Dielectric barrier discharge plasma promotes disinfection-residual-bacteria inactivation via electric field and reactive species

Traditional disinfection processes face significant challenges such as health and ecological risks associated with disinfection-residual-bacteria due to their single mechanism of action. Development of new disinfection processes with composite mechanisms is therefore urgently needed. In this study, we employed liquid ground-electrode dielectric barrier discharge (lgDBD) to achieve synergistic sterilization through electric field electroporation and reactive species oxidation. At a voltage of 12 kV, Pseudomonas fluorescens (ultraviolet and ozone-resistant) and Bacillus subtilis (chlorine-resistant) were completely inactivated within 8 and 6 min, respectively, surpassing a 7.0-log reduction. The lgDBD process showed good disinfection performance across a wide range of pH values and different practical water samples. Staining experiments suggest that cellular membrane damage contributes to this inactivation. In addition, we used a two-dimensional parallel streamer solver with kinetics code to fashion a representative model of the basic discharge unit, and discovered the presence of a persistent electric field during the discharge process with a peak value of 2.86 × 106 V/m. Plasma discharge generates excited state species such as O(1D) and N2(C3Πu), and further forms reactive oxygen and nitrogen species at the gas-liquid interface. The physical process, which is driven by electric field-induced cell membrane electroporation, synergizes with the bactericidal effects of reactive oxygen and nitrogen species to provide effective disinfection. Adopting the lgDBD process enhances sterilization efficiency and adaptability, underscoring its potential to revolutionize physicochemical synergistic disinfection practices.

Water disinfection using hydrogen peroxide with fixed bed hematite catalyst - kinetic and activity studies

A lab-scale reactor with a fixed-bed hematite catalyst for the effective decomposition of H2O2 and bacteria inactivation was designed. The bactericidal effect is the largest at a low initial bacterial count of 2·103 CFU/L, which is typical for natural surface waters. When using a 5 mM H2O2 solution and a residence time of 104 min, the reduction in the number of E. coli bacteria is about 3.5-log. At a higher initial bacterial count of 1-2·104 CFU/L, a 5 mM H2O2 solution reduces the bacteria number by about 4-log. The H2O2 decomposition follows the log-linear kinetics of a first-order reaction while the bacterial inactivation does not. The kinetics of bacterial inactivation was described using the Weibull model in the modified form: log10(N0/N) = b · tn. The values of the non-linearity parameter n were found to be lower than 1, indicating that bacterial inactivation slows down over time. With increasing initial H2O2 concentration, the rate parameter b increases while the non-linearity parameter n decreases. With increasing temperature, both parameters increase. The stability of the catalyst has been proved by XRD, FTIR, SEM, and ICP-OES. The concentration of iron leaching into water during disinfection is much lower than the limit declared by WHO for iron in drinking water. The results show that technical-grade hematite is a promising Fenton-like catalyst for water disinfection. The fixed-bed reactor can be the basis of the mobile installations for water purification in emergencies.

Visible light-driven photocatalytic bacterial inactivation on PPE, supported by the DFT and bactericidal study

A novel ZnO-MoO₃-ZnMoO₃@graphene GZM composite catalyst prepared by microwave hydrothermal process for personal protective equipment textiles (PPE) is presented in this study. The results indicated that the GZM with defect vacancy sites of two types as observed by EPR showed significantly superior inactivation of the E. coli bacteria compared to GZM without the lower defect vacancy sites and concomitant lower electron densities. Photocatalytic activated oxidation by the GZM composites coatings was observed to proceed in acceptable times as well as the bacterial inactivation (log bact. C/C_o > 10⁷ within 3 h). Defect sites in the GZM seem to be important leading to the bacterial inactivation process. DFT calculations on the GZM with and without catalyst defect sites were carried out. The electron densities were estimated by the Fourier mapping. The results found in this study showed the potential of GZM-PPE for practical applications.

Photocatalytic investigation of textile dyes and E. coli bacteria from wastewater using Fe3O4@MnO2 heterojunction and investigation for hydrogen generation on NaBH4 hydrolysis

Various impurities found nowadays in water can be detrimental to human health. This work focused on utilizing Fe₃O₄@MnO₂ nanocomposite for cleaning organic contaminants from water, including rhodamine B (RhB) and Escherichia coli (E. coli). Analysis methods such as XRD, UV-vis, TEM, and FTIR were used to describe the nanocomposite. The results showed that the developed nanocomposite has good photocatalytic activity against pollutants in wastewater. The E. coli was destroyed after 90 min, and the RhB photodegradation rate was 75%. Moreover, the Fe₃O₄@MnO₂ efficiency as a catalyst for producing hydrogen as an alternative energy source was tested. According to the calculations, the nanomaterial's turnover frequency, activation energy, enthalpy, and entropy are 1061.3 h^-1, 28.93 kJ/mol, 26.38 kJ/mol, and -128.41 J/mol.K, respectively. Four reusability tests were completed, and the average reusability was 78%. The obtained data indicated the excellent potential for the developed Fe₃O₄@MnO₂ nanomaterial to act as an adsorbent, thus representing an alternative to the classical depollution methods. This study showed that nanoparticles have a photocatalytic effect against pathogenic bacteria and RhB azo dye in polluted waters and offer an effective catalytic activity to produce hydrogen as an alternative energy source.

