Disinfection Performance Research Articles

Ag enhanced CuS nanoflower catalyst coupling dielectric barrier discharge plasma for disinfection performance and mechanism

In this study, the hydrothermal method was employed to grow submicron CuS on carbon cloth (CC), and the photoreduction method was used to grow Ag nanoparticles on the CuS submicron flowers, thus forming the Ag/CuS/CC catalytic electrode. The application of Ag/CuS/CC electrode-coupled dielectric barrier discharge (DBD) plasma in the disinfection of pathogenic bacteria in water was studied. The Ag/CuS/CC electrode exhibits strong antibacterial activity, and under an external voltage of 30 V, the degradation efficiency of Bacillus subtilis reaches 99.99% within 15 min without regeneration. After five cycles, the inactivation rate of Bacillus subtilis reached 99.99% within 25 min. The practical applicability of the Ag/CuS/CC-coupled DBD system for treating actual wastewater was evaluated, and the changes in biological toxicity were investigated. The results indicate that the prepared Ag/CuS/CC coupled DBD has great potential for safe disinfection of pathogenic bacteria in water through integrated processes.

Performance and potential mechanisms for reactive electrochemical ceramic membrane system to inhibit resistance transmission in antibiotic-resistant contaminated wastewater: From a microbial perspective

Due to the widespread presence of antibiotic resistance genes (ARGs) in traditional biological wastewater treatment systems, electrochemical disinfection techniques have received extensive attention. The rTNA/Sb-SnO2/PbO2 Reactive Electrochemical Ceramic Membrane (RECM) system has demonstrated outstanding performance in effectively removing refractory antibiotics. However, its capacity to remove antibiotic resistant bacteria (ARB) remains unclear. In this study, an antibiotic resistant strain of Escherichia coli (AR E. coli) was employed to investigate the disinfection efficiency of the RECM system at a macroscopic level, along with its disinfection mechanism at a microscopic level. Furthermore, the secondary effluent from an antibiotic production wastewater treatment plant was collected to validate the disinfection performance of this system against ARB in actual wastewater. In the RECM system, the inactivation of AR E. coli and the removal of ARGs were primarily governed by the electrocatalytic process, with notable influences from critical factors such as current density, electrolyte type, and hydraulic retention time. Morphological observation and flow cytometry experiments confirmed that the AR E. coli in the RECM system was inactivated by alterations in cell morphology, leading to fragmentation, and by improvement in cell membrane permeability. More significantly, this system exhibited noteworthy efficiency in treating wastewater contaminated with antibiotic resistant pollutants, effectively eliminating both antibiotics and ARGs from the secondary effluent. Overall, our study comprehensively investigated the performance and underlying mechanisms of the RECM system in mitigating the dissemination of ARGs, as well as its potential feasibility of practical application.

Combined performance of upper-room UVGI and ceiling-mounted air cleaners for removing active bioaerosol

Upper-room ultraviolet germicidal irradiation (UR-UVGI) and ceiling-mounted air cleaner (CM-AC) technologies contribute to curbing the spread of infectious diseases such as COVID-19. However, there is a lack of detailed studies on the performance differences between these two control technologies for reducing viral concentrations and infection risk in isolation ward environments with different ventilation modes, especially when used alone versus in combination. Therefore, this study performed numerical simulations under three ventilation modes, namely, downward ventilation (DWV), stratum ventilation (SV), and displacement ventilation (DV), by the Eulerian-Lagrangian method combined with the UV inactivation model. The viral disinfection performance of UR-UVGI and CM-AC was parametrically analyzed. The effectiveness of the combined application of these two control technologies in wards was evaluated. The results showed that expanding the irradiation range was more effective in enhancing the UR-UVGI performance with the same total UV flux. When using UR-UVGI only, DWV disinfected better at the same irradiation flux. In CM-AC cases, the viral aerosol removal efficiency was the greatest in DV. UR-UVGI and CM-AC had advantages in active bioaerosol removal in overall and localized indoor spaces, respectively. The combined application was recommended to maximize the air cleanliness. Under the role of UR-UVGI, a high level of disinfection could be achieved using CM-AC with low ventilation rates. When the CM-AC ventilation rate was 150 m3/h and the UV irradiance was 30 μW/cm2, the viral disinfection of DV exceeded 90 %, while that of DWV was also close to 90 %. The findings could provide insights to further lower the transmission risk of infectious diseases.

