Environ. Sci. Technol. 2008, 42, 8170
Comment on “Nitrification in Premise Plumbing: Role of Phosphate, pH, and Pipe Corrosion” Research by Zhang et al. provides interesting insights on the degradation of potable water in premise plumbing systems (Nitrification in Premise Plumbing: Role of Phosphate, pH and Pipe Corrosion, Environ. Sci. Technol. 2008, 42 (12), 4280-4284). Based on my experience, however, it is difficult to compare the experimental findings to conditions in an actual public water system, as Zhang does. This experiment, an unusual situation or setting using stored water, was “set up” to synthesize or enhance the growth of nitrifers in various plumbing situations. The synthesized potable water used to condition the pipes contained no disinfectant, and the municipal water was dechlorinated before it was added to the system. Therefore, the experimental conditions are not representative of “typical drinking water conditions.” Typically, drinking water is chlorinated and is distributed to a community with a pH of 7.0-7.5 and a chlorine residual of 0.2-0.5 ppm. This water would have few, if any, nitrifiers in it. If chloramine is used in low concentrations (2.5 mg/L) in place of free chlorine at pH 8.6, it does not dissipate as quickly in the water as Zhang et al. state.
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 21, 2008
Because ammonia can form via chloramine decay and can support microbial nitrification and growth of heterotrophic bacteria, it is important to maintain a consistent disinfection residual throughout a community distribution system to protect the public’s health. In addition, if water remains in a distribution system, storage tanks, or household plumbing for long periods of time, then the water must be flushed and the system disinfected. The Zhang paper relies on a reference from Kimbrough (J. Am. Water Works Assoc. 2007, 99 (8), 70-76) to support speculation regarding the degradation of brass fittings in plastic pipe systems exposed to chloraminated water. The real-life plastic system studied by Kimbrough has very alkaline water and no suggestion that it becomes acidic, as does the water in the Zhang experiments. After coming to equilibrium there is no difference between the plastic system and the traditional system; thus, any speculative concern expressed by Zhang for plastic systems exposed to chloraminated water seems unsupported by Kimbrough’s real life data.
Sanford M. Brown Professor Emeritus, Department of Health Science, California State University, 5471 N. Lead Avenue, Fresno, California 93711 ES801977S
10.1021/es801977s CCC: $40.75
2008 American Chemical Society
Published on Web 09/24/2008
