Issue 9, 2020

Purification and removal of the low molecular weight fraction of polyDADMAC reduces N-nitrosodimethylamine formation during water treatment

Abstract

Cationic polymers are critical coagulant aids at drinking water plants, but the same polymers are simultaneously N-nitrosodimethylamine (NDMA) precursors upon chloramine exposure. We hypothesized the low-molecular fraction, which represents a small mass residual in polyDADMAC cationic polymer, reacts with chloramines, may not be well removed during coagulation, and is thus responsible for forming parts-per-trillion (ppt) concentrations of NDMA in finished water. To identify strategies capable of reducing post-coagulation residual polymer associated with NDMA formation, this study fractionated polyDADMAC by molecular weight, characterized reactivity of each fraction, and quantified precursor contributions to NDMA formation potential during bench-scale test and NDMA concentration due to formation during treatment during pilot tests. Diaultrafiltration of the cationic polymer produced a low molecular weight fraction (<10 kDa) and a purified polyDADMAC (>10 kDa). Native organic matter in bench- and pilot- tests contributed 19–38% of NDMA formed throughout treatment, while polymers were responsible for 62–81% of NDMA formed. The <10 kDa fraction of polyDADMAC was more reactive (450–540 ng NDMA per mg DOC) and formed >10× NDMA than non-purified polyDADMAC in jar tests. Purified polyDADMAC, with <10 kDa fraction removed, formed 54% less NDMA during pilot tests (and 63% less during jar tests) than non-purified polyDADMAC. There was no adverse effect on coagulation or subsequent filter performance by using purified polyDADMAC, but significantly (p < 0.05) less NDMA formed in filtered water when using diaultrafiltered cationic polymer. Thus, removing the low molecular weight impurities (<10 kDa) by polymer suppliers would lead to an equally-effective coagulant-aid that substantially lowers NDMA formation during drinking water treatment.

Graphical abstract: Purification and removal of the low molecular weight fraction of polyDADMAC reduces N-nitrosodimethylamine formation during water treatment

Supplementary files

Article information

Article type
Paper
Submitted
25 Apr 2020
Accepted
19 May 2020
First published
19 May 2020

Environ. Sci.: Water Res. Technol., 2020,6, 2492-2498

Author version available

Purification and removal of the low molecular weight fraction of polyDADMAC reduces N-nitrosodimethylamine formation during water treatment

A. J. Atkinson, N. Fischer, S. Donovan, J. Bartlett, O. Alrehaili, S. Sinha, S. Kommineni, P. Herckes and P. Westerhoff, Environ. Sci.: Water Res. Technol., 2020, 6, 2492 DOI: 10.1039/D0EW00392A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements