EFFECT OF TITANIUM-DIOXIDE CONCENTRATION ON THE SURVIVAL OF PSEUDOMONAS-STUTZERI DURING IRRADIATION WITH NEAR-ULTRAVIOLET LIGHT

Cells of Pseudomonas stutzeri in suspensions of TiO2 ranging in concen tration from 0.5 to 4.0 g l(-1) were irradiated with a blacklight blue u.v. source displaying peak emissivity at approximately 370 mm. Irrad iation under these conditions is known to result in the generation of lethal free radicals. During irradiation the suspensions were agitated , using a specially modified laboratory shaker, to ensure efficient ex posure of the TiO,. A u.v. radiation dose oi 175 kJ m(-2) resulted in cell fractional survival ranging from 5.5 x 10(-5), at the lowest TiO2 concentration, to 1.0 x 10(-6), at the highest TiO2 concentration. Th e advantages of contactors employing TiO2 suspensions are briefly comp ared to immobilized TiO2 systems.