Degradation of tert-butyl alcohol in dilute aqueous solution by an O3/UV process

Advanced oxidation processes for water and wastewater treatment - Guidance for systematic future research

Advanced oxidation processes (AOPs) are a growing research field with a large variety of different process variants and materials being tested at laboratory scale. However, despite extensive research in recent years and decades, many variants have not been transitioned to pilot- and full-scale operation. One major concern are the inconsistent experimental approaches applied across different studies that impede identification, comparison, and upscaling of the most promising AOPs. The aim of this tutorial review is to streamline future studies on the development of new solutions and materials for advanced oxidation by providing guidance for comparable and scalable oxidation experiments. We discuss recent developments in catalytic, ozone-based, radiation-driven, and other AOPs, and outline future perspectives and research needs. Since standardized experimental procedures are not available for most AOPs, we propose basic rules and key parameters for lab-scale evaluation of new AOPs including selection of suitable probe compounds and scavengers for the measurement of (major) reactive species. A two-phase approach to assess new AOP concepts is proposed, consisting of (i) basic research and proof-of-concept (technology readiness levels (TRL) 1-3), followed by (ii) process development in the intended water matrix including a cost comparison with an established process, applying comparable and scalable parameters such as UV fluence or ozone consumption (TRL 3-5). Subsequent demonstration of the new process (TRL 6-7) is briefly discussed, too. Finally, we highlight important research tools for a thorough mechanistic process evaluation and risk assessment including screening for transformation products that should be based on chemical logic and combined with complementary tools (mass balance, chemical calculations).

Removal of organic pollutants through hydroxyl radical-based advanced oxidation processes

The use of Advance Oxidation Process (AOPs) has been extensively examined in order to eradicate organic pollutants. This review assesses the efficacy of photolysis, O3 based (O3/UV, O3/H2O2, O3/H2O2/UV, H2O2/UV, Fenton, Fenton-like, hetero-system) and sonochemical and electro-oxidative AOPs in this regard. The main purpose of this review and some suggestions for the advancement of AOPs is to facilitate the elimination of toxic organic pollutants. Initially proposed for the purification of drinking water in 1980, AOPs have since been employed for various wastewater treatments. AOPs technologies are essentially a process intensification through the use of hybrid methods for wastewater treatment, which generate large amounts of hydroxyl (•OH) and sulfate (SO4·-) radicals, the ultimate oxidants for the remediation of organic pollutants. This review covers the use of AOPs and ozone or UV treatment in combination to create a powerful method of wastewater treatment. This novel approach has been demonstrated to be highly effective, with the acceleration of the oxidation process through Fenton reaction and photocatalytic oxidation technologies. It is clear that Advance Oxidation Process are a helpful for the degradation of organic toxic compounds. Additionally, other processes such as •OH and SO4·- radical-based oxidation may also arise during AOPs treatment and contribute to the reduction of target organic pollutants. This review summarizes the current development of AOPs treatment of wastewater organic pollutants.

Enhanced photoelectrocatalytic oxidation of hypophosphite and simultaneous recovery of metallic nickel via carbon aerogel cathode

Carbon aerogel (CA) cathode was adopted to an undivided-chamber photoelectrocatalytic system with TiO₂ nanotube arrays (TNA) photoanode to enhance the oxidation of hypophosphite (H₂PO₂^-) and simultaneous recovery of metallic nickel (Ni). Both the efficiencies of H₂PO₂^- oxidation and Ni recovery were significantly enhanced after replacing Ti or carbon fiber paper cathode with CA cathode. With 1.0 mM H₂PO₂^- and 1.0 mM Ni²⁺, the ratio of PO₄^3- production increased from ∼41% or ∼54% to ∼100%, and the ratio of Ni recovery increased from ∼20% or ∼ 37% to ∼93% within 180 min at 3.0 V. H₂PO₂^- was finally oxidized to PO₄^3- by •OH radicals, which was speculated to be generated from UV/H₂O₂ and bound on TNA photoanode. Meanwhile, Ni²⁺ was eventually electro-reduced to metallic Ni by a two-electron reduction reaction. The efficiencies of H₂PO₂^- oxidation and Ni recovery were favored at higher cell voltage, faintly acid conditions and larger H₂PO₂^- concentration. The stability of this system exhibited that the ratio of PO₄^3- production increased significantly in each cycle, which was attributed to the increase of H₂O₂ in-situ-generation via CA cathode caused by deposition of metallic Ni. Finally, the treatment of actual electroless nickel plating effluents was demonstrated.

