Just Another Day at the Beach
Membrane systems help expand Palm Beach County Water Treatment Plant
The Palm Beach (Fla.) County Water Treatment Plant #3 needed to expand capacity to meet the increasing demand of a growing population.
Located in Delray Beach, the plant had a 10-year-old reverse osmosis (RO) membrane system and an even older conventional lime softening system.
Together, these systems were insufficient for near-term demand and they fell far short of the projected future needs for this fast-growing community.
The RO system performed satisfactorily, producing approximately 10 mgd, but it needed updating and the membrane elements were due for replacement.
The county’s consulting engineering firm, Camp Dresser & McKee, recommended against investing any further in the aging systems.
Instead, it recommended installing a completely new 25-mgd RO system to replace both the existing RO system and the lime softening system.
Having used both an RO membrane system and a conventional lime softening system at the Delray Beach plant, Palm Beach County officials understood the advantages of membrane separation technology in potable water production.
Reliable and automated
Palm Beach County officials chose to deploy an RO membrane system to achieve the 25-mgd capacity because membranes have proven more reliable and automated than conventional filtration methods, and because they provide a positive physical barrier between contaminants in the feedwater and the purified product water.
Membranes can also meet new municipal water requirements with few chemical additives and no sludge disposal.
During the qualification process for the new RO systems, three membrane manufacturers conducted pilot tests. According to Palm Beach County officials, the Fluid Systems TFC-S element from Koch Membrane Systems (KMS) was able to meet the specifications best.
“Unlike the other two vendors, the KMS membranes did not foul,” said Dennis Ford, chief operator at Palm Beach County Water Treatment Plant #3. “After a few weeks of piloting, the other vendors’ elements showed significant increases in pressure drop and decreases in productivity, while the KMS elements continued to perform well. After the pilot, it was not difficult to decide to go with KMS.”
The KMS element utilizes a proprietary Thin-Film-Composite polyamide membrane, which achieves 98% hardness rejection. This element was specifically designed as a cost-effective and energy-efficient solution for municipal water treatment when softening and reducing trihalomethanes formation potential are the main objectives.
The spiral wound construction of the element provides membrane packing area with a low cost per square foot. The element is housed in a fiber-reinforced polymer outerwrap.
The new RO system at Palm Beach County Water Treatment Plant #3 uses TFC–S elements with an 8 in. diameter and a 40 in. length, for a membrane area of 400 sq ft per element.
Advanced Environmental Water Technologies constructed the 10-train system. The 61 pressure vessels each contain seven elements, for a total of 4,270 TFC–S elements. Poole & Kent served as general contractor for the project.
The installation was an enormous logistical challenge. The new RO system was installed and commissioned, while the old systems continued running in the same general proximity within the plant. The migration took place in stages, as controls, power supplies and pumps were switched to the new system. The new system was brought into service, and the old systems were removed, without depriving citizens of water during the entire process.
“I am surprised at how well things have gone, considering the complexities of pulling this project off,” Ford said, who has been responsible for the day-to-day operation since the beginning of the project. “And everything continues to run quite well.”
The new system has been in operation since the summer of 2004.
Due to a shortage of well capacity, the plant can operate only a maximum of seven trains at any given time. The plant is rotating all 10 trains, on a daily basis. Three additional wells are expected to be available by the end of 2005, and at that time, the plant will run at full capacity.
The RO system has been economical to operate, utilizing minimal energy at the low operating pressure of 115-120 psi. An important advantage of KMS membranes is that they require minimal cleaning and application of chemicals.
No antiscalants are being used at Palm Beach County Water Treatment Plant #3 and chemicals are only applied to adjust pH in order to retard precipitation of sparingly soluble salts. The feed water is pretreated with 5-micron (nominal) prefilters. Prior to distribution, the water is chlorinated to prevent biological growth, and the county is in the process of instituting fluoridation.
Looking toward the future
Palm Beach County purchased the membranes directly from KMS, and county officials are pleased with the service and consulting expertise that it has received.
“KMS provided us with a good instructional class, and they have been very helpful with their consulting,” Ford said. “They have a great deal of experience with similar municipal water treatment plants, and I know that I can call them whenever I need to.”
The population in the service area is projected to grow rapidly, outstripping the capacity of the new 25-mgd plant in a few years.
Unfortunately, the current plant has little room for expansion. The county has begun to consider strategies for meeting this demand, and it is considering using KMS’ new Mega-Magnum elements to increase production capacity without putting up new buildings.
These elements utilize the same TFC membranes that have proven successful at Palm Beach County Water Treatment Plant #3, packed into the industry’s largest spiral—18-in. diameter and 61-in. long. A single spiral element contains more than 2,800 sq ft of membrane surface area, compared to 400 sq ft in similar 8 x 40 in. elements.
MegaMagnum spiral arrays require only 50% of the floor space used by 8-in. racks to achieve the same production capacity. For a space-constrained plant like the one mentioned in Palm Beach County that serves a high growth population, the savings in building construction costs could be enormous.