Impact of Particle Aggregated Microbes on UV Disinfection

摘要

Aggregation of microbes with particles can reduce the effectiveness of ultravioletrn(UV) disinfection. This study evaluated the comparative impact of dispersed spores,rndispersed spores mixed with clay particles (non aggregated), spore-spore aggregates andrnspore-clay aggregates on 254 nm UV disinfection performance in simulated drinkingrnwaters. Spore clay aggregates were induced by flocculation with alum. It was concludedrnthat spores within aggregates of the spore-clay system tested were protected from UVrnirradiation compared to non-aggregated spores and the difference between these systemsrnwas found to be statistically significant throughout UV range tested.rnUltraviolet (UV) absorbance measurements are subject to significant error using arnstandard spectrophotometer when particles or aggregates that scatter light are present.rnTrue UV absorbance for highly turbid waters should be measured using integratingrnsphere (IS) spectrophotometry that allows the collection of reflected and transmittedrnradiation simultaneously. This is especially important when the effects of scatteringrnimpact UV disinfection – such as with the presence of aggregates. The impact of lightrnscattering of particle-aggregated microbes on UV disinfection was evaluated byrncomparing standard spectrophotometer and IS absorbance measurements for UV fluencerndetermination. Spore-clay aggregates in simulated drinking waters and spore aggregatesrnwith natural particles from raw waters were induced by flocculation. Coagulated systemsrnsignificantly decreased the UV inactivation effectiveness compared to the non-coagulatedrnsystem with the effects more pronounced for raw natural water. Absorbance measurementrnof suspensions and aggregates using standard spectrophotometry in the calculations ofrnfluence resulted in overdosing whereas the use of IS spectroscopy did not. The resultsrndemonstrated that the use of proper absorbance measurement techniques, accounting forrnparticle scattering, is essential for correct interpretation of the results.