By Kevin Westerling,
Since the U.S. EPA's Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules (DBPRs) were implemented, many drinking water utilities have made or are considering the switch from chlorine to chloramine (chlorine + ammonia) to avoid formation of the regulated chlorine-based disinfection byproducts (DBPs). But chloramine presents potential problems of its own, according to a recent report from the Water Research Foundation (WRF).
"Chloramination can be a complex process and improper management can lead to unintended consequences," states WRF's Djanette Khiari, author of The Role and Behavior of Chloramines in Drinking Water (September 2016), which essentially summarizes 30 years’ worth of research on chloramine use.
While negative consequences are numerous and may show a pattern, the circumstances leading to failure may be mitigated or avoided with proper planning. Therefore, chloramine use should not be discounted or considered bad practice; rather, utilities should have a clear-eyed understanding of potential issues before making the switch from chlorine.
Which brings us to Red Flag #1:
A Difficult Transition
“Switching to chloramines is certainly not easy and requires advance planning,” the WRF report notes. Many utilities that adopted chloramine soon after the DBPRs came into effect surely underestimated this fact, or simply did not foresee the challenges. The possible outcomes (and outcries) to stay ahead of include public perception on the remaining “red flags” listed below, in addition to aesthetic impacts — taste, odor, or color changes — and mounting concerns over safety. The single-most important factor to consider is how chloramine will react with the distribution system. An earlier WRF report, Long-Term Effects of Disinfection Changes on Water Quality, is recommended reading, as well as WRF’s step-by-step guide to implementation and manual for optimizing chloramine treatment.
Red Flag #2:
With finished water in the distribution system, there is a correlation between ammonia-oxidizing bacteria (AOB) and the rate of nitrification, which is a threat to water quality and EPA standards regulating coliform, nitrite, and disinfectant residual. This correlation exists with chlorine or chloramine, but chloramine seems to exacerbate the problem. According to WRF, “Two-thirds of the medium and large systems in the United States using chloramination experience nitrification to some degree.”
The rate of nitrification and presence of AOB may be influenced by other factors, new WRF research finds. Contributing water quality factors include pH, temperature, and concentrations of organic compounds, but also some clearly chloramine-centric parameters such as chloramine residual, ammonia concentration, and chlorine-to-ammonia ratio. Contributing distribution system factors include detention time, reservoir design and operation, sediment, pipeline tuberculation (mounds of corrosion), biofilm, and the absence of sunlight. In whatever ways these factors conspire to cause nitrification, the issue is more common than not when chloramine is the disinfectant.
Red Flag #3:
Although chloramine is an effective solution for regulated chlorine disinfection byproducts, namely total trihalomethanes (TTHM), haloacetic acids (HAA5), bromate, and chlorite, it may simply trade regulated DBPs for unregulated DBPs — among them the suspected carcinogens N-nitrosodimethylamine (NDMA), iodinated DBPs (I-DBPs), and hydrazine.
NDMA and I-DBPs are formed by the reaction of chloramine with certain precursors. NDMA precursors can be found in treated wastewater and some polymers used for coagulation/flocculation, such as polyDADMAC or polyamine. WRF offers tips for controlling the formation of nitrosamines, including NDMA, here.
I-DBPs occur when multiple iodinated precursors are present along with either chlorine or chloramine, according to WRF, but “formation of I-DBPs is favored during chloramination, especially when chlorine or ozone is used as a pre-oxidant in the treatment process.”
Hydrazine, called “a potent carcinogen” in the report, results when monochloramine and ammonia react under certain water quality conditions. WRF found that formation is “highly dependent on pH and ammonia concentration,” pointing to its prior studies on the formation and quantification of hydrazine in chloraminated water.
Red Flag #4:
Lead and Copper Release
As the Flint saga made clear, it matters what flows through the pipes, even if the water is safe as it leaves the treatment plant. Changing the properties of the water, like switching from chlorine to chloramine, can incite lead-leaching from lead, brass, and copper distribution system components.
The good news: If your pipes and/or components are unpassivated (without buildup), WRF research found that disinfectants were either not a significant factor in lead-leaching (for lead or bronze materials) or, in the case of copper, leaching was “transient” during disinfectant conversion and could be reduced by a phosphate inhibitor.
On the other hand: “For lead plumbing materials that are passivated and likely to have developed scales that are rich in lead oxide, changes in disinfectant — that is, conversion to chloramines or some other low oxidation-reduction potential (ORP) conditions — are likely to cause a notable increase of lead leaching.”
The Effect of Changing Disinfectants on Distribution System Lead and Copper Release provides additional detail.
Red Flag #5:
Elastomeric Material Degradation
Elastomeric (rubber-like) valves, gaskets, and fittings are suited for all types of piping material and “have performed well in the water distribution system,” notes WRF, leading to their widespread use. However, municipalities that switched from chlorine to chloramine have reported an increase in elastomeric component failures — a higher incidence of leaks and line losses, with a corresponding rise in O&M, budget planning issues, and customer complaints. A WRF study on elastomeric material degradation includes life expectancy values for components under various conditions to assist with product procurement and asset management.
On the whole, considering the red flags and research cited above, the work and worry of switching disinfectants may exceed the trouble of complying with the EPA’s chlorine DBP rules that chloramine is meant to circumvent.
Through well-established control strategies, including precursor removal, modified treatment practices, and DBP removal after formation, you can keep chlorine if the alternative seems more daunting.