Enhanced photoelectrocatalytic decomplexation of Ni-EDTA and simultaneous recovery of metallic nickel via TiO2/Ni-Sb-SnO2 bifunctional photoanode and activated carbon fiber cathode

In order to enhance Ni-EDTA decomplexation and Ni recovery via photoelectrocatalytic (PEC) process, TiO₂/Ni-Sb-SnO₂ bifunctional electrode was fabricated as the photoanode and activated carbon fiber (ACF) was introduced as the cathode. At a cell voltage of 3.5 V and initial solution pH of 6.3, the TiO₂/Ni-Sb-SnO₂ bifunctional photoanode exhibited a synergetic effect on the decomplexation of Ni-EDTA with the pseudo-first-order rate constant of 0.01068 min^-1 with 180 min by using stainless steel (SS) cathode, which was 1.5 and 2.4 times higher than that of TiO₂ photoanode and Ni-Sb-SnO₂ anode, respectively. Moreover, both the efficiencies of Ni-EDTA decomplexation and Ni recovery were improved to 98% from 86% and 73% from 41% after replacing SS cathode with ACF cathode, respectively. Influencing factors on Ni-EDTA decomplexation and Ni recovery were investigated and the efficiencies were favored at acidic condition, higher cell voltage and lower initial Ni-EDTA concentration. Ni-EDTA was mainly decomposed via ·OH radicals which generated via the interaction of O₃, H₂O₂, and UV irradiation in the contrasted PEC system. Then, the liberated Ni²⁺ ions which liberated from Ni-EDTA decomplexation were eventually reduced to metallic Ni on the ACF cathode surface. Finally, the stability of the constructed PEC system on Ni-EDTA decomplexation and Ni recovery was exhibited.

Comparative evaluation of MSW incineration leachate treatment by heterogeneous catalytic O3 and UV/O3: The unexpected contribution of high salinity and overlooked role of excited state

The efficiency and mechanism of heterogeneous catalytic O₃ and UV/O₃ for municipal solid waste (MSW) incineration leachate advanced treatment was systematically compared. Prior to comparison, catalyst used in heterogenous catalytic O₃ and operation parameters for each technology were optimized. The COD removal of CuO@Al₂O₃/O₃ under its optimal parameters was 57.2%, which failed to meet the standard (≥75%). In contrast, the COD removal by UV/O₃ could be 82.3%. The superior efficiency of UV/O₃ over CuO@Al₂O₃/O₃ could be summarized into three aspects: (I) Cu bounded ·OH (≡Cu-O·) preferentially attacked hydrophilic groups, while free hydroxyl radical (·OH) was non-selective, thus UV/O₃ exhibited a unique three-stage mechanism; (II) The oxidation potential of ≡Cu-O· was higher than that of ·OH, therefore was more vulnerable to the negative effect of radical self-quenching; (III) The existence of UV-induced excited states made organics in UV/O₃ more active than in CuO@Al₂O₃/O₃ system, thus high concentration of anions enhanced COD removal in UV/O₃ but affected that in CuO@Al₂O₃/O₃. The study further revealed the characteristics of heterogeneous catalytic O₃ and UV/O₃, and UV induced excited state should be considered in UV-based advanced oxidation processes (AOPs).

Enhanced generation of active oxygen species induced by O3 fine bubble formation and its application to organic compound degradation

By using O₃ fine bubbles that promote the mass transfer of O₃ to the liquid phase and the conversion of the dissolved O₃ into active oxygen species with a high oxidation potential, an improved liquid-phase oxidation technique was developed to accelerate the degradation of an organic compound at a constant O₃ flow rate. By the use of a dielectric-barrier-discharge reactor, O₂ was converted into O₃ at an O₂ flow rate of 0.56 mmol/(L·min), with 5 mol% O₂-to-O₃ conversion. Using a self-supporting bubble generator, O₃ bubbles with an average diameter (d_bbl) of 50 µm were continuously supplied into a solution in TBA (OH• scavenger) at 303 K, and the TBA being degraded. For comparison, O₃ bubbles with d_bbl values of 200-5000 µm were obtained using a dispersing-type generator. It was found that the minimization of bubble diameter accelerated both O₃ dissolution, as a consequence of the increase in the gas-liquid interfacial area and the residence time of the bubbles, and enhanced OH• generation, because of the increase in contact probability between dissolved O₃ and OH^- at the minute gas-liquid interfaces, caused by the accumulation of OH^- around the fine bubble surfaces. To ascertain the influence on organic compound degradation of the improved oxidation potential, bisphenol A, as a model compound, was degraded by O₃ bubble injection at different d_bbl values. Sequentially, the high OH• selectivity obtained by minimizing the bubble diameter can effectively achieve the rapid degradation of organic compounds and intermediates under a constant O₃ flow rate.

