Bulletin Spring‧Summer Autumn‧Winter 1999

Dr. P.K. Wong obtained his B.Sc. and M . P h i l . from The Chinese University of Hong Kong in 1977 md 1979 respectively, and his Ph.D. from the University of California, USA in 1983. He joined CUHK as lecturer in biology in 1986 and was promoted to senior lecturer in 1994. Dr. Wong's research interest is in environmental biotechnology and environmental toxicology. Dr. Wong is concurrently associate director of the Centre for Environmental Studies. effluent wh i ch turns the nickel ions into nickel hydroxide, wh i ch is then precipitated as a slurry sludge. The sludge is removed, and is often bu r i ed i n landfills; but it may seep f r om the landfill, creating further problems. However, such methods also tend to be expensive, and reaction conditions have to be controlled rather precisely. Alternatives have to be explored, and a clever biological scheme that Dr. Wong has developed appears to offer very good promise. The idea is a three-step process. I n short, one tries to let the nickel attach itself to bacteria, let the bacteria attach themselves to magnetite, and finally let the magnetite attach itself to a strong magnet. N i ckel ions carry positive charges. It turns out that certain types of bacteria carry negative charges on their cell walls, so very naturally the n i c k el w i l l adhere to the bacteria. But the bacteria, wh i ch are less than 10-9 of a cm3 i n size, float about i n the waste l i qu id and are difficult to collect. So the second step is to let these bac t e r i a a t t a ch t hems e l v es to ma g n e t i t e. Magnetite is a magnetic species of i r on oxide. Under certain acidity conditions, magnetite exhibits a slight positive charge, so naturally the bacteria, wh i ch are still negatively charged, w i l l adhere to the magnetite. I n fact, it is speculated that the magnetite may have a h i gh ly porous structure, and once the bacteria bu r r ow their way into these pores, they may become trapped and are unable to come out, quite apart f r om the electrical attraction. The bacteria are said to be immobilized. Finally, the magnetite, because of its magnetic property, can be separated f r om the effluent using a strong magnet — i n mu ch the same wa y as a toy magnet picks u p metal paper clips. To recover the nickel that has been attached, one need only apply an acidic solution onto the magnetite. The nickel w i l l be separated and washed away w i t h the solution. The remaining bacteria that have been i mmo b i l i z e d b y the magnetite can be regenerated b y app l y i ng a neutral buffer. Promising Research Results This separation scheme was p r opo s ed i n a p r imi t i ve f o rm some eight years ago. Dr. Wong has investigated the basic science, and made several very significant improvements. A class of bacteria has been identified that has a special affinity for nickel. The research team has also established the best conditions for the removal and recovery processes: temperature, acidity, dissolved oxygen concentration etc. It has also been f o u nd that five to t en m i nu t es u n d e r moderate stirring is sufficient to remove most of the nickel — this is very fortunate, and is likely to lead to a very efficient removal process. Once the basic science has been established, the next step is to make a bioreactor. A prototype laboratory scale reactor w i t h five litre capacity has been built and tested. Design studies are i n hand fo r scaling up to 1,000 litres, wh i ch w i l l be large enough to be tested i n a realistic small factory situation. A prototype bioreactor to remove heavy metals from polluted water Research 20