Climate-Resilient Decentralized Wastewater Treatment Systems for Arid Regions

Water scarcity in arid and semi-arid regions continues to restrict wastewater reuse and increase the demand for dependable small-scale treatment systems. This study examined six constructed wetland installations under hot climates using weighted multi-criteria evaluation of BOD₅, COD, solids, nutrients, and pathogen reduction alongside operational and environmental aspects. Hybrid systems combining horizontal and vertical flow units showed the most stable treatment, with organic matter removal usually above 85 % and pathogen reduction around 3-4 log units. In comparison, single-stage wetlands presented larger variations in nutrient removal, mainly due to differences in vegetation, filter media, and water distribution. The analysis indicated that linking vertical and horizontal units improves oxygen transfer and gives better overall resilience under high temperature stress. When planted with local species and maintained properly, hybrid wetlands can produce water of adequate quality for reuse. Such systems support the objectives of Vision 2030 and SDG 6 by improving sustainable water management. More pilot studies in Saudi Arabia are still needed to confirm durability and adapt design criteria to local field conditions.