Degradation of extracellular antibiotic resistance genes using peracetic acid (PAA) and performic acid (PFA)

Antibiotic resistant bacteria (ARB) associated infections are identified as a major threat to human health in the 21st century. Wastewater contains antibiotic resistance determinants and they are discharged to aquatic environments with treated or untreated effluents. These antibiotic resistance determinants can be taken up by environmental bacteria via horizontal gene transfer (HGT) and they can become antibiotic resistant. Among antibiotic resistance determinants, extracellular DNA containing antibiotic resistance genes can be up taken by environmental bacteria via natural transformation. Therefore, we evaluated the suitability of low-cost disinfectants peracetic acid (PAA) and performic acid (PFA) on inactivating total and functional extracellular ARGs in ultrapure water and secondary wastewater effluent matrices using pUC19 as a model ARG. Performance of PAA and PFA in inactivating extracellular ARGs was compared with the performance of free chlorine disinfection. RT-qPCR results showed that inactivation of ampR gene in pUC19 plasmid suspended in ultrapure water and wastewater secondary effluent by free chlorine was higher compared to PAA and PFA. However, the reduction of functional pUC19 by PAA and PFA were comparable to free chlorine. Transformation frequency of pUC19 treated by PAA and PFA achieved the maximum possible reduction within a shorter time compared to free chlorine treatment, highlighting the possibility of having disinfection chambers with smaller footprints in wastewater treatment plants. These results suggest the suitability of PAA and PFA for inactivation of ARGs in aquatic samples as alternative disinfectants to free chlorine.

Localized heating coupling with radical oxidation eliminating antibiotic resistance genes (ARGs) in interfacial photothermal Fenton-like disinfection process

Conventional oxidative disinfection processes are inefficient in eliminating intracellular antibiotic resistance genes (iARGs) due to the barrier of the cell membrane and the competitive reaction of cellular constituents within antibiotic-resistant bacteria (ARB), resulting in the widespread prevalence of ARGs in recycled water. This study presented the first application of localized heating coupling with advanced oxidation to destroy the resistant Escherichia coli cells and improved subsequent iARGs (blaTEM-1) degradation in a novel photothermal Fenton-like disinfection process. The Fe-Mn@CNT microfiltration membrane, comprising carbon nanotubes wrapped with Fe and Mn nanoparticles (Fe-Mn@CNT), was employed as a nanomaterial for photothermal conversion and H2O2 activation. The highly efficient absorption of full-spectrum photons by CNTs enabled the Fe-Mn@CNT membrane to concentrate light to generate localized intense heat, resulting in the destruction of ARB nearby, and the subsequent release of iARGs. Interfacial heat favored Fe-Mn-induced H2O2 activation, leading to the production of more ·OH, which in turn promoted the oxidation for ARG degradation and ARB cell damage. The results of the acetylcysteine quenching experiments indicated that interfacial heating and radical oxidation-induced accumulation of intracellular reactive oxygen species contributed to the elimination of about 1-log iARGs through direct attack. The integrity of the cell membrane, the morphology of ARB and the variation of i/e ARG copy numbers were observed to reveal that the introduction of interfacial heating aggravated the cell lysis and accelerated the iARGs release, resulting in the inactivation of 7.27-log ARB and the elimination of 4.64-log iARGs and 2.23-log eARGs. Localized heating coupling with ·OH oxidation achieved a 143 % increase in iARGs removal compared to the conventional Fenton-like oxidation. The interfacial photothermal Fenton-like disinfection process exhibited remarkable material stability, robust disinfection performance, and effective suppression of horizontal gene transfer, underscoring its immense potential to mitigate the risk of ARG dissemination in reclaimed water systems.

