Aqueous Ozonation Research Articles

Engineering Triune Active Sites on Alkali Metal-Doped Graphite Carbon Nitride for Aqueous Catalytic Ozonation

Engineering Triune Active Sites on Alkali Metal-Doped Graphite Carbon Nitride for Aqueous Catalytic Ozonation

Impact of ozonation on the formation of particulate nitrosodi-methylamine (NDMA) in atmosphere

The contribution of ozonation to the formation of particulate nitrosodi-methylamine (NDMA) in the aqueous aerosol phase was investigated using measurement data from 2018 in Seoul, Republic of Korea and a box model. The correlation between the NDMA concentration and aerosol liquid water content and box model results showed that aqueous aerosol phase reactions, including nitrosation and ozonation, might contribute to the formation of NDMA. The concentration of NDMA and the ratio of O3/dimethylamine exhibited a negative correlation, suggesting that the contribution of ozonation to NDMA formation may not be significant. Furthermore, when the daily concentration of NDMA exceeded 10 ng/m3, the pH was 3.96 ± 0.48, indicating that the impact of ozonation on NDMA concentration might not be significant. To quantitatively investigate the contribution of ozonation, the ozonation mechanism that forms NDMA was included in the box model developed in our previous study. The model results showed that the ozonation contributed to the ambient concentration of NDMA (7.9 ± 3.8% (winter); 1.9 ± 3.0% (spring); 10.0 ± 0.77% (summer); 3.6 ± 7.3% (autumn)). It is estimated that the relatively higher O3/NOx ratio in summer (1.63 ± 0.69; 0.64 ± 0.52 (winter); 1.14 ± 0.92 (spring); 0.52 ± 0.54 (autumn)) could enhance ozonation and that relatively lower pH in summer (2.2 ± 0.4; 5.3 ± 1.2 (winter); 3.9 ± 1.2 (spring); 3.9 ± 0.7 (autumn)) could hinder nitrosation compared to that in other seasons.

Theoretical study on the degradation mechanism, kinetics and toxicity for aqueous ozonation reaction of furan derivatives

The compounds including furan-2,5-dicarboxylic acid (FDCA), 2-methyl-3-furoic acid (MFA), and 2-furoic acid (FA), containing Furan ring are considered to be possessing high ozone reactivity, although in depth studies of their ozonation processes have not been carried out yet. Hence, mechanism, kinetics and toxicity by quantum chemical, and their structure activity relationship are being investigated in this study. Studies of reaction mechanisms revealed that during the ozonolysis of three furan derivatives containing C=C double bond, furan ring opening occurs. At temperature (298 K) and pressure of 1 atm, the degradations rates of 2.22 × 103 M−1 s−1 (FDCA), 5.81 × 106 M−1 s−1 (MFA) and 1.22 × 105 M−1 s−1 (FA) suggested that the reactivity order is: MFA > FA > FDCA. In the presence of water, oxygen and ozone, the Criegee intermediates (CIs) as the primary products of ozonation would produce lower molecule weight of aldehydes and carboxylic acids by undergoing degradation pathways. The aquatic toxicity reveals that three furan derivatives play green chemicals roles. Significantly, most of the degradation products are least harmful to organisms residing in the hydrosphere. The mutagenicity and developmental toxicity of FDCA is minimum as compared to FA and MFA, which shows the applicability of FDCA in a wider and broader field. Results of this study reveal its importance in the industrial sector and degradation experiments.

Ozone exposure tunes the physicochemical properties of sweet potato starch by modifying its molecular structure

Ozonation is an efficient method for improving the technical performance of some starches, but the feasibility of its use for sweet potato starch remains unknown. The effects of aqueous ozonation on the multi-scale structure and physicochemical properties of sweet potato starch were explored. Structurally, ozonation did not generate significant alterations at the granular level (size, morphology, lamellar structure, and long-range and short-range ordered structures), but led to tremendous changes at the molecular level, including converting hydroxyl groups to carbonyl and carboxyl groups and depolymerizing starch molecules. These structural changes resulted in prominent alternations in the technological performance of sweet potato starch, such as increases in water solubility and paste clarity and decreases in water absorption capacity, paste viscosity, and paste viscoelasticity. For these traits, their amplitudes of variation elevated when the ozonation time was extended and peaked at the longest ozonation time (60 min). The greatest changes in paste setback (30 min), gel hardness (30 min), and the puffing capacity of the dried starch gel (45 min) were observed at moderate ozonation times. In summary, aqueous ozonation is a new method for fabricating sweet potato starch with improved functionality.

