Abstract The manifestation of critical fluxes in membrane filtration has typically served to set an upper value above which detrimental fouling events and a substantial increase of membrane resistance occurs. Despite the usefulness of critical flux concepts for conducting sustainable membrane processes, the specific phenomena causing them cannot be easily identified via conventional membrane filtration modes. Usually arbitrary fouling rates are selected to delimit the boundary between under- and over-critical flux operation. Timescales respective for colloidal matter accumulation are overlooked. Frequency response analysis of transmembrane pressures has been recently presented as a highly-sensitive method to track fouling in ultrafiltration. This hydraulic impedance spectroscopy method allows not only measuring membrane resistances but also corresponding time constants related to colloidal matter accumulation. In this work, hydraulic impedance spectra are gained for the ultrafiltration of different model foulants to assess the origin of critical fluxes for two different membranes. A correlation among characteristic impedance features and the type of fouling could be established: the evolution of phase shift between flux and pressure at increasing fluxes allows identifying the formation of external fouling layers, while registering of hysteresis loops at reversed frequency sequences signals the development of irreversible internal fouling. The hydraulic impedance method emerges as a precise and more sensitive monitoring tool to diagnose the beginning and nature of critical fouling.

中文翻译：

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通过水力阻抗谱评估超滤中污垢的去除和可逆性

摘要 膜过滤中临界通量的表现通常用于设置一个上限值，高于该值会发生有害的污染事件和膜阻力的显着增加。尽管关键通量概念对于进行可持续的膜过程很有用，但通过传统的膜过滤模式无法轻易识别导致它们的具体现象。通常选择任意的结垢率来界定低于临界和过临界通量操作之间的界限。胶体物质积累的时间尺度被忽略了。跨膜压力的频率响应分析最近被提出作为一种高灵敏度的方法来跟踪超滤中的污垢。这种水力阻抗谱方法不仅可以测量膜电阻，还可以测量与胶体物质积累相关的相应时间常数。在这项工作中，获得了不同模型污垢超滤的水力阻抗谱，以评估两种不同膜的临界通量的来源。可以建立特征阻抗特征和污垢类型之间的相关性：通量和压力在增加通量时相移的演变允许识别外部污垢层的形成，而在反向频率序列记录磁滞回线表明不可逆的发展内部结垢。水力阻抗法作为一种精确和更灵敏的监测工具出现，用于诊断严重结垢的开始和性质。