Bacterial Inactivation Rate Research Articles

Photodynamic antibacterial activity of CoTiO3/ZnIn2S4 Z-type heterojunction and its efficient enhancement mechanism by reactive oxygen species

The Solar-powered photocatalytic antibacterial technology has received widespread attention as a safe and efficient environmental self-cleaning technology, but its application remains a challenging task. Taking inspiration from the design of heterojunction structures in photocatalytic materials, this study employed a precipitation in-situ synthesis method to successfully construct a CoTiO3/ZnIn2S4 (CTZIS) Z-scheme heterojunction with excellent photocatalytic performance by depositing layered ZnIn2S4 nanosheets in situ on a rod-shaped CoTiO3 support. After visible-light irradiation for 20 min, the CTZIS antimicrobial agent (100 μg/mL) exhibited an ultra-high bacterial inactivation rate of 99.9 %, which was 10 and 11 times higher than that of ZnIn2S4 and CoTiO3 under the same conditions, using E. coli as the study object. Meanwhile, bacteria treated with CTZIS exhibited the highest degree of cell membrane lipid peroxidation and the lowest activity of intracellular respiratory chain dehydrogenase, demonstrating excellent antibacterial performance. After testing and calculation, it was found that the excellent antibacterial activity comes from the solid gap electric field between heterojunctions, which enhances the effective spatial separation of photo-generated carriers and effectively increases the quantum yield of reactive oxygen species (ROS). The synergistic antibacterial mechanism of CTZIS from bacterial surface to bacterial interior co-damage was revealed, in which the production of • O2‐ and •OH are a key active substance in the process of bacterial oxidative stress inactivation.

Graphitic carbon nitride loaded with FeOOH quantum dots for synergistic photocatalysis-Fenton inactivation of pathogenic marine bacteria: Mechanisms and coupling coefficients

Sustainable and environmental benign technologies for inactivation of pathogenic marine bacteria in ballast water remains a challenge. Herein, graphitic carbon nitride (g-C3N4) loaded with FeOOH quantum dots (QDs) were fabricated and a synergistic photocatalysis-Fenton system was established, which inactivated Vibrio alginolyticus (7 log) in ballast water within 30 min under visible light irradiation. The bacterial inactivation rate constant in the coupling system was 26.5 and 6.6 times higher than traditional photocatalysis and Fenton system, respectively, exhibiting 88.8 % of synergistic coupling coefficient. The bactericidal efficiency remained consistent across varying pH levels, allowing direct application of this method in alkaline marine conditions. Free radicals including OH and O2− were proved to be the predominant contributors in the coupling system. The loading of FeOOH QDs could upshift conduction band potential of g-C3N4, thus photogenerated electrons were more easily trapped by O2 to enhance the separation of charge carriers. The photogenerated electrons also accelerated the faster circulation of Fe(III)/Fe(II), which further inhibited electron-hole recombination. Furthermore, bacterial inactivation mechanisms were elucidated by examining total protein changes, intracellular ROSs level and enzyme activities. This work offers innovative approaches for marine bacterial inactivation and ballast water disinfection, which can also find applications in other environmental-related fields.

Synthesis and characterization of a dithiodiglycolic acid-incorporated poly(glycerol sebacate) exhibiting lipase resistance and antibacterial properties

Poly(glycerol sebacate) (PGS), a crosslinked network synthesized by polycondensation of glycerol and sebacic acid, has found successful utilization in various tissue engineering applications because of its biocompatibility, ease of synthesis, surface-erosion biodegradability, rubber-like elasticity, and adjustable mechanical properties. However, its fast in vivo degradation and lack of intrinsic antibacterial activity may be a concern for specific applications. The functional groups of glycerol and sebacic acid can react with those of other monomers, offering unlimited possibilities for generating new crosslinked networks tailored for particular purposes. Herein, we synthesized a series of poly(glycerol sebacate dithiodiglycolate) (PGSDTG) by incorporation of dithiodiglycolic acid (DTG) in the synthesis of PGS. PGSDTG exhibited reduced stiffness, sensitivity to glutathione (GSH), resistance to lipase degradation, and inhibition of bacterial adhesion and growth. The PGSDTG containing 45.6 wt% of DTG exhibited the lowest degradation rate with more than 80 wt% of PGSDTG remained at day 28 and the lowest bacterial inactivation rates of 99.2 ± 0.5 % and 82.5 ± 11.0 % against S. aureus and E. coli, respectively. This study suggested that PGSDTG may serve as a suitable antibacterial scaffold material for repairing or regenerating tissues characterized by a slow healing rate.

