Ozonation System Research Articles

Stratosphere‐Troposphere Exchange of Air Masses and Ozone Concentrations Based on Reanalyses and Observations

AbstractThis study estimates the stratosphere–troposphere exchange (STE) of air masses and ozone concentrations averaged over 2007 to 2010 using the Modern Era Retrospective‐Analyses for Research and Applications 2 (MERRA2) and ERA5 reanalyses, and observations. The latter includes Microwave Limb Sounder (MLS) for ozone, MLS and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) for temperatures, and A‐Train measurements for diabatic heating. The extratropical downward ozone fluxes are 538 Tg year−1 from the ERA5 reanalysis, 543 Tg year−1 from the MERRA2 reanalysis, and 528–539 Tg year−1 from the observations, consistent with previous studies. Previous studies, however, did not consider tropical upward ozone flux. Here we show that the tropical upward ozone flux is 183–193 Tg year−1, which compensates about 35% of the extratropical downward ozone fluxes and should not be neglected. After considering the tropical upward ozone flux, the global ozone STE is 346 Tg year−1 from the ERA5 reanalysis, 360 Tg year−1 from the MERRA2 reanalysis, and 336–346 Tg year−1 from the observations. Those estimates (347 ± 12 Tg year−1) can be used as the contribution of ozone STE to the tropospheric ozone budget. We also investigate cloud radiative effects on the STE of air mass and ozone. At 380 K, cloud radiative effects enhance downward fluxes in the extratropics from both reanalyses and observation, but reduce and enhance upward fluxes in the tropics from reanalyses and observation, respectively. The discrepancy in the tropics is related to the tropical tropopause layer thin cirrus that is missing in the reanalyses. We find that cloud radiative effects enhance the global ozone STE by about 21%–29%.

Comparative Life Cycle Assessment of two advanced treatment steps for wastewater micropollutants: How to determine whole-system environmental benefits?

Advanced wastewater treatment (AWT) technologies are now considered to target urban micropollutants (MPs) before discharge into receiving water bodies and to comply with specific criteria for reuse. Extra energy and/or resources are necessary to achieve the elimination of MPs. Using the Life Cycle Assessment framework, this study assesses net environmental efficiencies for two AWTs (i) ozone systems (air-fed and pure oxygen-fed) and (ii) granular activated carbon filter. Sixty-five MPs with proven removal efficiency values and toxicity and/or ecotoxicity potentials were included in this study building on results from recent research. Consolidated Life Cycle Inventories with data quality and uncertainty characterization were produced with an emphasis on operational inputs. Results show that the direct water quality benefits obtained from AWT are outweighed by greater increases in indirect impacts from energy and resource demands. Future research should include water quality aspects not currently captured in life cycle impact assessment, such as endocrine disruption and whole-effluent toxicity, in order to assess the complete policy implications of MP removal strategies.

Improving the Treatment Efficiency and Lowering the Operating Costs of Electrochemical Advanced Oxidation Processes

Electrochemical advanced oxidation processes (EAOP®) are promising technologies for the decentralized treatment of water and will be important elements in achieving a circular economy. To overcome the drawback of the high operational expenses of EAOP® systems, two novel reactors based on a next-generation boron-doped diamond (BDD) anode and a stainless steel cathode or a hydrogen-peroxide-generating gas diffusion electrode (GDE) are presented. This reactor design ensures the long-term stability of BDD anodes. The application potential of the novel reactors is evaluated with artificial wastewater containing phenol (COD of 2000 mg L−1); the reactors are compared to each other and to ozone and peroxone systems. The investigations show that the BDD anode can be optimized for a service life of up to 18 years, reducing the costs for EAOP® significantly. The process comparison shows a degradation efficiency for the BDD–GDE system of up to 135% in comparison to the BDD–stainless steel electrode combination, showing only 75%, 14%, and 8% of the energy consumption of the BDD–stainless steel, ozonation, and peroxonation systems, respectively. Treatment efficiencies of nearly 100% are achieved with both novel electrolysis reactors. Due to the current density adaptation and the GDE integration, which result in energy savings as well as the improvements that significantly extend the lifetime of the BDD electrode, less resources and raw materials are consumed for the power generation and electrode manufacturing processes.

