Impacts of Goethite Particles on UV Disinfection of Drinking Water

Abstract

A unique association between bacterial cells and small goethite particles (ϳ0.2 by 2 m) protected Escherichia coli and Pseudomonas putida from UV inactivation. The protection increased with the particle concentration in the turbidity range of 1 to 50 nephelometric turbidity units and with the bacterium-particle attachment time prior to UV irradiation. The lower degree of bacterial inactivation at longer attachment time was mostly attributed to the particle aggregation surrounding bacteria that provided shielding from UV radiation.Particles may inhibit chemical disinfection of water and wastewater and enhance the regrowth of pathogens in drinking water distribution systems (14,26,27), thus causing outbreaks of waterborne diseases (10,29). Mechanisms for the reduced chemical disinfection efficiency, analogous to the biofilm system (3,4,8), could be through colonization of particle surfaces by bacteria, where the disinfectant is present at a lower concentration due to (i) the high reactivity of particle surfaces for disinfectant degradation and (ii) limitation of mass transfer to the interface. Particle-attached bacteria are known to be more resistant to chemical disinfection than suspended bacteria (23,30).UV radiation has been increasingly used in the United States as an alternative approach for drinking water disinfection, promoted by the need of reducing potentially carcinogenic disinfection by-products (11,21,22,31). Similar to chemical processes, UV disinfection is also negatively affected by the presence of suspended particles (6,15,19). However, particles can protect bacterial cells from UV radiation via shielding, absorbing, scattering, and blocking (25, 31), not necessarily through bacterial attachment to particles as in chemical disinfection. Microorganisms can be present in the "shadow" cast by attaching to particles, thus allowing escape from full exposure to the UV radiation (6, 9, 15). The protective effects against UV inactivation of attached bacteria depend on particle sizes (9, 15) and turbidity levels (6, 7). Past research on particle-associated bacteria and UV shielding mostly used particles greater than 10 m (12, 28).Little information is available on the effects of small-sized particles on bacterial inactivation in drinking water. Predominant mechanisms of UV attenuation in such systems are unknown. Although research conducted using wastewater provides useful information on UV attenuation in drinking water, particles in drinking water and wastewater are different in nature, likely affecting UV transmission differently (6). For example, suspended particles in water supplies can be smaller and have more mineral components, including clays and metal oxides. Studies have shown that Na-montmorillonite clay can neither prevent viruses from being inactivated by chlorine (26) nor protect bacteriophage (MS2) from UV disinfection at low concentrations (24). Very little information is available on the effect of other clays and mineral oxides such as goethite (␣-FeOOH), which is one of the most common met...

Bacterioneuston Community Structure in the Southern Baltic Sea and Its Dependence on Meteorological Conditions

“…This suggests that increasing exposure to UVinduced stress alters the community composition of nonattached, active bacterioneuston members, which again is favored during low wind conditions. In contrast, variability in the particle-attached fingerprints was not related to changing levels of radiation, probably due to the sheltering from UV exposure conferred by particle association (22,53).…”

Biotic and abiotic particles protect marine heterotrophic bacteria during UV and ozone disinfection

“…Reported disinfection doses using the community approach and our results are significantly higher than the doses recommended in aquaculture (Wedemeyer 1996, Liltved 2002. Earlier studies (Liltved & Cripps 1999, Wu et al 2005) of particle effects on UV-irradiated water also demonstrate protection of bacteria, but little is known about the effects of increased disinfection dose (UV or ozone), particle concentration, and particle type on the inactivation of heterotrophic bacteria in seawater. Based on our data, it is possible to elaborate on the differences in inactivation of free-living and particle (biotic and abiotic)-associated bacteria by UV irradiation and ozonation of seawater.…”

“…The effect of chemical disinfection agents can be reduced due to disinfectant degradation at the particle surface and rate-limited transport of disinfectants into the particle (Perrins et al 2006a). Bacteria colonising the particle surface or inside, similar to the biofilm system, are known to be more resistant than free-living bacteria to chemical disinfection at lower concentrations of disinfectant (Wu et al 2005). Many bacteria are known to be particle-associated and this could be a strategy to survive unfavourable conditions.…”

Formation of disinfection byproducts in a recirculating mariculture system: emerging concerns

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“…Every month, about 20-25% of the seawater in the animal tanks is replaced by the fresh ASW. All animal tanks in Beijing Aquarium are indoor with seawater temperature maintained in the range of [20][21][22][23][24][25] C.…”