School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Advanced Environmental Biotechnology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Singapore 637141, Singapore.
Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Hong Kong, China.
Water Res. 2016 Nov 1;104:44-52. doi: 10.1016/j.watres.2016.07.065. Epub 2016 Aug 1.
On-line chemical cleaning of membranes with sodium hypochlorite (NaClO) has been commonly employed for maintaining a constant permeability of membrane bioreactor (MBR) due to its simple and efficient operation. However, activated sludge is inevitably exposed to NaClO during this cleaning process. In spite of the broad applications of on-line chemical cleaning in MBR such as chemical cleaning-in-place (CIP) and chemical enhanced backwash (CEB), little information is currently available for the release of emerging dissolved organic matter (DOM) and byproducts from this prevalent practice. Therefore, in this study, activated sludge suspended in a phosphate buffered saline solution was exposed to different doses of NaClO in order to determine the generation of potential DOM and byproducts. The results showed the occurrence of significant DOM release (up to 24.7 mg/L as dissolved organic carbon) after exposure to NaClO for 30 min. The dominant components of the released DOM were characterized to be humic acid-like as well as protein-like substances by using an excitation-emission matrix fluorescence spectrophotometer. Furthermore, after the contact of activated sludge with NaClO, 19 kinds of chlorinated and brominated byproducts were identified by ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, eight of which were confirmed and characterized with standard compounds. Many byproducts were found to be halogenated aromatic compounds, including halopyrroles and halo(hydro)benzoquinones, which had been reported to be significantly more toxic than the halogenated aliphatic ones. Consequently, this study offers new insights into the practice of on-line chemical cleaning, and opens up a window to re-examine the current operation of MBR by looking into the generation of micropollutants.
在线化学清洗是利用次氯酸钠（NaClO）来维持膜生物反应器（MBR）的恒定渗透率，因其操作简单、高效而被广泛应用。然而，在清洗过程中，活性污泥不可避免地会接触到次氯酸钠。尽管在线化学清洗在 MBR 中的应用非常广泛，如化学清洗（CIP）和化学增强反冲洗（CEB），但目前对于这种普遍做法中新兴溶解有机物（DOM）和副产物的释放情况知之甚少。因此，在这项研究中，将悬浮在磷酸盐缓冲盐溶液中的活性污泥暴露于不同剂量的 NaClO 中，以确定潜在 DOM 和副产物的生成情况。结果表明，活性污泥在暴露于 NaClO 30 分钟后会发生显著的 DOM 释放（高达 24.7 mg/L 的溶解有机碳）。采用激发-发射矩阵荧光分光光度计对释放的 DOM 的主要成分进行了表征，发现其为类腐殖质和类蛋白物质。此外，在活性污泥与 NaClO 接触后，通过超高效液相色谱/电喷雾电离-三重四极杆质谱联用仪鉴定出 19 种氯化和溴化副产物，其中 8 种副产物通过标准化合物得到了确认和表征。许多副产物被鉴定为卤代芳香族化合物，包括卤代吡咯和卤代（氢）苯醌，它们被报道比卤代脂肪族化合物毒性更大。因此，本研究为在线化学清洗实践提供了新的见解，并为通过研究微污染物的生成来重新审视 MBR 的当前运行情况开辟了一个窗口。
