Boron as a Surrogate for N‑Nitrosodimethylamine Rejection by Reverse Osmosis Membranes in Potable Water Reuse Applications Kha L. Tu, † Takahiro Fujioka, † Stuart J. Khan, ‡ Yvan Poussade, § Annalie Roux, ⊥ Jö rg E. Drewes, ‡,¶ Allan R. Chivas, ∥ and Long D. Nghiem* ,† † Strategic Water Infrastructure Laboratory, School of Civil Mining and Environmental Engineering, The University of Wollongong, NSW 2522, Australia ‡ UNSW Water Research Centre, School of Civil and Environmental Engineering, The University of New South Wales, NSW 2052, Australia § Veolia Water Australia, Level 15, 127 Creek Street, Brisbane, QLD 4000, Australia ⊥ Seqwater, Level 2, 240 Margaret St, Brisbane, QLD 4000, Australia ¶ Advanced Water Technology Center (AQWATEC), Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, United States ∥ GeoQuEST Research Centre, School of Earth and Environmental Sciences, The University of Wollongong, NSW 2522, Australia ABSTRACT: The results of this study reveal a strong linear correlation (R 2 = 0.95) between the rejections of boron and N-nitrosodimethylamine (NDMA) by six diﬀerent reverse osmosis (RO) membranes, suggesting that boron can be used as a surrogate for NDMA rejection. This proposal is based on the premise that the rejection of both boric acid and NDMA is governed by steric hindrance and that they have similar molecular dimensions. The concept proposed here is shown to be valid at pH 8 or below where boron exists as the neutral boric acid species and NDMA is also a neutral solute. Observed changes in the rejections of these two species, as a function of permeate ﬂuxes and feed solution temperatures, were also almost identical. Boron rejection increased from 21 to 79%, and the correlation coeﬃcient of the linear regression between boron and NDMA rejections was 0.99 as the permeate ﬂux increased from 5 to 60 L m −2 h −1 . Similarly, a linear correlation between boron and NDMA rejections was observed as the feed solution temperature increased from 10 to 40 °C. This linear correlation was also validated in a tertiary treated eﬄuent matrix. 1. INTRODUCTION The presence of N-nitrosodimethylamine (NDMA) in recycled water and drinking water has recently emerged as a signiﬁcant concern for human health. 1 NDMA can be formed when precursor-containing wastewater eﬄuents are disinfected with chloramines or chlorine. NDMA is known to induce tumors at multiple sites in rodents exposed by various routes and has been classiﬁed as a probable human carcinogen. 2,3 As a result, water authorities in Australia, the United States, and several other countries have set a limit on NDMA concentration in drinking water and recycled water intended for potable water reuse of 10 ng L −1 or below. NDMA concentrations in secondary treated eﬄuents are commonly above this guideline value. 1 Thus, in many potable water reuse schemes, NDMA concentration is reduced by a sequence of reverse osmosis (RO) ﬁltration and UV/advanced oxidation processes. NDMA rejection by RO membranes can be profoundly inﬂuenced by the types of membrane used 1,4 and operating conditions such as permeate ﬂux and temperature. 5 This represents a major water quality compliance challenge for potable water reuse schemes and can have a signiﬁcant impact on overall plant design and operation such as inclusion of UV/advanced oxidation processes in the treatment train. 4 Reliable chemical analysis at low part per trillion levels (ng L −1 ) is a further signiﬁcant technical challenge for the control of NDMA. In fact, despite their signiﬁcance in drinking water, reliable analytical methods for N-nitrosamines are only available at a few commercial and research laboratories around the world. Boron is ubiquitous in municipal wastewater. It is an important ingredient of soaps, detergents, and glassware products. 6 In municipal wastewater, boron commonly occurs at concentrations in the range of 0.3−4 mg L −1 . 7 In some water reuse applications, boron removal may also be required, particularly if the reclaimed water is used for irrigation because boron can be toxic to a range of plant species at concentrations as low as 0.5 mg L −1 . 8 In the aqueous phase, at pH values below the pK a of 9.2 (which is typical for secondary treated eﬄuent), boron exists predominantly as neutral boric acid. Being a low- molecular-weight and neutral species, boric acid rejection by Received: February 18, 2013 Revised: May 9, 2013 Accepted: May 13, 2013 Published: May 13, 2013 Article pubs.acs.org/est © 2013 American Chemical Society 6425 dx.doi.org/10.1021/es400732x | Environ. Sci. Technol. 2013, 47, 6425−6430