SYNOPSIS

            Based on reports in the technical literature, laboratory research, and operational experience with the MIOX mixed-oxidant solution (MOS), it is speculated that MOS causes steady oxidation of organic chloramines (and cyanogen chloride (CNCl)) and rapid completion of the breakpoint reaction on -N- fragments from that oxidation in swimming pool water rather than allowing accumulation of them (including volatile NHCl₂, NCl₃, and CNCl) in the pool water, as is likely the case using chlorine (to wit, the common swimmer's complaints of "chlorinous" odors and burning eyes when bleach/hypochlorite is used for disinfection).  This steady removal of organic nitrogen and rapid completion of the breakpoint reaction would be expected to cause the following beneficial effects, as have been noted by swimmers in and operators of several pools using MOS as a replacement for chlorine for disinfection:

 

 •  Maintenance of an acceptable disinfection residual at lower doses of FAC as MOS than required using chlorine;

• Nil production of chlorinous odors in air overlying the pool water and no burning eyes among swimmers;

• The "nil chlorinous odor" feature has the associated benefit to swimmers that dramatically lower concentrations of the chloramines are inhaled; as a result, swimmers report feeling refreshed rather than "groggy" by their swimming exercise and, indeed, that the water feels "faster"; [this feature should also be welcomed by asthmatics although no such reports have been received to date].

• The need to "shock" the water with excessive bleach/hypochlorite and/or persulfate to remove combined chlorine (the sum of chlorine as chloramines and organic chloramines) is dramatically reduced or eliminated [i] ;

• Elimination of shocking, as well as of draining and replacing pool water, for management of combined chlorine concentrations causes a reduction in the rate of accumulation of Total Dissolved Solids (TDS) in the water and a reduction in costs associated with draining and replacing.

• Better disinfection both because the mixed-oxidant solution is a better disinfectant than chlorine alone and the bulk of the disinfection residual in the pool water would be present as FAC not the combined chlorines; and

• Improved clarity of the water both because the organic amine substrate would not be present to stimulate bacterial growth and disinfection activity is increased.

 

Possibly related to improved water clarity, as well as to reduced chlorinous odors, is swimmers report that they no longer "feel the need to shower after swimming"; rather they feel clean and refreshed by their swim.

 

BACKGROUND

 

            The MIOX-generated MOS has been used as a replacement for chlorine (as gas or bleach/hypochlorite) for disinfection treatment of swimming pools since the first installation at Longmont, CO in 1994.  That early installation, while not successful for operational reasons, resulted nevertheless in reports that the pool operators and users were very pleased with the quality of the pool water.  Complaints by swimmers of burning eyes and greenish tinge to hair, prominent when chlorine (as bleach/hypochlorite solution) was used, virtually ceased using MOS.

 

As the numbers of pool installations worldwide has grown, similar glowing reports on the benefits of the MOS have been received repeatedly.  Operators and users of the indoor pool at San Jacinto Community College in Houston, TX report exceptionally clear water, and no complaints of the "swimming pool smell", burning eyes, or green hair that characterize pools disinfected with chlorine.  Similar reports were received in December, 1999 from a survey of pools using MOS at: Embassy Suites Hotels, Lahaina, HI; Kaiapoi Aquatic Center, New Zealand; the outdoor Olympic pool on Johnston Island; and an outdoor pool in Korea.  Possibly the most dramatic demonstration of the benefits of the MOS was presented in a meeting at MIOX Corporation offices in Albuquerque, NM with Toshi Higa and a delegation of MIOX representatives from Japan on 16 December 1999.  The delegation brought pictures of two pools taken from both overhead and underwater (through glass) showing before (chlorination only) and after MOS application.  Over a period of about one week following the startup of treatment using MOS, the clarity of the pool water transformed from cloudy to crystal clear to the point that one could see clearly the full length of a 50-meter pool to read the markings on the opposite wall.

