Impact of Particle Aggregated Microbes on UV Disinfection. I: Evaluation of Spore–Clay Aggregates and Suspended Spores

Abstract

Aggregation of microbes with particles can reduce the effectiveness of ultraviolet ͑UV͒ disinfection. This study evaluated the comparative impact of dispersed spores, dispersed spores mixed with clay particles ͑nonaggregated͒, spore-spore aggregates, and sporeclay aggregates on UV disinfection performance in simulated drinking waters. Aggregates were induced by flocculation with alum and characterized by particle size analysis ͑count, volume, and surface area͒ of dispersed and aggregated systems, scanning electron microscopy ͑SEM͒ and energy dispersive X-ray ͑EDX͒ analysis. It was concluded that spores within aggregates of the spore-clay system were protected from UV irradiation compared to nonaggregated spores and the difference between these systems was found to be statistically significant throughout the UV range tested. In addition SEM-EDX analysis suggested that aggregate composition is nonhomogeneous with respect to the ratio of spores and clay particles among aggregates. It was estimated that 30-50% of the spores in the aggregates tested were protected from UV irradiation.

Impact of Particles on Uv Disinfection of Water and Wastewater Effluents: A Review

“…Research has shown that biological floes formed in wastewater treatment processes have extremely high UV absorbance and may harbor coliform organisms and shield them from UV light ) by decreasing light through an aggregate mostly due to absorption Mamane and Linden, 2006a;Mamane et al 2006). In water supplies, however, particles can protect microorganisms from UV inactivation mainly by shielding, scattering, absorbing or blocking UV light and not necessarily by particle association as with effluents.…”

“…Particles from the activated sludge plant 78 Brought to you by | University of Birmingham Authenticated Download Date | 5/31/15 3:57 AM are dominated by Cl, Si, and Ca, while particles from the aerated lagoons maturation ponds are dominated mostly by P, K and Ca, which is typical for an algal environment . SEM-EDX can also be a tool to study the non-homogeneity of the aggregate or floe elemental surface composition (Mamane and Linden, 2006a).…”

“…UV light penetrates to wastewater floes due to the porosity of the particles that creates pathways for light penetration and not due to light transmittance as UV light is unable to penetrate even a few microns within the floe due to the high absorbance of wastewater particles that is sufficient to block UV light . In a study by Mamane and Linden (2006a) spores were induced to aggregate with clay particles in simulated drinking water. It was found that spores in the aggregates are protected from UV light across a UV fluence increase, with a steady decrease in the percent of spores within an aggregate that are protected from UV as the UV fluence increases.…”

UV-induced self-aggregation of E . coli after low and medium pressure ultraviolet irradiation

“…It is important to note that even in the absence of particulate matter in the water matrix to be disinfected, aggregation of cells among themselves may lead to formation of sufficiently large and dense flocs to cause tailing, and thus hinder the disinfection performance. For instance, Mamane and Linden [17] reported that spore-spore aggregates were in fact equally effective at protecting the spores from UV inactivation as were the spore-clay aggregates.…”

Ultraviolet (Uv) Disinfection of Grey Water: Particle Size Effects

“…Total coliform survival continued a gradual decline with increasing UV dose in the tailing region of the inactivation curve, indicating some level of particle penetration by UV light. Mamane and Linden[30] investigated the inactivation of aggregated Bacillus subtilis spores by UV light and suggested that greater UV exposure time increased the likelihood of spore exposure to UV light in locations within the aggregate where light pathways exist.Total coliforms were still enumerated in grey water following an extremely high UV dose of 1107mJ·cm -2 , at a mean concentration of 0.9±0.4 log 10 MPN.100m l -1 (data not shown), indicating that the grey water contained coliform bacteria deeply embedded within particulate matter and completely shielded from UV light. The data show that total coliforms are the most conservative of the three bacterial indicators for the disinfection of grey water by UV light due to their higher initial and residual concentrations and are therefore the most suitable for assessment of disinfection performance.…”