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.     

Toxicity and Biodegradability Behavior of Xenobiotic Chemicals Before and After Ozonation: A Case Study with Commercial Textile Tannins

Ozonation of a natural tannin (NT; COD_o?=?1195 mg/L; TOC_o?=?342 mg/L; BOD_5,o?=?86 mg/L) and a synthetic tannin ST; COD_o?=?465 mg/L; TOC_o?=?55 mg/L; BOD_5,o?=?6 mg/L) being frequently applied in the polyamide dyeing process was investigated. Synthetic wastewater samples containing these tannins individually were prepared and subjected to ozonation at varying ozone doses (625– 1250 mgO₃/L wastewater), at pH?=?3.5 (the application pH of tannins) and pH?=?7.0 at an ozone dose of 1125 mgO₃/L wastewater. The collective environmental parameters COD, TOC, BOD₅, UV₂₅₄ and UV₂₈₀ (UV absorbance at 254 nm and 280 nm, representing aromatic and unsaturated moieties, respectively) were followed during ozonation. Changes in the biodegradability of the tannins were evaluated in terms of BOD₅ measurements conducted before and after ozonation. In addition, activated sludge inhibition tests employing heterotrophic biomass were run to elucidate the inhibitory effect of raw and ozonated textile tannins towards activated sludge biomass. Partial oxidation (45% COD removal at an ozone dose of 750 mg O₃/L wastewater and pH?=?3.5) of ST was sufficient to achieve elimination of its inhibitory effect towards heterotrophic biomass and acceptable biodegradability improvement, whereas the inhibitory effect and biodegradability of NT could not be reduced via ozonation under the same reaction conditions.     

Effective Ozonation of Secondary Effluents with Initial Ozone Demand

It is clarified that the ozone consumption during the initial stage of ozonation before dissolved ozone appears is the same value as that during the initial 20 seconds in batch mode experiment. This initial ozone consumption was defined as initial ozone demand (IOD) in this study. IOD of secondary effluent was shown to be 0.3–0.5 mgO₃/mgC₀. More than 90% of 17β-estradiol (E2) was reduced, and formation of ozonation by-products was controlled within this ozone demand. This state can be also characterized by reduction of the values of UV₂₅₄, fluorescence intensity at 345 nm (Excitation)/435 nm (Emission) and that at 240 nm/435 nm to 0.06 /cm, 35 and 15, respectively.     

Kinetic Study and Optimum Control of the Ozone/UV Process Measuring Hydrogen Peroxide Formed In-situ

This study was conducted to develop a kinetic model of the ozone/UV process by monitoring the trend of in-situ hydrogen peroxide formation. A specifically devised setup, which could continuously measure the concentration of hydrogen peroxide as low as 10 μg/L, was used. The kinetic equations, comprised of several intrinsic constants with semi-empirical parameters (k_chain and k_R3) were developed to predict the time varied residual ozone and hydrogen peroxide formed in situ along with the hydroxyl radical concentration at steady state,[OH°]_ss, in the ozone/UV process. The optimum ozone dose was also investigated at a fixed UV dose using the removal rate of UV absorbance at 254 nm (A₂₅₄) in raw drinking water. The result showed that the continuous monitoring of hydrogen peroxide formed in situ in an ozone/UV process could be used as an important tool to optimize the operation of the process.     

Post-Treatment of Pulp and Paper Industry Wastewater by Advanced Oxidation Processes

The aim of this study was to investigate the effectiveness of chemical oxidation by applying ozonation, combination of ozone and hydrogen peroxide and Fenton's processes for decolorization and residual chemical oxygen demand (COD) removal of biologically pretreated pulp and paper industry effluents. The batch tests were performed to determine the optimum operating conditions including pH, O₃, H₂O_2, and Fe²⁺ dosages. H₂O₂ addition reduced the reaction times for the same ozone dosages; however combinations of ozone/hydrogen peroxide were only faintly more effective than ozone alone for COD and color removals. In the Fenton‘s oxidation studies, the removal efficiencies of COD, color and ultraviolet absorbance at 254 nm (UV₂₅₄) for biologically treated pulp and paper industry effluents were found to be about 83, 95, and 89%, respectively. Experimental studies indicated that Fenton oxidation was a more effective process for the reduction of COD, color, and UV₂₅₄when compared to ozonation and ozone/hydrogen peroxide combination. Fenton oxidation was found to have less operating cost for color removal from wastewater per cubic meter than the cost for ozone and ozone/hydrogen peroxide applications.     

