Water Journal : Water Journal May 2012
contaminants of concern refereed paper technical features 80 MAY 2012 water NDMA, NDEA, NDPA, NPyr and NDPhA. In the meantime, California has adopted state-based risk and notification levels for NDMA, NDEA and NDPA of 10 and 300, 10 and 100, and 10 and 500ng/L respectively. The notification level is the concentration at which the water provider is expected to take the supply out of service (Californian Department of Public Health website, www. cdph.ca.gov/certlic/drinkingwater/Pages/ NotificationLevels.aspx). Canada recently established a guideline for the maximum acceptable concentration (MAC) of 40ng/L for NDMA, while the province of Ontario has an interim standard for NDMA of 9ng/L. New Zealand's Drinking Water Standards document, published in 2005 and revised in 2008, does not have a maximum acceptable value (MAV) for NDMA. Similarly, Japan's water quality standards and the European Union's Water Framework Directive don't include NDMA or other nitrosamines. In late 2008 the United Kingdom Drinking Water Inspectorate issued guidance information about NDMA to water service suppliers in England and Wales on their website. Similar to the Californian Department of Health, they suggest a tiered approach to management of NDMA in drinking water, involving actions to be undertaken at various NDMA concentrations. For concentrations > 10ng/L the recommendation is to implement strategies to reduce the levels to < 10ng/L, and at > 200ng/L the actions are to "consult with health professionals and reduce consumer exposure within days" (dwi.defra.gov.uk/stakeholders/ guidance-and-codes-of-practice/ NDMA%20concentrations%20in%20 drinking%20water.pdf). Summary Nitrosamines can contaminate drinking and wastewater treatment plant influent through industrial waste or agricultural run-off. They can be formed during the treatment process if chloramination, or chlorination in the presence of ammonia, is practiced. The most problematic of the nitrosamines is NDMA; however, NMor can be found in high concentrations in some wastewater treatment plant influents. Although the major pathway for most nitrosamines occurrence is reaction of precursor material with chloramines, high concentrations of NDMA and other nitrosamines can also be attributed to leaching from rubber components of new pipework, even in the absence of chloramination. The main risk factors associated with the presence of nitrosamines in drinking or recycled water are: • The presence of chloramines, particularly dichloramine; • Highly urbanised or industrialised catchment for wastewater plants, industrialised or agricultural catchment, or source water impacted by wastewater for drinking water; • Poor source water quality, frequent algae blooms, high dissolved organic carbon concentration and colour; • The use of cationic polymers; • Recycling lagoon supernatant and/or backwash water to the head of the plant; • Ineffective/insufficient treatment barriers for organic carbon and contaminant removal; • New pipes containing rubber products. When the main nitrosamine contribution to the distributed water is from leaching in new pipework, flushing is the only method for reducing the concentrations. For nitrosamines entering the treatment plant various processes can be applied to remove them, although few are very effective. The principal method for the minimisation of nitrosamines is the control of their formation through: I. removal or inactivation of precursor material; and II. application of appropriate operational measures to minimise formation. Following are some general strategies that can be applied to reduce nitrosamine formation; however, it is important to note that any of these should only be applied if there is no adverse impact on water quality or potential risk to public health. • Minimise sludge supernatant return; • Apply activated carbon prior to disinfection to reduce chemical contaminants from wastewater and industrial or agricultural run-off that could contribute to the precursor levels; • Optimise coagulation with the aim of minimising polymer dosing if this is contributing to formation; • Optimise organics removal by coagulation; • Adjust pH to a range that minimises NDMA formation; • Dose chlorine prior to ammonia. Although the individual factors that can influence the production of nitrosamines, and NDMA in particular, have been identified and studied extensively, the impact of individual parameters, and the synergy between them, is not well understood at the full scale. Probably the most important reason for this is the extremely low concentrations that are of concern for such potent carcinogens. Very small changes in the operational parameters or precursor concentrations could have a significant, but unpredictable, effect on the concentration of nitrosamines. Therefore, an overall nitrosamine minimisation strategy should combine as many measures as possible for their control. Acknowledgement The authors would like to acknowledge Water Quality Research Australia for funding Project 1018 "Occurrence and management of NDMA and other nitrogenous disinfection by-products in Australian drinking and recycled waters". Optimised coagulation with minimised polymer dosing can reduce NDMA in some plants.
Water Journal July 2012
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