A novel thin film photoreactor

A novel thin film photoreactor is described and characterised. The photoreactor was based on a nozzle of special design which generated an unsupported thin liquid film commonly referred to as a liquid ‘bell’. The arrangement described permitted liquids to be irradiated without making contact with either the UV sources or any solid walls in the vicinity of the sources. High speed ciné photography of air bubbles entrained by the liquid films enabled estimates of film velocities and thicknesses to be made. The films accelerated under the influence of gravity with velocities in excess of 2·8 × 102 cm s−1 being obtained near the bottom edge of the bells. Film thicknesses decreased correspondingly, measuring approximately 0·3 cm at the top of the bell and only 1·0 × 10−2 cm near the bottom. From the film thicknesses, internal and external bell surface areas and volume could be determined: these were respectively 2697·1 cm2, 2705·0 cm2 and 80·4 cm3. A bioassay based on the bacterium Escherichia coli was used to determine the UV dose accumulated by the bell. The doses obtained ranged from 2·03 mW-s cm−2 for irradiation by a single source, to 4·84 mW-s cm−2 for irradiation by all five sources. The properties of the bell photoreactor make the unit potentially applicable to areas of photo-technology in addition to UV sterilisation of liquids.