TIBTECH - JULY 1989 [Vol. 7]

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The ultrasound probe. On the left is the reflector which delimits the measuring volume. On the right is the transducer~holder.

needed. However, both the reflector and the membrane are in contact with the fermentation medium. There were no problems due to cell adhesion in previous experiments 7, but it remains to be seen first, whether such problems arise with the new probe geometry and second, how far the autocalibration can compensate for them.

Ideally, the direction of bubble flow should be perpendicular to the probe axis. However, this may not occur under real operating con- ditions and it is possible that the presence of the probe alters the dispersion characteristics it is trying to measure.

Conclusions Despite these open questions, we

believe the ultrasound pulse trans- mission technique could soon be- come a very helpful tool. For instance, the measurement of a under real process conditions, combined with a standard kLa measurement will permit the determination of kn, thereby contributing to our know- ledge of mass transfer. Equally, measurements made under various viscosities and surface tension con- ditions will provide a better under- standing of bubble generation pro- cesses.

Local measurements of a and Osm

will allow improvements to be made in vessel geometry, impeller shape and sparser design, leading eventu- ally to greater productivity, re- duced waste and reduced down- stream processing costs.

Furthermore, the ultrasound probe could also be applied in l iquid- liquid, l iquid-solid or even three- phase dispersions. The theory which has been developed for size determi- nation with the probe also applies to optical systems and could be used to characterize any disordered solid

gas or liquid-gas system (e.g. sand grains or rain drops).

References 1 Strays, A. and yon Stockar, U. (1985)

Chem. Eng. Sci. 40, 1169-1175 2 Calderbank, P. H. (1958) Trans. Inst.

Chem. Eng. 36,443-459 3 Calderbank, P. H. and Pereira, J. [1977)

Chem. Eng. Science 32, 1427-1433 4 Steinemann, J. and Buchholtz, R.

(1984) Part. Charact. 1, 102-107 5 Weiland, L., Bentrup, L. and Onken, U.

(1980) Get. Chem. Eng. 3, 296-302 6 Bugmann, G. and von Stockar, U.

(1989) HeM Phys. Acta 62, 314-317 7 Stravs, A., Pittet, A., von Stockar, U.

and Reilly, P.J. (1986)Biotechnol. Bioeng. 28, 1302-1309

8 Bugmann, G. and von Stockar, U. (1988) Swiss patent (pending) 02768881

GUIDO BUGMANN

URS VON STOCKAR

Institute of Chemical Engineering, Swiss Federal Institute of Tech- nology, CH-1015 Lausanne, Switzer- land.

Will biotechnology be outmoded by emotion?

Your editorial on the 'Gen-ethic Net- work '1 and its conclusions omitted to point out one feature of the organiza- tion's demands. Two of the eight demands (the first and fifth) made explicit their assumption that al- ternative (ie non-recombinant DNA) solutions to any problem were of necessity 'socially and ecologically' preferable to the biotechnological ones. Our company is involved both in biotechnology (including genetic engineering), and in environmental impact assessment and moderation, so we have a genuine motive to see arguments both for and against deliberate release. To see such an assumption made by a major pressure group is therefore rather depressing, as it suggests that the expertise that

biotechnology companies possess is going to be outmoded by emotion before it can even be used. Is there to be any role for science in this debate? Let us hope so, and that the Gen-ethic network either retract this question- begging approach or, if they cannot, that the general public be told enough of the other side to recognize a vested interest when it sees it.

Reference 1 Hodgson, J. (1989) Trends Biotechnol.

7, 107-109

W. BAINS

P. A. Consulting Group, Cambridge Laboratory, Melbourn, Royston, Hefts SG8 6DP, UK.

~) 1989, Elsevier Science Publishers Ltd (UK) 0167 - 9430/89/$02.00