Constructed wetlands as a nature-based solution for sustainable use of non-conventional water in arid and semi-arid regions: A scoping review

Background Constructed wetlands (CWs) are increasingly recognized as a nature-based solution (NbS) for improving water quality and supporting circular water management in water-scarce settings. In this review, non-conventional water (NCW) refers to water sources such as greywater, municipal wastewater effluents, and agricultural drainage water that can be treated and reused. Objectives This scoping review aimed to map CW applications for NCW treatment in arid and semi-arid regions, synthesize reported treatment performance, and evaluate reuse suitability, with a specific focus on the Middle East and North Africa (MENA) region and the Sudano-Sahel zone. Methods Following PRISMA-ScR guidance, literature was identified from major electronic databases and institutional repositories. Eligible studies evaluated CWs treating NCW in arid/semi-arid contexts. Extracted data included CW configuration, operational conditions, pollutant removal performance, and compliance with reuse criteria. Results Fourteen studies met the inclusion criteria. CWs consistently achieved high removal of biochemical oxygen demand over 5 days (BOD₅) (85–92%), chemical oxygen demand (COD) (80–90%), and total suspended solids (TSS) (85–93%). Nutrient removal was moderate, with total nitrogen reductions of 60–75% and total phosphorus reductions of 55–65%. Fecal coliform reduction was generally 3–4 log units, frequently meeting WHO-aligned irrigation reuse thresholds. Long-term findings indicated reasonable operational stability, although clogging and salinity build-up remained recurrent constraints. Conclusions Framing CWs within an NbS lens highlights their dual value for pollution control and climate-adaptive water reuse in arid and semi-arid regions. Across MENA and Sudano-Sahel contexts, CWs show strong potential for irrigation-oriented reuse when properly designed and maintained. Future work for the study area should prioritize long-term multi-season field validation, optimization of nutrient and salinity management, and harmonized monitoring frameworks that also include emerging contaminants to strengthen safe scale-up.