Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Water Res. 2016 Jan 1;88:266-273. doi: 10.1016/j.watres.2015.10.018. Epub 2015 Oct 22.
Microbial desalination cells (MDCs) taking advantage of energy in wastewater to drive desalination represent a promising approach for energy-efficient desalination, but concerns arise whether contaminants in wastewater could enter the desalinated stream across ion exchange membranes. Such back diffusion of contaminants from the anolyte into the desalinated stream could be controlled by two mechanisms, Donnan effect and molecule transport. This study attempted to understand those mechanisms for inorganic and organic compounds in MDCs through two independently conducted experiments. Donnan effect was found to be the dominant mechanism under the condition without current generation. Under open circuit condition, the MDC fed with 5 g L(-1) salt solution exhibited 1.9 ± 0.7%, 10.3 ± 1.3%, and 1.8 ± 1.2% back diffusion of acetic, phosphate, and sulfate ions, respectively. Current generation effectively suppressed Donnan effect from 68.2% to 7.2%, and then molecule transport became more responsible for back diffusion. A higher initial salt concentration (35 g L(-1)) and a shorter HRT (1.0 d) led to the highest concentration gradient, resulting in the most back diffusion of 7.1 ± 1.2% and 6.8 ± 3.1% of phosphate and sulfate ions, respectively. Three representative organic compounds were selected for test, and it was found that organic back diffusion was intensified with a higher salt concentration gradient and molecular weight played an important role in compound movement. Principal component analysis confirmed the negative correlation between Donnan effect and current, and the positive correlation between molecule transport and concentration gradient related conditions.
微生物脱盐电池 (MDC) 利用废水中的能量来驱动脱盐，代表了一种有前途的节能脱盐方法，但人们担心废水中的污染物是否会穿过离子交换膜进入脱盐后的水流。这种污染物从阳极室扩散到脱盐后的水流中的反向扩散可以通过两种机制来控制，即 Donnan 效应和分子传输。本研究通过两个独立进行的实验，试图了解 MDC 中无机和有机化合物的这些机制。发现 Donnan 效应是在没有电流产生的情况下的主要机制。在开路条件下，用 5 g/L 盐溶液进料的 MDC 分别表现出 1.9±0.7%、10.3±1.3%和 1.8±1.2%的乙酸、磷酸盐和硫酸盐离子反向扩散。电流的产生有效地将 Donnan 效应从 68.2%抑制到 7.2%，然后分子传输对反向扩散的作用更为重要。较高的初始盐浓度 (35 g/L) 和较短的 HRT (1.0 d) 导致最高的浓度梯度，导致磷酸盐和硫酸盐离子的反向扩散分别达到 7.1±1.2%和 6.8±3.1%。选择了三种有代表性的有机化合物进行测试，发现有机反向扩散随着盐浓度梯度的增加而加剧，分子量在化合物运动中起着重要作用。主成分分析证实了 Donnan 效应与电流呈负相关，分子传输与浓度梯度相关条件呈正相关。