Modeling of Ozonation for Dissolved Ozone Dosing

Experimental research was carried out for calibration and validation of a model describing ozone decay and ozone exposure (CT), decrease in UV absorbance at 254 nm (UVA₂₅₄), increase in assimilable organic carbon concentration and bromate formation. The model proved to be able to predict these parameters on the basis of the applied ozone dosage. The experimental ozone dosages ranged from 0.4 mg-O₃/L to 0.9 mg-O₃/L for natural water with a dissolved organic carbon concentration of 2.4 mg-C/L. The UVA₂₅₄ was found to be an effective parameter for estimation of rapid ozone decay for natural water under experimental conditions tested. The experimental setup consisted of a bench-scale plug flow reactor (approximately 100 L/h) with dissolved ozone dosing.     

Identification of Oxidation Intermediates in Humic Acid Oxidation

The effects of using ultraviolet irradiation (UV), ozone (O₃) and the combined O₃-UV advanced oxidation process (AOP) on humic acid (HA), which is regarded as the main disinfection by-products (DBPs) precursor, have been evaluated and compared. In particular, aromatic acids, short-chain aldehydes and carboxylic acids were measured. The purpose of this study was to determine the different classes and yields of oxidation intermediates, compare O₃, UV and O₃-UV for HA removal, as well as investigate the effects of O₃, irradiation time, UV intensity on the mineralization of HA. Based on that, the knowledge gap of DBPs generation was made up. The results showed that by UV irradiation and O₃ oxidation, HA broke down into smaller molecules that were more hydrophilic, namely formaldehyde, acetaldehyde, propaldehyde, butyraldehyde, glyoxal, methyl-glyoxal, formic, acetic, fumaric, benzoic, phthalic, protocatechuic and 3-hydroxybenzoic acids. Meanwhile, unsaturated conjugated double bonds in the structure of HA were destroyed, which lead to UV₂₅₄ a slight decrease. Due to the synergistic effect of O₃-UV, DOC and UV₂₅₄ significantly decreased and remained stable after the reaction of 10 min, indicating that O₃-UV system had stronger potential of mineralization and lower nonselectivity. Besides, the kinds and concentration levels of the intermediates were obviously reduced with light intensity increasing. Hydroxyl radical (^.OH) could mineralize some organics that could not be mineralized by O₃.     

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.     

Effect of Ozone and GAC Process for the Treatment of Micropollutants and DBPs Control in Drinking Water: Pilot Scale Evaluation

To improve the quality of water supplied to the City of Seoul in Korea, a pilot-scale evaluation of how the conventional treatment process could be upgraded was conducted. Three candidate processes were evaluated and compared: a conventional process (consisting of coagulation, sedimentation, and rapid sand filtration) plus GAC (Train A); a conventional process plus ozone and GAC (Train B); and a process consisting of coagulation, sedimentation, intermediate ozone, sand filtration, and GAC (Train C). Treatment efficiency of the unit process and overall treatment trains were evaluated using several parameters such as turbidity, dissolved organic carbon (DOC), UV absorbance at 254 nm (UV₂₅₄), specific ultraviolet absorbance (SUVA), micropollutants (pesticides, benzenes, and phenols), disinfection by-products (trihalomethanes (THMs), haloacetic acids (HAAs) and aldehydes), and total organic halogen (TOX). Results showed that ozone and/or GAC was effective for removing micropollutants and controlling chlorinated by-products such as THMs and HAAs. However, any synergistic effect of ozonation (adsorption and biodegradation) on GAC was observed due to the low concentration of aldehydes in raw and process water.     

