Treatment of road run-off water in Sweden : Problems and possibilities

The conditions for handling of run-off water differs notably compared to the handling of potable water, sewage water and industrial effluent water. For conventional water treatment the time variations of flow and quality of the contaminated waters is well established and known. The legal aspects for conventional water production and treatment are clearly defined and not ambiguous. This is not the case for handling and treatment of run-off water. In the EU directive 1991/271/EEC run-off water is defined as sewage water. The EU Water Directive refers to 1991/271/EEC and points to run-off water as a pollutant source for ground water. Elevated levels of pollutant can be found in run-off water from catchment areas with dense traffic loads. Depending on road maintenance, use of studded tires, type of pavement, traffic load, velocity, type of vehicle, residential and industrial areas, tunnels the degree of mobility of the pollutants will vary in the ambient air and the run-off water. An aspect that only to some extent has been elaborated on is the influence of pavement types and its wear in regards to the mobility of the pollutants. A treatment technique commonly used in Sweden is storm water ponds. The pollutant removal efficiency varies for different ponds, due to different specific pond areas, i.e. pond area in relation to catchment area. Ponds act as sedimentation basins, collecting particles and bounded pollutants. However, the solute transport of e.g. heavy metals should be trapped by other means. A filtration unit has been developed and tested in Sweden.
QC 20120221