Post-Treatment Of Desalinated Water

The use of synthetic membrane processes for desalination and production of drinking water has increased over the past five decades primarily in coastal areas with limited freshwater sources. Desalting techniques are primarily intended for the removal of total dissolved salts (TDS) that generally cannot be removed by conventional treatment processes. Water desalination had initially been used to produce or augment drinking water supplies through the use of evaporative or distillation methods. Beginning in the 1970s the water industry began to focus on commercially viable desalination applications using synthetic membranes. Today, reverse osmosis (RO), nanofiltration (NF), and electrodialysis reversal (EDR) are the most commonly used desalting processes for potable water treatment in the United States, typically treating brackish or impaired water supplies. Globally, many seawater RO water treatment plants (WTPs) have been operating successfully for more than 30 years (Redondo 2001. Busch and Mickols 2004). However, synthetic membrane processes produce permeate water depleted in minerals and often is found to be aggressive towards distribution system components. Moreover, the water produced by membrane processes is typically incompatible with existing water distribution system infrastructure. Post-treatment is thus needed for municipal water treatment before the membrane-treated water is delivered to the distribution system as finished water. Studies regarding the application and effectiveness of brackish and seawater desalination to augment drinking water supplies have focused primarily on pretreatment challenges, process optimization, energy efficiency and concentrate management; however, less has been documented with regards to post-treatment requirements, water quality and secondary impacts. The behavior of desalinated water in the distribution system remains largely non-documented, and potential issues that may arise after introducing desalinated water into existing distribution systems include impacts on internal corrosion control, disinfectants and disinfection by-products, hydraulics, infrastructure maintenance, water quality, aesthetics, and customer acceptance. This article discusses the post-treatment of synthetic membrane processes used for desalting drinking water supplies. 2009 © American Water Works Association WQTC Conference Proceedings. All Rights Reserved