The development of diatomic elemental gas chlorine applications in the disinfection of water was claimed by LIFE Magazine in 1997 as one of the “greatest advancements in the history of public health” and listed it as the 46th most significant event of the millennium. In 1998, it was hailed by the Center of Disease Prevention and the World Health Organization as “One of the centuries greatest health achievements.” Chlorine, from the Greek work meaning greenish-yellow, was discovered in 1774 by the Swedish chemist Karl Wilhelm. Since that time, the halogen can be attributed with innumerous contributions to everything from photography to dry-cell batteries, from polyvinyl chloride (PVC) to textiles, from pharmaceutical germicides to perhaps the greatest household and commercial disinfectant known to man. Yet when you ask an untrained layperson about chlorine and its contributions to the swimming pool industry, they immediately turn up their nose, and think only of red eyes, itchy skin and a disagreeable odor that often times remains with them long after they have left the swimming pool. Throw in some disinfection byproducts in chlorobromo hydrogen carbons such as trihalomethane chloroform (thought to be carcinogenic), renal and liver complications, eczema, asthma, frontal sinus inflammation, and enormous storage and handling concerns, and it will leave even the most devoted proponent wondering why we are still having this stuff delivered by the truckload.
The answer is simple……chlorine does two thing extremely well: Oxidation and Sanitation. Oxidation, the process of chemically “burning” organic debris from the pool water, and sanitation, the process of deactivating the pathogenic organisms in the pool water, can both be achieved with relative predictability with a reasonable residual of free, active, unadulterated chlorine. This ability to perform both of these functions while holding a residual is what has made chlorine the one-stop shopping treatment remedy for many years.
Chlorine was first introduced in the treatment of swimming pool water in the late 1920’s and the powerful disinfection and oxidation properties inherent in its insertion made enormous advances in the treatment process that would later be coupled with recirculation efforts in the 1940’s. However, the undesirable byproducts, unsubstantiated health concerns, and the misunderstanding of the complexities associated with treating swimming pool water led researchers to begin immediately looking for an alternative.
Today, more times than not we are still chlorinating swimming pools. Amidst the auspices of “Science and Technology” there are several “challenges” to traditional chlorinated swimming pool treatments, some of which have financially entrenched themselves in the residential swimming pool market for many years to come. Seldom do we see any marketing campaign launched surrounding some new fan fangled treatment mechanism or chemical protocol that is not invariably accompanied by the claim that it will significantly reduce or eliminate entirely the need for chlorine.
But the commercial swimming pool is a different beast all together. Today our swimming facilities are subjected to enormous organic introductions that not only require, but demand our ongoing diligence and attention. Today, it is not enough for our aquatic professionals to only have a remedial understanding of acceptable and ideal chemical tolerances. Today, we must come to understand the relationship of the multitude of attributes in operating a swimming pool “system”. That is to say, that we must not only understand that a chemical is present or a system is running properly, but we must also fully understand what it is charged with doing, how it relates and influences the other components of our overall chemistry, and how it compares with other alternatives, both from a performance and financial standpoint.
To know what enters, and eventually exits the commercial marketplace and to have an understanding of the advantages and disadvantages of these “snake oils” may prove invaluable in protecting the fiscal integrity of those charged with the safe operation of a commercial aquatic facility.
Authors Note: This section is provided for informational purposes and those of you who are adept at chemistry will fully understand the simple equations of how chemicals react in solution. While the overall outcome that the chemical provides and the understanding that the chemicals are inextricably linked in function and performance is essential in understanding swimming pool chemistry, to have a complete understanding the chemical behaviors, given a significant number of variables remains virtually unimportant in ensuring the success of the operator. These equations, by their definition, are academic and offer little practical assurance of being proficient with their application in the field. In other words, if these equations merely confuse you, do not allow that to diminish the experience associated with understanding the fundamental practical applications of their administration in real terms.
