Electrolytic Chlorine Generators
By Connie Sue Centrella
The growing use of Electrolytic Chlorine Generators (ECGs) in the public-pool sector is not a fad but a trend--one that has been spurred on by pool operators who have become increasingly aware of the documented benefits of this technology. The efficient and effective use of ECGs has proven not only to provide better water quality, but also to eliminate the dangerous effects of bulk chlorine handling.
Salt has played a major role throughout history for its medicinal properties. Over 2,000 years ago, Greek medicine discovered the topical use of salt for skin lesions and digestive troubles, and the inhaling of salt for respiratory diseases (Science Tribune, 1999). Bathing in a brine solution was increasingly used in the treatment of skin diseases like psoriasis, dermatitis, chronic eczema, as well as for arthritis. While these mixtures are a stronger saline solution than used in pool applications, the theory behind salt utilization in swimming-pool water provides insight into why the process is gaining acceptance.
ECGs, known as Salt Water Systems, were first introduced in the late 1970s for swimming pools and spas when the technology was unknown to the industry. This same process--invented in the 1960s--was widely used for waste-water treatment and industrial applications. Since the late 1990s, there has been a major shift in acceptance. ECGs have gained world-wide approval, and are now recognized as the best methodology for generating a chlorine sanitizer for both private and public pools and spas.
How They Work
Salt is added to the pool or spa to establish a 3,000-parts-per-million (ppm) concentration. This is equal to only 7 percent of the salinity level in sea water, which is 35,000 ppm. The pool user cannot taste the salt at 3,000 ppm, as this level is below the normal taste-threshold, and less than the human body’s salt concentration of 4,000 ppm. One of the best features of this electrolytic process is that the salt continuously recycles itself. Adding salt is infrequent--normally about two or three times a year in outdoor pools and even less in indoor pools. Indoor air quality immediately improves as well when the salt system is utilized. (Pure food-grade salt is added at 50 pounds per 2,000 gallons of pool water to meet the 3,000 ppm standard.)
An electrolytic cell or cells is installed in the recirculation system after the filter and heater. As the filtered water flows through the cell, a small amount of DC current is applied to the cell blades, which under electrolysis, produces hypochlorous acid, hydrochloric acid, sodium hydroxide and hydrogen gas. The electrolytic process reaches break-point chlorination, destroying bacteria and chloramines, which are the source of chlorine odor, red eyes and most of the negative reactions blamed on chlorine. The process repeats itself, based on the chlorine demand in the pool or spa.
Chlorine Demand Factors
There are eight factors that affect chlorine demand:
1. Volume and surface area of the pool
2. Average water temperature
3. Level of cyanuric acid (CYA) maintained. CYA slows the destruction of chlorine by the sun’s ultraviolet rays in outdoor pools.
4. Bather load. As the number of bathers increase, so does sanitizer demand.
5. Amount of direct sunlight/UV exposure. More sunlight exposure increases the rate at which sanitizer is consumed.
6. Exposure to vegetation and airborne debris. Dense landscaping increases nitrates and phosphates, which are the nutrients that enhance algae growth, thus requiring additional chlorine usage.
7. Chemical dilution due to rainfall, backwashing, etc. Loss of water also creates loss of sanitizer.
8. Main filter runtime and pool circulation patterns. Sanitizer is only introduced when the pump is running. Waterfalls and other water features increase the demand for sanitizer.
The major advantage to utilizing the ECG systems is safety. These systems provide a safe method of sanitization--no need for bulky, heavy containers of powdered chlorine or tablets, or liquid-bleach carboys. There is no possibility of a chlorine leak or inexperienced personnel mixing chlorine with dangerous chemicals. Erosion feeders are eliminated from this process, which has been the cause of many accidents. Facility safety is of the utmost importance in aquatic venues; liability is one of the major factors in swimming-pool operation. The installation of the safer chlorine generator systems has proven to eliminate the exposure to gaseous fumes, which has plagued operators for years.
Few chemical adjustments are necessary with salt systems. Organic sanitizers, such as tri-chlor, have a pH range of 2.8 to 3.5, which inherently lower the pH of the pool water, requiring the addition of sodium carbonate to raise the pH. The ECGs produce a near-neutral pH. Most public-pool operators install a muriatic acid chemical feeder to automatically maintain the pH level.
Recent changes in some health codes now recommend an Oxidation Reduction Potential (ORP) device to continually measure the activity of oxidation. Recent technologies couple a chlorine generator with a muriatic acid feeder, ORP and ozonator to provide the ultimate in sanitization and oxidation.
Another benefit is that the installation is easy and the equipment takes up little mechanical space. There are only four components to the ECG system: the power supply, the electrolytic cell, flow protection device and, of course, salt, which is dissolved in the pool water.
The systems today are enhanced with digital readouts that allow the operator to precisely manage the pool-water quality. The pool operator has confidence, knowing there is continuous chlorine sanitation (and localized super-chlorination in the cell) occurring, thus eliminating potential instances of poor water quality and exposure to diseases.
And finally, the patrons will enjoy a feeling of soft, silky water, with no red eyes, itchy skin and faded swimwear. Their comfort level is enhanced because there is no chlorine smell (chloramines) in indoor facilities. Keeping the visitors comfortable and coming back are the keys to operating a successful aquatic complex.
Connie Gibson Centrella is a professor and Program Director for the online Aquatic Engineering Program at KeiserUniversity eCampus. She was twice-honored with the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” 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.