Synergistic role of in-situ Zr-doping and cobalt oxide cocatalysts on photocatalytic bacterial inactivation and organic pollutants removal over template-free Fe2O3 nanorods

Herein, we synthesized in-situ Zr-doped Fe₂O₃ NRs photocatalyst by successive simple hydrothermal and air quenching methods. The synergistic roles of CoO_x (1 wt%) and Zr-doping on bacteria inactivation and model organic pollutants over Fe₂O₃ NRs photocatalyst were studied in detail. Initially, rod-like Zr ((0-8) %)-doped Fe₂O₃ NRs were produced via a hydrothermal method. CoO_x was loaded onto the Zr ((0-8) %)-doped Fe₂O₃ NRs) surface by a wet impregnation approach. The Zr-doping conditions and CoO_x loadings were judiciously optimized, and a highly photoactive CoO_x(1 wt%)/Zr(6%)-doped Fe₂O₃ NRs photocatalyst was developed. The CoO_x(1 wt%) loaded Zr(6%)-doped Fe₂O₃ NRs photocatalyst revealed 99.4% inactivation efficiency compared with (0, 4 and 8)% Zr-doped Fe₂O₃ NRs, respectively. After CoO_x(1 wt%)/Zr(6%)-doped Fe₂O₃ NRs photocatalyst treatment, Bio-TEM images of bacterial cells showed extensive morphological deviations in cell membranes, compared with the non-treated ones. Additionally, the optimum CoO_x(1 wt%)/Zr(6%)-doped Fe₂O₃ NRs photocatalyst exhibited 99.2% BPA and 98.3% orange II dye degradation after light radiation for 3 h. This work will provide a rapid method for the development of photostable catalyst materials for bacterial disinfection and organic degradation.

Advances in 2D MXenes-based materials for water purification and disinfection: Synthesis approaches and photocatalytic mechanistic pathways

MXenes two-dimensional materials have recently excited researchers' curiosity for various industrial applications. MXenes are promising materials for environmental remediation technologies to sense and mitigate various intractable hazardous pollutants from the atmosphere due to their inherent mechanical and physicochemical properties, such as high surface area, increased hydrophilicity, high conductivity, changing band gaps, and robust electrochemistry. This review discusses the versatile applications of MXenes and MXene-based nanocomposites in various environmental remediation processes. A brief description of synthetic procedures of MXenes nanocomposites and their different properties are highlighted. Afterward, the photocatalytic abilities of MXene-based nanocomposites for degrading organic pollutants, removal of heavy metals, and inactivation of microorganisms are discussed. In addition, the role of MXenes anti-corrosion support in the lifetime of some semiconductors was addressed. Current challenges and future perspectives toward the application of MXene materials for environmental remediation and energy production are summarized for plausible real-world use.

Photoelectrocatalytic inactivation mechanism of E. coli DH5α (TET) and synergistic degradation of corresponding antibiotics in water

The occurrence and proliferation of antibiotic-resistance genes (ARGs) / antibiotic-resistant bacteria (ARB) have been currently aggravating due to the increase of antibiotic residues in the aquatic environment. The interaction of ARB/ARGs with antibiotics inevitably occurred during water purification, yet their synergistic purification mechanism remains unclear. Herein, a systematic approach was developed to understand, in-depth, the synergistic mechanism in the coexisted E. coli DH5α (TET) inactivation and tetracycline hydrochloride (TET) degradation using photoelectrocatalysis (PEC) as a model technology. Results showed that low dosage (0 - 40 ppm) of TET exerted a negative influence on ARB inactivation with prolonged bactericidal time from 60 to 160 min. Addition of TET in environmental concentration (5 - 60 ppm) resulted in sub-lethal damage and prolonged PEC treatment time (100 - 160 min), accounting for inhibition effects on ARB inactivation. The major reactive species (RSs) involved in ARB inactivation and TET degradation were evidenced as photogenerated hole, ^•OH and O₂^•-, whereas hole and O₂^•- were demonstrated to be the major disinfectants for ARB/ARG inactivation. The bacterial defense system displayed increased antioxidative activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) to protect ARB cells against oxidative stress. Exposure to 60 ppm TET was a threshold where certain ARB cells were induced into viable but nonculturable bacterial cell (VBNC) state, as evidenced by plate counting and ATP activity analysis, together with the integral cell membranes observed by flow cytometry (FCM) and scanning electron microscope (SEM). These findings appeal for appropriate technical adjustments for water and wastewater treatment to ensure safety of water.

