Water Journal : Water Journal May 2012
refereed paper contaminants of concern water MAY 2012 77 NDMA analysis. NDPA was not detected in any sample. In an earlier publication the authors showed that the majority of samples contained NDMA concentrations of < 10ng/L; however, there were a number of samples above 50ng/L, with the highest concentration reported of 630ng/L (Blute et al., 2010). Occasional samples in other published surveys show elevated levels of between 50 and 160ng/L (Swaim et al., 2008; Zhao et al., 2008; Charrois et al., 2004; Charrois et al., 2007). Zhou and co- workers published the results of a survey of nine nitrosamines in a chloraminated drinking water supply (Zhou et al., 2006). They detected NDMA, NPyr, NPip and NDPhA, and found that the levels increased with increased detention time in the distribution system. The highest concentrations of NDMA and NPip found were 108ng/L and 117ng/L respectively. In Australia, chloramination is widely practiced and in South Australia the South Australian Water Corporation implemented a routine monitoring program for NDMA in four systems in 2007. From these results it is clear that the levels in the distribution system vary considerably with time, indicating a seasonal influence due to variations in detention time controlled by demand. There was also evidence of a strong influence of water quality during a period of high flow, colour and turbidity in the river feeding the treatment plants. However, the average concentration of NDMA of more than 750 samples analysed from 2007 to present was low, < 20ng/L. Knight et al. (2011) recently reported nitrosamine data from five drinking water treatment plants in South-East Queensland. Three of these plants practice chloramination, one uses chlorination, and the other a combination of ozone and chlorine for disinfection. Sampling took place over a three-to- four month period at each plant. NDMA was not detected above the limit of quantification (5ng/L) for any samples. However, the authors noted that the sampling in the distribution system was probably insufficient to conclude that there was no NDMA formed at some distance from the plants. In 2010/2011, Newcombe et al. (2012) conducted three surveys of three chlorinated and six chloraminated drinking water and 16 chlorinated recycled water systems over a one-year period. A total of 130 samples were analysed for NDMA, NDEA and NMor. NMor was not detected in any drinking water sample taken during the survey periods, while it was present in 42% of the chlorinated recycled water samples. NDEA was not detected in any sample. The limit of detection for both compounds was 10ng/L. NDMA was detected in 75% of all samples analysed, including some chlorinated drinking water samples. While there was some variation between the survey periods, for both drinking water and recycled water most of these samples (72% and 63% respectively) had NDMA concentrations ≤ 10ng/L. In summary, nitrosamines can be found in the effluent of drinking and wastewater treatment plants and in distribution systems through three pathways: • They may be formed during the treatment process; • They may be introduced as contaminants into the water during treatment or distribution; • They may be present in the influent to the plant and are not removed during treatment. It appears that NDMA, and some other nitrosamines, are present in drinking and recycled waters produced using many different treatment processes and sources. While the majority of samples contain 10ng/L or less of these disinfection by-products, levels of over 100ng/L are regularly reported and drinking water suppliers should be aware that the levels may vary seasonally due to water quality and operational changes. Formation of Nitrosamines The most common formation pathway for nitrosamines is through the chloramination of a range of organic nitrogen-containing precursor compounds -- particularly those containing amine groups -- that can be found in water and wastewater. Chloramines can be used as a primary disinfectant, as in many drinking water treatment plants, or they can be formed on chlorination of wastewater in the presence of ammonia, where chloramines are produced as a by-product. It is now believed that the form of chloramine that is most important in the formation of NDMA is dichloramine (Schreiber and Mitch, 2006a); therefore, chlorine to ammonia ratio, pH, the order of addition of chlorine and ammonia and the efficiency of mixing are important parameters (Portillo et al., 2008). The application of optimum operational conditions for monochloramine formation will minimise dichloramine formation; however, even a low concentration of dichloramine is thought to be sufficient for the formation of NDMA (Shah and Mitch, 2012). Dimethylamine (DMA) is an important precursor of NDMA (Choi and Valentine, 2002; Schreiber and Mitch, 2006a). As DMA is known to be formed during wastewater treatment processes, NDMA in drinking water has been associated with input from wastewater treatment plants upstream of the source (Schreiber and Mitch, 2006b). NDMA has also been shown to be formed on ozonation of water containing DMA in the absence of chlorine or chloramines (Andrzejewskia et al., 2008). During their survey of nitrosamine occurrence Wang et al. (2011) detected the secondary amine precursors of the six nitrosamines they detected in the drinking water, with DMA and diethylamine (DEA) the most abundant. The authors suggested that the secondary amines in the source waters were the most important precursors for the nitrosamines in these systems. Cationic water treatment polymers have been identified by a number of researchers as significant precursors to these DBPs, with polyDADMAC being the Chemical dosing facilities at a regional South Australian treatment plant. Chloramines are commonly used for country plants with long distribution systems.
Water Journal July 2012
Water Journal April 2012