Advanced oxidation processes for destruction of cyanide from thermoelectric power station waste waters

Several advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined‐cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi‐batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo‐first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H₂O₂ and/or UV is faster at pH 9.5. The optimum concentration of H₂O₂ was 20.58 × 10^?2 M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O₃/H₂O₂(20.58 × 10^?2 M ) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O₃/UV or O₃/H₂O₂/UV was about 75%, while in the processes with H₂O₂ and/or O₃/H₂O₂ was lower than 57% and was insignificant, when using ozone alone. Copyright © 2003 Society of Chemical Industry     

Oxidation of 1,3,5‐trichlorobenzene using advanced oxidation processes

The oxidation of 1,3,5‐trichlorobenzene (TCB) by ozone, ozone/UV, ozone/H₂O₂ and ozone/UV/H₂O₂ was studied. All studies were conducted in a continuously‐flowing completely mixed reactor (CFCMR), operated at steady‐state conditions using a hydraulic retention time of 10 minutes. The greatest removal of TCB using ozone/H₂O₂ treatment was achieved using a H₂O₂ concentration of 60 μM. At low pH values (approx. 2) ozone/UV performed significantly better than either ozone alone or ozone/H₂O₂. However, at circumneutral pH, the removal efficiencies of TCB by ozone/UV and ozone/H₂O₂ and ozone/UV/H₂O₂ were essentially equal (～ 97% for TCB). The removal efficiency of ozone alone was ～93% for TCB. At high pH (> 9) there was no advantage in supplementing ozone with either UV or H₂O₂ as the removal efficiencies for all processes studied were essentially equal.

The effect of humic acid and bicarbonate on the removal of TCB was studied. At 1.6 mg/L humic acid, 92–95% of the TCB was oxidized by the processes studied. The removal of TCB by ozone alone was significantly affected by the presence of bicarbonate ion. For the other processes at 10 mM bicarbonate, approximately 80% of the TCB was oxidized.     

Decolorization and Modeling of Synthetic Wastewater Using O3 and H2O2/O3 Processes

This research deals with the decolorization of synthetic wastewater, prepared with the acid 1:2 metal-complex textile dye C.I. Acid Blue 193, using the ozonation (O₃) and H₂O₂/O₃ processes. To minimize the number of experiments, they were performed using the 2^k factorial design. Five influential parameters were examined: initial dye concentration, ozone flow rate, initial pH value, decolorization time and H₂O₂ addition. The decolorization efficiency was 95% in 20 minutes (pH = 7; O₃ flow rate of 2 g/L.h) and a higher increase in the toxicity after the ozonation process (39%) indicates the formation of carcinogenic by-products. According to the variance test analysis, the initial dye concentration, the ozone flow rate, the initial pH value and the decolorization time and their first- and second-order interactions are significant, while the H₂O₂ addition was not important with respect to the discussed range. With the help of these significant factors a regression model was constructed and the adequacy of the model was checked. The obtained regression polynomial was used to model the relation between the absorbance and the influential parameters by fitting the response surface. This response surface may be used to predict the absorbance result from a set of influential parameters, or it can be rearranged in such a way as to predict the set of process decolorization parameters necessary to reduce the absorbance of wastewater with the given initial dye concentration, below the prescribed limit. It is also shown that the 2^k factorial design can be suitable for predicting the operating expenses of the ozonation.     

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.     

Reduction of Biocide-Polluted Wastewater Using O3 and H2O2/O3 Oxidation Processes

The objective of the presented study was to test various oxidation processes with the aim being to reduce the concentration and toxicity of biocide wastewater from a Slovenian phytopharmaceutical factory. Laboratory-scale experiments employing two AOP processes – ozonation (O₃) and peroxone (H₂O₂/O₃) – were applied to reduce the concentration of the active components involved, i.e., methylisothiazolone (MI), chloromethylisothiazolone (CMI) and dichloromethylisothiazolone (DCMI). The reduction of the biocide wastewater load for the performed oxidation processes was evaluated using ecological parameters. The H₂O₂/O₃ oxidation procedure using an O₃ flow rate of 1g/L h, at a pH value of 10 and with the addition of 5 ml of H₂O₂ (0.3 M) proved to be the most effective treatment. The toxicity of the biocide-load wastewater with an initial EC₅₀ = 0.38%, decreased to EC₅₀ (24h) >100% and EC₅₀ (48h) = 76%.     

