|Ph.D Student||Nir Oded|
|Subject||Removal of Boron from Seawater by Reverse Osmosis Membranes:|
New Operational Approach and Advanced Process
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Ori Lahav|
|Full Thesis text|
This work is focused on the challenge of boron removal from desalinated water, a topic closely related to the food-water-energy nexus. Over the last decades, water scarcity became a global crisis, mainly driven by increased water consumption due to elevating living standards accompanied by human population growth. In addition, conventional freshwater sources such as rivers, lakes and aquifers are continuously depleting and deteriorating as a result of pollution, overuse and climatic changes. According to most water resources experts, seawater desalination will be a major part of any sustainable solution to the global water crisis. Desalinated water is increasingly used for agriculture, the most water consuming human activity, both directly and indirectly (via wastewater reuse). However, adjusting desalinated water to meet quality requirements for irrigation, necessitates further treatment, thus pushing cost and energy consumption higher. The main purpose of this further treatment is to remove dissolved boron, which has detrimental effects on many edible crops. Reverse osmosis membrane filtration, the leading desalination technology today, efficiently removes dissolved salts such as NaCl, however small and neutral solutes such as boric-acid (the dominant dissolved form of boron in seawater) are poorly rejected by the membranes. In the first part this work, a novel process which significantly increases the efficiency of boron rejection by reverse osmosis membranes is presented. The process began with the acidification of the seawater feed, followed by the removal of dissolved carbon-dioxide using aeration towers and base addition to obtain high pH. Adjusting the acid-base chemistry of the feed water in this fashion, resulted in boron rejection over 90% and at the same time significantly reduced the risk of membrane blockage by precipitated calcium carbonate. Due to the improved boron rejection, further treatment could be abandoned, thus reducing cost and energy consumption. The second part of the work is dedicated to advanced modeling and simulation of reverse osmosis processes. Modeling efforts were focused on the transport of weak-acid species (like boric acid), which is highly challenging due to the complex interconnections between membrane transport phenomena and numerous chemical reactions occurring during filtration. This challenge was met by applying a cutting edge reactive-transport approach, which couples thermodynamic and transport models through the linking of two computer platforms, thus considerably improving model predictions for pH, boric acid and the carbonate system in all process stages. Furthermore, a new technique for accurate pH measurement in desalination brines, which was missing from literature, was developed.