UV - Disinfection of Drinking Water – the new DVGW Work Sheet 94 Parts 1 –

Andreas Kolch* Managing Director and Partner, HYTECON GmbH, Humboldtstrasse 11, 32052 Herford, Germany Email: [email protected] DEVELOPMENT OF THE DVGW WORK SHEET The potential of UV for the disinfection of drinking water was clearly identified in Europe in the middle 1980’s, when a group of researchers and companies from Germany, Austria and The Netherlands collected data to establish a standard for a secured operation of UV systems in drinking water. This work was first published by the German Gas and Water Association in 1994 (DVGW 1994) as work sheet W 293. The content mainly focused on very substantial requirements for UV systems and its applications, and this first set of regulations are still valid in this form today. Three years later, the DVGW published the first W 294 version (DVGW 1997) with more detailed descriptions of the main technology requirements and even more important the first standardized concept for a full size equipment performance test for UV systems based on a bioassay standard using Bacillus subtilis spores. The main hurdle for a UV system was and still is the requirement to deliver a bioassay proven UV fluence of 400 J/m2 (40 mJ/cm2) continuously as a minimum over time and under all circumstances, such as transmittance changes or variances of flow. Parallel to the DVGW work sheet, a similar standard was established in Austria (ÖNorm 2001), which was subsequently expanded to cover medium pressure UV systems (ÖNorm 2003). For the first time it was now possible for engineers, operators and authorities to compare different UV systems from different vendors on a neutral and transparent base. Now ten years after the first publication, it was considered necessary to revise the work sheet on the basis of new experience which has been gathered. BACKGROUND Ultraviolet (UV) Systems for the disinfection of drinking water have gained increasing popularity as an alternative to chemical disinfectants on a worldwide basis. Following recent market data the annual growth rate of the technology is more than 10% per year and thus the use of UV is one of the fastest growing water treatment technologies. In the 1990’s, the process still had the image of being an option for small and medium sized water supplies, but projects in Canada and the United States have shown that UV can be the technology of choice for water supplies with flow rates more than 10,000 m3/h (240 ML per day or 63 MGD). One of the main drivers for UV, besides its environmental friendliness and economic application, is the large amount of available operational and research data, which makes UV disinfection one of the best documented of any disinfection process. However, in the phase of early applications of UV at beginning of the 20th century, UV seemed not to be a success story. After the first technical use of UV for water disinfection in France, the technology was forgotten for the next 60 years. But then it was ‘reinvented’ in the early 1980’s, when research looked for alternatives to chemical disinfectants, which had been shown to form carcinogenic byproducts, which are known to affect human health. Being an alternative at that stage, it became quite clear that the technical UV process had to be improved in terms of its robustness and cost. Standards were missing at that time and the transparency of the process made it difficult to find some early adapters using the technology. The new DVGW work sheet (DVGW 2006), which is a well known German standard for the operation of UV systems for drinking water, was published (in German) last year after a long-term review process. This updates the first DVGW UV Regulations published in 1997 (DVGW 1997). The structure and content of the work sheet has changed quite substantially from the 1997 version. The following review summarizes these changes and explains how to use the revised version with a focus on operators and engineering consulting companies as an effective working tool.