Assessing the effectiveness and mechanisms of Fe/PS, Fe/H2O2, and O3 treatment for water disinfection: Spotlight on VBNC bacteria

Advanced oxidation processes (AOPs) exhibit significant potential for water disinfection due to their generation of large quantities of highly oxidizing free radicals. However, the neglect of viable but nonculturable (VBNC) cells obscures their true disinfection efficacy and potential environmental health risks. Therefore, the study evaluated the disinfection effectiveness and mechanisms of typical AOPs, including Fe/H2O2, Fe/persulfate (PS), and O3, from the perspective of the production of VBNC bacteria. The results indicate that Fe/PS exhibits the strongest bacterial inactivation rate (99.94%), and the cells lose their ability to reactivate. Fe/H2O2 and O3 induce more cells to enter the VBNC state compared to Fe/PS. Moreover, different AOPs result in varying levels of free radical production and utilization efficiency, with SO4•− and O3 exhibiting greater selectivity in deactivating bacteria compared to HO•. The inhibition of VBNC bacteria production by Fe/PS treatment may be attributed to the combined action of HO• and SO4•− on microorganisms, leading to oxidative stress and metabolic disruption in bacteria through the inhibition of biofilm formation and aminoacyl-tRNA biosynthesis (p < 0.05), thereby causing direct bacterial death rather than entry into the VBNC state. In contrast, Fe/H2O2 and O3 result in the upregulation of the metabolism of alanine, aspartate, and glutamate, as well as styrene degradation capacity by the bacteria, leading to the production of more VBNC bacteria. Overall, the study offers insights into mitigating potential biological risks in water disinfection and developing environmentally friendly and efficient disinfection technologies.

Investigation of plasma parameters, distributions, and optical emission for the anti-microbial performance of non-woven fabric under direct current glow discharge

The distribution of electron temperature Te and density Ne for direct current glow plasma discharge was investigated, using a single Langmuir probe, inserted inside the plasma cell. The radial temperature distribution has the same values, except with a small increment variation at the cathode edge, and an axial decrement for the temperature Te distribution profiles from the cathode fall region, passing the abnormal glow region, up to the faraway axial region.The radial distribution of the electron density Ne has its highest value at the cathode, with very intense plasma at the cathode fall region, and more Ne decrement in the abnormal glow region, passing the abnormal glow region up to the faraway axial region. In the axial Ne distribution, an increase in Ne from the cathode fall region reaches maximum values in the abnormal glow region and decreases in the faraway axial region.The optimal plasma surface treatment of non-woven silk fabric (n-WSF) can be achieved by utilizing a high plasma density and low energy of electrons to inactivate viable cells attached to (n-WSF) at very short application times, leading to complete inactivation, where the bacterial inactivation rate increases in the abnormal glow region. Based on analyses of the experimental data of initial and final densities of viable cells using survival curves in the abnormal glow discharge region, a dramatic inhibitory effect of plasma discharge on the residual survival microbe ratio was observed.

Optimizing ozone dose and contact time for removal of antibiotic-resistant P. aeruginosa, A. baumannii, E. coli, and associated resistant genes in effluent of an activated sludge process in a municipal WWTP.

This study aimed to investigate the impact of ozonation on inactivation of antibiotic-resistant bacteria (ARB) including E. coli, P. aeruginosa, and A. baumannii, as well as on removal of 16S-rRNA gene and their associated antibiotic-resistant genes (ARGs) indigenously present in effluent of municipal wastewater treatment plant. The Chick-Watson model was used to describe bacterial inactivation rates at specific ozone doses. Maximum reduction of total cultivable A. baumannii, E. coli, and P. aeruginosa were found to be 7.6, 7.1, and 4.7 log, respectively, with the highest ozone dose of 0.48 gO3/gCOD at 12min contact time. According to the study results, complete inactivation of ARB and bacterial regrowth was not observed after 72h incubation. The culture methods overestimated the performance of disinfection processes and propidium monoazide combined with qPCR, and showed the presence of viable but non-culturable bacteria after ozonation. ARGs were more persistent to ozone than ARB. The results of this study highlighted the significance of specific ozone dose and contact time in ozonation process considering the bacterial species and associated ARGs as well as the wastewater physicochemical characteristics, in order to help diminish the entrance of the biological microcontaminants into the environment.

