PRB Articles

Swimming Pool Chemical Technology Automation

The increasing awareness of recreational water illnesses has led to the prolific advancement and acceptance of swimming pool chemical treatment equipment. Today there is a wider acceptance of automatic chemical controllers, and a tremendous movement to install electrolytic chlorine generators, ORP controllers, ozonators and UV generators. This change is a leading indicator of the mind-shift occurring with aquatic professionals, who are rapidly embracing industry research and investing in newer technologies.

Electrolytic Chlorine Generators

Electrolytic chlorine generators (ECGs) were introduced to the swimming pool trade in the early 1980s and regarded initially as very expensive, and awkward to install and use. Manufacturers of ECGs listened to the aquatic managers’ concerns, and incorporated technology to create a user-friendly device. Recent statistics indicate an emergence of acceptance throughout the aquatic industry. One of the main reasons for the growth is the ability of the ECGs to deliver 100% chlorine by simply adding salt to the pool. These devices generate chlorine by separating ordinary salt (NaCl) into its basic chemical elements through a process called electrolysis. Most manufacturers advise that the salt content in pool water be 2,500 to 3,500 ppm. This mild saline solution is so low that it is almost impossible to taste the salt. By comparison, the ocean’s salt content is approximately 35,000 ppm, human tears contain 4,000 to 9,000 ppm, and human taste level of salt is approximately 3,500 ppm.

Aquatic professionals who are using chlorine generators say that their customers experience a smooth, silky feeling on their skin, no longer have red eyes, and complain less about skin irritation.

For an aquatic facility manager, storage and handling are major safety concerns. ECGs provide a huge benefit because there is no longer a need to store chlorine on-site, thus eliminating the dangers of fire and explosions. Risk managers appreciate the reduced trauma and liability from these types of accidents.

The Process Is Simple

Chlorine generator cells are installed inline. Under electrolysis, the salt water passes through the cell and is broken down into chlorine gas, sodium hydroxide and hydrogen gas. There is such a high concentration of chlorine as the pool water passes through the cells that superchlorination actually occurs, thus eliminating the buildup of chloramines. Once the chlorine is generated, it reverts back to salt, and the process repeats itself.

Additional salt needs to be added if you see many bathers splash out, you are backwashing the filtration system, or you are draining the pool. Due to a slight increase in pH residuals with ECGs, advanced technology by some of the ECG manufacturers now incorporates a small acid pump to neutralize the pH. Of course, you must still adhere to the water balance parameters and maintain total alkalinity between 80 to-120 ppm and calcium hardness from 200 to 400 ppm. Cyanuric acid levels in outdoor facilities should be within 30 to 50 ppm.

Sizing parameters are of utmost importance and necessary to obtain maximum performance. One mistake many aquatic professionals make is to purchase a generator solely based on volume (gallons) of pool water. To properly size a generator, you must consider additional information, such as bather load, indoor vs. outdoor facilities, the pump run-time, additional water features and water temperature.

Oxidation Reduction Potential (ORP)

The level of disinfectant can change rapidly in an aquatic facility. For over 30 years automatic sensors have been available to constantly monitor the fluctuations in chlorine residuals. The ORP probe is designed to indicate the oxidizing/reducing capability of pool water by measuring its electron activity. The ORP test is expressed in millivolts (mV).

Here’s how it works:

In science, oxidizers accept electrons. Reducers lose electrons. An increase in oxidation will result in a decrease in reduction, and vice versa. Chlorine is an oxidizer and provides a positive ORP. The ORP electrode uses an inert metal (platinum or gold) that will give up electrons to an oxidant and accept electrons from a reductant. The variables which affect ORP readings are temperature, total dissolved solids, cyanuric acid levels and pH, but the greatest factor is pH. As the pH of the water goes up, the effectiveness of the chlorine goes down. This produces fewer millivolts, hence a lower ORP. Any oxidizer (chlorine, bromine, ozone, iodine, non-chlorine shock, chloramines or hydrogen peroxide) in the water will have an ORP. The recommended range of ORP level is 650 mV to 750 mV.

The Power Of Ozone

The best way to understand ozone is to go outside after a thunderstorm. Ozone produces that fresh, clean scent you notice. Ozone is a reactive, unstable gas found in nature. It is a powerful, naturally occurring oxidizer that has been used safely in swimming pools and spas.

