Effective technology for treating surface water

New generation of treatment technologies

The next generation of river basin management plans will ensure cleaner watercourses and lakes in Denmark. The prospect of more rainfall, and with this the discharge of more contaminated surface water into receiving water bodies such as harbours, lakes and watercourses, calls for new and effective treatment technologies. This is particularly relevant for cities where the water cannot be conveyed into large basins where contaminants can settle. Contamination from surface areas typically stems from roads, pavements, car parks, etc., from cars directly, and from animal excrement.

The Danish company HydroSystems is behind one of the new treatment technologies on the market. In collaboration with HOFOR, a Danish utilities company, HydroSystems has adapted its HydroSeparator for use in harbour areas in the Copenhagen; a previous industrial port currently under intense residential development, which places stricter demands on the water bodies. Extensive measurements have been carried out on the effectiveness of the HydroSeparator; primarily with regard to treatment of surface water runoff from roads.

Good test results

Bonnerup Consult has tested seven HydroSeparators in collaboration with HOFOR. The separators are located at Holmen, Sluseholmen and Teglholmen in the Port of Copenhagen. Since 2008, with adjustments along the way, the HydroSeparator devices have been treating surface water runoff from the harbour areas. The measurement results show a treatment effect on suspended substances of 50-80% and a similar effect on a number of environmentally hazardous substances. The discharge values for suspended substances are 20-30mg/l. The devices are contributing to keeping the port water clean, so that the port can be used for recreational purposes, such as bathing.

In addition to the installations in Copenhagen, the HydroSeparator has also been installed in the Municipality of Middelfart. Here, it treats the surface water runoff before it is conveyed to the receiving water body. As a result, the receiving water body is receiving far fewer contaminants from sewers. Furthermore, the quality of the bathing water has been improved where the surface water runoff is led out into the sea near recreational beaches.

The HydroSeparator is fully automatic and self-cleaning and therefore requires only limited maintenance. The device is relatively small and can be installed below ground. This makes it easy to find space for a HydroSeparator. The device requires connection to a power source and to the wastewater/sewage system. Furthermore, a permit from the Danish environmental authorities is required in line with the permit required for other situations involving output to receiving water bodies.

Several known technologies in one solution

The HydroSeparator combines several integrated cleaning and treatment solutions. First, a basin retains the most contaminated water in a tank. The water passes through a lamellar structure and is cleaned for all large particles, while a fine-meshed filter takes care of the smaller particles. The tank is emptied and the water is pumped into the sewage system after each downpour. Then the tank is hosed down with the treated water, making it ready for the next downpour. The solution can be fitted so that the relatively clean surface water passes by the HydroSeparator in the event of prolonged rainfall events. The standard capacity is 5 litres per second, but the HydroSeparator comes with a capacity of up to 200 litres per second. With integrated bypass functionality, the HydroSeparator can manage up to 4,000 litres per second.

The HydroSeparator also has a PLC (Programmable Logic Controller) and can be connected to a remote monitoring system. The HydroSeparator can therefore be operated by remote control, so that the best possible treatment and cleaning effect can be achieved during both normal and extreme rainfall events.

Operating costs are an important parameter

According to HydroSystems, the acquisition price of a HydroSeparator is around DKK 200,000 or more, depending on the device's capacity. The total annual operating costs are assessed to be less than DKK 1 per m3 rainwater, including depreciation.

According to Jes Clauson-Kaas from HOFOR, "operating costs are an important parameter for utility companies".

"Jointly with DHI, we are in the process of deciding e.g. on criteria for conveying water runoff to harbours, lakes and watercourses in the Greater Copenhagen area. We already have a close eye on new, emerging technologies, but operating costs and treatment efficacy will undoubtedly be more important than the acquisition price when we decide whether to invest in treatment technologies," said Jes Clauson-Kaas.