No one-size-fits-all. Multicriteria selection of nature-based wastewater treatment solutions across simulated scenarios

Nature-based solutions (NBS) are increasingly promoted as sustainable alternatives for wastewater treatment, offering environmental and social co-benefits beyond pollutant removal. However, selecting the most appropriate NBS for a given context remains challenging due to the diversity of available technologies and the complexity of stakeholder priorities. In this study, we used the Nat4Wat decision-support system to simulate 40,000 wastewater treatment scenarios, applying a multicriteria decision analysis (MCDA) across four water types. We analysed selection patterns, factors limiting solution suitability, and the influence of decision criteria. Results showed that no solution fits all contexts. Some NBS were suitable in only a few contexts, but when applicable, they consistently outperformed other options. Space requirements and capital costs were the most influential criteria, while environmental impact and treatment performance played a smaller role in selection. Notably, 62 % of raw wastewater and 24 % of greywater scenarios had no suitable solution, primarily due to strict nutrient removal requirements. Some NBS consistently underperformed and were never selected. These findings highlight the importance of contextualised planning, the need to address suitability gaps, and the value of structured tools like Nat4Wat for transparent and informed NBS selection. • Simulated 40,000 NBS across four water types using Nat4Wat. • No single NBS was optimal across all contexts. • Space and cost criteria strongly influenced solution selection. • 62 % of raw wastewater and 24 % of greywater scenarios had no suitable NBS solution. • Emphasises the need for new or combined NBS to address critical treatment gaps.