Zhang Xin, Reible Danny
Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409-3121, USA.
Department of Civil, Environmental and Construction Engineering, Texas Tech University, Lubbock, TX 79409-1023, USA.
Membranes (Basel). 2021 Mar 24;11(4):231. doi: 10.3390/membranes11040231.
Water softening is desirable to reduce scaling in water infrastructure and to meet industrial water quality needs and consumer preferences. Membrane capacitive deionization (MCDI) can preferentially adsorb divalent ions including calcium and magnesium and thus may be an attractive water softening technology. In this work, a process model incorporating ion exclusion effects was applied to investigate water softening performance including ion selectivity, ion removal efficiency and energy consumption in a constant voltage (CV) mode MCDI. Trade-offs between the simulated Ca selectivity and Ca removal efficiency under varying applied voltage and varying initial concentration ratio of Na to Ca were observed. A cut-off CV mode, which was operated to maximize Ca removal efficiency per cycle, was found to lead to a specific energy consumption (SEC) of 0.061 kWh/mole removed Ca for partially softening industrial water and 0.077 kWh/m removed Ca for slightly softening tap water at a water recovery of 0.5. This is an order of magnitude less than reported values for other softening techniques. MCDI should be explored more fully as an energy efficient means of water softening.
水软化对于减少水基础设施中的结垢以及满足工业水质需求和消费者偏好是很有必要的。膜电容去离子化（MCDI）可以优先吸附包括钙和镁在内的二价离子，因此可能是一种有吸引力的水软化技术。在这项工作中，应用了一个包含离子排斥效应的过程模型，来研究恒压（CV）模式MCDI中的水软化性能，包括离子选择性、离子去除效率和能耗。观察到在不同的施加电压和不同的钠钙初始浓度比下，模拟的钙选择性和钙去除效率之间的权衡。发现一种截止CV模式，其运行目的是使每个循环的钙去除效率最大化，对于部分软化工业用水，去除每摩尔钙的特定能耗（SEC）为0.061千瓦时，对于在水回收率为0.5时轻微软化自来水，去除每立方米钙的特定能耗为0.077千瓦时。这比其他软化技术报告的值低一个数量级。应更全面地探索MCDI作为一种节能的水软化手段。
