Treatment of tunnel wash water and implications for its disposal.
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.
Halfor AB, Ingrid Bergmans väg 15, 169 40 Solna, Sweden E-mail: magnus.hallberg@halfor.se.
M
M
Hallberg
Division of Land & Water Resources Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden.
G
G
Renman
Sweco Environment AB, 100 26 Stockholm, Sweden.
L
L
Byman
GS Ekotox AB, 194 46 Upplands Väsby, Sweden.
G
G
Svenstam
Swedish Transport Administration, 172 90 Sundbyberg, Sweden.
M
M
Norling
D004784:Environmental Monitoring; D006863:Hydrogen-Ion Concentration; D014186:Transportation; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D014874:Water Pollutants, Chemical