The presence of micropollutants, particularly pesticides, in surface waters across Canada has been of concern not only for their environmental impact, but also for their potential effects on human health and recalcitrant nature to conventional water treatment methods. Although ozone has been mainly applied for disinfection of drinking water, oxidation of trace organics by ozonation has been considered potentially effective. In an effort to meet increasingly stringent drinking water regulations, different solid catalysts have been used to enhance the removal of water contaminants by ozonation. In spite of the increasing number of data demonstrating the effectiveness of heterogeneous catalytic ozonation, the influence of different factors on the efficiency of micropollutants oxidation is still unclear.<p> In the present work, application of three solid catalysts in ozonation of two model micropollutants in pure water was examined using a laboratory-scale reaction system over a range of operating conditions. The three catalysts investigated were activated carbon, alumina, and perfluorooctyl alumina, and the two model micropollutants were the pesticides atrazine and 2,4-dichlorophenoxyactic acid. The effects of solution pH, presence of a radical scavenger, pesticide adsorption on catalyst, and catalyst dose on micropollutant removal were investigated. Solution pH was found to significantly influence the catalyst ability to decompose ozone into free hydroxyl radicals. The effect of these free radicals was markedly inhibited by the radical scavenger resulting in a negative impact on pesticides degradation. In general, the removal rate of pesticides was found to increase with increasing doses of catalyst.<p> In the ozonation process in the presence of activated carbon, atrazine removal rates increased four and two times when using a catalyst dose of 0.5 g L-1 at pH 3 and 7, respectively, whereas observed reaction rates for 2,4-D increased over 5 times in the presence of 1 × 10-4 M tert-butyl alcohol at pH 3. In the ozonation system catalyzed by 8 g L-1 alumina, the observed reaction rate constant of atrazine removal notably improved at neutral pH by doubling the micropollutant removal rate. For the pesticide 2,4-D in the presence of 1 × 10-4 M tert-butyl alcohol at pH 5, the observed removal rate was over ten times higher than that for the non-catalytic ozonation process using also using a catalyst dose of 8 g L-1. Modification of alumina to produce perfluorooctyl alumina resulted in a material able to significantly adsorb atrazine, while not exhibiting affinity for adsorption of 2,4-D. In spite of its adsorptive properties, perfluorooctyl alumina was found to enhance neither molecular ozone reactions nor ozone decomposition into hydroxyl radicals. Thus, the observed removal rates for atrazine and 2,4-D by ozonation in the presence of perfluorooctyl alumina did not increase significantly.

The presence of micropollutants, particularly pesticides, in surface waters across Canada has been of concern not only for their environmental impact, but also for their potential effects on human health and recalcitrant nature to conventional water treatment methods. Although ozone has been mainly applied for disinfection of drinking water, oxidation of trace organics by ozonation has been considered potentially effective. In an effort to meet increasingly stringent drinking water regulations, different solid catalysts have been used to enhance the removal of water contaminants by ozonation. In spite of the increasing number of data demonstrating the effectiveness of heterogeneous catalytic ozonation, the influence of different factors on the efficiency of micropollutants oxidation is still unclear.<p> In the present work, application of three solid catalysts in ozonation of two model micropollutants in pure water was examined using a laboratory-scale reaction system over a range of operating conditions. The three catalysts investigated were activated carbon, alumina, and perfluorooctyl alumina, and the two model micropollutants were the pesticides atrazine and 2,4-dichlorophenoxyactic acid. The effects of solution pH, presence of a radical scavenger, pesticide adsorption on catalyst, and catalyst dose on micropollutant removal were investigated. Solution pH was found to significantly influence the catalyst ability to decompose ozone into free hydroxyl radicals. The effect of these free radicals was markedly inhibited by the radical scavenger resulting in a negative impact on pesticides degradation. In general, the removal rate of pesticides was found to increase with increasing doses of catalyst.<p> In the ozonation process in the presence of activated carbon, atrazine removal rates increased four and two times when using a catalyst dose of 0.5 g L-1 at pH 3 and 7, respectively, whereas observed reaction rates for 2,4-D increased over 5 times in the presence of 1 × 10-4 M tert-butyl alcohol at pH 3. In the ozonation system catalyzed by 8 g L-1 alumina, the observed reaction rate constant of atrazine removal notably improved at neutral pH by doubling the micropollutant removal rate. For the pesticide 2,4-D in the presence of 1 × 10-4 M tert-butyl alcohol at pH 5, the observed removal rate was over ten times higher than that for the non-catalytic ozonation process using also using a catalyst dose of 8 g L-1. Modification of alumina to produce perfluorooctyl alumina resulted in a material able to significantly adsorb atrazine, while not exhibiting affinity for adsorption of 2,4-D. In spite of its adsorptive properties, perfluorooctyl alumina was found to enhance neither molecular ozone reactions nor ozone decomposition into hydroxyl radicals. Thus, the observed removal rates for atrazine and 2,4-D by ozonation in the presence of perfluorooctyl alumina did not increase significantly.

