Applicability of Ozonation Combined with Electrolysis to 1,4-Dioxane Removal from Wastewater Containing Radical Scavengers

In this paper, applicability of ozonation combined with electrolysis as an advanced oxidation process for the removal of 1,4-dioxane from synthetic wastewater, has been studied. The combined process easily decomposed 1,4-dioxane, and two byproducts were detected in treated water. Although bicarbonate alkalinity was a strong radical scavenger, its influence was abated by air-stripping of carbon dioxide at the anodic compartment of the reactor. Free chlorine produced through anodic oxidation of chloride ion accelerated the COD removal from wastewater, despite the fact that this ion acted as a weak radical scavenger. The combined process was demonstrated to be applicable to the treatment of wastewater containing high concentration of bicarbonate alkalinity and chloride ions.     

Evaluation Of Genotoxic Potency On Substances Contained In Night Soil And Its Reduction Performance By Ozonation

Bacterial assay which can detect the genotoxicity, induction of error-prone repair genes on DNA was applied to samples which were collected at a night soil treatment plant. The genotoxicity of each sample was measured by using this bacterial assay, called the umu test. Strong genotoxic potency was found in the sediments of raw night soil, that is, human feces. There are some substances which show toxicity to the DNA and are attributable to the baked foods or metabolites in human digestive organs. These potencies could not be removed easily in the biological decomposition process through survey of the treatment plant. It was quite clear that more effective reduction could be achieved by ozonation at the treatment condition of about 1 mg O₃/mg C.     

Effect of Separation of Ozonation and Electrolysis on Effective Use of Ozone in Ozone-Electrolysis Process

For improving the ozone consumption efficiency (OCE) of the ozone-electrolysis process, an ozone-electrolysis system with an independent electrolytic cell from an ozone contactor (indirect ozone injection system) and a three-dimensional electrode were introduced in this study. The reactor successfully enhanced the OCE and the ratio of 1,4-dioxane degradation rate to ozone injection rate (RDO) in comparison with the previous reactor. The three-dimensional electrode also contributed the improvement of the OCE and the RDO due to lowering the current density on the cathode. As the indirect ozone injection system allows higher degree of freedom for the reactor design, it is useful for application of ozone-electrolysis to practical water treatments.     

Catalytic Ozonation of Sulfosalicylic Acid

The investigation of heterogeneous catalytic ozonation of sulfosalicylic acid (SSal) in aqueous solution is reported in this paper. It was found that catalytic ozonation in the presence of V-O supported on silica gel had a more positive effect on the removal rate (62% in 30 min) of total organic carbon (TOC) than that of ozonation alone (20% in 30 min), and the catalyst supported on TiO₂ had similar results. The experimental results also showed that the ozone dosage should be sufficient for achieving the catalytic effect. Efficient removal of TOC in catalytic ozonation was probably attributed to producing more powerful oxidants than molecular ozone.     

Removal of Pesticides by a Combined Ozonation/Attached Biomass Process Sequence

Different combinations of ozonation and biological treatments were tested on an industrial effluent containing high pesticide concentrations. Ozonation was performed in 450 L columns at 1.5 h HRT each. Biological treatment was carried out in a submerged filter (BIOFOR). Ozone was effective in removing herbicides but dosages up to 1000 mg L^?1 were needed. The improved biodegradability of the organic compounds after pre-ozonation was demonstrated by Oxygen Uptake Rates (OUR) tests and by the efficiency of biological treatment towards COD, and pesticides. The Italian discharge limit of 50 ppb total pesticides was achieved by combining pre-ozonation, biological treatment, and post- ozonation.     

Performance and Mechanism on Degradation of Estriol Using O3/PS Process

In this study, enhanced ozonation of estriol (E3) with persulfate (PS) was investigated in aqueous solution. Simultaneous generation of hydroxyl radical (?OH) and sulfate radical (?SO₄^?) by O₃/PS process was proposed and experimentally verified. Kinetic results revealed that the degradation of E3 was affected by the solution pH, PS concentration, O₃ dosage and E3 initial concentration. The optimal reaction rate was observed in alkaline solutions. The mechanism for the synergistic effect was preliminarily explored by the addition of hydroxyl and sulfate radical scavengers. The enhanced degradation of E3 by O₃/PS was also observed in actual water samples, which provided impetus for practical applications. The degradation intermediates were detected using LC/MS. Results showed that the phenol structures of the estrogens were mostly oxidized to cyclohexenone moieties and quinone-like structures.     