Ozone Decontamination of Medical and Nonmedical Devices: An Assessment of Design and Implementation Considerations.

The control of infectious diseases can be improved via carefully designed decontamination equipment and systems. Research interest in ozone (a powerful antimicrobial agent) has significantly increased over the past decade. The COVID-19 pandemic has also instigated the development of new ozone-based technologies for the decontamination of personal protective equipment, surfaces, materials, and indoor environments. As this interest continues to grow, it is necessary to consider key factors affecting the applicability of lab-based findings to large-scale systems utilizing ozone. In this review, we present recent developments on the critical factors affecting the successful deployments of industrial ozone technologies. Some of these include the medium of application (air or water), material compatibility, efficient circulation and extraction, measurement and control, automation, scalability, and process economics. We also provide a comparative assessment of ozone relative to other decontamination methods/sterilization technologies and further substantiate the necessity for increased developments in gaseous and aqueous ozonation. Modeling methodologies, which can be applied for the design and implementation of ozone contacting systems, are also presented in this review. Key knowledge gaps and open research problems/opportunities are extensively covered including our recommendations for the development of novel solutions with industrial importance.

The synergistic antibacterial activity of ozone and surfactant mists.

The microbiological safety of medical equipment and general surfaces is paramount to both the well-being of patients and the public. The application of ozone (a potent oxidant) has been recognised and implemented for this purpose, globally. However, it has primarily been utilised in the gaseous and aqueous forms. In this study, we investigate the potency of fine ozone mists and evaluate the synergistic effect when combined with cationic, anionic and non-ionic surfactants (dodecyl trimethyl ammonium bromide - DTAB, sodium dodecyl sulfate - SDS, alkyl polyglycoside - APG) as well as polyethylene glycol (PEG). Ozone mist is generated via a nebuliser (equipped with a compressed gas stream) and the piezoelectric method; whereas fabric substrates contaminated with Escherichia coli and Staphylococcus aureus are utilised in this study. Contamination levels on the fabric swatches are evaluated using agar dipslides. Compared to gaseous ozonation and aqueous ozonation (via nanobubble generation), the produced ozone mists showed significantly inferior antimicrobial properties for the tested conditions (6 ppm, 5-15 min). However, the hybrid mist-based application of 'ozone + surfactants' and 'ozone + PEG' showed considerable improvements compared to their independent applications (ozone mist only and surfactant mist only). The 'ozone + DTAB' mist had the highest activity, with better results observed with the micron-mist nebuliser than the piezoelectric transducer. We propose a likely mechanism for this synergistic performance (micellar encapsulation) and demonstrate the necessity for continued developments of novel decontamination technologies.

Influence of aqueous ozonation on physicochemical properties and incidence of phytopathogens in minimally processed strawberries

Minimally processed strawberries are perishable and susceptible to the development of pathogenic agents, making their post-harvest life limited. Thus, sanitization is a crucial step to ensure the quality of this produce. The objective was to evaluate the effect of treatment with ozone gas dissolved in water on the physicochemical properties and the incidence of pathogens in minimally processed strawberries stored under refrigeration. After minimal processing, “Camino Real” strawberries were submitted to five different treatments: immersion in ozonated water (OW) at three different concentrations (0.2; 0.5; and 1.0 mg L-1) at 10 ºC for 5 min; chlorine sanitization (Sumaveg®) in two steps, at 150 mg L-1 and 5 mg L-1, at 10 ºC for 10 min. The control treatment corresponded to fruits without sanitation. After the treatments, the fruits were stored under refrigeration at 5 ºC and 90% RH and evaluated for 12 days regarding postharvest quality (physical, physicochemical and biochemical), as well as the incidence of diseased fruits (%). The results showed that the sanitization of fruits with ozonized water, regardless of the concentration, favored the quality and health of strawberries during storage compared to fruits subjected to sanitization with chlorinated water and control fruits. Ozonated water treatment is an alternative to traditional sanitization with chlorine, maintaining the physicochemical quality of the minimally processed “Camino Real” strawberries stored under refrigeration.

