Stockholm waterworks turns to UV disinfection technology
Wedeco AG Water Technology, a manufacturer of water disinfection systems based on ultraviolet (UV) light, has won a major contract in Sweden in the drinking water sector. Wedeco AG Water Technology, a manufacturer of water disinfection systems based on ultraviolet (UV) light, has won a major contract in Sweden in the drinking water sector. The Lovö waterworks in northwest Stockholm will make use of UV technology to disinfect drinking water.
The Stockholm waterworks operator (Stockholm Vatten AB) plans to drastically reduce disinfection with chloramine, which has been the method used at the plant since 1942, and to rely on the more environmentally-friendly UV disinfection method. According to the Swedish company, all forms of chlorination result in undesirable secondary products such as THM (trihalomethanes) and AOX (adsorbable organic halogens). These compounds can only be eliminated from drinking water at considerable cost. Also, easily degradable organic compounds are formed during chlorination. These compounds can cause regrowth problems in the distribution net.
The Lovö waterworks supplies an average of 144,000 cubic metres of drinking water each day to around 200,000 households. The water is taken directly from the Lake Mälaren, approximately 17 km out of Stockholm´s centre. The surface water is passed through a treatment cascade. After the raw water has been subjected to micro sievers, chemical precipitation, sedimentation and sand filtration, its pH is adjusted and it is then disinfected. Microorganisms are frequently found in surface water and must therefore be killed to protect consumers.
The UV unit consists of two K-type reactors arranged in parallel that can handle a maximum flow of 6000 m3/h. The reactors can be operated alternately or in parallel, depending on requirements. Several hundred low-pressure Spectrotherm lamps with an output of 200 J/m2 ensure that the water is continuously disinfected. The system can be upgraded with additional rows of lamps to achieve the usual European output level of 400 J/m2 (based on DVGW, SVGW and ÖNORM guidelines). The reactor performance and thus the effectiveness of the disinfection are continuously monitored by UV sensors.
The system is scheduled to become operational in October 2001. Installation work will start in the spring.