Ozonation as a Post-Treatment Step for Tannery Wastewater to Reduce Foam Formation in a River

Foam formation in a transboundary river, accompanied by protests of local stakeholders, made it necessary to investigate measures to quantify and reduce foam formation. It was previously reported that 80% of the occurring foam formation was provided by three tanneries. Therefore, laboratory-scale experiments were run with wastewater from the three tanneries for six months to investigate the influence of ozonation and biological post-treatment on foam formation. Ozonation with biological post-treatment showed a significant positive effect, with up to 50% additional COD reduction and the elimination of > 70% of the foam formation on river catchment scale. Biological post-treatment alone did not show any effect on the foam formation. The new legal standards for tannery wastewater can be kept at the investigated tanneries through ozonation and biological post-treatment.     

Ozonation of a Complex Industrial Effluent: Oxidation of Organic Pollutants and Removal of Toxicity

This work deals with the ozonation of a chemical industry wastewater, which contains many complex organic pollutants and presents high chloride content and toxicity. Batch experiments were carried out until ozone absorption reached 0.1 to 3 gO₃/L. Ozonation promoted low to moderate levels of organic matter removal even when high ozone doses were applied. Organic matter removal tended to decrease when chloride content increased. Toxicity removal increased with the ozone dose up to 0.5 gO₃/L. High or complete toxicity removal was attained after ozonation of the wastewater samples. Ozonation was also very effective in removing the polycyclic aromatic compounds found in the wastewater.     

Understanding the Effects of Ozonation on a Combined Municipal/Industrial Secondary Effluent

An increase in the biodegradability of secondary effluent after ozonation as measured by CBOD₅ (carbonaceous BOD₅), generally has been considered to be due to the conversion of non-biodegradable organic material. Experiments on a specific combined unicipal/industrial waste containing a high percentage of malting plant wastewater showed that an increase in CBOD5 realized at the waste treatment plant was due to a shift in the oxygen uptake curve. Ozonation was found to affect both non-biode-gradable and biodegradable organic matter and resulted in improved overall effluent quality despite the observed increase in CBOD₅. As an indication of effluent quality, the CBOD₅ test is felt to be inadequate.     

Aqueous Ozonation of Pesticides: A Review

The ozonation reactions of pesticides in aqueous solution have been reviewed. Degree of reaction and reaction product identity are included. Compounds are classified into five groups: chlorinated hydrocarbons, organophosphorus compounds, phenoxyalkyl acid derivatives, organonitrogen compounds, and phenolic compounds. Experimental conditions for each study are summarized. Much work has been carried out under conditions atypical of those encountered at drinking water treatment plants. Thus, the findings of the papers reviewed cannot be applied directly to potable water treatment.     

Sequential Ozonation and Biological Oxidation of Wastewaters: A Model Including Biomass Inhibition by Residual Oxidant

We modeled the potential impact of a residual oxidant (ozone in the present case, known to be a strong bactericide) on the performance of a combined chemical and biological water treatment. This model is fashioned by adapting a recent model for the kinetics of ozone disinfection to an activated sludge system performing in the presence of ozone residuals. Our new model allows prediction of the bioreactor performance under different substrate loadings and residual oxidant concentrations, helping to identify regimes where air stripping would be necessary before the second step.     

Application of Response Surface Methodology for Coffee Effluent Treatment by Ozone and Combined Ozone/UV

This paper reports a study using ozone (O₃) and combined ozone/ultraviolet (O₃/UV) processes for color removal and caffeine degradation from synthetic coffee wastewater using a second-order response surface methodology (RSM) with a three-level central composite face-centered (CCF) design. The effects of O₃ concentration, initial pH, and reaction time were examined for both processes. The reaction time and pH were statistically significant for caffeine degradation and color removal. In the ozonation process, higher caffeine degradation and color removal were observed in alkaline pH, indicating that ozone attacks indirectly, consequently generating hydroxyl radicals. Regarding the ozone/UV process, it was observed that lower caffeine degradation and color removal occurred at neutral pH, indicating an adverse effect due to lower ozone dissolution and consequently the production of a smaller amount of free hydroxyl radicals. The achieved results showed that the techniques were efficient for color removal (85% and 99%, respectively) and caffeine degradation (88% and 98%, respectively).     

Kinetic Description of Industrial Wastewater Ozonation Processes

Literary and experimental data on the ozonation kinetics of aqueous solutions and wastewater were analyzed. COD was suggested to be used as a kinetic parameter from the solution side. On the basis of the results obtained from the ozonation of model solutions and wastewater, the rate coefficient by COD of the reaction was shown to be constant during separate stages of the process. Due to the consumption of fast-reacting components and entering into the reaction of more slowly reacting intermediate products, the rate coefficient changed spasmodically with transition from one stage to another. The reaction order with respect to the COD of the solution was shown to be equal to the reaction order with respect to the pure component.     

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.     

