Ozonation-pelleting of nitrogen-enriched wheat straw: Towards improved pellet properties, enhanced digestibility, and reduced methane emissions

The livestock industry needs to use crop straws that are highly digestible to improve feed productivity and reduce ruminal methane emissions. Hence, this study aimed to use the ozonation and pelleting processes to enhance the digestibility and reduce the ruminal methane emissions of wheat straw enriched with two nitrogen sources (i.e., urea and heat-processed broiler litter). Various analyses were conducted on the pellets, including digestibility indicators, mechanical properties, surface chemistry functionalization, chemical-spectral-structural features, and energy requirements. For comparison, loose forms of the samples were also analyzed. The nitrogen-enriched ozonated wheat straw pellets had 43.06 % lower lignin, 28.30 % higher gas production for 24 h, 12.28 % higher metabolizable energy, 13.78 % higher in vitro organic matter digestibility for 24 h, and 28.81 % higher short-chain fatty acid content than the nitrogen-enriched loose sample. The reduction of methane emissions by rumen microorganisms of nitrogen-enriched wheat straw by ozonation, pelleting, and ozonation-pelleting totaled 89.15 %, 23.35 %, and 66.98 %, respectively. The ozonation process resulted in a 64 % increase in the particle density, a 5.5-time increase in the tensile strength, and a 75 % increase in the crushing energy of nitrogen-enriched wheat straw. In addition, ozone treatment could also reduce the specific and thermal energy consumption required in the pelleting process by 15.10 % and 7.61 %, respectively.

Oxidative power loss control in ozonation: Nanobubble and ultrasonic cavitation

Nanobubble and ultrasonic cavitation were applied to support and prolong oxidation reactions of ozonation. Nanobubbles increased ozone dissolution by a factor of 16 due to low buoyancy, high surface area, and stability in water. Hydroxyl radicals generated by ultrasonic cavitation produced hydrogen peroxide rather than recombining due to additional oxygen atoms supplied by the nanobubbles. The generated hydrogen peroxide formed hydroperoxyl ions that reacted with ozone to generate hydroxyl radicals. The process achieved improvements in both the loss of emitted ozone and radical recombination. Rhodamine B decomposition was used to gauge the effectiveness of the process, with the highest rhodamine B decomposition evident at a high initial pH and power and a frequency of 132 kHz as revealed in ultrasonic experiments. The process achieved more than 99% of the rhodamine B decomposition in 20 min under the most efficient conditions. The generation of hydrogen peroxide exhibited tendencies similar to those of rhodamine B decomposition, supporting the proposed mechanism. An ozonation process combined with nanobubble and ultrasonic cavitation can therefore sustain oxidizing power using continuous dissolution by nanobubbles and successive radical generation caused by hydrogen peroxide generated by cavitation.

Efficiency of ozonation and O3/H2O2 as enhanced wastewater treatment processes for micropollutant abatement and disinfection with minimized byproduct formation

Ozonation, a viable option for improving wastewater effluent quality, requires process optimization to ensure the organic micropollutants (OMPs) elimination and disinfection under minimized byproduct formation. This study assessed and compared the efficiencies of ozonation (O₃) and ozone with hydrogen peroxide (O₃/H₂O₂) for 70 OMPs elimination, inactivation of three bacteria and three viruses, and formation of bromate and biodegradable organics during the bench-scale O₃ and O₃/H₂O₂ treatment of municipal wastewater effluent. 39 OMPs were fully eliminated, and 22 OMPs were considerably eliminated (54 ± 14%) at an ozone dosage of 0.5 gO₃/gDOC for their high reactivity to ozone or ^•OH. The chemical kinetics approach accurately predicted the OMP elimination levels based on the rate constants and exposures of ozone and ^•OH, where the quantum chemical calculation and group contribution method successfully predicted the ozone and ^•OH rate constants, respectively. Microbial inactivation levels increased with increasing ozone dosage up to ∼3.1 (bacteria) and ∼2.6 (virus) log₁₀ reductions at 0.7 gO₃/gDOC. O₃/H₂O₂ minimized bromate formation but significantly decreased bacteria/virus inactivation, whereas its impact on OMP elimination was insignificant. Ozonation produced biodegradable organics that were removed by a post-biodegradation treatment, achieving up to 24% DOM mineralization. These results can be useful for optimizing O₃ and O₃/H₂O₂ processes for enhanced wastewater treatment.

