Jonathan Clement – författare

Wastewater and drinking water treatment are essential elements of urban infrastructure. In the course of the last century there has been enormous technical development, so successful that for the general public in industrialized countries this infrastructure is hardly noticed. Nevertheless there is ongoing activity to further improve the existing processes. The IWA Leading Edge Technology conference held in Prague helped to stimulate this development and this book helps disseminate the results. A selection of presentations from the conference are included in this volume. Wastewater and drinking-water treatment are normally considered as two separate fields due to the very different boundary conditions that apply. Nevertheless several issues such as membrane processes, removal of micropollutants and water reuse are of crucial importance to both. This potential for cross-fertilization further enhances the value of this collection of high-quality articles that delineate the leading edge of research and development in water and wastewater treatment.

Chlorine has been used in the treatment of drinking water in the United States since 1908. Since the Safe Drinking Water Act of 1974 and its amendments, utilities around the country have made changes to their disinfection strategies to meet more stringent regulations for either microbial contaminants or disinfection by-products (DBPs). Specifically, utilities have investigated and implemented the use of alternatives to chlorine. Consequently, ozone and chlorine dioxide have been tested and applied at treatment plants for primary disinfection, and the use of chloramines has increased for secondary disinfection.? While it is well accepted by many in the drinking water community that many of these changes will have beneficial impacts, it is not well known how these changes in disinfection will affect distribution system water quality in the long term. Based on a comprehensive literature review and the experience of 26 participating water utilities, potential positive and adverse water quality impacts were identified and summarized when changing from chlorine to either chloramines, ozone, chlorine dioxide, or ultraviolet (UV) light. The data indicated better microbial quality, such as lower coliform levels and heterotrophic plate counts (HPC) and reduced levels of disinfection by-products like trihalomethanes and haloacetic acids. Disinfection changes also led to reduced numbers of customer complaints regarding red or discolored water and tastes and odors. However, two of the more common adverse impacts included some higher HPC levels when using chloramines or ozone and nitrification when using chloramines.?

This study has shown that higher levels of carbon supported greater biofilm growth and planktonic populations on the materials that were tested, although the effect was most pronounced on iron pipe. Utilities with significant amounts of iron pipe in their distribution systems may be faced with the greatest regrowth potential. For utilities that also distribute water that is high in natural carbon, this problem may be compounded. Therefore, reducing the organic carbon in the finished water may be effective for any utility wishing to reduce regrowth problems in their distribution system. Other alternatives for utilities wishing to reduce biofilms in the distribution system can include any or all of the following: replacing or relining iron pipe in the system, increasing disinfectant, and implementing effective corrosion control.? Originally published by AwwaRF for its subscribers in 2003 ? ?

When water leaves a treatment works and travels through a distribution system, its quality, with respect to many chemical and biological parameters, will degrade. The quality of the delivered water will be largely influenced by: The quality of treated water supplied into the network   The condition of distribution assets within the network   The retention time within the network. The water industry has focused predominantly on the quality of treated water and the physical condition of distribution assets when improving the quality of water at the customer?s tap. However the quality of the water delivered is also affected by the time the water is retained in the different elements of the distribution network. Retention time is controlled both by the physical characteristics of the system and the operational regime. Physical characteristics such as pipe roughness may change throughout the life of the asset or be modified by rehabilitation. The aim of this research is to demonstrate that water quality within distribution networks can be managed effectively by controlling retention time and to develop practical and pragmatic methodologies for doing so.