Ozonation of Cyanide Catalyzed by Activated Carbon

In this work, the removal of cyanide from aqueous solutions was accomplished by using the synergetic effect of activated carbon and an oxidizing agent. A basic-character coconut shell activated carbon (CAC) was used; experiments were conducted in a semi-batch reactor, at 25 °C, initial pH of 11.5, and using cyanide solutions with initial concentration up to 1200 mg/mL. In particular, the beneficial effect of an oxidizing agent such as air, oxygen or ozone on the removal of cyanide by CAC was evaluated. At the optimum operating conditions found in this study, 1200 mg/mL of cyanide were totally decomposed in about 3 h, by using 1 g of CAC and about 2 mgO₃/min. The experimental results were rationalized based on different mechanisms reported in the literature. The findings provide the basis to optimize the removal of cyanide from aqueous solutions in mining or metallurgical effluents by using the synergetic effect of CAC and ozone.     

Formation of Nitrates in Aqueous Solutions Treated with Pulsed Corona Discharge: The Impact of Organic Pollutants

Pulsed corona discharge (PCD) in oxygen-nitrogen mixtures results in formation of nitrogen oxides, transformed to aqueous nitrates in contact with water. The experimental research into the impact of formate and oxalate to nitrate formation in aqueous solutions treated with PCD was undertaken. The impact of paracetamol, ibuprofen, indomethacin and their oxidation products to nitrate formation was also analyzed. Pharmaceuticals obstructed nitrate formation, while carboxylic anions and pharmaceuticals’ oxidation products noticeably improved nitrate formation in treated solutions as compared to water. The nitrate formation enhancement is explained by the aqueous ozone decomposition and hydroxyl radical formation known to be improved by carboxylic anions.     

Solid Phase Catalytic Ozonation Process for the Destruction of a Model Pollutant

Pure metal oxides, mixed metal oxides, and platinum metals were evaluated as ozonation catalysts. Batch reactor experiments were performed using deionized water at pH 7 and semi-continuous ozonation experiments were performed using a natural water. p-Chlorobenzoic acid (pCBA), a non-adsorbing model micropollutant that does not react directly with molecular ozone, was included in both solution matrixes. Titanium dioxide, cobalt oxide, nickel oxide, copper oxide, and a mixed metal oxide comprised of copper, zinc, and aluminum did not accelerate the removal pCBA in deionized water. However, cobalt oxide and the mixed metal oxide catalyst were effective at accelerating the removal of pCBA in a natural water matrix. The mixed metal oxide catalyst may have the most potential as an ozonation catalyst because it also was very stable (i.e., low solubility). A ruthenium / alumina catalyst also increased the removal of pCBA, but this metal may follow a different reaction mechanism than the metal oxide catalysts.     

Influence of Carbonate on the Ozone/Hydrogen Peroxide Based Advanced Oxidation Process for Drinking Water Treatment

The influence of carbonate on the ozone/hydrogen peroxide process has been investigated. Carbonate radicals, which are formed from the reaction of bicarbonate/carbonate with OH radicals, act as a chain carrier for ozone decomposition due to their reaction with hydrogen peroxide. The efficiency of bicarbonate/carbonate as a promoter for the radical-based chain reaction in presence of hydrogen peroxide has been calibrated and compared to a well-known chain promoter (methanol) and an inhibitor (tert-butanol). Relative to tert-butanol, the hydrogen peroxide induced ozone decomposition is accelerated by bicarbonate/carbonate. Relative to methanol, bicarbonate/carbonate in presence of hydrogen peroxide is less effective as a promoter under comparable experimental conditions.     

Oil-Refinery Wastewater Treatment Aiming Reuse by Advanced Oxidation Processes (AOPs) Combined with Biological Activated Carbon (BAC)

The treatment of a refinery wastewater by Advanced Oxidation Processes (AOP) coupled with Biological Activated Carbon (BAC) was investigated aiming to generate water for reuse. O₃/UV and H₂O₂/UV processes were employed to oxidize the organic matter and the BAC process to remove residual organic matter from the AOP effluent. AOP promoted oxidation of recalcitrant organic matter as observed by moderate drops on the treated wastewater absorbance (31–79%) and TOC values (10–18%). BAC filters showed to be effective, reaching average efficiencies of 65% in a sufficiently long period of operation (84 days), while GAC filters were saturated after 28 days. Effluent TOC values in the range of 4 to 8.5 mg/L were achieved by the combined treatment (H₂O₂/UV + BAC), allowing water reuse.     

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.     