Overlooked Formation of H2O2 during the Hydroxyl Radical-Scavenging Process When Using Alcohols as Scavengers

Hydroxyl radical (•OH) is an active species widely reported in studies across many scientific fields, and hence, its reliable analysis is vitally important. Currently, alcohols are commonly used as scavengers for •OH determination. However, the impacts of alcohols on the reliability of •OH detection remain unknown. In this study, we found that adding different types and different amounts of alcohols in water samples treated with ultraviolet irradiation undesirably produced substantial amounts of hydrogen peroxide (H₂O₂), which is a known •OH precursor. This means that the conventional •OH determination method using alcohols is likely unreliable or even misleading. Through careful investigation, we revealed an overlooked reaction pathway during H₂O₂ and •OH transformations. Varying oxygen concentrations, pHs, alcohol dosages, and types altered H₂O₂ formation, which can affect •OH determination accuracy. Among alcohols, n-butanol is the best scavenger because it quenches •OH rapidly but re-forms little H₂O₂.

Influence of salinity on the heterogeneous catalytic ozonation process: Implications to treatment of high salinity wastewater

The heterogeneous catalytic ozonation process is a promising treatment option for high salinity reverse osmosis concentrate (ROC) however the influence of salts on the catalyst performance is not well understood. In this work, we investigate the effect of salts on the performance of the catalytic ozonation process for treatment of synthetic ROC using a commercially available Fe-loaded Al₂O₃ catalyst. Our results show that the presence of salts influences the rate and extent of degradation of organic compounds present in the synthetic ROC when subjected to the heterogeneous catalytic ozonation process. Scavenging of aqueous O₃ by chloride ions and/or transformation of organics (particularly humics) to more hydrophobic form as a result of charge shielding between adjacent functional groups and/or intramolecular binding by cations inhibits the bulk oxidation of organics to a measurable extent. While the scavenging of aqueous hydroxyl radicals at the salt concentrations investigated here was minimal, the accumulation of chloride ions in the electric double layer near the catalyst surface, particularly when pH< pH_pzc, results in more significant scavenging of surface associated hydroxyl radicals. Overall, the presence of salts (particularly chloride ions) has a significant influence on the performance of both conventional and catalytic ozonation processes with some scope to mitigate this effect through appropriate choice of catalyst.

Treatment of shale gas produced water by magnetic CuFe2O4/TNTs hybrid heterogeneous catalyzed ozone: Efficiency and mechanisms

Magnetic spinel ferrite (CuFe₂O₄) has been applied to catalyze ozone for treating the practical shale gas produced water (PW) in our previous study. In this work, CuFe₂O₄/titanium nanotubes (TNTs) catalyst was successfully prepared by an impregnation-calcination method. Characterization results revealed that the crystal form of CuFe₂O₄ was bound to the surface of TNTs, the particle size is much smaller than the pure CuFe₂O₄ crystal particle, which could weaken the influence of the internal diffusion process on its catalytic efficiency. The experimental results showed that the removal ratio of COD_Cr in the CuFe₂O₄/TNTs/O₃ system was approximately 14% higher than that of the CuFe₂O₄/O₃ system. The dissolution of metal elements decreased to one-third that of the CuFe₂O₄/O₃ system. The inhibition ratio of PW on the growth of E. coli K12 decreased 68% after the CuFe₂O₄/TNTs catalytic oxidation process. Experimental results of complete capture experiments illustrated that the yield of HO• of the CuFe₂O₄/TNTs/O₃ system was 10-19% higher than that of the CuFe₂O₄/O₃ system. The elemental valence analysis revealed that the transition of Cu(II)-Cu(III) and Fe(II)-Fe(III) coexisted in the catalytic system. Besides, the surface hydroxyl groups promoted the electron transfer process and enhanced the ozone adsorption affinity. The proposed catalytic mechanisms of the CuFe₂O₄/TNTs/O₃ system were proposed via the above analysis.

The promotions on radical formation and micropollutant degradation by the synergies between ozone and chemical reagents (synergistic ozonation): A review

The combination of ozone (O₃) and chemical reagents (such as H₂O₂) shows synergies on the radical formation and micropollutant degradation. The promoting performance was associated with various parameters including chemical reagents, micropollutants, solution pH, and the water matrix. In this review, we summarized existing knowledge on radical formation pathways, radical yields, and radical oxidation for different synergistic ozonation processes in various water matrices (such as groundwater, surface water, and wastewater). The increase of radical yields by synergistic ozonation processes was positively related to the increase of O₃-decay, with the increase being 1.1-4.4 folds than ozonation alone (0.2). Thus, synergistic ozonation can promote the degradation rate and efficiency of O₃-resistant micropollutants (second order rate constant, k_P,O3 < 200 M^-1 s^-1), but only slightly affects or even minorly inhibits the degradation of O₃-reactive micropollutants (k_P,O3 > 200 M^-1 s^-1). The water matrices^, such as the dissolved organic matters, negatively suppressed the degradation of micropollutant by quenching O₃-oxidation and radical oxidation (i.e. maximum promoting was decreased by 1.3 times), but may positively extend the promoting effects of synergistic ozonation to micropollutants that are more reactive to O₃ (i.e. k_P,O3 was extended from <200 to <2000 M^-1 s^-1). The formation of bromate would be increased through increasing radical oxidation by synergistic ozonation, but can be depressed by relative higher H₂O₂ as the reducing agent of HOBr/OBr^- intermediate. The increase in bromate formation by O₃/permononsulfate is a considerable concern due to permononsulfate cannot reduce the HOBr/OBr^- intermediate.