Oxidation of Parachloronitrobenzene in Dilute Aqueous Solution by O3 + UV and H2O2 + UV : A Comparative Study

This laboratory study was designed to investigate the degradation of 4-chloronitrobenzene ([CNB] = 2.4 × 10^?6 mol L^?1; pH = 7.5) by H₂O₂/UV and by O₃/UV oxidation processes which involve the generation of very reactive and oxidizing hydroxyl free radicals. The effects of the oxidant doses (H₂O₂ or aqueous O₃), liquid flow rate (or the contact time), and bicarbonate ions acting as OH· radical scavengers on the CNB removal rates were studied. For a constant oxidant dose, the results show that the O₃/UV system appears to be more efficient than the H₂O₂/UV system to remove CNB because of the greatest rate of OH· generation by ozone photodecomposition compared to H₂O₂ photolysis. However, for a given amount of oxidant decomposed, the H₂O₂/UV oxidant system was found to be more efficient than O₃/UV. Moreover, high levels of bicarbonate ions in solution (4 × 10^?3 mol L^?1) significantly decrease the efficiency of CNB removal by H₂O₂/UV and by O₃/UV oxidation processes.     

Dye decomposition kinetics by UV/H2O2: Initial rate analysis by effective kinetic modelling methodology

The wastewater from textile industries containing non-biodegradable and toxic dye compounds is one important sources of environmental contamination. This study aims at investigating the decomposition of azo dye by UV/H₂O₂ process with varying H₂O₂ concentrations, dye concentrations, initial pHs, and UV irradiation powers. The results show that the initial rate increases with increase in initial H₂O₂ concentration, initial dye concentration to a certain point and then decreases with further increase in the above factors; the initial rate remains almost constant at lower pH and then decreases with increase in pH; the initial rate linearly increases with increase in UV irradiation power. A comprehensive kinetic model, based on reaction network analysis, was developed to predict the effects of H₂O₂ concentration, dye concentration, solution pH, and UV irradiation power on the initial dye reaction rate. The experimental data and the predicted results are in good agreement.     

UV/H2O2 treatment of Rhodamine B in aqueous solution: Influence of operational parameters and kinetic modeling

The decolorization and degradation of Rhodamine B (RB) were investigated using UV radiation in the presence of H₂O₂ in a batch photoreactor at different light intensities. H₂O₂ and UV light have a negligible effect when they were used on their own. Removal efficiency of RB was sensitive to the operational parameters such as initial concentrations of H₂O₂ and RB, initial pH and light intensity. The results indicated that efficiency of process decreased with addition of inorganic ions and alcohols to the dye solution as hydroxyl radical scavengers. The semilogarithmic graphs of the concentrations of RB versus time were linear, suggesting pseudo-first order reaction for decolorization and degradation processes. A simple kinetic model is proposed which confirms pseudo-first-order reaction. The electrical energy per order (EE/O) values for decolorization and degradation of RB solution were calculated. Results shows that applying an optimum hydrogen peroxide concentration can reduce the EE/O.     

Slaughterhouse wastewater treatment by combined anaerobic baffled reactor and UV/H2O2 processes

Combined processes of biological anaerobic baffled reactor (ABR) and UV/H₂O₂ at a laboratory scale were studied to treat a synthetic slaughterhouse wastewater. In this study, the total organic carbon (TOC) loadings of 0.2-1.1 g/(L day) were used. The results revealed that combined processes had a higher efficiency to treat the synthetic slaughterhouse wastewater. Up to 95% TOC removal was obtained for an influent concentration of 973.3 mgTOC/L at the hydraulic retention time (HRT) of 3.8 days in the ABR and 3.6 h in the UV photoreactor. Meanwhile, up to 97.7% and 96.6% removal of chemical oxygen demand (COD) and 5-day carbonaceous biochemical oxygen demand (CBOD₅) were observed in the ABR for the same influent concentration, respectively. Comparatively, for an influent concentration of 157.6 mgTOC/L, the UV/H₂O₂ process alone with the TOC loading of 0.06-1.9 g/(L h) was also studied, in which, up to 64.3%, 83.7%, and 84.3% of TOC, COD, and CBOD₅ removal were observed, respectively, at the HRT of 2.5 h with hydrogen peroxide (H₂O₂) concentration of 529 mg/L. It was found that individual ABR and UV/H₂O₂ processes enhanced the biodegradability of the treated effluent by an increased CBOD₅/COD ratio of 0.4 to 0.6. An optimum H₂O₂ dosage of 3.5 (mgH₂O₂)/(mgTOC_in h) was also found for the UV/H₂O₂ process.     

