Experimental and Theoretical Investigation of Forward Osmosis and Membrane Distillation Hybrid System

近年来，随着全球人口和经济增长的增加，对清洁水的需求增加已成为许多国家的主要关切。各种研究表明，水资源短缺有可能影响全球数十亿人，Burek等人（2016）最近的一项研究表明，到2050年，多达57亿人可能生活在面临水资源短缺的地区。因此，为了满足全球对清洁水的需求，人们对可持续水工程领域投入了越来越多的研究。水净化技术通常可分为膜分离技术和热分离技术。热分离技术已经在工业中使用多年，并且主要基于蒸馏过程操作。然而，能够提供比热分离技术更上级分离的膜的开发和应用已经导致研究向基于膜的技术转变。目前，反渗透（RO）是最广泛使用的膜分离工艺，并已用于海水淡化等应用。RO通过向进料溶液施加液压来工作，这导致水流过膜。虽然由于膜的高选择性，该方法是有效的，但是需要大量的能量来产生和维持可能超过60-70巴的液压。这与RO预处理要求和膜污染问题（例如，膜性能随时间劣化）结合，可能导致显著的资本、操作和维护费用，这可能导致RO对于贫困社区是不切实际的。因此，有必要进一步研究，以找到一个可靠的和成本效益的水净化技术，以建立清洁水的长期可用性。该项目正在进行的工作，其中福尔斯属于EPSRC工程研究领域，集中在一个相对较新的膜分离过程称为正渗透（FO）。FO具有提供与RO类似的分离能力的潜力。然而，与RO不同，FO利用通过使用浓缩的“汲取”溶液产生的自然渗透压梯度，以便从进料溶液中分离水，而不是施加液压。因此，FO可以提供一种有前途的低能耗解决方案，有助于缓解全球清洁水短缺的问题。已经投入大量研究来寻找更有效的汲取溶液（例如，产生更高的渗透压）和改善膜性能。然而，很少有研究将联合收割机FO与合适的提取液再生技术相结合，这对于分离所得提取液和水混合物以分离水产物和再循环提取液是必要的。因此，在该项目中，一种新型的Aquaporin InsideTM FO膜与一种有前途的热驱动再生技术膜蒸馏（MD）相结合，该技术可以在相对较低至中等温度下操作。本计画的主要目的是探讨FO-MD复合工艺应用于净水的可行性。已经确定了四个关键目标，以实现这一目标，这些目标中的每一个都被设计为通过理论和/或实验研究来探索FO-MD混合工艺的新特性。本项目的主要目标和创新性工作包括：（i）FO-MD混合系统的数学模型和混合系统中FO和MD过程的平衡（ii）FO-MD混合系统在废水处理中的应用（iii）FO-MD混合系统的能量需求分析和使用低品位能源的可行性

With increasing global population and economic growth during recent years, the rise in demand for clean water has presented a major concern for many countries. Various studies have shown that water shortages have the potential to affect billions of people around the world, with a recent study by Burek et al. (2016) suggesting that up to 5.7 billion people could be living in areas that are facing water scarcity by 2050. As a result, increasing research attention is being invested into the sustainable water engineering field to find novel technologies that can contribute to meeting the global demand for clean water.Water purification technologies can generally be classified into membrane separation and thermal separation techniques. Thermal separation techniques have been used in industry for many years and primarily operate based on the process of distillation. However, the development and application of membranes that can offer superior separation to that of thermal separation techniques has led to a shift in research towards membrane based technologies. Currently, reverse osmosis (RO) is the most widely used membrane separation process and has been used for applications such as seawater desalination. RO works through the application of hydraulic pressure to a feed solution, which results in a flow of water through the membrane. Whilst this process is effective due to the high selectivity of the membrane, a significant amount of energy is required to generate and maintain the hydraulic pressure that can be in excess of 60-70 bar. This, in conjunction with RO pre-treatment requirements and membrane fouling issues (e.g. deterioration of membrane performance with time), can lead to significant capital, operating and maintenance expenses that can result in RO being impractical for impoverished communities. Thus, further research is necessary to find a reliable and cost effective water purification technology in order to establish the long-term availability of clean water.The work being carried out in this project, which falls within the EPSRC Engineering research area, focuses on a relatively new membrane separation process known as forward osmosis (FO). FO has the potential to offer similar separation capabilities to that of RO. However, unlike RO, FO utilises a natural osmotic pressure gradient that is generated through the use of a concentrated 'draw' solution in order to separate water from the feed solution as opposed to the application of hydraulic pressure. As a result, FO could present a promising low-energy solution that can help to alleviate the global shortages of clean water. Significant research has been invested into finding more effective draw solutions (e.g. generation of higher osmotic pressures) and improving membrane performance. However, few research studies have been conducted to combine FO with a suitable draw solution regeneration technology, which is essential to separate the resulting draw solution and water mixture to isolate the water product and recycle the draw solution. Therefore in this project, a novel Aquaporin InsideTM FO membrane has been coupled with a promising thermally driven regeneration technology, membrane distillation (MD), which can be operated at relatively low to moderate temperatures. The main aim of this project is to investigate the feasibility of applying the FO-MD hybrid process for the purpose of water purification. Four key objectives have been identified to achieve this aim and each of these objectives have been designed to explore novel features of the FO-MD hybrid process through theoretical and/or experimental investigations. The objectives and novel work in this project include:(i) Mathematical modelling of the FO-MD hybrid system and balancing of FO and MD processes within the hybrid system(ii) Application of FO-MD hybrid system to wastewater treatment(iii) Analysis of FO-MD hybrid system energy requirements and feasibility of using low-grade energy sources