AWWA ACE60077

The Water Supplies Department (WSD), the Government of the Hong Kong Special Administrative Region (HKSAR) of the People's Republic of China (PRC) recently completed an investigation showing seawater desalination could be a secure, long-term source of freshwater and that reverse osmosis (RO) is the most cost-competitive method of desalination. As a result of this investigation, the WSD has undertaken a 30-month study to establish technical, engineering, environmental, and budgetary information required to reach an informed decision on how best to implement seawater RO desalination. The scope of the study includes: identifying prospective plant sites and conducting pilot trials to define RO design requirements at two sites; identifying the most effective RO pre- and post-treatment processes; and, developing capital and operating cost estimates for one or more full-scale facilities. The pilot program is comprehensive and will involve testing for a continuous 12-month period at two separate locations (24 months total) selected to represent the two types of water quality characteristics of Hong Kong's marine geography: western region quality comprising variable salinity and turbidity influenced by runoff from the Pearl River; and, the eastern region more representative of open ocean water. Further, the program will include water quality sampling at four additional marine locations to allow a comparison of water quality at six different areas of Hong Kong for future plant site considerations. A unique aspect of this pilot program will be the ability to assess the relative performance of microfiltration /ultrafiltration (MF/UF) with conventional granular media filtration for seawater RO (SWRO) pre-treatment. Each test site will be equipped with three individual SWRO trains, each of which is preceded by a different pretreatment system. Pre-treatment systems to be simultaneously compared include pressurized MF/UF, submerged (or immersed) MF/UF, and two-stage granular media filtration. In addition, each SWRO train will include equal numbers of membrane modules from three different SWRO membrane manufacturers. This combination will allow independent evaluation of each pre-treatment system in combination with each type of SWRO membrane. This paper presents the many design issues considered throughout the site selection and pilot plant design process evaluated to provide WSD with the information necessary to cost and implement SWRO facilities and will describe the piloting protocol, specific test objectives and the design and operation of MF/UF and SWRO systems used in the testing. The information will benefit utilities and the wider water industry who are interested in how SWRO desalination can play a role in supplementing water resources and serve as an alternative supply of potable water. It will also identify the issues and costs that must be considered in implementing a desalination program. Includes tables, figures, appendices.