Degradation of organic pollutants by ultraviolet/ozone in high salinity condition: Non-radical pathway dominated by singlet oxygen

In this work, the combined ultraviolet ozone process (UV/O₃) was applied for organic contaminant (Reactive Blue K-GL, RB) degradation in high salinity. The degradation rates of RB in both O₃ and UV/O₃ systems were enhanced by NaCl (the k increased from 0.080 to 0.116 to 0.132 and 0.267 min^-1 respectively), while mineralization rate varied at different salt conditions. In addition, UV irradiation promoted the degradation efficiency of RB with the presence of salt. Singlet oxygen (¹O₂) was the primary active species in the UV/O₃ system. The quenching experiments and signal intensity of ¹O₂ corresponded well to the mineralization of RB. Under conditions of high salinity and high pH, O₃ has high mass transfer coefficient (k_La, 3.303 min^-1) and self-decomposition (k_d, 0.600 min^-1), which further promoted the formation of ¹O₂ for mineralization of RB. Furthermore, UV/O₃ system was efficient in real textile wastewater treatment (COD_Cr removal rate 91.7% and decolorization rate 98.7%).

Recovery of phosphorus and metallic nickel along with HCl production from electroless nickel plating effluents: The key role of three-compartment photoelectrocatalytic cell system

A three-compartment photoelectrocatalytic (PEC) cell system combined with ion exchange and chemical precipitation was proposed to recover phosphorus and nickel from electroless nickel plating effluents containing hypophosphite (H₂PO₂^-) and nickel ions (Ni²⁺). Ion exchange was used to concentrate and separate Ni²⁺ and H₂PO₂^-. As a key unit, the established PEC system consisted of TiO₂/Ni-Sb-SnO₂ photoanode and Ti cathode. With 25.8 mM NaH₂PO₂ and 500 mM NiCl₂, 100 % H₂PO₂^- was oxidized to PO₄^3- in the anode cell, 78 % Ni²⁺ was recovered as metallic Ni in the cathode cell, and 900 mM HCl was obtained in the middle cell within 24 h at 3.0 V. Based on quenching experiments and ESR technique, OH radicals were mainly responsible for H₂PO₂^- oxidation. In situ Raman spectroscopy indicated that Ni²⁺ initially reacted with OH^- to form α-Ni(OH)₂, which was gradually reduced to metallic Ni. Fortunately, a slight pH decrease in the cathode cell in the three-compartment cell system was beneficial for Ni²⁺ reduction to Ni°. The obtained PO₄^3- was recovered by chemical precipitation. Finally, recovery of phosphorus and metallic nickel along with HCl production from an actual electroless nickel plating effluents in terms of efficiency, cost-benefit, and stability assessment were demonstrated.

Recovery of Phosphorus from Hypophosphite-Laden Wastewater: A Single-Compartment Photoelectrocatalytic Cell System Integrating Oxidation and Precipitation

Recovery of phosphorus through precipitation from hypophosphite-laden wastewater is more difficult than from orthophosphate-laden wastewater because of the higher solubility of hypophosphite (H₂PO₂^-). Herein, a single-compartment photoelectrocatalytic (PEC) cell system consisting of a TiO₂/Ni-Sb-SnO₂ bifunctional photoanode and an activated carbon fiber (ACF) cathode with dosing Fe²⁺ ions was developed for recovery of phosphorus in the form of FePO₄ from hypophosphite-laden wastewater. In the PEC process, H₂PO₂^- with an initial concentration of 1.0 mM was completely oxidized and recovered within 30 min at 3.0 V, and the pseudo-first-order rate constant of H₂PO₂^- oxidation was ∼4 times than that in the electrocatalytic process and even ∼89 times than that in the photocatalytic process. The bifunctional photoanode can simultaneously generate ^•OH radicals and O₃; the ACF cathode can electrogenerate H₂O₂; H₂O₂, O₃, and the added Fe²⁺ can interact with each other to produce ^•OH radicals and Fe³⁺ ions. ^•OH radicals mainly from the Fenton process were responsible for oxidation of H₂PO₂^- to PO₄^3-, which immediately combined with Fe³⁺ to form FePO₄ at the optimized conditions to realize recovery of phosphorus. The long-term stability of this system was demonstrated. The efficiency for actual electroless nickel plating effluents was exhibited.

