They are available as liquid or solid products and selected, like most products, based on what is to be accomplished under your exact conditions.

Chlorine (bleach) is an old favorite based on price. It is easy to use, comes as a liquid, and provides an excellent bacterial kill in pH conditions below 8.5.

Bromine is becoming more widely used due to increases in Raw water pH. Bromine is effective above a pH of 8.5.

In 1992, the EPA issued new rulings on allowable lead levels in drinking water. The old 50 PPB standard for lead was replaced with the new 15 PPB standard. Many municipal water supplies now increase the pH to reduce lead leaching. This has been effective.

Others have opted to add corrosion inhibitors such as ortho phosphate. The City of New York adds approximately 1 PPM ortho phosphate and carries a free halogen residual of 1.0 PPM.

The changes in Raw water have moved many Cooling Tower biocide programs away from chlorine and into bromine based technologies for the bulk water sterilizer. Alternating biocide programs are still the rule, and an expensive nonoxidizer is also used to round off any good biocide program.

The draw back to the halogens are that they do need to be controlled and will breakdown the organic components of the water treatment program, such as Tolytriazole and the polymers if improperly used.

Bromine is available in a variety of forms. You can mix sodium bromide liquid and hypochlorite liquid in generally a 3 to 1 concentration through a static mixer and use ORP to control the levels in the system. This is a fairly sophisticated set-up; requires some upfront equipment costs; needs good monitoring; is very cost-effective long term; and is recommended for large systems.

The most popular bromine donor product is the hydantoin. This solid bromine donor is fed via a brominator and controlled with a solenoid valve. It is best to use Raw water as the brominator drive water since this eliminates forcing the Tolytriazole and polymers through a 10,000 PPM halogen field. We generally recommend that the halogens be slug fed a few times per week to reduce the oxidation of the organic components of the treatment program. Results have been good.

It is no secret that the two Titans in the water treatment industry, fierce competitors, provide most of the R&D and constantly develop new products to address the problems we face in the industry.

The two main problems with the halogen issue are the fact that many customers do not like handling the solid hydantoin product and the fact that halogens will attack the very important copper corrosion inhibitor Tolytriazole. Neither of these are insurmountable problems but they are concerns.

The two Titans have attacked this issue from opposite sides of the coin.

One has introduced a single drum liquid bromine product which makes bromine feed as easy as the old hypochlorite (bleach) feed. Costs of course are higher.

The other has introduced a halogen resistant azole, which allows for better copper protection when using halogens.

Both of these new products are quite innovative and provide easy solutions to the problems at hand.

Other solutions involve tighter control of halogen feed; the use of Raw water to drive the Brominator; greater dependence on the more expensive nonoxidizers; and adjunct Tolytriazole feed.