Zi-Chen
Yang
a,
Wen-Long
Wang
a,
Zi-Bo
Jing
a,
Yi-Qing
Jiang
a,
He-Qing
Zhang
b,
Min-Yong
Lee
c,
Lu
Peng
*a and
Qian-Yuan
Wu
a
aKey Laboratory of Microorganism Application and Risk Control of Shenzhen, Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Institute of Environment and Ecology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China. E-mail: penglu@sz.tsinghua.edu.cn
bCSCEC Scimee Sci.&Tech. Co., Ltd., Beijing 100084, PR China
cNational Institute of Environment Research, Ministry of Environment, Incheon 22689, Republic of Korea
First published on 7th February 2024
The control of viruses in water is critical to preventing the spread of infectious viral diseases. Many oxidants can inactivate viruses, and this study aims to systematically compare the disinfection effects of ozone (O3), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2) on MS2 coliphage. The effects of oxidant dose and contact time on disinfection were explored, as were the disinfection effects of three oxidizing agents in secondary effluent. The 4-log inactivation of MS2 coliphage required 0.05 mM O3, 0.5 mM PMS, or 25 mM H2O2 with a contact time of 30 min. All three oxidants achieved at least 4-log disinfection within 30 min, and O3 required only 0.5 min. In secondary effluent, all three oxidants also achieved 4-log inactivation of MS2 coliphage. Excitation–emission matrix (EEM) results indicate that all three oxidants removed dissolved organic matter synchronously and O3 oxidized dissolved organic matter more thoroughly while maintaining disinfection efficacy. Considering the criteria of oxidant dose, contact time, and disinfection efficacy in secondary effluent, O3 is the best choice for MS2 coliphage disinfection among the three oxidants.
Environmental significanceDisinfection is considered to be a critical step in controlling the spread of viruses in water. Oxidants are effective viral disinfectants. However, conclusive studies are lacking in the relative efficacy of oxidants for viral inactivation, and the disinfection performance in real water samples is not fully clear. In this study, the disinfection effects of ozone (O3), hydrogen peroxide (H2O2), and peroxymonosulfate (PMS) against MS2 coliphage with different doses and contact times were evaluated. The results showed that O3 inactivated MS2 coliphage at lower doses with the shortest contact time. To achieve 4-log disinfection of MS2 coliphage, the oxidant doses required were ranked as O3 < PMS < H2O2 and the contact times required were ranked as O3 < H2O2 < PMS. Besides, the disinfection performance of the three oxidants in deionized water and secondary effluent was comprehensively compared. All three oxidants achieved 4-log inactivation of MS2 coliphage. Excitation–emission matrix (EEM) results indicated that all three oxidants removed dissolved organic matter synchronously and O3 oxidized dissolved organic matter more thoroughly while maintaining disinfection efficacy. To sum up, O3 is the best choice for MS2 coliphage disinfection among these three oxidants. The results enriched the research of virus disinfection in water and provided a theoretical basis for further studies of the dosage of oxidants in industrial practice. |
Bacteriophages are common surrogates for virus disinfection because of their safety of cultivation,12 and they are similar to mammalian viral pathogens in many characteristics such as size and morphology.13 MS2 coliphage, which is from Leviviridae, is an icosahedral virus with positive-sense single-stranded RNA.14 The host of MS2 is Escherichia coli, and it appears frequently in sewage. In previous environmental virology studies, MS2 coliphage is used as a surrogate for many human enteric viruses,15 such as hepatitis A virus16 and norovirus.13 Therefore, it is feasible to use MS2 coliphage as a surrogate to study virus inactivation in water.
