Editorial: Urban runoff of pollutants and their treatment

Abstract

Floods are one of the most common natural disasters worldwide. Their increasing incidence in the past years is mainly due to the consequences of climate change coupled with a general trend of the increase of surface impermeabilization in the cities. In particular, the past years’ rapid urbanization and human land use originated environment modification, with consequent surface modification: in the urban area, most of the surface is covered by buildings and impermeable pavements, which strongly limits snowmelt and rainwater infiltration into the subsurface. However, floods are sometimes predictable events (Enríquez et al., 2022). To account for the vulnerability of a territory, due to extreme events, patterns of development coupled with demographic studies are considered. As a result, the score of flood risk is available as a risk index, evaluated by a dedicated committee of the European (European Commission, 2022). The 2022 flood risk is shown in Figure 1. It appears that only a few countries have a relatively low risk (less than 5), and Vietnam and Bangladesh are the countries with the higher flood risk (the index score is 10). Urban runoff is water deriving from rain and outdoor water usage, comprising stormwater and snowmelt, which drains from roofs, roads, car parks sidewalks, driveways, and other surfaces, and does not soak into the ground. It is widely recognised as a major carrier for the pollutants transport and release in the urban environment. Therefore, it also represents a significant contributor to the degradation of surface water bodies (EPA, 2003). As a consequence, urban runoff is one of the key pathways in the transfer of pollutants to the aquatic and marine environment. The contaminants associated with urban runoff can be divided into different categories such as heavy metals, solids, toxic chemicals, biodegradable organic matter (chemical or biochemical oxygen demand COD/BOD), organic micropollutants (among them polycyclic aromatic hydrocarbons PAHs, polychlorinated biphenyls PCBs), pathogenic microorganisms (such as Escherichia Coli), nutrients (nitrogen and phosphorus) and microplastics (Wei et al., 2013; Piñon-Colin et al., 2020). For example, Wang et al. (2022) reveal that the concentrations of microplastics in urban stormwater are much higher than those found in wastewater effluents. The source of pollutants can be natural (soil, leaves and organic debris) or anthropogenic (construction materials, exhausted particles, roadway debris, fertilizers, and so on) (TrujilloGonzález et al., 2019). Generally, the road deposited sediment represents one of the primary contaminants contributors to urban runoff (Piñon-Colin et al., 2020). In the worst cases, when the stormwater collection is in connection with the sanitary sewage system, an accidental release of raw sewage may also happen because of important precipitation events, with the result of dramatic environmental and economic impacts. OPEN ACCESS