Assessment of the UV/Chlorine Process in the Disinfection of Pseudomonas aeruginosa: Efficiency and Mechanism

Abstract

UV irradiation and chlorination have been widely used for water disinfection. However, there are some limitations, such as the risk of generating viable but nonculturable bacteria and bacteria reactivation when using UV irradiation or chlorination alone. This study comprehensively evaluated the feasibility of the UV/chlorine process in drinking water disinfection, and Pseudomonas aeruginosa was selected as the target microorganism. The number of culturable cells was effectively reduced by more than 5 orders of magnitude (5-log 10 ) after UV, chlorine, and UV/chlorine treatments. However, intact and VBNC cells were detected at 10 3 to 10 4 cells/mL after UV and chlorine treatments, whereas they were undetectable after UV/chlorine treatment due to the primary contribution of reactive chlorine species (Cl • , Cl 2•− , and ClO • ). After UV/chlorine treatment, the metabolic activity determined using single cell Raman spectroscopy was much lower than that after UV. The level of toxic opr gene in P. aeruginosa decreased by more than 99% after UV/chlorine treatment. Importantly, bacterial dark reactivation was completely suppressed by UV/chlorine treatment but not UV or chlorination. This study suggests that the UV/chlorine treatment can completely damage bacteria and is promising for pathogen inactivation to overcome the limitations of UV and chlorine treatments alone.

Misconceptions about the chemistry of aqueous chlorine atoms and HClOH˙(aq), and a revised mechanism for the photochemical peroxydisulfate/chloride reaction

“…11 Here we report an additional 37 publications that have mechanisms including this loop. 51,64,65,[67][68][69][70][71][81][82][83]85,[87][88][89][90][92][93][94][95]97,[99][100][101][102][103][104][105][106][108][109][110][111][112][113]118,119 In our previous report we showed that correcting Loop ''D'' by supplying the requisite value for the reverse rate constant in the first step had no effect on the simulations of the overall mechanism in one of the publications. This outcome was traced to the fact that the first step could be eliminated entirely without affecting the results of the simulation.…”

“…Two examples of published illegal loops involving HClOH˙ are discussed below. A total of 18 such illegal loops have been published, 10,18,20,21,23,26,27,30–33,35,39,40,46–118 and these are described in the ESI †…”

“…In addition to the 24 publications previously identified as having illegal Loop 7 (“E”), it also appears in 26 newly identified publications. 23,30,32,35,40,68,70,81,82,85,89,90,92,96,99–104,108–113,117,119 The rate constants in Xiang et al 2022 require a value of 5.7 × 10 11 M −1 s −1 for the reverse of the first step. 117 Simulations of Loop 7 (“E”) at pH 3 with 1 mM Cl − and 1 μM show that the steady-state concentration of HClOH˙ changes from 9.8 × 10 −14 M to 2.6 × 10 −10 M when the reverse rate constant of the first step is increased from zero to its required value.…”

Evaluation of the disinfection effect and mechanism of SO4•- and HO• in UV / persulfate salts from the perspective of VBNC bacteria

“…Bacterial resuscitation ability was measured in 96-well microplates, using OD600 as the standard to determine the growth of bacteria (Wang et al 2021a. Simply, the bacteria treated in different ways were diluted according to the previous culture results to ensure that the bacteria are all in the VBNC state.…”

Treatment of hospital wastewater by electron beam technology: Removal of COD, pathogenic bacteria and viruses

“…Chlorination could completely inactivate bacteria, such as Escherichia coli and Enterococcus faecalis, but partially inactivate virus ( Tree et al, 2003 ). To guarantee the chlorination disinfection effect for bacteria and virus, especially for COVID-19, higher dose of chlorine and longer contact time were required ( Chu et al, 2021b ; Wang et al, 2020a , Wang et al, 2020b ), which could cause potential risk, such as generating viable but non-cultivable bacteria ( Wang et al, 2021 ). UV could also inactivate Escherichia coli and Enterococcus faecalis , but the bacteria could regrow after UV disinfection ( Li et al, 2017 ; Wen et al, 2019 ).…”