Combining ozone with UV and H2O2 for the degradation of micropollutants from different origins: lab-scale analysis and optimization

The degradation of micropollutants (MPs), including pesticides, herbicides, pharmaceuticals and endocrine disrupting compounds, by ozone-based advanced oxidation techniques (AOP) was investigated in this study. The effect of different factors, such as ozone concentration, hydrogen peroxide concentration and initial pH, on the removal rate was studied in detail. The combination of UV with ozone/ H₂O₂ increased the MPs degradation. For example, atrazine removal increased from 12.6% to 66.9%. Increasing the concentration of ozone and H₂O₂ can enhance the degradation efficiency of MPs, while excess H₂O₂ plays a role as a scavenger for ^•OH. In addition, the optimizing conditions of degradation of MPs by an ozone-based AOP were investigated in this study. The optimal dosages of ozone for atrazine (ATZ), alachlor (ALA), carbamazepine (CBZ), 17-α-ethinylestradiol (EE2) and pentachlorophenol (PCP), were in the range of 0.6-0.75, while for ATZ a much higher dosage (5.4 mg/l) is needed. The optimal dosages of H₂O₂ concentration were at 0.75, 0.2, 0.47, 0.75 and 0.63 mM, and pH were at 10, 10, 7, 10 and 10, and reaction time at 38.5, 33.5 43, 6 and 6 min, respectively. Ozone-based AOP and in particular combination of UV with ozone and H₂O₂ is efficient to degrade atrazine, alachlor, carbamazepine, 17-α-ethinylestradiol and pentachlorophenol, and is attractive for future application of real wastewater treatment.

Kinetics and efficiency of ozone for treatment of landfill leachate including the effect of previous microbiological treatment

The application of conventional physicochemical and microbiological techniques for the removal of organic pollutants has limitations for its utilization on wastewaters as landfill leachates because of their high concentration of not easily biodegradable organic compounds. The use of ozone-based technologies is an alternative and complementary treatment for this type of wastewaters. This paper reports the study of the degradation of landfill leachates from different stages of a treatment plant using ozone and ozone + UV. The experimental work included the determination of the temporal evolution of COD, TOC, UV254, and color. Along the experimental runs, the instantaneous off-gas ozone concentration was measured. The reaction kinetics follows a global second order expression with respect to COD and ozone concentrations. A kinetic model which takes into account the gas liquid mass transfer coupled with the chemical reaction was developed, and the corresponding parameters of the reacting system were determined. The mathematical model is able to appropriately simulate COD and ozone concentrations but exhibiting limitations when varying the leachate type. The potential application of ozone was verified, although the estimated efficiencies for COD removal and ozone consumption as well as the effect of UV radiation show variations on their trends. In this sense, it is interesting to note that the relative ozone yield has significant oscillations as the reaction proceeds. Finally, the set of experimental results demonstrates the crucial importance of the selection of process conditions to improve ozone efficiencies. This approach should consider variations in the ozone supply in order to minimize losses as well as the design of exhaustion methods as multiple stage reactors using chemical engineering design tools.

Decoration of Coiled-Coil Peptides with N-Cysteine Peptide Thioesters As Cyclic Peptide Precursors Using Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) Click Reaction

The development of a copper-catalyzed azide-alkyne cycloaddition (CuAAC) protocol for the decoration of coiled coils with N-cysteine peptide thioesters as cyclic peptide precursors is presented. The reaction conditions include tert-butanol/PBS as the solvent and CuSO₄/THPTA/ascorbate as the catalytic system. During these studies, partial formylation of N-terminal cysteine peptides is observed. Mechanistic analysis leads to identification of the formyl source and, hence, to the development of reaction conditions, under which the undesired side reaction was suppressed.

The removal of COD and NH3-N from atrazine production wastewater treatment using UV/O3: experimental investigation and kinetic modeling

In this study, a UV/O₃ hybrid advanced oxidation system was used to remove chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), and atrazine (ATZ) from ATZ production wastewater. The removal of COD and NH₃-N, under different UV and O₃ conditions, was found to follow pseudo-first-order kinetics with rate constants ranging from 0.0001-0.0048 and 0.0015-0.0056 min^-1, respectively. The removal efficiency of ATZ was over 95% after 180 min treatment, regardless the level of UV power. A kinetic model was further proposed to simulate the removal processes and to quantify the individual roles and contributions of photolysis, direct O₃ oxidation, and hydroxyl radical (OH·) induced oxidation. The experimental and kinetic modeling results agreed reasonably well with deviations of 12.2 and 13.1% for the removal of COD and NH₃-N, respectively. Photolysis contributed appreciably to the degradation of ATZ, while OH· played a dominant role for the removal of both COD and NH₃-N, especially in alkaline environments. This study provides insights into the treatment of ATZ containing wastewater using UV/O₃ and broadens the knowledge of kinetics of ozone-based advanced oxidation processes.