 

Beginning in 2003, Mr. Rick Dempsey, founder and President of Simply Water, LLC., Houston, TX, the distributor for MIOX for recreational water applications in the US, and consultant (with over 12 years experience) on chemistry and operations to the commercial pool industry, reported these same observations with considerable quantitative detail added, plus additional observations, in his clients' pools when they replaced MIOX MOS for bleach/hypochlorite for disinfection.  Mr. Dempsey compiled a list of, currently, over 60 benefits in 11 operational, management, and safety categories of using MIOX MOS (compared to bleach/hypochlorite solution) for disinfection in commercial pools.  These benefits stem largely from the short list summarized in the SYNOPSIS of this paper.

 

Chemistry and Chemical Mechanisms

 

It is quite clear from observations beginning in 1994 and, more recently, Mr. Dempsey's reports which are based on years of experience using primarily bleach/hypochlorite solution for pool water disinfection plus other chemicals for pool water quality management, that the MIOX MOS behaves differently, and beneficially to swimming pools by comparison, from bleach/hypochlorite.

 

            The chemical mechanisms responsible for these benefits are not nearly as clear as the pool water produced.  Part of the reason for this lack of clarity in knowledge stems from the fact that swimming pool maintenance technology appears to have reached the point that some practices can best be described as "folklore", that is practices for which the chemistry is either not well established, is sometimes misunderstood by the practitioner, or is not discussed in such comprehensive texts on the chemistry of disinfection as Faust and Aly [1] or White [2] .  Pool maintenance practices are generally straightforward, typically controlling the pH to a range of 7.2 - 7.6 and a disinfectant (chlorine) residual of no less than 2 mg/L (often an upper limit of 5 mg/L is set by a state regulatory agency).  But it is usually unclear when discussing maintenance practices with a pool operator whether the disinfectant residual is as Free Available Chlorine (FAC) or as Total Chlorine (TC) [ii] . 

 

The distinction between FAC and TC is important because TC includes FAC and the so-called "combined chlorine" compounds which are chlorine reacted with an amine (nitrogen) group.  The chloramines (predominantly NH₂Cl, but also NHCl₂, and NCl₃) are used widely in potable water disinfection because they provide a disinfectant residual necessary to meet regulatory requirements and are weaker oxidants than FAC and therefore less reactive, forming less disinfection byproducts (Trihalomethanes or THMs).  They provide some biocidal (disinfection) action but less than that of FAC.  Chlorine in its various forms in potable and pool water also impart taste and odor.  White² (p. 395-396) notes that "[T]astes and odors from the application of chlorine are not likely to occur from the chlorine compounds themselves up to the [concentration] limits listed below:"

 

 

Faust and Aly¹ (p. 105), however, note that NH₂Cl imparts a chlorine-like odor and flavor to potable water and NHCl₂ is associated with a swimming-pool-like, bleach-like taste and odor.  Fortunately for the drinking water consumer, NH₂Cl, with its higher threshold of complaint due to taste and odor, predominates in potable water systems with NHCl₂ and NCl₃ forming only at pH's less than about 7.0, which is lower than typical, and in chlorine dose to ammonia nitrogen (Cl/NH₃-N) ratios greater than about 10:1, which is much higher than the typical < 6:1 used in potable water treatment [3] .

 

The combined chlorine component of TC also includes chlorine reacted with the nitrogen groups of organic amines to form organic chloramines.  The technical literature strongly indicates that the organic chloramines have nil disinfection capability.  But at least a portion of these compounds detect as TC in standard wet chemical analyses; thus their presence can easily mislead a pool operator into thinking he has adequate disinfectant residual and, thus, adequate disinfection, when in fact he does not.

 

While tastes and odors imparted by the organic chloramines are not discussed in recent texts, significantly from the standpoint of pool maintenance, White² (p. 460) notes that high Cl/NH₃-N ratios (12:1) with high organic nitrogen compound concentrations in water forms NCl₃ which has a geranium-like odor, an odor that can be taken as chlorinous.  Elsewhere White² (p. 260) states that NCl₃ "…is characterized by its pungent, chlorine-like odor".  And (p. 396) White² notes that NCl₃ solubility in water is negligible, it will aerate with the slightest agitation, and at concentrations [in air] too low to get a response from the olfactory system, it will cause the eyes to tear profusely."

