AWWA MTC69791

The City of Phoenix is planning the Western Canal Water Treatment Plant (WTP) to meet future population growth in the southwest planning area of the City. The major consideration for the water supply in the area is the finished product water quality which will be impacted by the highly variable feedwater sources that would supply the water treatment plant. Of major importance to the project is the limited control the City will have over the water quality they receive at the WTP, and therefore must plan for significant operational flexibility in the process selection. The major treatment objective of the WTP is to provide a water supply that meets the Stage 2 Disinfection/Disinfection Byproducts Rule and the Long Term 2 Enhanced Surface Water Treatment Rule, and to remove Total Dissolved Solids to a target level of 700 mg/l. The system will use a combination of pretreatment solids removal, granular activated carbon, microfiltration, primary reverse osmosis, lime precipitation processes on the primary RO concentrate, concentrate treatment RO systems and ultimately concentrate treatment systems. In 2007, as part of the planning process for the WTP, the City embarked upon a 12 month pilot program to demonstrate the major process components. The pilot consisted of microfiltration pretreatment (for surface water only), primary RO, solids contact lime clarification, and secondary RO on the lime treated concentrate. This pilot study would build upon a previous high recovery RO pilot study as part of a Bureau of Reclamation project. The pilot system was designed to operate on groundwater from a local well for a period of 3 months. Following the initial 3 month test, the pilot would then be operated on a surface water supply and then return to groundwater for a final 3 month test. The initial bench testing for assisting in selection of the appropriate membrane was started in November 2007. Initial pilot testing started in April 2008 and will be completed in early 2009. This paper discusses the design and current operation of the WTP Pilot System, and specifically focuses on the bench testing and pilot testing results for the RO systems. The paper highlights the importance of a good pilot testing system design to match as closely as possible the full scale system and how the pilot information will be used in the water treatment plant design. Includes 2 references, figures.