Chlorine-resistant bacteria (CRB) in the reverse osmosis system for wastewater reclamation: Isolation, identification and membrane fouling mechanisms

On-Site Inactivation for Disinfection of Antibiotic-Resistant Bacteria in Hospital Effluent by UV and UV-LED

The problem of antimicrobial resistance (AMR) is not limited to the medical field but is also becoming prevalent on a global scale in the environmental field. Environmental water pollution caused by the discharge of wastewater into aquatic environments has caused concern in the context of the sustainable development of modern society. However, there have been few studies focused on the treatment of hospital wastewater, and the potential consequences of this remain unknown. This study evaluated the efficacy of the inactivation of antimicrobial-resistant bacteria (AMRB) and antimicrobial resistance genes (AMRGs) in model wastewater treatment plant (WWTP) wastewater and hospital effluent based on direct ultraviolet (UV) light irradiation provided by a conventional mercury lamp with a peak wavelength of 254 nm and an ultraviolet light-emitting diode (UV-LED) with a peak emission of 280 nm under test conditions in which the irradiance of both was adjusted to the same intensity. The overall results indicated that both UV- and UV-LED-mediated disinfection effectively inactivated the AMRB in both wastewater types (>99.9% after 1-3 min of UV and 3 min of UV-LED treatment). Additionally, AMRGs were also removed (0.2-1.4 log10 for UV 254 nm and 0.1-1.3 log10 for UV 280 nm), and notably, there was no statistically significant decrease (p < 0.05) in the AMRGs between the UV and UV-LED treatments. The results of this study highlight the importance of utilizing a local inactivation treatment directly for wastewater generated by a hospital prior to its flow into a WWTP as sewage. Although additional disinfection treatment at the WWTP is likely necessary to remove the entire quantity of AMRB and AMRGs, the present study contributes to a significant reduction in the loads of WWTP and urgent prevention of the spread of infectious diseases, thus alleviating the potential threat to the environment and human health risks associated with AMR problems.

Full-length 16S rRNA gene sequencing reveals the operating mode and chlorination-aggravated SWRO biofouling at a nuclear power plant

Reverse osmosis (RO) membrane fouling and biological contamination problems faced by seawater desalination systems are microbiologically related. We used full-length 16S rRNA gene sequencing to assess the bacterial community structure and chlorine-resistant bacteria (CRB) associated with biofilm growth in different treatment processes under the winter mode of a chlorinated seawater desalination system in China. At the outset of the winter mode, certain CRB, such as Acinetobacter, Pseudomonas, and Bacillus held sway over the bacterial community structure, playing a pivotal role in biofouling. At the mode's end, Deinococcus and Paracoccus predominated, with Pseudomonas and Roseovarius following suit, while certain CRB genera still maintained their dominance. RO and chlorination are pivotal factors in shaping the bacterial community structure and diversity, and increases in total heterotrophic bacterial counts and community diversity in safety filters may adversely affect the effectiveness of subsequent RO systems. Besides, the bacterial diversity and culturable biomass in the water produced by the RO system remain high, and some conditionally pathogenic CRBs pose a certain microbial risk as a source of drinking water. Targeted removal of these CRBs will be an important area of research for advancing control over membrane clogging and ensuring water quality safety in the future.

Nanowire-assisted electroporation via inducing cell destruction for inhibiting formation of VBNC bacteria: Comparison with chlorination

The induction of viable but nonculturable (VBNC) bacteria with cellular integrity and low metabolic activity by chemical disinfection causes a significant underestimation of potential microbiological risks in drinking water. Herein, a physical Co3O4 nanowire-assisted electroporation (NW-EP) was developed to induce cell damage via the locally enhanced electric field over nanowire tips, potentially achieving effective inhibition of VBNC cells as compared with chemical chlorination (Cl2). NW-EP enabled over 5-log removal of culturable cell for various G+/G- bacteria under voltage of 1.0 V and hydraulic retention time of 180 s, and with ∼3-6 times lower energy consumption than Cl2. NW-EP also achieved much higher removals (∼84.6 % and 89.5 %) of viable Bacillus cereus (G+) and Acinetobacter schindleri (G-) via generating unrecoverable pores on cell wall and reversible/irreversible pores on cell membrane than Cl2 (∼28.6 % and 41.1 %) with insignificant cell damage. The residual VBNC bacteria with cell wall damage and membrane pore resealing exhibited gradual inactivation by osmotic stress, leading to ∼99.8 % cell inactivation after 24 h storage (∼59.4 % for Cl2). Characterizations of cell membrane integrity and cell morphology revealed that osmotic stress promoted cell membrane damage for the gradual inactivation of VBNC cells during storage. The excellent adaptability of NW-EP for controlling VBNC cells in DI, tap and lake waters suggested its promising application potentials for drinking water, such as design of an external device on household taps.

