Methodological guide and roadmap to assess the compliance of wastewater treatment plants with sustainability and circularity criteria.

Environmental certification has come up as a voluntary action to demonstrate a minimum quality level when it comes to the introduction of ecological-friendly principles in decision-making. However, most of the work done so far has focused on the food and agroforestry sectors and on the production and processing stages of the value chain rather than end-of life strategies. The present study aims to provide a roadmap that facilitates the evaluation of the performance wastewater facilities from sustainable and circularity perspectives. A six-step framework has been proposed with the objective of serving as the basis for a future certification system for this sector. First, mandatory requirements were collected from European legislative documents to identify the targets to be met. Subsequently, the collected data have been classified into five levels ranging from the definition of pillars, principles, criteria, requirements to the compliance of indicators. The selection of indicators was carried out taking into account the existing literature to gather both sustainability (167) and circularity (32) indicators, which were then associated with the defined requirements. The final step is to consider the testing or validation of the methodology to case studies, in this case, the design and operation of two large-scale wastewater treatment plants. The results indicated that most of the indicators are qualitative and about 61 % of the quantitative requirements of the framework could be calculated with routine plant information. For those indicators for which estimation was not possible due to lack of data, an easily manageable, fact sheet-type template was created so that companies were aware of data required to address the framework. Moreover, the application of this assessment framework to wastewater treatment plants identified some gaps to consider: (1) thresholds could not be defined for many of the indicators, (2) there is a lack of guidelines for data collection, (3) legislation needs improvement regarding circularity metrics in this sector and (4) the requirements should be strengthened to account for the specific characteristics of facilities operating at different scales and using various technologies.