AWWA WQTC64171

The City of Scottsdale (City) plans to expand the Central Arizona Project (CAP) Water Treatment Plant (WTP) by adding 30 MGD for a net total production of 80 MGD. As part of the treatment process selection and conceptual design for the 30 MGD expansion, a detailed evaluation of the various alternatives was conducted. A workshop-based approach was used to identify thirteen configurations, short-list to four alternatives, and select a treatment process train. Ultimately, a side-stream treatment (referred to as Plant III) consisting of high rate clarification and membrane filtration (MF) was selected as the most appropriate process configuration for the plant expansion. Initially, dissolved air flotation (DAF) was selected as the high-rate clarification; however, during the pilot testing, the clarification technology was expanded to also include sand ballasted flocculation (SBF). A five-month pilot study was conducted at the CAP WTP to evaluate the performance of clarification and membrane filtration technologies and to establish operating parameters for the design of the proposed 30 MGD plant. The clarification technologies tested consisted of two DAF systems and sand ballasted flocculation (SBF). Note that the SBF was introduced later in the pilot testing program and was only tested for approximately one month. Five membrane manufacturers submitted their Statement of Qualifications (SOQ) for participation in the pilot program. After review of the SOQs, three membrane systems were selected for the pilot testing. The entire pilot project was divided into two phases. Phase I consisted of optimization of operating parameters followed by long-term operation of the DAF and membrane units. After the completion of the initial optimization phase, the DAF systems operated in a near steady-state mode to minimize the variations in the water quality feeding the membranes systems. The MF units participated in two consecutive flux confirmation tests with a chemical clean performed between the two tests. Phase II was the extended pilot period to test the DAF and SBF units under ambient and artificially elevated turbidity conditions. Includes tables, figures.