Solar-driven free chlorine advanced oxidation process for simultaneous removal of microcontaminants and microorganisms in natural water at pilot-scale

Contamination of natural water (NW) by emerging contaminants has been widely pointed out as one of the main challenges to ensure high-quality drinking water. Thus, the effectiveness of a solar-driven free chlorine advanced oxidation process simultaneously investigating the elimination of six organic microcontaminants (OMCs) and three bacteria from NW at a pilot-scale was evaluated in this study. Firstly, the solar/free chlorine process was studied at lab-scale using a solar simulator to evaluate the effect of free chlorine concentration (0.5-10 mg L^-1) on OMC degradation and generation of toxic oxyanions (e.g., ClO₃^- ions). Thus, the best free chlorine concentration observed was applied for the simultaneous removal of OMCs and pathogens under natural solar light at pilot scale. At lab-scale, the solar/free chlorine (2.5 mg L^-1) process achieved 80% of total degradation in 5 min (1.4 kJ L^-1 of accumulative UV energy) with an oxidant consumption of 0.3 mg L^-1 and without ClO₃^- generation. Similar results were attained under natural solar irradiation at a pilot-scale. For all bacteria strains, the legally required detection limit (DL = 1 CFU 100 mL^-1) for reclaimed water reuse was attained in a short contact time. Still, more importantly, the solar/free chlorine (2.5 mg L^-1) process effectively avoided the possible bacterial regrowth in the post-treated sample after six days. Finally, the combination of free chlorine with solar irradiation provided a simple and energy-efficient process for OMC and bacteria removal in NW at a pilot-scale.

Co-existing siderite alleviates the Fe(II) oxidation-induced inactivation of Fe(III)-reducing bacteria

Abiotic Fe (II) oxidation widely occurs in the natural subsurface environment and engineered dynamic processes, which possibly impacts the growth of indigenous microbes. As previously discovered, the oxidation of aqueous Fe²⁺ at neutral pH effectively inactivates iron-reducing bacteria Shewanella oneidensis strain MR-1 (MR-1). Herein, the impacts of co-existing iron mineral on the oxidation of aqueous Fe²⁺ and the subsequent disinfection activity on MR-1 were investigated with siderite selected as a representative iron mineral in the subsurface environment. The oxidation rate of aqueous Fe²⁺ and the amount of generated OH radical increased as the content of siderite increased, while the MR-1 inactivation was alleviated. An initial concentration of 2.0 × 10⁶ CFU/mL MR-1 was inactivated by about 2.7 orders of magnitude during oxidation of 0.2 mM FeSO₄ alone for 30 min, which was reduced to only about 0.6 orders of magnitude in the presence of 4.3 mM co-existing siderite. ROS scavenging results confirmed that the OH radical generated in the bulk solution was not the leading role for the inactivation of MR-1. Morphological changes of the cells observed by SEM demonstrated that the disruption of the cell membrane was alleviated by siderite, which was further supported by the XRD and FTIR spectra. The underlying mechanism was proposed to be the reduced contact time of Fe²⁺ and MR-1 cells due to the accelerated oxidation. This work provides new insights into the disinfection behavior of heterogeneous Fe (II) oxidation on iron cycling bacterial in the natural environment.

Chromium and cerium co-doped magnetite/reduced graphene oxide nanocomposite as a potent antibacterial agent against S. aureus

The development of innovative antibacterial samples with high efficacy has received a great deal of interest. Herein, we synthesized magnetite modified by Cr and co-modified by Cr and Ce, along with their reduced graphene oxide (rGO)-based nanocomposites via facile hydrothermal and co-precipitation methods. The rGO-based samples showed proper magnetic behavior, high porosity, and vast specific surface area. The high specific surface area provided more adsorptive active sites with higher potentials for the decomposition of Staphylococcus aureus (S. aureus) cells. The antibacterial performance of the samples against S. aureus was evaluated at 50 and 100 μg mL^-1 through the colony-forming unit (CFU) method and the minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) values were subsequently determined. As per results, not only chromium cations could effectively damage the DNA of bacteria, but also the antibacterial efficacy was further enhanced by co-doping of cerium and the integration with rGO nanosheets. The antibacterial results were confirmed through the changes observed in the morphology and topology of the bacteria before and after the treatment using SEM and AFM analyses. Ultimately, the plausible S. aureus inactivation mechanism of the samples was disclosed.

