Chlorine based biocide

During the last 20 years, the use of programs based on bromine chemistry has become standard practice. Bromine/chlorine-based biocides have become internationally accepted as mainstream products for all types of cooling water systems, brewery pasteurizers, and many other... 

Since those days, various other bromine-based biocides and biocide intermediates have been introduced onto the global market or found renewed favor. The most notable are sodium bromide, isocyanurate/NaBr blends, and DBNPA (a nonoxidizer available as a powder or solution, and recently introduced in tablet form). Most bromine biocides employ chlorine in some form as an activator to produce the primary biocidal species hypobro-mous acid (HOBr). 

These ongoing risks and consequences associated with these materials depend on the availability of precise knowledge and the formulation of instructions for their correct and responsible use. In particular, those chlorine-based substances which are summarized as biocides, are included in the EC directive 98/8, and regulatory as well as a chlorine risk assessment programs are preceded voluntarily by the industry. 

PHMB is very toxic to fish and aquatic life. It is moreover irritating to skin and may cause sensitization by skin contact. It can cause irritation to the eyes, nose and respiratory tract. The PHMB is not compatible with most common swimming pool chemicals. Not compatible with chlorine and chlorinated chemicals and bromine donors. Not compatible with ionic sterilizers, copper based QAC-algicides, anionic detergents, water softening chemicals, persulfate oxidants etc. The defence of the inventors of PHMB is that one should not combine it with other biocides because it should be a bactericide/algicide. But the algicidal properties of PHMB are very weak in brochures and manuals the dose is 200 ppm. 

The results of recent trials conducted at the Cranfield University pilot-scale swimming pool are also presented. This research is based largely on chlorination using hypochlorite, but includes other technologies. Results give a clear indication of the extent to which chlorinated byproducts within the swimming pool, as well as the relative levels of DBPs formed between bromination and chlorination. The implications of this research on the future of the use of chemical biocides in swimming pools is considered. 

NOTE The only common theme in the development of the bromine biocide market has been the relatively high prices charged for most bromine-based products (and especially the various types of bromine/chlorine tablets) by the manufacturers and ultimately the service companies. 

Biocide/biostat programs based on sodium bromide oxidation provide a much safer option to cooling system operators than gaseous chlorine and a lower cost option compared with the addition of bleach (also the total volume of liquid consumed is decreased compared with bleach). 

HOCl is a strong oxidizing agent ( hoci/ci- = 1-49 V, pH = 0) in acid but not in alkaline solution. Hence, oxidation goes only from HOCl or its protonized form HOCIH" with the direct transfer of Cl (chlorination), similar to the reaction of HOBr and HOI. It disproportionates into chloride and chlorate singlet oxygen is then partly formed, which can oxidize organic compounds (the biocide application of hypochlorite is based on this) ... 

Because the halogenated hydantoins are anchored and do not readily release fi ee chlorine, conventional methods for demonstrating antimicrobial efficacy based on the diffusive release of fi ee biocide into the local microenvironment— the so-called zone of microbial inhibition— cannot be applied. Inhibitory zones are minimal under circumstances where the challenge method depends on the slow release of biocides into an area populated by growing organisms, the net effect of which is to kill those which fall within a range of concentrations that is lethal. Retention of Cl on the grafted hydantoin demands that a test method be... 

May be used in conjunction with chlorination or other nonoxidizing biocides, but has been found to be effective when used as the sole means for biological control. This provides a simple treatment approach based on chemical inventory requirements and operator training. 

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