Ozonation is an efficient method to degrade refractory organics in textile wastewaters. In recent years, catalytic ozonation is applied to reduce ozone consumption and to increase chemical oxygen demand and total organic carbon (TOC) removal efficiencies. The ozonation of two industrial dyes, namely Acid Red-151 (AR-151) and Remazol Brilliant Blue R (RBBR) was examined separately both in a semi-batch reactor and also in a fluidized bed reactor (FBR) by conventional and catalytic ozonation with alumina and perfluorooctyl alumina (PFOA) catalysts. The conventional and catalytic ozonation reactions followed a pseudo-first order kinetics with respect to the dye concentration. The highest COD reductions were obtained in the presence of the catalysts at pH=13, with alumina for AR-151 and with PFOA for RBBR. Residence time distribution experiments were performed to understand the degree of liquid mixing in the reactor. The behaviour of the FBR was almost equivalent to the behaviour of one or two completely stirred tank reactors in series in the presence of the solid catalyst particles. The volumetric ozone-water mass transfer coefficients (kLa) were found at various gas and liquid flow rates and catalyst dosages in the FBR. A model was developed to find kLa in the reactor by comparing the dissolved O3 concentrations in the experiments with the model results. kLa increased significantly by the increase of gas flow rate. Higher catalysts dosages at the fluidization conditions yielded higher kLa values indicating higher rates of mass transfer. Dye ozonation experiments without catalyst and with alumina or PFOA catalyst were conducted at different conditions of the inlet dye concentration, gas and liquid flow rates, inlet ozone concentration in the gas, catalyst dosage, particle size and pH. The dye and TOC removal percentages were increased with the increase of gas flow rate and with the decrease of both the liquid flow rate and inlet dye concentration. The addition of the catalyst was beneficial to enhance the TOC degradation. The ozone consumed per liter of wastewater was much lower when the catalyst was present in the reactor. In terms of TOC removal and O3 consumption, the most efficienct catalyst was PFOA. According to the organic analysis, the intermediate by-products were oxalic, acetic, formic and glyoxalic acids in RBBR and AR-151 ozonation. The dye and dissolved ozone concentration profiles were predicted from a developed model and the model results were compared with the experimental results to obtain the enhanced kLa values. The presence of the chemical reaction and the catalysts in the FBR, enhanced the kLa values significantly. The enhancement factor (E) was found as between 0.97 and 1.93 for the non-catalytic ozonation and 0.96 and 1.53 for the catalytic ozonation at pH = 2.5. The dimensionless number of Hatta values were calculated between 0.04-0.103 for the sole ozonation of RBBR and AR-151 solutions. According to the calculated Ha values, the reaction occurred in the bulk liquid and in the film being called as the intermediate regime in the literature.

Textile wastewaters are highly colored and non-biodegradable having variable compositions of colored dyes, surfactants and toxic chemicals. Recently, ozonation is considered as an effective method that can be used in the treatment of industrial wastewaters / catalytic ozonation being one of the advanced oxidation processes (AOPs), is applied in order to reduce the ozone consumption and to increase the chemical oxygen demand (COD) and total organic carbon (TOC) removals. In this study, catalytic ozonation of industrial textile wastewater (ITWW) obtained from AKSA A.S. (Yalova, Istanbul) textile plant has been examined in a three phase fluidized bed reactor at different conditions. The effects of inlet chemical oxygen demand concentration (CODin), pH, different catalyst types [perflorooctyl alumina (PFOA) and alumina] and catalyst dosage on ozonation process were determined. Moreover, the changes in the organic removal efficiencies with gas to liquid flow rate ratio were investigated. The dispersion coefficients (DL) and volumetric ozone-water mass transfer coefficients (kLa) were estimated at various gas and liquid flow rates in order to observe the effect of liquid mixing in the reactor on ozonation process. It was observed that increasing both gas and liquid flow rates by keeping their ratio constant provided higher organic removal efficiencies due to the higher mixing in the liquid phase. The dyes present in ITWW sample were known to be Basic Blue 41 (BB 41), Basic Red 18.1 (BR 18.1) and Basic Yellow 28 (BY 28). The &ldquo / absorbance vs. concentration&rdquo / calibration correlations were developed to estimate the amounts of these colored dyes in the ITWW sample. This provided the opportunity to examine the degradation of each dye in this wastewater separately. While PFOA catalyst was found to increase the removal efficiency of BY 28 at an acidic pH of 4, alumina yielded highest color removals for BB 41 and BR 18.1 at a pH of 12. The highest TOC and COD reductions being 24.4% and 29.5%, respectively, were achieved in the catalytic ozonation of the ITWW using alumina as the catalyst at a pH of 12 and at a gas to liquid flow rate ratio of 1.36 (QG = 340 L/h, QL = 250 L/h). At the same conditions, also the highest overall color removal in terms of Pt-Co color unit, namely 86.49%, were obtained due to the lower BY 28 concentration in the WW sample than those of the BB 41 and BR 18.1. In addition, the oxidation of BB 41, BR 18.1 and BY 28 dyes were investigated in a semi-batch reactor by sole and catalytic ozonations with alumina and PFOA catalyst particles. The sole and catalytic ozonation reactions followed a pseudo-first order kinetics with respect to dye concentration. The highest TOC and COD removals being 58.3% and 62.9%, respectively, were obtained at pH of 10 for BB 41 and 55.2% and 58.8%, respectively, for BR 18.1 with alumina catalyst. On the other hand, for BY 28 PFOA catalyst yielded highest TOC and COD reductions being 61.3% and 66.9%, respectively, at pH of 4.

