Stormwater quality, pollutant sources, processes, and treatment options

Increasing urbanization is a common phenomenon around the world, which results in the conversion of previously vegetated areas into impervious surfaces. Natural sources and anthropogenic activities common to urban areas deposit a range of physical, chemical, and microbial pollutants on these impervious surfaces. These include, gross pollutants, sediments, nutrients, oxygen-demanding waste, metals, hydrocarbons, and microbial pollutants. These pollutants undergo continuous physical and chemical transformations after deposition, which will result in changes to their toxicity, mobility, and bioavailability. These transformations are due to factors such as abrasion by vehicle tyres, resuspension by wind turbulence, and exposure to atmospheric moisture and photolysis. Pollutant deposition or build-up and consequent pollutant wash-off with stormwater runoff results in the discharge of pollutants to receiving waters, often exceeding their assimilation capacity. Additionally, the presence of impervious surfaces and hydraulically efficient stormwater conveyance systems result in the discharge of increased stormwater runoff volumes. The quality and quantity impacts on stormwater due to urbanization are influenced by a range of factors, including, urban form, land-use activities, traffic characteristics, and climate characteristics. These impacts pose a threat to human and ecosystem health. Mitigation of these adverse impacts is essential for improving receiving water quality and thereby human well-being. In the context of safeguarding urban water ecosystems, Water Sensitive Urban Design (WSUD) offers an effective solution where a range of devices are available for targeting specific pollutants. However, the design of WSUD devices is constrained by the lack of understanding of how natural and anthropogenic factors influence the underlying mechanisms of pollutant export, transformation, and removal. Furthermore, stormwater pollutant processes and treatment performance of WSUD devices are expected to be significantly influenced by the predicted impacts of climate change. Consequently, it is important to quantitatively assess the changes to stormwater quantity and quality, and the resulting performance of WSUD devices to ensure adaptability to a changing climate.