High-performance of anti-bacterial composite membrane prepared from polyethersulfone-polyethylene glycol-silver nanoparticles

A bench-scale study of river water treatment using composite polyethersulfone (PES) membrane was carried out. Polyethylene glycol-silver nanoparticles (PEG-AgNPs) additive was designed to support the simultaneous filtration and disinfection performance of PES membranes via in situ incorporation. Significant improvements in the PES membranes after modification with PEG-AgNPs were observed. The experimental results showed that the PEG-AgNPs increased the PES membrane water flux from 2.87 to 172.84 L/m2·h. The anti-fouling test of the PES membrane toward humic acid molecules after the addition of PES/PEG-AgNPs increased the reversible fouling and decreased the irreversible fouling. In terms of filtration performance, the PES/PEG-AgNP membranes showed high filtration performance, with a water disinfection ability of 99.99 %. Moreover, the leach of silver particles from the PES membrane forced by ultrasonication was <50 ppb, indicating the security and stability of the PES/PEG-AgNP membrane.

Eco‐efficiency improvement strategies for disinfectants

AbstractDisinfectants are essential products for reducing health risks, but they also have significant environmental impacts. This study assessed the Eco‐efficiency of disinfectants based on the NBR ISO 14045:2014. Primary data were collected from Brazilian producers, while secondary data were obtained from patents and the Ecoinvent database. The system boundaries encompassed cradle‐to‐consumer use. The selling price was adopted as the product system value indicator (economic analysis). Raw materials production had the greatest impact on the environmental performance of disinfectants A (Antibacterial, surfactant and preservative) and C (Antibacterial, surfactant and opacifier). Disinfectant B, in addition to raw materials production (Antibacterial, opacifier and surfactant), also experienced significant impacts from consumer transport. These critical processes represent more than 60% of the overall impacts in both categories. The Eco‐efficiency matrix (profile) related environmental and economic indicators. All disinfectants occupied quadrants three or four, indicating high impact on the environmental categories. Disinfectant C had the highest Eco‐efficiency while disinfectant B had the lowest, mainly due to its product system value. Sensitivity analysis indicated environmentally viable changes in the products' composition, such as replacing the antibacterial, surfactant, preservative, and opacifier. Energy and water consumption did not significantly impact the assessed products.

Advanced pyro-/piezoelectric catalytic disinfection of water via porous spontaneously polarized ceramic with strong local electric field induced by micro-nano bubbles

In-situ electroporation disinfection technology inactivates microorganisms by local electric field penetrating antioxidant membranes without producing by-products, which reduces the consumption of oxidants. However, this individual technology exhibits weak disinfection performance for high water fluxes. Herein, a disinfection system based on the synergy of porous spontaneously polarized ceramic (PSPC) and micro-nano bubbles (MNB) (PSPC/MNB disinfection system, PMDS) was constructed for efficient disinfection of drinking water. Pyro-/piezoelectric effects of PSPC induced by MNB collapse constructed a 1.92 × 108 V/m of local electric field (simulated by COMSOL Multiphysics) and generated reactive oxygen species (ROS; •OH, 1O2, •O2−, and H2O2), resulting in electroporation damage on microorganisms and subsequent fatal oxidation of the intracellular contents by ROS. PMDS completely inactivated 107 CFU/mL of E. coli within 45 min, about 10 times faster than the MNB process, which is attributed to that the abundant porous and rough surface in PSPC increased the specific surface area and dipoles for pyro-/piezoelectric catalysis. Moreover, MNB collapse enriched •OH and induced pyro-/piezoelectric effects of PSPC through local temperature and pressure gradients. Synergistic interaction of PSPC/MNB collected additional thermal and mechanical energies besides the collapse of MNB, and the pyro-/piezoelectricity-induced in-situ electroporation–ROS deep oxidation avoided oxidant consumption and hazardous by-products. PMDS presented favorable disinfection efficiency in actual drinking water source, expected to be a practical system for eliminating microbial hazards in drinking water.