Hybrid system coupling ozonation and nanofiltration with functionalized catalytic ceramic membrane for ibuprofen removal

The investigations on the removal of ibuprofen (IBU) in a hybrid system coupling ozonation and nanofiltration with functionalized catalytic ceramic membrane are presented. The gaseous ozone into feed water in concentration of 11 g Nm^-3 was supplied. Positive influence of catalytic ozonation on ibuprofen decomposition was observed. The application of catalytic nanofiltration membrane led to the ibuprofen removal of 91% after the first 15 min from the beginning of the O₃/NF process, while at the same time, for the pristine membrane, it was equal to 76%. The investigations revealed incomplete degradation of drug under pH 3 after 2 h, i.e., 89%. On the other hand, the addition of inorganic salts did not affect the catalytic ibuprofen removal efficiency. Under acidic pH, the highest permeate flux decline (26%) was noted, whereas no differences between permeate flux measured under natural and alkaline conditions were observed. During the treatment process, three IBU by-products were detected, which significantly affected the permeate toxicity; however, after 2 h of catalytic nanofiltration, the product of treatment process was found as non-toxic.

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 12 min contact time. According to the study results, complete inactivation of ARB and bacterial regrowth was not observed after 72 h 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.

Enzymatic post-treatment of ozonation: laccase-mediated removal of the by-products of acetaminophen ozonation

Ozonation is a powerful technique to remove micropollutants from wastewater. As chemical oxidation of wastewater comes with the formation of varying, possibly persistent and toxic by-products, post-treatment of the ozonated effluent is routinely suggested. This study explored an enzymatic treatment of ozonation products using the laccase from Trametes versicolor. A high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis revealed that the major by-products were effectively degraded by the enzymatic post-treatment. The enzymatic removal of the by-products reduced the ecotoxicity of the ozonation effluent, as monitored by the inhibition of Aliivibrio fischeri. The ecotoxicity was more effectively reduced by enzymatic post-oxidation at pH 7 than at the activity maximum of the laccase at pH 5. A mechanistic HPLC-HRMS and UV/Vis spectroscopic analysis revealed that acidic conditions favored rapid conversion of the phenolic by-products to dead-end products in the absence of nucleophiles. In contrast, the polymerization to harmless insoluble polymers was favored at neutral conditions. Hence, coupling ozonation with laccase-catalyzed post-oxidation at neutral conditions, which are present in wastewater effluents, is suggested as a new resource-efficient method to remove persistent micropollutants while excluding the emission of potentially harmful by-products.

Removal of antibiotic resistant bacteria and plasmid-encoded antibiotic resistance genes in water by ozonation and electro-peroxone process

The electro-peroxone (EP) process is an electricity-based oxidation process enabled by electrochemically generating hydrogen peroxide (H₂O₂) from cathodic oxygen (O₂) reduction during ozonation. In this study, the removal of antibiotic resistant bacteria (ARB) and plasmid-encoded antibiotic resistance genes (ARGs) during groundwater treatment by ozonation alone and the EP process was compared. Owing to the H₂O₂-promoted ozone (O₃) conversion to hydroxyl radicals (•OH), higher •OH exposures, but lower O₃ exposures were obtained during the EP process than ozonation alone. This opposite change of O₃ and •OH exposures decreases the efficiency of ARB inactivation and ARG degradation moderately during the EP process compared with ozonation alone. These results suggest that regarding ARB inactivation and ARG degradation, the reduction of O₃ exposures may not be fully counterbalanced by the rise of •OH exposures when changing ozonation to the EP process. However, due to the rise of •OH exposure, plasmid DNA was more effectively cleaved to shorter fragments during the EP process than ozonation alone, which may decrease the risks of natural transformation of ARGs. These findings highlight that the influence of the EP process on ARB and ARG inactivation needs to be considered when implementing this process in water treatment.

