A nature-based closed-loop wastewater treatment system at vehicle-washing facilities: From linear to circular economy.

Pakistan, among the top five most water-stressed nations globally, grapples with water scarcity owing to inadequate treatment infrastructure and groundwater overextraction. We demonstrate a successful nature-based closed-loop system to treat wastewater from urban vehicle-washing facilities, previously reliant on groundwater. An eco-friendly integrated system containing floating treatment wetlands (FTWs), subsurface flow constructed wetlands (SSF-CWs), and sand filtration (SF) was designed and installed at three vehicle-washing facilities for wastewater treatment and reuse in a loop. While the system is still operational after years, a consistent and significant reduction in water quality indicators is recorded, successfully meeting the national environmental quality standards of Pakistan. By reducing per unit water treatment costs to as low as $0.0163/m³ and achieving payback periods under a year, the embrace of these closed-loop strategies vividly underscores the imperative of transitioning to a circular economy in the domains of wastewater treatment and resource conservation.