Removal of refractory humic acid-like components from UF filtrate of landfill leachate through pH adjustment and coupled electrochemical process

Mature landfill leachate contains large quantities of a wide range of hazardous and refractory pollutants, especially humic acid-like (HA) and fulvic acid-like (FA) substances. These have poor biodegradability and a considerable ultraviolet-light quenching capacity, severely inhibiting the performance of wastewater treatment and post ultraviolet-light disinfection, but this aspect has attracted little previous research. The Fenton reaction has proved to be a feasible method for removing ultraviolet-quenching substances (UVQSs) but in conventional systems it is unable to completely mineralize organic contaminants. In this study, a novel electro-oxidation process was developed consisting of a flow-through reactor with a Cu2O cathode to catalyze Fenton-type reactions, and oxidation at a RuO2 anode. The combination of pH adjustment and electro-oxidation was evaluated for the treatment of real ultrafiltration (UF) filtrate of mature landfill leachate. A series of analytical techniques were used to determine the performance for the removal of HA and FA. Under optimal conditions, the elimination of fluorescence characteristics of HA and FA reached 100 % and 99.3 %, respectively, according to PARAFAC results based on EEM spectra. TOC was removed by 25.5 %∼30.4 % during the pH adjustment step and 51 % by electrochemical oxidation. Changes in the molecular weight distribution and fluorescence content showed that pH adjustment played an important and significant role in removing UVQSs, and the remaining TOC after electrochemical oxidation was attributed to bioavailable amino acid-like substances. Overall, the results have demonstrated the successful development of an effective method of treating the UF filtrate from mature landfill leachate, with particular respect to the removal of the problematic HA and FA content.

Gravity‐driven packed bed filter, with copper‐impregnated activated carbon, for continuous water disinfection in absence of electricity

AbstractAvailability of safe drinking water is a major concern in many parts of the world. While many filtration units operating on various principles are available to combat this, most require electricity, which may not be consistently available in such areas. In the present study, we have designed and demonstrated a water disinfection system that can operate purely on gravity, without any electricity. For this, a potassium hydroxide modified copper‐impregnated activated carbon (KOH‐Cu‐AC) hybrid was used as a filter medium for disinfection, because it is less expensive, with performance comparable to previously reported hybrids containing silver. To maintain a constant water flow rate under gravity, during disinfection, a Mariotte bottle was used as the reservoir of the contaminated water. Using this and a constant head between the bottle and the treated water exit point, the required water‐filter contact time of 25 min (for decontamination) is maintained in the filter column, regardless of tank‐fill level. The demonstrated lab‐scale system can perform disinfection of simulated contaminated water (with an initial concentration of 104 CFU mL−1 Escherichia coli), for at least 6 h, with a flow rate of 150 mL h−1. The disinfection performance from the gravity‐based filter was further validated with the conventional pump‐driven filter, used for continuous disinfection of drinking water. Equivalence of results between pump‐ and gravity‐driven operations helps us to eliminate the need for power, without any compromise in disinfection efficacy. Finally, copper concentration from treated water (106 ppb at steady state) remains very well within the safe limit (1000 ppb as per USEPA guideline). Hence, the lab‐scale design of gravity‐based packed bed filter will be useful for domestic and community‐based supply of safe drinking water in resource‐constrained areas, because it eliminated electricity requirement of conventional power‐driven systems.Practitioner Points Cost‐effective KOH‐Cu‐AC hybrid is developed as a disinfection material. Mariotte bottle used for maintaining constant disinfected water flow rate works without any electrical power supply. This system can be used for getting on‐spot, continuous disinfected water supply. The concentration of copper in the treated water is well within the safety limit. It can be applicable in rural and remote areas (no electric power source) as well as natural calamity‐affected areas.