Effect of different doses of trichloroisocyanuric acid on aquaculture pond water

Understanding the bacterial dynamics in aquaculture ponds is imperative for the assessment of disinfection efficiency and regulation of subsequent pond ecosystems. In this study, the objective was to evaluate the impact of trichloroisocyanuric acid (TCCA) (0.135 mg/L, LG; 0.405 mg/L, HG) on the water quality index, heterotrophic bacteria, microbial community and ecological function. Nine separated artificial customized tanks were inserted into the pond sediment to form relatively independent pond bodies with similar environments. 16S rRNA gene amplicon sequencing was used to evaluate the dynamics of bacterial relative abundance within 192 h. Furthermore, the functional composition of the microbial community was inferred. The results indicated that both doses of TCCA had little influence on water quality. The residual chlorine was lower than the detection limit (0.03 mg/L) in the both LG and HG within 30 min. The bacterial inactivation rate was 65.04% in the HG compared with the control group within 1 h., whereas the number of heterotrophic bacteria increased to 1.26 × 105 cfu/mL at 24 h. and 4.53 × 105 cfu/mL at 48 h., 6.03 and 6.38 times higher than the CG (P < 0.05), respectively. The TCCA in the HG significantly decreased the microbial diversity and changed the relative abundance of the pond at 24 h. and 48 h. There were 28 and 35 significantly different genera between the CG and HG (P < 0.05), and the relative abundance of Bacillariophyta in the HG was significantly higher than that in the CG at 24 h. and 48 h. (P < 0.05).There were 7 and 4 significantly different functions (except other function) between the HG and CG (P < 0.05) at 24 h. and 48 h., respectively. The results indicated that the active chlorine disappeared immediately after using TCCA, 0.405 mg/L active chlorine had a strong influence on the heterotrophic bacteria, microbial community and function, and the effect lasted for 96 h., whereas 0.135 mg/L TCCA usage had little influence on the pond water.

Inactivation of Pathogens via Visible-Light Photolysis of Riboflavin-5'-Phosphate.

Riboflavin-5'-phosphate (or flavin mononucleotide; FMN) is sensitive to visible light. Various compounds, including reactive oxygen species (ROS), can be generated from FMN photolysis upon irradiation with visible light. The ROS generated from FMN photolysis are harmful to microorganisms, including pathogenic bacteria such as Staphylococcus aureus (S. aureus). This article presents a protocol for deactivating S. aureus, as an example, via photochemical reactions involving FMN under visible light irradiation. The superoxide radical anion () generated during the FMN photolysis is evaluated via nitro blue tetrazolium (NBT) reduction. The microbial viability of S. aureus that is attributed to reactive species was used to determine the effectiveness of the process. The bacterial inactivation rate is proportional to FMN concentration. Violet light is more efficient in inactivating S. aureus than blue light irradiation, while the red or green light does not drive FMN photolysis. The present article demonstrates FMN photolysis as a simple and safe method for sanitary processes.

Synthesis and Characterization of TiO2 Nanotubes (TiO2-NTs) Decorated with Platine Nanoparticles (Pt-NPs): Photocatalytic Performance for Simultaneous Removal of Microorganisms and Volatile Organic Compounds.

This work reports on the effect of TiO2 nanotubes (TiO2-NTs), decorated wih platinum nanoparticles (Pt-NPs), on the removal of bacteria and volatile organic compounds (VOCs). The Pt-NPs were loaded onto the TiO2-NTs using the electrodeposition method at four decoration times (100, 200, 300, and 600 s). The realized Pt-NPs/TiO2-NTs nanocomposites were used for the degradation of cyclohexane, a highly toxic and carcinogenic VOC pollutant in the chemical industry. The achieved Pt-NPs/TiO2-NTs nanocomposites were characterized using X-ray diffraction (XRD), photoluminescence (PL), diffuse reflectance spectroscopy (UV–Vis), and scanning (SEM) and transmission (TEM) electron microscopy. To understand the photocatalytic and antibacterial behavior of the Pt-NPs/TiO2-NTs, simultaneous treatment of Escherichia coli and cyclohexane was conducted while varying the catalyst time decoration. We noticed a complete bacterial inactivation rate with 90% VOC removal within 60 min of visible light irradiation. Moreover, the Langmuir–Hinshelwood model correlated well with the experimental results of the photocatalytic treatment of indoor air.

