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Professor Kazuo Yamamoto


Citation for Professor Kazuo Yamamoto



Professor Kazuo Yamamoto of Japan is awarded the Lee Kuan Yew Water Prize for 2020 for his pioneering work in developing the submerged membrane bioreactor (MBR).

His successful demonstration, in 1989, of the first operational submerged MBR was a major breakthrough in the field of wastewater treatment. And since then, the global application of submerged MBR technology has fundamentally transformed the sewage treatment process and improved the lives of hundreds of millions of people.

Wastewater needs to be treated to remove contaminants in order to produce an effluent of acceptable quality, so that it may be returned to nature, or to be further recycled for subsequent human use. Wastewater treatment, a biological process, involves using bacteria and protozoa to precipitate the dissolved organic matter within, which can then be removed as solids. Before the advent of MBRs, the process necessitated significant infrastructural investment in the form of large retention tanks and clarifiers.

Following the availability of synthetic membranes in the 1960s, MBRs were added as a side-stream process to wastewater treatment. Although side-stream MBRs could negate the need for huge settling tanks, the membranes are expensive and tend to foul easily. Their operation also, even today, extract a significant energy penalty and are hence only viable in niche use cases.

In the mid-1980s, Yamamoto began experimenting with the (then) inconceivable idea of submerging membrane modules directly into the biological treatment tank. In doing so, his design aimed to use low negative pressure, or suction, to drive the filtration process, hence circumventing the energy-intensive recirculation loop that had prevented side-stream MBRs from becoming more mainstream.

At the time, Yamamoto’s efforts were greeted with wide skepticism, and even ridicule, from other researchers. The very idea of immersing membranes inside used water went totally against prevailing scientific thinking. Unsurprisingly, many so-called experts had dismissed his notion as a ridiculous one that was doomed to fail. But Yamamoto held fast and persevered regardless. As it turned out, his persistence paid off and proved to be nothing less than game-changing.

Yamamoto’s great insight laid in operating the filtration process intermittently, instead of continuously, to prevent severe fouling from occurring. When paired with regular air scouring, sustainable membrane operation was achievable, resulting in the first-ever viable submerged-design prototype. His invention represented the world’s first successful application of submerged membrane technology for wastewater treatment.

Yamamoto’s submerged MBR, once considered an engineering impossibility, led to a paradigm shift in the scientific community’s fundamental understanding of membrane science and the limits of its application. It also marked the start of a new era in advanced used water treatment. Yamamoto successfully demonstrated the submerged MBR to be substantially superior to its side-stream cousin. Submerged MBR systems save space, use much less energy, foul less readily and can operate at low flux.

After proving everyone wrong, Yamamoto, most remarkably, chose to give up the intellectual rights for his invention. Instead, he opted to keep the new knowledge in the public domain. This allowed other scientists and engineers to build freely on his discovery and go on to create new advances and innovation for the benefit of all. In turn, this greatly hastened the adoption and commercialisation of submerged MBR technology globally. Within just 15 years of first publication, almost half of all sizable sewage treatment plants in the world had gone on to implement submerged MBRs in one form or another.

Today, submerged MBRs are commonplace in wastewater treatment. Highly energy-efficient, these systems consistently and sustainably produce treated effluent of high quality. Specifically, the superior effluent quality means that lengthy discharge outfalls can be replaced with much shorter nearshore options, saving water utilities many millions in infrastructure cost. Capable of substantively reducing bacterial and viral levels, the use of submerged MBRs significantly lessen the impact of releasing treated used water into the environment, enhancing public health in the process.

The submerged MBR’s ability to reliably produce particle-free filtrate currently provides the cheapest and most effective way to achieve the exacting quality standards required of feedstock for potable reuse. And so, its invention has greatly facilitated water recycling and reclamation — the only feasible answer for the world’s increasing water scarcity.

We in Singapore have benefitted tremendously from Yamamoto’s work. His creation lets us build very compact water reclamation plants, freeing up land for other uses. Tuas WRP — currently under construction and the world’s largest MBR plant when it becomes operational in 2026 — occupies only half the usual footprint because of his discovery. The high quality of effluent that will come out of Tuas, again because submerged MBRs first invented by Yamamoto, will enhance NEWater production and further advance the circularity of Singapore’s water economy.

The Lee Kuan Yew Water Prize 2020 recognises Professor Yamamoto for his pioneering invention and contributions to wastewater treatment, which have enhanced public health and increased water security for hundreds of millions of people all over the world.

About Professor Kazuo Yamamoto

With distinguished professorial positions held in the University of Tokyo, the Asian Institute of Technology, Chuo University, and Kindai University, Professor Kazuo Yamamoto is one of the most globally renowned and respected researchers in the field of wastewater engineering and membrane science. He has led and participated in membrane-related research and infrastructural projects totalling close to 11 billion Japanese yen (approximately SGD$139 million), establishing advanced water reuse and wastewater treatment facilities both in Japan and abroad. Professor Yamamoto holds a PhD in Engineering from the University of Tokyo.

Throughout his career, Professor Yamamoto has authored or co-authored 20 books and more than 130 scientific publications and was conferred 12 awards from international institutions including the European Desalination Society, the Japan Society on Water Environment, and the International Water Association, primarily for his notable invention of the world’s first operationally viable submerged membrane bioreactor (MBR).

In addition to these accolades, Professor Yamamoto’s relentless passion in improving MBR technology and accelerating its commercialisation has earned him advisory and leadership positions in over 40 academic societies, industrial associations, and scientific advisory boards apart from numerous faculty positions. Professor Yamamoto is currently serving as the President of the Water Reuse Promotion in Japan and Audit & Supervisory Board Member of IDEA Consultants Inc.