An energy efficiency and cost analysis of utilizing high-intensity profile UVC systems on air handling unit under cool-humid climate

The feasibility of the ultraviolet germicidal irradiation (UVGI) application has been proven over the past few decades, especially in disinfection performances; however, a small number of studies were found that explored the energy efficiency improvement and cost savings of real buildings by implementing the UVC systems on cooling coils. The goal of this study is to verify the energy efficiency improvements and cost savings of AHU in a real building environment by removing biofilms on the cooling coil surfaces with the UVC irradiation techniques that can provide higher lamp output (300 μW/cm2) as well as higher intensity levels (1000–4000 μW/cm2) on the cooling coil surfaces. A series of experiments were conducted in an AHU in a medical center located in Michigan, US, to estimate energy efficiency improvement of cooling coils, chiller, and fan with UVC application. The results show that after 7 weeks of UVC operation increased coil overall enthalpy-based thermal conductance by 15.62 %, achieved chiller-side energy savings by up to 28.2 %, reduced pump energy by 32.1 %, and fan energy by 17.7 %. A return on investment (ROI) based only on energy savings is estimated to be 43 % and has a payback period of 2.32 years. When the labor, chemical, and water-saving costs for coil cleaning were included, the ROI was increased to 49 % and reduced the payback period to 2.04 years. When it comes to UVC's disinfection performances, six pathogens showed a more than 99 % removal rate while Klebsiella pneumoniae and Clostridium difficile showed a relatively lower 94 % removal rate.

Experimental study on the effect of light source arrangements on the disinfection performance of upper-room 222 nm Far-UVC

The air disinfection efficacy of upper-room 222 nm Far-UVC was experimentally investigated in a real-size chamber under well-mixed air conditions. Two bacteria (Escherichia coli, Staphylococcus epidermidis) and two bacteriophages (MS2, and P22) were selected for the test. The study considered different lamp source arrangements, including single and double sources, stationary and rotating operating modes, and an overlapping mode with a 45° irradiation angle. A numerical view-factor model was developed to analyze the irradiance distributions. Four irradiation angles, 30°, 45°, 60°, and 90°, were chosen. The results show that the lamps operating with an irradiation angle of 45° provide the highest chamber-averaged irradiance. This suggests an optimal irradiance level for a given room dimension, as inferred from the view factor model. Experimental results indicated that the overlapping mode with a 45° irradiation angle consistently outperformed both the stationary mode and rotating mode in disinfection. This can be attributed to the higher chamber-averaged irradiance, which is also supported by the numerical model predictions. The increment ratios ranged from 14.9 % to 42.9 % compared to the stationary mode. The susceptibility constants of Escherichia coli, Staphylococcus epidermidis, MS2, and P22 were measured as 0.572 m2/J, 0.099 m2/J, 0.060 m2/J, and 0.081 m2/J respectively.

Optimizing ozone treatment for pathogen removal and disinfection by-product control for potable reuse at pilot-scale

Reclaimed water poses environmental and human health risks due to residual organic micropollutants and pathogens. Ozonation of reclaimed water to control pathogens and trace organics is an important step in advanced water treatment systems for potable reuse of reclaimed water. Ensuring efficient pathogen reduction while controlling disinfection byproducts remains a significant challenge to implementing ozonation in reclaimed water reuse applications. This study aimed to investigate ozonation conditions using a plug flow reactor (PFR) to achieve effective pathogen removal/inactivation while minimizing bromate and N-Nitrosodimethylamine (NDMA) formation. The pilot scale study was conducted using three doses of ozone (0.7, 1.0 and 1.4 ozone/total organic carbon (O3/TOC) ratio) to determine the disinfection performance using actual reclaimed water. The disinfection efficiency was assessed by measuring total coliforms, Escherichia coli (E. coli), Pepper Mild Mottle Virus (PMMoV), Tomato Brown Rugose Fruit Virus (ToBRFV) and Norovirus (HNoV). The ozone CT values ranged from 1.60 to 13.62 mg min L−1, resulting in significant reductions in pathogens and indicators. Specifically, ozone treatment led to concentration reductions of 2.46–2.89, 2.03–2.18, 0.46–1.63, 2.23–2.64 and > 4 log for total coliforms, E. coli, PMMoV, ToBRFV, and HNoV, respectively. After ozonation, concentrations of bromate and NDMA increased, reaching levels between 2.8 and 12.0 μg L−1, and 28–40.0 ng L−1, respectively, for average feed water bromide levels of 86.7 ± 1.8 μg L−1 and TOC levels of 7.2 ± 0.1 mg L−1. The increases in DBP formation were pronounced with higher ozone dosages, possibly requiring removal/control in subsequent treatment steps in some potable reuse applications.

