Distinct synergetic effects in the ozone enhanced photocatalytic degradation of phenol and oxalic acid with Fe3+/TiO2 catalyst

In this work, phenol and oxalic acid(OA) degradation in an ozone and photocatalysis integrated process was intensively conducted with Fe~(3+)/TiO_2 catalyst. The ferrioxalate complex formed between Fe~(3+) and oxalate accelerated the removal of OA in the ozonation, photolysis and photocatalytic ozonation process, for its high reactivity with ozone and UV. Phenol was degraded in ozonation and photolysis with limited TOC removal rates, but much higher TOC removal was achieved in photocatalytic ozonation due to the generation of ·OH. The sequence of UV light and ozone in the sequential process also influences the TOC removal, and ozone is very powerful to oxidize intermediates catechol and hydroquinone to maleic acid. Fenton or photo-Fenton reactions only played a small part in Fe~(3+)/TiO_2catalyzed processes, because Fe~(3+) was greatly reduced but not regenerated in many cases.The synergetic effect was found to be highly related with the property of the target pollutants. Fe~(3+)/TiO_2 catalyzed system showed the highest ability to destroy organics, but the TiO_2 catalyzed system showed little higher synergy.     

Ozonation of estrone, estradiol, diethylstilbestrol in waters

The ozonation of three environmental endocrine disrupters (EDCs), estrone(E₁), estradiol(E₂), and diethylstilbestrol(DES), in aqueous solutions were investigated. Batch experiments were carried out to research the effect of initial EDCs concentrations, initial pH values and ozone dosages on the degradation efficiency. At pH 9.0, the degradation efficiency of estrone (E₁) reached to 94% after 8 min; diethylstilbestrol could be totally degraded after 6 min, and even estradiol was completely degraded after only 4 min. After 6 min for ozonation, the degradation efficiency of E₂ was nearly 48% with ozone dosage of 0.13 mg min^− 1. Compared with the ozone dosage of 0.38 mg min^− 1, E₂ entirely degraded after 6 min. Ozone dosage on degradation of E₁ was in a similar way. DES had analogous rule. At four different concentration solutions (5-20 mg L^− 1) of EDCs exposed to ozone, the higher the initial EDCs concentration, the lower EDCs degradation efficiency was obtained. During the ozonation process, the rapid decreasing of pH and the sharp increasing of electrical conductivity indicated the higher polarity by-products were produced during ozonation, which was confirmed by high performance liquid chromatography (HPLC) analysis. The results could provide some useful information for the potential treatment of EDCs by ozonation in waters.     

Degradation and Transformation of Organic Compounds in Songhua River Water by Catalytic Ozonation in the Presence of TiO2/Zeolite

This paper presents experimental results of the catalytic ozonation of Songhua River water in the presence of nano-TiO₂ supported on Zeolite. The removal efficiency of TOC and UV₂₅₄, the variation of AOC and molecular weight distribution of organics was studied. Results showed that TOC and UV₂₅₄ removal efficiency by ozone was improved in the presence of TiO₂/Zeolite, and increased by 20% and 25%, respectively. The part of organic compounds less than 1000 Da increased in ozonation, but decreased in catalytic ozonation. The AOC of water increased in catalytic ozonation, and the increase of AOC was particularly obvious when ozone dose increased from 28.8 mg·L^?1 to 46.6 mg·L^?1. The degradation and transformation of organic compounds was analyzed by means of GC-MS. The total number of organic compounds was reduced from 50 in the untreated water to 36 and 20, respectively, in ozonation and catalytic ozonation. The removal efficiency of the total organic compounds peak area in ozonation and catalytic ozonation were 23.5% and 62.5%, respectively. Most of the hydrocarbons could be removed easily in ozonation and catalytic ozonation. The organic compounds having hydroxyl, carboxyl or carbonyl groups were hard to be removed in ozonation, but could be removed efficiently in the presence of TiO₂/Zeolite.     

