Abstract
Growing uncertainty in the future availability of freshwater sources has led to an increase in installations for desalination of seawater. Reverse osmosis (RO), currently the most widely adopted technique, has caused environmental concerns over the high associated greenhouse gas emissions and generation of large amounts of chemicals-containing brine. Significant consumption of electricity for RO desalination is an additional challenge, particularly in remote locations. In this review, forward osmosis (FO), membrane distillation (MD) and capacitive deionisation (CDI) are assessed as potential substitute technologies and the major recent advancements in each field are discussed. These emerging technologies offer significant advantages over RO, such as higher salt rejection (CDI, MD), higher recovery of water (MD), fewer pre-treatment stages (MD, FO) and the ability to use low-grade energy (MD, FO). In their current state, stand-alone technologies cannot compete with RO until certain challenges are addressed, including pore-wetting (MD) and high energy consumption (MD, CDI, FO). Hybrid systems that combine RO and emerging technologies may be useful for feed waters that cannot be treated by RO alone and their benefits may be able to offset the increase in capital costs. These and other aspects, such as operational stability should be considered in larger-scale, long-term studies.
Highlights
3% of all global water reserves is available as freshwater
This review aims to inform about the ongoing questions regarding the use of reverse osmosis (RO) and the above-mentioned emerging technologies for seawater desalination
It is worth noting that, while reducing fouling would extend the lifetime of RO membranes, the environmental impacts related to the manufacturing, transportation and incineration of membranes are insignificant relative to the impacts from the RO process associated with electricity consumption and brine production [53]
Summary
3% of all global water reserves is available as freshwater. Much of this is in the form of glaciers and ice caps with the remaining 97% being seawater [1]. Improvements in the conservation, distribution and management of water are important but additional availability of freshwater is essential in ensuring that the growing demand can be met Given its abundance, this can be achieved through desalination of seawater, which is becoming one of the key technologies for increasing the availability of clean, drinking water for the global population. The brine itself contains valuable resources, including magnesium sulphate, calcium carbonate and lithium, which cannot be recovered using current RO technology [31] Emerging technologies, such as forward osmosis (FO), membrane distillation (MD) and membrane capacitive deionisation (MCDI) are being explored to reduce the energy consumption, fouling and brine issues associated with desalination; successful breakthroughs in their development have led to a rapidly growing research interest [10].
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