Evaluation of Process Control Alternatives for the Inactivation of Escherichia coli,MS2 Bacteriophage,and Bacillus subtilis Spores during Wastewater Ozonation

Dissolved ozone concentration integrated over time (CT) is a reliable indicator of disinfection efficacy in drinking water treatment. However, ozone CT may not be measurable in some wastewater ozone applications. In this study, alternative process control parameters, specifically ozone to total organic carbon (O₃:TOC) ratio, differential UV₂₅₄ absorbance (ΔUV₂₅₄), and differential total fluorescence (ΔTF), were correlated with the inactivation of Escherichia coli, the bacteriophage MS2, and Bacillus subtilis spores in five secondary wastewater effluents. CT values greater than 9 mg-min/L were generally required for measurable inactivation of B. subtilis spores, and CT values of 1 and 2 mg-min/L consistently achieved greater than 6- and 5-log inactivation of MS2 and E. coli, respectively. The O₃:TOC, ΔUV_254, and ΔTF correlations for MS2 and B. subtilis were useful for predicting inactivation, while those of E. coli were characterized by greater variability. [Supplementary materials are available for this article. Go to the publisher's online edition of Ozone: Science & Engineering for the following free supplemental resources: additional figures and data tables.]     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

The Combination of Ozone/Hydrogen Peroxide and Ozone/UV Radiation for Reduction of Trihalomethane Formation Potential in Surface Water

Applied ozone dosages of 20, 25, and 30 mg/L to lake water utilized by the city of Shreveport, LA produced no significant reductions in trihalomethane formation potentials (THMFP). However, the addition of 20 mg/L of hydrogen peroxide and/or 0.67 W/L of UV radiation (254 nm) in combination with ozone produced decreases in THMFP of over 60% in 60 minutes. Smaller THMFP decreases were seen with shorter contact times. The use of H₂O₂ and/or UV in combination with O₃ increased the percentage of applied ozone consumed by the lake water (i.e., enhanced the ozone mass transfer) five times over simple ozonation.     

Advanced Oxidation Treatment of Drinking Water: Part II. Turbidity,Particles and Organics Removal from Lake Huron Water

Pre-coagulation ozonation has been reported to be effective in drinking water treatment processes. Limited data are available on the impact of advanced oxidation processes (AOPs) on Lake Huron water which serves as a primary source of drinking water for many communities around the Great Lakes region. Impact of ozone/hydrogen peroxide based AOP on Lake Huron water was studied. The results show that AOPs can achieve higher particles removal in finished water and deliver improved filtered water turbidity compared to the conventional treatment process. Sharp decline in ultraviolet absorbance at 254 nm (UV₂₅₄) was observed immediately following AOP treatment while only minimal overall decrease in dissolved organic carbon (DOC) was achieved.     

Degradation of Carbamazepine by Photo-assisted Ozonation: Influence of Wavelength and Intensity of Radiation

This article presents the results of an investigation into the function of UV in a photo-assisted ozonation process for treatment of carbamazepine (CBZ) in treated domestic wastewaters. Experiments were conducted on synthetic spiked water and secondary treated municipal wastewater. Degradation of CBZ was studied for various combination of O₃ dosage ranging from 4.8 to 14.4 mg/h and UV intensities with varying intensity and wavelength (UVC: λ = 254 nm and UVA: 352 nm). In synthetic spiked water, CBZ was degraded to below detectable limits within 0.5 min for ozone dose of 14.4 mg/h. The rate of degradation of CBZ increased exponentially with increase in ozone dose following a zero-order rate at each dose level. The degradation rate of CBZ in wastewater was slower compared to deionized water (DI) water by 40–75% for various doses of ozone, presumably due to the presence of organic matter remaining in treated wastewater. Optimal UV intensities for UVA and UVC were obtained as 0.62 and 0.82 mW/cm² for all doses of ozone in synthetic spiked water samples and UV intensities beyond this resulted in lower rates of degradation of CBZ. For photo-assisted ozonation with ozone doses of 9.6 and 14.4 mg/L, rate constants were two times higher for UVA irradiations as compared to UVC irradiation. Contrary to observations in DI water, experiments in wastewater showed increase in rate of degradation with higher UV intensities. Overall, photo-assisted ozonation was found to be appropriate for both water and wastewater treatment by exploiting the benefit of direct attack of ozone and of produced ^?OH radicals to yield a greater extent of mineralization of CBZ.     

