Chemical imbalance: why one water park switched its water-chemistry system
For more than a century, Columbian Park in Lafayette, Ind., has been a place for visitors to enjoy high-quality leisure time with family and friends. In June 1999, the Lafayette Parks & Recreation Department enhanced the visitor experience at the 43-acre park by opening the Tropicanoe Cove family aquatic center.
The $4.6-million city parks project, part of a master plan developed in 1998 through open public meetings and surveys, encompasses 16 acres inside the park. The aquatic center features a 640-foot lazy river, a 168,000-gallon zero-depth leisure pool, a 33,000-gallon plunge pool, plus many other aquatic features, including a 300-foot tube slide, a water playground and two high-energy drop slides. The center is open Memorial Day through Labor Day and, besides family fun, offers scheduled activities such as aquatic fitness programs. Attendance at the center in 2002 was 76,000.
Maintaining proper water chemistry in the center’s three distinct water bodies (leisure pool, plunge pool and lazy river) is of paramount importance. State regulations require 1.0 to 3.0 parts per million free chlorine residual and pH values of between 7.2 and 7.8 at all times. With highly fluctuating and, often disparate bather loads between the plunge pool and leisure pool, maintaining consistent chlorine residual presented a major challenge for facility staff. Because of this challenge, last year the center changed water-chemistry systems. Included in that change was switching from sodium hypochlorite to calcium hypochlorite as the sanitizing agent.
Problems in the Pool
The center wanted to find an alternative to using sodium hypochlorite For several reasons. Although effective in performing its sanitizing task, commercial sodium hypochlorite has certain problematic inherent characteristics. Chief among these was safety. The center’s staff was concerned about the potential for personnel exposure to injury using the high-solution strength liquid chemical under a pressurized system.
There were also maintenance concerns associated with sodium hypochlorite usage. Commercial sodium hypochlorite is highly corrosive to metals, and presented a high potential for creating a corrosive environment inside the equipment building, adversely affecting pumps, piping valves and surroundings. There were also concerns regarding the common problem of chemical metering pumps becoming air-bound owing to sodium hypochlorite off-gassing.
Another concern was the inconsistent concentration of sodium hypochlorite. Commercial sodium hypochlorite solutions are subject to degradation and byproduct formation because of time, temperature and other factors. The concentration of chemical delivered to the aquatic facility and stored on site in two 500-gallon tanks often varied. Although the facility’s water-chemistry control system compensated for losses in solution strength, it required pumping more solution to meet the chlorine-residual requirements in the pool. In the long run, using the degrading product cost more because the facility had to use higher volumes of the chemical to achieve the desired results.
In addition, commercial sodium hypochlorite contains sodium hydroxide (caustic soda), which is added by manufacturers to help stabilize the bleach solution. High sodium hydroxide levels in the pool water can produce higher levels of total dissolved solids, which can adversely affect water clarity, feel and taste.
Because chlorine residual values in the water would fluctuate, operators often had to set the facility’s oxidation-reduction potential controller’s set-point (or operating range) high to ensure that state regulations were met; this practice further increased chemical usage. These fluctuations were caused by a number of factors, including limitations of the original pool chemistry-control system in adjusting feed rates to address the disparate bather loadings between the leisure pool and plunge pool. Because of head pressure coming off the liquid metering pump, unwanted siphoning in the chemical injectors also occurred, and often resulted in feeding sodium hypochlorite into the system when it was not needed.
After comparing other sanitizing agents commonly used in recreational aquatic facilities, including chlorine gas, bromine and ozone, the aquatic center decided to switch to calcium hypochlorite.
Calcium hypochlorite briquettes are a solid form of chlorine, with an available chlorine concentration of 65 percent. Because it is a solid product, it must either be pre-dissolved or added by a chemical feeder. The product is basic and, because it is slightly alkaline, requires the use of an acidic chemical for pH adjustment. The primary advantages of calcium hypochlorite briquettes are excellent water appearance (clarity), safety and ease in handling, and low total dissolved solids build-up. In addition, its calcium base helps balance water chemistry and protects pool surfaces from damage.
Total dissolved solids build-up with calcium hypochlorite is less than half that of liquid bleach. In addition, calcium hypochlorite requires less than half the amount of pH adjustment chemicals than sodium hypochlorite. Calcium hypochlorite briquettes also have up to a two-year shelf life, as opposed to commercial sodium hypochlorite, which can lose one-third of its strength in only 30 days.
