Research Center for Environmental Quality Management, Graduate School of Engineering, Kyoto University, 1-2 Yumihama, Otsu, Shiga, 520-0811, Japan.
Research Center for Environmental Quality Management, Graduate School of Engineering, Kyoto University, 1-2 Yumihama, Otsu, Shiga, 520-0811, Japan.
Water Res. 2019 Oct 15;163:114868. doi: 10.1016/j.watres.2019.114868. Epub 2019 Jul 15.
The seasonal and diurnal patterns of N-nitrosomorpholine (NMOR) and its formation potential (NMOR FP) were examined with water samples taken from five outlets of four sewage treatment plants (STPs), seven main stream sites, and five tributary sites in the Yodo River basin. STPs were shown to be the main sources of downstream NMOR load. The highest NMOR levels were found in the discharge from one STP (26.4-171 ng/L). Continuous sequential samplings over a period of 24 h at this STP revealed that NMOR flux at the influent point fluctuated in both summer (0.4-3.2 g/h) and winter (0.3-5.4 g/h), while it was steady in the effluent. In addition, levels of NMOR remained stable during the biological treatment and disinfection processes. The present research demonstrated that NMOR could be formed from morpholine (MOR) in raw sewage treated by this STP, with a possible mechanism being formaldehyde-catalyzed nitrosation of MOR by nitrites, prior to raw sewage entering the STP. This implies that the NMOR detected here might not be a disinfection byproduct per se under low-chlorine disinfection (around 1.0 mg/L), but is primarily a contaminant that is difficult to remove during sewage treatment. NMOR attenuated significantly in the rivers in the daytime with production of MOR, but persisted during nights, which demonstrated the importance of monitoring NMOR levels in the water environment during periods of low UV intensity, especially nights.
本研究采集了 4 座污水处理厂（STP）的 5 个出水口、7 个主要河道监测点和 5 个支流监测点的水样，考察了 N-亚硝基二甲胺（NMOR）及其生成潜能（NMOR FP）的季节性和日变化规律。研究结果表明，STP 是下游 NMOR 负荷的主要来源。其中一个 STP 的污水中 NMOR 浓度最高（26.4-171ng/L）。该 STP 的连续 24 小时顺序采样结果表明，进水口 NMOR 通量在夏季（0.4-3.2g/h）和冬季（0.3-5.4g/h）均有波动，而出水口 NMOR 通量则保持稳定。此外，NMOR 水平在生物处理和消毒过程中保持稳定。本研究表明，该 STP 处理的污水中，MOR 可能在甲醛催化亚硝酸盐的作用下生成 NMOR，这可能是污水进入 STP 之前 NMOR 形成的机制。这意味着，在低氯消毒（约 1.0mg/L）条件下，此处检测到的 NMOR 本身可能不是消毒副产物，而是污水处理过程中难以去除的污染物。NMOR 在白天随着 MOR 的产生而显著衰减，但在夜间持续存在，这表明在紫外线强度较低的时期，特别是夜间，监测水环境中 NMOR 水平非常重要。