Environmental regulations have imposed limitations on a wide variety of organic and inorganic pollutants in industrial textile wastewaters. There are several degradation methods used in literature studies. Among these methods ozonation is one of the most considered way to degrade refractory chemicals in textile wastewaters. In recent years, catalytic ozonation as being one of the advanced oxidation processes (AOPs), is applied to reduce the ozone consumption and to increase the Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removals. Ozonation and catalytic ozonation of single and mixed dye solutions have been examined both in a semi-batch reactor and also in a three phase fluidized bed reactor. The dyes that are used in this study are Basic Blue 41 (BB-41), Basic Yellow 28 (BY-28) and Basic Red 18.1 (BR-18.1), these dyes are obtained from AKSA A.S. (Yalova, Istanbul) textile plant. In order to measure the concentration of each dye in the mixed dye solution, &ldquo / absorbance vs. concentration&rdquo / calibration correlations were developed. The effect of inlet dye concentration, inlet gas and liquid flow rates, pH, catalyst type [perflorooctyl alumina (PFOA) and alumina] and catalyst dosage were determined experimentally. Catalyst characterization analyses were done in order to determine the maximum number of times that the catalyst can be used and it was found to be 3 times. Gas washing bottle experiments are conducted to find the v amount of ozone required to oxidize one mole of each dye used in the study. Oxidation of BB-41, BR-18.1 and BY-28 dyes were investigated in a semi-batch reactor as single dye solutions by sole and catalytic ozonation with alumina and PFOA catalyst particles. The highest TOC and COD removals being 58.3% and 62.9%, respectively, were obtained at pH of 10 for BB-41 and 55.2% and 58.8%, respectively, for BR-18.1 with alumina catalyst. On the other hand, for BY-28 PFOA catalyst yielded highest TOC and COD reductions being 61.3% and 66.9%, respectively, at pH of 4. Minimum fluidization velocity (uL,min), the hold-up values of gas, liquid and solid phases, the dispersion coefficients (DL), and volumetric ozone-water mass transfer coefficients (kLa) were estimated at various gas and liquid flow rates in order to observe the effect of liquid mixing in the reactor on ozonation process. While PFOA catalyst was found to be effective in oxidizing BY-28 in acidic conditions (pH=4), BR-18.1 and BB-41 are degraded in alkaline medium (pH=10) with alumina catalyst better compared to acidic conditions. For catalytic ozonation reactions in fluidized bed reactor, the highest dye removals in mixed dye solution were observed for BY- 28 being 99.29% for gas flow rate (QG) of 340 L/h, liquid flow rate (QL) of 150 L/h and pH=4, initial dye concentration being 30 mg/L of each dye with PFOA catalyst, while for BR-18.1 and BB-41 being 95.39% and 97.95% respectively for QG = 340 L/h, QL = 150 L/h and pH=10, initial dye concentration being 30 mg/L of each dye with alumina catalyst. The highest TOC and COD reductions, 25.2% and 32.4%, respectively, were achieved in the catalytic ozonation of the mixed dye using PFOA as the catalyst at a pH of 4 and at a gas to liquid flow rate ratio of 2.26 (QG = 340 L/h, QL = 150 L/h). Highest dye removals were obtained at the same gas and liquid flow rates as those of the highest TOC and COD reductions in the experiments. Empirical TOC removal equations were obtained as a function of inlet TOC concentration, solution pH, gas and liquid flow rates.