In the current regulatory environment, it is a good idea to reexamine the use of chlorine gas. Since the beginning of the century, chlorine has ended epidemics such as cholera and improved the quality of life for millions. Chlorine is one of the most effective disinfectants available, and chlorine gas is still the most economical way to disinfect water in most situations.
The problem of disinfection by-products has caused some people to look at other disinfectants. There are similar problems with most alternatives to chlorine. These problems are usually minimized by removal of the precursors of the by-products. If there is a modern coagulation filtration step in the water treatment process prior to chlorination, by-products can be reduced.
Chlorine resistant pathogens also have caused designers to look to other means of disinfecting water. Again, a good coagulation filtration step removes several logs of the chlorine resistant pathogens, but the end result is dependent on the source water loading.
One of the areas where chlorine is unparalleled is in providing a persistent residual to prevent microbiological re-growth in the water main all the way to the last customer. This persistence can be enhanced by the use of chloramines, a chlorinated ammonia compound that is slower to react and more stable, so that a lower residual can be used to provide a longer lasting residual. This lowering of the residual also lessens the potential of disinfection byproducts. The biggest shortcoming of other disinfectants is the lack of a persistent residual, and a lack of a full understanding of the by-products of alternate disinfection technologies.
The least expensive method of disinfecting water is almost always chlorine gas. Local regulatory requirements sometimes shift this balance toward one of the other methods of feeding chlorine (bleach or on site production of bleach), but when it comes to spending a disinfection dollar, chlorine may still be the best value for money of all disinfectants. For this reason, chlorine gas and hypochlorite are still the most used disinfectant in the United States. The bulk price of hypochlorite is usually five to ten times the cost of chlorine gas. Even when scrubbers are required, chlorine gas is usually the most cost-effective choice. The other method that figures into the equation is on site hypochlorite generation.
There were dire predictions of mass public outrage as the normal response to the filing of a RMP (Risk Management Program), the EPAs new safety and prevention regulation that must have been filed no later than June 22, 1999. The public reaction to the RMP filings to date has largely been a non-event. Where it has been noted at all, the main point that came through the filing was the safe and professional manner in which chlorine has been used to protect the quality of drinking water.
Safety is a point on which chlorine gas has suffered an unwarranted hit. Chlorine is the most widely understood disinfectant in use today, and with the modern design of vacuum feed equipment, and its emphasis on safety, chlorine can be a safe and reliable choice.
When all things are considered, chlorine gas still deserves to be the first choice for most disinfection needs. With all of the data that has been collected over the years, and the proven track record for safety and economy, chlorine is still the clear leader.