Biofilm formation and antioxidation were responsible for the increased resistance of N. eutropha to chloramination for drinking water treatment

Chloramination is an effective strategy for eliminating pathogens from drinking water and repressing their regrowth in water distribution systems. However, the inevitable release of NH4+ potentially promotes nitrification and associated ammonia-oxidizing bacteria (AOB) contamination. In this study, AOB (Nitrosomona eutropha) were isolated from environmental water and treated with two disinfection stages (chloramine disinfection and chloramine residues) to investigate the occurrence mechanisms of AOB in chloramination. The results showed that N. eutropha had considerable resistance to monochloramine compared to Escherichia coli, whose inactivation rate constant was 19.4-fold lower. The higher resistance was attributed to high levels of extracellular polymer substances (EPS) in AOB, which contribute to AOB surviving disinfection and entering the distribution system. In AOB response to the chloramine residues stage, the respiratory activity of N. eutropha remained at a high level after three days of continuous exposure to high chloramine residue concentrations (0.5-1.5 mg/L). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) suggested that the mechanism of N. eutropha tolerance involved a significantly high expression of the intracellular oxidative stress-regulating (sodB, txrA) and protein-related (NE1545, NE1546) genes. Additionally, this process enhanced EPS secretion and promoted biofilm formation. Adhesion predictions based on the XDLVO theory corroborated the trend of biofilm formation. Overall, the naturally higher resistance contributed to the survival of AOB in primary disinfection; the enhanced antioxidant response of surviving N. eutropha accompanied by biofilm formation was responsible for their increased resistance to the residual chloramines.

Aeromonas spp. in Freshwater Bodies: Antimicrobial Resistance and Biofilm Assembly

Aeromonas spp. are environmental bacteria able to infect animals and humans. Here, we aim to evaluate the role of biofilms in Aeromonas persistence in freshwater. Aeromonas were isolated from water and biofilm samples and identified by Vitek-MS and 16S rRNA sequencing. Antibiotic susceptibility profiles were determined according to EUCAST, and a crystal violet assay was used to assess biofilm assembly. MTT and the enumeration of colony-forming units were used to evaluate biofilm and planktonic Aeromonas susceptibility to chlorination, respectively. Identification at the species level was challenging, suggesting the need to improve the used methodologies. Five different Aeromonas species (A. salmonicida, A. hydrophila, A. media, A. popoffii and A. veronii) were identified from water, and one species was identified from biofilms (A. veronii). A. veronnii and A. salmonicida presented resistance to different antibiotics, whith the highest resistance rate observed for A. salmonicida (multiple antibiotic resistance index of 0.25). Of the 21 isolates, 11 were biofilm producers, and 10 of them were strong biofilm producers (SBPs). The SBPs presented increased tolerance to chlorine disinfection when compared with their planktonic counterparts. In order to elucidate the mechanisms underlying biofilm tolerance to chlorine and support the importance of preventing biofilm assembly in water reservoirs, further research is required.

Inactivation of antibiotic-resistant bacteria in hospital wastewater by ozone-based advanced water treatment processes

The emergence and spread of antimicrobial resistance (AMR) continue on a global scale. The impacts of wastewater on the environment and human health have been identified, and understanding the environmental impacts of hospital wastewater and exploring appropriate forms of treatment are major societal challenges. In the present research, we evaluated the efficacy of ozone (O3)-based advanced wastewater treatment systems (O3, O3/H2O2, O3/UV, and O3/UV/H2O2) for the treatment of antimicrobials, antimicrobial-resistant bacteria (AMRB), and antimicrobial resistance genes (AMRGs) in wastewater from medical facilities. Our results indicated that the O3-based advanced wastewater treatment inactivated multiple antimicrobials (>99.9%) and AMRB after 10-30 min of treatment. Additionally, AMRGs were effectively removed (1.4-6.6 log10) during hospital wastewater treatment. The inactivation and/or removal performances of these pollutants through the O3/UV and O3/UV/H2O2 treatments were significantly (P < 0.05) better than those in the O3 and O3/H2O2 treatments. Altered taxonomic diversity of microorganisms based on 16S rRNA gene sequencing following the O3-based treatment showed that advanced wastewater treatments not only removed viable bacteria but also removed genes constituting microorganisms in the wastewater. Consequently, the objective of this study was to apply advanced wastewater treatments to treat wastewater, mitigate environmental pollution, and alleviate potential threats to environmental and human health associated with AMR. Our findings will contribute to enhancing the effectiveness of advanced wastewater treatment systems through on-site application, not only in wastewater treatment plants (WWTPs) but also in medical facilities. Moreover, our results will help reduce the discharge of AMRB and AMRGs into rivers and maintain the safety of aquatic environments.