Ozonation of lake water and wastewater: Identification of carbonous and nitrogenous carbonyl-containing oxidation byproducts by non-target screening

Ozonation of drinking water and wastewater is accompanied by the formation of disinfection byproducts (DBPs) such as low molecular weight aldehydes and ketones from the reactions of ozone with dissolved organic matter (DOM). By applying a recently developed non-target workflow, 178 carbonous and nitrogenous carbonyl compounds were detected during bench-scale ozonation of two lake waters and three secondary wastewater effluent samples and full-scale ozonation of secondary treated wastewater effluent. An overlapping subset of carbonyl compounds (20%) was detected in all water types. Moreover, wastewater effluents showed a significantly higher fraction of N-containing carbonyl compounds (30%) compared to lake water (17%). All carbonyl compounds can be classified in 5 main formation trends as a function of increasing specific ozone doses. Formation trends upon ozonation and comparison of results in presence and absence of the ^•OH radical scavenger DMSO in combination with kinetic and mechanistic information allowed to elucidate potential carbonyl structures. A link between the detected carbonyl compounds and their precursors was established by ozonating six model compounds (phenol, 4-ethylphenol, 4-methoxyphenol, sorbic acid, 3-buten-2-ol and acetylacetone). About one third of the detected carbonous carbonyl compounds detected in real waters was also detected by ozonating model compounds. Evaluation of the non-target analysis data revealed the identity of 15 carbonyl compounds, including hydroxylated aldehydes and ketones (e.g. hydroxyacetone, confidence level (CL) = 1), unsaturated dicarbonyls (e.g. acrolein, CL = 1; 2-butene-1,4-dial, CL = 1; 4-oxobut-2-enoic acid, CL = 2) and also a nitrogen-containing carbonyl compound (2-oxo-propanamide, CL =1). Overall, this study shows the formation of versatile carbonous and nitrogenous carbonyl compounds upon ozonation involving ozone and ^•OH reactions. Carbonyl compounds with unknown toxicity might be formed, and it could be demonstrated that acrolein, malondialdehyde, methyl glyoxal, 2-butene-1,4-dial and 4-oxo-pentenal are degraded during biological post-treatment.

A chemical credit framework to predict the removal performance of organic chemicals of concern from water through an ozonation process

Ozonation is an effective barrier for removing a wide spectrum of organic Chemicals of Concern (CoC) in a water treatment process. In this study, bench- and full-scale tests were conducted on a secondary treated effluent at the Eastern Treatment Plant (ETP) of Melbourne Water to probe the performance of ozonation in removing CoC in a wastewater discharge. From the secondary treated effluent as the feed to the ozone process, 58 organic chemicals were measured out of a possible 949 compounds by using the AIQS-DB analytical method. A chemical credit framework for the ozonation process has been established according to the bench-scale results. Chemical classifications based on the chemical structures (aromatics, aliphatic and halogenated aliphatic compounds) and reaction rate constants with O₃ (K_O3) and the ∙OH radical (K_∙OH) and a combined O₃/TOC ratio and O₃ CT value as operating parameters were confirmed to be useful and important in determining whether a chemical would be removed by ozone. It is shown that an O₃/TOC ratio of >0.404 was shown to be necessary to overcome the instantaneous ozone demand (IOD) to guarantee enough ozone to oxidise CoC. For CoC with K_O3 >10⁵M ^- 1s ^- 1 and K_∙OH >10⁹M ^- 1s ^- 1, an O₃/TOC ratio of ≥0.461 or a measurable O₃ CT of ≥0.063 mg min/L can achieve log reduction values (LRVs) of ≥1, these are chemicals with aromatic structures; For CoC with low K_O3 and high K_OH, a combined O₃/TOC ratio and O₃ CT value inclusive of a chemical structure classification is indicated as necessary criteria to evaluate the removal. UV₂₅₄ and TOC were demonstrated to be good online surrogates of ozone barrier performance in the absence of continuous O₃/TOC ratio and O₃ CT value measurements. Full-scale operational results confirm the effective predictions of the chemical credit framework, which highlights the necessity and importance of monitoring both the O₃/TOC ratio and O₃ CT values to predict the removal efficiency of a given chemical with a known response to O₃ or a known chemical structure.

Impact of chlorination and ozonation of dissolved organic matter on its photo-induced production of long-lived photooxidants and excited triplet states

