Assessment of process water quality (depending on the presence of process water systems) in car wash facilities across Germany and the Netherlands

There are around 2,500 car wash lines in Germany, consuming around 30 million cubic metres of drinking water per year. In view of the increasing scarcity of water, this level of consumption could soon be restricted by law, as is already the case in some countries. There are only a few systematic studies on process water systems in car wash lines in Middle Europe; we therefore carried out a survey to determine process water quality parameters (COD, turbidity, water hardness, pH, conductivity, dissolved O-2, and temperature). Data were collected and analysed from 63 different locations in Germany and the Netherlands. In addition, longitudinal parameters were measured for 1 year at a single state-of-the-art site in Germany. The scatter of the observed values was quite considerable. The average COD in water of car wash sites with biological treatment was found to be significantly lower than in car wash sites working with filter treatment. Overall, the deviation of the pollution parameters was higher than expected. Surprisingly, there is hardly any reliable data on freshwater consumption in the car wash facilities. As most of the long-established facilities do not have a modern water treatment system, the freshwater consumption is up to 300 litres per car washed.