Characterization and effectiveness of a miniaturized dielectric barrier discharge module for air disinfection

Effective inactivation of airborne pathogens is crucial for air quality control and the prevention of infectious diseases, especially in indoor human-living environments. In this work, a novel air disinfector based on surface dielectric barrier discharge (DBD) plasma was proposed. The discharge characteristics and the disinfection performance of the disinfector were investigated under different applied voltages, airflow rates, and humidity. The used DBD mainly works in the O3-dominant product mode with a discharge power of 1–3 W. The decreases in N2(C-B) emission intensity, ozone, discharge power, and discharge current with the increasing airflow humidity were observed. Humidity was found to be the most pronounced factor promoting the single-pass disinfection efficiency. The Z value reached 0.32 l/J for relative humidity of 70%–80%. Additionally, ozone and ions were found to play a minor role in plasma-mediated bacterial inactivation. The antibacterial effectiveness of the disinfector was also validated by 2-h circulating disinfection experiments. Efficiency was maintained above the disinfection level (&amp;gt;99.9%) after a 5000-h continuous running. Meanwhile, the ozone emission was below the standard limit requirements. The proposed air disinfector is promising for household use with the advantages of small size, bacterial inactivation capability, low ozone emission, and high perceptibility.

Air disinfection performance of upper-room ultraviolet germicidal irradiation (UR-UVGI) system in a multi-compartment dental clinic

Multi-compartment dental clinics present significant airborne cross-infection risks. Upper-room ultraviolet germicidal irradiation (UR-UVGI) system have shown promise in preventing airborne pathogens, but its available application data are insufficient in multi-compartment dental clinics. Therefore, the UR-UVGI system's performance in a multi-compartment dental clinic was comprehensively evaluated in this study. The accuracy of the turbulence and drift flux models was verified by experimental data from ultrasonic scaling. The effects of the ventilation rate, irradiation zone volume, and irradiation flux on UR-UVGI performance were analyzed using computational fluid dynamics coupled with a UV inactivation model. Different patient numbers were considered. The results showed that UR-UVGI significantly reduced virus concentrations and outperformed increased ventilation rates alone. At a ventilation rate of six air changes per hour (ACH), UR-UVGI with an irradiation zone volume of 20% and irradiation flux of 5 μW/cm2 achieved a 70.44% average virus reduction in the whole room (WR), outperforming the impact of doubling the ventilation rate from 6 to 12 ACH without UR-UVGI. The highest disinfection efficiency of UR-UVGI decreased for WRs with more patients. The compartment treating patients exhibited significantly lower disinfection efficiency than others. Moreover, optimal UR-UVGI performance occurs at lower ventilation rates, achieving over 80% virus disinfection in WR. Additionally, exceeding an irradiation zone volume of 20% or an irradiation flux of 5 μW/cm2 notably reduces the improvement rates of UR-UVGI performance. These findings provide a scientific reference for strategically applying UR-UVGI in multi-compartment dental clinics.