Recent studies suggested that long-lived photooxidants (LLPO), which are reactive intermediates formed during irradiation of dissolved organic matter (DOM), may consist of phenoxyl radicals derived from phenolic moieties of the DOM. Besides the well-studied excited triplet states of chromophoric DOM (³CDOM*), LLPO presumably are important photooxidants for the transformation of electron-rich contaminants in surface waters. The main objective of this study was to further test the potential role of phenoxyl radical as LLPO. Suwannee River fulvic acid (SRFA) as a model DOM was pre-oxidised using the phenol-reactive oxidants chlorine and ozone, followed by its characterization by the specific UV absorption at 254 nm (SUVA₂₅₄), the ratio of absorbance at λ = 254 nm and λ = 365 nm (E2:E3), and the electron donating capacity (EDC). Subsequently, the photoreactivity of pre-oxidized SRFA was tested using 3,4-dimethoxyphenol (DMOP) as a LLPO probe compound at two initial concentrations ([DMOP]₀ = 0.1 and 5.0 μM). Linear inter-correlations were observed for the relative changes in SUVA₂₅₄, E2:E3, and EDC for increasing oxidant doses. Pseudo-first-order transformation rate constants normalized to the changing SRFA absorption rate (i.e., k_0.1^obs/r_CDOM^absand k_5.0^obs/r_CDOM^abs, for 0.1 and 5.0 µM, respectively) exhibited the following distinct trends: The LLPO-dominated k_0.1^obs/r_CDOM^absratio decreased with increasing oxidant dose and with decreasing SUVA₂₅₄ and EDC, while the ³CDOM*-dominated k_5.0^obs/r_CDOM^absratio positively correlated with E2:E3. Finally, it was concluded that precursors of ³CDOM* and LLPO are chemically modified differently by pre-oxidation of DOM, and LLPO precursors likely consist of phenolic moieties of DOM, suggesting phenoxyl radicals as LLPO.

Biotreatability Improvement of Antibiotic-Contaminated Waters: High Efficiency of Direct Ozonation in Comparison to Hydroxyl Radical Oxidation

Efficiencies of direct ozonation and hydroxyl radical oxidation by Fenton process were compared, aiming to improve biotreatability of antibiotics contaminated water (tiamulin, amoxicillin and levofloxacin).  Biodegradability, COD (chemical oxygen demand) and TOC (total organic carbon) were measured before and after applying oxidative process. It was confirmed that significantly smaller molar dose of ozone (1.1 mgO3 / mgatb) against the hydrogen peroxide (17 mgH2O2 / mgatb), deliver comparable improvements of biodegradability; Tiamulin biodegraded up to 60 %, levofloxacin close to 100 %. Ozonation removed more TOC (10%, 29% and 8% for tiamulin, levofloxacin and amoxicillin, respectively) than Fenton process. This is confirming mineralization of antibiotics, not only biodegradable intermediates formation. In terms of costs, ozonation is more feasible in oxidizing complex antibiotics in water, as it targets functional groups which carry antimicrobial properties. This brings not only improved biodegradability needed for a conventional biological treatment plant, but also reduces long-term impacts of the antibiotics in the environment.

Remediation of pesticides in commercial farm soils by solarization and ozonation techniques

Soil contamination by pesticides is a growing environmental problem. Even though nowadays numerous soil remediation technologies are available, most of them have not been tested at field scale. This study attempts to demonstrate the efficiency of solarization-ozonation techniques for the removal of twelve pesticides at full scale. Initial solarization and ozonation trials were conducted in plots located in a greenhouse using freshly and aged contaminated soils under controlled pilot conditions. The combination of solarization and ozonation treatment was efficient for all the studied pesticides both in freshly and in aged contaminated soils, being the lower degradation values found for the second type. This low removal suggests that the increase of pesticides' adsorption on soil resulting from ageing decreases their availability. Once the essays were carried out at pilot scale, the solarization-ozonation applicability was evaluated in a commercial farm soil. This trial was carried out in a greenhouse whose soil had previously been contaminated with some of the pesticides studied. A significant degradation (53.8%) was observed after 40 days of treatment. Pesticides' main metabolites were identified during the different remediation experiments. In addition, the cost of the combined solarization and ozonation technology was evaluated. Finally, our results suggest that this combination of techniques could be considered a promising technology to degrade pesticides in soil.

Drinking water treatment and associated toxic byproducts: Concurrence and urgence

Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.