Purification of Hg0 from flue gas by wet oxidation method and its mechanism: a review

The vast majority of Hg²⁺ can be removed while elemental mercury (Hg⁰) can hardly be removed due to its characteristic of high volatility and insolubility in water. Till now, how to oxidize Hg⁰ to Hg²⁺ is the key for the purification of Hg⁰, especially when there are others pollutants, such as HCl, SO₂, and NOx. In this review, the method and mechanism of Hg⁰ purification from flue gas by H₂O₂, KMnO₄, NaClO₂, and O₃ are reviewed comprehensively. It is concluded that the oxidation of Hg⁰ mainly depends on the electronic supply efficiency from the solution. The Fenton reagent, composed of H₂O₂ and metal cations, is superior to O₃ and the solution of KMnO₄ and NaClO₂. Moreover, HCl, SO₂, and NOx in the flue gas can influence the oxidation and purification mechanism of Hg⁰. It is found that HCl in flue gas had obvious auxo-action on the oxidation of mercury, and SO₂ and NOx have different effects on the oxidation of Hg⁰ with the change of compositions and concentration of pollutants in the flue gas. In general, SO₂ and NOx can slightly promote the oxidation of Hg⁰ due to the synergistic effect.

Heterogeneous Chemiluminescence from Gas-Solid Phase Interactions of Ozone with Alcohols, Phenols, and Saccharides

Gas-solid phase reactions between ozone (O₃) and three representative solids (alcohols, phenols, and saccharides) were investigated through a heterogeneous chemiluminescence (CL) strategy. When interactions between these two species occurred at the surface of the solid powder, an obvious CL effect was obtained. This performance could be attributed to the evolution of a ROOOH intermediate, which subsequently released emissive ¹O₂ species. This is the first report analyzing the gas-solid phase CL performance of O₃ with alcohols, phenols, and saccharides. It is believed that this strategy can be extended to applications in other gas-solid phase CL analyses utilizing the O₃ system. This has also created a novel area of gas-solid CL performance; thus, relevant processes and mechanisms can be deduced and identified.

Degradation of sulfadiazine in water by a UV/O3process: performance and degradation pathway

In this study, the performance of a combined UV/O₃process for aquatic sulfadiazine (SDZ) removal was investigated.

Advanced treatment of acrylic fiber manufacturing wastewater with a combined microbubble-ozonation/ultraviolet irradiation process

This work investigated the effectiveness of a combination of microbubble-ozonation and ultraviolet (UV) irradiation for the treatment of secondary wastewater effluent of a wet-spun acrylic fiber manufacturing plant.

SMX degradation by ozonation and UV radiation: a kinetic study

The rate constants of sulfamethoxazole (SMX) degradation by ozonation and UV(254) radiation were investigated under various parameters including influent ozone gas concentration, initial SMX concentration, UV light intensity, ionic strength, water quality in terms of varying anions (bicarbonate, sulfate and nitrate), humic acid (HA) and pH. The results indicated that the removal of SMX by ozonation and UV(254) radiation fitted well to a pseudo first-order kinetic model and the rate constants were in the range of (0.9-9.8)×10(-3) and (1.7-18.9)×10(-3) s(-1), respectively. The second-order rate constants of SMX with ozone (ko(3)), under varying operational parameters, were also determined and varied in the range of (0.60-3.38)±0.13×10(5)M(-1) s(-1). In addition, SMX degradation through UV pretreatment followed by ozonation in the presence of HA was proved to be an effective method which can remove SMX with a low ozone dose. The results suggested that ozonation of SMX was more affected by concentration of influent ozone gas, alkalinity, and HA, while incident UV light intensity, pH, and HA were the dominant factors influencing UV degradation of SMX.

Chlorophene degradation by combined ultraviolet irradiation and ozonation

Ozonation combined with UV irradiation (UV/O(3)) is an advanced oxidation technique that is very promising for the destruction of organic compounds in aqueous solution. In this study, chlorophene was chosen as a model substrate to investigate the effects of pH, initial substrate concentration, ozone dose, and UV light intensity in degradation experiments. The pseudo-first-order rate constant for total organic carbon (TOC) removal was 2.4 × 10(-2), 9.8 × 10(-4), and 6.4 × 10(-2) min(-1) for O(3), UV, and UV/O(3) treatment, respectively. Clearly, UV-enhanced ozonation leads to a synergetic increase in the overall degradation efficiency. Comparative experiments were performed to investigate the effect of the matrix (distilled water or sewage) on chlorophene removal. The organic compounds in sewage retarded the rate of chlorophene removal by 38%, probably by competitively reacting with the oxidizing agent and screening light. The compound 2-benzoylbenzo-1,4-quinone, benzo-1,4-quinone, hydroquinone and maleic acid were identified as primary intermediates by gas chromatography-mass spectrometry. The concentrations of acetic, formic and oxalic anions were detected by ion chromatography. A possible degradation pathway is proposed on the basis of the reaction products identified.

