Israel – one of the driest countries on Earth – now produces more freshwater than it needs and even sells a lot of it to its neighbor Jordan, which is landlocked and where people in the northern cities have water in their faucets only about once every two weeks.
How did Israel accomplish this turnaround? Israel has learned how to squeeze more out of a drop of water than any country in the world. Today some 585 million cubic meters of water per year – or 80% of its water supply – are desalinated from Mediterranean Seawater.
Water treatment is required for a sustainable potable water supply and can be leveraged to harvest valuable elements. Crucial to these processes is the removal of charge pH-dependent species from polluted water, such as boron, ammonia, and phosphate. Desalination removes mineral particles (salts) from saltwater, making it fit for human consumption and for irrigation. The chemical properties of some particles make them more challenging to remove than others.
South of Tel Aviv, the Sorek desalination plant lies the largest reverse-osmosis desal facility in the world. The most commonly used desalination method is by means of a membrane – a sort of sieve that allows water to pass through it, while blocking other particles, based on their size or charge.
Boron, which is naturally found in high quantities in the Mediterranean Sea, is among the hardest minerals to remove, as change in acidity causes it to change its properties. It is toxic in high concentrations and harms plant growth, which is a problem when the water is used for irrigation. The normal process of removing boron involves dosing the water with a base in order to facilitate removing the boron, followed by removal of the base.
The World Health Organization (WHO) guideline of standard boron concentration in drinking water is 0.3 mg/L in 1990. It is difficult to comply to this standard due to the available treatment technology reality.
However, this membrane is expensive and needs to be replaced periodically. Now, scientists from the Technion-Israel Institute of Technology in Haifa and the Wageningen University and Wetsus, a European center of excellence for sustainable water in the Netherlands have developed a way to improve the quality of desalinated water, while reducing the costs of the process. The findings of the international team’s study were published in PNAS (Proceedings of the National Academy of Sciences of the United States of America) under the title “Electrochemical removal of amphoteric ions.”
Boron is an essential micronutrient for plants and animals as well as a useful component for numerous industries. For green plants, a small amount of boron is necessary for their growth and development, but boron becomes toxic if the amount is slightly greater than required.
It is necessary to produce low boron containing water from reverse osmosis desalination plants for both human consumption and for agriculture. Desalinated seawater from such facilities often contains high boron content and, when used for irrigation, has been proven to be damaging to crops including blackberry, lemon and grapefruit.
Technion doctoral students Amit Shocron and Eric Guyes, under the supervision of Prof. Matthew Suss of the Faculty of Mechanical Engineering, together with their Dutch collaborators, developed a new modeling technique to predict the behavior of boron during desalination by means of capacitive deionization.
This is an emerging technique for water treatment and desalination using relatively cheap porous electrodes, as opposed to the expensive membrane. When an electric current is applied, charged particles (like boron under high pH conditions) are adsorbed by the electrodes and hence removed from the water.
Shocron formulated the theoretical framework that allowed this breakthrough, while Guyes constructed the experimental setup. Working together, they were able to develop the novel system. They found that for optimal boron removal, the positive electrode should be placed upstream of the negative electrode – counter to the accepted wisdom in their field. They also calculated the optimal applied voltage for the system, finding that higher voltage does not necessarily improve the system’s effectiveness.
The team said that the same method they developed could be used to solve other water treatment challenges as well – for example the removal of medicine residues and herbicides, which are difficult to remove using conventional methods.