Synergistic effects of simultaneous coupling ozonation and biodegradation for coking wastewater treatment: Advances in COD removal, toxic elimination, and microbial regulation

Coking wastewater contains high concentrations of cyanide, phenols, pyridine, quinoline, and polycyclic aromatic hydrocarbons. Its high toxicity and low biodegradability leads to long hydraulic retention time of biological process and high cost of advanced oxidation process. In this study, the simultaneous combination of ozonation and biodegradation (SCOB) was proposed to treat coking wastewater. Through this process, ozonation breaks the refractory organics, and the biodegradable intermediates are rapidly mineralized by microorganisms protected by porous carriers. Thus, the performances of SCOB, individual biodegradation and ozonation systems were compared. The long-term stability of the SCOB system was evaluated, the contributions of ozonation and biodegradation were analyzed, and their synergistic mechanisms were elaborated. Results showed that biological activity was inhibited in the biodegradation system, and chemical oxygen demand (COD) removal was only 27.6% for the ozonation system. COD and total phenol removal of SCOB system reached 48.5% and 79.3%, respectively, and its kinetic degradation constant of COD was 55.6% higher than that of the ozonation system. Ozonation contributed to the oxidation of organics with unsaturated functional groups as well as soluble microbial products (SMPs), causing the effluent toxicity and chroma to decrease by 82.7% and 270 times, respectively. The higher abundances of microorganisms and functions were enriched in the core of carrier, which became dominant region for biodegradation. Consequently, COD removal of the SCOB system stabilized at >80% for real coking wastewater treatment, confirming its promising potential for the treatment of highly polluted industrial wastewater.

Enhanced ozonation of polystyrene nanoplastics in water with CeOx@MnOx catalyst

The nanoplastics released into the environment pose a critical threat to creatures, and thus it is necessary to remove them. However, their natural decomposition usually takes years or even decades, which raises an imminent demand for an efficient removal technology. Herein we report a core-shell CeOx@MnOx catalyst for enhancing ozonation of polystyrene nanoplastics in water. Ozonation achieves 31.67% molecular weight removal of polystyrene nanoplastics in the first 10 min reaction, which is increased to 51.67% in catalytic ozonation by MnOx and further improved to 73.33% in catalytic ozonation via CeOx@MnOx. The remarkable thing is the CeOx@MnOx could achieve almost 96.70% molecular weight removal after 50 min reaction. The specific catalytic mechanism is ozone decomposes into reactive oxygen radicals (•OH, •O₂^- and ¹O₂) after capturing electrons from MnOx, improving the polystyrene nanoplastics removal. Meanwhile, the Mn averaged valence state increases, making it harder to donate electrons to ozone. This can be alleviated by encapsulating the CeOx core in the MnOx, enabling electrons replenishment from the CeOx core to the MnOx shell, which is verified by the experiment and density functional theory calculations. The repeated experiment demonstrates the CeOx@MnOx possesses excellent stability, maintaining 95.25-96.70% removal efficiency of polystyrene nanoplastics. This research provides a possibility for the efficient removal of nanoplastics in water.

Formation of carbonyl compounds during ozonation of lake water and wastewater: Development of a non-target screening method and quantification of target compounds

Ozonation of natural waters is typically associated with the formation of carbonyl compounds (aldehydes, ketones and ketoacids), a main class of organic disinfection byproducts (DBPs). However, the detection of carbonyl compounds in water and wastewater is challenged by multiple difficulties inherent to their physicochemical properties. A non-target screening method involving the derivatisation of carbonyl compounds with p-toluenesulfonylhydrazine (TSH) followed by their analysis using liquid chromatography coupled to electrospray ionisation high-resolution mass spectrometry (LC-ESI-HRMS) and an advanced non-target screening and data processing workflow was developed. The workflow was applied to investigate the formation of carbonyl compounds during ozonation of different water types including lake water, aqueous solutions containing Suwannee River Fulvic acid (SRFA), and wastewater. A higher sensitivity for most target carbonyl compounds was achieved compared to previous derivatisation methods. Moreover, the method allowed the identification of known and unknown carbonyl compounds. 8 out of 17 target carbonyl compounds were consistently detected above limits of quantification (LOQs) in most ozonated samples. Generally, the concentrations of the 8 detected target compounds decreased in the order: formaldehyde > acetaldehyde > glyoxylic acid > pyruvic acid > glutaraldehyde > 2,3-butanedione > glyoxal > 1-acetyl-1-cyclohexene. The DOC concentration-normalised formation of carbonyl compounds during ozonation was higher in wastewater and SRFA-containing water than in lake water. The specific ozone doses and the type of the dissolved organic matter (DOM) played a predominant role for the extent of formation of carbonyl compounds. Five formation trends were distinguished for different carbonyl compounds. Some compounds were produced continuously upon ozonation even at high ozone doses, while others reached a maximum concentration at a certain ozone dose above which they decreased. Concentrations of target and peak areas of non-target carbonyl compounds during full-scale ozonation at a wastewater treatment plant showed an increase as a function of the specific ozone dose (sum of 8 target compounds ∼ 280 µg/L at 1 mgO₃/mgC), followed by a significant decrease after biological sand filtration (> 64-94% abatement for the different compounds). This highlights the biodegradability of target and non-target carbonyl compounds and the importance of biological post-treatment.