Treatment of wastewater effluents from Bogotá - Colombia by the photo-electro-Fenton process: Elimination of bacteria and pharmaceutical

In this work, the occurrences of bacteria families and relevant pharmaceuticals in municipal wastewater effluents from Bogotá (Colombia), and their treatment by the photo-electro-Fenton process were studied. Twenty-five representative pharmaceuticals (azithromycin, carbamazepine, ciprofloxacin, clarithromycin, diclofenac, enalapril, gabapentin, iopromide, metoprolol, sulfamethoxazole, trimethoprim, valsartan, clindamycin, erythromycin, levamisole, lincomycin, norfloxacin, oxolinic acid, phenazone, primidone, salbutamol, sulfadiazine, tetracycline, tramadol, and venlafaxine) were quantified in the effluent by LC-MS/MS analysis. Four of these target compounds (azithromycin, diclofenac, trimethoprim, norfloxacin) were found at concentrations that represent an environmental risk. In addition, several bacteria families related to water and foodborne diseases were identified in such effluents (e.g., Pseudomonadaceae, Campylobacteraceae, Aeromonadaceae, Enterobacteriaceae, and Bacteroidaceae), via shotgun-metagenomic technique. Then, a bench-scale photo-electro-Fenton (PEF) system equipped with a DSA anode (Ti/IrO₂-SnO₂) and a GDE cathode was applied to treat such effluents. After 60 min, this treatment led to a decrease in the ratio of the bacterial content in the original samples, ~150 thousand times, and a pondered removal of 66.12% for the pharmaceuticals. The study of the process pathways indicated that the bacteria and pharmaceuticals elimination mainly occurred through attacks of hydroxyl and chlorine radicals. Interestingly, in the case of pharmaceuticals, their environmental risk quotients were diminished after the PEF application. Furthermore, the prolonged action of this electrochemical process induced ~15% of mineralization and a significant reduction of the total DNA (removal >85%). Hence, the photo-electro-Fenton process showed to be a promising alternative to deal with municipal effluents for limiting the waterborne diseases, pollution by pharmaceuticals, and mobility/availability of genetic material coming from microorganisms.

Refined regulation and nitrogen doping of biochar derived from ramie fiber by deep eutectic solvents (DESs) for catalytic persulfate activation toward non-radical organics degradation and disinfection

Sulfate radical-based advanced oxidation process (SR-AOPs) has great promise in water treatment, there is thereby a pressing need yet still a significant challenge to rationally design an efficient and green catalyst for heterogeneous catalytic reactions. In this study, deep eutectic solvents (DESs) were prepared and employed to simultaneously achieve structural engineering of fibrils separation and surface modifying of nitrogen doping on biochar derived from filaments biomass (NRBF) of Ramie (Boehmeria nivea (L.) Gaud). The more regular structure and pure carbon with reasonable configuration, and the N doped in hexatomic ring of NRBF were great impetus to improve the catalytic performance for peroxydisulfate (PDS) activation, with 4.5 times higher degradation rate of tetracycline than pristine biochar. The in-depth mechanistic study of PDS activation confirmed that dominated pathway was in transition from original reactive species (¹O₂) in pristine biochar system to a direct electron-shuttle pathway in NRBF system. Moreover, the non-radical dominated NRBF/PDS system showed good potential for bacteria (Escherichia coli) inactivation in disinfection application. Therefore, this work provides the underlying insights to guide the design of a functional and green biochar converting from Ramie filaments by an environmentally friendly facile protocol to achieve multiple purposes of wastewater decontamination and disinfection.

Growth in a biofilm sensitizes Cutibacterium acnes to nanosecond pulsed electric fields

The Gram-positive anaerobic bacterium Cutibacterium acnes (C. acnes) is a commensal of the human skin, but also an opportunistic pathogen that contributes to the pathophysiology of the skin disease acne vulgaris. C. acnes can form biofilms; cells in biofilms are more resilient to antimicrobial stresses. Acne therapeutic options such as topical or systemic antimicrobial treatments often show incomplete responses. In this study we measured the efficacy of nanosecond pulsed electric fields (nsPEF), a new promising cell and tissue ablation technology, to inactivate C. acnes. Our results show that all tested nsPEF doses (250 to 2000 pulses, 280 ns pulses, 28 kV/cm, 5 Hz; 0.5 to 4 kJ/ml) failed to inactivate planktonic C. acnes and that pretreatment with lysozyme, a naturally occurring cell-wall-weakening enzyme, increased C. acnes vulnerability to nsPEF. Surprisingly, growth in a biofilm appears to sensitize C. acnes to nsPEF-induced stress, as C. acnes biofilm-derived cells showed increased cell death after nsPEF treatments that did not affect planktonic cells. Biofilm inactivation by nsPEF was confirmed by treating intact biofilms grown on glass coverslips with an indium oxide conductive layer. Altogether our results show that, contrary to other antimicrobial agents, nsPEF kill more efficiently bacteria in biofilms than planktonic cells.

Treating Porcine Abscesses with Histotripsy: A Pilot Study

Infected abscesses are walled-off collections of pus and bacteria. They are a common sequela of complications in the setting of surgery, trauma, systemic infections and other disease states. Current treatment is typically limited to antibiotics with long-term catheter drainage, or surgical washout when inaccessible to percutaneous drainage or unresponsive to initial care efforts. Antibiotic resistance is also a growing concern. Although bacteria can develop drug resistance, they remain susceptible to thermal and mechanical damage. In particular, short pulses of focused ultrasound (i.e., histotripsy) generate mechanical damage through localized cavitation, representing a potential new paradigm for treating abscesses non-invasively, without the need for long-term catheterization and antibiotics. In this pilot study, boiling and cavitation histotripsy treatments were applied to subcutaneous and intramuscular abscesses developed in a novel porcine model. Ultrasound imaging was used to evaluate abscess maturity for treatment monitoring and assessment of post-treatment outcomes. Disinfection was quantified by counting bacteria colonies from samples aspirated before and after treatment. Histopathological evaluation of the abscesses was performed to identify changes resulting from histotripsy treatment and potential collateral damage. Cavitation histotripsy was more successful in reducing the bacterial load while having a smaller treatment volume compared with boiling histotripsy. The results of this pilot study suggest focused ultrasound may lead to a technology for in situ treatment of acoustically accessible abscesses.