Nanocarbon shells with self-inherent N, P derived from chlorella pyrenoidosa for aqueous catalytic ozonation: nonradical-dominated mechanisms

Nanocarbon shells with self-inherent N, P derived from waste chlorella pyrenoidosa (CP) as N/P/C precursors were prepared for the first time using a one-step pyrolysis method to remove ibuprofen (IBU) for catalytic ozonation. The CP at 1000 °C (NPC1000) had superior catalytic ozonation performance over MnO2, Al2O3, and g-C3N4. The catalytic ozonation process follows a nonradical oxidation mechanism via surface adsorbed atomic oxygen (*Oad), singlet oxygen (1O2) and electron transfer pathway. The result indicated that graphitic N, pyridinic N and C3PO functional groups were the major active sites based on the correlation between material structure and catalytic performance. Furthermore, the catalytic activity has little impact on the removal of IBU wastewater containing inorganic anions and humic acid (HA). This study opens new applications for microalgae-derived biocarbon materials and provides a new insight into the mechanism of metal-free heterogeneous ozone catalyst.

Microbial Inactivation: Gaseous or Aqueous Ozonation?

For decades, ozone has been known to have antimicrobial properties when dissolved or generated in water and when utilized in its gaseous form on different substrates. This property (the ability to be used in air and water) makes it versatile and applicable to different industries. Although the medium of ozonation depends on the specific process requirements, some industries have the inherent flexibility of medium selection. Thus, it is important to evaluate the antimicrobial efficacy in both media at similar concentrations, an endeavor hardly reported in the literature. This study provides insights into ozone’s efficacy in air and water using two Gram-negative bacteria (Escherichia coli NTCC1290 and Pseudomonas aeruginosa NCTC10332), two Gram-positive bacteria (Staphylococcus aureus ATCC25923 and Streptococcus mutans), and two fungi (Candida albicans and Aspergillus fumigatus). For gaseous ozonation, we utilized a custom-made ozone chamber (equipped with ultraviolet lamps), whereas an electrolysis oxygen radical generator was applied for ozone generation in water. During gaseous ozonation, the contaminated substrates (fabric swatches inoculated with bacterial and fungal suspensions) were suspended in the chamber, whereas the swatches were immersed in ozonated water for aqueous ozone treatment. The stability of ozone nanobubbles and their resulting impact on the aqueous disinfection efficiency were studied via dynamic light scattering measurements. It was observed that ozone is more effective in air than in water on all tested organisms except Staphylococcus aureus. The presented findings allow for the adjustment of the treatment conditions (exposure time and concentration) for optimal decontamination, particularly when a certain medium is preferred for ozonation.

Nanocarbon Shells with Self-Inherent N, P Derived from Chlorella Pyrenoidosa for Aqueous Catalytic Ozonation: Nonradical-Dominated Mechanism

Nanocarbon Shells with Self-Inherent N, P Derived from Chlorella Pyrenoidosa for Aqueous Catalytic Ozonation: Nonradical-Dominated Mechanism

Aqueous ozonation of furans: Kinetics and transformation mechanisms leading to the formation of α,β-unsaturated dicarbonyl compounds

Despite the widespread occurrence of furan moieties in synthetic and natural compounds, their fate in aqueous ozonation has not been investigated in detail. Reaction rate constants of seven commonly used furans with ozone were measured and ranged from kO3 = 8.5 × 104 to 3.2 × 106 M−1 s−1, depending on the type and position of furan ring substituents. Transformation product analysis of the reaction of furans with ozone focusing on the formation of toxic organic electrophiles using a novel amino acid reactivity assay revealed the formation of α,β-unsaturated dicarbonyl compounds, 2-butene-1,4-dial (BDA) and its substituted analogues (BDA-Rs). Their formation can be attributed to ozone attack at the reactive α-C position leading to furan ring opening. The molar yields of α,β-unsaturated dicarbonyl compounds varied with the applied ozone concentration reaching maximum values of 7% for 2-furoic acid. The identified α,β-unsaturated dicarbonyls are well-known toxicophores that are also formed by enzymatic oxidation of furans in the human body. In addition to providing data on kinetics, transformation product analysis and proposed reaction mechanisms for the ozonation of furans, this study raises concern about the presence of α,β-unsaturated dicarbonyl compounds in water treatment and the resulting effects on human and environmental health.