Exploring Br-'s roles on non-brominated NDMA formation during ozonation: Reactive oxygen species contribution and brominated intermediate path validation

Bromide ions (Br^-) affected non-brominated nitroso-dimethylamine (NDMA) formation during ozonation, but the mechanism is still unclear. 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene) di-semicarbazide (TMDS) was chosen to further probe this problem. The results indicated that low levels of Br^- (≤20 μM) enhanced NDMA from 3.27 to 7.56 μg/L, while its amount slightly dropped to 6.22 μg/L raising Br^- to 100 μM. It was experimentally verified that intermediates 1,1-dimethylsemicarbazide (DMSC) and 1,1-dimethylhydrazine (UDMH) played important roles on promoting NDMA generation, whose contribution rates were 40.2% and 32.2%, respectively. The brominated substances with higher NDMA molar yields were detected. ∙OH reduced NDMA formation without Br^-, while it played promotion role with Br^-; the corresponding contribution rates were - 26.9% and 29.2%, respectively. No matter with or without Br^-, both ∙O₂^- and ^lO₂ brought a boost to NDMA formation, their contribution ratios were 34.9% and 58.1% without Br^-, while raised significantly to 64.6% and 81.5% when Br^- existed. Br^- not only facilitated NDMA formation, but also benefited the degradation of TMDS. Based on the calculation results and intermediates detected, the influence mechanisms of Br^- were proposed. The results would provide theoretical basis and technical guarantee for treating NDMA precursors and bromide co-existing water in the future.

Insights into the efficient ozonation process focusing on 2,4-di-tert-butylphenol - A notable micropollutant of typical bamboo papermaking wastewater: Performance and mechanism

The present study applied the ozonation process to degrade 2,4-di-tert-butylphenol (2,4-DTBP), an emerging micropollutant detected in typical bamboo pulp and papermaking wastewater (BPPW). The effects of various influencing factors on the degradation performance and corresponding degradation mechanism were investigated. The results showed that ozone could degrade 2,4-DTBP rapidly with a reaction rate constant of (1.80 ± 0.05) × 10⁵ M^-1·s^-1. The removal efficiency of 2,4-DTBP (5 mg/L) could reach 100% when the ozone dosage exceed 6 mg/L in a neutral medium. The presence of coexisting chemicals in BPPW such as Cl^- and HCO₃^- promoted the removal performance of 2,4-DTBP. In contrast, NH₄⁺ and humic acid presented inhibition on 2,4-DTBP removal. The ozonation of 2,4-DTBP was dominated by the ozone molecule, and this was primarily attributed to electrophilic substitution and 1,3-dipolar cycloaddition reactions. Twenty-seven kinds of intermediate products were identified by UPLC-Q-TOF/MS. The variations in their productions were based on the changes in ozone dosage. The degradation pathways were proposed. The toxicity of 2,4-DTBP was weakened after ozonation. As for the ozonation of actual biochemical effluent of BPPW, the desirable treatment performance was obtained. This study proved the feasibility of ozonation and provided data basis for subsequent pilot study.

Ozonation/UV irradiation of dispersed Ag/AgI nanoparticles in water resources: stability and aggregation

Proliferation of nanoparticles (NPs) as aqueous pollutants is a matter of growing concern today. The aggregation kinetics of colloidal bare silver (Ag, 20.5 nm) and silver iodide (AgI, 15.3 nm) NPs were investigated during ozone/ultraviolet (O₃/UV) oxidation. Dynamic light scattering was applied to monitor the aggregation of NPs, and the z-average of treated samples was considered aggregate diameter. The effect of temperature, pH, and initial concentration of NPs was investigated on the aggregation rate constant and stability ratio. At a short oxidation period of approximately 1 min, the lower stability ratio was achieved for Ag NPs (< 50) than AgI NPs (> 100). Under acidic conditions, the negative surface charge of both NPs was neutralized that resulted in faster aggregation. In contrast, the impact of temperature and initial concentration of NPs on the aggregation rate was different for both NPs, which was due to the type of O₃/UV interaction with the surface of NPs and the thickness of the electrical double layer surrounding the NPs. The aggregation behavior of Ag NPs obeyed diffusion-limited regime, while an intermediate regime between diffusion- and reaction-limited was observed for AgI NP aggregation. The resulting aggregate morphologies showed that the clusters were ramified for Ag and compressed for AgI NPs. Applying the O₃/UV oxidation process for water treatment purposes leads to a significant reduction in aggregation time for inherently unstable Ag and stable AgI toxic NPs from several hours or days to several minutes.

