Assessment of Aesthetic Quality of Outdoor Green Walls: Investigating the Impact of Plant Growth-Promoting Bacteria and Recycled Water Irrigation

Outdoor green walls are gaining popularity for enhancing building aesthetics and promoting healthy and sustainable urban environment. However, concerns about their high water consumption in the context of ongoing water crises highlight the need for alternative water sources, such as recycled water. This research investigated the effects of recycled water irrigation and plant growth-promoting bacteria (PGPB) on four plant species for green walls in Mashhad, Iran: <i>Festuca ovina</i>, <i>Ophiopogon japonicus</i>, <i>Aptenia cordifolia</i>, and <i>Carpobrotus edulis</i>. Over nine months (March to December 2022), researchers conducted experiments using three water types (graywater, wastewater, and urban water) as the main factor and four bacterial treatments (Mix B1, Mix B2, Mix B3, and a control) as the sub-factor, with three replications of split-plot layout based on a randomized complete block design. Results showed significant differences in aesthetic qualities, with optimal visual quality achieved by applying Mix B2 or B3 with wastewater for <i>Aptenia cordifolia</i>, <i>Carpobrotus edulis</i>, and <i>Festuca ovina</i>; and <i>Ophiopogon japonicus</i> performed best with Mix B1 and graywater. The research highlights the potential of using <i>Aptenia cordifolia</i> with Mix B3 and wastewater irrigation for outdoor green walls, especially in arid and semi-arid climates.