Obtaining Pure Water

As a chemist and microbiologist who spent most of his career detecting and helping to eliminate bacterial endotoxin (pyrogen) in pharmaceutical water systems, I can sympathize with the challenge of providing clean drinking water, even though the required purity is orders of magnitude less than what I have dealt with (C&EN, July 22, page 10).

During my career I saw the development of micro- and ultrafilters that were capable of removing not only the bacterial source of endotoxin, but also the endotoxin itself. Invariably, all of these filters/membranes became fouled with microorganisms, even on the downstream side, and eventually became a source of contamination themselves, requiring extensive cleaning and, ultimately, replacement. Thus, any proposal for the use of filtration will always be subject to a high degree of maintenance and resupply.

In addition, larger systems will require energy, as will the devices themselves. Two devices that are or should be familiar to all chemists are distillation and filtration through asbestos. Though rejected for other reasons, asbestos remains one of the least expensive and most effective ways of removing particulates and certain toxins from water. Likewise, distillation remains one of the best methods for separating contaminants from solution and for making pure water. Of course, distillation requires energy, which may be of greater importance in regions where potable water is scarce. But solar-energy-driven pumps could provide heat energy for a scalable, easily cleanable, and robust distillation system with asbestos-based prefiltration. We should not lose track of all available technologies.

Thomas J. Novitsky
East Falmouth, Mass.

I am curious as to how C&EN decided which companies to highlight in its July 22 articles regarding water treatment (pages 10 and 33). Nalco, where I work as a senior research scientist, has been the leader in industrial water treatment for decades, yet it is not mentioned. Even though Nalco is now a division of Ecolab, its brands are still the highest revenue generating and most recognizable in that market.

James J. Michels
Naperville, Ill.