Implementation of a Non-Thermal Atmospheric Pressure Plasma for Eradication of Plant Pathogens from a Surface of Economically Important Seeds.

Plant pathogenic bacteria cause significant economic losses in the global food production sector. To secure an adequate amount of high-quality nutrition for the growing human population, novel approaches need to be undertaken to combat plant disease-causing agents. As the currently available methods to eliminate bacterial phytopathogens are scarce, we evaluated the effectiveness and mechanism of action of a non-thermal atmospheric pressure plasma (NTAPP). It was ignited from a dielectric barrier discharge (DBD) operation in a plasma pencil, and applied for the first time for eradication of Dickeya and Pectobacterium spp., inoculated either on glass spheres or mung bean seeds. Furthermore, the impact of the DBD exposure on mung bean seeds germination and seedlings growth was estimated. The observed bacterial inactivation rates exceeded 3.07 logs. The two-minute DBD exposure stimulated by 3–4% the germination rate of mung bean seeds and by 13.4% subsequent early growth of the seedlings. On the contrary, a detrimental action of the four-minute DBD subjection on seed germination and early growth of the sprouts was noted shortly after the treatment. However, this effect was no longer observed or reduced to 9.7% after the 96 h incubation period. Due to the application of optical emission spectrometry (OES), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM), we found that the generated reactive oxygen and nitrogen species (RONS), i.e., N2, N2+, NO, OH, NH, and O, probably led to the denaturation and aggregation of DNA, proteins, and ribosomes. Furthermore, the cellular membrane disrupted, leading to an outflow of the cytoplasm from the DBD-exposed cells. This study suggests the potential applicability of NTAPPs as eco-friendly and innovative plant protection methods.

Isothermal inactivation of Salmonella, Listeria monocytogenes, and Enterococcus faecium NRRL B-2354 in peanut butter, powder infant formula, and wheat flour

Pathogens in low water activity foods are an important emerging food safety concern due to notable survival and thermotolerance. Limited but growing data are publicly available to compare the thermotolerance of Listeria monocytogenes, Salmonella spp., and Enterococcus faecium NRRL B-2354 (a Salmonella surrogate). The aims of this study were to determine and assess bacterial thermal inactivation rates of two pathogens and a well-established surrogate across three different low-moisture food matrices containing different levels of fat using a dry inoculation method. Three low-moisture foods (0.11 aw, 45% fat peanut butter; 0.20 aw, 27% fat powder infant formula; and 0.45 aw, < 2% fat wheat flour) were inoculated at room temperature (24.8 °C) with a dry inoculum containing either E. faecium, a Salmonella spp. cocktail, or a L. monocytogenes cocktail. Uniform bagged samples across the 9 treatments were sandwiched in copper plates and heat-treated via immersion in a hot water bath during isothermal treatments ranging from 60 °C to 90 °C. The tests were conducted in triplicate. Bacterial survival was detected via direct plating on tryptic soy agar with 0.6% yeast extract. In peanut butter and most of the powder infant formula treatments, Salmonella spp. had significantly higher D-values than L. monocytogenes using comparable temperatures (p < 0.05). However, D65°C- and D75°C-values between Salmonella spp. and L. monocytogenes in wheat flour and D85°C-values in powder infant formula were undifferentiated. E. faecium had significantly higher D-values than L. monocytogenes and Salmonella spp. in each food matrix (p < 0.05). The singular exception was observed with D85°C-values between Salmonella spp. and E. faecium in peanut butter which were not statistically different. The observed matrix effect on thermotolerance for each of the bacteria was reported in descending order as powder infant formula > peanut butter > wheat flour for the vast majority of the comparable D-values. While Salmonella is the primary pathogen of concern in low-moisture foods due to survival and outbreaks, these results indicate L. monocytogenes can exhibit similar thermotolerances in low-water activity food matrices including peanut butter and powder infant formula.

Inactivation effect and mechanisms of combined ultraviolet and metal-doped nano-TiO2 on treating Escherichia coli and Enterococci in ballast water.