Pilot Study on Pre-Ozonation Enhanced Drinking Water Treatment Process

The enhancement of TOC, COD_Mn, and UV₂₅₄ reduction in the conventional drinking water treatment process by pre-ozonation was investigated in South China on treating dam source water with a pilot plant consisting of pre-ozonation, coagulation-sedimentation, and filtration units. Pre-ozonation enhanced the reduction of NOM in the conventional coagulation-sedimentation and filtration process, and the total removals of UV₂₅₄, COD_Mn and TOC were improved for 34.6%, 18.1% and 15.3%, respectively by the adoption of pre-ozonation under an ozone dose (in ozone consumption base) of 0.85 mg/L. The enhancement of UV₂₅₄ and COD_Mn removals was mainly achieved through direct ozonation on humic substances, and that for TOC removal was achieved through biodegradation in sand filtration. In comparison with the TOC removal of 38%, a removal of 49% was acquired for SDS-THM under a pre-ozonation dose of 0.80 mg/L, indicating the selective removal of THMFP. The reduction of SDS-THM paralleled the reduction of COD_Mn to a significant degree, suggesting that the COD_Mn might be an effective surrogate parameter for SDS-THM if the raw water does not contain the reductive inorganic matters. Although the source water contains 13.2–27.0μg/L bromide, the formation of bromate was negligible when the ozone dose was below 1.0 mg/L.     

Integration of continuous biological and chemical (ozone) treatment of domestic wastewater: 1. Biodegradation and post‐ozonation

The continuous treatment of domestic wastewater by an activated sludge process and by an integrated biological–chemical (ozone) oxidation process were studied in this work. Chemical oxygen demand (COD), biochemical oxygen demand (BOD), absorbance at 254 nm (UV₂₅₄) and nitrogenous compound content were the parameters followed in order to evaluate the performance of the two processes. Experimental data showed that both UV₂₅₄ and COD reductions are improved in the combined biological–chemical oxidation procedure. Thus, reductions of 59.1% and 37.2% corresponding to COD and UV₂₅₄, respectively were observed after the biological process (hydraulic retention time = 5 h; mixed liquor volatile suspended solids concentration = 3142 g m⁻³) compared with 71.0% and 78.4% obtained when a post‐ozonation step ( D _O3 = 41.7 g m⁻³) was included. During conventional activated sludge treatment, appropriate nitrification levels are only achieved with high hydraulic retention time and/or biomass concentration. Ozonation after the secondary treatment, however, allows improved nitrogen content reduction with total nitrite elimination. Post‐ozonation also leads to a higher biodegradability of the treated wastewater. Thus, the ultimate BOD/COD ratio goes from 0.16 after biological oxidation to 0.34 after post‐ozonation with 41.7 g O₃ m⁻³. © 1999 Society of Chemical Industry     

Comparison of Ozone and Hydroxyl Radical-Induced Oxidation of Chlorinated Hydrocarbons in Water

The efficiency of ozonation and advanced oxidation processes such as ozone/UV, ozone/H₂O₂ and H₂O₂/UV was assessed for chlorinated hydrocarbons using a closed batch-type system. 1,1-Dichloropropene (DCPE), trichloroethylene (TCE), 1-chloropentane (CPA), and 1,2-dichloroethane (DCA) were used as model compounds.