With the adoption of the new water-sanitizing program at the Tropicanoe Cove aquatic center, dry calcium hypochlorite briquettes are now used in two “spray technology” systems to teed water sanitizer to the pool water. The current chlorinator uses dry solid calcium hypochlorite briquettes containing a minimum of 65 percent available chlorine by weight, and also all inhibitor to reduce the potential for carbonate scale associated with the alkalinity component of water.
The chlorinator incorporates three primary components: a briquette hopper, a manifold spray section and a discharge tank. The highly soluble briquettes are scooped into the unit’s briquette hopper. Water from the pool enters the unit via an inlet port, and a spray manifold distributes the water onto a briquette grid, creating a chlorinated solution. The solution falls into the units discharge tank and is discharged into the pool’s recirculation system. New oxidation-reduction potential controllers determine the amount of chlorine discharged.
When the new chlorination system was set up, a post-filter recirculation loop was added to the main pool recirculation system. The recirculation loop provides the inlet water supply to the chlorinators as well as the vacuum to evacuate the chlorinated solution from the units. The solution is drawn by vacuum from the chlorinators’ discharge tanks to the facility’s recirculation system. The vacuum is created by a venturi installed in the post-filter recirculation loop driven by a 1-horsepower pump. The venturi is installed on the discharge side of the pump, creating a flow through the venturi that provides the suction on the chlorinator’s discharge valve.
With the switch from sodium hypochlorite to calcium hypochlorite briquettes and spray technology feed system, maintaining consistently good water chemistry at the facility is easier, and water chemistry control in the vacuum delivery system is safer. Also, the entire system is much more user-friendly from an operations standpoint. Because calcium hypochlorite is a more stable chemical than sodium hypochlorite, it allows for better dosage control and excellent water clarity, and a proper balance in chlorine residual between the leisure pool and the plunge pool is now much more easily maintained.
Each morning, a member of the pool maintenance staff tops off the chlorinators’ 200-pound-capacity briquette hoppers. There is enough dry calcium hypochlorite chemical stored in both units’ hoppers to last for at least 24 hours of operation. The facility could actually fill the boppers every two days, but the once-a-day schedule allows maintenance staff to routinely check the equipment. Also, lifeguards check briquette levels several times a day, further enhancing the facility’s safety regime. The only other scheduled attention to the unit is removing and cleaning its briquette grid approximately every two weeks (although cleaning intervals could be extended). This is a 30-minute procedure, which involves soaking the grid in a solution of muratic acid and water.
Given the chemical solution strength and its vacuum delivery (as opposed to a pressurized delivery system), the new calcium hypochlorite feed system has greatly improved safety and has resulted in fewer potential hazards to facility personnel. Safety training and proper chemical handling remains important at the facility for dealing with calcium hypochlorite in solid form.
Another major advantage the center management has found has been the up-to-two year shelf life, of the briquettes. It had been a challenge to monitor and manage liquid chlorine usage so that a large inventory of sodium hypochlorite did not remain at the end of the operating season. If 200 gallons of sodium hypochlorite were left in the bulk storage tanks at the end of the season, then approximately $200 worth of chemical would be wasted With new calcium hypochlorite briquettes and feed systems, however, any remaining briquette inventory serves as the start-up inventory for the following season.
Calcium hypochlorite costs more than the equivalent amount of sodium hypochlorite on an available chlorine basis. However, the center has found that the facility consumes about 80 pounds of briquettes per day, compared to about 100 gallons of sodium hypochlorite per day with the old system. This is because of a number of factors, including better stability of the chlorine solution, eliminating the siphoning that had occurred with the former system and better control with the new oxidation-reduction potential controllers. Combined with the fact that no unused chemical is wasted at the end of each season, this lower consumption makes the cost of using calcium hypochlorite briquettes tit the facility comparable to that of liquid bleach.
For Lafayette’s Tropicanoe Cove family aquatic center, the switch to calcium hypochlorite has proven to be an efficient solution to providing accurate chlorination, while effectively ending long-standing concerns associated with sodium hypochlorite use. Calcium hypochlorite use is providing excellent water appearance, safety in handling, low total dissolved solids build-up and peace of mind.
Mike Moss and Clay Finney are manager and amusement manager, respectively, of Columbian Park, in Lafayette, Ind.
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