The discharge of ship ballast water (containing large amounts of alien organisms) has caused severe ecological hazards to marine environments. In this study, three metal elements (Ag, Fe, and Gd) were doped to nano-TiO2 material respectively (content: 0.4%, 0.7%, and 1.0%) to improve inactivation effect of Escherichia coli and Enterococci in ballast water. Experimental results indicate that compared with the sole ultraviolet (UV) and the UV and original nano-TiO2, the UV and metal-doped nano-TiO2 increased the bacterial inactivation rate to different extents. For each metal element, high external metal content (1.0%) corresponded to high inactivation effort. The doping of Ag resulted in optimal inactivation effort, and the addition of Fe and Gd caused unobvious effort. At the end of the inactivation process (20 s), the UV and 1% Ag-doped nano-TiO2 reached the highest logarithmic sterilization rates (0.915 for Escherichia coli and 0.805 for Enterococcus). The doping of Ag, Fe, and Gd did not change the anatase phase TiO2 crystal form, and 1% Ag-doped nano-TiO2 had the smallest particle diameter and the evenest distribution of nanoparticles. Compared with the sole UV, the UV and Ag-doped nano-TiO2 treatment resulted in higher malondialdehyde contents (0.0646 μmol/L for Escherichia coli and 0.0529 μmol/L for Enterococci) and lower superoxide dismutase activities (0.672 U/mL for Escherichia coli and 0.792 U/mL for Enterococci), which were in accordance with high inactivation rates in these cases.

Synthesized OH-radical rich bacteria cellulosic pockets with photodynamic bacteria inactivation properties against S. ureus and E. coli

Inulin as an external carbon source was used as the fructose substitute to Gluconacetobacter xylinus (ATCC 10245) bacterial strain in a successful synthesis of cellulosic pockets to be used in drug delivery and storage. It was observed that inulobiose trans conformation was in agreement with ϕ = Ψ = ω = 180° and angular rotation of ϴ (C1-C2-0-CI''), ϴ (C2-0-C 1'-C2') and ϴ (0-C1'-C2'-0') respectively. A bacterial susceptibility test revealed a successful inactivation of Staphylococcus aureus and Escherichia coli in the presence of photons. Fourier Transform Infrared Spectroscopy analysis confirmed an OH absorption was verified at 3423 cm-1. Pocket drug uptake test revealed a highly absorbent structure with the thermal stability directly proportional to the increase in drug uptake, while the increase in the degree of polymerization resulted in the increase in antioxidant activity and rate of bacterial inactivation. HYPOTHESIS: Inulin as an inert polysaccharide is neutral to cellular activity, therefore, could not be an agent for bacteria inactivation.

Simultaneous removal of bacteria and volatile organic compounds on Cu2O-NPs decorated TiO2 nanotubes: Competition effect and kinetic studies

In this work, we study the effect of decorating TiO2 nanotubes (TiO2-NTs) with Cu2O nanoparticles (Cu2O-NPs) on photocatalytic degradation of volatile organic compounds (VOCs) and on bacterial disinfection. The Cu2O-NPs were loaded on the TiO2-NTs by the electrodeposition method. The butane-2, 3-dione (BUT) was used as a target VOC-pollutant of food industry due its adverse environmental impact (high toxicity and confirmed carcinogenicity). The achieved Cu2O-NPs/TiO2-NTs nanocomposites were characterized using X-ray diffraction (XRD), photoluminescence (PL), diffuse reflectance spectroscopy (UV–vis) and scanning (SEM) and transmission (TEM) electron microscopy. In order to investigate the photocatalytic and antibacterial behavior of the Cu2O-NPs/TiO2-NTs, simultaneous removal of Escherichia coli (E. coli) and butane-2, 3-dione (BUT) were tested with the optimized catalyst. We observed a bacterial inactivation rate of 98 % and a concomitant 99.7 % VOC removal within 60 min and 25 min of visible light irradiation, respectively.

Microbial decontamination of black peppercorns by simultaneous treatment with cold plasma and ultraviolet C