DNA pom-pom nanostructure as a multifunctional platform for pathogenic bacteria determination and inactivation

Pathogenic bacteria levels are significantly related with disease control, clinical diagnosis, and even environmental monitoring. It is becoming highly urgent to achieve ultrasensitive detection of pathogenic bacteria and efficient combat of bacterial infection. Toward this end, we have assembled a DNA Pom-Pom nanostructure (PP-N) based multifunctional platform for pathogenic bacteria determination and inactivation. In particular, one DNA oligonucleotide probe that serve as a trigger was specifically designed for the autonomous cross-opening of metastable DNA hairpin probes and long dsDNA structure formation, achieving a catalytic self-assembly of DNA nanostructure. Numerous DNA strands in this PP-N assembly provide sufficient interaction sites for functional domains and connector, showing high programmability, excellent biostability, as well as selective target recognition. With these properties, the fluorescence dyes modified PP-N platform showed excellent bacteria analysis with both excellent selectivity and ultrasensitive determination limit as low as 2.0 CFU/mL. Furthermore, the aptamer-functionalized and antibiotics loaded PP-N platform demonstrate excellent merits of high antibiotics-loading capacity and negligible cytotoxicity to targets. Therefore, this DNA PP-N assembly based multifunctional platform promise its great application in targeted sensing, combating bacterial infection, and potential clinic therapy.

Novel strategy for membrane biofouling control in MBR with CdS/MIL-101 modified PVDF membrane by in situ visible light irradiation

Novel control strategies for membrane biofouling with eco-friendly photocatalytic technology are critically needed in practical operation of membrane bioreactors (MBRs). In this study, a metal-organic frameworks (MOF) based photocatalytic membrane was firstly applied in an anammox MBR for a long-term biofouling control, where bacteria were inactivated and foulants were degraded simultaneously, with environmentally friendly and renewable visible light energy. By physicochemical characterization, the synthesized photocatalyst of CdS/MIL-101 showed superior visible-light photocatalytic ability, and the 1 wt% CdS/MIL-101 modified membrane C2 showed enhanced hydrophilicity and water permeability compared with the pristine membrane C0. In the long-term operation of anammox MBRs under waterproof lights irradiation, the filtration cycles of C2 (25-26 d) were obviously extended compared with C0 (10-14 d), while their average total nitrogen removal efficiencies were comparable up to 84%, indicating an excellent biofouling alleviation effect by using C2 with a satisfactory nitrogen removal performance maintained. By analysis of the biofilm on the fouled membranes, the organic foulants (especially extracellular polymeric substances) were degraded, and the live bacteria were inactivated effectively by the photocatalytic reactions of CdS/MIL-101 on C2. In the antimicrobial tests against model bacteria, C2 exhibited remarkable antimicrobial effect against both Gram-negative and Gram-positive bacteria with visible light irradiation by destruction of cell integrity with the inhibition rate of 92% for Escherichia coli and 95% for Staphylococcus aureus, respectively. In the model foulants (bovine serum albumin, sodium alginate, and humic acid) filtration tests, C2 showed higher antifouling capabilities, lower flux declining rates, and higher foulants rejection rates under visible light irradiation compared with C0. The reactive species of ·OH, e^- and h⁺ generated on C2 were verified to play the predominant role in the anti-biofouling processes by simultaneous bacteria inactivation and foulants degradation. The findings offer a novel insight into the biofouling controlling in MBRs by simultaneous bacteria inactivation and foulants degradation with an eco-friendly method.

Solar driven self-sustainable photoelectrochemical bacteria inactivation in scale-up reactor utilizing large-scale fabricable Ti/MoS2/MoOx photoanode

Here we present photoelectrochemical (PEC) bacterial inactivation properties of large-scale fabricable Ti/MoS₂/MoO_x photoanode with a strong solar light absorbance capacity. Specifically, by thermal oxidation of the as-prepared MoS₂/Ti film at 250 °C for 15 min in aerobic condition, the visible light performance of photocurrent generation and Escherichia coli (E. coli) inactivation are markedly enhanced. Complete inactivation of 10⁶ CFU/mL E. coli in NaCl electrolyte is achieved with 0.5 V bias in 2 h under visible light irradiation, and H₂O₂ and O₂^- have been found as key reactive oxidative species to destroy E. coli. The bacteria inactivation performance of present photoanode is comparable with reported visible light photoanodes such as Cu₂O or N-doped TiO₂. The markedly improved PEC performance and inhibited photocorrosion could be attributed to the formation of heterojunction of MoS₂/MoO_x on the surface due to thermal oxidation. Furthermore, the PEC E. coli inactivation performance and stability of the large dimensional electrode are evaluated in a scale-up reactor. As an example of self-sustainable PEC water treatment system powered by only solar panels, wastewater containing inorganic, organic, macromolecule and microbial pollutants is attempted to be treated employing the developed electrodes under illumination of LED lamps.