Investigation of the Disinfection Effect of Some Environmental Friendly Applications on Cotton Fabrics

ABSTRACT Today, the importance of health is kept on top of many things. Because people understood that neither the money they earn nor the life they live without their health is of any importance. Textile materials are together in every field during the day with us and they can be exposed to the attacks of microorganisms quite easily. Hence, ways of getting rid of these attacks in easy and environmental approaches should be considered in most cases. In this context, disinfection processes of textile products were investigated in this study. For this aim cotton fabrics were contaminated separately with two different types of bacteria. These bacterial species are Staphylococcus aureus (ATCC 29,213) and Escherichia coli (ATCC 25,922). Then bacterial contaminated fabric samples were treated with ozone and UV-C for different periods of time by a set of ozone and UV-C application system. Additionally hydrogen peroxide based disinfection has been tested as well. After these processes, bacterial reduction tests were carried out. In addition, SEM images of some fabric samples were taken to observe the surface modification. As a result, it was found that necessary and sufficient disinfection effect was obtained on cotton fabric in very short application time by using especially ozone gas.

Comparative study on heterogeneous and homogeneous catalytic ozonation efficiency in micropollutants' removal

Abstract Catalytic ozonation was applied for the removal of small concentrations (4 μM) of micropollutants benzotriazole, carbamazepine, p-CBA from aqueous solutions at pH 7. These compounds present different physicochemical characteristics and different kinetic rate constants, when reacting with ozone or hydroxyl radicals in the ranges of <0.15–3 × 105, 5.2 × 109, and 8.8 × 109 M−1s−1, respectively. Calcite was used as heterogeneous catalyst and its catalytic activity evaluated, by applying (and optimized) different experimental conditions (i.e., pH, temperature, ozone concentration), concerning the removal efficiency of p-CBA. Study of micropollutants' removal showed all examined organic compounds can be sufficiently removed by application of catalytic ozonation either by use of calcite, or by presence of Co(II) or Fe(II) (applied as homogeneous catalysts), while the optimum catalyst between them was found to be calcite. Carbamazepine with kO3 = 3 × 105 M−1s−1 can be easily removed, even by application of single ozonation, while benzotriazole and p-CBA resulted in 50% and 68.2% higher removal after application of catalytic ozonation within 3 min of oxidation reaction, due to acceleration of hydroxyl radicals' production by presence of calcite in the ozonation system. The contribution of hydroxyl radicals in removal of all three micropollutants was evaluated by extraction of Rct and f•OH parameters.

Unraveling the multiple roles of Ag species incorporation into OMS-2 for efficient catalytic ozonation: Structural properties and mechanism investigation

Silver incorporated manganese oxide octahedral molecular sieves (Ag-OMSX-T) were successfully synthesized via a hydrothermal-calcination method. Due to the multiple roles of Ag species doping, the optimal Ag-OMS0.2-180 nanocatalyst with the Ag/Mn molar ratio of 0.2 had the highest TOF value (2.94 × 10−5 mol g−1 h−1), which could completely degrade 50 mg L−1 OA at pH 5.0 in 30 min much higher than those of OMS-2 (22.3%) in catalytic ozonation system. The results of systematic characterization (such as XRD, XPS, Py-IR, and O2-TPD) and catalytic performance tests of Ag-OMS0.2-180 clearly demonstrated that the proper amount of Ag incorporation not only facilitated the electron transfer but also induced more formation of Lewis acid sites in Ag-OMS0.2-180 as well as metals (Ag and Mn) as activation sites to collectively favor the catalytic ozonation degradation of OA. In addition, the higher mineralization rate has been achieved (79.6%) and the Ag-OMS0.2-180 exhibited the satisfactory stability and reusability with low metal release during multiple consecutive cycles (≥ 5). Meanwhile, the electron spin resonance spectra and radical scavenger tests confirmed that superoxide radical and singlet oxygen were the main reactive oxygen species in catalytic process. The mechanism of solid-liquid interface reaction and the pathway of cycling of oxygen vacancies were also elaborated, which present a new insight for water decontamination.

