Towards a modelling framework for nature-based solutions in wastewater treatment.

This article presents the authors' perspectives on modelling best practices for nature-based solutions (NBS). The authors led a workshop on NBS modelling as part of the 8th IWA Water Resource Recovery Modelling Seminar (WRRmod2022+) in January 2023, where the discussion centred around the design, use cases, and potential applications of NBS models. Four real-world case studies, encompassing an aerated lagoon, a biofilm-enhanced aerated lagoon, a stormwater basin, and a constructed wetland were reviewed to demonstrate practical applications and challenges in modelling NBS systems. The initial proposed modelling framework was derived from these case studies and encompassed eight sub-models used for these NBS types. The framework was subsequently extended to include eight additional NBS categories, requiring a total of 10 sub-models. In a subsequent step, with a different perspective, the framework was refined to focus on 13 primary use cases of NBS, identifying 10 sub-models needed or potentially required for these specific NBS applications. These frameworks help to identify the necessary sub-models for the NBS system at hand or the use case. This article also discusses the benefits and challenges of applying water resource recovery modelling best practices to NBS, along with recommendations for future research in this area