Chlorine is one of the most abundant and useful chemicals on Earth and is produced industrially from the compound sodium chloride, otherwise known as ordinary table salt. Its diatomic or elemental gaseous form can be derived by applying electricity:
2 NaCl + 2H2O Cl2 + 2NaOH + H2
Sodium Chloride Water Electricity Chlorine Gas Sodium Hydroxide Hydrogen Gas
(Salt) (Caustic Soda-Lye)
This is the elemental formation and is largely done the same way in modern day chlorine (salt) generation systems. Whether chlorine is introduced as chlorine gas (elemental) or in one of many compounds, an utterly predictable result occurs:
XCl + H2O HOCL + XBP
Chlorine Water Hypochlorous Acid Chlorine Byproduct
Product
pH
Dependant
OCl- H+
Hypochlorite Ion Hydrogen Ion
Hypochlorous Acid is the active oxidizing a sanitizing agent and it is the strong desire of the operator to encourage conditions that would lead to the most significant HOCl activity with each pound of chlorine that is added to the pool. The disassociated (ionized) molecular structure in OCl- and H+ are far less effective from a performance standpoint. In all cases, regardless of the type or method chlorine delivery, powerful Hypochlorous Acid is developed, along with a byproduct that largely dictates the pH influence of the chemical:
Elemental Chlorine Cl2 + H2O HOCl + H+ + Cl-
(Gas) Gas Water Hypochlorous
Acid Hydrochloric Acid
pH <1.0
Sodium Hypochlorite NaOCl + H2O HOCl + Na+ + (OH)-
(Liquid Bleach) Sodium Water Hypochlorous
Hypochlorite Acid Sodium Hydroxide
pH >13
Calcium Hypochlorite Ca(OCl)2 + 2H2O HOCl + Ca+2 + 2(OH)-
(Granular/Briquette) Calcium Water Hypochlorous
Hypochlorite Acid Calcium Hydroxide
pH 11.8
Lithium Hypochlorite LiOCl + H2O HOCl + Li+ + (OH)-
(Powder) Lithium Water Hypochlorous
Hypochlorite Acid Lithium Hydroxide
pH 10.7
Cyanuric acid (C3N3O3H3), often times called “Stabilizer” or even “Conditioner” for reasons that we cannot comprehend, was then heavily utilized in outdoor installations to protect the chlorine molecule from complete destruction due to the destructive UV rays of sunlight. As luck would have it, the capital venture folks pressed the cyanuric acid into the chlorine compound and the birth of two chlorinated isocyanurics came about:
Trichlor C3N3O3Cl3 + 3H2O HOCl + C3H3N3O3
(Tablets) Trichloroisocyanuric Water Hypochlorous Cyanuric
Acid Acid Acid pH 3
Dichlor NaCl2C3N3O3 + 2H2O HOCl + NaOCl + C3H3N3O3
(Powder) Sodium Water Hypochlorous Sodium Cyanuric
Dichloroisocyanurate Acid Hypochlorite Acid
pH 6.8
Admittedly ominous looking, these two chemicals act in their simplicity with utter predictability in that the desired hypochlorous acid is developed and a byproduct, in this case, cyanuric acid remains. Hence, the dilemma of elevated levels of cyanuric acid and consequent poor chemical performance is validated. This debate is outside of the scope of this topic and is therefore not addressed further.
Remember high school or college chemistry? Some less than socially acceptable professor likely asked you at one time or another to memorize this seemingly ridiculous chart, or at least a series of properties associated with the first eighteen. Being the studious person you were, you applied every clever mnemonic device, regurgitated it in class, and promptly forgot it all in hopes of never having to see it again. Not to be the bearer of bad news, but if you tax your selective memory, you will remember that the periodic chart was situated this way for a reason. Based on the atomic orbital and the number of electrons in the outer shell, the elements would be positioned into periods and groups and then into families based on their chemical properties and behaviors. The Halides are a family of elements that are just one electron shy of a full outer shell. Why is this important? It is not. What is important is that this makes this family of halogens extremely reactive and gives rise to perhaps the most widely used challenge to traditional chlorine.
