Prof. Ora Kedem, a pioneer of membrane science whose work helped shape modern desalination and water treatment, died in February at the age of 101. Born and raised in Vienna during the rise of the Nazi Party, she swam to the shores of British Mandate Palestine at age 16 as a survivor of the doomed Patria and went on to become a world-leading scientist in her field.
Kedem’s scientific legacy is profound, encompassing foundational theoretical advancements and practical applications. Together with Prof. Aharon Katzir-Katchalsky (1914-1972), she developed tools that helped scientists understand how substances like water, salts, and chemicals move through biological and artificial membranes—thin, permeable barriers that control the exchange of materials, generate energy, and spur chemical or biochemical reactions.
These tools include the “Kedem-Katchalsky framework”, developed in the 1950s and 60s, which served as a cornerstone for the development of membrane-based separation technologies such as kidney dialysis, water purification and desalination, industrial filtration, and some medical and biotech devices. For their joint work, Kedem and Katzir won the Israel Prize in Natural Sciences in 1961. Their theory continues to be widely cited and remains foundational in the study of transport through both biological and synthetic membranes.
Following Katzir’s tragic death in a terrorist incident in 1972, Kedem committed to continuing their scientific mission. She founded and chaired the Department of Membrane Research at the Weizmann Institute and played a key role in the early development of Ben-Gurion University of the Negev in the 1960s. She co-founded one of Israel’s first biotech start-up companies, Membrane Research Weizmann, and helped build the Desalination and Water Treatment Department at Ben-Gurion University, which she headed for eight years.
Survivor of the Patria
Ora Kedem was born Josefa Katz on July 2, 1924, in Vienna, the youngest of three siblings, with an older sister and a brother. Her mother was a seamstress, her father a perfumer who was highly educated. After Austria was annexed by the Nazis in 1938, an event historically known as the Anschluss, the Katz family’s businesses were liquidated. Her brother and sister had previously immigrated to Israel with the Youth Aliya movement, as did her father who came separately as part of the clandestine immigration of Jews to Mandatory Palestine known as “Aliya Bet”. Ora and her mother stayed behind temporarily, and her mother made money by tutoring wealthy women in their homes. Ora hadn’t been able to attend school for two years because of the anti-Jewish laws enacted that year.
In 1940, mother and daughter were among the last group of Austrian Jews allowed to leave the country before the Nazi extermination of the country’s Jews began in earnest. In November, Ora, who was 16, and her mother boarded a ship on the Danube that would take them via the Black Sea, where they reunited with her father, and from there to Palestine.
As the ship neared the shore, it was intercepted by a British blockade against Jewish immigration to Palestine, and passengers were transferred to the Patria, bound for detention to Mauritius with 1,800 European Jewish refugees aboard. To protest the deportation policies of the British mandate, members of the Haganah, the Jewish paramilitary organization of pre-state Israel, had planted a bomb on board. The explosion, on November 25, caused more damage than anticipated and the Patria sank rapidly.
The experience remained one of the defining events of her life and, she remarked in later years, helped shape her lifelong sense of independence and responsibility.
Ora and her mother, along with around 2,000 other passengers, were forced to swim to lifeboats. Around 200 refugees and a number of British soldiers drowned. Ora was supposed to be on kitchen duty that day in the ship’s hull—a place from which few managed to escape. But by chance she had agreed to trade places with another passenger. When the blast occurred, she took charge of saving her mother and another passenger who, like her mother, didn’t know how to swim. The experience, she said later, led to her belief that a person can rely only on themselves to survive and thrive.
On shore, citizens of the “Yishuv,” the local Jewish settlement, gave the new arrivals dry clothes and the British police transferred them to the detainment camp in Atlit, where they received food and shelter. They were taught basic Hebrew in the camp and Ora enrolled in the Levinsky Seminar for teachers, hoping to realize her dream of becoming a teacher.
Her mother, while she had had little education herself, “made sure, with determination, that I would study, whether it was difficult or not,” Kedem said in a 2009 interview. While studying, she helped support her family by working as a cleaner and tutoring in physics. She also helped care for her sister, who was ill and frail.
Ora stood out among the young women in the Seminar for her unusual accomplishments in physics, and her physics teacher encouraged her interest. She decided to pursue an undergraduate degree at the Hebrew University of Jerusalem. After excelling in the rigorous entrance examinations, she received a merit-based grant of 28 Israeli liras—the equivalent of $112—which she recalls as “a great, great deal of money at that time”. It was enough to fund her studies and living expenses.
