正渗透（FO）技术具有膜污染轻，分离效率高等优势，已被广泛应用于废水处理、海水淡化、化工浓缩等领域。然而，FO技术的放大推广应用正面临着严峻挑战，这主要是因为缺乏高性能的FO膜，以及难以实现汲取液的回收循环利用。为此，本论文主要研制了具有高渗透选择性的薄层复合（Thin-film composite, TFC）FO膜，并制备了抗浸润疏水疏油纳米纤维膜，采用膜蒸馏（MD）过程浓缩前段正渗透中被持续稀释的汲取液，构建了稳定可持续运行的正渗透-膜蒸馏（FO-MD）集成系统。并将FO-MD集成系统用于市政污水处理过程，考察了正渗透-膜蒸馏集成系统用于污水处理过程中的性能参数，最终实现了以污水为进水到高品质出水的膜集成水处理过程。随后又将FO-MD集成系统用于果汁浓缩过程，开发了防腐剂山梨酸钾汲取液，主要研究结果如下：

（1）高渗透选择性正渗透复合膜的制备及性能评价

首次采用聚砜基嵌段共聚物聚砜-聚乙二醇（PSF-b-PEG）膜材料制备超滤支撑层，通过界面聚合反应制备聚酰胺活性层，制得正渗透复合膜。研究结果发现，以1 mol/L氯化钠为汲取液，在聚酰胺活性层朝向汲取液侧（AL-DS）操作模式下，所制的正渗透复合膜水通量高达45.1 L/(m²·h)，NaCl反向盐通量仅为2.8 g/(m²·h)，并且TFC膜渗透选择性的A/B值高达19.56 bar^-1（其中，A为水渗透系数，1.76 L/(m²·h·bar)；B为NaCl盐渗透系数，0.09 L/(m²·h)），高于HTI公司商业化正渗透复合膜A/B值的3倍。这说明嵌段共聚物PSF-b-PEG用作正渗透膜支撑层，有助于获得具有高渗透选择性的正渗透膜，可以打破传统正渗透膜普遍存在的渗透选择的上线平衡。

本研究还考察评价了高性能正渗透膜的抗污染性能。在正渗透错流测试系统中，以牛血清白蛋白（BSA）模型污染物，发现基于嵌段共聚物支撑层的TFC膜通量的衰减和水力反洗通量恢复率分别为39.1%和80.6%，优于传统TFC膜的通量衰减及通量恢复（47.6%和63.9%）。这说明正渗透膜的PSF-b-PEG支撑层，可以有效降低蛋白污染物在膜面的粘附，显著缓解TFC膜的膜污染。

（2）高通量疏水纳米纤维膜的制备及其在膜蒸馏中的性能评价

针对膜蒸馏过程中疏水微孔膜易被浸润的问题，我们采用静电纺丝法制备高渗透性聚偏氟乙烯-六氟丙烯（PVDF-HFP）疏水纳米纤维膜，采用低表面能1H, 1H, 2H, 2H-全氟癸基三乙氧基硅烷（FAS）改性剂对PVDF-HFP纳米纤维膜进行表面改性。研究结果表明，在动态错流直接接触式膜蒸馏装置中，FAS改性的PVDF-HFP纳米纤维膜可以有效抵抗进料液中表面活性剂十二烷基硫酸钠（SDS）的浸润，保持截盐性能不变。这说明我们制备的疏水疏油纳米纤维膜具有良好的膜蒸馏膜抗浸润性能。

（3）FO-MD集成系统在市政污水处理中的应用

针对市政污水中有机物含量高的特点，对获得的高性能FO膜进行表面改性，随后利用氯化钠作为正渗透过程的汲取液，并采用静电纺丝制备PVDF-HFP纳米纤维膜进行膜蒸馏，实现正渗透中被持续稀释的汲取液的浓缩，构建了正渗透-膜蒸馏集成系统，优化系统运行参数实现正渗透和膜蒸馏过程中膜通量的匹配，并处理市政污水，考察了正渗透-膜蒸馏集成系统的运行稳定性和市政污水的处理效果。研究结果显示，当FO过程和MD过程的膜通量可稳定保持在18 L/(m²·h)，系统连续运行75 h，产出高品质纯水（电导率~ 10 μS/ cm）。

（4）FO-MD集成系统在果汁浓缩中的应用

利用防腐剂山梨酸钾作为正渗透过程的汲取液，研究发现山梨酸钾不仅具有高水溶性、高渗透压、低粘度、低反渗通量等优异汲取液的性能特点，同时还具有无毒并可抑制微生物滋长等适用于食品加工行业的性能优势。结果表明，在FO-MD集成系统中，AL-FS（聚酰胺活性层朝向进料液侧）模式下，以2 mol/L山梨酸钾溶液为汲取液，FO过程和MD过程的膜通量可稳定保持在5 L/(m²·h)，连续运行240 h，可获得浓缩倍数高达4.25倍的苹果汁及高品质纯水（电导率 < 25 μS/ cm）。另外，测试发现浓缩果汁中的可滴定酸度及维生素C等营养成分含量无损失，同时山梨酸钾在浓缩果汁中累积量仅为0.45 g/L，远低于国标食品中的添加量。这说明FO-MD集成系统不仅可以有效浓缩果汁，获得高浓缩倍数的果汁，同时果汁品质良好。

