3P Technik Filtersysteme GmbH, a specialist in local rainwater treatment, has developed a product portfolio that targets "environmentally friendly ways to make good use of water." Its technology for cleaning rainwater won it the GreenTec Award in 2013.

Rainwater that accumulates on roads, parking lots and rooftops is usually contaminated with heavy metals such as cadmium, zinc, lead, ammonium and/or polycyclic aromatic hydrocarbons (PAHs). 3P's Hydrosystem prevents these pollutants seeping into groundwater via the soil or through the sewer system. The Hydrosystem can be scaled up or down depending on the size of the space to be treated and the level of pollution. It can also be fitted with a variety of filters. The Hydrosystem 400, for instance, is ideal for spaces of up to 175 m2. Since it can be sunk into the ground, it takes up virtually no room – a tremendous advantage in inner-city locations, where space is at a premium.

An upflow process drives the rainwater through the filter elements. First, it flows through an inlet pipe into a hydrodynamic separator. Gravity and sedimentation lead to a "teacup effect", causing solid particles – mostly sand – to settle in the silt trap below the separation chamber. The silt trap can be emptied via an outlet and removed for cleaning. The filter element is positioned above the separation chamber and covers the full width of the shaft.

Pressure from the incoming water volume forces the rainwater up through all the filter elements. This is where the principal steps in the treatment process take place. Filtration – the first step – keeps about 98 percent of all solid particles with diameters of more than 0.4 millimeters in the chamber. Sedimentation then causes these particles to settle in the silt trap. Adsorption binds heavy metals, before precipitation – the third chemical reaction in the filter substrates – transforms the molecules so that they become insoluble, are adsorbed, or experience sedimentation. Phosphorus, for example, is bound in this way. Following these treatment processes, rainwater exits the Hydrosystem via an outlet and can be returned to the natural hydrologic cycle.

3P Technik Filtersysteme GmbH also sells its local rainwater treatment technologies abroad. Headquartered in Donzdorf, Baden-Württemberg, the company has a presence in Europe, North and South America and a number of Asian countries.