Several oxidants are effective viral disinfectants. Currently, chlorination is commonly used for disinfection in practical applications, but the potential health risks of disinfection by-products cannot be ignored,17,18 and other oxidants must be identified. Ozone (O3) is an extensively used oxidant to which most viruses are sensitive.19 O3 is effective in removing enteroviruses including astrovirus, hepatitis A virus, hepatitis E virus, norovirus, mengovirus, and rotavirus. Ozone-based inactivation exceeds 4-log disinfection (achieved by conventional treatment) by an additional 1–2 logs, and most enteroviruses are reduced to undetectable levels following ozonation.20 This shows that O3 disinfection is effective in preventing the spread of viruses in water. Peroxymonosulfate (PMS) is a broad-spectrum oxidant that can inactivate viruses. The concentration and contact time of PMS affect the inactivation performance against viruses, and Tulalamba et al. found that 93.7% of SARS-CoV-2 virions can be inactivated with a 1:100 w/v potassium peroxymonosulfate solution.21 Hydrogen peroxide (H2O2) is a widely used oxidizing agent that is common in oral therapy because it quickly inactivates pathogenic microorganisms.22 H2O2 is also used for the sterilization of surfaces and surgical tools because it is effective against various pathogenic microorganisms.
Although O3, H2O2, and PMS are all proven viral disinfectants, conclusive studies are lacking on the relative efficacy of these oxidants for viral inactivation. Previous studies have used different conditions so it is difficult to make comparisons. More research is also required on the performance of these three oxidants in actual water disinfection. In this study, O3, H2O2, and PMS were used to disinfect MS2 coliphage under uniform experimental conditions while exploring the effects of dose and contact time, which were the common parameters of water disinfection.23 In addition, the potential of these oxidants in practical applications was investigated by testing disinfection performance against MS2 coliphage in deionized (DI) water and secondary effluents as a reference for actual water treatment. This study aimed at comparing the potential of O3, PMS, and H2O2, in virus disinfection in water, and providing a theoretical basis for the selection and dosage of oxidants in industrial practice.
O3 was provided by saturated ozonated ultrapure water, which was generated by using an ozone generator (Absolute Ozone ATLAS 30, Absolute Ozone, Canada), and the concentration of ozone was determined with a PTH 043 ozone analyzer (Palintest, UK). H2O2 and PMS were prepared in a volumetric flask, and the concentration of H2O2 was measured by the KI method.24 PMS was determined by the DPD colorimetric method with a Hach Pocket Colorimeter II (Loveland, CO).
For disinfection, O3, H2O2, or PMS was added in conical flasks, with the beginning of contact time. In oxidant dose experiments, 0.001, 0.005, 0.01, 0.03, 0.05, 0.10, 0.25, 0.50, and 1 mM O3, 0.01, 0.1, 0.25, 0.50, 0.75, 1.00, 2.50, and 5.00 mM PMS, and 0.01, 0.05, 0.10, 0.50, 1.00, 2.50, 5.00, 10.00, 25.00, 50.00, 100.00, and 200.00 mM H2O2 were added. And 1 mL sample was taken from the system at 30 minutes. In the contact time experiments, 1 mL sample was taken at 0.5, 1, 1.5, 3, 5, 10, and 30 minutes.
In the secondary effluent disinfection experiment, the secondary effluent was obtained from a municipal sewage treatment plant in Shenzhen, China. The secondary effluent was first filtered through a 0.22 μm PES microporous membrane and stored in a refrigerator at 2–4 °C. Before the disinfection experiment, the secondary effluent was filtered through a 0.22 μm PES microporous membrane, and its water quality was determined. And 1 mL MS2 coliphage stock (109 PFU mL−1) was added into 1 L secondary effluent, and 50 mL aliquots (106 PFU per mL MS2 coliphage) were added into the conical flasks. 0.1 mM O3, 1 mM PMS, and 50 mM H2O2 were added into the conical flasks, and 1 mL sample was taken at 30 minutes.
The residual oxidant was quenched with sodium thiosulfate at 1.5 times the stoichiometric ratio. Experiments were performed in triplicate.
To evaluate each disinfection process, the logarithmic inactivation efficiency of MS2 coliphage was calculated according to eqn (1):
Logarithmic inactivation efficiency = log10(N0/Nt) | (1) |
The CT of PMS and H2O2 was calculated by multiplying the geometric mean of the initial and final residual concentration and the contact time, and the CT of O3 was calculated from the integrated area under the ozone decay curve. The excitation–emission matrix (EEM) of water samples was tested by using an F-7000 fluorescence spectrophotometer (Hitachi Ltd. of Japan) and analyzed by the fluorescence regional integration (FRI) method.
