Here's a look at chemical processes:
- Bromine. A member of the halide family, bromine is similar to chlorine. It is a sanitizer and oxidizer.And, just like chlorine, in outdoor pools it can be destroyed by sunlight.
Bromine in pools and spas originates from two basic sources: sodium bromide and “stick bromine.” Once added to the water,sodium bromide requires activation by an oxidizer (usually chlorine or ozone). Stick bromine is eroded into the water and fed through a typical erosion chemical feed system.
The target compound is hypo-bromous acid (HOBr, the most active bromine compound). Pool test kits can’t differentiate between bromamines (combined bromine compounds) and hypo-bromous acid. But a common DPD chlorine test kit can be used to figure the bromine residual, by doubling the reading. Maintaining the proper sodium bromide salt concentration and oxidizer activation takes a well-trained, diligent operator.
It takes approximately twice the bromine to accomplish the same amount of work as chlorine — and it’s about six times the average cost of chlorine. Still, bromine is popular in spas because, unlike chloramines (combined chlorine compounds), a bromamine (combined bromine compound) does not have an offensive odor. Claims that bromine works better in warm water are not warranted.
- Hydrogen peroxide. Hydrogen peroxide (HP)is another way to use a powerful, but unstable, form of oxygen.Though HP is a powerful oxidizer, because of its limited disinfection properties, it is generally only used in spas where the turnover is 30 minutes and the water is seen relatively quickly by a required conventional UV system. Concentrations of 30 to 40 ppm are the standard for maximum effectiveness. This oxidizer cannot be used with automation because the oxidation potential does not increase with increasing concentrations. It is typically fed via a small liquid chemical pump on a timer.
The compound H2O2 is clear and has the characteristics of water, but HP is rated a hazardous chemical and special precautions must be taken for handling, storage and feeding. Hydrogen peroxide also is expensive, up to eight times the cost of liquid chlorine.
- Ionizers. Another supplement to conventional disinfection is ionization. Ion generators use a small amount of electricity to place ions from silver and copper in the water.
Silver ions kill most bacteria. Copper ions destroy algae. While they address disinfection, neither provides any real oxidation potential to destroy organics. That being the case, ionization doesn’t generate any savings on chemical costs.
- Enzymes. Enzymes are an emerging supplemental option in handling organics. Unlike other processes,enzymes are protein-based and actually digest oils and organic material. Moderate successes are being reported with helping control organic compounds in pools. Nevertheless, it's important to keep in mind that while enzymes can help with organic compounds, they don’t sanitize. For the most part, they are unregulated by health agencies.
- Potassium monopersulfate. Nonchlorine oxidizers such as potassium monopersulfate (PM) can be added as a supplement to chlorine pools experiencing chloramine issues. In contrast to ionizers, potassium monopersulfate is an oxidizer only, not a disinfectant. In recent experiments, monopersulfate has been fed on a continual basis to aid in the control of chloramines and air quality. These systems have met with some success, but there are drawbacks including the high cost, which limits its practicality. n Chlorine dioxide. Recent investigations reveal that this green-yellow, highly soluble gas is an excellent oxidizer and sanitizer. Though its use is limited, it shows great promise because of the very strong oxidizing potential — especially with nitrates — helping solve issues with chloramines.
Like all other chemicals used in pools, the directions for use, including handling, storage, concentrations and safety precautions, should be strictly followed. Local health and hazmat overseers should be contacted prior to their implementation. Operators should make sure they follow the information and directions for handling found on each chemical’s MSDS.
Some chemicals can lead to unique issues. For example, stick bromine is hydantoin-based and over time, because the hydantoin accumulates, spas may turn green in color as it builds up. The only solution is to drain and refill the water.
With ionization, copper (green) and silver (black) staining can occur if the ions become excessive and the water is out of balance. The conductivity of the water increases with high total dissolved solids, which can disrupt the ion-generation process.
Potassium monopersulfate shows up on DPD test kits as total chlorine, so operators must be careful to not overdose. In any case, maintaining total water balance is a key.