Reverse Osmosis Shifts Chloramine Speciation Causing Re-Formation of NDMA during Potable Reuse of Wastewater,Environmental Science & Technology

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Reverse Osmosis Shifts Chloramine Speciation Causing Re-Formation of NDMA during Potable Reuse of Wastewater
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2017-07-18 00:00:00 , DOI: 10.1021/acs.est.7b01641
Daniel L. McCurry ₁ , Kenneth P. Ishida ₂ , Gregg L. Oelker ₃ , William A. Mitch _{1,

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Affiliation

UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH₄⁺ promotes conversion of the residual monochloramine (NH₂Cl) in the permeate to dichloramine (NHCl₂) via the reaction: 2 NH₂Cl + H⁺ ↔ NHCl₂ + NH₄⁺. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.

中文翻译：

反渗透改变氯胺的形态，导致在饮用水的可重复利用过程中重新形成NDMA

基于紫外线的高级氧化工艺（AOP）可有效地降解N-亚硝基二甲基胺（NDMA），使其通过高级处理系统中的反渗透（RO）单元，可用于城市污水的饮用水回用。但是，某些公用事业公司已经观察到AOP之后，AOP产品水中残留的氯胺和NDMA前体之间的反应会重新形成NDMA。使用动力学模型和实验室规模的RO实验，我们证明了RO渗透液中的低pH（〜5.5）以及NH ₄⁺的有效排阻会促进渗透液中残留的一氯胺（NH ₂ Cl）转化为二氯胺（ NHCl ₂）通过反应：2 NH ₂ Cl + H ⁺↔NHCl ₂ + NH ₄⁺。二氯胺是已知可与NDMA前体反应形成NDMA的氯胺类。在进行UV / AOP处理后，公用事业公司通常使用石灰或其他技术来提高最终水的pH值，以防止分配系统腐蚀。建模表明，尽管pH值的增加阻止了二氯胺的形成，但它会将基于胺的NDMA前体转化为更具反应性的中性形式。通过建模以及在实验室规模和现场规模上的实验，我们证明减少RO处理和最终pH调节之间的时间间隔可以通过最大限度地减少在达到最终目标pH值之前形成的二氯胺的量来显着减少NDMA的重整。。

更新日期：2017-07-19

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