Treatment of Flue Gas from an Infectious Waste Incinerator using the Ozone System

Recently, levels of air pollution caused by exhaust gases from infectious waste combustion have been rising at a startling rate. Pollutant gases such as carbon monoxide (CO) and nitrogen dioxide (NO2) have numerous health implications when unsafe amounts are released into the atmosphere. Thus, Pollution Control Systems (PCS) and Gas Cleaner Systems (GCS) play an important role in industries and the monitoring of incinerators. This research evaluated the GCS of rotary kilns in medical facilities located in the Northeast of Thailand. Data was collected from various sites, analyzed, and examined. Furthermore, Ozone (O3) technology was applied to the rotary kiln allowing for the collection of new information on the pollution treatment systems. O3 technology was installed along with the Wet Scrubber System (WSS) catalyzing the oxidation of O3 and pollutant gases. In addition, a chiller was added to control and stabilize the temperature of the water. After the water temperature was controlled, the concentration of O3 increased resulting in an efficient pollution treatment system. Levels of pollutant gas emission were found to be beneath control standards of both Thailand and those of the U.S. EPA. TSP content was reduced significantly from 22.0 mg/m³ to 3.4 mg/m³ (97%), CO content from 13.6 mg/m³ to 1.7 mg/m³ (96%), and NO₂ content fell from 16.3 (mg/m³) to 2.0 mg/m³ (99%). It is clear that the rotary kiln and Ozone technology should be used together in order to create a new and far more effective method of pollution treatment in small and mid-sized cities of Thailand.

Using Fe/Ag nanostructures covered by Zn for the degradation of 2, 4 dichlorophenoxyacetic acid assisting with light irradiation and ozonation; optimisation and kinetic studies

ABSTRACT A nanostructure comprising Fe/Ag covered by ZnO was fabricated using a facile chemical method based on the degradation of 2,4-D using an ozonation system under the irradiation of UV/Visible light generated from an LED source. The Fe/Ag covered by ZnO was characterised using XRD, SEM and FTIR. The degradation of 2,4-D was studied as a function of variables pH, initial 2,4-D concentration, dose of catalyst and the time of irradiation by developing a quadratic model derived from central composite design (CCD). An independent kinetic study was then established under the basis of the optimised values of the independent factors obtained from CCD model. The optimised values of pH, 2,4-D initial concentration, dose of catalyst and time of irradiation were 5, 62 mgL−1, 0.078 gL−1 and 63 min, respectively. ANOVA results of the quadratic model showed the adjusted R 2 of 0.97% and the value of 0.55 for the Lack of Fit (LoF). According to the kinetic study, the pseudo second model reveals a good fit on the experimental results (R 2 = 0.98). Maximum removal of 80% was obtained in the optimum condition and in the presence of ozone. Considering the safety and technical restrictions of applying UV light as an activator agent in full scale treatment systems, it seems that the use of LED in the degradation systems acquires promising results in terms of pesticides degradation.

On-Site Pilot Testing of Hospital Wastewater Ozonation to Reduce Pharmaceutical Residues and Antibiotic-Resistant Bacteria.

Hospital sewage constitutes an important point source for antibiotics and antibiotic-resistant bacteria due to the high antibiotic use. Antibiotic resistance can develop and cause problems in sewage systems within hospitals and municipal wastewater treatment plants, thus, interventions to treat hospital sewage on-site are important. Ozonation has proven effective in treating relatively clean wastewater, but the effect on untreated wastewater is unclear. Therefore, we piloted implementation of ozonation to treat wastewater in a tertiary hospital in Uppsala, Sweden. We measured active pharmaceutical ingredients (APIs) using liquid chromatography-mass spectrometry and antibiotic-resistant Enterobacteriaceae using selective culturing pre- and post-ozonation. Comparing low (1 m3/h) and high (2 m3/h) flow, we obtained a ‘dose-dependent’ effect of API reduction (significant reduction of 12/29 APIs using low and 2/29 APIs using high flow, and a mean reduction of antibiotics of 41% using low vs. 6% using high flow, 25% vs. 6% for all APIs). There was no significant difference in the amount of antibiotic-resistant Enterobacteiaceae pre- and post-ozonation. Our results demonstrate that ozonation of untreated wastewater can reduce API content. However, due to the moderate API decrease and numerous practical challenges in the on-site setting, this specific ozonation system is not suitable to implement at full scale in our hospital.