University years
In the mid-1940s, during the first year of studies, Ora joined the Science Corps (HEMED, in Hebrew) of the Haganah and led a group of women responsible for developing materials for weapons. In tandem, she studied under Prof. Ladislaus Farkas (1904-1948), also of Austro-Hungarian origin and who had immigrated to Israel in 1935 and founded Hebrew University’s Department of Physical Chemistry. Back in Germany, he had been the personal assistant to the famous but controversial German chemist Prof. Fritz Haber (1868-1934) who won the 1918 Nobel Prize in Chemistry.
When Kedem first met him, she recalled, “Farkas was a young man—33—and he was already a very well-known physical chemist. He had no Jewish education. He never spoke Hebrew properly. He lectured not only with a Hungarian accent but with Hebrew mistakes. He was a great man who did not receive his rightful place… I admired him very much. He was a very elegant and polite man and there was something unique about him.”
She had completed her bachelor’s and considered stopping her studies in order to devote herself to the Science Corps. Farkas encouraged her to keep going. He arranged a special scholarship that involved working with Dr. Moshe Rudolph “Rudi” Bloch (1902-1985), the chief scientist of the Dead Sea Works who later received the 1966 Israel Prize. The company had been granted concession for extracting salts and minerals from the Sea, which contains up to 80 times the bromide levels of standard ocean water, and thus was an excellence source for bromine extracted via an industrial process.
By the end of the War of Independence, Ora had completed a master’s degree on the adsorption of bromine. During this time, she met her future husband, Abraham Kedem, a refugee from Transylvania, at HEMED, where she also met Katzir, commander of the Corps.
She began her doctoral research in 1949 at the Weizmann Institute, initially under Prof. Ephraim Katzir (1916-2009), Aaron’s brother (and fourth President of Israel), and then with Aaron Katzir in the Department of Polymer Research. Her PhD degree, awarded in 1953, is from the Hebrew University because Weizmann did not yet have a formal degree-granting track at that time.
She remembered fondly the euphoria on the small Institute campus in those early years, which she attributed to “a combination of the sense of impact, plus the aura around the new Institute, plus the new State of Israel. The world was coming to us. You did not need to run around [the world]… You could sit in Rehovot and sooner or later everybody would come by. The lecturers who visited—today I can no longer follow it but in those days all the great figures of the world came as guests, at one time or another, and one could meet them and see them.”
This was despite the fact that the Institute was small, with just a handful of buildings. She worked in the Ziskind Building, which “very quickly became crowded,” she recalled. Lab equipment was sparse and she built her own, which included glassblowing. The Institute lacked experts in many subjects, so many of the students adopted a particular subject, researched it, and lectured on it to their peers. Kedem took upon herself the subject of membranes.
Plentiful water in a dry land
Abraham Kedem studied mechanics and taught briefly at a technical school. For a time, they lived in Tivon, near Haifa, while Abraham worked in HEMED and Ora was working on her doctorate.
During Ora’s early days at Weizmann pursuing her doctorate, she came across a book on plant physiology. It described experiments on water and solute movement that tied in closely with the theoretical work on membranes with which she was familiar, including thermodynamic principles. Inspired, she embarked on a series of studies with Katzir on transport in biological membranes, which were published starting in 1958 and were well-received. A mere three years later, they were awarded the Israel Prize.
“The field grew by several orders of magnitude very quickly,” Kedem remarked. “In that sense, we simply got on the right train.”
She also credits two conferences, including a Gordon Research Conference in 1963, for truly launching her career and drawing her to the desalination field.
In pioneering the application of nonequilibrium thermodynamics to biomembrane processes, she and Katzir extended the principles of irreversible thermodynamics, originally developed by Prof. Lars Onsager (1903-1976), a Norwegian physical chemist and theorical physicist who won the Nobel Prize for Chemistry in 1968.
Kedem’s and Katzir’s main joint contribution, the Kedem-Katchalsky framework, was a mathematical theory that explains how substances move through membranes that let some things pass while blocking others. It applied ideas from thermodynamics—the physics of energy and flow—to biological and artificial membranes. This helped engineers and scientists alike make determinations about how quickly water or other liquids and dissolved substances like salt can move through certain membranes; what drives the movement (via pressure, concentration, or electrical forces); and how liquids and substances dissolved in the liquids affect each other.
