Water Journal : Water Journal September 2011
46 SEPTEMBER 2011 water conference reviews Disinfection By-Products (DBPs) Workshop Steve E Hrudey, Jeffrey WA Charrois & Andrew Humpage Ozwater'11, which took place in Adelaide in May, featured a workshop titled Disinfection By-Products (DBPs) -- Relevance to Human Health. Combined with a subsequent AWA co- sponsored workshop hosted by the Curtin Water Quality Research Centre in Perth, WA, it featured contributions from six international and three Australian speakers. The workshop speakers are also contributing manuscripts on this topic to a forthcoming book, which is jointly sponsored by AWA and IWA Publishing and edited by Professor Steve E Hrudey (University of Alberta, Canada) and Associate Professor Jeffrey WA Charrois (Curtin Water Quality Research Centre). Associate Professor Charrois provided a history of DBPs in drinking water within an Australian context. The Australian drinking water industry has been near the cutting edge of DBP research developments for 35 years. Improvements in analytical methods have increased our ability to identify DBP species that were once difficult, if not impossible, to detect. Notable emerging DBP classes now being studied in Australia (as well as globally) include: N-nitrosamines, iodo-DBPs, halonitromethanes, haloamides, halogenated furanones, haloaldehydes and haloquinones. A reflection of increasing DBP interest is noted in several updates of the Australian Drinking Water Guidelines (1987, 1996, 2004, and 2011 (draft)). The Guidelines have evolved from general comments on total trihalomethanes (THMs) and no DBP guideline values (1987), through an expanded list of 23 potential DBP species (1996), to a focus on risk management with the Framework for Management of Drinking Water Quality (2004). Improved national coordination efforts are now required to evaluate the occurrence of emerging DBPs of health concern, in addition to considering transformation by-products, mixtures and the role of toxicity testing. Utility Management of DBPs Richard Walker (Water Corporation, WA) provided a utility perspective on the management of DBPs. Australian utilities face a range of treatment challenges, including: above-ground pipelines, long distribution systems, high concentrations of natural organic matter, algal blooms, and naturally elevated bromide and iodide -- all of which impact on DBP formation potentials. As such, many utilities are faced with the challenge of balancing THM excursions (regulatory risk) with other public health risks that have more immediate adverse consequences (ie, pathogen risk). In the case of Water Corporation, it treats DBPs like any other hazard and attempts to manage them through the Water Safety Plan process and by establishing an acceptable operating envelope (between the THM guideline value (max) and the disinfectant dose required to meet a minimum CT-value). Operators need to "know their system" and be alert for changes in DBP concentrations as an indicator of system problems. However, a utility must never compromise disinfection, even at the risk of exceeding DBP guideline values. Stuart Krasner (Metropolitan Water District of Southern California) prepared a summary of the major and emerging issues regarding halogenated DBPs. Control of the originally regulated DBPs (THMs and haloacetic acids (HAAs)), as well as total organic carbon (TOC), had been expected to control other halogenated DBPs. However, other non-regulated DBPs have been found to increase when certain alternative disinfectants are adopted to reduce formation of THMs and HAAs. Based on expected toxicity, some non-regulated DBPs such as iodine-containing THMs, haloacetonitriles (HANs), haloketones, halonitromethanes (HNMs), haloacetaldehydes, haloacetamines and halogenated furanones are drawing attention and bringing greater scrutiny to the consequences of alternative treatments aimed at reducing regulated DBPs. Dr William Mitch (Yale University) provided a summary of major and emerging issues regarding nitrogenous DBPs. The original focus on THMs and HAAs was based on understanding that they were formed by reactions between halogenated disinfectants and natural organic matter (NOM), ie, humic materials. Because NOM contains little nitrogen, the focus on the original DBPs involved little consideration of formation of nitrogenous DBPs. However, nitrogenous organic matter from sewage effluent and from algal biomass has been found to be a precursor to a wide range of nitrogenous DBPs including N-nitrosamines, halonitriles and halonitroalkanes. The formation of more toxic nitrogenous DBPs, as noted for the non-regulated halogenated DBPs, makes the choice of alternative treatments for reducing THMs and HAAs more complicated. Professor Xing Fang Li (University of Alberta) provided an overview of a class of newly discovered DBPs, the halogenated benzoquinones (HBQs). Based on quantitative structure toxicity relationships performed by Dr Richard J Bull (MoBull Consulting, Washington) on plausible DBPs of health significance, HBQs were identified and their toxicity was predicted to be 1000 to 10,000-fold greater than THMs. Consequently, a sensitive and specific analytical technique was developed. With a reliable technique in hand, sampling was performed on raw and treated water at full scale water treatment plants and the occurrence and formation as DBPs of a series of HBQs (2,6-dichlorobenzoquinone, 2,6-dichloro- 3-methylbenzoquinone, 2,3,6-trichlorobenzoquinone) has been demonstrated. Studies on the cytotoxicity and DNA- binding capability of these compounds have been initiated to aid in judging the relative importance of these previously unrecognised DBPs. presented at Professor Steve Hrudey speaking at the DBP Workshop at Ozwater'11.
Water Journal November 2011
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