Chlorine
Bromine
Halides
I. Bromine
As one might expect, Bromine when added to water, reacts similarly to chlorine. It is administered to pool water in two different ways, though only one commercially. Sodium Bromide is a stand-alone salt that is added to the pool and needs an oxidizer to activate it, usually chlorine, potassium monopersulfate, or ozone. BCDMH, or stick bromine is a hydantoin based compound that is actually bound to an organic molecule and carries its own oxidizer, usually chlorine in an amount of 25-30% of the weight per pound. In either application, the desired result is Hypobromous Acid. Sound familiar? If not, take a look;
XBr + H2O HOBr + XBP
Bromine Water Hypobromous Acid Bromine Byproduct
Product
pH
Dependant
OBr- H+
Hypobromite Ion Hydrogen Ion
One of the characteristics of bromine is that its active component in hypobromous acid is unavailable without the assistance of a catalyst. BCDMH applications produce both HOBr and HOCl which might well serve as argumentative fuel against bromine as many of the undesirable byproducts will be realized with the addition of chlorine. With that being said, let’s examine the advantages and disadvantages.
Advantages:
Ø Bromine is far more stable in elevated heat conditions. Chlorine begins its temperature degradations at 37º F. Bromine does not begin temperature degradation until the water reaches 105º F. This is why we see Bromine as a realistic choice for commercially operated whirlpools and hot tubs, customarily kept at 103-104º F.
Ø Bromine combines with ammonia (NH3) to form bromamines (Monobromamine NH2Br, Dibromamone NHBr2, and Nitrogen Tribromide NBr3). However, these combined ammoniated contaminants are still excellent disinfectants, have a far less disagreeable odor and are less irritating to the eyes, skin and mucus membranes than their chloramine counterpart.
Ø Hypobromous acid activity is greater than hypochlorous acid at the pH tolerances of usual swimming pool water. For instance, at a pH of 7.5 bromine yields 94% hypobromous acid activity while at the same pH, chlorine will only convert 50% to active hypochlorous acid.
Ø Bromine is considerably more pH neutral than any form of chlorine (With the exception of dichlor which is not widely used for a number of reasons). BCDMH carries a pH influence of about 4, which makes the pH remediation program relatively simple using nominal amounts of soda ash or sodium bicarbonate to counterbalance the lowering pH influence.
Ø In BCDMH applications, once HOBr reacts with the organic matter in the water, Bromide ions are produced (Br-). This “spent” bromine can be reactivated into active hypobromous acid (HOBr) in the presence of hypochlorous acid (HOCl) already present from the BCDMH product. Therefore a “Bromide Bank” of sorts in a regenerative system exists.
Disadvantages:
Ø Bromine is a substantially weaker oxidizer than chlorine, even at elevate residuals. It is however, an exceptional sanitizer. But remember that disinfection, though arguably the more important of the two functions of water treatment, is the easier of the two treatment obligations to achieve. In other words, oxidation is the hard part, and sanitation is the easy part. On heavily used commercial pools, bromine is simply incapable of “keeping up” with the tremendous organic load experienced. This may lead to cloudy and dull water conditions that often times necessitate regular shock treatments using what else? Chlorine!
Ø Bromine applications are comparatively more expensive than all chlorine treatment options.
Ø BCDMH contributes to considerable total alkalinity loss, which will necessitate notable and costly sodium bicarbonate additions.
Ø Bromine is equally, if not more readily degraded by sunlight and is incapable of being stabilized by a chemical such as cyanuric acid. This makes bromine a poor choice for outdoor installations.
Ø Marcite plaster installations become noticeably yellowed using BCDMH applications.
Ø There is presently no test that will determine the amount of sodium bromide present in the pool, only the amount that is activated. This can cause operators to sometimes “fly blind” in respect to actual pool conditions as they are metering their appropriate levels in a brominated pool by adding a chemical that has no bromine component to it.
Ø Bromine is soft on algae and algae blooms have been known to thrive even at elevated levels of hypobromous acid. To deactivate the algae bloom, the operator is often time forced to add….. ya’ guessed it, Chlorine!
II. Hydrogen Peroxide and UV Light
Remember when you were a kid and you got that cut or scrape and immediately mom pulled out that brown bottle of hydrogen peroxide? She would pour it over the wound and it would bubble….. that is sanitation.
Then, in the 1980’s when every partially blonde adolescent wanted that Loni Anderson look and that same brown bottle did the trick? Well, that is oxidation…..or at least a portion thereof. Hopefully this sounds familiar to the two processes that we attempt to perform on our swimming pools and yes, for some time Hydrogen Peroxide has done a fair enough job to deserve mention.