Techno-economic evaluation of ozone-oxidation for sludge reduction at the full-scale. Comparison between the application to the return activated sludge (RAS) and the sludge digestion unit

Ozone oxidation was applied to a fraction (30 %) of the return activated sludge (RAS) of a full-scale Wastewater Treatment Plant for reducing the high sludge production (20 t/week). The amount of sludge sent to final disposal was decreased by 50 % and 75 % at 0.55 kgO3/h and 0.80 kgO3/h dosage, respectively. When the same ozonation system was applied to the aerobic digestion (0.06, 0.50, 0.67 kgO3/h), the reduction was 27–77 %.A thorough economic analysis was carried out considering the overall sludge quantity finally extracted from the plant in the presence and absence of ozonation, the corresponding costs of final disposal and the ozone oxidation operation costs. The net cost saving for sludge disposal was calculated to be 66.6 €/d and 109.9 €/d due to ozone in the return activated sludge at the two dosages, respectively. When ozonation was applied to the recycled sludge of the digestion unit, the net cost saving was in the range 235–655 €/d, depending on the reduction percentage achieved. The ozone oxidation showed to become economically convenient for a sludge disposal cost lower than that sustained by the Company. The results obtained prove feasibility of ozonation for sludge reduction in both locations of the WWTP: therefore, with respect to other disintegration techniques, ozonation possesses a high technical and economic advantage along with a high versatility. Furthermore, it is also shown the feasibility of lowering the applied dosages with respect to the past experiences, since effectiveness of the system is still guaranteed.

V2O5-(NH4)2V6O16·1.5H2O composite catalysts as novel platforms for high-efficiency catalytic ozonation of NO under low temperature

In this study, the catalytic ozonation of NO by V-based catalysts was investigated with the aim of reducing O3 consumption and pay attention to the role of V-based species in the catalytic ozonation system. Vanadium oxide treated with varying ammonium fluoride were synthesized and the catalytic ozonation of NO were systematically studied. The VF1 catalyst displayed the highest catalytic ozonation of NO efficiency, with which NO oxidation efficiency of 71% and O3 leakage of less than 1 ppm at the molar ratio of O3/NO = 0.5. The phase of catalysts revealed that VFx (x = 0, 0.25, 0.5, 1, 1.5) was transformed from V2O5 to (NH4)2V6O16·1.5H2O species, and the surface of catalyst became rougher as the amount of ammonium fluoride treatment gradually increased. Besides, chemical properties analysis of the catalyst revealed that (NH4)2V6O16·1.5H2O promoted the content of surface –OH and the absorption of H2O, which was conducive to the generation of ·OH and ·O2− radicals with O3 introduced. Furthermore, the effect of SO2 and reaction temperature was also investigated in this system, which exhibited that SO2 was favorable for NO2 removal and temperature had little effect on NO oxidation efficiency.

Evaluation and comparison of advanced oxidation processes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D): a review.

Organochlorine pesticides have generated public concern worldwide because of their toxicity to human health and the environment, even at low concentrations, and their persistence, being mostly nonbiodegradable. The use of 2,4-dichlorophenoxyacetic acid (2,4-D) has increased in recent decades, causing severe water contamination. Several treatments have been developed to degrade 2,4-D. This manuscript presents an overview of the physicochemical characteristics, uses, regulations, environmental and human health impacts of 2,4-D, and different advanced oxidation processes (AOPs) to degrade this organic compound, evaluating and comparing operation conditions, efficiencies, and intermediaries. Based on this review, 2,4-D degradation is highly efficient in ozonation (system O3/plasma, 99.8% in 30 min). Photocatalytic, photo-Fenton, and electrochemical processes have the optimal efficiencies of degradation and mineralization: 97%/79.67% (blue TiO2 nanotube arrays//UV), 100%/98% (Fe2+/H2O2/UV), and 100%/84.3% (MI-meso SnO2), respectively. The ozonation and electrochemical processes show high degradation efficiencies, but energy costs are also high, and photocatalysis is more expensive with a separation treatment used to recover the catalyst in the solution. The Fenton process is a viable economic-environmental option, but degradation efficiencies are often low (50-70%); however, they are increased when solar UV radiation is used (90-100%). AOPs are promising technologies for the degradation of organic pollutants in real wastewater, so evaluating their strengths and weaknesses is expected to help select viable operational conditions and obtain optimal efficiencies.

