The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
When a customer calls with a problem, a water specialist should know where to find answers and provide a solution if possible. The following case study was performed with two objectives in mind: One was to help the customer find a solution, and the other was to validate the use of ozone and copper ionization in swimming pool disinfection. Both objectives were met.
Educating the Homeowner
The client had purchased a new home with a pool and was struggling to keep the pool water clear. The water would turn green after a bather load or rainfall. Even with constant chlorine shocking and the use of clarifiers, this pool was a nuisance.
Educating the homeowner on pool water chemistry was the key to a successful solution, plus the addition of a multimedia filter, ozone injection and copper ionization system. Teaching the customer the basics of balancing water and attaining proper pH and alkalinity wasn’t difficult, and with the addition of a treatment system, maintaining the pool was an easy task.
Proper pH and alkalinity help the halogens used in disinfection work more efficiently. Chlorine works better when the pH is in the 7.0 to 7.6 range and alkalinity is between 80 and 120 ppm. The H+ and OH- are balanced, and the chemical reactions of the halogens work more efficiently because of the equal number of electrons available. Water in this range does not cause as much corrosion or scaling on plumbing or pool fixtures.
Ozone and copper can perform the brunt of the bacteria control, and chlorine reduction can be achieved, sometimes as much as 75 to 90%.
UV ozone systems only produce 0.05 to 0.1% concentration of ozone by weight, whereas corona discharge systems can deliver 2 to 9% concentration of ozone by weight. UV ozone systems don’t provide maximum bacteria kill rate, but they do help flocculate body oils and other contaminants, which makes them more filterable. Corona systems are more effective at disinfection and chlorine reduction. The copper helps control algae and some bacteria. The copper itself is a good bactericide and algaecide, but the small electrical charge produces hydroxyl radicals, which enhances disinfection. When used together, ozone and ionization have a synergistic effect, and the amount of chlorine used as a final sanitizer can be reduced drastically.
Many times, the ozone is piped into existing piping. The pool is basically used to dissolve the ozone into the water. This method is very inefficient. The best method is to use a contact tank to put the ozone under pressure for more efficient solubility. Care needs to be taken when doing this to prevent backpressure on the sand or multimedia filter, which can cause damage and possible injury. The use of a booster pump is recommended to prevent flow and pressure drop.
Sand filters are commonly used for pool filtration. Multimedia filters cost more but are more effective because they can filter a smaller micron contaminant. This reduces the need to use clarifiers, and over the long run, the cost difference in pool maintenance and chemical use will more than pay for a good multimedia filter.
For this project, we did a side stream setup after the sand filter. We used a multimedia filter, contact tank, booster pump and copper flow cell to deliver the ozone and copper into the water. This setup worked rather well and did not compromise the filtering capabilities of the original sand filter. Yet, it filtered enough water through the multimedia filter so that no clarifiers were needed for the rest of the season. This reflected a chlorine reduction of at least 75% and still maintained a residual of 1 ppm of total chlorine and 1 ppm of free chlorine because the ozone and copper did most of the bacteria control. Copper levels were recorded between 0.2 and 0.5 ppm. Low levels of copper are sufficient and do not stain.
Once we commissioned the system, the pool stayed clear, plus chlorine shocking and clarifiers were no longer used. We monitored the oxidation reduction potential and maintained a level of 400 mV or above. We used calcium hypochlorite tablets in the skimmer basket for chlorine application. A larger, hockey puck-sized tablet was broken apart every other day—about three tablets per week. Most other homeowners we talked to used 10 to 12 of these tablets per week.
The pH and alkalinity remained stable because we used very little chemicals. The water was crystal clear, soft on the skin and very pleasant for swimming. The customer commented that it did not cause the hair to feel like straw, skin to itch or eyes to burn. The clarity of the water was never altered, even after a bather load or a heavy rain.
The 25,000-gal pool in this installation was an in-ground pool with a vinyl liner. The ozone generator used was a four-chamber system designed for pools 30,000 gal and smaller. Corona discharge generators provide higher concentrations of ozone and are therefore more effective in bacteria control. These units could reduce chlorine use even further, but the cost is more significant.
Chemical savings can offset this cost and provide customers with a fast return on investment. Pool maintenance is another cost concern when considering adding a system of this caliber. After all, time is money. If customers are paying for a cleaning service, this could also result in great savings.
The UV systems, however, do a decent job of flocculating contaminants and thus reduce the need for clarifiers. Whether the systems are for residential or commercial use, ozone and copper ionization can greatly diminish chlorine and other chemicals in pool care.
The customer was very pleased with the results imparted by the ozone and copper ionization system. Easier maintenance, less chemical use and a better swimming environment made the pool more enjoyable and less work.
Pools and spas are purchased for relaxation and entertainment, but soon owners find out they create a lot of extra maintenance work. Hotels and resorts have pools and spas for the pleasure of their guests, but the maintenance and chemical use reduce their bottom line. Educating consumers on the use of ozone and copper ionization can help them enjoy their pool or spa. Commercial users can benefit from significant savings on chemicals and provide their guests with a more enjoyable swimming experience.
The use of ozone and ionization is nothing new and has been used for decades in pools and spas. Several manufacturers on the market produce many types of ozone generators. Some are UV, and others are corona discharge.
Ionization systems also use silver and copper together because silver is a very good bacteria-controlling agent.
When these systems are applied properly and the water quality is analyzed closely, the systems can create very favorable results. Keep in mind, however, that one size does not fit all; each pool or spa must be sized accordingly. In addition, bather load must be calculated closely. To achieve desired results, source water must be analyzed and treated properly. Dealers who understand this type of product can add increased revenue and diversification by expanding their operations.