Ozone occurs in nature in two ways--through UV radiation from the sun or electrical energy from lightning strikes. High-energy ultraviolet radiation strikes an oxygen molecule and causes it to split into two free oxygen atoms, then the free oxygen atoms collide with molecules of oxygen to form O3 or ozone molecules. The UV radiation ozone is used in most small-pool applications as well as portable spas. The other type of ozone is produced by the Corona discharge reaction. This reaction uses high electrical voltage to split the O2 in oxygen atoms that form O3. Ozone is a powerful oxidizer and eliminates the need for manual shocking in most cases.

The Move To UV Water Purifiers

With the increasing popularity of interactive water features, aquatic facility managers are faced with protecting users from challenging sanitation and bacteriological concerns. Several states are now incorporating ultraviolet (UV) water purification systems into their public codes. Ultraviolet treatment of pool water photo-oxidizes and destroys combined chlorine and other pollutants. This provides major improvements to the pool environment and water quality, yet with significantly lower levels of chlorine. The combination of chlorine, combined chlorine (chloramines) and ozone in an indoor facility can be very corrosive to equipment. UV purifiers replace ozone and control chloramine levels, eliminating the chlorine odors bathers may experience in some indoor environments.

Carbon Dioxide Lowers pH

The issue of chemical handling is a major cost factor in most aquatic facilities, and threatens not only the public, but the aquatic staff, which historically is responsible for handling the chemicals. Most aquatic facility managers have used either sodium hypochlorite or calcium hypochlorite as the sanitizer of choice. Because both raise the pH, sodium hypochlorite and calcium hypochlorte are used in combination with muriatic acid to lower the pH.

As more aquatic managers attempt to make their equipment room environmentally safe, the use of carbon dioxide in place of muriatic acid is becoming more prevalent. Carbon dioxide, like muriatic acid, lowers pH.

When dissolved in water, it produces carbonic acid, which lowers pH, but unlike muratic acid, it has the tendency to increase total alkalinity.

Handle With Care

As a caution, since carbon dioxide is heavier than air, colorless and odorless, the storage of CO2 should be in a forced ventilation room. It is recommended that the handling of CO2 cylinders should be done by trained staff, much like the handling of chlorine gas tanks in the past. Again, as with all chemical feeders we have discussed, the CO2 should be injected into the circulation line downstream (return line) of all filtration equipment, including the sanitizer injection.

Automated Chemical Controllers Help Reduce Risk

Reducing risk from recreational water illness is a compelling reason to also install a complete, automated control system. Some aquatic professionals may shy away due to initial costs of chemical sensors and control systems; however, if you want to encourage people to visit and use your facilities, you must continue to find ways to reduce the risk of disease outbreaks. Aquatic facilities with automatic controllers have proven to reduce the number of recreational water illnesses, and therefore worth the initial investment.

Chemical controllers use microprocessors as the basis for operation. These microprocessors are designed to recognize low sanitizer levels and low or high pH levels, and make adjustments accordingly. Sophisticated systems have been designed to relay messages to the aquatic manager. These messages can be complex and have the ability to incorporate remote communication: log data on a continuous basis by means of digital readouts and alarms to warn the aquatic manager of dangers. A wide variety of alarms are now being incorporated in the chemical controllers. Chemical fluctuations are the main purpose; however, many controllers actually will advise the manager when the system water flow is low so backwashing can be initiated. With the increase of computer wireless modems, the controllers can send messages to the aquatic manager through pagers, PDAs, phone or a combination of these.

With all this new technology, aquatic managers and staff must be trained to identify mechanical problems. Most chemical feeder manufacturers provide training either on-site or at their manufacturing facilities. It is of the utmost importance that the operators understand swimming pool water chemistry and recognize the need to diagnose and fix the problems. The equipment discussed is only as good as the operator who monitors activity. A personal understanding of all the chemical parameters of water treatment is the most important factor in the development of an automated system. Aquatic managers should periodically attend educational seminars provided by the aquatic industry, read publications, and continue to update their facilities to provide a safe and healthy environment for the swimmers.

Connie Gibson Centrella is Program Director for the online Aquatic Engineering Program at KeiserUniversity eCampus. She was recently honored with the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Ms. Centrella is an industry veteran with over 40 years experience in the pool and spa industry. She is a former pool builder with extensive knowledge in pool construction and equipment installation as well as manufacturing.

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