Integrating Membrane Treatment in Large Water Utilities

Microfiltration and ultrafiltration (MF/UF) have evolved into widely accepted methods of water filtration and disinfection. Their evolution from industrial applications began with filtration of clean water supplies not requiring pretreatment to use on waters requiring significant treatment prior to filtration. Cost and system design innovations have led to the increase in the size of MF/UF facilities. In recent years, retrofits of granular media filtration facilities with MF/UF have been explored by researchers, engineers, and system vendors in order to reduce the cost of implementing the technology. Several examples of retrofit facilities with varying degrees of existing infrastructure reuse exist; however, many of the retrofit projects do not reuse equipment common to both MF/UF and granular media filters. The objective of this project was to investigate potential cost-saving infrastructure reuse options for membrane retrofits of granular media filtration cells. Of key interest was the feasibility of retrofitting granular media filter cells with membranes operating within the hydraulic gradeline of the plant, essentially a direct exchange of media filtration with membrane filtration. Perhaps the most critical infrastructure reuse cost component requirement for the integrated membrane retrofits evaluated in the study was that all membrane related equipment fit within the limits of the existing filter building (membranes, racks, chemical tanks, and any membrane system specific equipment). The footprint of each membrane system was directly related to the maximum flow (flux) through an individual module while still meeting membrane performance criteria established for the project. In order to determine the maximum acceptable flux for each system, a 6-month pilot study was conducted at the Kansas City Water Services Department's 240 mgd lime softening plant. The results of the pilot study were then used to develop design criteria for each system and retrofit scenario, conceptual layouts, and cost estimates.