Chemicals are added throughout the treatment process.
Time for an Upgrade
In 2013, Flagler County purchased the facility with the goal of improving water quality and bringing the plant back into regulatory compliance. To determine the best treatment solution, the county prepared a weighted treatment decision matrix to study potential alternatives.
Based on results from the evaluation, nanofiltration (NF) was selected for implementation to remove organics, color and hardness, and to reduce DBP formation potential. Concurrent with preliminary and final design, a pilot study was conducted using the well with the highest organics and color.
Based on the pilot testing and the design team’s experience with other facilities with similar water quality, the treatment processes will include oxidation, pressurized multimedia filtration, dechlorination, pH adjustment, antiscalent, cartridge filtration, membrane softening, permeate stabilization and disinfection. The system will include a two-stage NF system with an overall recovery of approximately 80%. A partial NF bypass stream is planned and will be used to add pH and alkalinity to the permeate water, resulting in lower chemical usage and operational costs. Because the chloride levels of the water supply are so low (approximately 25 mg/L), the concentrate from the NF system will be beneficially used for reuse water irrigation with no damage to plants, grass and other landscaping. The concentrate will be blended with the reclaimed water to supplement the county’s reclaimed water system that is used to irrigate the Plantation Bay Country Club. This approach to concentrate reuse also provides the benefit of eliminating the need for deep well injection or surface water discharge.
The new treatment facility will include a membrane softening process designed to remove hardness, organics, color and other contaminants. The NF process will include three skids capable of producing a combined 756,000 gpd of finished water. The process will be expandable to 1 million gal per day as demands increase. A brief description of the major components of the reverse osmosis (RO) process is as follows.
An inline booster pump station will be constructed and will include three pumps to provide ample feed pressure to the pressurized filters so that a minimum of 20 psi is available at the suction side of the NF feed pumps.
Three vertical pressure filters will be installed upstream of the RO skids as a means of pretreating the raw water. The filters will mainly serve to remove iron so as to mitigate iron fouling, which typically occurs on the lead elements of the first NF stage. Sodium hypochlorite will be used as an oxidant to aid in iron removal.
Via a membrane separation process, the NF membranes will treat the filtered water to meet all drinking water standards. NF will remove the color and allow some hardness and alkalinity to pass through the process, thereby reducing costs associated with post-treatment stabilization. The NF skids will include 5-µ cartridge filters to further protect the membranes, and high-pressure feed pumps to provide approximately 90 psi at the membrane inlet. A clean-in-place skid will provide for periodic cleaning using high pH solutions for biofouling and lowering pH solutions to remove scaling.
