How to make membrane distillation greener: a review of environmentally friendly and sustainable aspects

Abstract

There is an urgent need for the development of new water resources in order to solve the problem of the world's growing demand for clean water. Membrane distillation (MD) is a promising alternative to conventional seawater desalination. Although MD itself is often defined as sustainable desalination technology, there are many aspects within the membrane manufacture and process operation that make it far from being green. For instance, non-biodegradable polymers, toxic solvents and fluoroalkyl silanes are typical chemicals that unfortunately are used in membrane fabrication protocols. Additionally, the huge amount of wastewater generated from membrane fabrication processes makes solvent-free methods more attractive and desirable for extensive investigation. Apart from this, the low energy efficiency of the MD process can be effectively overcome by integrating MD systems with low-grade waste heat. This review critically addresses and discusses the recent advances in methods and strategies to improve the sustainability of MD technology, which is not a common scope of study among the research community. Here, our attention has been devoted to the main aspects of MD membrane fabrication, such as polymers, solvents (and their costs), nonsolvents, additives, solvent-free fabrication procedures, fluoro-free post-modification, and MD operation (energy consumption). This review intends to introduce inspiration for membrane scientists for the development of the next-generation MD process, by promoting the sustainable transformation of today's approaches into a greener way. In this latter scenario, we provide some timely considerations that could be followed by the researchers in the field.