Reducción de la concentración de DQO y COT en aguas residuales de la industria farmacéutica empleando ozono catalizado por Fe2+. Estudio de caso a escala real

El presente trabajo fue realizado con el fin de mejorar el desempeño de un sistema de ozonización utilizado para el tratamiento de aguas residuales en una industria farmacéutica. Con el objeto de mejorar la mineralización de la materia orgánica, se aplicó como catalizador sulfato ferroso al sistema de reacción. Seguido de esto, se ajustó el pH del agua entre 8,5 y 10 para que el proceso se lleve a cabo en condiciones alcalinas. Finalmente, se inyectó O3 a través de un tubo Venturi con el fin de mejorar el intercambio de masa entre el gas y el agua. Los datos preliminares de operación del sistema de tratamiento señalan que este alcanza remociones de demanda química de oxígeno (DQO) menores a 10 %. Los ensayos fueron realizados a escala real y las variables de calidad del agua fueron analizadas a diferentes tiempos de reacción. Se determinó que para una dosis de ozono igual a 10 g/h y 10 mg/L de Fe2+ y un pH inicial del agua igual a 9 se requieren de 4,5 horas a fin de lograr una reducción de 30,73 % de DQO y 36,85 % de carbón orgánico total (COT). Los resultados realizados con un pH inicial superior a 9,5 señalan que la efectividad del proceso se reduce, hecho que puede ser ocasionado por la rápida formación de Fe(OH)3 insoluble, con lo cual disminuye la disponibilidad del catalizador para la formación de radicales OH* en el agua.

Experimental evaluation of in-duct electronic air cleaning technologies for the removal of ketones

Reducing volatile organic compounds (VOCs) concentrations in built environments is necessary to achieve acceptable indoor air quality or comply with workplace regulations. Different air cleaning technologies are applied for the removal of VOCs. Unlike conventional adsorption-based technologies like activated carbons, so-called electronic air cleaning (EAC) technologies generate reactive species directly or indirectly to oxidize VOCs. In this study, dynamic single pass tests were conducted in a test rig consisting of four identical test ducts with individual flow control, allowing simultaneous evaluation of four different air purification systems under identical conditions. Three oxidation-based air-cleaning technologies were considered: photocatalytic oxidation (PCO), non-thermal plasma (NTP), and ozonation (O3). A total of 17 different configurations of EAC systems were tested for acetone and/or methyl ethyl ketone (MEK) removal. These include 12 different commercial PCO units, one in-house pilot PCO, two plasma, and two ozonation units. Sixteen of them were tested for the removal of 0.1 ppm MEK and their single pass removal efficiencies varied from 0 to 37%. Eleven of them were examined for the removal of 0.1 and 1 ppm of acetone and the removal efficiencies were between 0 and 23%. Ozonation and PCO-based system using ozone generating vacuum UV lamps generally showed a higher efficiency than PCO-based system with non-ozone generating UVC lamps or plasma units. Formaldehyde, acetaldehyde, and acetone were detected as the oxidation by-products in MEK testing. PCO-based systems tend to generate more by-products.

Ternary catalyst Mn-Fe-Ce/Al2O3 for the ozonation of phenol pollutant: performance and mechanism.

In this study, a novel ternary catalyst Mn-Fe-Ce/Al2O3 was synthesized by co-impregnation method, and was characterized by XRD, SEM, XPS, and FTIR. The catalytic performance of this ternary catalyst was evaluated in the heterogeneous catalytic ozonation of phenol pollutants and it improved the removal rate and mineralization degree of phenol pollutants. The changes of dissolved ozone in water and the TBA experiment proved that the ternary catalyst could accelerate the decomposition of ozone into hydroxyl radicals, thus accelerating the oxidation of phenol. Phosphate experiments and surface hydroxyl density measurements proved that surface hydroxyl was the active site of the catalyst. XPS analysis showed that the ternary catalysts accelerated electron transfer through the redox cycles of Mn2+-Mn3+-Mn4+, Fe2+-Fe3+, and Ce3+-Ce4+, which also contributed to the high catalytic activity. Moreover, the catalyst maintained high catalytic activity after five cycles of use. Therefore, the ternary catalyst was considered an efficient and promising catalyst for catalytic ozonation system.

