Evaluating Polymers to Avoid Polymer‐Induced N‐Nitrosodimethylamine Formation

Abstract

Chloramines are often used instead of free chlorine as a residual disinfectant in order to limit formation of regulated halogen‐substituted disinfection by‐products that form more readily in the presence of free chlorine. However, the use of chloramines can form carcinogenic nitrosamines. Some polymers, particularly polyDADMAC, contribute nitrosamine precursors (as confirmed in this research). Alternative polymers produced from natural products evaluated in bench and pilot testing produced clarification and filtration performance as good as or better than that with polyDADMAC or other currently used polymers while contributing little or no nitrosamine precursors. However, there was indication of high biological growth in filters that were not chlorinated. Replacing readily biodegradable acetic acid with a mineral acid (e.g., hydrochloric acid) during synthesis of chitosan might reduce the potential for biological activity with this polymer. Performance variations in different source waters suggest that site‐specific determination of the best polymer type, dose, and application point should be completed before using any polymer.