Mineralization and biodegradability enhancement of natural organic matter by ozone-VUV in comparison with ozone, VUV, ozone-UV, and UV: effects of pH and ozone dose

The increase in mineralization and biodegradability of natural organic matter (NOM) by ozone-vacuum ultraviolet (VUV) in comparison with ozone, VUV, ozone-ultraviolet (UV), and UV were investigated. The effects of operating parameters including pH and ozone dose were evaluated. Results showed that the mineralization rate of dissolved organic carbon (DOC) provided by the processes tested was in the following order: ozone-VUV > VUV > ozone-UV > ozone > UV. Among three pH studied (7, 9, and 11), pH 7 provided the highest DOC mineralization rate and biodegradability increase. A synergistic effect was observed when combining ozone with UV or VUV at pH 7 and 9 but not at pH 11. The oxidized NOM samples were separated into six fractions based on polarity (hydrophobic/hydrophilic) and charge (acid/neutral/base) to reveal NOM characteristic changes. Ozone-VUV was effective in mineralizing hydrophobic neutral and acid fractions. The hydrophilic neutral fraction was a major NOM fraction after oxidation (39-87%) and was contributed to by the biodegradable DOC produced during oxidation. High performance size exclusion chromatography results revealed that the combination of UV or VUV with ozone was more effective in the decomposition of high molecular weight compounds than ozone alone.

Rapid decolorization of azo dyes in aqueous solution by an ultrasound-assisted electrocatalytic oxidation process

In this study, we developed a novel ultrasound-assisted electrocatalytic oxidation (US-EO) process to decolorize azo dyes in aqueous solution. Rhodamine B was decolorized completely within several minutes in this developed US-EO system. Oxidation parameters such as applied potentials, power of the ultrasound, initial pH of the solution, and initial concentration of RhB were systematically studied and optimized. An obvious synergistic effect was found in decolorization of RhB by the US-EO process when comparing with either ultrasound (US) process or electrocatalytic oxidation (EO) one. Additionally, the decolorization of other azo dyes, such as methylene blue, reactive brilliant red X-3B, and methyl orange, were also effective in the US-EO system. The results indicated that US-EO system was effective for the decolorization of azo dyes, suggesting its great potential in dyeing wastewater treatment.

Degradation of tert-butyl formate and its intermediates by an ozone/UV process

In this paper, the oxidation of tert-butyl formate (TBF) in aqueous solution by an ozone/UV process was described. The oxidation process was investigated experimentally in a semibatch reactor. The results of the study indicated that the ozone/UV process was very effective in oxidizing TBF. tert-Butyl alcohol (TBA), hydroxy-iso-butyraldehyde (HiBA), acetone, formaldehyde, and formic acid were identified as major primary intermediates during the oxidation of TBF. About 90% organic carbon balance was obtained indicating that most reaction intermediates have been identified and quantified. Some of the primary intermediates were also oxidized in the ozone/UV system. Accordingly, HiBA, acetone, formaldehyde, and formic acid were the primary intermediates of TBA oxidation. The oxidation of acetone in the ozone/UV system generated formaldehyde, pyruvaldehyde, acetic acid, formic acid as primary intermediates. It was also observed that the reaction intermediates formed during the oxidation of TBF react well in the ozone/UV system and complete mineralization could be achieved by the process.

Treatment of groundwater contaminated with gasoline components by an ozone/UV process

In this paper, the treatment of real groundwater samples contaminated with gasoline components, such as benzene, toluene, ethylbenzene, and xylene (BTEX), methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), and other gasoline constituents in terms of total petroleum hydrocarbons as gasoline (TPHg) by an ozone/UV process was investigated. The treatment was conducted in a semi-batch reactor under different experimental conditions by varying ozone gas dosage and incident UV light intensity. The groundwater samples contained BTEX compounds, MTBE, TBA, and TPHg in the ranges of 5-10000, 3000-5500, 80-1400, and 2400-20000 microgl(-1), respectively. The ozone/UV process was very effective compared to ozonation in the removal of the gasoline components from the groundwater samples. For the various gasoline constituents, more than 99% removal efficiency was achieved for the ozone/UV process and the removal efficiency for ozonation was as low as 27%. The net ozone consumed per mol of organic carbon (from BTEX, MTBE, and TBA) oxidized varied in the range of 5-60 for different types of groundwater samples treated by the ozone/UV process. In ozonation experiments, it was observed that the presence of sufficient amount of iron in groundwater samples improved the removal of BTEX, MTBE, TBA, and TPHg.

