AWWA WQTC59024

To help meet the future water needs of eastern Central Florida, a treatability study is being conducted by the St. Johns River Water Management District and CH2M HILL to quantify the treatment requirements and costs for a potential surface water treatment facility to be located along the reach of the St. Johns River between the southern end of Lake Monroe in Sanford and De Land. This pilot study will identify the feasibility, appropriate use, treatment technologies and costs to use surface water to offset groundwater demands. The St. Johns River water has typical surface water characteristics for Florida. The characteristic dark brown color of the water is due to the organics in the water. These organics are mostly dissolved humic and fulvic matter. Total organic carbon concentrations are often in excess of 30 mg/L with colors exceeding 400 Pt-Co. Additionally, the St. Johns River has unique characteristics due to the brackish content of the water. This brackish surface water has total dissolved solids (TDS) concentrations ranging from 400 milligrams per liter (mg/L) to 1,060 mg/L and chloride concentrations ranging from 139 mg/L to 455 mg/L. Because of these unique characteristics, partial desalting must be used along with conventional treatment. Selecting treatment technologies for any water treatment system is driven primarily by drinking water regulations and the meeting of consumer expectations. For surface water treatment, the primary regulations are the Enhanced Surface Water Treatment Rules (ESWTR) and the Disinfectant/Disinfectant Byproduct (D/DBP) Rules. The planning process for any treatment facility on the St. Johns River has a 5- to 10-year window. Therefore, upon construction of this facility, compliance would likely be required for the Long Term 2 (LT2) ESWTR and Stage 2 D/DBP rules. The approach to meeting these regulations is multi-barrier treatment involving the following unit processes: coagulation and flocculation; clarification; filtration; and, disinfection. This approach requires each process to remove waterborne pathogens, with each process operating at a high rate of efficiency. The effectiveness is cumulative, in that each unit process helps the subsequent unit process work more effectively than if operated alone. The basis and goals of the pilot testing was to evaluate pretreatment of the raw water for particle and organics removal. The pretreatments were further evaluated with respect to reverse osmosis membrane performance based on the pretreated water quality. Pilot testing consisted of several different phases, each with different goals. During the first phase, Phase 1A, pretreatment systems were evaluated based on treated water quality and reverse osmosis membrane response. The following three pretreatment systems were evaluated during Phase 1A: the Super Pulsator (SuperP) blanket clarifier followed by dual media gravity filtration; the Actiflo micro-sand ballasted clarifier followed by dual media gravity filtration; and, the Zenon immersed ultra-filter with coagulation in tank. Based on the results of Phase 1A, all three pretreatment systems were determined to be viable pretreatments for reverse osmosis membrane systems. The goal of the second phase of testing, Phase 1B, was to compare the four different membranes and select the best performing membrane for further testing in a multi-element high recovery system. During Phase 1B, the SuperP/media filtration pretreatment was used for pretreatment to the following four single element membranes: Filmtec BW30FR; TriSep X-20; Hydranautics LFC1; and, Osmonics SG. This paper summarizes the results of the Phase 1B lead element membrane selection. Includes tables, figures.