Enhancement of chlorine-resistant bacteria inactivation via coupling Magnéli phase Ti4O7-based electrochemical oxidation and chlorination

The widespread use of chlorination prompts the selection of chlorine-resistant bacteria in drinking water, posing a great threat to public health. Herein, according to sequential electrochemical oxidation/reduction (Ox/Red) processes with a flow-through mode, electrochemical devices (ED) with sequential Ox-Red, Red-Ox and Ox-Red-Ox processes were coupled with chlorination (AC) to evaluate their synergistic effects and mechanisms for inactivation of chlorine-resistant bacteria in drinking water. ED/AC enabled ∼ 3.0 log of synergistic effect and ∼ 2.5 times lower energy consumption for inactivation of various chlorine-sensitive/-resistant bacteria and gram-positive/-negative bacteria in DI and tap waters. Especially, ED/AC with Ox-Red-Ox device exhibited the best disinfection performance with achieving over 6.7 log inactivation of Bacillus cereus at 4.0 V and 0.5 mg/L-Cl2 as compared with ED alone (∼1.25 log) and AC (∼2.67 log) disinfection. The electrochemical oxidation on Ti4O7-based anode promoted the generation of free chlorine radicals and H+ ions, which was accompanied with the formation of neutral HClO molecules. Characterizations of SEM and flow cytometer suggested that oxidative species of neutral HClO molecules and free chlorine radicals enhanced the bacterial inactivation via severe damages of cell structures. This work provided a promising strategy via coupling electrochemical oxidation and chlorination for eliminating chlorine-resistant bacteria in drinking water.

Fabrication of close-contact S-scheme Cr2Bi3O11-Bi2O3/Fe3O4@porous carbon microspheres based on in-situ reaction: Enhanced photo-Fenton wastewater treatment

Low photo-induced carrier recombination rate, exceptional light absorption, and advantageous recycling performance are crucial attributes of semiconductor photocatalyst for wastewater purification. Herein, based on in-situ reaction, close-contact S-scheme bismuth chromate/bismuth oxide/ferroferric oxide@porous carbon microspheres (Cr2Bi3O11-Bi2O3/Fe3O4@PCs) (F-CBFP) was fabricated using alginates as precursor. Due to the abundance of functional groups on the porous carbon (PCs), Bi2O3 and Cr2Bi3O11 nanoparticles (NPs) are in situ deposited onto the highly conductive 3D magnetic porous Fe3O4@PCs microsphere surface, which not only form tight interfacial contacts and reduces interfacial potential barriers but also prevent agglomeration or shedding of the NPs during photocatalytic reactions. Moreover, density functional theory (DFT) calculations further confirm that the formation of a robust built-in electric field (BIEF) within F-CBFP prompts photo-induced electrons in the conduction band (CB) of Bi2O3 to combine with holes in the valence band (VB) of Cr2Bi3O11, effectively constructing a S-scheme heterojunction system. Also, Fe3O4 can act as a Fenton catalyst, activating the H2O2 generated by Cr2Bi3O11 under illumination. In wastewater treatment, the obtained F-CBFP shows remarkable photo-Fenton degradation (towards methyl orange (97.8 %, 60 min) and tetracycline hydrochloride (95.3 %, 100 min)) and disinfection performance (100 % E. coli inactivation), and exceptional cyclic stability.

Efficient disinfection of combined sewer overflows by ultraviolet/peracetic acid through intracellular oxidation with preserving cell integrity

Combined sewer overflows (CSOs) introduce microbial contaminants into the receiving water bodies, thereby posing risks to public health. This study systematically investigated the disinfection performance and mechanisms of the combined process of ultraviolet and peracetic acid (UV/PAA) in CSOs with selecting Escherichia coli (E. coli) as a target microbial contaminant. The UV/PAA process exhibited superior performance in inactivating E. coli in simulated CSOs compared with UV, PAA, and UV/H2O2 processes. Increasing the PAA dosage greatly enhanced the disinfection efficiency, while turbidity and organic matter hindered the inactivation performance. Singlet oxygen (1O2), hydroxyl (•OH) and organic radicals (RO•) contributed to the inactivation of E. coli, with •OH and RO• playing the prominent role. Variations of intracellular reactive oxygen species, malondialdehyde, enzymes activities, DNA contents and biochemical compositions of E. coli cells suggested that UV/PAA primarily caused oxidative damage to intracellular molecules rather than the damage to the lipids of the cell membrane, therefore effectively limited the regrowth of E. coli. Additionally, the UV/PAA process displayed an outstanding performance in disinfecting actual raw CSOs, achieving a 2.90-log inactivation of total bacteria after reaction for 4 min. These results highlighted the practical applicability and effectiveness of the UV/PAA process in the disinfection of CSOs.