Advanced oxidation of raw and biotreated textile industry wastewater with O3, H2O2 /UV‐C and their sequential application

The advanced chemical oxidation of raw and biologically pretreated textile wastewater by (1) ozonation, (2) H₂O₂ /UV − C oxidation and (3) sequential application of ozonation followed by H₂O₂ /UV − C oxidation was investigated at the natural pH values (8 and 11) of the textile effluents for 1 h. Analysis of the reduction in the pollution load was followed by total environmental parameters such as TOC, COD, UV–VIS absorption kinetics and the biodegradability factor, f_B. The successive treatment combination, where a preliminary ozonation step was carried out prior to H₂O₂ /UV − C oxidation without changing the total treatment time, enhanced the COD and TOC removal efficiency of the H₂O₂ /UV − C oxidation by a factor of 13 and 4, respectively, for the raw wastewater. In the case of biotreated textile effluent, a preliminary ozonation step increased COD removal of the H₂O₂ /UV − C treatment system from 15% to 62%, and TOC removal from 0% to 34%. However, the sequential process did not appear to be more effective than applying a single ozonation step in terms of TOC abatement rates. Enhancement of the biodegradability factor (f_B) was more pronounced for the biologically pretreated wastewater with an almost two‐fold increase for the optimized Advanced Oxidation Technologies (AOTs). For H₂O₂ /UV − C oxidation of raw textile wastewater, apparent zero order COD removal rate constants (k_app), and the second order OH· formation rates (r_i) have been calculated. © 2001 Society of Chemical Industry     

Oxidation of Propylene Glycol Methyl Ether Acetate Using Ozone-Based Advanced Oxidation Processes

The present study investigates the degradation of PGMEA and its TOC removal using O₃, UV/O₃, O₃/H₂O₂, and UV/H₂O₂ processes under various experimental conditions. Ozonation of PGMEA was substantially enhanced in the presence of UV light and H₂O₂. Approximately 33% of TOC enhancement was noted in UV/O₃ process over ozonation process. A linear relationship between PGMEA and H₂O₂ decomposition was observed in O₃/H₂O₂ and UV/H₂O₂ processes. The influence of solution pH on the decomposition of PGMEA was investigated and found that basic medium was the most efficient in all AOPs. After 60 minutes 62.4%, 100%, 90% and 54% of PGMEA decomposition at pH 10.0 was observed in O₃, UV/O₃, O₃/H₂O₂, and UV/H₂O₂ processes, respectively. It is concluded that UV/O₃ process is a promising approach for the oxidation and removal of PGMEA.     

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.     

Efficiency and Kinetics of Catalytic Ozonation of Acid Red B over Cu-Mn/γ-Al2O3 Catalysts

The efficiency and kinetics of catalytic ozonation of Acid Red B over Cu-Mn/γ-Al₂O₃ catalysts were investigated. Cu-Mn/γ-Al₂O₃ catalysts were prepared by impregnation and characterized by X-ray diffraction and X-ray fluorescence. The removal efficiencies of Acid Red B and total organic carbon were up to 99.35% and 54.38%, respectively. The Cu-Mn/γ-Al₂O₃ catalysts were stable and easy to be reused. The interim products were analyzed by means of Vis-UV absorption spectrum. Cu-Mn/γ-Al₂O₃ catalytic ozonation of Acid Red B conformed to the pseudo–first-order kinetics reaction model.     

The Chemistry of Water Treatment Processes Involving Ozone,Hydrogen Peroxide and Ultraviolet Radiation

Advanced oxidation processes are defined as those which involve the generation of hydroxyl radicals in sufficient quantity to affect water purification. The theoretical and (practical yield of OH from O₃ at high pH, 0₃/H₂0₂, O₃/UV and H₂O₂/UV systems is reviewed. New data is presented which illustrates the importance of direct photolysis in the O₃/UV process, the effect of the H₂0₂:0₃ ratio in the O₃/H₂O₂ process, and the impact of the low extinction coefficient of H₂O₂ in the H₂0₂/UV process.     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