 

Because chloramine formation is known to progress with increasing Cl/NH₃-N ratios from NH₂Cl to NHCl₂ to NCl₃ and finally to N₂ (the breakpoint), it is reasonable to expect that the nitrogen in organic amines, after being fragmented by oxidation, releasing -N- fragments to the water, reacts with chlorine in the same manner with progressive Cl/NH₃-N dose ratios.  Thus a significant fraction of the total chloramines (combined chlorine) present in a swimming pool water may occur as NHCl₂ and, with increasing doses, as NCl₃ in the presence of high organic nitrogen (amine) concentrations and progressively higher Cl/NH₃-N dose ratios.  Indeed, Hery and Hecht [4] showed that "Éroughly 90% of the swimming pool atmosphere pollution by the chlorine species is due to nitrogen trichloride [trichloramine, NCl₃]".  [note added by Bradford].

 

            In addition, Shang et.al. [5] examined in detail the formation of cyanogen chloride (CNCl) by reaction of chlorine with amino acids and nucleic acids in water.  CNCl is a volatile, colorless gas, slightly soluble in water, highly toxic, and causes irritation of the nose and respiratory tract.  CNCl is a chemical warfare (CW) agent; the CW literature consistently indicates that lacrimatory (tearing) and irritating effects are so great that its odor cannot be noticed.  Shang et.al.⁵ also observed a breakpoint-like phenomenon with CNCl with increased chlorine dosing; that is, higher chlorine doses decomposed the CNCl, presumably to CO₂, N₂ and Cl^-.  While Shang et.al. did not indicate that the chlorine on CNCl detects as a combined chlorine in standard analysis, it would be expected to do so because of the structural similarity (at the C-N bond) with cyanuric acid which, in chlorinated form, does detect as TC.

 

            In summary, the technical literature demonstrates chemical mechanisms for formation of three compounds by reaction of chlorine with organic nitrogen (amines) - NHCl₂, NCl₃, and CNCl - all three of which have properties that are consistent with observations of pool users of objectionable conditions.  NHCl₂ and NCl₃ both have chlorinous, bleach-like odors; and NCl₃ and CNCl are volatile, slightly soluble in water, and cause tearing and irritation of the nose and respiratory tract at concentrations [in air] that are below thresholds of odor.  Moreover, NHCl₂, NCl₃, CNCl (probably), and organic chloramines detect as TC but provide nil biocidal action; thus the pool operator can easily believe that he has adequate TC residual for disinfection when in fact, he does not.

 

Relevance to the Bather Load in Swimming Pools

 

            Organic amines are known to be abundant in body oils, urine, and suntan lotions; thus a typical swimming pool water has a ready source of organic amines [these contribute greatly to a tendency of the pH of pool water to increase with bather load in addition to the effects discussed herein].

 

To further complicate the chemistry, pool maintenance practice often includes the addition of cyanuric acid as a chlorine "stabilizer".  Cyanuric acid has even been characterized by some pool operators as a buffer or stabilizer against the ultraviolet (UV) component of sunlight, slowing the rate of decomposition of chlorine in sunlight.  In fact, cyanuric acid is an organic amine, known as a triazine (three nitrogens) with -OH groups attached at the 3 carbon atoms of a 6-membered unsaturated ring [6] .  In pool applications the nitrogen groups react with chlorine to form an organic chloramine³ which, like any chloramine, is less reactive than FAC.  Thus the measurable TC residual is maintained longer than if only FAC were used [it should be noted that none of the swimming pools mentioned above in paragraph 2 use cyanuric acid].  Cyanuric acid and, presumably, the chlorinated form of cyanuric acid, has some biocidal activity but there is no evidence that it provides protection against chlorine decomposition by UV.  The stabilizing action of cyanuric acid can be explained as being due to solely the formation of an organic chloramine.

