Photolytic and photocatalytic treatment of an aqueous solution containing microbial cells and organic compounds in an annular-flow reactor

A method for simultaneous treatment of an aqueous solution to photolyticall y sterilize microbial cells and photocatalytically decompose organic compou nds was studied using an annular-flow photocatalytic reactor with a 6-W ger micidal lamp (wavelength; 254 nn) as a light source. All the experiment wer e carried out in a batch recirculation mode. When a thin film of titanium o xide was located on the outer surface of a quartz glass tube, which was set to protect the germicidal lamp from direct contact with an aqueous solutio n flowing through the annulus, i.e., when the photocatalyst was located at the inner surface of the annulus, the sterilization and decomposition slowe d down. This is due to the fact that the degree of transparency of UV light s with wavelengths less 300 nm is significantly deceased by the film of tit anium oxide. When the film of titanium oxide was located at the outer surfa ce of the annulus, on the other hand, both the rates of sterilization and d ecomposition became higher. An experimental result using an aqueous solutio n containing E. coli and formaldehyde showed that the sterilization off. co li is dependent on the circulation rate of the solution but the photocataly tic decomposition of formaldehyde is independent of it and can be approxima ted by a perfectly-mixed reactor model. Consequently, it was found that the annular-flow photocatalytic reactor used in the present work makes it poss ible to simultaneously carry out the photolytic sterilization of microbial cells and the photocatalytic decomposition of organic compounds. (C) 1999 E lsevier Science Ltd. All rights reserved.