At low concentrations, O3 and PMS can inactivate MS2 coliphage. As shown in Fig. 1a–c, O3 and PMS reach 0.9-log inactivation of MS2 coliphage at concentrations of 0.005 mM and 0.01 mM, while H2O2 has no obvious effect at this dose. Fang et al. found 0.1 mg per L O3 achieved around 1-log inactivation of MS2 coliphage,25 which is similar to our result. O3 may inactivate MS2 coliphage at low doses because O3 can degrade amino acids at low doses. Methionine on the MS2 coliphage surface was preferentially targeted.26 H2O2 is only effective (reaching 0.8-log inactivation) at concentrations of 1 mM and above.
The inactivation potential of O3 increases at higher concentrations, achieving complete inactivation (6.9-log) of MS2 coliphage at 0.25 mM, while higher doses of PMS (2.5 mM) and H2O2 (100 mM) are required to achieve the same effect. Thus, O3 is more potent than PMS and H2O2 by a factor of 10× and 400×, respectively, possibly because many viruses are sensitive to O3. Kong et al. found that 2 mg min per L O3 can achieve 4-log inactivation of most viruses.19 Shin et al. found that 0.37 mg per L O3 can achieve 3-log inactivation of poliovirus 1 virus and >3-log inactivation of Norwalk virus within 10 s.5 The protein folding and higher-order structures of capsid proteins are more vulnerable to O3 at tyrosine, histidine, cysteine, and methionine residues.27
As shown in Fig. 2, disinfection by O3 is more effective and with a very brief contact time; O3 achieves 4.6-log disinfection within 0.5 min, and this increases to 5.4-log disinfection in 30 min. According to previous studies, O3 disinfection mainly relies on ozone molecules,5,28 and residual O3 decreases rapidly in 30 s.23,29 These results demonstrate that O3 can achieve 4-log inactivation of MS2 coliphage in 0.5 min (CT: 2.28 mg min L−1).
Fig. 2 Inactivation efficiency of MS2 coliphage using O3 (0.1 mM), PMS (1 mM), and H2O2 (50 mM) at different contact times (a) 0.5–3 min, and (b) 5–30 min. |
H2O2 requires a relatively short contact time, achieving 3.2-log disinfection within 0.5 min (CT: 836.72 mg min L−1), and 4.7-log disinfection can be achieved after 1.5 min (CT: 2513.28 mg min L−1) and then remaining stable. H2O2 mainly disinfects via hydroxyl radicals (˙OH),30 and the slow diffusion of hydroxyl radicals in viruses may limit disinfection by H2O2.31
MS2 coliphage inactivation by PMS reaches only 1.8-log at 0.5 min (CT: 155.44 mg min L−1), and disinfection slowly increases to 5.0-log at 30 min (CT: 8495.22 mg min L−1). Rhee et al. found that 0.3 g per L PMS achieves 4-log inactivation of MS2 coliphage within 30 min,32 which is consistent with the result. Disinfection by PMS occurs via the production of ˙OH, sulfate radicals (SO4˙−), and 1O2.33 Both H2O2 and PMS require free radical production to disinfect MS2 coliphage, and the disinfection rates of these oxidants are significantly slower than that of O3. Extended contact times may allow lower concentrations of PMS and H2O2 to disinfect to the same degree. In some studies, 25 ppm H2O2 vapor achieves around 3-log inactivation of MS2 coliphage in 2 h.34
Fig. 3 Inactivation efficiency of MS2 coliphage using O3 (0.1 mM), PMS (1 mM), and H2O2 (50 mM) with a contact time of 30 min in DI water and secondary effluent. |
The EEM diagram of water samples before and after disinfection is shown in Fig. 4, and the horizontal and vertical coordinates of Fig. 4 were the emission and excitation wavelengths respectively. The color reflected the peak intensity of fluorescence at a specific excitation/emission wavelength. The integrated fluorescence intensity of 5 FRI regions of water samples is shown in Fig. 5. According to the excitation/emission range, the EEM can be divided into five regions, representing five types of organic matter shown in Table S3.†36 The EEM diagram of secondary effluent (3-fold diluted) is shown in Fig. 4a. The maximum fluorescence of the secondary effluent samples was observed at λex/λem = 230/340 nm. As shown in Fig. 5, the secondary effluent has obvious integrated fluorescence intensity in region I–V, indicating the presence of aromatic protein fragments, soluble microbial by-products, and substances related to humic acid and fulvic acid.37 After adding MS2 to the secondary effluent (Fig. 4b), the fluorescence peak was also observed at λex/λem = 275/340 nm, and the integrated fluorescence intensity in region II and region IV increased significantly, indicating that the absorption peaks in this region correspond to the MS2 coliphage.
