2000 AFS Chair - Wallace Leung

Prof. Wallace Leung, our November saluted chair, was the AFS chair in 2000. He received his MSc in 1978 and Doctor of Science in 1981 both in Mechanical Engineering from MIT. Since 2005 he is associated with the Hong Kong Polytechnic University, Hong Kong, as Chair Professor of Innovative Products and Technologies in the Mechanical Engineering Department. He also assumes a concurrent appointment as Director of the new institution-wide Research Institute of Innovative Products and Technologies, which incorporates interdisciplinary and interdepartmental approach on product development in healthcare and medical applications.

Previously, he worked in Water Purification Associates 1978-1980; Gulf Oil Corporation 1981-1983; Schlumberger 1984-1986; Bird/Baker Hughes 1986 – 2004; and Advantech Engineering 2004-2005. Prof. Leung was Chairman of the AFS conferences respectively held in Chicago 1993, Boston 1999, and most recently New Orleans 2004. The latter was the celebrated 9th World Filtration Congress in which delegates from over 35 countries attended the 7-day event with more than 300-paper presentation.

He was also the Chairman of the International Delegation on Filtration Association (2000-2004) and he has recruited three additional member countries to join the association with 10 members at present – Austria, Belgium, China, France, Germany, Hungary, Japan, Nordic Countries, UK, and USA. He has published numerous technical papers on filtration and separation, delivered several keynotes, written two books on centrifugation, holds 36 US patents on separation technologies, invented and commercialized over 10 centrifuge products and technologies.

Why did you join the AFS and filtration industry?

After obtaining my BSc from Cornell, I was planning to continue my study in fluid mechanics specializing in re-entry vehicles but my advisor at MIT, Prof. Ronald Probstein, changed his interests to application of fluid mechanics to improve water purification. I researched ultrafiltration, a relatively new field then using hydrodynamics knowledge to reduce adverse effects of protein build-up on membranes due to filtration – this was back in 1977.

Concentration polarization is still one of the concerned problems today despite the membrane industry has been advanced with leaps and bounce in the past 30 years and has made significant improvement in alleviating the problem based on operation below critical flux. My doctoral research was involved in inclined plate sedimentation, applicable to clarification in water treatment and minerals processing.

My work at Gulf Oil was in flow in a compressible porous media, which is analogous to flow in a filter cake. In 1986, I have published two papers on dual-porosity, dual-permeability of fractured petroleum reservoir – a concept that is re-used today in the filtration research of porous filter cake with cracks or fibers. I returned to filtration and separation field after spending 6 years in the oil patch, and for the next 20 years I carried out R&D work to improve centrifugation, filtration and separation of different equipment and on various processes including biotechnology. There is room for improvement which makes the subject interesting and challenging.

AFS is the place where I run into people with different background, experiences, and talents such as the late Prof. Frank Tiller. It is an ever-changing Society with new faces and new blood. Through the annual meetings and topical meetings I get ideas and additional food-for-thoughts in the field of filtration and separation. The networking possibility in the AFS family is just great for all who work in this field.

What changes (technology, economic, governmental, environmental etc) have had the most impact on the filtration industry?

I believe that advancement in technologies has breeze “fresh air” into filtration and separation in both knowledge and practice. Membrane technologies in reverse osmosis, nanofiltration, ultrafiltration and microfiltration have improved in both selectivity and permeation rate of solution and suspension. In solid-liquid and solid-gas separation and filtration, polymer (for liquid only), equipment design and operation control, advanced filter media, and instrumentation all bring anywhere from incremental to significant strides in the field.

New chemical, mineral and biotechnology processes also demand special tailored made filtration and separation. Environmental regulations also imposes stringent discharge standard from 2.5-micron standard (PM2.5) down to 1-micron standard (PM1) for air pollution. This demands special filters such as nanofiber filters to effectively remove submicron aerosols.

Where do you see the filtration industry in 5-10 years?

Hybrid membrane technologies (membrane distillation, membrane bioreactors etc.) would become more matured and popular. Numerous “custom-made” liquid (e.g. prescribed sodium concentration etc.) processed through membrane system will gain wide-acceptance in the market due to competitive pricing.

Filter media will continue enjoy attention from high-temperature application in power plant (to remove damaging particulates before gas turbine) to application for removing challenging submicron particulates yet with lower pressure drop.

Also more practical application in high-valued (biotechnology, specialty chemical) to lower-value (mineral processing) will be targeting in the liquid side of separation of submicron to micron sized particles. This will present a challenge to existing technologies, and more R&D work needs to be carried out to address this challenge.