Destruction of <i>Escherichia coli</i> and Broad-Host-Range Plasmid DNA in Treated Wastewater by Dissolved Ozone Disinfection under Laboratory and Field Conditions

Abstract

Broad-host-range plasmids are frequently associated with antibiotic resistance genes and can quickly spread antibiotic resistant phenotypes among diverse bacterial populations. Wastewater treatment plants have been identified as reservoirs for broad-host-range plasmids carrying resistance genes. The threat of broad-host-range plasmids released into the environment from wastewater treatment plants has identified the need for disinfection protocols to target broad-hostrange plasmid destruction. Here we evaluate the efficacy of dissolved ozone at 2 and 8 mg·L -1 as a primary means for the destruction of broad-host-range plasmid and chromosomal DNA in simulated effluent. Pilot-scale tests using an experimental unit were carried out in municipal wastewater treatment plant effluent and compared with ultraviolet (UV)-irradiation and chlorination methodologies. Genes specific to Escherichia coli (uidA) and IncP broad-host-range plasmids (trfA) were monitored using real-time quantitative polymerase chain reaction (qPCR), and total DNA was monitored using absorbance spectroscopy. In wastewater treatment plant experiments, E. coli qPCR results were compared to a recognized culture-based method (Colilert ® ) for E. coli. In laboratory experiments, dissolved ozone at 8 mg·L -1 significantly destroyed 93% total, 98% E. coli, and 99% of broad-host-range plasmid DNA. Ozonation, UV-irradiation, and chlorination significantly reduced DNA concentrations and culturable E. coli in wastewater treatment plant effluent. Chlorination and UV disinfection resulted in 3-log decreases in culture-based E. coli concentrations in wastewater treatment plant effluent while changes were not significant when measured with qPCR. Only ozonation significantly decreased the IncP broad-host-range plasmid trfA gene, although concentrations of 2.2 × 10 5 copies trfA·L -1 remained in effluent. Disinfection processes utilizing high dissolved ozone concentrations for the destruction of emerging contaminants such as broad-host-range plasmid and total DNA may have utility as methods to ensure downstream environmental health and safe water reuse become more important.

Comparison of Antibiotic Resistance Removal Efficiencies Using Ozone Disinfection under Different pH and Suspended Solids and Humic Substance Concentrations

“…Advanced oxidation processes (AOPs) are designed to remove toxic or nonbiodegradable organic compounds through the action of a number of reactive oxygen species (ROS) including ozonide radical (O 3 – • ), hydrogen trioxyl radical (HO 3 • ), hydroperoxyl radical (HO 2 • ), and hydroxyl radical ( • OH) . Recently, several studies have shown that AOP technology shows promise for removing micropollutants such as pharmaceuticals and microbial contents. − Among these AOP options, ozone processing has gained attention for removing micropollutants not only in drinking water treatment processes but also in WWTPs. , McKinney and Pruden, however, showed that UV disinfection has limited potential to damage ARGs in water and wastewater effluents . Michael et al demonstrated the capacity of solar-driven AOP (solar photo Fenton) to not just reduce wastewater toxicity but also completely eliminate ARB .…”

“…Although several studies have recently been conducted on ARB and ARG removal efficiencies during water or wastewater disinfection processes, ,− few comprehensive studies have been conducted using ozonation. Alexander et al recently conducted an investigation on an ozone treatment system and its ARB and ARG reduction .…”

Remote delivery of hydroxyl radicals via secondary chemistry of a nonthermal plasma effluent

“…In the plasma only treatment state, the negative correlations of bacterial inactivation are most likely due to the corresponding decrease in ozone. Ozone, in addition to membrane damage discussed below, is capable of pervasive DNA damage (Asfahl and Savin, 2012; Ishizaki et al, 1987). The fact that this trend is reversed with the addition of hydrogen peroxide to the device effluent strongly suggests the presence of mechanisms driven by hydrogen peroxide.…”

Emerging Technologies in Water Treatment: Recent Advances

“…Research investigations to destroy gram-negative and gram-positive bacteria's have been conducted [2,3,5]. A procedure to destroy enterobacterias such as E. coli at 95°F, using ozone, requires an ozone range between 0.1 and 0.5 mg/l and maintaining an adequate redox potential to reach a higher disinfection efficiency [6].…”