Using radish (Raphanus lativus L.) germination to establish a benchmark dose for the toxicity of ozonated-petroleum byproducts in soil

The concentration-response relationship between the germination outcome of radish (Raphanus lativus L.) and ozonated petroleum residuals was determined experimentally. The outcomes were used to produce an ecological risk assessment model to predict the extra risk of adverse outcomes based on the concentration of ozonated residuals. A test soil with low organic matter (0.5% w/w) was mixed with raw crude oil, artificially weathered, and treated at three doses of ozone (O₃) gas (5 g, 10 g, and 40 g O₃ per 600 g of soil). Total petroleum hydrocarbons (TPH) and produced dissolved organic carbon (DOC) were measured. TREATMENT categories (control, petroleum, petroleum + 5 g O₃, petroleum + 10 g O₃, and petroleum + 40 g O₃) were then used to create a dilution series using different proportions of the test soil and a commercially available potting mix (∼75% w/w organic matter) to evaluate the effects of background organic matter (b-ORGANIC) in conjunction with TPH and DOC. Multivariable logistic regression was performed on the adverse germination outcome as a function of TPH, DOC, TREATMENT, and b-ORGANIC. The parameters controlling germination were the continuous variable DOC and the categorical variables TREATMENT and b-ORGANIC. Radish germination was strongly harmed by DOC from ozonation, but DOC's ecotoxicity decreased with increasing O₃ dose and the presence of b-ORGANIC beyond 10% (w/w). We used the germination outcome of radish to produce a logistic regression model that computes margins of DOC (± std. error) that create 10%, 25%, and 50% extra risk of adverse germination effects.

Degradation of dibutyl phthalate by ozonation in the ultrasonic cavitation-rotational flow interaction coupled-field: performance and mechanism

Dibutyl phthalate (DBP) is present in hydraulic fracturing flowback and produced water. Degradation of DBP in aqueous by means of ozonation in ultrasonic cavitation-rotational flow interaction coupled-field (UC-RF coupled-field) was studied. The effect of ozone dosage, ozone intake flow, operating temperature, initial pH, DBP initial concentration, liquid flow rate, and ultrasonic power on the DBP removal was investigated. Results indicated that the DBP degradation rate was strongly influenced by the liquid flow rate and the ultrasonic power over the range investigated. HCO₃^- and Cl^- revealed an inhibitory effect on the DBP removal. SO₄^2- seemed to have no effect on DBP removal. The ozone utilization efficiencies in the UC-RF coupled-field were 2.77 and 1.13 times higher than those in the conventional microporous aeration (CMA) and rotating-flow microbubble aeration (RFMA), respectively. The DBP degradation rate was diminished in the presence of tert-butyl alcohol. Cavitation bubbles are considered as innumerable microreactors. Degradation of DBP by direct ozonation, hydroxyl radical (·OH) oxidation, high pressure, and high-temperature pyrolysis was demonstrated. Finally, a possible degradation pathway of DBP is obtained on the basis of the main reaction intermediates.

Insight into advanced oxidation processes for the degradation of fluoroquinolone antibiotics: Removal, mechanism, and influencing factors

The enrichment and transport of antibiotics in the environments pose many potential hazards to aquatic animals and humans, which has become one of the public health challenges worldwide. As a widely used class of antibiotics, fluoroquinolones (FQs) generally accumulated in the environments as traditional sewage treatment plants cannot completely remove them. Advanced oxidation processes (AOPs) have been shown to be a promising method for the abatement of antibiotic contamination. In this review, influencing factors and relevant mechanisms of FQs removal by various AOPs were summarized. Compared with other AOPs, photocatalytic ozone may be considered as a cost-effective method for degrading FQs. Finally, the benefits and application restrictions of AOPs were discussed, along with proposed research directions to provide new insights into the control of FQs pollutant via AOPs in practical applications.

