UV ABILITY TO INACTIVATE MICROORGANISMS COMBINED WITH FACTORS AFFECTING RADIATION

In the present study, the effect of UV radiation on the inactivation o f a range of microorganisms was studied. Each organism was seeded into sterile tap water and exposed to UV in batch experiments with changin g turbidities. In addition, the effect of UV on microbial communities in river Nile water was examined. It was found that 1min contact time (0.5L/min flow rate) was effective against vegetative cells levels alm ost reaching zero (except with Staphylococcus aureus). On the other ha nd, spore-forming bacteria, Candida albicans and coliphage were more r esistant to UV. This contact time caused coenobia cells in single form with Scenedesmus obliquus while for Microcystis aeruginosa colonies b roke into smaller groups. Exposure of Nile water microbial communities to UV showed that yeasts and Aeromonas survived better than the other organisms while in the phytoplankton partial fragmentation occurred i n some algal groups. The protective effect of turbidity differed betwe en organisms, with increased contact time under conditions of stable t urbidity having no effect on the organisms. At 20 NTU the ITV radiatio n had no effect on the morphological characters of algal cells. In rea ctivation experiments, it is clear that photoreactivation, and not dar k repair, takes place with bacterial cells. Only coliphage had no phot oreactivation and dark repair responses although with coliphage and ho st, both reactivation processes worked well. Moreover, the irradiated algae regained their normal shape after 3 days in suitable media and e nough light. (C) 1997 IAWQ. Published by Elsevier Science Ltd.