 

CHLORINE VERSUS MIXED-OXIDANT SOLUTION EFFECTS

 

Expected Chemistry in a Typical Pool Maintenance Scenario Using Chlorine

 

            In a typical pool maintenance scenario using chlorine for disinfection, muriatic acid (HCl) for downward pH adjustment as required and, possibly, cyanuric acid as a TC stabilizer, one would expect both organic amines and, with continuing chlorination [iii] , organic chloramines, CNCl, and -N- fragments (chlorinated as chloramines) from oxidative decomposition of organic amines to accumulate.  As the Cl/NH₃-N dose ratio rises, NHCl₂ and NCl₃ are produced as discussed in the background text above.  The presence of these compounds would be expected to lead at once to complaints of swimming-pool-like, chlorinous odors and burning eyes, symptoms which are well documented in the technical literature as being associated with these compounds and typical of pools using chlorine [green hair cannot be explained from the technical literature at present].

 

            Reductions in water clarity with time and bather load in a typical swimming pool using chlorine for disinfection may be due solely to that fact that biocidal activity does not increase with increasing chlorine dose, despite accumulation of organic chloramines.  Indeed, biocidal activity may decrease because the organic chloramines provide nil biocidal activity, even though the TC concentration would appear to the operator to increase.  Moreover, the organic amines are food substrate for bacteria.  It would be expected that, as organic amines increase in concentration but biocidal activity stays constant or decreases, certain bacteria can find a niche in the pool water, develop into colonies, and contribute to loss of water clarity.

 

MIOX MOS and the Breakpoint Reaction

 

            The MOS has been shown in laboratory [7] and subsequently in potable water systems in Texas [8] and in Iowa [9] to oxidize ammonia (NH₃-N) and chloramines to nitrogen gas (N₂) at Cl/NH₃-N dose ratios lower than either the theoretical (7.6:1) or the practical (8 - 10:1; in fact, ratios as high as 15:1 have been reported to be used) ratios required to drive the breakpoint reaction

 

 

At the Fonda, IA water treatment plant⁹, for example, Cl/NH₃-N dose ratios as low as 5.2:1 as MOS caused a breakpoint-like reaction leading to complete loss of NH₃-N from the raw water.  The most plausible chemical explanation for this effect is that the non-chlorine components of the MOS, rather than the chlorine, react preferentially with ammonia and chloramines causing loss of the ammonia as nitrogen gas but reduced (compared to chlorine alone) consumption of the chlorine.

 

While research on the chemical effect of the MOS on organic chloramines has not been performed as yet, it is hypothesized and expected that the MOS, which is known to be a stronger oxidant than chlorine alone, causes steady decomposition of the organic chloramines and CNCl to -N- fragments rather than an accumulation of them in swimming pool water [iv] .  This steady decomposition of organic amines to -N- fragments is followed (in the presence of FAC as MOS) by rapid completion of the breakpoint reaction, allowing little if any accumulation of the volatile, chlorinous-odor causing NHCl₂ and NCl₃ reaction intermediates.  Such an effect would be completely consistent with other information and observations accumulated over 10-years of research and operational experience on the superior disinfection and chemical oxidation behavior of the MOS [10] .  Likewise, rapid and stoichiometrically-efficient destruction of CNCl would be consistent with the observations of Boyle et.al. [11] on the destruction of cyanide wastes by MOS.

 

Expected Chemistry in a Pool Maintenance Scenario Using MIOX MOS

 

            A swimming pool maintenance scenario using MOS instead of chlorine for disinfection, muriatic acid for downward pH adjustment as needed [v] , but no cyanuric acid for TC stabilization, would be expected to show the following features due to: 1) better disinfection; 2) presumed steady oxidation of organic chloramines to -N- fragments followed by rapid completion of the breakpoint reaction; and 3) steady oxidation past breakpoint of CNCl by the MOS (chemical behavior in sharp contrast to that of bleach/hypochlorite):

 

•  Maintenance of an acceptable disinfection residual (both FAC and TC) at lower FAC doses than required using chlorine;

•  Nil accumulation of volatile NHCl₂, NCl₃, or CNCl in the water and, as a result, no chlorinous odors in the air overlying the pool water and no burning eyes among swimmers;

•  Dramatic reduction or complete elimination of the need to periodically "shock" the pool water with excessive bleach/hypochlorite and/or persulfate to remove combined chlorine;

•   Better disinfection both because the MOS is a better disinfectant than chlorine alone and the bulk of the disinfection residual in the pool water would be present as FAC not the combined chlorines; and

•   Improved clarity of the water both because the organic amine substrate would not be present to stimulate bacterial growth and disinfection effectiveness is increased.

