Green roofs provide multi-functional benefits to the built environment. They minimize urban heat island effects, enhance biodiversity, reduce carbon footprints, provide hydraulic benefits to urban runoff, and improve overall environmental sustainability.However, their application is limited or rare in arid climates. On the other hand, greywater is becoming a popular alternative water resource in water-scarce regions. A greywater-fed green roof system was developed and studied in the city of Al Ain, United Arab Emirates (UAE). The effluent (treated greywater) from the green roofs can be used to irrigate amenity plantations. Two intensive and two extensive green roof prototypes were constructed, planted with reed canary grass (Phalaris arundinacea L.), and irrigated with greywater. The greywater influents and the green roof effluents were monitored for changes in greywater quality. The study showed that the intensive system performed well, which is attributable to the greater depth of soil media. Treated greywater effluent from the green roofs met the local standards for recycled wastewater-based irrigation for a number of parameters (pH, electrical conductivity, salinity, and total dissolved solids), but exceeded the maximum allowable limits for turbidity, COD, and sodium ions (Na + ), which may be because of the short retention time of the experiment. Both the intensive and the extensive systems were inefficient in reducing the total bacterial count of the greywater.

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This study investigated the distribution of heavy metals in vegetative biofiltration columns irrigated by synthetic greywater. Twelve species of ornamental plants (three plants from each species) were planted in the same designed 36 biofiltration columns. Samples of effluent water, soils, roots, shoots and leaves were collected and analyzed. It was observed that before irrigation, the distribution of copper was in soils (0%), roots (42%), leaves (37%) and shoots (21%). After irrigation, this distribution changed to soils (29%), roots (39%), leaves (17%) and shoots (15%). It was found that lead concentrations decreased in soils from (84% to 7%), but increased in plants (from 16% to 93%) following irrigation with greywater. In contrast, the distribution of zinc changed from leaves (46%), roots (22%) and soils (16%) before irrigation to 89% in leaves and soils and 11% in shoots following irrigation. The chromium distribution before and after irrigation was found to be almost unchanged in soils, shoots and effluent water, but it increased in roots (19.4% to 26.9%) and decreased in leaves (11.4% to 5.8%). The outcomes of this study demonstrated that heavy metals mostly accumulate in soils and roots, and it is necessary to investigate their potential detrimental effects on the receiving environment.

Greywater recycling and reuse is becoming a popular choice in many water-scarce regions. Greywater is the largest component of domestic indoor wastewater. However, in many arid regions, including the United Arab Emirates (UAE), this unconventional resource is under-utilized. Although, traditionally, a biofiltration system operates using stormwater, findings have shown that the operation of biofiltration systems in arid regions can be successful using greywater. This research endeavors to assess how the quality of the effluent from a biofiltration system changes with different vegetation, both native and introduced to the arid region (UAE). The prototype biofilters, planted with twelve ornamental plant species, were irrigated daily with an equal amount of synthetic greywater and the water quality parameters were monitored on a weekly basis. Analysis of variance (ANOVA) was performed in order to statistically evaluate the consistency of results between the three replicates of each of the twelve species and, subsequently, the variation of treatment effectiveness among the twelve species with respect to eight water quality parameters.Most of the plants show a high degree of consistency between replicates; however, significant differences were observed across the selected plant species. The species Ficus nitida and Canna indica performed well in reducing pH. Except in the earlier stages of the experiment, all the systems were found to reduce turbidity by almost 100%. Overall, it was observed that Ficus nitida, Canna indica and Pennisetum setaceum performed well to improve greywater quality in the biofiltration columns.