Inactivation of Bacteria in Water by Ferrate(VI): Efficiency and Mechanisms

Ferrate (Fe(VI)) is an emerging green disinfectant and has received increasing attention nowadays. This study conducted systematic analyses of Fe(VI) disinfection on six typical bacteria in different water matrices. The results showed that Fe(VI) was more effective in inactivating Gram-negative (G-) bacteria than Gram-positive (G+) bacteria, and the disinfection performance of Fe(VI) was better in a phosphate buffer than that in a borate buffer and secondary effluent. The inactivation rate constants of G- bacteria were significantly higher than those of G+ bacteria. The cell membrane damage of G- bacteria was also more severe than that of G+ bacteria after Fe(VI) treatment. The cell wall structure, especially cell wall thickness, might account for the difference of the inactivation efficiency between G- bacteria and G+ bacteria. Moreover, it is revealed that Fe(VI) primarily reacted with proteins rather than other biological molecules (i.e., phospholipids, peptidoglycan, and lipopolysaccharide). This was further evidenced by the reduction of bacterial autofluorescence due to the destruction of bacterial proteins during Fe(VI) inactivation. Overall, this study advances the understanding of Fe(VI) disinfection mechanisms and provides valuable information for the Fe(VI) application in water disinfection.

Insight into mixed chlorine/chloramines conversion and associated water quality variability in drinking water distribution systems

Mixed chlorine/chloramines are common in drinking water distribution systems (DWDSs); however, their transformation and impact on chemical and microbial characteristics are not well understood. We systematically investigated water quality parameters associated with mixed chlorine/chloramine species conversion in 192 samples (including raw, finished, and tap water) collected throughout the year in a city in East China. Various chlorine/chloramine species (free chlorine, monochloramine [NH₂Cl], dichloramine [NHCl₂], and organic chloramines [OC]) were detected in both chlorinated and chloraminated DWDSs. NHCl₂ + OC increased with transport distance along the pipeline network. The maximum proportion of NHCl₂ + OC in over total chlorine in tap water reached 66 % and 38 % from chlorinated and chloraminated DWDSs, respectively. Both free chlorine and NH₂Cl showed a rapid decay in the water pipe systems, but NHCl₂ and OC were more persistent. Correlations between chlorine/chloramine species and physicochemical parameters were established. Models for predicting the sum of chloroform/TCM, bromodichloromethane/BDCM, chlorodibromomethane/CBDM, and bromoform/TBM (THM₄) (R² = 0.56) and haloacetic acids (HAAs) (R² = 0.65) exhibited greater accuracy based on machine learning tuned with chlorine/chloramine species, particularly NHCl₂ + OC. The predominant bacterial communities in mixed chlorine/chloramine systems were those resistant to chlorine or chloramine such as proteobacteria. NH₂Cl was the most significant explanatory factor (28.1 %) for the variation in microbial community assemblage in chloraminated DWDSs. Although residual free chlorine and NHCl₂ + OC, accounted for a smaller proportion of chlorine species in chloraminated DWDSs, they played an essential role (12.4 % and 9.1 %, respectively) in the microbial community structure.

Uncovering novel disinfection mechanisms of solar light/periodate system: The dominance of singlet oxygen and metabolomic insights

