UV inactivation of humic-coated bacteriophages MS2 and T4 in water

Abstract

This bench-scale study investigated the hypothesis that humic acids may thinly coat the surfaces of viruses (bacteriophages MS2 and T4) and thereby protect them from inactivation by UV light (254 nm). The model viruses were mixed in buffered water (pH 5.5) that contained Aldrich® humic acid (AHA) concentrations of 0, 10, 50, and 150 mg/L and were exposed to UV light at 40 and 80 mJ/cm2 for bacteriophage MS2 and 2 and 7 mJ/cm2 for bacteriophage T4 using a low pressure UV collimated beam. No steps were taken to form particles (i.e., no coagulant was added). The UV inactivation of both bacteriophages decreased to a statistically significant degree (based on 95% confidence level, Student's t test) at a humic acid concentration of 150 mg/L at the higher UV doses for each phage. This was despite the increased UV absorbance at 254 nm (UV254) caused by the humic acid being taken into account in the UV dose calculation. It was therefore hypothesized that the humic acid was coating the phage surfaces with a thin UV-shielding layer. As a further investigation of this hypothesis, samples containing humic acid, both with and without phage, were pelletized by ultracentrifugation and re-suspended in pure Milli-Q® water and the resulting UV254 values were compared. It was anticipated that the re-suspended pellets from the solutions containing humic acid and phage would exhibit higher UV254 than those of the pellets from solutions containing either phage or humic acid, due to the coating interaction. While there were statistically significant differences in UV254 among some of the re-suspended pellets, the results were inconsistent due to limitations of the experiment. As such, while some supporting evidence for the humic coating hypothesis was provided by this initial proof of concept study, further research is needed to more fully understand this phenomenon. Key words: ultraviolet light, disinfection, humic acid, bacteriophage, MS2, T4.

Interactions between humic matter and bacteria when disinfecting water with UV light

“…1 indicate the magnitude of the reduction in UV effectiveness increased with humic content suggesting the level of protection is concentration dependent. A reduction in log inactivation in the presence of AHA is consistent with data presented by Templeton et al. (2006) for inactivation of MS2 and T4 phages.…”

“…The extent to which humic matter interacts with viruses has been the topic of recent study. Templeton et al. (2006) reported that soil‐derived humic acid coated the surface of viruses, protecting them from UV disinfection.…”

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

“…Sorption of organic matter on colloids or larger particles may impact UV disinfection. In support of this possibility, studies showed that soil-derived humic acid possibly coated the surface of viruses and bacteria, protecting them from UV disinfection (Templeton et al 2006;Cantwell et al 2008).…”

“…Non-natural interactions between microorganisms and particles can occur during treatment, such as during coagulation and flocculation or iron/manganese oxidation during water treatment (Cairns et al 1993;Petri et al 2000;Templeton et al 2006) or during activated sludge floe formation in wastewater treatment (Parker and Darby, 1995;Emerick et al 1999Emerick et al , 2000Loge et al 1996, 200la, 200Ib;Jolis et al 2001). UV disinfection may be negatively affected by aggregation of particles that may occur naturally or during flocculation or with wastewater effluents if these floes are not adequately removed.…”

“…A study by Templeton et al (2006) showed that phages associated with iron oxide particles in groundwater are shielded from UV light even at a relatively low turbidity level of 2.7 NTU, when water was experimentally aerated for 2 hrs. Iron precipitation is a result of oxidation of reduced dissolved iron in groundwater.…”