 

Additional observations and reports by swimmers and pool operators, most numerous from Mr. Dempsey's commercial pool clients using MIOX MOS (replacing bleach/hypochlorite), as noted in the SYNOPSIS of this paper, are likely derived from these superior chemical and biocidal features of the MOS.

 

 

  OTHER ASSOCIATED OBSERVATIONS

 

            Incidents of chlorinous odors and burning eye complaints have been reported by workers in the poultry processing industry when chlorine as bleach/hypochlorite has been used for disinfection.  In two poultry processing plants where such complaints have been reported and the plants subsequently replaced bleach/hypochlorite with MIOX MOS for disinfection in the chiller tank(s), the complaints declined in numbers and severity, often disappearing altogether.  The maximum TC concentration in the chiller tank allowed by the USDA is 50 mg/L; some plants are unable to reach this concentration using bleach/hypochlorite for reasons that are not completely clear, but the most common operational reason given is that odors develop at concentrations approaching this level.  Where the MIOX MOS is used, the 50 mg/L TC limit is routinely achieved without odors developing; indeed, there are occasional reports that this concentration is exceeded without odors developing.  In addition, the logic behind the 50 mg/L TC standard is not clear; it may be more related to the development of odors using bleach/hypochlorite (or chlorine gas) and, therefore, for worker protection than for any reason related to the condition of the completely processed birds.

 

These complaints customarily, and incorrectly, have been interpreted as chlorine off-gassing from the chiller tank as Cl₂.  In all cases where we have investigated the chlorine concentrations, the pH, and other water quality conditions in the chiller tank that would affect off-gassing, there has never been clear evidence that the conditions were correct for off-gassing to occur [vi] .

 

An alternative working hypothesis that would be more consistent with the anecdotal reports is that as birds are processed and FAC is gradually consumed both in complete reduction by oxidant-demanding organic material (blood, carcass oils) and by reactions with organic amines, the organic chloramines, -N- fragments from the oxidation of organic amines, NHCl₂, NCl₃, and CNCl would accumulate in the chiller water.  The analogy of this situation with that of the swimming pool is exact except that the chiller tank typically accumulates much more organic material and organic chloramines than a swimming pool, and the chiller tank is much colder, reducing the volatilization of NHCl₂, NCl₃, and CNCl.  Nevertheless, it would be expected that continued reaction with freshly-added FAC into the recirculated chiller water would tend to drive the progressive formation of NH₂Cl, NHCl₂, and NCl₃ as well as CNCl.  As these products develop, first chlorinous swimming pool-like odors would be sensed (NHCl₂ and to a lesser extent initially NCl₃) and subsequently workers eyes would burn (NCl₃ and CNCl).

 

Because chlorinous odors and burning eyes have been reported when bleach/hypochlorite is used but not at all (or to a much reduced degree) when the MOS is used for chiller water disinfection, it is likely that the MOS is steadily oxidizing the organic chloramines to -N- fragments, followed by rapid completion of the breakpoint reaction to nitrogen gas (N₂), allowing little accumulation of the odorous forms of the chloramines (NHCl₂ and NCl₃).  It is likely also that MOS is steadily and efficiently oxidizing CNCl to CO₂, N₂, and Cl^-.

 

If true, the benefits from such a set of reactions by MOS would include reduction in worker complaints and, more importantly for the disinfection of the birds, a reduction in the concentrations of the relatively non-biocidal forms of chlorine (the chloramines and organic chloramines), enabling higher makeup doses of MOS and, therefore, higher concentrations of the highly-biocidal FAC forms of chlorine.  This would result, in turn, in a reduced probability of unacceptable E. coli concentrations on the bird surfaces and reduced probability of positive Salmonella tests, both of which have been reported in the research laboratory and in practice at poultry processing plants..