Destruction of Volatile Organic Contaminants in Drinking Water by Ozone Treatment

Controlled, pilot-plant ozone treatment tests were conducted on twenty-nine volatile organic contaminants in distilled water and groundwater. Results show that aromatic compounds and alkenes are well removed by ozone treatment, but that alkanes are poorly removed. Also, efficiency of destruction improved for the alkenes and aromatic compounds with increasing applied ozone dosage and, for some alkanes, with increasing pH. For most compounds, the efficacy of ozone was not severely affected by the background water matrix. Generally, information gathered from the literature regarding rate constants for the ozone treatment of compounds in the gaseous phase or in organic solution predicted, to a useful degree, the effectiveness of ozone in treating aqueous solutions in the present study.

Several of the test conditions selected for this preliminary study may be similar to those found in drinking water treatment plants. Consequently the findings of this research may help guide utilities in their choice of alternative treatments to meet Maximum Contaminant Levels for volatile organic contaminants such as trichloroethylene and benzene.     

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.     

Removal of Adsorbable Organic Halides from Water Containing Bromide Ions by Conventional and Advanced Oxidation

The article focuses on an assessment of adsorbable organic halides degradation during the process of conventional ozonation and advanced oxidation as far as the water containing bromides is concerned. The amount of AOX in the water examined varied from 59 to 105 μg Cl^?/L, and the bromides concentration exceeded 200 μg Br^?/L. The effects obtained by O₃ and O₃/UV methods were compared with the results achieved for the water which underwent only UV irradiation. The analysis of presented research results shows that out of the examined oxidation methods, in water of pH 6.8–9.5 and temperature of approximately 287 K, the highest degree of AOX decomposition, was achieved by UV irradiation of water, which was previously subjected to ozonation. However, when the ozone dose reached ≥ 0.3 mg O₃/mg C in an alkaline environment, bromates were formed in amounts exceeding the maximum contaminant level in both processes.     

Application of Oxidation by a Combined Ozone/Ultraviolet Radiation System to the Treatment of Natural Water

When treating natural water, the simultaneous use of ozone and UV rays can lead to high level oxidation of the ozone–refractory organics. The main parameters affecting the efficiency of the O₃/UV system are: the ozonation rate, the average UV radiation intensity, the pH measurement, alkalinity, and the type of compound to be oxidized.

In optimum Ou/UV system application conditions, the abatement of COD in water from the Seine river is never above 30%. On the other hand, TOC removal is increased in weakly carbonated pond water loaded with humic matter. The O₃/UV system also ensures oxidation of saturated volatile organic halogens, with the exception of carbon tetrachloride.     

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.     

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.     

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.