Kinetic modeling of lag times during photo-induced inactivation of E. coli in sunlit surface waters: Unraveling the pathways of exogenous action

This work presents a kinetic analysis of the exogenous photo-induced disinfection of E. coli in natural waters. Herein, the inactivation of bacteria by light and photo-generated transient species, i.e., hydroxyl radical (HO^•), excited triplet states of organic matter (³CDOM*) and singlet oxygen (¹O₂), was studied. It was found that the exogenous disinfection of E. coli proceeds through a lag time, followed by an exponential phase triggered by photo-generated HO^•, ¹O₂ and ³CDOM*. Also, we report that the concentration increased of transient species (and especially HO^•) precursors decreased the lag times of bacteria inactivation. Due to the limitations of the competition kinetics methodology to include the lag phase, an alternative strategy to study the interaction between E. coli and photo-generated transient species was proposed, considering the log-linear pseudo-first order rate constants and lag-times. On this basis and by using APEX software, a full kinetic analysis of exogenous bacterial inactivation, taking into account both lag-time and exponential decay, was developed. This approach provided insights into the conditions that could make exogenous inactivation competitive with the endogenous process for the E. coli inactivation in natural sunlit waters. Hence, this research contributes to the understanding of fundamental kinetic aspects of photoinduced bacterial inactivation, which is the basis for light-assisted processes such as the solar disinfection (SODIS).

N-doped graphitic biochars from C-phycocyanin extracted Spirulina residue for catalytic persulfate activation toward nonradical disinfection and organic oxidation

Biochars are low-cost and environmental-friendly materials, which are promising in wastewater treatment. In this study, biochars were manufactured from C-phycocyanin extracted (C-CP) Spirulina residue (SDBC) via thermal pyrolysis. Simultaneously, N-doping was also achieved from the protein in the algae for obtaining a high-performance carbocatalyst for peroxydisulfate (PDS) activation. The SDBC yielded large specific surface areas, nitrogen loading, and good conductivity, which demonstrated excellent oxidation efficiencies toward a wide array of aqueous microcontaminants. An in-depth mechanistic study was performed by integrating selective radical scavenging, solvent exchange (H₂O to D₂O), diverse organic probes, and electrochemical measurement, unveiling that SDBC/PDS did not rely on free radicals or singlet oxygen but a nonradical pathway. PDS intimately was bonded with a biochar (SDBC 900-acid, pyrolysis at 900 °C) to form a surface reactive complex that subsequently attacked an organic sulfamethoxazole (SMX) adsorbed on the biochar via an electron-transfer regime. During this process, the SDBC 900-acid played versatile roles in PDS activation, organic accumulation and mediating the electron shuttle from SMX to PDS. This nonradical system can maintain a superior oxidation efficiency in complicated water matrix and long-term stable operation. More importantly, the nonradical species in SDBC 900-acid/PDS system were capable of inactivating the bacteria (Escherichia coli) in wastewater. Therefore, the biochar based nonradical system can provide a mild and high-efficiency strategy for disinfection in waste and drinking water by green carbocatalysis. This study provides not only a value-added biochar catalyst for wastewater purification but also the first insight into the bacteria inactivation via nonradical oxidation.

Determination of live:dead bacteria as a function of antibiotic treatment

Antibiotics are drugs that react against, kill, or inhibit the growth of bacteria. The method most often employed to evaluate the effectiveness of an antibiotic to kill bacteria requires at least 16 to 24 h for bacterial incubation. The requirement of long periods of time for the determination of the number of bacteria still alive after antibiotic treatment, may, in many cases, be detrimental to the patient's health. In addition, with increasing of bacterial antibiotic resistance, the need to utilize methods for distinguishing between live and dead bacteria within a short period of time after treatment with antibiotic agents, is becoming more crucial. To that effect, we have utilized a hand-held double monochromator to record in situ and within minutes the synchronous and normal fluorescence spectra of bacteria and other species. The fluorescence spectra of bacterial components such as tryptophan, tyrosine and DNA are clearly displayed. In addition, principal component analysis, PCA, makes it possible to display live and dead bacteria separately and determine the ratio of live:dead bacteria before and after treatment with antibiotics.