Efficient degradation of <Emphasis Type="Italic">para</Emphasis>-chlorobenzoic acid in water by catalytic ozonation with La–Ce–MCM-41

La–Ce–MCM-41 was directly synthesized by a hydrothermal method and applied as heterogeneous catalyst for the ozonation process of para chlorobenzoic-acid (pCBA). La³⁺ and Ce³⁺ were successfully incorporated into the framework of MCM-41 and the formation of degradation products (p-chlorophenol, p-dihydroxybenzene, maleic acid and oxalic acid) were monitored qualitatively using gas chromatography–mass spectrometer and high performance liquid chromatography. Due to the synergy of bimetal and the fast degradation of accumulated intermediates, total organic carbon (TOC) removal efficiency was significantly improved (92 %) in La–Ce–MCM-41/O₃ process compared with ozonation (40 %) at identical reaction condition. The presence of tert-butanol (TBA) in La–Ce–MCM-41/O₃ process indicated that the oxidation of pCBA was mainly due to the function of hydroxyl radicals in the liquid bulk, and a plausible degradation pathway was proposed. TOC removal slightly decreased from 90 to 86 % after La–Ce–MCM-41 being re-utilized three times, which illustrated that La–Ce–MCM-41 was an efficient of promising catalyst for ozonation of pCBA.     

Degradation of Acid Black 210 by advanced oxidative processes: O3 and O3/UV

Acid Black 210 (AB-210) dye is one of the most black dyes used by the leather industry. In the present work, AB-210 degradation in aqueous solution by ozonation (O₃) and ozonation with ultraviolet (UV) radiation (O₃/UV) was investigated. The effects of pH, initial dye concentration and UV radiation were studied in laboratory scale. Removal was evaluated in terms of residual AB-210 concentration in the treated solution and mineralization efficiency was evaluated by total organic carbon (TOC) analysis. The results indicated that AB-210 is quickly degraded after 15 min but not totally mineralized. It was observed that dye removal of 100% was achieved at pH 3, 7, and 11, while mineralization was found to increase with the pH (55% at pH 11). Concerning UV-C radiation, it enhanced AB-210 degradation at pH 3 but did not reveal any significant effect at pH 7 and 11.     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

Catalytic Ozonation of Sulfosalicylic Acid

The investigation of heterogeneous catalytic ozonation of sulfosalicylic acid (SSal) in aqueous solution is reported in this paper. It was found that catalytic ozonation in the presence of V-O supported on silica gel had a more positive effect on the removal rate (62% in 30 min) of total organic carbon (TOC) than that of ozonation alone (20% in 30 min), and the catalyst supported on TiO₂ had similar results. The experimental results also showed that the ozone dosage should be sufficient for achieving the catalytic effect. Efficient removal of TOC in catalytic ozonation was probably attributed to producing more powerful oxidants than molecular ozone.     

Ozonation of Trace Nitrobenzene in Water in the Presence of a TiO2/Silica-Gel Catalyst

Heterogeneous catalytic ozonation was investigated for the degradation of nitrobenzene in the presence of TiO₂ supported on Silica-gel as a solid catalyst. The conditions in preparing the catalyst are experimentally optimized. The catalytic activity of the supported TiO₂ is strongly influenced by the calcination temperature. The TiO₂/Silica-gel calcined at 500 °C showed the highest activity for the degradation of nitrobenzene. An approximate increase of 21% in removal efficiency was achieved for catalytic ozonation compared with the case of ozonation alone. Nitrobenzene degradation was significantly influenced by the presence of carbonate and t-butanol, which confirmed that TiO₂/Silica-gel catalyzed ozonation followed a radical-type mechanism. Kinetic study demonstrated that catalytic ozonation is pseudo–first-order with no respect to the initial nitrobenzene concentration. The effect of catalyst dosage and pH on the oxidation efficiency of nitrobenzene was also investigated. Catalyst dosage exerted a positive influence on nitrobenzene removal, and nitrobenzene degraded more completely under neutral or basic conditions. Finally, the catalyst stability was tested through repeated experiments.     

