Abstract: This paper studied the feasibility of multiple-effect membrane distillation(MEMD) with ion exchange in the process of desalination and deep-concentration of fresh seawater and brine from a desalination plant. The selective decalcification process could remove >90% of calcium ions，effectively preventing membrane fouling from CaSO4 precipitation in highly concentrated seawater. This research investigated the influences of various operational conditions on the performances of the MEMD process and evaluated permeate flux (J)，gained output ration (GOR)，and permeate conductivity. The experimental results showed that the maximum J and GOR were 6.07 L/(m2?h) and 13.2 respectively. When the decalcified seawater were concentrated to 250 g/L under optimized operational conditions，the electrical conductivity of the permeate was less than 200 μm/cm，and J and GOR were up to 3.61 L/(m2?h) and 4.96 respectively. Two MEMD modules from different membranes demonstrated a long-term stability of at least 45 days，indicating the feasibility of this process for deep desalination of sweater.

Key words: multiple-effect membrane distillation, gained-output ratio, seawater, decalcification, deep-concentration, operational stability

摘要： 研究了离子交换法选择性脱钙与多效膜蒸馏相结合用于海水淡化和淡化厂浓水深度浓缩的可行性。海水或浓海水中钙离子能脱除90%以上，可防止高倍数浓缩时海水中硫酸钙沉淀对膜造成污染。本文以膜通量、造水比和馏出液电导率为多效膜蒸馏过程的性能指标，研究了操作条件对过程性能的影响。膜通量最高可达6.07 L/(m2?h)，造水比最高可达13.2；当海水浓缩至250 g/L时，馏出液的电导率小于200 μm/cm，膜通量和造水比仍可达3.61 L/(m2?h)和4.96。以除钙后的浓海水为料液，利用两种多效膜蒸馏组件分别进行了持续45天的操作稳定性实验研究，在试验期间膜组件性能没有明显下降。该研究结果表明，多效膜蒸馏结合选择性脱钙是适合于海水深度浓缩及资源综合利用的高效节能技术。

关键词: 多效膜蒸馏, 造水比, 海水, 脱钙, 深度浓缩, 操作稳定性