A facile method to prepare translucent anatase thin films in monolithic structures for gas stream purification

In the present work, a facile method to prepare translucent anatase thin films on cellulose acetate monolithic (CAM) structures was developed. A simple sol-gel method was applied to synthesize photoactive TiO₂ anatase nanoparticles using tetra-n-butyl titanium as precursor. The immobilization of the photocatalyst on CAM structures was performed by a simple dip-coating method. The translucent anatase thin films allow the UV light penetration through the CAM internal walls. The photocatalytic activity was tested on the degradation of n-decane (model volatile organic compound-VOC) in gas phase, using a tubular lab-scale (irradiated by simulated solar light) and pilot-scale (irradiated by natural solar light or UVA light) reactors packed with TiO₂-CAM structures, both equipped with compound parabolic collectors (CPCs). The efficiency of the photocatalytic oxidation (PCO) process in the degradation of n-decane molecules was studied at different operating conditions at lab-scale, such as catalytic bed size (40-160 cm), TiO₂ film thickness (0.435-0.869 μm), feed flow rate (75-300 cm³ min^-1), n-decane feed concentration (44-194 ppm), humidity (3 and 40%), oxygen concentration (0 and 21%), and incident UV irradiance (18.9, 29.1, and 38.4 W_UV m^-2). The decontamination of a bioaerosol stream was also evaluated by the PCO process, using Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) as model bacteria. A pilot-scale unit was operated day and night, using natural sunlight and artificial UV light, to show its performance in the mineralization of n-decane air streams under real outdoor conditions. Graphical abstract Normally graphics abstract are not presented with captions/legend. The diagram is a collection of images that resume the work.

Synthesis and characterization of alginate beads encapsulated zinc oxide nanoparticles for bacteria disinfection in water

The use of polymer nanocomposites as novel materials for water remediation has emerged as a promising alternative for disinfection of bacteria contaminated water. Sodium alginate, a natural biopolymer has been investigated in this study by encapsulating antimicrobial zinc oxide nanoparticles supported bentonite. The confirmation of the alginate nanocomposites was done by use of TEM, SEM-EDS and XRD. The antimicrobial activity of the alginate nanocomposites was investigated by batch studies using surface water and synthetic bacteria contaminated water containing Staphylococcus aureus. The effect of nanocomposite amount and initial bacteria concentration has been studied. The inactivation results indicated that the nanocomposite effectively inactivated bacteria in both the synthetic and surface water. With an amount of 0.5 g of the nanocomposites, no bacteria was observed in the water after 70 min of contact time with initial bacteria concentration of 200 cfu/ml for synthetic water and within a min, no bacteria was observed in the water for surface water. It is worth noting that 200 cfu/ml is the bacteria concentration range in which environmental water is likely to contain. Therefore, the results of this study have indicated that the alginate nanocomposites can be deemed as a potential antimicrobial agent for water disinfection.

Highly efficient inactivation of bacteria found in drinking water using chitosan-bentonite composites: Modelling and breakthrough curve analysis

Disinfection of bacterially-contaminated drinking water requires a robust and effective technique and can be achieved by using an appropriate disinfectant material. The advanced use of nanomaterials is observed as an alternative and effective way for the disinfection process and water treatment as a whole. Hence, the inactivation of Escherichia coli (E. coli) using chitosan-Bentonite (Cts-Bent) composites was studied in a fixed bed column. Cts-Bent composites were synthesized using in situ cross-linking method using Bent-supported silver and zinc oxide nanoparticles. These composites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The effect of the composite bed mass, initial concentration of bacteria, and flow rate on the bacterial inactivation was investigated. The characterization results revealed that the composites were successfully prepared and confirmed the presence of both silver and zinc oxide nanoparticles in the chitosan matrix. The growth curves of E. coli were expressed as breakthrough curves, based on the logistic, Gompertz, and Boltzmann models. The breakthrough time and processed volume of treated water at breakthrough were used as performance indicators, which revealed that the composites performed best at low bacterial concentration and flow rate and with substantial bed mass. The chitosan composites were found to be highly effective, which was demonstrated when no bacteria were observed in the effluent sample within the first 27 h of analysing river water. All the models were suitable for adequately describing and reproducing the experimental data with a sigmoidal pattern. Therefore, the prepared composite is showing potential to work as a disinfectant and provide an alternative solution for water disinfection; hence this study should propel further research of the same or similar materials.

Efficient bacteria capture and inactivation by cetyltrimethylammonium bromide modified magnetic nanoparticles

Functionalized magnetic nanoparticles have shown great application potentials in water treatment processes especially for bacterial removal. Antibacterial agent, cetyltrimethylammonium bromide (CTAB), was employed to modify Fe3O4 nanoparticles to fabricate bactericidal paramagnetic nanoparticles (Fe3O4@CTAB). The as-prepared Fe3O4@CTAB could effectively capture both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis from water. For both cell types, more than 99% of bacteria with initial concentration of 1.5 × 10(7)CFU/mL could be inactivated by Fe3O4@CTAB (0.5 g/L) within 60 min. Fe3O4@CTAB could remove more than 99% of cells over a wide pH (from 3 to 10) and solution ionic strength range (from 0 to 1000 mM). The copresence of sulfate and nitrate did not affect the bacterial capture efficiencies, whereas, phosphate and silicate slightly decreased the bacterial removal rates. However, more than 91% and 81% of cells could be captured at 10mM of phosphate and silicate, respectively. Over 80% of cells could be removed even in the presence of 10mg/L of humic acid. Moreover, Fe3O4@CTAB exhibited good reusability, and greater than 83% of cells could be captured even in the fifth regeneration cycle. Fe3O4@CTAB prepared in this study have great application potentials for water disinfection.