Effect of oxidant-to-substrate ratios on the degradation of MTBE with Fenton reagent

Prior studies have shown the effectiveness of Fenton reagent (FR) for degrading low concentrations (1.0-2.0mg/L) of methyl tert-butyl ether (MTBE), similar to those found in contaminated groundwater. The present study investigates the effect of increasing FR doses on the extent of degradation and mineralization of a given initial MTBE concentration. The FR to MTBE molar ratio (FMMR) was the operating variable, and was investigated at values between 0.5:1 and 200:1. This approach provided sequential snapshots of the MTBE degradation process, which may help to improve the understanding of MTBE degradation with FR. The initial MTBE concentration (MTBE(0)) was approximately 22.7 microM ( approximately 2.0mg/L), and FR was used in a 1:1 molar ratio of ferrous iron (Fe(2+)) and hydrogen peroxide (H(2)O(2)). The concentrations of MTBE and the following main reaction byproducts: tert-butyl formate (TBF), tert-butyl alcohol (TBA), acetone and methyl acetate were determined from samples collected at specific intervals over a total reaction time of 1h. Total organic carbon (TOC) was monitored to determine MTBE mineralization, and the total concentration of tert-butyl compounds (tBC) was monitored due to the suspected toxicity associated with this functional group. The results showed that the minimum FMMR necessary for achieving complete MTBE degradation was 20:1, but at that FMMR, TOC and tBC reduction were only 45.6% and 24.9%, respectively. Complete MTBE mineralization was not achieved in any case, even at FMMRs as high as 200:1, where only 63.3% of mineralization was observed (although tBC reduction reached 99.6%, since traces of TBA were still detected). These results confirm the relative inability of FR to achieve complete mineralization of a target substrate, even those that are highly reactive with the hydroxyl radical.

Degradation of DMSO by ozone-based advanced oxidation processes

The present study investigates the oxidation of dimethyl sulfoxide (DMSO) by conventional ozonation and the advanced oxidation processes (AOPs). The major degradation products identified were methanesulfinate, methanesulfonate, formaldehyde, and formic acid in ozonation process. The subsequent degradation of intermediates shows that methanesulfonate is more resistance to ozonation, which reduces the mineralization rate of DMSO. The effect of t-butanol addition and ozone gas flow dosage on the degradation rate was evaluated. The rate constant of the reaction of ozone (k(D)) with DMSO was found to be 0.4162 M(-1)S(-1). In the second part of this study, DMSO degradation and TOC mineralization were investigated using O(3)/UV, O(3)/H(2)O(2) and UV/H(2)O(2) processes. In all theses processes the degradation of target organics is more pronounced than TOC removal. The efficiencies of these processes were evaluated and discussed. The formation of sulfate ion in all AOPs have been identified and compared with other processes. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of DMSO in wastewater.

Modeling aqueous ozone/UV process using oxalic acid as probe chemical

A kinetic model that describes the removal of organic pollutants by an ozone/UV process is described. Oxalic acid, which reacts with a very low rate constant with ozone and relatively high rate constant with hydroxyl radical (OH*), was used as the probe chemical to model the process. The model was verified by experimental data on concentrations of oxalic acid and hydrogen peroxide (H202) under various experimental conditions, i.e., ozone gas dosage, UV light intensity, and varying oxalic acid concentrations.

Sonochemistry in environmental remediation. 1. Combinative and hybrid sonophotochemical oxidation processes for the treatment of pollutants in water

Sonoprocessing is the utilization of sonic and ultrasonic waves in chemical synthesis and processes. It is a new and rapidly growing research field with broad applications in environmental engineering, green chemical synthesis, and processing. The application of this environmentally benign technique in environmental remediation is currently under active research and development. Sonochemical oxidation is effective in treating toxic effluents and reducing toxicity. However, the ultrasonic treatment is highly energy intensive since sonication is relatively inefficient with respect to total input energy and is therefore not economically attractive or feasible alone. Hence, sonochemistry has not yet received much attention as an alternative for industrial and large-scale chemical and environmental processes. One of the most interesting topics in the recent advances in sonochemistry is the possibility of double or more excitations with ultrasound and other types of energy. The coupling of ultrasound with other free energy sources (i.e., UV) or chemical oxidation utilizing H2O2, O3, or ferrous ion presents interesting and attractive approaches. Therefore, many recent efforts have been devoted to improving the efficiency of sonochemical reactions by exploiting the advantages of combinative or hybrid processes involving the simultaneous or sequential use of ultrasonic irradiation and other advanced oxidation processes, electrochemical processes, and biological treatment. This paper provides a critical review of the applications of ultrasound in environmental remediation, focusing on recent developments and unifying analysis of combinative or hybrid systems, namely, sonophotochemical oxidation processes.