Study on By-Products of Ozonation during Ammonia Removal under the Existence of Bromide: Factors Affecting Formation and Removal of the By-Products

Factors affecting the formation of by-products of ozonation during ammonia removal under the existence of bromide were investigated. The presence of reducible N compounds could significantly reduce the formation of bromate and brominated organics; however, it was difficult to completely prevent formation of the by-products. It was therefore concluded that while the method used in this study was an effective process to decompose ammonia, it should be applied to the treatment of wastewaters containing low concentration of TOC. For power plant condensate demineralization wastewater containing TOC of 3 to 4mg/L, TOX formed during ammonia removal ranged from 0.20 to 0.30 mgBr L^?1. The only halogenated organic substance of the power plant wastewater detected on GC spectrum was bromoform, whose concentration varied from 0.11 to 0.14 mg L^?1. Column test results indicated that bromate could almost completely be decomposed to bromide by activated carbon under proper space velocity and pH. Activated carbon was also very effective in adsorption of CHBr₃: 1 g activated carbon adsorbed ca. 20.3 mg of CHBr₃.     

Rapid Removal of Tetracycline (TC) by Ozonation after Extraction TC from Water into Acetic Acid Solution Using Granular Activated Carbon

This study quantifies the rapid removal of tetracycline (TC) in acetic acid solution by ozonation after extraction from water into acetic acid solution using granular activated carbon (GAC). Systematic laboratory experiments show that GAC can be used as an adsorbent to transfer TC from water to acetic acid. Ozone gas has a high degree of stability and solubility in acetic acid, and therefore apparently enhances the removal rate of TC. TC removal efficiency is better in 10% acetic acid solution than that in water, 15% and 20% acetic acid solution. Removal rate of TC in the acetic acid solution decreases as the initial molar ratio of TC and O₃ increases. Inhibition effect of tertiary butyl alcohol (TBA) on TC removal is smaller in acetic acid than that in water. metal-TC complex was produced in the presence of Fe³⁺ and Co³⁺, which inhibited the degradation of TC by ozone in acetic acid. Removal of TC by ozone in the acetic acid solution might be affected by multiple factors, which should be considered in practical applications.     

Removal of a Toxic Anthraquinone Dye by Combination of Red Mud Coagulation and Ozonation

Removal of a toxic anthraquinone dye—Disperse Blue 56 (DB56) by single red mud (RM) coagulation, single ozonation and combined RM coagulation/ozonation (RM/O₃) was carried out in laboratory-scale experiments. RM/O₃ treatment exhibited more effective in toxicity removal, color removal and chemical oxygen demand (COD) reduction than the other two methods. The effect of several operational parameters, including initial dye concentration, pH value, RM coagulant dose and O₃ dose, on color removal and COD reduction was also investigated. Among these factors, pH value had the most important effect.     

Ozonation of Two Acidic Azo Dyes with Different Substituents

The ozonation of two differently substituted azo dyes (Schwarz GRS and Orange Acid 8) in water media is studied. The influence of pH on the effectiveness of the ozonation at various initial concentrations of each dye is explored. It was found out that the rates of decolorization for amino-group substituted dyes reflect the considerable influence by the widely varying initial pH from 4.5 to 10. Specifically, the highest effect of decolorization of this dye was obtained at the highest pH studied (pH 10) for all initial concentrations of the solutions. Considering the dye without an amino-group substitute, the rates of color disappearance in ozonation reflected to a lower degree the variations of the initial pH. Pseudo-first-order trends of decolorization were observed in all the experimental runs. Regarding the kinetic results obtained, an attempt to explain the different dyes reactivity was made based on the absolute electronegativity (E_lumo + E_homo) of both dyes. The COD/BOD analysis shows that the ozonation of both azo dyes can reduce the sample COD but it could not improve the biodegradability ratio (BOD₅/COD). BOD decrease with ozonation time indicates that the intermediates of the ozonation are of lower biodegradability. Oxalic acid was found as the final product of ozonation of both dyes.     

The Use Of Ozoflotation For The Removal Of Algae And Pesticides From A Stored Lowland Water

Tophill Low, a water treatment plant supplying the city of Hull, in Yorkshire, England, suffers from water quality problems due to algae and small residuals of pesticides. This plant is due for upgrading, and investigations into new compact processes were carried out to determine a cost-effective (treatment process to meet the current standards. A pilot plant was constructed to determine the efficiency of the Ozoflot® process and results for the removal of algae and oxidation of pesticides are presented, together with data on the formation and reduction of biodegradable organic carbon.     