An intervention technology employing simultaneous ultraviolet (UV)-C and cold plasma (CP) treatments was developed to inactivate indigenous mesophilic aerobic bacteria in black peppercorns. At higher UV intensity of UV-CP treatment and water activity of black peppercorns, microbial inactivation levels increased up to 0.6 and 1.7 log CFU/g, respectively. Using a response surface analysis, optimum CP voltage and treatment time for inactivating indigenous bacteria in black peppercorns by UV-CP treatment were predicted to be 10.3 kV and 22.1 min, respectively; these inactivated indigenous bacteria and Bacillus tequilensis spores by 3.4 log CFU/g and 1.7 log spores/g, respectively, with minimal increase in temperature (4.5 ± 1.2 °C). The bacterial inactivation rate (3.4 log CFU/g) achieved by UV-CP treatment was higher than the sum (2.7 log CFU/g) of the inactivation rates of individual UV and CP treatments. UV-CP treatment did not alter the color of black peppercorns and shows potential for application in non-thermal microbial decontamination of black peppercorns. Industrial relevanceThis study has developed a novel system for non-thermal microbial inactivation in black peppercorns using simultaneous UV-C and CP treatment (UV-CP treatment). UV-CP treatment was effective in inactivating indigenous bacteria in black peppercorns, including Bacillus tequilensis spores, and had an additive effect on microbial inactivation. The efficacy of treatment in microbial inactivation increased with higher water activity of black peppercorns. The bacterial inactivation efficacy was also influenced by the UV intensity and treatment time. The results of this study demonstrated that UV-CP treatment has the potential to be employed as a non-thermal technology to disinfect black peppercorns and possibly other spices, without affecting their color.

Microwave-assisted synthesis of defective tungsten trioxide for photocatalytic bacterial inactivation: Role of the oxygen vacancy

Surface defect modulation has emerged as a potential strategy for promoting the photocatalytic activity of photocatalysts for various applications, while the impact of the oxygen vacancy on bacterial inactivation is still debated. In this study, oxygen vacancies were introduced to tungsten trioxide nanosheets (WO3–x) via a microwave-assisted route. The as-prepared WO3–x nanosheets exhibited excellent visible-light-driven photocatalytic activity toward E. coli K-12 inactivation, and 6 log orders of the bacterial cells could be completely inactivated within 150 min. The obtained bacterial inactivation rate constant was 15.2 times higher than that of pristine WO3 without oxygen vacancies, suggesting that the surface oxygen vacancy could significantly promote the bacterial inactivation efficiency. The mechanism study indicated that the inactivation of bacterial cells occurs via a direct h+ oxidation pathway. In addition, the role of the oxygen vacancy was studied in detail; the oxygen vacancy was found to not only promote interfacial charge separation but also tune the band structure of WO3, thereby leading to increased h+ oxidation power. Finally, a possible oxygen vacancy-dominated photocatalytic bacterial inactivation mechanism is proposed. This work is expected to offer new insights into the microwave-assisted synthesis of defective photocatalysts and the use of the oxygen vacancy for promoting photocatalytic antibacterial activities.

Improving visible light photocatalytic inactivation of E. coli by inducing highly efficient radical pathways through peroxymonosulfate activation using 3-D, surface-enhanced, reduced graphene oxide (rGO) aerogels

In this work, we synthesized highly porous reduced graphene oxide foams, presenting augmented antibacterial activity in presence/absence of peroxymonosulfate (PMS). To date, this is the first investigation of photocatalytic PMS disinfection by 3D-rGO materials. The foams were prepared through hydrothermal (3DG-W) and solvothermal method (3DG-EG), and analyzed by SEM, PXRD, FTIR, Raman spectroscopy and BET. Hydrothermally synthesized aerogels (3DG-W) were better organized and had higher specific surface area. The higher ratio of ID/IG in 3DG-W showed the greater removal of oxygen functional groups, larger density of structural defects and a smaller average size of the sp2 domains. Although in the dark PMS activation by 3DG and the subsequent bacterial inactivation likely proceeds via a non-radical pathway, under visible light, the bacterial inactivation rate for 3DG-W was ~3 times higher than that of 3DG-EG and radical pathways are dominant. The generated germicidal reactive species were identified using appropriate scavengers and accordingly, an overview of the occurring photocatalytic and PMS activation pathways is discussed, while the mechanisms leading to bacterial inactivation are hereby detailed.

Commercial fertilizer as effective iron chelate (Fe3+-EDDHA) for wastewater disinfection under natural sunlight for reusing in irrigation

