Dept of Engineering Science, University of Oxford, United Kingdom.
Adv Colloid Interface Sci. 2011 May 11;164(1-2):38-44. doi: 10.1016/j.cis.2010.12.008. Epub 2011 Feb 1.
Critical flux theory evolved as a description of the upper bound in the operating envelope for controlled steady state environments such as cross-flow systems. However, in the application of UF membranes in the water industry, dead-end (direct-flow) designs are used. Direct-flow is a pseudo steady state operation with different fouling characteristics to cross-flow, and thus the critical flux concept has limited applicability. After a review of recent usage of the critical flux theory, an alternative concept for providing design guidelines for direct-flow systems namely that of the threshold flux is introduced. The concept of threshold flux can also be applicable to cross-flow systems. In more general terms the threshold flux can be taken to be the flux that divides a low fouling region from a high fouling region. This may be linked both to the critical flux concept and to the concept of a sustainable flux. The sustainable flux is the one at which a modest degree of fouling occurs, providing a compromise between capital expenditure (which is reduced by using high flux) and operating costs (which are reduced by restricting the fouling rate). Whilst the threshold flux can potentially be linked to physical phenomena alone, the sustainable flux also depends upon economic factors and is thus of a different nature to the critical and threshold fluxes. This distinction will be illustrated using some MBR data. Additionally the utility of the concept of a threshold flux will be illustrated using pilot plant data obtained for UF treatment of four sources of water.
临界通量理论是在描述控制稳态环境（如错流系统）的操作范围上限时发展起来的。然而，在水工业中使用 UF 膜时，采用的是死端（直接流）设计。直接流是一种具有与错流不同的污垢特性的伪稳态操作，因此临界通量概念的适用性有限。在回顾了最近对临界通量理论的应用之后，引入了一个用于为直接流系统提供设计指南的替代概念，即阈值通量概念。阈值通量的概念也可适用于错流系统。更一般地说，阈值通量可以是将低污染区域与高污染区域分开的通量。这可能与临界通量概念和可持续通量概念都有关。可持续通量是指适度污染发生的通量，在使用高通量降低资本支出（通过使用高通量降低资本支出）和运营成本（通过限制污染速率降低运营成本）之间提供了折衷。虽然阈值通量可能仅与物理现象有关，但可持续通量还取决于经济因素，因此与临界通量和阈值通量的性质不同。使用一些 MBR 数据来说明这种区别。此外，还将使用为 UF 处理四种水源获得的中试厂数据来说明阈值通量概念的实用性。