Aqueous Pesticide Degradation by Ozonation and Ozone-Based Advanced Oxidation Processes: A Review (Part I)

Pesticide pollution of surface water and groundwater has been recognized as a major problem in many countries because of their persistence in aquatic environment and potential adverse health effects. Among various water and wastewater treatment options, ozonation and ozone-based advanced oxidation processes, such as ozone/hydrogen peroxide, ozone/ultraviolet irradiation, and ozone/hydrogen peroxide/ultraviolet irradiation, are likely key technologies for degrading and detoxifying these pollutants in water and wastewater. In this paper, ozone-based treatment of four major groups of pesticides, namely carbamates, chlorophenoxy compounds, organochlorines, and organophosphates, are reviewed. Degree of pesticide degradation, reaction kinetics, identity and characteristics of degradation by-products and intermediates, and possible degradation pathways are covered and discussed.     

Aqueous Pesticide Degradation by Ozonation and Ozone-Based Advanced Oxidation Processes: A Review (Part II)

Pesticides are known to be persistent in surface water and groundwater supplies and as a result, their existence in these water sources has been recognized as a major problem in many countries. The occurrence of these persistent pesticides in water bodies can also cause potential adverse public and environmental health effects. Among many water and wastewater treatment options, ozonation and ozone-based advanced oxidation processes, such as ozone/hydrogen peroxide, ozone/ultraviolet irradiation, and ozone/hydrogen peroxide/ultraviolet irradiation, possess a high potential for degrading and detoxifying these pollutants in water and wastewater. In this paper, ozone based treatment of four major groups of pesticides, namely aniline-based compounds, pyridines and pyrimidines, triazines, and substituted ureas, as well as that of several miscellaneous pesticides are reviewed. Degree of pesticide degradation, reaction kinetics, identity and characteristics of degradation by-products, and possible degradation pathways are covered and discussed.     

Combined Ozonation Using Alumino-Silica Materials for the Removal of 2,4-Dimethylphenol from Water

This study deals with an advanced oxidation process combining adsorption and ozonation for treating petrochemical effluents. The compound 2,4-dimethylphenol (DMP) was the paradigm molecule and faujasite-Y, mordenite, ZSM-5 and γ-alumina were tested. Single ozonation showed rapid DMP degradation but limited by gas to liquid ozone transfer. No catalytic effect occurred during ozonation combined with any of the adsorbents: DMP removal was not accelerated. However, a good synergistic effect was observed for TOC removal with γ-alumina, yet the various zeolites are less efficient. Some specific oxidation by-products produced during ozonation are eliminated by adsorption in the presence of γ-alumina, although they persist in the other cases.     

Ozonation and Precipitation for Treatment of Bleachery Effluents from Pulp Mills

Results from precipitation of an oxygen/peroxide-bleachery effluent from pulp mills with and without preozonation are presented. Reductions in DOC levels by about 60% were achieved at the pH optimum of 5.5 at an AI/D0C ratio of 0.25 g/g. Increasing alum dosages did not improve the elimination. Ozonation at pH 2 reduced COD, DOC, UV and color levels, while under alkaline conditions an increase of color could be obtained. This effect, based on a polymerization of organics, could be improved at low ozone dosages, by reducing the ozone dosage rate, elevating the pH up to 11 and diluting the wastewater. However, the shift towards high and low molecular weight fractions indicated competing degradation reactions, which counteract a suggested improvement of precipitation by preozonation.     

Optimization of High-Strength Semiconductor Wastewater by Sequential Fenton Oxidation and Gas-Induced Ozonation

Treatment of organic-containing wastewater from a semiconductor plant treated by chemical oxidation was experimentally investigated. The wastewater was characterized by strong color, high chemical oxygen demand (COD) and low biodegradability. Treatment of this wastewater by traditional activated sludge method was essentially impossible. In the present work, advanced chemical oxidations by Fenton’s reagent and ozonation were utilized to tackle the problems of wastewater color and low biodegradability. To facilitate the particulate removal after Fenton oxidation, chemical coagulation using polyaluminum chloride and polymer was adopted as an integral part of the Fenton process. Experimental tests were conducted to determine the effectiveness and the optimum operating conditions of the chemical oxidation methods. Test results demonstrate that the two advanced oxidations were able to lower the wastewater COD concentration from as high as 15,000 mg/L to below 150 mg/L and completely eliminating the wastewater color, resulting in very good quality of the treated wastewater. A generalized kinetic model was employed to describe and elucidate the oxidation mechanisms of oxidation processes and the kinetic parameters of the models were appropriately identified using the test data.     

Ozonation of Substituted Phenols in Aqueous Solutions over CuO-Al2O3 Catalyst

The oxidation of aqueous solutions of substituted phenols, chlorophenols (CPs) and nitrophenols (NPs), at 21±0.5°C and atmospheric pressure, by ozone over a copper–alumina catalyst system was studied. The total disappearance of phenol compounds for 15 to 30 minute reaction times was observed. The presence of the catalyst increased the reaction rate, diminished the ozone consumption and caused an advanced degradation of phenols. A number of six by-products was identified by gas chromatography/mass spectrometry technique (GC/MS), with or without silylation. Based on the experimental data several mechanistic suggestions for the catalytic ozonation are made.