Inactivation of Enterobacter aerogenes in reconstituted skim milk by high- and low-frequency ultrasound

The inactivation of Enterobacter aerogenes in skim milk using low-frequency (20kHz) and high-frequency (850kHz) ultrasonication was investigated. It was found that low-frequency acoustic cavitation resulted in lethal damage to E. aerogenes. The bacteria were more sensitive to ultrasound in water than in reconstituted skim milk having different protein concentrations. However, high-frequency ultrasound was not able to inactivate E. aerogenes in milk even when powers as high as 50W for 60min were used. This study also showed that high-frequency ultrasonication had no influence on the viscosity and particle size of skim milk, whereas low-frequency ultrasonication resulted in the decrease in viscosity and particle size of milk. The decrease in particle size is believed to be due to the breakup of the fat globules, and possibly to the cleavage of the κ-casein present at the surface of the casein micelles. Whey proteins were also found to be slightly affected by low-frequency ultrasound, with the amounts of α-lactalbumin and β-lactoglobulin slightly decreasing.

Inactivation of bacteria and yeast using high-frequency ultrasound treatment

High-frequency (850 kHz) ultrasound was used to inactivate bacteria and yeast at different growth phases under controlled temperature conditions. Three species of bacteria, Enterobacter aerogenes, Bacillus subtilis and Staphylococcus epidermidis as well as a yeast, Aureobasidium pullulans were considered. The study shows that high-frequency ultrasound is highly efficient in inactivating the bacteria in both their exponential and stationary growth phases, and inactivation rates of more than 99% were achieved. TEM observation suggests that the mechanism of bacteria inactivation is mainly due to acoustic cavitation generated free radicals and H2O2. The rod-shaped bacterium B. subtilis was also found to be sensitive to the mechanical effects of acoustic cavitation. The study showed that the inactivation process continued even after ultrasonic processing cessed due to the presence of H2O2, generated during acoustic cavitation. Compared to bacteria, the yeast A. pullulans was found to be more resistant to high-frequency ultrasound treatment.

Inactivation of microorganisms by low-frequency high-power ultrasound: 2. A simple model for the inactivation mechanism

A simple theoretical model based on shear forces generated by the collapse of the ultrasound cavities near the surface of a microorganism is proposed. This model requires two parameters which take into account the number of acoustic cavitation bubbles, and the resistance of the cell wall of the microorganism to the shear forces generated by bubble collapse. To validate the model, high-power low frequency (20 kHz) ultrasound was used to inactivate two microorganisms with very different sizes, viz., a bacterium, Enterobacter aerogenes and a yeast, Aureobasidium pullulans. The inactivation ratio was experimentally measured as a function of sonication time for different ultrasound power and for different initial cell numbers. For both E. aerogenes and A. pullulans the Log of the inactivation ratio decreased linearly with sonication time, and the rate of inactivation increased (D-value decreased) with the increase in sonication power. The rate of inactivation was also found, for both microorganisms, to increase with a decrease in the initial cell number. The fits, obtained using the proposed model, are in very good agreement with the experimental data.

Inactivation of microorganisms by low-frequency high-power ultrasound: 1. Effect of growth phase and capsule properties of the bacteria

The aim of this study was to determine the effects of high-intensity low-frequency (20 kHz) ultrasound treatment on the viability of bacteria suspension. More specifically, we have investigated the relationship between the deactivation efficiency and the physical (size, hydrophobicity) and biological (gram-status, growth phase) properties of the microbes. Enterobacter aerogenes, Bacillus subtilis, Staphylococcus epidermidis, S. epidermidis SK and Staphylococcus pseudintermedius were chosen for this study owing to their varying physical and biological properties. The survival ratio of the bacteria suspension was measured as a function of the ultrasound power (up to 13 W) for a constant sonication time of 20 min. Transmission electron microscopy was used to evaluate the ultrasound-induced damages to the microbes. Ultrasound treatment resulted in lethal damage to E. aerogenes and B. subtilis (up to 4.5-log reduction), whereas Staphylococcus spp. were not affected noticeably. Further, E. aerogenes suspensions were more sensitive to ultrasonication in exponential growth phase than when they were in stationary phase. The results of this study demonstrate that the main reason for bacterial resistance to ultrasonic deactivation is due to the properties of the bacterial capsule. Microbes with a thicker and "soft" capsule are highly resistant to ultrasonic deactivation process.