The extent of sludge solubilization allows to estimate the efficacy of ozonation for removal of polycyclic aromatic hydrocarbons (PAHs) in municipal sewage sludge

Ozone treatment has been proven as an effective technology for removing PAHs in municipal sewage sludge. However, given the complex interaction of PAHs with sludge extracellular polymeric substances (EPS), effective sludge disintegration is required to make PAHs more accessible to oxidants, which also affects PAHs partitioning. Here, we investigated two treatment systems, namely ozonation (ozone) and sequential hydrodynamic cavitation and ozonation (HC+ozone), under varied conditions, to determine whether the extent of sludge disintegration can estimate a measurable removal of PAHs. The results showed that both the PAHs removal efficiency and kinetics highly depended on pH and ozone dose. Although no significant removal of PAHs occurred during HC treatment, the observed rate constants for Σ16 PAHs removal in HC+ozone system were 1.2–1.4-fold higher than those obtained in ozone system under the same condition. The accelerated PAHs removal could be attributed to the reduced flocs size (80% smaller) and increased soluble EPS concentration (5-fold higher) with HC pretreatment. Lastly, a positive correlation was noted between the PAHs removal efficiency and soluble EPS concentration (R2 = 0.85), indicating the important role of dissolved and colloidal matter (DCM) for PAHs partitioning between aqueous and particulate phases.

Effects of advanced oxidation processes on leachates and properties of microplastics

Microplastics (MPs) in natural environments undergo various aging processes. So far, little is known about the effects of chemical oxidation on leachates and properties of MPs. Here, we investigated the removal of pigment red from MPs by ozonation, Fenton, and heat-activated persulfate treatments, and further explored the nanoscale surface properties of treated MPs. Experimental results indicated that advanced oxidation processes effectively degraded pigment red released from MPs and the degradation rate was much faster than the leaching rate of pigments. Dominant reactive oxygen radicals in the ozone, Fenton, and heat-activated persulfate systems were identified as O2•−, HO•, and SO4•−, respectively. Height ranges of untreated, ozone-treated, Fenton-treated, and persulfate-treated MPs were 73 nm, 163 nm, 195 nm, and 206 nm, respectively. Oxidation of the -CH3 and -CH2 bonds occurred on the surface of treated MPs and the persulfate system achieved more serious oxidation degree than the ozone and Fenton systems. Addition of pigment red to the plastic polymer increased the glass transition temperature of MPs, which then showed a decline after advanced oxidation treatments except Fenton. The surface of persulfate-treated MPs was the stiffest, but the stiffness distribution of the ozone-treated and Fenton-treated MPs was more uneven. These research findings provide promising strategies to accelerate the aging process of MPs and contribute to a better understanding of the effects of aging on the environmental behavior of MPs.

A comparative study on the removal of dimethyl sulfoxide from water using microbubbles and millibubbles of ozone

Ozone-based microbubble-aided technology has been gaining popularity as a new potential alternative method for the oxidation of organic pollutants present in water/wastewater. In this work, the potential of the ozone microbubbles (OMBs) for the oxidation of dimethyl sulfoxide (DMSO) was investigated, and the results were compared with those of the conventional ozone millibubbles (OMLBs). Keeping constant other operational parameters, the OMLBs needed a longer time for complete removal of DMSO, and hence a higher consumption of ozone took place. Therefore, a higher stoichiometric ratios of ozone consumed to the DMSO removed was obtained for the OMLBs. Higher ozone utilization efficiencies were observed for the OMBs (i.e., 65–79 %) than the OMLBs (i.e., 21–48 %). Coupling of H2O2 with the ozonation systems improved the oxidation of DMSO by enhancing the formation of ·OH. Conversely, a large dosage of H2O2 had a negative effect. The degradation of DMSO to methane sulfonic acid (MSA) was achieved via two paths (i.e., direct conversion to MSA by the reaction with ·OH, and a two-stage conversion via the formation of DMSO2 by molecular ozone, followed by further oxidation of DMSO2 to MSA by the ·OH). In terms of the TOC removal efficiency, the effectiveness was in the following order: OMLBs < OMLBs/H2O2 < OMBs < OMBs/H2O2. Oxidation of DMSO by ozone followed an overall second-order kinetics for the OMBs, and first-order kinetics for the OMLB system. Higher enhancement factor and volumetric mass transfer coefficient were obtained for the OMBs as compared to OMLBs.