Disinfection plays an essential role in waterborne pathogen control and disease prevention, especially during the COVID-19 pandemic. Catalyst-free solar light/periodate (PI) system has recently presented great potential in water disinfection, whereas the in-depth chemical and microbiological mechanisms for efficient bacterial inactivation remain unclear. Our work delineated firstly the critical role of singlet oxygen, instead of reported hydroxyl radicals and superoxide radicals, in dominating bacterial inactivation by the PI/simulated sunlight (SSL) system. Multi-evidence demonstrated the prominent disinfection performance of this system for Staphylococcus aureus in terms of culturability (&gt; 6 logs CFU), cellular integrity, and metabolic activity. Particularly, the excellent intracellular DNA removal (&gt; 95%) indicated that PI/SSL system may function as a selective disinfection strategy to diminish bacterial culturability without damaging the cell membrane. The PI/SSL system could also effectively inhibit bacterial regrowth for &gt; 5 days and horizontal gene transfer between E. coli genera. Nontargeted metabolomic analysis suggested that PI/SSL system inactivated bacteria by triggering the accumulation of intracellular reactive oxygen species and the depletion of reduced glutathione. Additionally, the PI/SSL system could accomplish simultaneous micropollutant removal and bacterial inactivation, suggesting its versatility in water decontamination. Overall, this study deciphers more comprehensive antibacterial mechanisms of this environmentally friendly disinfection system, facilitating the technical development and application of the selective disinfection strategy in environmental pathogen control.

Synergistic nanowire-assisted electroporation and chlorination for inactivation of chlorine-resistant bacteria in drinking water systems via inducing cell pores for chlorine permeation

The widespread use of chlorination (Cl₂) in drinking water systems causes the selection of chlorine-resistant bacteria commonly with dense extracellular polymeric substance (EPS) against chlorine permeation, posing significant threat to public health. Herein, a nanowire-assisted electroporation (EP) via locally enhanced electric field was combined with Cl₂ to construct the synergistic EP/Cl₂ disinfection, with the purposes of inducing cell pores for chlorine permeation and bacterial inactivation. The synergistic effects of EP/Cl₂ were observed for inactivation of chlorine-resistant Bacillus cereus (G+, 304 μg DOC-EPS/10⁹ CFU) and Aeromonas media (G-, 35.8 μg), and chlorine-sensitive Escherichia coli (G-, 5.1 μg) that were frequent occurrence in drinking water systems. The EP/Cl₂ enabled above 6 log B. cereus inactivation (undetectable live bacteria) at 1.5 V-EP and 0.9 mg/L-Cl₂, which was much higher than the individual EP (1.11 log) and Cl₂ (1.13 log) disinfection. The cell membrane integrity, intracellular free chlorine levels, and morphology analyses revealed that the electroporation-induced pores on cell wall/membrane destructed the bound EPS barrier for chlorine permeation, and the pore sizes were further enlarged by chlorine oxidation, hence facilitating bacterial inactivation via destroying the cell structures. The excellent disinfection performance for tap water and lake water also suggested its sound application potentials.

Control for chlorine resistant spore forming bacteria by the coupling of pre-oxidation and coagulation sedimentation, and UV-AOPs enhanced inactivation in drinking water treatment

Spore forming bacteria (SFB) are strongly chlorine resistant. Their presence in drinking water may cause diseases and pose threat to public health. Three SFB strains, i.e. Bacillus alvei, Bacillus cereus, and Lysinibacillus fusiformis, were isolated and identified from the finished water of a drinking water treatment plant where bacteria colonies occasionally reached the limit value. Due to their chlorine resistance, a SFB control strategy coupling pre-oxidation, coagulation sedimentation, and UV-AOPs inactivation in water treatment process was studied in lab scale. Five minutes pre-oxidation treatment by applying Cl₂ and ClO₂ induced remarkable spore transformation. Longer pre-oxidation exposure time didn't have apparent improvement. Cl₂ and ClO₂ dosages of 0.9 mg/L and 0.5 mg/L were suggested, respectively. The formed spores can be efficiently removed by the following coagulation sedimentation treatment. At a suggested dosage combination of 20 mg/L PAC and 0.08 mg/L PAM, spore removal efficiency reached about 3.15-lg. Comparing to applying sole UV irradiation, enhanced UV inactivation by adding 0.1 mM H₂O₂, or Cl₂, or peroxymonosulfate (PMS) substantially improved the inactivation of the most chlorine resistant SFB strain, Lysinibacillus fusiformis. UV-AOPs stably achieved 2-lg inactivation rate at UV dosage of 40 mJ/cm². UV/H₂O₂, UV/Cl₂ and UV/PMS inactivation kinetically enhanced 1.20 times, 1.36 times and 1.91 times over sole UV irradiation. Intracellular DNA and ATP leakages were detected, and remarkable damages of Lysinibacillus fusiformis cells' surface and ultrastructure were observed. These findings evidenced cell wall and cell membrane destructions, guaranteeing substantial SFB cells inactivation. This study was carried out based on three SFB strains isolated from a finished water, and common engineering practical operations. By providing engineeringly relevant references, the outcomes obtained would be helpful for dealing with SFB outbreak risk in drinking water treatment.