FWRJ Florida Brackish Water and Seawater Desalination: Challenges and Opportunities Christopher P. Hill lorida has historically been the pioneer in face water. As the population of Florida has desalination in the United States. As a grown and the availability of fresh groundwa - Christopher P. Hill, P.E., BCEE, is drinking matter of necessity, it was one of the first ter has diminished, there has been a move - F water technical leader with Brown and states to embrace desalinated groundwater as a ment towards alternative water supplies, Caldwell in Tampa. source of drinking water. Florida installed its including brackish groundwater, surface water, first desalination facility in 1969, which was a and seawater. small electrodialysis (ED) facility in Siesta Key. Today, Florida boasts more than 150 desalina - Desalination and In the mid-2000s, much of Florida was fac - tion facilities, with a combined capacity of more Water Supply Planning ing looming water shortages and the need for al - than 515 million gallons per day (mgd) and ac - ternative water supplies was imminent. As a counting for nearly 25 percent of Florida’s total Florida’s five water management districts result, many water providers maximized exist - water supply (Figure 1). are responsible for sustainable management of ing supplies and began developing alternative From groundwater to seawater, no state its water resources. Each of the districts devel - supplies. Now, in the midst of the national hous - has more operating desalination capacity. ops a regional water supply plan (RWSP) every ing and economic crises, many of these same Florida accounts for more than 50 percent of five years that evaluates the adequacy of exist - water suppliers find themselves flush with un - the U.S. desalination market. There are several ing drinking water supplies and identifies po - derutilized supplies built for growth that has yet reasons for this. Much of the state has histori - tential future supplies. The most recent RWSP to come. In other cases, while the need for alter - cally relied upon groundwater for public water for each of the districts identify a total of 126 native water supplies and desalination still supply. This is due not only to the widespread brackish water and 11 seawater projects with looms, the urgency has been reduced signifi - availability of groundwater resources, but also combined capacities of up to 545 mgd and 290 cantly. The economic downturn has resulted in to the limited availability of reliable, fresh sur - mgd, respectively (Figure 2). Continued on page 24 Figure 2. Brackish and Seawater Supply Projects Contained in Regional Water Supply Plans Figure 1. Florida Desalination Facilities (Northwest Florida Water Management District, 2006; Suwannee River Water Manage - (Florida Department of Environmental Protection, 2010) ment District, 2010; St. Johns River Water Management District, 2009; Southwest Florida Water Management District, 2010; South Florida Water Management District, 2006). 22 September 2012 • Florida Water Resources Journal Figure 3. Deep Injection Well Locations within Florida Figure 4. Map of the Floridan Aquifer Boulder Zone (Florida Department of Environmental Protection, 2012) (U.S. Geological Survey, 1990) Continued from page 22 of the state. The “boulder zone” is a deeply minimization and zero-liquid discharge (ZLD) a renewed focus on conservation, even though it buried zone of cavernous permeability in the technologies may not only make sense from a is difficult to quantify in some cases. Although Lower Floridan Aquifer that underlies a 13- water supply perspective, but they may be neces - the need for seawater or brackish water is still county area in southern Florida (Figure 4). The sary in regions with few options for concentrate present, economic necessity has resulted in pro - permeability of the boulder zone is extremely discharge. Utilities in central Florida may see con - tracted project delays. high because of its cavernous nature, which pre - centrate as another (albeit small) source of supply vents pressure buildup in injection wells, and and choose to recover that water rather than dis - Technical Challenges coupled with the fact that the zone contains salt - charge it. Veolia Water has patented zero discharge and Opportunities water, makes it ideal for receiving concentrate. desalination (ZDD) wherein the concentrate is Though many of the possible brackish further processed to improve system recovery to As Florida continues to grow and fresh water and seawater facilities shown in Figure 2 as high as 97 percent (Figure 5). Concentrated water supplies become increasingly limited, the lie within the boundaries of the boulder zone, a salts from the ZDD process can be dried in evap - use of brackish and