Microbial communities and processes in biofilters for post-treatment of ozonated wastewater treatment plant effluent

Ozonation is an established solution for organic micropollutant (OMP) abatement in tertiary wastewater treatment. Biofiltration is the most common process for the biological post-treatment step, which is generally required to remove undesired oxidation products from the reaction of ozone with water matrix compounds. This study comparatively investigates the effect of filter media on the removal of organic contaminants and on biofilm properties for biologically activated carbon (BAC) and anthracite biofilters. Biofilms were analysed in two pilot-scale filters that have been operated for >50,000 bed volumes as post-treatment for ozonated wastewater treatment plant effluent. In parallel, the removal performance of bulk organics and OMP, including differentiation of adsorption and biotransformation through sodium azide inhibition, were carried out in bench-scale filter columns filled with material from the pilot filters. The use of BAC instead of anthracite resulted in an improved removal of organic bulk parameters, dissolved oxygen, and OMP. The OMP removal observed in the BAC filter but not in the anthracite filter was based on adsorption for most of the investigated compounds. For valsartan, however, biotransformation was found to be the dominant pathway, indicating that conditions for biotransformation of certain OMP are better on BAC than on anthracite. Adenosine triphosphate analyses in the media-attached biofilms of the pilot filters showed that biomass concentrations in the BAC filter were significantly higher than in the anthracite filter. The microbial communities (16S rRNA gene sequencing) appeared to be similar with respect to the types of organisms occurring on both filter materials. Alpha diversity also exhibited little variation between filter media. Beta diversity analysis, however, revealed that filter media and bed depth substantially influenced the biofilm composition. In practice, the impact of filter media on biofilm properties and biotransformation processes should be considered for the design of biofilters.

FeS combined ozonation to remove p-aminobenzenesulfonamide from water: Density functional theory insights into the mechanism

The applicability and performance of FeS in ozonation process to remove p-aminobenzenesulfonamide (SN) from water was assessed, and the working mechanism of FeS was comprehensively explored by both experimental means and density functional theory (DFT) simulation. FeS combined ozonation achieved 74% of SN removal in 60 min under the optimal condition, which was 37% higher than by ozonation alone, and 12% higher than FeO combined ozonation. Highly active species of •OH, •SO4-, 1O2 and •O2- were detected in the FeS combined ozonation system, the evolution pathway of the involved species was expounded with the aid of DFT calculation. The results revealed that •O2-, H2O2 and SO42- were originally formed via interface reactions on FeS surface, then gradually transformed into •OH, 1O2 and •SO4- through subsequent chain reactions. Moreover, FeS had a lower energy barrier of 0.16 eV than FeO with a value of 0.83 eV for the transformation of ozone to active atomic oxygen. The presented study provided a significant insight into the role of Fe-based materials in ozonation, and was of great importance to guide the route for ozonation process improvement.

Integrated strategies for robust growth of Chlorella vulgaris on undiluted dairy farm liquid digestate and pollutant removal

Undiluted dairy farm liquid digestate contains high levels of organic matters, chromaticity and total ammonia nitrogen (TAN), resulting in inhibition to microalgal growth. In this study, a novel cascade pretreatment with ozonation and ammonia stripping (O + S) was employed to remove these inhibitors, and was compared with single pretreatment approach. The optimum parameters for ozonation and ammonia stripping were obtained and the mechanisms of inhibition elimination were investigated. The results show that ozonation contributed to the degradation of non-fluorescent chromophoric organics through the direct molecular ozone attack, which mitigated the inhibition of chromaticity to microalgae, while ammonia stripping relieved the inhibition of high TAN to microalgae. After cascade pretreatment, TAN, total nitrogen (TN), COD and chromaticity were reduced by 80.2 %, 75.4 %, 20.6 % and 75.8 % respectively. When C. vulgaris was cultured on different pretreated digestate, it was found that cascade pretreatment was beneficial for retaining high PSII activity and synergistically improved microalgal growth. The highest biomass increment and productivity achieved 5.40 g L^-1 and 900 mg L^-1 d^-1 respectively in the integration system of cascade pretreatment with microalgae cultivation (O + S + M). After O + S + M treatment, the removal efficiencies of TAN, TN, COD and total phosphorus (TP) were 100 %, 92.8 %, 46.7 % and 99.6 %, respectively. This work provided a promising strategy (O + S + M) for sustainable liquid digestate treatment, along with nutrient recovery and value-added biomass production.