Over the last several decades, drinking water treatment plants have optimized their treatment processes to cost-effectively comply with DBP (i.e., THM, HAA, bromate, chlorite) regulations while meeting disinfection requirements (i.e., for Giardia, viruses).  With the discovery of emerging DBPs (e.g., NDMA, iodoacids, halonitromethanes [HNMs], haloacetaldehydes [HAs]), which are of higher health concern than many of the regulated DBPs, researchers have been examining how best to control their formation.  However, the control of some emerging DBPs may conflict with how plants are currently being operated to control the regulated DBPs.  Thus, there is a need to cost-effectively balance the control of a wide range of DBPs of health and regulatory concern, while meeting other treatment objectives.  Pre-oxidation can destroy/transform the precursors for some DBPs, whereas it may increase the formation of others.  For example, pre-chlorination or pre-ozonation can destroy NDMA precursors and oxidize iodide to iodate, which minimizes the formation of two classes of chloramine DBPs (i.e., nitrosamines, iodo DBPs).  Ozone at low CT and chlorine at high CT (high contact time) tend to be similar in effectiveness.  However, the tradeoff is the formation of THMs, HAAs, and other chlorobromo DBPs or bromate.  Moreover, pre-ozonation can increase the formation of HNMs, HAs or cyanogen halides during post-disinfection, whereas biofiltration may help remove the precursors for the latter DBPs.  Medium-pressure UV, an emerging disinfection process, may destroy NDMA precursors, but can increase the formation of HNMs or HAs during post-disinfection.  Thus, there is a need to balance the control of regulated DBPs with that of emerging DBPs, where there is a need to optimize a series of various unit processes to minimize the formation of a wide range of DBPs.  Moreover, one may need to consider the relative toxicity of the different DBPs to help guide the most effective balance.

Balancing the control of regulated and emerging DBPs while meeting other treatment objectives

248th National Meeting (2014)

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