Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review

Urban rooftops covered with plants known as green roofs or vegetative roofs have recently attracted intense research interest because of their unique benefits and recognition in various countries as a potential best management practice. However, most of these benefits are just theoretical assumptions, and only few research efforts have been performed to draw a definitive conclusion. Of these, the quality of runoff from vegetative roofs often comes under debate. Hence, this critical review article primarily focuses on the quality of water from vegetative roofs, as well as directions to achieve better quality runoff. This review briefly introduces the fundamentals and benefits of vegetative roofs, followed by the quality of runoff as observed by other investigators. Until now, the vegetative roof substrate and plant types have not been selected based on their potential to decontaminate runoff. To improve the quality of runoff, we highlight the necessity to consider the sorption capacity of the substrate and phytoremediation potential of plants. For the first time, various sorbents that can be used as additives in the vegetative roof substrate, as well as practical plant species that can phytoextract contaminants in the substrate are presented. Some recommendations regarding the future research are also provided.