Heterogeneous catalytic ozonation of atrazine with Mn-loaded and Fe-loaded biochar

After reaction with permanganate or ferrate, the resulted Mn-loaded and Fe-loaded biochar (MnOx/biochar and FeOx/biochar) exhibited excellent catalytic ozonation activity. O3 (2.5 mg/L) eliminated 48% of atrazine (ATZ, 5 μM) within 30 min at pH 7.0, while under identical conditions, ozonation efficiency of ATZ increased to 83% and 100% in MnOx/biochar and FeOx/biochar (20 mg/L) heterogeneous catalytic systems, respectively. Radical scavenger experiment and electron paramagnetic resonance (EPR) analysis confirmed that hydroxyl radical (•OH) was the dominant oxidant. Total Lewis acid sites on MnOx/biochar and FeOx/biochar were 3.5 and 4.1 times of that on the raw biochar, which induced enhanced adsorption of O3 and its subsequent decomposition into •OH. Electron transfer via redox pairs on MnOx/biochar and FeOx/biochar was observed by cyclic voltammetry scans, which also functioned in the improved catalytic capacity. Degradation pathways of ATZ in MnOx/biochar and FeOx/biochar ozonation systems were proposed, with 34.6% and 44.8% of dechlorination effect accomplished within 30 min of reaction, which was improved by 4.1 and 5.3 times compared to pure ozonation. After 12-hour treatment, acute toxicity of ATZ oxidation products was reduced from 38.3% of pure ozonation system to 14.5% and 6.3% of activated ozonation systems with MnOx/biochar and FeOx/biochar, respectively. Mn-loaded biochar and Fe-loaded biochar have great potential for heterogeneous catalytic ozonation of polluted water.

Organic input practice alleviates the negative impacts of elevated ozone on soil microfood-web

Elevated ozone threatens the sustainability of soil ecosystems by negatively affecting underground ecological processes. Crop residue, as an energy source with a low risk of environmental influence, can alleviate the negative impacts caused by climate change. However, little knowledge is comprehended about the influences of crop residue input on soil nematode metabolic activities and microfood-web under elevated ozone. Soil microfood-web consisting of microorganisms and nematodes plays a significant role in the underground processes such as energy flow and nutrient turnover. Thus, the objectives of this study were to explore the responses of soil nematode metabolic activities and microfood-web to different elevated ozone levels and crop residue application managements. The pot experiment was a split-plot design with elevated ozone system as main plot and residue addition treatment as subplot utilizing the open-top chambers. Elevated ozone systems included three levels (control, 45 ± 5 ppb; lower elevated ozone level, 80 ± 10 ppb and higher elevated ozone level, 110 ± 10 ppb). Residue addition treatments were soil without residue addition and soil with residue addition. The results showed that elevated ozone generated negative influences on soil microorganisms and nematodes by decreasing their biomass carbon. Crop residue input practice increased the functional metabolic footprints of nematodes under elevated ozone. The carbon utilization of soil biological communities shifted from soil organic carbon to extractable organic carbon after crop residue incorporation. Soil nitrate-nitrogen was the main supplier to meet the nitrogen demand of soil biota. The analysis of structural equation modeling revealed that the system under elevated ozone without crop residue addition was predominated by a bacterial decomposition channel. While the application of crop residue into soils also made a contribution to the fungal decomposition pathway. Consequently, it can be concluded that organic input practice strengthens the cooperation of soil microfood-web channels, which plays an important role in alleviating the negative effects of elevated ozone on the stability of soil microfood-web.