Mineral scale formation on membrane surfaces is a significant challenge in reverse osmosis water purification. Laboratory fouling experiments are typically run such that the transmembrane pressure (TMP) is fixed, and the permeate flux decreases over time as scales accumulate on the membrane surface. However, this change in flux means that the hydrodynamic conditions at the membrane surface are continuously changing, which could affect crystallization and foulant deposition processes. Operating under constant permeate flux conditions, in contrast, is advantageous because it keeps the hydrodynamic conditions relatively consistent, making it possible to compare how membrane properties (e.g., surface chemistry) affect fouling propensity. Industrial reverse osmosis operations are not run strictly in either constant TMP or constant flux mode; while they may start at a constant TMP, feed pressure may be periodically adjusted to maintain permeate water production within a specified range. The scarcity of constant permeate flux reverse osmosis scaling experiments reported in the literature frustrates efforts to compare membrane fouling processes under constant TMP and constant flux conditions. For the first time, the evolution of the fouling layer resistance was compared as a function of cumulative permeate volume per membrane area during constant TMP and constant flux reverse osmosis filtrations. Scaling experiments were conducted by challenging commercial reverse osmosis membranes with a model feed solution nearly saturated with calcium sulfate dihydrate (gypsum). At low fluxes, the increase in fouling layer resistance was quantitatively similar for the two operational modes. In contrast, at high fluxes, the fouling layer resistance increased more rapidly in constant flux filtration than in constant TMP filtration. The mechanism of scale formation in constant TMP and constant flux operation was self-limiting and self-reinforcing, respectively.

中文翻译：

---

在恒定通量和恒定跨膜压力条件下，错流反渗透过程中矿物垢的形成


膜表面形成矿物垢是反渗透水净化中的一个重大挑战。实验室污染实验通常使跨膜压力 （TMP） 保持固定，并且随着水垢在膜表面的积累，渗透通量会随着时间的推移而降低。然而，这种通量变化意味着膜表面的流体动力学条件不断变化，这可能会影响结晶和污垢沉积过程。相比之下，在恒定的渗透通量条件下运行是有利的，因为它使流体动力学条件相对一致，从而可以比较膜特性（例如。g.，表面化学）影响结垢倾向。工业反渗透操作并不严格在恒定 TMP 或恒定通量模式下运行;虽然它们可能以恒定的 TMP 开始，但可以定期调整进料压力，以将产水量保持在指定范围内。文献中报道的恒定渗透通量反渗透结垢实验的稀缺性阻碍了比较恒定 TMP 和恒定通量条件下膜污染过程的努力。首次将恒定 TMP 和恒定通量反渗透过滤期间每个膜面积的累积渗透体积的污染层阻力的变化与累积渗透体积进行了比较。通过用几乎用硫酸钙二水合物（石膏）饱和的模型进料溶液挑战商业反渗透膜进行结垢实验。在低通量下，两种操作模式的污垢层电阻增加在数量上相似。 相比之下，在高通量下，恒定通量过滤中的污垢层阻力比在恒定 TMP 过滤中增加得更快。恒定 TMP 和恒定磁通量操作中结垢的机制分别是自限性和自强化的。