Practical Studies of the Electrolysis and Volatilization of the Bromide from Drinking Water to Minimize Bromate Production by Ozonation

In four recently published articles, a process for the oxidation of bromide to bromine and the volatilization of bromine from drinking water sources was presented. This process was shown to be able to remove up to 35% percent of the bromide found naturally in the California State Water Project. Although bromide itself is quite harmless, it has been shown to react with commonly used disinfectants to produce compounds or disinfection by-products (DBPs) of suspected carcinogens. Bromide reacts with ozone to form bromate. This article presents two studies of pilot scale, flow-through electrolytic reactors that oxidize bromide to bromine and volatilize bromine at <pH 3.5, which occurs at the anode as a result of the oxidation of water. One reactor had 14 anodes that were 91 cm deep and the other had 13 anodes 1.2 cm deep. The bromide removal rates were studied at several different water flows and power settings for different bromide concentrations for both reactors. The results show removal of bromide is impacted by water flows and power settings for different bromide concentrations. Effluent from the deep reactor did show some reduction in bromate concentration as compared to control samples but the results were inconsistent. This appeared to be caused by significant differences in the ozone demand produced by different experimental conditions, difficulty determining the concentration of chlorine, and the use of hydrogen peroxide as a dechlorinating agent. Using the shallow reactor, these difficulties were overcome by developing a more consistent determining chlorine concentration, using much larger ozone doses to overwhelm the ozone demand, and by using ascorbic acid instead of hydrogen peroxide. With these changes, it could be shown that the electrolytic reactor not only lowered the concentration of bromide in the water but when ozonated, the amount of bromate formed was reduced in direct proportion to the amount of bromide removed for an equal dose of ozone.     

State-of-the-Art of the Application of Ozonation in BENELUX Drinking Water Treatment

Major objectives for drinking water treatment are microbiological integrity, organic contaminant control and the production of biologically stable water. In view of these objectives many BENELUX water supply companies have upgraded their treatment plants. In many retrofit plants ozonation has been implemented.     

Catalytic Ozonation with Supported Titanium Dioxide. The Stability of Catalyst in Water

This paper presents the results obtained with heterogeneous catalytic ozonation in which model and natural waters are ozonated in the presence of titanium dioxide (TiO₂) supported on alumina. In this work the stability of the catalyst is investigated. Four consecutive ozonations with the same catalyst revealed no reduction in the organic matter oxidation. The results obtained in natural waters with catalysts that had been previously used indicated that the applied catalysts did not appear to lose any of their efficiency after use.     

Degradation of Oxalic Acid and Bisphenol A by Photocatalytic Ozonation with g-C3N4 Nanosheet under Simulated Solar Irradiation

Photocatalytic ozonation of organics under simulated solar irradiation with a g-C₃N₄ nanosheet was investigated. g-C₃N₄ was prepared by calcinations of urea and characterized by TEM, BET, XRD and UV-Vis. Oxalic acid and bisphenol A were used as model substances to evaluate its catalytic ability. The results showed that g-C₃N₄ possess 2D nanosheet structure. The degradation ratio of oxalic acid and bisphenol A with g-C₃N₄/O₃/Solar was 1.50 and 1.92 times as great as the sum ratio when it was individually degraded by g-C₃N₄/Solar and O₃, separately. The results of recycling experiment indicated that g-C₃N₄ catalyst is very stable under experimental conditions.     

Effect of Inorganic Ions on the Oxidative Efficiency of Ti(IV)-Catalyzed H2O2/O3 Process in the pH Range of 1.0 to 6.0

The oxidative efficiency of Ti(IV)-catalyzed H₂O₂/O₃ (Ti(IV)/H₂O₂/O₃) for acetic acid (HAc) degradation was investigated in the initial pH range of 1.0 to 6.0, and the effects of some common inorganic ions were also discussed in detail. The results showed that the effects of SO₄ ^2? and NO₃ ^? on the efficiency of Ti(IV)/H₂O₂/O₃ were negligible. However, adding Br^? greatly reduced the removal rate of HAc. The presence of Cl^? also reduced the efficiency of Ti(IV)/H₂O₂/O₃, but its negative effect became negligible in the initial pH range of 4.5 to 5.5. The presence of H₂PO₄ ^? could improve the removal rate of HAc, and addition of sodium carbonate had no influence on the efficiency of Ti(IV)/H₂O₂/O₃ in the initial pH range of 4.5 to 5.5.     

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.     

Degradation of Refractory Organic Pollutants by Catalytic Ozonation—Activated Carbon and Mn-Loaded Activated Carbon as Catalysts

A novel catalyst for the ozonation process was prepared by loading manganese on the granular activated carbon (GAC). Nitrobenzene was used as a model refractory organic micropollutant in this study. The catalytic activity of GAC and the Mn-loaded GAC were studied respectively. The removal efficiency of nitrobenzene by Mn-loaded GAC catalyzed ozonation could reach 34.2–49.9%, with the oxidation efficiency being about 1.5–2.0 times higher than that achieved in GAC catalyzed ozonation and 2.0–3.0 times higher than that achieved by ozonation alone. The effect of pH and the t -butanol on the GAC/ozone process was discussed. The optimum condition for preparing the catalyst was studied.