Sequential Treatment of Tequila Industry Vinasses by Biopolymer-based Coagulation/Flocculation and Catalytic Ozonation

This article describes the study of the treatment of tequila industry vinasses based on the sequential application of coagulation-flocculation and heterogeneous catalytic ozonation. Coagulation-flocculation treatment used biopolymers to reduce the nondissolved organic matter and to reduce the degree of color units in effluent. Among six different substances, chitosan was the most efficient biopolymer to remove the highest chemical organic demand (COD) concentration (84.0%). The response surface technique was used to obtain the best attainable operation conditions of coagulation-flocculation process. The initial organic matter concentration, the reaction period and biopolymer concentration were selected as the independent variables. Two levels of analysis were performed: optimally and sensibility. The best reaction conditions were 3.23 × 10⁴ mg L^?1 of initial COD, 125.4 mg L^?1 of chitosan concentration, and 60.0 min of reaction. Ozonation process was performed on the effluent of coagulation-flocculation treatment. A batch reaction with 30 mg L^?1 of ozone in gaseous phase and a flow of 0.1 L min^?1 was implemented. Nickel oxide (100 mg L^?1) was used as the catalyst of the ozonation reaction. Twice larger COD concentration removal was obtained when the catalyst participated in the reaction compared to the so-called conventional ozonation (12.00% in conventional case vs 26.70% in catalyst presence). An ultraviolet-visible (UV-Vis) spectroscopy study was conducted to obtain a preliminary evaluation of organic compounds removal by effect of the sequential method proposed in this study. A significant total organics removal from the tequila industry wastewater (measured as the integral of UV-Vis spectrum) of 398.6 conditional units was obtained when the conventional ozonation was used after coagulation-flocculation, but that value was increased up to 1609.12 conditional units when the catalyst was inserted into the reaction.     

Systematic Analysis of the Biochemical Characteristics of Activated Sludge During Ozonation for Lowering of Biomass Production

Properties of activated sludge during ozonation were analyzed. The structure and surface characteristics altered with the increase of ozone dosage. At low ozone dosage, the floc structure was completely dismantled. Floc fragments reformed through reflocculation at an ozone dosage greater than 0.20 g O₃·g^?1 mixed liquor suspended solids (MLSS). Inactivation of microorganisms in the activated sludge mixture was caused by ozonation. Microbial growth decreased by up to 65% compared to the control. Simultaneously, 92.5% of nucleotide and 97.4% of protein in microbial cells of the sludge were released. Organic substance, nitrogen and phosphorus were released from the sludge during the ozonation process. The initial value of soluble chemical oxygen demand (SCOD) was 72 mg·L^?1. When the ozone dosage was 0.12 g O₃·g^?1 MLSS, the value of SCOD rapidly reached 925 mg·L^?1, increased by almost 12-fold. Simultaneously, 54.7% of MLSS was reduced. The composition of MLSS was changed, indicating that the inner water of cells and volatile organic substance decreased during the ozonation process.     

Application of Ozone Involving Advanced Oxidation Processes to Remove Some Pharmaceutical Compounds from Urban Wastewaters

Different UVA radiation and advanced oxidation systems, most of them involving ozone, have been applied to remove mixtures of three contaminants of pharmaceutical type: diclofenac (DCF), sulfamethoxazole (SMT) and caffeine (CFF), both in ultrapure and secondary treated wastewater. The influence of the water matrix has been studied in terms of individual compound concentration and TOC removal. Also, biodegradability of the treated wastewater before and after the advanced oxidation process, as BOD/COD ratio, the partial oxidation yield, the increment of average state of carbon oxidation and ozone consumption have been determined. For mgL^?1 to 100 μgL^?1 concentrations and regardless of the ozone process and water type, DCF and SMT are removed in less than 10 min mainly by direct reaction with ozone, especially in the case of DCF. CFF, on the contrary, is mainly removed through hydroxyl radicals. For lower concentration (≤100 μgL^?1), DCF still disappears by direct ozonation, CFF by hydroxyl radicals oxidation and SMT through both direct ozonation and hydroxyl radical oxidation. Once DCF and SMT have disappeared, TOC is removed by reacting with hydroxyl radicals, regardless of the water matrix. Photocatalytic ozonation allows the highest TOC degradation rate, partial oxidation yield, increment of average state of carbon oxidation and biodegradability together to the lowest ozone consumption per mg TOC eliminated.     

