Swedrop’s unique storm water filters manage pollution as close to the source as possible. The filters float in the storm water drain, purifying both incoming and already present water from more than 30 pollutants.

The EU water framework directive clearly states that our waters are to be clean and unpolluted. The directive sets minimum objectives for EU countries in terms of water quality and access to good quality water in sufficient quantity. One of the sources of water pollution is storm water – that is, rainwater and runoff from yards, streets, roofs, industrial lots and other sites.

Storm water may be polluted by vehicle emissions, pollutants in the rain water, oil and heavy metals. Swedrop’s storm water filter absorbs more than 30 different substances in a three-stage process. Photo: Swedrop.

”Ensuring water quality is a challenge, and we have developed a unique storm water filter, patented in 40 countries, to prevent harmful substances from reaching lakes or streams. We want to treat the water cost-efficiently, as close to the source as possible”, says Bengt Jäderberg, Chief Communications Officer at Swedrop.

How the filter works

”Rainwater is channeled into the filter by a funnel placed right below the stormwater drain. This simplifies maintenance, since sand, leaves and twigs are directed outside of the filter and end up in the sludge trap. The filter fits all kinds of storm water drains, and purifies the water in a three-stage process”, Bengt Jäderberg says.

The first stage captures hydrocarbons, oils and certain organic solvents, by means of a polypropylene fibre filter. The second stage uses granules of activated carbon to filter out heavy metals. The granules have a very large active surface area, that adsorbs ions of chrome, copper, led, zinc and other elements that commonly occur in runoff from roads and parking lots. The ballast is five kg of blast furnace slag, with great capacity to absorb heavy metals, phosphorus and ammonium.

In the third stage, both the surface water and the standing water in the drain is purified, thanks to the fact that the filter floats. According to Swedrop, the filter maintains it capacity for a year, and is then easily replaced with a new one with a quick operation. The used filter is collected for incineration, in order to remove the pollutants from the water cycle.

Minimized cost

The floating storm water filter purifies both the incoming rain water and the standing water. Photo: Swedrop.

”Our solution is simple and low-weight, which makes handling, transport and maintenance easier. The shape and the fact that it floats makes sure that it purifies both the incoming rain water and the water that is already present in the storm water system. We see many benefits over conventional filters, such as:

  • The floating filter does not obstruct water flow. Most of the incoming water goes through the filter capsule and out on the side of the float. When flow is high, more of the incoming water can pass through, without reduced flow capability.
  • When it is not raining, the filter continues to treat surface and standing water, removing oils and other contaminants.
  • An independent laboratory (ALS Scandinavia) has evaluated the filter’s capacity to adsorb 33 substances that are prioritized according to the water directive. Ten of the substances were removed by more than 90 percent. Thirteen of the pollutants had removal rates of 51-90 percent. The remaining substances, except for one, were reduced 5-50 percent.
  • The filter is simply dropped in the drain, and the used filter is removed and sent to a proper incineration facility. RFID-tags makes it possible to monitor the filter throughout the life cycle, and to verify that it is properly disposed of.
  • To minimize maintenance cost, the filter exchange operation can be combined with the regular sludge removal from the drain”.

”We believe that it is essential to clean storm water cost-efficiently. Many conventional methods have substantial deployment costs and require continous maintenance. A simple, disposable absorbing filter that is dropped into the drain dramatically changes the cost structure of cleaning storm water at the source.

The purpose of the EU water directive is of course to ensure water quality, but it also creates a business opportunity for companies that develop efficient water treatment technologies”, Bengt Jäderberg says.

The article was published in April 2017.