This and other theoretical frameworks on membrane transport were instrumental in advancing practical membrane-based technologies for desalinations, enabling efficient water purification in arid regions like Israel. With Prof. K.S. Spiegler (1922-2012), she devised the Kedem-Spiegler transport model in 1966, which characterizes the transport of water and salt through reverse osmosis and nanofiltration membranes. This contributed to Israel’s adoption of reverse osmosis plans which, starting in the 1970s, helped address chronic water shortages and boosted agricultural output. Spiegler, a professor at the University of California at Berkeley, maintained a strong research collaboration with Ben-Gurion University.
Also in that year, she was invited to Germany by scientific colleagues. She deliberated about visiting, given her childhood experiences in Austria. Ultimately, she agreed to go as long as Abraham could join, for emotional support. “Austria would have been too close for comfort, but Germany was easier for me,” she said. She spoke fluent German to her colleagues there and continued to travel to Germany throughout her career.
“There is no point in living in hatred. I became convinced that there is genuine goodwill in our generation,” she said.
Katzir died tragically in a terrorist incident at Lod Airport in 1972, after arriving from a scientific conference in Europe which he had attended with Kedem. Kedem was on a sabbatical that year in Basel, Switzerland, and she had flown back to Basel while Katzir flew to Israel. The sudden death of her longtime research partner and friend deeply unsettled her, and she determined to advance his scientific legacy. She was asked to take over the leadership of membrane research at Weizmann. Given the many developments of the field, she went on to found, in 1973, a department solely devoted to the study of membranes, the Department of Membrane Research, which was later absorbed into other departments.
In 1976, Kedem joined the faculty of the Department of Water Desalination at Ben-Gurion University, which she headed from 1995-2003. In 2006, the department became the Zuckerberg Institute for Water Research at the Jacob Blaustein Institutes for Deser Research. She remained scientifically active at Weizmann for the following decades.
Beyond her research contribution, Kedem trained generations of students who hold leading positions in academia and in the water sector in Israel and beyond.
If Kedem was focused on the porous nature of membranes in her research, she saw the metaphorical permeability of Weizmann departments and faculties as a major asset for scientific research. “There are no walls between departments. In many respects—people, the way of working, the relationships, the administration—the Institute is simply in another place,” she recalled. Moreover, her colleagues also allowed her the flexibility to combine research and parenting obligations, such that “there was truly a feeling of family… I saw that the good feelings of friendship that existed when we began continued” throughout the years. That was wonderful.”
A cup runneth over
While committed to basic science, Kedem was always minded toward applications for everyday life. She collaborated extensively with water engineers who leveraged her insights for commercial breakthroughs that helped transform Israel’s water challenges into solutions.
“I very much wanted to do applied things,” she recalled. In 1976, she co-founded Membrane Products Rehovot (later Membrane Products Weizmann Ltd.), with Dr. Rene Bloch, who committed suicide in 1976; she took over as Chief Scientist. The company focused on commercializing membrane technologies and was the second company to be established in the Science Park adjacent to the Institute.
Beyond desalination, Kedem applied membrane applications to wastewater treatment and chemical separation. She patented her so-called “cake filtration” method for water softening. This environmentally friendly approach precipitates and filters calcium minerals without generating polluting byproducts, and softens Israel’s hard water which contains stone. The company was not successful in commercializing the product because a competitor had already commercialized a similar product, according to her son Michael.
Among her engineering collaborators was Prof. Sidney Loeb (1917-2008), an American-born chemical engineer who is widely regarded as the co-founder of reverse osmosis along with Indian-born scientist Prof. Srinivasa Sourirajan (1923-2022) whom he met at UCLA. Reverse osmosis filters out salts, heavy metals, bacteria and chemical contaminants, leaving behind highly purified water via a membrane using pressurized water. Loeb and Sourirjan made the process commercially and economically viable. Loeb worked at the Negev Institute, which became Ben-Gurion University, where he trained a generation of desalination engineers.
Israel’s desalination industry took off in the early 2000s. Today, Israel has a large network of desalination plants which supply the vast majority of Israel’s drinking water and the country is a world leader in this resource-saving process.
Kedem remained active in research into her later years, co-authoring patents with her husband Abraham. She was named an International Member of the U.S. National Academy of Engineering in 2005, and was an honorary fellow of the European Membrane Society which she helped establish.
Abraham Kedem died in 2016. Ora Kedem is survived by her son Michael, a daughter, Ilana, and three grandchildren.