

The shift from traditional linear economic models to circular economy principles has gained momentum, particularly in the wastewater treatment sector. This transition relies on resource use efficiency, waste minimisation, and value creation. Nevertheless, a review of 83 articles, yielding 386 key performance indicators, reveals a significant lack of standardised methodologies for assessing circular economy performance in Wastewater Treatment Plants. This absence allows ambiguous outcomes and hinders comparative analyses across facilities and countries. There is a clear need for a universally applicable Key Performance Indicators-based framework that evaluates all environmental dimensions without forgetting the technical component while encompassing the various circularity strategies. Such a framework should not discard defined parameters’ costs and data availability, avoiding abstract parameters that may lead to data manipulation and require extensive additional costs. Standardising Key Performance Indicators with explicit units of measurement is essential to ensure data comparability. In addition, they should comply with the regulatory institutions’ evaluation requirements, at least while these methodologies have not yet evolved to incorporate broader circular and environmental considerations. Developing a standardised Key Performance Indicators-based framework is crucial for effectively evaluating circular economy performance in Wastewater Treatment Plants, ensuring comprehensive environmental assessment, data comparability, and alignment with regulatory standards. This approach would facilitate a more consistent and transparent evaluation of circular economy initiatives across diverse contexts.