Influences of humic acids and photoreactivation on the disinfection of Escherichia coli by a high-power pulsed UV irradiation

Abstract

The characteristics of inactivation and photoreactivation of Escherichia coli by a high-power pulsed ultraviolet (PUV) irradiation and the influence of the humic acids on disinfection performance were investigated. The pulsed power source was operated at 2,400 V, with 200 J of energy being stored in a 100-µF capacitor. This energy dissipated in the xenon-filled flashlamp within 150 µs, generating a megawatt-level peak power per pulse. The light source was operated at 12 pulses per second (12 Hz). More than a 6-log reduction was achieved via 5 sec of irradiation at a distance of 20 cm, which corresponds approximately to a UV dose of 23 mJ/cm 2 . The inactivation efficiency decreased with increasing concentrations of humic acids (HA). At the distance of 20 cm, 10 ppm HA reduced the inactivation efficiency to 50%. UV absorption by HA and, in part, the growth-promoting effect of humic acids were implicated in reductions of inactivation performance in the presence of HA. After a disinfection procedure with PUV, the possibility of photoreactivation was greatly reduced and an additional reduction of approximately 1-log was also achieved during 8 h under visible light after inactivation with a UV dosage of 9.0 mJ/cm 2 (3 sec at 30 cm). The extent of additional inactivation under visible light was reduced with increasing concentrations of humic acids in water.

A Comparative Study on the Pulsed UV and the Low‐Pressure UV Inactivation of a Range of Microbial Species in Water

“…Although humic acid reduced the inactivation efficiency of a PUV system at doses below 4.32 lJ/cm 2 , significant microbial inactivation was still achieved with prolonged exposure. Studies by Lee et al (2009) suggested that the primary cause of the reduced inactivation performance in the presence of humic acid is the result of the UV absorption features of humic acid or the influence that humic acid has on microbial growth and reported that the presence of humic acid in water promoted the growth of E. coli at certain concentrations (10 ppm). Results of this study agree with the findings of Lee et al (2009) and suggest that although humic acid reduces the efficiency of PUV inactivation, PUV still provides a mechanism of disinfecting water containing humic acid at the concentration tested.…”

Effects of salinity and temperature on inactivation and repair potential of Enterococcus faecalis following medium- and low-pressure ultraviolet irradiation

“…It is known that organic matter (humic acids, Wright and Cairns ; Lee et al . ) and inorganic ions (Cl − , and , Rincon and Pulgarin ) exposed to UV light can not only absorb UV light (Wright and Cairns ) but also form radicals that interact with bacteria (Buschmann et al . ).…”

“…To our best knowledge, the effect of salinity on MP UV inactivation has not been reported before. It is known that organic matter (humic acids, Wright and Cairns 1998;Lee et al 2010) and inorganic ions (Cl À , HCO À 3 and SO 2À 4 , Rincon and Pulgarin 2004) exposed to UV light can not only absorb UV light (Wright and Cairns 1998) but also form radicals that interact with bacteria (Buschmann et al 2005). Hence, the effect of salinity on UV inactivation is likely dependent on the sum of both UV light attenuation and radical formation.…”

A Study of Treatment Efficiency of Reflectors for CSOs Disinfection by Pulsed UV

“…)를 이용하는 공정, pulsed UV (Ali et al, 2006;Sharifi-Yazdi and Darghahi, 2006;Elmnasser et al, 2007;Maclean et al, 2008;Lee et al, 2008;Lee et al, 2009)를 이용하는 공정, Chlorine (David et al, 2005;Macauley et al, 2006;Gideon et al, 2008)을 이용하는 방법, 오존 (Silva et al, 2010) …”