Assessment of aqueous phase ozonation on aggregation of polyvinylpyrrolidone-capped silver nanoparticles.

Due to the antibacterial characteristics, numerous-growing applications of silver nanoparticles (AgNPs) and its coated forms impact water treatment by ozone. The influence of ozone on the aggregation of bare AgNPs and polyvinylpyrrolidone-capped form (PVP-AgNPs) was investigated, as toxicity of NPs depends on particle aggregation/surface charge. Full factorial experimental design was employed to investigate the impact of pH, concentration of NPs' suspension, and ozonation time on bare and PVP-capped AgNPs. Z-Average, zeta potential, and polydispersity index (PdI) of NPs were measured as aggregation criteria. The most effective variables on aggregation of NPs were the coating layer (40-75.5% contribution), pH (14.1-29.6% contribution), and ozonation time (6.5-10.1% contribution), respectively. The aggregation rate increased with increasing ozonation time and decreased with pH. The aggregation of ozonated AgNPs (Z-average up to ~ 4000 nm) was much greater than that of ozonated PVP-AgNPs (Z-average up to ~ 450 nm) due to interaction of ozone-PVP stabilizing layer. During ozonation, the PVP-AgNPs' surface charge shifted from - 6.62 (steric repulsion) to - 29.17 mV (electrosteric repulsion) at pH 7.5, thereby requiring more treatment time to aggregate compared with AgNPs. Graphical abstract.

Kinetics and mechanistic study on degradation of prednisone acetate by ozone

Prednisone acetate (PNSA) is one of the regular glucocorticoid medicines that have been detected in surface water. In this work, the removal of PNSA by ozone was systematically studied under various conditions, and degradation intermediates and reaction pathways were proposed. The results showed that aqueous ozonation was able to remove PNSA effectively, and low pH favored this reaction. The addition of tertiary butanol did not inhibit the oxidation of PNSA by ozone, suggesting that the degradation was caused mainly by the direct oxidation effect of ozone molecules. Moreover, the presence of carboxylated or hydroxylated multiwalled carbon nanotubes can enhance the removal efficiency of PNSA by ozone. Under neutral and acidic conditions, the degradation of PNSA followed pseudo-first-order reaction. Seven intermediates were detected via liquid chromatography-mass spectrometry, and the degradation pathways were then proposed by considering the relative charge density of the frontier orbitals calculated with the Gaussian program. The electrophilic reaction and the Criegee mechanism were the primary reaction mechanisms in the degradation of PNSA by ozone. Formic acid, acetic acid, and oxalic acid were detected as the final reaction products via ion chromatography. Additionally, the aquatic toxicity of the ozonation products was predicted using ECOSAR method. The biodegradation potentials of the pollutant and the ozonation products were estimated using BIOWINTM, suggesting that O3 treatment could significantly enhance the biodegradable potentials of PNSA and its transformation intermediates in the biological post-treatment process. This work can provide useful information for the treatment of PNSA-containing wastewaters.

Occurrence of both hydroxyl radical and surface oxidation pathways in N-doped layered nanocarbons for aqueous catalytic ozonation

Metal-free catalysts such as N-doped nanocarbons are sustainable alternatives to metal-based catalysts for the degradation of persistent organic pollutants (POPs), but cost-efficient methods are required for their large-scale synthesis. In this study, a facile and scalable strategy was established for synthesizing layered N-doped nanocarbons via the pyrolysis of β-cyclodextrin (β-CD) and melamine in a N2 atmosphere. Compared with undoped pyrolyzed β-CD, N-doping led to a 30.3-fold enhancement in the pseudo-first-order rate constant for catalytic ozonation of oxalic acid (OA), and complete degradation of 50 mg/L OA was achieved in 45 min. Apart from the specific surface area boosting from 78.9 to 16.2 m2/g after N doping, the OA degradation results and material characterization also suggested that quaternary N was the main active site, which was further validated by density functional theory (DFT) simulations. DFT simulations also suggested that C atoms with high charge densities adjacent to N dopants exhibited considerable potential for the catalytic dissociation of ozone. Electron paramagnetic resonance (EPR), radical quenching, and in situ Raman studies indicated occurrence of surface oxidation pathway apart from the radical-based one. Ozone on the catalyst surface was decomposed into surface-adsorbed atomic oxygen (*Oad) and free peroxide (*O2 free). Both *Oad and OH, which was further evolved on the surface or in bulk solution, contributed to OA destruction. These insights into the catalytic ozonation mechanism on N-doped nanocarbons will advance their practical application to the catalytic degradation of organic pollutants.

