Expansion of Scottsdale Water Campus Reverse Osmosis System Using Large Diameter Technology

The City of Scottsdale is expanding the Advanced Water Treatment (AWT) plant at the Water Campus to provide up to 20 mgd of reverse osmosis permeate to be blended with tertiary effluent for irrigation at several golf course in north Scottsdale. The existing AWT has the capability to produce approximately 13.8 mgd of reverse osmosis permeate and uses standard 8-inch diameter elements in 14 units. In order to optimize capital cost and reduce building footprint, the City opted to use large diameter reverse osmosis (RO) elements for the expansion. The paper discusses the process for evaluating the cost impact of replacement of existing equipment with large diameter RO equipment as compared to expanding the building. This paper discusses in detail the design considerations that are involved in large diameter RO systems as compared to the 8 inch diameter system designs. Additionally, the paper discusses the current market and the costs, benefits and considerations for bidding two different RO train designs.