综上所述，本论文针对正渗透技术在实际应用推广中所面临的挑战，研制了高渗透选择性的正渗透复合膜，构建和评价了FO-MD集成系统，并开发了高通量抗浸润膜蒸馏膜，以常见环境污水体系中的市政污水处理为实际应用案例进行实验探索，最终实现了膜集成系统的长期连续运行，并最终产出高品质纯水。此外，此工作开发的正渗透复合膜，高通量纳米纤维膜，以及FO-MD集成系统也在果汁浓缩领域进行了初步尝试，获得较好的浓缩效果。这也说明该集成技术也可推广到其它污水处理、海水淡化等环境保护水处理领域及食品加工、医药、化工领域等含有热敏性物质的分离或浓缩领域，具有很好的实际应用价值。

Forward osmosis (FO) has been developed as an emerging membrane separation technology with outstanding performances including low membrane fouling and potential high separation efficiency. However, the absence of a high-performance membrane is a major challenge to efficiently operate FO process for its further development. Moreover, FO is a self-dilution process and the re-concentration of draw solution is needed to make FO work sustainably. Herein, this work aims to fabricate a high-performance FO membrane with good perm-selectivity and integrate the membrane distillation (MD) process with FO process to reconcentrate the draw solution. Finally, the integrated forward osmosis-membrane distillation (FO-MD) process is used to treat municipal waste water and the operation parameters are investigated. In addtion, the FO-MD process is also used to concentrate juice and the juice quality is evaluated. The major research focuses on the following:

(1) Fabrication of high performance thin-film composite (TFC) FO membrane and its properties characterization

The amphiphilic block copolymer of polysulfone-block-poly (ethylene glycol) (PSF-b-PEG) was used as membrane materials to cast the support layer for TFC membrane through the phase inversion method. The polyamide selective layer was fabricated via interfacial polymerization on top of the PSF-b-PEG membrane support. Results show that the optimized TFC membrane with the PSF-b-PEG support achieved an improved water flux (45.1 L/(m2·h)) and a comparable reverse salt flux of 2.8 g/(m2·h) when using deionized water as feed solution and 1 mol/L NaCl as draw solution in the AL-DS mode. The fabricated TFC FO membrane exhibited a great performance with high permeability-selectivity A/B ratio of 19.6 bar-1 (water permeability coefficient, A, 1.76 L/(m2·h·bar), salt permeability coefficient, B, 0.09 L/(m2·h)), which are about 3-fold higher than the commercial TFC FO membrane from HTI. The results indicate that the TFC FO membrane with the PSF-b-PEG support breaks the pemeability-selectivity trade-off to improve the FO membrane performance.

The anti-fouling performance of the TFC (PSF-b-PEG) and TFC (PSF) membrane was investigated using bovine serum albumin (BSA) as model protein foulant. The dynamic fouling experimental results showed that the TFC membrane with the PSF-b-PEG support has a lower water flux decline (39.1%) and higher recovery (80.6%) towards BSA foulants than the corresponding 47.6% and 63.9% of TFC membrane with the PSF support.

(2) Fabrication of highly permeable electrospun nanofibrous membranes for anti-wetting performance in membrane distillation

Polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) nanofibrous membranes were fabricated through electrospinning. 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS) was used to fluorinate PVDF-HFP fibers and was then crosslinked upon dealcoholization under thermal treatment. The FAS modified PVDF-HFP nanofibrous membranes exhibited long-term robust antiwetting performance during the MD process in the presence of surfactant sodium dodecyl sulfate in the feed saline solution.

(3) The integration of forward osmosis-membrane distillation (FO-MD) membrane process for municipal wastewater treatment

The FO membrane was modified via surface modification for treating the municipal wastewater which has a characteristic of high concentration of organic substance. The fabricated TFC FO membranes and PVDF-HFP electrospun nanofibrous membranes were employed in the FO and MD processes, respectively. An integrated FO-MD process was systematically investigated for wastewater treatment. The simulative municipal wastewater and NaCl solution were used as feed solution and draw solution in the FO process, respectively. The MD process was used to maintain the constant concentration of draw solution from the FO process and thus keep the constant water flux of FO membrane. Results find that the integrated system of FO-MD exhibited an equal and stable water flux (~18 L/(m2·h)) for both FO and MD membranes over long-term operation of 75 h. The high-quality pure water (Conductivity, ~ 10 μS/ cm) was obtained to confirm the successful application of the FO-MD system for municipal wastewater treatment.

(4) The integration of forward osmosis-membrane distillation (FO-MD) membrane process for juice concentration

Potassium sorbate, as a preservative and electrolyte, has high osmotic pressure, high water solubility and good thermal stability, non-toxicity and relative low viscosity, exhibiting a great potential as a draw solute used in the FO process. When 2.0 mol/L potassium sorbate solution was used as a draw solution, the integrated system of FO-MD exhibited an equal and stable water flux (~5 L/(m2·h)) for both FO and MD membranes over long-term operation of 240 h. 4.25-fold concentrated apple juice were obtained to confirm the successful application of the FO-MD system for juice concentration. Importantly, the concentrated juice has almost no loss in nutrition and also has low amount of potassium sorbate far below the required maximum level in food industry.

In conclusion, this work has fabricated a high-performance TFC FO membrane with good perm-selectivity, integrated the membrane distillation (MD) process with the FO process to reconcentrate the draw solution for municipal wastewater treatment, and developed a non-toxic food preservative potassium sorbate as a renewable draw solute in FO-MD process for juice concentration. A sustainable FO-MD integrated system along with the high-performance FO membrane and MD membrane was thus demonstrated as an applicable technology for wastewater treatment and juice concentration, which has promising scale-up and practical applications in the other fields.