For O3 disinfection, the synchronous removal of viruses and dissolved pollutants in water was obvious. Fig. 4c shows the EEM diagram of the water sample after disinfection with O3. The peak intensity of the water sample after disinfection with O3 was obviously weak, while that after disinfection with PMS and H2O2 still remained. And in Fig. 5, the fluorescence intensity of the water sample after O3 disinfection decreased significantly across all regions. In 5 regions, the fluorescence intensity decreased by 95.16%, 96.13%, 90.19%, 92.64%, and 83.59%. This indicates that O3 synchronously removes pollutants in secondary effluent more strongly and with the same MS2 coliphage disinfection effect. Some studies report that O3 can degrade some macromolecular organic substances into small molecules, thereby reducing the amount of dissolved organic carbon in the water.38 Protein-like components and fulvic acid-like substances (regions I–III) were preferentially oxidized by O3 because of their lower molecular weights and the presence of amide and phenolic groups.39 Therefore, O3 has a synchronous removal effect on viruses and dissolved organic pollutants, and the oxidation of MS2 coliphage and other dissolved organic carbon is more thorough, indicating that decolourization and flavour removal are more effective.
PMS and H2O2 also remove organic matter in secondary effluents with similar disinfection effects (4.0-log and 4.4-log). As shown in Fig. 5, after PMS disinfection, the fluorescence intensity of 5 regions after PMS disinfection decreased by 65.46%, 60.92%, 43.23%, 57.23%, and 22.62%, and it decreased by 91.53%, 84.35%, 79.10%, 35.28%, and 12.54% after H2O2 disinfection. The fluorescence intensity of region IV and region V after PMS treatment was lower than that after H2O2 treatment, indicating that the ability of PMS to synchronously oxidize soluble microbial by-products and humic acid-like components is greater than that of H2O2. And H2O2 oxidized more aromatic protein and fulvic acid-like components (regions I–III) than PMS. That was possibly because hydroxyl radicals remove protein-like components and fulvic acid-like substances more thoroughly.40 In addition, the fluorescence peak in region IV shifted to λex/λem = 275/300 nm after PMS treatment (Fig. 4d). That was possibly because of the formation of tryptophan-like substances.
(1) The doses of the three oxidants required to achieve 4-log disinfection of MS2 coliphage are ranked as O3 < PMS < H2O2. O3 is more effective in inactivating MS2 coliphage at low doses; 0.05 mM O3 achieves 4-log inactivation within 30 min, while 0.1 mM O3 achieves 5-log inactivation within 30 s and 0.25 mM O3 achieves complete 6-log inactivation within 30 min.
(2) The oxidant contact time required to achieve 4-log disinfection of MS2 coliphage is ranked as O3 < H2O2 < PMS. The contact time required for O3 is briefer, and 4-log MS2 coliphage inactivation can be achieved within 30 s.
(3) O3, PMS, and H2O2 also disinfect MS2 coliphage in secondary effluent with an efficacy only 1-log lower than that in DI water, as treatment with O3 (0.1 mM), PMS (1 mM), and H2O2 (25 mM) still achieves 4-log inactivation of MS2 coliphage within 30 min.
(4) O3, PMS, and H2O2 can simultaneously remove some organic pollutants while achieving 4-log disinfection of MS2 coliphage in secondary effluent, and O3 outperforms the other oxidants in synchronous removal.
The results enriched the research of virus disinfection in water and provided a theoretical basis for further studies of disinfection by oxidizing agents. In addition, it showed the significance of the dosage of oxidants in the actual wastewater treatment toward virus disinfection.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3em00527e |
This journal is © The Royal Society of Chemistry 2024 |