The direct reaction between substrates and ozone predominated at lower pH, which resulted in the efficient oxidation of the olefin, DCPE. At higher pH, ozonation resulted in more efficient oxidation of the chlorinated alkanes, with a corresponding decrease in the efficiency of DCPE oxidation. Consistent results were observed for ozone/H₂O₂ and ozone/UV treatment. Due to slow UV-induced decomposition of H₂O₂, the process using H₂O₂/UV (254 nm) resulted in very slow oxidation of all four compounds.

The total ozone requirement to achieve a given degree of elimination (to 37% of the original concentration), δ0.37, was used to assess the combined effects of the direct and indirect reactions for different types of waters.     

Ozonolysis Post-Treatment of Anaerobically Digested Distillery Wastewater Effluent

ABSTRACT

In this study, the ozonolysis of real anaerobically digested distillery wastewater (DWW) was carried out. The effect of operating parameters, such as pH, initial concentration, and ozone dosage, on the efficiency of ozone utilization, color removal, and sludge solubilization was studied. The highest ozone utilization of 99% was observed at the highest initial concentration (COD of 3000 mg/L) and lowest ozone flowrate (22.5 mg O₃/L/min), but with a very low color reduction of 20%, after 60 minutes of ozonolysis. To achieve a higher color reduction >80% and at ozone utilization >95%, the DWW had to be diluted twice (COD 1500 mg/L), and the flowrate doubled to 45 mg O₃/L/min. The reduction in color signified the oxidation of the color causing biorecalcitrant aromatic melanoidin compounds. This was confirmed by the 47% reduction in ultraviolet absorbance at 254 nm indicating the breakdown of the complex aromatic compounds into low molecular weight organics. Moreover, increases in average oxidation state from ?0.6 to ?0.2 suggested a decline in aromaticity and formation of easily biodegradable aliphatic compounds. The ozonolysis process was found to follow the first-order reaction kinetic model with the highest rate constant of 0.0326 min^?1 obtained. A reduction in suspended COD by 88% indicated solubilization of the sludge contained in the effluent.     

The degradation of an azo dye in a batch slurry photocatalytic reactor

The photocatalytic degradation of a commercial azo-reactive textile dye, Remazol Red F-3B, has been investigated in a batch slurry reactor using semiconductor catalysts like, ZnO and TiO₂, and two UV sources emitting mainly at 254 and 365 nm. Non-irradiated catalysts and non-catalyzed UV irradiation have negligible effect on the dye degradation. Initial pH, dye concentration, light power and catalyst loading as well as the catalyst type and UV wavelength are considered as process variables. The results showed that decolorization and TOC removal efficiencies of ZnO are higher under 365 nm UV. On the other hand, when two photocatalysts are compared, the decolorization performance of ZnO is higher than TiO₂ under 365 nm UV_, while TiO₂ performs better under 254 nm UV. Furthermore, from the TOC removal point, TiO₂ performs better than ZnO irrespective of the UV wavelength. TiO₂ irradiated under 254 nm UV degrades successfully both benzene and naphthalene derivatives.     

Evaluation of Decolorization,Mineralization, and Toxicity Reduction of Tropaeolin O in Water by Ozonation with UV Irradiation

The combination of ozonation with UV irradiation can remove Tropaeolin O (AO6) and its by-products effectively and completely. The ozone dose affects the rate of decolorization, AO6 species removal, and dissolved organic carbon (DOC) reduction significantly. After 240 minutes of ozonation, the average DOC removal efficiency (η_DOC) for O₃ alone was about 0.79, while η_DOC for O₃/UV was 1.0. The average DOC removal rate was low at early stage of ozonation due to decolorization and low DOC. At later stage of ozonation, average DOC removal rate decreases because of the formation of persistent intermediates. The ozone consumption was consistent with η_DOC. The ratio of ozone consumption to ozone applied decreased from 14 to 12% when η_DOC < 40% because the decolorization in the early stage of the ozonation of AO6 may consume a relatively large amount of ozone. It was found that NO₂, NO, CO₂, and small amount of SO₂ was detected in the off-gas. The effective concentration (EC50) increased from 23.48% to 100%, suggesting that the toxic reduction was achieved, and O₃/UV system was superior to O₃ alone system