Treatment of tunnel wash water and implications for its disposal

Abstract

The use of road tunnels in urban areas creates water pollution problems, since the tunnels must be frequently cleaned for traffic safety reasons. The washing generates extensive volumes of highly polluted water, for example, more than fivefold higher concentrations of suspended solids compared to highway runoff. The pollutants in the wash water have an affinity for particulate material, so sedimentation should be a viable treatment option. In this study, 12 in situ sedimentation trials were carried out on tunnel wash water, with and without addition of chemical flocculent. Initial suspended solids concentration ranged from 804 to 9,690 mg/L. With sedimentation times of less than 24 hours and use of a chemical flocculent, it was possible to reach low concentrations of suspended solids (<15 mg/L), PAH (<0.1 μg/L), As (<1.0 μg/L), Cd (<0.05 μg/L), Hg (<0.02 μg/L), Fe (<200 μg/L), Ni (<8 μg/L), Pb (<0.5 μg/L), Zn (<60 μg/L) and Cr (<8 μg/L). Acute Microtox(®) toxicity, mainly attributed to detergents used for the tunnel wash, decreased significantly at low suspended solids concentrations after sedimentation using a flocculent. The tunnel wash water did not inhibit nitrification. The treated water should be suitable for discharge into recipient waters or a wastewater treatment plant.

Microplastics in Terrestrial and Freshwater Environments

“…zinc, copper, cadmium, nickel) and organic pollutants (e.g. polycyclic aromatic hydrocarbons, organophosphates, octylphenols, phthalates) (Grung et al 2017;Hallberg et al 2014;Meland et al 2010a, b;Meland and Rødland 2018). Road runoff has received renewed interest in recent years due to the presence of particles with polymer components; it has been identified as one of the largest sources of microplastic particles in the environment (Baensch-Baltruschat et al 2020;Kole et al 2017;Wagner et al 2018).…”

“…Only a small fraction of these tunnels receives any kind of treatment of the tunnel drainage water, and most release the runoff directly into a water recipient (Rødland and Helgadottir 2018). Several studies have documented high levels of particulate matter in tunnel wash water (Hallberg et al 2014;Meland et al 2010a, b;Meland and Rødland 2018); however, there are very few that investigate concentrations of TWP or other microplastics in this matrix. It is expected that tunnel wash waters may be highly enriched in RAMP.…”

Occurrence of Tire and Road Wear Particles in Urban and Peri-Urban Snowbanks, and Their Potential Environmental Implications

“…Total particle concentrations have been reported for a range of environmental samples, such as roadside snow (5-12,700 mg/L: Moghadas et al (2015), Viklander (1999), tunnel wash water (8-31,000 mg/L, Meland and Rødland (2018), Hallberg et al (2014))) and sedimentation pond effluent (<15 mg/L, Hallberg et al (2014)). Compared to previous studies, the total particle concentrations found for the roadside snow in this study are significantly higher, from 1800 to 355,000 mg/L in meltwater and 6340 to 2,810,000 mg/m 2 .…”

Reducing the Release of Microplastic from Tire Wear: Nordic Efforts

“…The efficiency of the different basins as is not stated and may differ. Most basins are built for road runoff, and not for tunnels, even though tunnels are considered a hot-spot for road-related pollution (Grung et al, 2017;Hallberg et al, 2014;Meland & Rødland, 2018;Roseth & Meland, 2006;Åstebøl et al, 2011). Norway has in total 1229 tunnels registered in Vegkart, with more under construction and planning.…”