Greywater treatment using vegetated walls for sustainable urban greening and water reuse in Qatar

Over 80% of the global population lives in urban areas. This concentration of human development has significant impacts on the local environment including increasing surrounding temperature, stressing local water resources, and resulting in emissions to air, land and water associated with anthropogenic activities. Urban greening, particularly through vegetated building structures, is seen as a way to mitigate some of these impacts through creation of a more natural ground-surface environment. These technologies bring benefits of passive cooling, improved aesthetics, air filtration, acoustic dampening and stormwater retention. However, the uptake of this technology in the Middle East has been limited due to high water requirements, a scarce and precious resource in the Middle East, which for Qatar comes primarily from energy intensive desalination. Herein, we propose the integration of greywater treatment and reuse by using living wall and green façade systems, taking lightly polluted water streams from within residential and commercial buildings and using the media and plant elements to provide water purification. This treated water can then be used for subsequent reuse in landscaping, outdoor cleaning or toilet flushing. In this way sufficient water is used to support vegetated wall infrastructure while also enabling water reuse, further reducing reliance on desalinated water supplies. However, the greywater treatment requirements on vegetated walls brings with it numerous challenges including selection of suitable plants that can both survive and aid in phytoremediation of the greywater; media which is both lightweight and non-clogging; and appropriate water application strategies to find an optimum pollutant removal, maximized with long greywater residence times in the system; and water recovery which is maximized with short retention times. Additionally, to ensure high quality of treated water for reuse, reduction of high-risk contaminants must be assured. In order to achieve these goals the project will comprise lab-scale testing of various media and plant combinations with real and synthetic greywaters to understand removal mechanisms and performance; the system will be taken to small outdoor pilot scale wall to evaluate seasonal and operational effects on treatment performance and water loss; water recovery/loss models will be developed and validated; post-treatment requirements and processes will be assessed to meet particular end uses; and feasibility will be assess in line with technoeconomic and urban planning considerations. This will be in conjunction with key stakeholders including the Ministry of Municipality and Environment (MME) Urban Planning Department, the Gulf Organisation for Research and Development (GORD) as well as local landscaping company and green wall supplier, Green Maze Landscape & Design. We expect this research will lead to the future expansion of this widely adopted green building technology within the Middle East to meet three key strategic national research goals, namely energy efficiency, water reuse and improved urban/architectural technologies.

Hamad Bin Khalifa University (HBKU)