In this study, the use of a commercial iron fertilizer (Fe3+-EDDHA) employed to remediate iron chlorosis in agriculture has been investigated as a promoting bactericidal agent in solar wastewater disinfection processes. Two water matrices: isotonic water (IW) and synthetic fresh-cut wastewater (SFCWW) and two bacterial strains (E. coli O157:H7 and Salmonella enteritidis) have been investigated. The bacterial inactivation rates were compared with other solar processes (solar only, H2O2/solar, Fe3+/solar and Fe3+/H2O2/solar) at neutral pH and at laboratory scale (200 mL) under natural solar radiation. Reagents concentration tested was 0.5, 2.5 and 5 mg L−1 of Fe3+ or Fe3+-EDDHA and 1, 5 and 10 mg L-1 of H2O2.Microbial inactivation kinetics showed an improvement of the solar disinfection efficiency when using Fe3+-EDDHA/solar in comparison with Fe3+/H2O2/solar (conventional photo-Fenton) in both water matrices. Among all reagent concentrations tested, the best inactivation kinetic rate for both bacteria was obtained with 2.5/5 mg L−1 Fe3+-EDDHA/H2O2, reaching > 5-log reduction in 45 min of treatment or 31 Whm-2 of solar UVA-dose. In addition, an inactivation mechanism has been proposed based on changes in membrane permeability when Fe3+-EDDHA is present and on structural damages caused by hydroxyl radicals (HO•) for Fe3+-EDDHA/H2O2/solar process.Finally, this study highlights the possibility of efficient fresh-cut wastewater treat for further irrigation reuse in arid and semiarid regions using disinfected wastewater that already includes iron fertilizer, reducing water scarcity and with the additional advantage of diminished impact of iron chlorosis in crops.

Environmental inactivation and irrigation-mediated regrowth of Escherichia coli O157:H7 on romaine lettuce when inoculated in a fecal slurry matrix.

Field trials were conducted in July–August and October 2012 to quantify the inactivation rate of Escherichia coli O157:H7 when mixed with fecal slurry and applied to romaine lettuce leaves. Lettuce was grown under commercial conditions in Salinas Valley, California. One-half milliliter of rabbit, chicken, or pig fecal slurry, containing an average of 4.05 × 107 CFU E. coli O157:H7 (C0), was inoculated onto the upper (adaxial) surface of a lower leaf on 288 heads of lettuce per trial immediately following a 2.5 h irrigation event. To estimate the bacterial inactivation rate as a function of time, fecal matrix, irrigation and seasonal climate effects, sets of lettuce heads (n = 28) were sampled each day over 10 days and the concentration of E. coli O157:H7 (Ct) determined. E. coli O157:H7 was detected on 100% of heads during the 10-day duration, with concentrations ranging from ≤340 MPN/head (∼5-log reduction) to >3.45 × 1012 MPN/head (∼5-log growth). Relative to C0, on day 10 (Ct = 12) we observed an overall 2.6-log and 3.2-log mean reduction of E. coli O157:H7 in July and October, respectively. However, we observed relative maximum concentrations due to bacterial growth on day 6 (maximum Ct = 8) apparently stimulated by foliar irrigation on day 5. From this maximum there was a mean 5.3-log and 5.1-log reduction by day 10 (Ct = 12) for the July and October trials, respectively. This study provides insight into the inactivation and growth kinetics of E. coli O157:H7 on romaine lettuce leaves under natural field conditions. This study provides evidence that harvesting within 24 h post irrigation has the potential to increase the concentration of E. coli O157:H7 contamination, if present on heads of romaine lettuce; foliar irrigation can temporarily stimulate substantial regrowth of E. coli O157:H7.

Novel procedure for the numerical simulation of solar water disinfection processes in flow reactors

A novel procedure for the simulation of solar water disinfection (SODIS) processes in flow reactors is presented. The modeling approach includes the rigorous description of hydrodynamics, radiation transfer, mass transport and bacterial inactivation phenomena within the reactor by means of a computational fluid dynamics (CFD) software. The methodology has been evaluated in a tubular reactor coupled with a compound parabolic collector (CPC). Velocity profiles have been validated versus theoretical fully developed flow, and radiation fields versus both ray tracing and experimental actinometrical measurements. Incorporation of the solar vector calculation significantly improves the model capabilities for prediction of the potential performance of the SODIS process at different geographical coordinates and operation time. A mechanistic kinetic model was used for the description of the bacterial inactivation rate with explicit radiation absorption effects, coupling the radiation field with the mass balances of viable bacterial species. Model predictions successfully reproduce the experimental data of E. coli inactivation under different irradiances of both simulated and natural solar light with a normalized root mean squared logarithmic error (NRMSLE) of 6.65% and 9.72%, respectively. Therefore, this novel methodology is confirmed as a useful tool for the scaling-up of the SODIS process to large volume systems to be installed in remote communities where safe drinking water is not available.