Insights into influencing factor, degradation mechanism and potential toxicity involved in aqueous ozonation of oxcarbazepine (CHEM46939R1)

Oxcarbazepine (OXC), as a potent antiepileptic drug, is widely used in recent years, but its residue is potentially harmful to the environment. Although ozonation is a high-efficient technology for chemical oxidation during water treatment, it cannot completely mineralize organic matters, but partially transforms them into some unidentified by-products. In order to provide more insight into OXC ozonation process, the influencing factor, transformation mechanism and potential toxicity were comprehensively investigated in this study. The results showed that the optimal ozonation temperature was 20 °C with a pseudo-first-order reaction rate constant of 0.161 min−1. The increase of pH significantly enhanced OXC degradation, while the presence of bicarbonate caused a remarkable negative effect, manifesting that hydroxyl radical (OH) oxidation should play an important role in OXC ozonation. Moreover, transformation mechanism was further elucidated based on the identification of ten OXC-related by-products using UPLC-Q-TOF-MSn, which mainly consisted of electrophilic substitution, N-heterocyclic ring cleavage and re-arrangement, hydroxylation, carbonylation, demethoxylation and deamidation, etc. The toxicity evaluation, using US Environmental Protection Agency Toxicity Estimation Software Tool (US-EPA TEST), suggested that most identified by-products were probably more toxic than OXC itself. Besides, further experiments, by measuring inhibitory effect of ozonated mixture on Vibrio fischeri bioluminescence, demonstrated that by-products with higher toxicity tended to be accumulated under a short reaction time. Taken together, the present investigation provided valuable information for further understanding OXC ozonation process, and suggested that special attention should be paid to the control and elimination of toxic transformation by-products in future studies.

Effects of Ultrasonication and Aqueous Ozonation on Gelatinization and Flow Properties of Potato Starch

ABSTRACTUltrasonication and aqueous ozonation were applied to potato starch simultaneously. Flow properties (i.e., flow behavior index, n; consistency index, K; and apparent viscosity, ηapp) of samples were determined using a rheometer. A differential scanning calorimeter (DSC) was used to measure the gelatinization properties of samples (onset, peak and conclusion gelatinization temperatures and enthalpy of gelatinization). Results showed that ozonation caused a significant increase (p < 0.05) in onset gelatinization temperature (from 54.9 to 59.1 °C) and a significant decrease (p < 0.05) in enthalpy of gelatinization (from 14.6 to 12.2 J/g). There were no significant differences (p < 0.05) between the consistency index (ranged from 4.57 to 4.87 Pas) and apparent viscosity (ranged from 0.10 to 0.13 Pas) of samples treated with ozonation and ultrasonication with no regards of treating sequence. This showed that the order of treatment (i.e., ozonation and ultrasonication) does not have any significant effect on the flow properties of potato starch studied under the conditions applied in this research.

Sensory Analysis and Consumers Studies of Açai Beverage After Thermal, Chlorine and Ozone Treatments of the Fruits

Acai is a fruit of the Amazon region consumed as beverage, pulp, and other products, being exported to many countries because of its peculiar characteristic flavor and antioxidant power potential. For Acai there is still a need for improving sanitizing processes, making it more effective, reducing the microbiological contamination without affecting either the physicochemical and sensory characteristics of final product. Thermal (blanching at 80 and 90C) and nonthermal treatments (150 mg/L-1 chlorination and 4 mg/L-1 aqueous ozonation) were applied to fruits in order to evaluated their anthocyanins content and also processed beverages for coloring, sensory characteristics, and their purchase intentions. Ozonated fruits exhibited less anthocyanins content and beverage originated from this process showed higher color difference from the traditional beverage. Consumers could not distinguish among beverages processed thermally and sanitized by chlorination. Beverage from blanched fruits in both temperatures obtained good notes and positive purchase intention.

