Optimizing NF/RO Pretreatment at an Integrated Membrane Facility to Treat Challenging Florida Surface Water

Abstract

Lee County, Fla., owns and operates the 5-mgd Olga Water Treatment Plant. The plant treats Caloosahatchee River water for taste and odor, color, organics, hardness, and turbidity with conventional alum coagulation, flocculation, sedimentation, and granular dual-media filtration followed by granular activated carbon adsorbers. Powdered activated carbon is seasonally added upstream of coagulation to a dedicated contact basin to reduce taste and odor. For many years, seasonal salinity, taste and odor problems, and algal blooms in the river have negatively affected plant operations and caused regulatory concerns. As a result, the plant had to operate at reduced capacity and periodically received consumer complaints. A two-phase bench-scale testing program helped to identify and analyze water supply and treatment alternatives by assessing the benefits of pretreatment to reduce microfiltration (MF) membrane fouling and evaluating a combined pretreatment, MF, and low-pressure reverse osmosis treatment scheme.