Recent advances in process chemistry have lead to the development of a new generation of single-feed liquid bromine biocides. Highly concentrated stabilized bromine biocides permit the rapid establishment of target residuals. This feature is utilized in a number of case studies for the eradication and control of assorted algae in cooling tower water. Shock dosing to lethally high bromine residuals (> 5 ppm as Cl2) is accomplished quickly and efficiently so that minimal product is wasted in the blowdown.
Since their introduction in 1997, stabilized liquid bromine biocides have become a popular method of treating small and medium sized cooling towers for microbiological control. Perhaps the reason why the products have not found wider use in treating larger systems such as those in power plants and refineries is because of their relatively low active ingredient content - around 15% as Br2. This paper reports on the properties of a new generation of stabilized liquid bromine biocide that has a concentration of 23% as Br2. The advantages of using more concentrated products for cooling water chemicals include reduced shipping and container costs; more effective use of storage space; longer time between the swapping out of empty containers and lower container disposal or container management costs. In this discussion, the 23% as Br2 product will be referred to as HC SLB standing for High Concentration Stabilized Liquid Bromine. This paper attempts to answer the most frequently asked questions about HC SLB. These questions being: What is the similarity/difference between the HC SLB and the early generation stabilized liquid bromine biocides? What is the similarity/difference between the new product and solid bromine biocides? What are the advantages of highly concentrated products? Can highly concentrated liquid bromine biocides be used for algae control?
Oxidizing biocides are susceptible to degradation on storage. The US EPA requires one-year storage stability data on all registered biocides. An accelerated test involving subjecting the product to an elevated temperature of 120 °F for 30 days is often done to simulate the effects that would occur if it had been held for one year at ambient temperatures. The results of such testing is shown in Figure 1 which also charts the effects on lower concentration comparative products tested side-by-side, designated Comp 1 and Comp 2. Figure 1: Relative Storage Stability at Elevated Temperature (120 °F)
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Figure 2: Relative % Loss of Activity at Elevated Temperature (120 °F)
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It can be seen that all 3 products suffer some loss in active ingredient over the 30-day test period. However, when the results are expressed in terms of the relative % loss in active ingredient, it is apparent that HC SLB and Comp1 are noticeably more stable than Comp 2.
To gauge the effect of how persistent the product would be at use-concentration, a simulated cooling water matrix was prepared. This was adjusted to have a total alkalinity of 200 ppm (as CaCO3 calcium hardness of 250 ppm (as CaCO3tivity of 2500 µScm-1, 10 ppm of phosphonobutane tricarboxylic acid (PBTC) and a pH of 8.8.