Ozonation of chlortetracycline in the aqueous phase: Degradation intermediates and pathway confirmed by NMR

Chlortetracycline (CTC) degradation mechanism in aqueous phase ozonation was evaluated for degradation mechanism and its correlation with the biodegradability and mineralization. CTC was removed within 8 and 4 min of ozonation at pH 2.2 and 7.0, respectively. At pH 2.2, HPLC–triple quadrupole mass spectrometry (MS) detected 30 products. The structures for some of these products were proposed on the basis of ozonation chemistry, CTC structure and MS data; these structures were then confirmed by nuclear magnetic resonance (NMR) spectra. Double bond cleavages, dimethyl amino group oxidation, opening and removal of the aromatic ring and dechlorination, mostly direct ozonation reactions, gave products with molecular weights (m.w.) 494, 510, 524, 495 and 413, respectively. Subsequent degradations gave products with m.w. 449, 465, 463 and 415. These products were arranged into a degradation pathway. At pH 7.0, the rate of reaction was increased, though the detected products were similar. Direct ozonation at pH 2.2 increased the biodegradability by altering the structures of CTC and its products. Nevertheless, direct ozonation alone remained insufficient for the mineralization, which was efficient at pH 7.0 due to the production of free radicals.

Effect of aqueous ozonation on the pasting, flow and gelatinization properties of wheat starch

Wheat starch–water suspensions were exposed to ozone gas for 15, 30, and 60 min at 5 °C at a concentration of 0.00042 g dissolved ozone/100 g. Pasting properties were determined by using a Rapid Visco Analyzer (RVA) while a Bohlin rheometer was used to obtain flow behaviour (n) and consistency (K) indices. An enzymatic method using glucoamylase was applied to calculate percent starch gelatinization. Pasting temperature (PT) of ozonated starch samples decreased significantly (P < 0.05) as compared to that of native starch. Cooking stability starch samples increased upon ozonation indicated by lower breakdown viscosity (BV) values. The retrogradation tendency of wheat starch samples was reduced after ozonation which was indicated by lower setback viscosities (SV). Native and ozonated starch samples exhibited a shear-thinning behaviour with values of flow behaviour indices (n) between 0.57 and 0.76. The greater n values obtained for ozonated starch samples as compared to native starch showed that ozonation increased the shear-thinning behaviour of wheat starch. Percent gelatinization for all ozonated starch samples were significantly higher than the control starch samples (P < 0.05), probably due to, weakened hydrogen bonding between the starch molecules and partial depolymerization of starch molecules by ozonation.

Characterisation and liberation of chromium from fine ferrochrome waste materials

Three types of generic chromium (Cr)-containing wastes are generated during ferrochrome (FeCr) production, i.e. slag, bag filter dust (BFD) and venturi sludge. Slag is by volume the largest waste; however, fine FeCr waste materials (e.g. BFD, venturi sludge) are from an environmental perspective the most important. The loss of Cr units to FeCr waste streams represents both an added cost burden (related to disposal/storage) and a loss of revenue in terms of contained Cr units. In this paper, the novel idea of the liberation of Cr units from FeCr BFD and the ultra-fine fraction of slag (UFS) with aqueous ozonation and the advanced oxidation process was investigated. Several techniques were used to characterise both case study waste materials, i.e. particle size distribution, chemical composition, chemical surface composition and crystalline content analysis. Results indicated that limited Cr liberation could be obtained from the waste materials utilising aqueous ozonation. For BFD, only a maximum of 4.2% of total Cr liberation was achieved. However, the Cr liberation of BFD was substantially higher than that achieved for the UFS, which was attributed to the difference in characteristics of the two materials. Cr liberation observed was related to the formation of the OH radicals during the spontaneous decomposition of aqueous O3. Application of the advanced oxidation process by the addition of H2O2 during ozonation increased Cr liberation dramatically. More than 21% of total Cr liberation could be achieved for both the waste materials used in this investigation. Although the afore-mentioned Cr liberation level is unlikely to be commercially viable, the investigation proved that further research could optimise this process.