Tapping into salty water to grow healthy food

Significance 

Water scarcity is a global risk owing to the fact that, despite our planet being over 70% water, sources of pure fresh water required to sustain many economic activities are limited across much of the globe. Therefore, alternative sources of fresh water are urgently needed and one plausible alternative is to desalinate brackish water.

Brackish water has low salt content, as compared to sea water, hence adding some economic sense to subject it to desalination. Desalination is an expensive process, although Forward Osmosis (FO) desalination has been reported to yield promising results. However, the immaturity of this technology coupled with some technical shortfalls hinders its application. Worse off, to date, limited academic research has been conducted on brackish water FO desalination and there has been no pilot-scale assessment conducted by any industry due to the high operating costs associated.

FO technology utilizes the osmotic flow produced when a concentrated draw solution pulls water across a semi-permeable membrane from a contaminated feed water. The draw solution can then be regenerated by a secondary system to produce clean water or used directly for other purposes, depending on what solution is used.

The FO technique has potential to fertigate agricultural lands economically should the forward osmosis system be improved. In this view, researchers from the Centre for Water Advanced Technologies and Environmental Research at Swansea University: Wafa Suwaileh (PhD candidate), Dr. Daniel Johnson and led by Professor Nidal Hilal critically evaluated a Fertilizer Drawn Forward Osmosis (FDFO) system for desalinating brackish water and converting it into fertilizer solutions suitable for the fertigation of agricultural land. Specifically, they investigated the performance of the FDFO using four fertilizer based draw solutions at various concentrations and a polyamide thin film composite (TFC) FO membrane for brackish water desalination. Their work was recently published in the research journal, Desalination.

In their study, combinations of fertilizer compounds as draw solutions were used in conjunction with a polyamide (PA)-TFC membrane commercially manufactured specifically for FO processes as a potential method for improving the water permeability and reducing the reverse solute flux. Moreover, the effect of polyamide (PA)-TFC material on the water flux and reverse solute flux (RSF) was investigated. The composition and salinity concentration of the brackish water (BW) feed was also examined to highlight its effect on the membrane and fertilizer draw solutions performance.

The results revealed that KCl fertilizer draw solution achieved the highest water flux and an acceptable reverse salt flux as compared to other fertilizer draw solution. Additionally, it was reported that the mixture KCl + KNO3 and KH2PO4 fertilizer draw solution generated the lowest water permeation and reverse salt flux. KH2PO4 draw solute promoted the growth of salt scaling which affected the membrane productivity. The negative charge of the membrane surface was responsible for precipitation of salt on the selective layer.

In summary, the study by Professor Nidal Hilal (internationally recognized as a world-leader in desalination) and his research team presented an in-depth assessment of brackish water desalination by fertilizer drawn forward osmosis system. Results showed that the membrane Zeta potential indicated that the negatively charged surface could induce reverse salt flux, leading to scaling on the surface. FDFO does not require a recovery step to re-concentrate the draw solution, instead using diluted draw solution as a supplement to irrigation water via fertigation.

Water, this most precious of natural resources, is often taken for granted despite many campaigns reminding us that one in ten of the world’s population has no access to safe drinking water. If you don’t have clean water, you can’t grow healthy food and you’re more likely to be sick and unable to work or attend school. This in turn leads to people being trapped in poverty, with all the social and security issues that poverty brings. As such, improving the water/food sustainability is of major importance for significantly improving the lives of 100s of millions of people worldwide”. Said Professor Nidal Hilal the lead author in a statement to Advances in Engineering

About the author

Daniel Johnson is a senior research officer working with Professor Nidal Hilal at the Centre for water Advanced Technologies and Environmental research (CWATER) in Swansea University. He received a BSc in Biochemistry from the University of Sheffield, before pursuing a PhD investigating dissociation of peptide structures using force microscopy at the University of Nottingham, which he received in 2006. Since then his main research interests have been in the fields of membrane separation research, advanced water treatment, membrane surface characterisation and colloid and interface science. He has published around 75 articles in refereed scientific literature.

About the author

Professor Nidal Hilal is a chartered engineer (CEng) in the UK, a registered European Engineer (Euro Ing) and is an elected fellow of both the Institution of Chemical Engineers (FIChemE) and the Learned Society of Wales (FLSW).

He is the Founding Director of Centre for Water Advanced Technologies and Environmental Research (CWATER) at Swansea University and is currently establishing NYUAD Water Research Center at New York University in Abu Dhabi. His research interests lie broadly in the identification of innovative and cost-effective solutions within the fields of nano-water, membrane technology, and water treatment including desalination, colloid engineering and the nano-engineering applications of AFM. His internationally recognized research has led to the use of AFM in the development of new membranes with optimized properties for difficult separations.

He has published 7 handbooks, 56 invited book chapters and around 500 articles in refereed scientific literature. He has chaired and delivered lectures at numerous international conferences. In 2005 he was awarded Doctor of Science (DSc) from the University of Wales and the Kuwait Prize for applied science “Water resources development”.

He is the Editor-in-Chief for the international journal Desalination. He sits on the editorial boards of a number of international journals, is an advisory board member of several multinational organizations and has served on/consulted for industry, government departments, research councils and universities on an international basis.

About the author

Wafa Ali is a Chemical Engineering PhD student at Swansea University in the UK, working under professor Nidal Hilal’s supervision in the Centre for Water Advanced Technologies and Environmental research (CWATER). Her PhD investigates the optimization of fertilizer driven forward osmosis system as a potential process for brackish water desalination. She is also a Research Associate at Qatar Foundation and is the author and co-author of over 10 refereed journal papers. In addition, Wafa is a reviewer for some prestigious international journals including Desalination and Journal of Water Process Engineering.

Reference

Wafa Suwaileh, Daniel Johnson, Nidal Hilal. Brackish water desalination for agriculture: Assessing the performance of inorganic fertilizer draw solutions. Desalination, volume 456 (2019) page 53–63.

Go To Desalination

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