A flow-through Ti4O7 membrane electrode for ballast water treatment: Performance, mechanism, and comparison with Ti/RuO2-IrO2 electrode

Electrochemical Advanced Oxidation Processes (EAOPs) present a promising solution for ballast water treatment. However, due to the extremely short half-life of reactive oxygen species, the disinfection active zone is limited to the surface of the electrode, resulting in low disinfection current efficiency of EAOPs. To address this challenge, this study developed a flow-through electrochemical disinfection system utilizing a Ti4O7 membrane electrode. A comparative analysis was conducted against a conventional Ti/RuO2-IrO2 electrode to assess the Ti4O7 membrane electrode’s efficacy in ballast water disinfection. The flow-through mode significantly increased the probability of contact between E. coli and the surface of Ti4O7 membrane electrode, consequently leading to a notable increase in the inactivation rate from 1.05 min−1 to 1.63 min−1, at a current density of 20 mA/cm2, at a Cl- concentration of 16.5 g/L, and an initial E. coli concentration of 107 CFU/mL. Notably, at low current densities, the Ti4O7 membrane electrode exhibited superior disinfection performance compared to the Ti/RuO2-IrO2 electrode. The predominant disinfection active species in the Ti4O7 membrane electrode system were identified as reactive oxygen species, particularly •OH and •O2–, contrasting with the abundant generation of active chlorine species (ACSs) observed in the Ti/RuO2-IrO2 electrode system. Both electrode systems demonstrated the ability to disrupt the cellular structure of E. coli. However, due to the sustained effectiveness of ACSs, the degradation rate of total protein in the Ti/RuO2-IrO2 electrode system (40.53 %) surpassed that of the Ti4O7 membrane electrode system (12.39 %). Despite the minimal concentration of ACSs in the Ti4O7 membrane system (0.02 mg/L), no bacterial regeneration was observed, highlighting the efficacy of the Ti4O7 membrane electrode in preventing bacterial regrowth. This study elucidated a free radical-based disinfection mechanism for the Ti4O7 membrane electrode, affirming its feasibility for ballast water disinfection purposes.

Efficacy and Mechanism of Antibiotic Resistance Gene Degradation and Cell Membrane Damage during Ultraviolet Advanced Oxidation Processes.

Combinations of UV with oxidants can initiate advanced oxidation processes (AOPs) and enhance bacterial inactivation. However, the effectiveness and mechanisms of UV-AOPs in damaging nucleic acids (e.g., antibiotic resistance genes (ARGs)) and cell integrity represent a knowledge gap. This study comprehensively compared ARG degradation and cell membrane damage under three different UV-AOPs. The extracellular ARG (eARG) removal efficiency followed the order of UV/chlorine > UV/H2O2 > UV/peracetic acid (PAA). Hydroxyl radical (•OH) and reactive chlorine species (RCS) largely contributed to eARG removal, while organic radicals made a minor contribution. For intracellular ARGs (iARGs), UV/H2O2 did not remove better than UV alone due to the scavenging of •OH by cell components, whereas UV/PAA provided a modest synergism, likely due to diffusion of PAA into cells and intracellular •OH generation. Comparatively, UV/chlorine achieved significant synergistic iARG removal, suggesting the critical role of the RCS in resisting cellular scavenging and inactivating ARGs. Additionally, flow cytometry analysis demonstrated that membrane damage was mainly attributed to chlorine oxidation, while the impacts of radicals, H2O2, and PAA were negligible. These results provide mechanistic insights into bacterial inactivation and fate of ARGs during UV-AOPs, and shed light on the suitability of quantitative polymerase chain reaction (qPCR) and flow cytometry in assessing disinfection performance.