Gaseous Chlorine — Friend or Foe?

If you’re interested in a low-cost (free, actually) monthly magazine on water and wastewater issues, I recommend Water and Wastes Digest. As a free magazine, it is loaded with ads, of course, but each month has a few nice articles on current technological advances in our industry. (I’ve even had an article in here myself!)

In last September’s edition, Benjamin Grumbles of the Arizona Department of Environmental Quality has a provocative editorial on water security, including some public safety issues associated with our most common treatment chemical, gaseous chlorine. See:

Chlorine gas is a known and proven killer. Today’s photo is of a European battlefield from World War I, where chlorine was used as a weapon of mass destruction. Hopefully, it will never again be used for this purpose, but that potential will forever exist.

In the water industry, chlorine has been our oldest and dearest friend, eradicating killer diseases like cholera, typhoid, and dysentery. We still use it as a weapon of mass destruction! Our targets are the poor, unsuspecting pathogenic microorganisms that are often present in our raw water supplies. The fact that chlorine is lethal is what makes it such a great disinfectant. But we can never overlook the potential for disaster when using chlorine gas.

While this potential has always existed, our safety record using chlorine gas in the water industry has been excellent. Proper training, equipment, and respect for this chemical has made this record possible. But following the terrorist attacks on the United States on September 11, 2001, we have been forced to examine chlorine gas from a new perspective: that of a foe wishing to do harm. And a determined and informed foe could wreak havoc with the amounts of chlorine we routinely store.

What alternatives do we have to chlorine gas? For very large utilities, there is virtually no option available today. However, small to intermediate sized utilities have explored the other two common forms of chlorine for water disinfection: calcium hypochlorite granules and sodium hypochlorite solution. Both of these options are more expensive than chlorine gas, but inherently much safer to transport, store, and handle. And each has other drawbacks that have prevented either from replacing chlorine gas as our most common water disinfectant.

I am particularly interested in on-site generation of sodium hypochlorite. I think this technology is particularly well suited to small and intermediate sized utilities. It is a relatively new technology, though, and thus is still going through the normal “growing pains” that accompany the transition from idea to real world implementation.

The raw material that a plant must purchase for on-site generation is ordinary salt — of little interest to any saboteur or terrorist! The process does consume energy, which is certainly a drawback in today’s world. It also has the potential for by-product formation, including bromate and perchlorate. So, as with any new technology, it is not prudent to rush in. But there is much promise here for a much safer means of disinfecting public water supplies.

For the present, we all need to keep checking our gaseous chlorine safety gear, and run a few drills to make sure we can address emergencies appropriately. But post 9/11, we also need to secure our chlorine stores from those that seek to harm our customers. Our mission has always been — and will always remain — safeguarding public health.

After 9/11, our mission just got tougher.

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