Oxidation of Cyanuric Acid in Aqueous Solution by Catalytic Ozonation

The aim of this work was studying the activity of a Ru/CeO₂ powder catalyst in the ozonation of aqueous solution of cyanuric acid (CYA). Ozonation in the presence of the catalyst significantly enhances CYA degradation. Within this work, investigation of the influence of pH and initial concentration on the catalytic ozonation of CYA has been done in a semicontinuous reactor. The removing degree of CYA at pH 5.9 show better response in comparison to pH 2.5 and pH 8.2. The mineralization of CYA by catalytic ozonation formed nitrate ions (0.7 mol of NO₃^?/mol of CYA removed for 50% initial CYA abatement) and nitrite and ammonium ions in small amounts. Three transformation products formed during catalytic ozonation were identified from LC/MS and MS/MS analyses. The impact of oxidation on the toxicity was measured from the inhibition of Vibrio fisheri, which was found to increase continuously.     

Ozonation of Two Commercially Important Biocidal Finishing Agents

Ozonation of 2 commercially important textile biocidal finishing agents (called BI and BII herein) in aqueous solution was studied in a semi-batch bubble column reactor at different ozone feed rates (500, 750, and 900 mg/h) and pH (pH=7 and 12). Ozonation efficiency and kinetics were assessed in terms of COD, TOC and UV absorbance at 280 nm (UV₂₈₀) and 254 nm (UV₂₅₄), representing the aromaticity and unsaturated moieties of the studied textile biocides, respectively. Due to its chlorinated aromatic content, the fate of Adsorbable Organic Halogens (AOX) of BI was also followed during the ozonation experiments. At alkaline pH, appreciably higher COD and TOC removals were achieved, speaking for a free radical (^?OH) dominated degradation pathway for both tested biocides. AOX, UV₂₈₀ and TOC abatement rates obtained for BI ozonation at optimized reaction conditions indicated that the degradation of BI followed a sequential path of dechlorination, dearomatization, oxidation and mineralization, respectively.     

Low-Temperature NOX (x = 1, 2) Removal with •OH Radicals from Catalytic Ozonation over α-FeOOH

FeOOH(H), FeOOH(P) and FeOOH(O) prepared by hydrothermal, precipitant-hydrolysis and oxidation-hydrolysis methods were tested as ozonation catalysts for the low-temperature NO_X (x = 1, 2) removal. FeOOH(H) exhibits higher catalytic activities than FeOOH(P) and FeOOH(O), achieving 85.6% of NO_X removal efficiency with a low ozone concentration. Compared to FeOOH(P) and FeOOH(O), FeOOH(H) shows much higher BET surface areas and higher density of surface -OH, both of which are critical for the ?OH radical generation over the catalysts. These radicals can be successfully transferred into the duct under the coupling effect of hydroxyl radicals and O₃, oxidizing and removing the NO_X (x = 1, 2). Results of ion chromatography (IC) indicate that the oxidation products are all NO₃^? without any NO₂^? in the tail solutions.     

Ozone-Based Advanced Oxidation Processes for the Decomposition of N-Methyl-2-Pyrolidone in Aqueous Medium

The present study investigates the decomposition of N-Methyl-2-Pyrolidone (NMP) using conventional ozonation (O₃), ozonation in the presence of UV light (UV/O₃), hydrogen peroxide (O₃/H₂O₂), and UV/H₂O₂ processes under various experimental conditions. The influence of solution pH, ozone gas flow dosage, and H₂O₂ dosage on the degradation of NMP was studied. All ozone-based advanced oxidation processes (AOPs) were efficient in alkaline medium, whereas the UV/H₂O₂ process was efficient in acidic medium. Increasing ozone gas flow dosage would accelerate the degradation of NMP up to certain level beyond which no positive effect was observed in ozonation as well as UV light enhanced ozonation processes. Hydrogen peroxide dosage strongly influenced the degradation of NMP and a hydrogen peroxide dosage of 0.75 g/L and 0.5 g/L was found to be the optimum dosage in UV/H₂O₂ and O₃/H₂O₂ processes, respectively. The UV/O₃ process was most efficient in TOC removal. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of NMP in wastewater.     

