FACTORS AFFECTING NDMA FORMATION IN TREATED DRINKING WATER

摘要

Chloramination can result in production of the compound N-nitrosodimethylamine (NDMA) as a by-product. NDMA is known to produce cancer in animal studies, and is classified as a probable human carcinogen (Group 2A) by the International Agency for Research on Cancer (IARC, 1978). A study of the NDMA formation potential (NDMAFP) at five treatment plants using conventional coagulation and filtration found NDMAFP was generally higher after treatment. This suggests NDMA precursors are added during the treatment process, or compounds that may hinder the formation are removed and/or that the conditions (e.g. pH) after treatment are more conducive to NDMA formation. There was significant variation in NDMAFP in raw and treated waters with no clear correlation to conventional water quality or operational parameters. Laboratory studies identified factors that strongly influence NDMA levels such as the dose of polyDADMAC used, pH, detention time, sludge supernatant return and order of addition of ammonia and chlorine. However, at the full scale none of these factors alone appeared to be controlling the NDMA levels in the distribution system. The formation of NDMA is a complex reaction impacted by a range of water chemistry conditions, and as result the effect of each of the factors mentioned above cannot be predicted at full scale. In order to identify the controlling factors each parameter must be varied individually, and the impact measured through NDMA levels in the distribution system. A further study is planned in a full scale plant trial of factors influencing NDMAFP.