Aggregation of microbes with particles can reduce the effectiveness of ultraviolet(UV) disinfection. This study evaluated the comparative impact of dispersed spores,dispersed spores mixed with clay particles (non aggregated), spore-spore aggregates andspore-clay aggregates on 254 nm UV disinfection performance in simulated drinkingwaters. Spore clay aggregates were induced by flocculation with alum. It was concludedthat spores within aggregates of the spore-clay system tested were protected from UVirradiation compared to non-aggregated spores and the difference between these systemswas found to be statistically significant throughout UV range tested.Ultraviolet (UV) absorbance measurements are subject to significant error using astandard spectrophotometer when particles or aggregates that scatter light are present.True UV absorbance for highly turbid waters should be measured using integratingsphere (IS) spectrophotometry that allows the collection of reflected and transmittedradiation simultaneously. This is especially important when the effects of scatteringimpact UV disinfection, such as with the presence of aggregates. The impact of lightscattering of particle-aggregated microbes on UV disinfection was evaluated bycomparing standard spectrophotometer and IS absorbance measurements for UV fluencedetermination. Spore-clay aggregates in simulated drinking waters and spore aggregateswith natural particles from raw waters were induced by flocculation. Coagulated systemssignificantly decreased the UV inactivation effectiveness compared to the non-coagulatedsystem with the effects more pronounced for raw natural water. Absorbance measurementof suspensions and aggregates using standard spectrophotometry in the calculations offluence resulted in overdosing whereas the use of IS spectroscopy did not. The resultsdemonstrated that the use of proper absorbance measurement techniques, accounting forparticle scattering, is essential for correct interpretation of the results. Includes 2 references, figures.