Ozone/H2O2 Performance on the Degradation of Sulfamethoxazole

This work aims to analyze the contribution of H₂O₂ on ozonation of Sulfamethoxazole (SMX). A single ozonation was able to totally remove SMX. TOC and COD depletion rates after a transferred ozone dose of 60 mg/L was related to the formation and decomposition of H₂O₂. An increase on O₃ gas inlet concentration from 10 g/m³ to 20 g/m³ improved COD abatement from 11% to 36%. When the presence of H₂O₂ at the beginning of ozonation was tested, it was verified that COD and TOC degradation were enhanced, attaining maximum values of 76% and 32%, respectively, when compared with 35% and 15% reached in a single ozonation.     

Treatment of Leather Dyeing Wastewater with Associated Process of Coagulation-Flocculation/Adsorption/Ozonation

This study is based on the investigation of performance of associated wastewater treatments of coagulation-flocculation/adsorption (CF-ADS) and coagulation-flocculation/ozonation (CF-OZ) for the removal of pollutants from tannery wastewater. The chemical dosage was optimized and the use of waste from the tannery process was tested as a low-cost alternative adsorbent for wastewater treatment plants. For the CF-ADS the removal of TOC, COD, Na⁺ and color were 50.04%, 53.13%, 17.05% and 61.13%, respectively, and for the CF-OZ the removal were 46.50%, 56.25%, 11.10% and 85.34%. Also, BOD/COD and COD/TOC ratios were studied to verify the oxidation efficiency of the wastewater.     

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation,Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-COD_Cr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-COD_Cr dramatically increased. Until dissolved ozone was detected, 0.3 mgO₃/mgTOC₀ (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional COD_Cr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-COD_Cr, TOC and ATU-BOD₅ were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of COD_Cr and UV₂₅₄ had good linear relationship until the removal amounts of COD_Cr and UV₂₅₄ were 30 mg/L and 0.11 cm^?1, respectively. Therefore UV₂₅₄ would be useful for an indicator for COD_Cr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/COD_Cr.     

Performance and Mechanism on Degradation of Estriol Using O3/PS Process

In this study, enhanced ozonation of estriol (E3) with persulfate (PS) was investigated in aqueous solution. Simultaneous generation of hydroxyl radical (?OH) and sulfate radical (?SO₄^?) by O₃/PS process was proposed and experimentally verified. Kinetic results revealed that the degradation of E3 was affected by the solution pH, PS concentration, O₃ dosage and E3 initial concentration. The optimal reaction rate was observed in alkaline solutions. The mechanism for the synergistic effect was preliminarily explored by the addition of hydroxyl and sulfate radical scavengers. The enhanced degradation of E3 by O₃/PS was also observed in actual water samples, which provided impetus for practical applications. The degradation intermediates were detected using LC/MS. Results showed that the phenol structures of the estrogens were mostly oxidized to cyclohexenone moieties and quinone-like structures.     

Treatment of phenol formaldehyde production wastewater by electrooxidation-electrofenton successive processes

ABSTRACT

Treatments of phenol formaldehyde producing wastewater (PFPW) by electrooxidation (EO) and electro-Fenton (EF) successive processes were carried out in a batch electrolytic reactor using graphite (Gr) and stainless steel (Ss) electrodes. After the completion of the EO process, the wastewater was further treated with EF process. The influence of operating variables such as current density, operating time, initial pH_i and H₂O₂ concentration was evaluated for removals of phenol, TOC and COD in PFPW. Gr/Gr, Gr/Ss or Ss/Ss and Ss/Gr electrode pair were used as anode and cathode. The best removal efficiency in the EO process was obtained with Gr/Gr (93%) as compared to Gr/Ss (82%), Ss/Ss (63%) and Ss/Gr (55%). The removal efficiencies for the EO process using Gr-Gr electrode pair were obtained as 93% for phenol, 61% for COD and 44% for TOC at initial pH_i 7,5 g/L of NaCl, 50 mA/cm² and 5 h. In the EF process, the removal efficiencies at pH_i 3,5 mA/cm² and 30 mM H₂O₂ and 45 min were 100% for phenol, 76% for COD and 59% for TOC. This study provided that the successive processes are an effective method for the removal of phenolic compounds from the wastewater.