Diclofenac removal from water by ozone and photolytic TiO2 catalysed processes

BACKGROUND: The aim of this work was to establish the efficiency of single ozonation at different pH levels (5, 7 and 9) and with different TiO₂ photolytic oxidizing systems (O₂/UV‐A/TiO₂, O₃/UV‐A/TiO₂ or UV‐A/TiO₂) for diclofenac removal from water, with especial emphasis on mineralization of the organic matter. RESULTS: In the case of single ozonation processes, results show fast and practically complete elimination of diclofenac, with little differences in removal rates that depend on pH and buffering conditions. In contrast, total organic carbon (TOC) removal rates are slow and mineralization degree reaches 50% at best. As far as photocatalytic processes are concerned, diclofenac is completely removed from the aqueous solutions at high rates. However, unlike single ozonation processes, TOC removal can reach 80%. CONCLUSION: In single ozonation processes, direct ozone reaction is mainly responsible for diclofenac elimination. Once diclofenac has disappeared, its by‐products are removed by reaction with hydroxyl radicals formed in the ozone decomposition and also from the reaction of diclofenac with ozone. In the photocatalytic processes hydroxyl radicals are responsible oxidant species of diclofenac removal as well as by‐products. Copyright © 2010 Society of Chemical Industry     

Catalytic ozonation process using PAC/γ-Fe2O3 to Alizarin Red S degradation from aqueous solutions: a batch study

In the catalytic ozonation process used in this study, adsorption and chemical reactions were performed at the catalyst surface. This process can increase the efficiency of plain ozonation. The main aim of this study was to investigate the efficiency of the catalytic ozonation process in removing Alizarin Red S dye from colored water by Fe₂O₃ coated on PAC. In this work, activated carbon powder/γ-Fe₂O₃ nano-composite was modified. The BET results showed that the surface area in PAC and PAC-γ-Fe₂O₃ nano-composite was 654 and 450?m² g^?1, respectively. In this study, the best pH for removal of ARS was found to be 9. At a higher pH, the efficiency of the process decreased gradually. According to studies, catalysts increase surface area and active sites for more ozone degradation. Also, the characterization of the catalyst will play a very important role in the COP. Also, the maximum removal efficiency was observed in catalyst dose 1.1?g l^?1. The study results showed that the highest mineralization rate in ARS degradation was related to O₃/PAC/γ-Fe₂O₃. The amount of mineralization in the SOP, O₃-PAC, and O₃/PAC/γ-Fe₂O₃ was 13, 25, and 40%, respectively. The finding of mineralization of ARS using the SOP reflected the low power of the ozonation process for the mineralization of pollutants.     

Comparison of Low Pressure and Medium Pressure UV Lamps for UV/H2O2 Treatment of Natural Waters Containing Micro Pollutants

UV/H₂O₂ advanced oxidation is an effective barrier against organic micro pollutants. Several studies have focused on the degradation of a wide range of pollutants, but regarding the comparison of low-pressure mercury lamps (LP) with medium-pressure mercury lamps (MP) with respect to energy consumption by the UV/H₂O₂ process, little is known so far. Although the absorbance of H₂O₂ at 254 nm is low, the results of this research show that the yield of hydroxyl radical formation (OH_CT) with LP lamps is comparable or higher than with MP lamps. In a water matrix with a background absorbance due to organics and nitrate, H₂O₂ absorbs UV light very effectively at 254 nm. Generally, due to the contribution of direct photolysis, the degradation of pollutants is better with MP-UV/H₂O₂ than with LP-UV/H₂O₂ at the same UV fluence. Therefore, with LP-UV/H₂O₂ micro pollutants are predominantly degraded through reaction with OH radicals. However, due to the much higher efficiency of LP lamps in converting electrical energy to UV-C light, the energy required to achieve 90% degradation (E_EO) of pesticides and pharmaceuticals can be significantly lower with LP-UV/H₂O₂ than with MP-UV/H₂O₂. Results of bench-scale tests show E_EO data of the LP-UV/H₂O₂ process to be 30%–50% lower than for the MP-UV/H₂O₂ process. At these process conditions MS2 phage inactivation was found to be more than 8 logs for both MP-UV/H₂O₂ and LP-UV/H₂O₂.     

Photocatalytic Oxidation Processes In The Presence Of Polymers

The objective of the study was to investigate the removal of synthetic organic compounds and THM precursors by two photocatalytic oxidation processes in the presence of synthetic polymers. H₂0₂/UV and O₃/UV processes were tested on solutions of nitrobenzene and aquatic fulvic substances in the absence and presence of Polyethylene Oxide (PEO) and a Betz Polymer. The presence of high concentrations of PEO reduced the removal rate of nitrobenzene by competing with it for hydroxyl radicals. The presence of low concentrations of PEO did not significantly alter the removal rate of nitrobenzene and THM precursors. Experimental results indicated that even in the presence of the polymers, decomposition rather than coupling was the favored reaction pathway.