Department of Sanitary Engineering, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, The Netherlands.
Water Res. 2014 Jan 1;48:498-507. doi: 10.1016/j.watres.2013.10.008. Epub 2013 Oct 14.
Phosphate limitation has been reported as an effective approach to inhibit biofouling in reverse osmosis (RO) systems for water purification. The rejection of dissolved phosphate by negatively charged TiO2 tight ultrafiltration (UF) membranes (1 kDa and 3 kDa) was observed. These membranes can potentially be adopted as an effective process for RO pre-treatment in order to constrain biofouling by phosphate limitation. This paper focuses on electrostatic interactions during tight UF filtration. Despite the larger pore size, the 3 kDa ceramic membrane exhibited greater phosphate rejection than the 1 kDa membrane, because the 3 kDa membrane has a greater negative surface charge and thus greater electrostatic repulsion against phosphate. The increase of pH from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. At pH 8.5, the maximum phosphate rejections achieved by the 1 kDa and 3 kDa membrane were 75% and 86%, respectively. A Debye ratio (ratio of the Debye length to the pore radius) is introduced in order to evaluate double layer overlapping in tight UF membranes. Threshold Debye ratios were determined as 2 and 1 for the 1 kDa and 3 kDa membranes, respectively. A Debye ratio below the threshold Debye ratio leads to dramatically decreased phosphate rejection by tight UF membranes. The phosphate rejection by the tight UF, in combination with chemical phosphate removal by coagulation, might accomplish phosphate-limited conditions for biological growth and thus prevent biofouling in the RO systems.
磷酸盐限制已被报道为一种有效抑制反渗透（RO）系统中生物污染的方法，用于水净化。观察到带负电荷的 TiO2 紧密超滤（UF）膜（1 kDa 和 3 kDa）对溶解磷酸盐的排斥作用。这些膜有可能被采用为 RO 预处理的有效工艺，以通过磷酸盐限制来抑制生物污染。本文重点介绍紧密 UF 过滤过程中的静电相互作用。尽管孔径较大，但 3 kDa 陶瓷膜对磷酸盐的排斥率高于 1 kDa 膜，因为 3 kDa 膜具有更大的负表面电荷，因此对磷酸盐的静电排斥作用更大。pH 值从 6 增加到 8.5 导致两种膜的磷酸盐排斥率大幅增加，这是由于静电排斥的增加。在 pH 8.5 时，1 kDa 和 3 kDa 膜的最大磷酸盐排斥率分别为 75%和 86%。引入 Debye 比（Debye 长度与孔径半径之比）以评估紧密 UF 膜中的双层重叠。分别确定 1 kDa 和 3 kDa 膜的阈值 Debye 比为 2 和 1。低于阈值 Debye 比的 Debye 比会导致紧密 UF 膜对磷酸盐的排斥率显著降低。紧密 UF 的磷酸盐排斥作用，结合化学除磷的凝聚作用，可能会在 RO 系统中实现生物生长的磷酸盐限制条件，从而防止生物污染。