seawater clearly will play an substantial portion do not. For those facilities, orators/ crystallizers and evaporation ponds (not increased role in its future water supply. How - particularly inland brackish water facilities, likely in Florida), and may even generate a usable ever, there are still a number of technical chal - other alternatives to deep-well injection will be product (such as gypsum). lenges facing public water suppliers and required. Though technically possible and fea - Similar concentrate minimization regulators within Florida, including concentrate sibly permissible, surface water discharges will schemes are already being used in Florida. The management, marine impacts, energy manage - be a challenge for brackish water facilities (FAC City of Palm Coast is utilizing lime softening ment, and pretreatment. 62-4). Surface water discharges could be re - to precipitate hardness from its RO concen - quired to provide dilution between 30:1 and trate and recycle the softened concentrate to Concentrate Management 100:1 and would be subject to toxicity limita - the head of the treatment process. In Califor - Desalination processes, primarily nanofil - tions, as well as antidegradation requirements nia, the U.S. Army is planning to utilize lime tration/reverse osmosis (NF/RO) and electro - of the state. As a result, other methods of con - softening and RO to recover the concentrate dialysis, produce concentrate streams with salt centrate management are likely to be required if from an electrodialysis reversal (EDR) facility, concentrations from two to nearly ten times that brackish water desalination is to comprise any resulting in an increase in recovery from 92 of the source water. Concentrate management significant portion of future water supplies. percent to greater than 98 percent. represents a significant technical challenge to Brackish water desalination facilities may Seawater desalination is frequently co-lo - brackish and seawater supply development. discharge between 15 and 35 percent of the vol - cated with coastal power facilities to take ad - Many of the existing brackish water desalination ume of raw water pumped from the ground as vantage of their cooling water intake and facilities within the state currently discharge to concentrate. Furthermore, not only have they ex - discharge. For example, the Tampa Bay Water deep injection wells (Figure 3). pended considerable capital and operating cost to Seawater Desalination Facility is co-located with Discharge to deep injection wells is possible withdraw that water, but it can be expensive to a Tampa Electric Company (TECO) power primarily due to suitable hydrogeological and discharge it to a deep well that is several thousand plant. The TECO plant utilizes more than 1.4 water quality conditions in the southern portion feet deep. From that perspective, concentrate billion gallons of water per day and provides a 24 September 2012 • Florida Water Resources Journal nearly 70:1 dilution for the concentrate dis - charged from the Tampa Bay Water facility when operated at its design capacity. Co-loca - tion, however, will not always be an option. There is, for example, no existing power facility near the planned Coquina Coast seawater de - salination facility centered near Flagler County. In this case, the Coquina partners are investi - gating off-shore dispersion fields as the most likely, most environmentally-friendly method of concentrate discharge. Marine Impacts For seawater facilities, there are two signifi - cant opportunities to impact the marine envi - ronment: construction and operation of the intake, and construction and operation of the concentrate discharge. Co-location with existing power facilities has proven to be advantageous and can minimize the potential for adverse envi - Figure 5. Zero Discharge Desalination Schematic ronmental impacts, but, as previously men - (Courtesy of Veolia Water, N.A.) tioned, co-location is not always feasible. Minimizing the impacts of seawater intakes fective; in fact, smaller and bait fish actually use methods. is relatively straightforward. Impingement and the intake as a shelter from larger predators. Disposal of concentrate from seawater de - entrainment represent the two most significant Wedgewire screens are also being considered for salination facilities represents a much more sig - seawater intake challenges. Beach wells and sub - intakes (Figure 7) and West Basin Municipal nificant potential challenge. Concentrate must surface (i.e., below the seafloor) intakes can vir - Water District in California is currently con - be managed to minimize the potential for ad - tually eliminate the potential for impingement ducting demonstration testing. The primary verse environmental and marine impacts.