Bulletin Spring‧Summer Autumn‧Winter 1999

The Bacteria Legion i n a Battle against Water Pol lut ion The Use of Biological Techniques to Combat Electroplating Pollution The Problem of Water Pollution Affects A l l Water po l l u t i on is a global problem, and is particularly serious i n c r owded cities such as Ho ng Kong. The sorry state of the Shing Mun River near the University, for example, is k n o wn to many. I n general, water quality is threatened b y the disposal of untreated h uma n and an imal waste into rivers and seas; where there is r ap id industrialization, industrial wastes also pose serious problems. Effluents f r om the dye i ng industry c a n y residual dyes that are not easily degradable; effluents f r om the electroplating industry c an y large quantities of toxic heavy metals. N o w a research project i n the Department of B i o l ogy offers the prospect of he l p i ng to reduce wa t er p o l l u t i o n. The project on the removal and recovery of nickel ions i n effluent by bacterial cells immobilized on magnetites is carried out by Dr. P.K. Wong of the Department of Biology. It follows an earlier investigation on me t al r emoval f unded b y an i n t e r nal direct grant i n 1987, and w o n competitive f u n d i ng ($540,000) f r om the Research Grants Council i n 1992. Po l l ut i on Caused by Electroplating I n electroplating, metals are first dissolved i n acid, and plated onto the host object b y the passage of an e l ec t r ic c u r r e n t . I n mo s t electroplating processes, a layer of nickel is first deposited as a base on wh i ch the ultimate surface layer (which may be copper, silver or gold) is then deposited. As a result, nickel is one of the most common l y occurring metals i n the electroplating process, and also i n the discharged effluent. It is estimated that 800kg of nickel sulphate is discharged every day b y the electroplating industry i n Ho n g Kong. N i c kel is discharged as ions i n the effluent liquid, an i on being a nickel a t om wh i ch has lost t wo electrons, and hence carries t wo un i t s of pos i t i ve electric charge. Nickel ion, i n contrast to the metal itself, is easily absorbed if ingested and is toxic i n t wo significant ways: i n posing hazards to the neural s y s t em ( neu r o - t ox i c) a n d also i n pos s i b ly causing gene mutations (mutagenic). So the removal of nickel f r om electroplating effluents is a matter of top priority. Incidentally, nickel is also expensive, so its recovery should pay, i n part or all, for the cost of the abatement technology. A Three- Step Process to Remove and Recover Ni cke l f r om Industrial Waste The conventional technology for nickel recov- ery is chemical. Caustic soda is added to the Research 19