AWWA MTC64523

The City of Minneapolis, Minnesota, has just completed the procurement of the membrane system for the second of two low-pressure membrane treatment facilities. The resulting combined capacity of the two facilities is 165 MGD. This paper presents the results of the second procurement process and the associated performance testing results through which the membrane Equipment Contractor for the Fridley Membrane Filtration Plant was selected. The process employed by the Minneapolis Water Works (MWW) and the associated results are of significance to utilities seeking to implement membrane filtration through side-by-side competitive performance testing. The information in this paper will contribute to the water industry's knowledge base and assist in the piloting and design of future membrane filtration facilities. The development of a rigorous membrane performance testing protocol was an important component of the MWW process. Participating membrane pilot systems were operated strictly according to this protocol to demonstrate treatment efficacy and to establish the basis for comparison. The membrane testing units received the same feed water as the existing granular media filters. Pretreatment of the Mississippi River water for filtration involves softening and recarbonation (with powdered activated carbon addition) followed by chloramination and ferric chloride coagulation. Unique approaches were adopted in this program to demonstrate pathogen removal capability and allow flexibility in cleaning regimes. The MWW testing program has considerable applicability to other utilities, particularly those that draw from a surface water source with varying water quality. The key aspects of the performance testing protocol are briefly presented in this paper. The majority of the discussion will focus on the performance testing results with particular emphasis on the virus challenge test and applied cleaning philosophies. The test procedure and results for the virus challenge testing are presented. Virus removals of greater than 4 log were observed for all pilot units. Included in this discussion are the applicability of particle counting, turbidity monitoring, and direct integrity tests to assess long-term membrane system integrity monitoring. A comparison of the cleaning regimes, including changes initiated by the Equipment Contractors, are presented and the associated results discussed. The discussion provides an opportunity to evaluate the relative merits of chlorinated backwashes, performance-based cleaning initiation, and different chemical combinations and concentrations. Both chemical washes (frequent, low-dose cleanings) and clean-in-place (CIP) procedures (monthly, high-dose cleanings) were employed by the Equipment Contractors to remove fouling on the membranes. More effective cleans were achieved by adjusting chemicals, chemical concentrations, and cleaning intervals to reflect the changing feed water quality. Includes 3 references, table, figures.