Origin and Conditions of Ketoacid Formation During Ozonation of Natural Organic Matter in Water

The batch ozonation of some fractions of aqueous humic substances (humic, fulvic and hydrophilic acids) extracted from natural waters is studied. The reaction leads to oxidation byproducts such as low molecular aldehydes and ketoacids. Formation conditions and origin of some of them (glyoxylic, pyruvic and ketomalonic acids) regarding the extracted fraction of natural organic matter is established.     

Using Fractionated Natural Organic Matter to Quantitate Organic Byproducts of Ozonation

An improved procedure was used to isolate and fractionate natural organic matter (NOM) in water for subsequent ozonation and disinfection by-product (DBP) and color removal quantisation. Isolated NOM fractions from two different sources, accounting for approximately 50 to 60% of the dissolved organic material and 60 to 75% of the color, were characterized and then ozonated under conditions approximating those encontered during drinking water treatment. The natural waters also were ozonated. Organic DBPs of either health concern or which may contribute to biological instability of finished water were investigated, including aldehydes, oxoacids and low molecular weight carboxylic acids. pH and ozone dosage were the parameters having the greatest effect on DBP formation. On the basis of UV absorbance measurements, the fulvic acid fractions studied taken together accurately represented the natural water and may be the primary sources of precursor material for aldehydes and oxoacid DBPs. However, as yet unidentified NOM fractions contribute significantly to carboxylic acid formation upon ozonation.     

Influence of Ozonation Conditions on Aldehyde and Carboxylic Acid Formation.

The influence of ozonation conditions (i.e. ozone dose and contact time) on the aldehyde and carboxylic acids formation was studied on a pilot scale. The data derived from changes in the molecular weight distribution of natural organic matter (NOM) and the concentration of residual ozone can be applied to a selection of the optimum ozonation conditions. The results confirm the relative ease with which ozone reacts with the organic matter. The short contact time (4–6?min) appeared to be sufficient for the reaction. The higher molecular weight (1600?D) fraction of NOM seems to be slightly more reactive to ozone than the lower molecular weight fraction (500?D). It was also observed that carboxylic acids had been formed at much higher quantities than aldehydes. Two differently acting groups of aldehydes were identified. The concentration of the first one (i.e. formaldehyde, acetaldehyde) strongly depends on ozone dose, while the concentration of the second group of aldehydes (i.e. glyoxal, methylglyoxal) seems to be relatively independent of the ozone dose.     

Effect of Ozone in UF-Membrane Flux and Dissolved Organic Matter of Secondary Effluent

The focus of this work was to determine the effect of ozone on the removal of dissolved organic matter (DOM) from a secondary effluent and its relation with the permeated flux behavior in an ultrafiltration membrane. To assess the ozone action, the DOM of the secondary effluent was fractionated into its hydrophobic, transphilic and hydrophilic fractions, using XAD-8 and XAD-4 resins. Ozone increased the hydrophilic fraction from 32% to 42%, and this percentage remained unchanged after ultrafiltration of the secondary effluent. Permeate flux dropped to 52% in the first hour of membrane operation, but when ozone was applied as a pretreatment, it could be maintained at 84% within the first hour.     

Effect Of Ozonation On Some Physical and ChemicalProperties Of Aquatic Natural Organic Matter

Natural Organic Matter (N0M) was isolated and extracted from a moderately-colored surface water, then fractionated using hydrophobic and ion exchangeresins into eight groups. Each was subjected to batch ozonation, and the rateof loss of ozone was measured. Then, selected fractions were analyzed forchanges in functional group content, molecular size and hydrophobicity; somewere further fractionated by size prior to functional group analysis. Fulvicacids and humic acids were the most reactive. These groups also showed thegreatest change in carboxyl group content and hydrophobicity. The results arediscussed with respect to impacts on coagulation. Although hydrophilicneutrals were of low to moderate reactivity, they showed the greatest promisefor improved coagulation following preozonation.     

Effects Of Ozone-Hydrogen Peroxide Combination On The Formation Of Biodegradable Dissolved Organic Carbon

The effects of ozone and ozone/hydrogen peroxide on BDOC formation were studied with the “Ozotest” method, a laboratory technique that permits the assessment of oxidation efficiency. Oxidation treatments were performed on river water and sand filter effluent samples. Ozone consumption, reduction of UV absorbance, and BDOC formation were monitored during the experiments. The ratio of 0.35-0.45 mg H₂O₂ per mg O₃ used to degrade pesticides also was optimal for the oxidation of organic matter. BDOC formation versus ozone dose curves with ozone alone or ozone/peroxide system were similar. BDOC formation was optimum at an applied ozone dose of 0.5-1 mg O₃/mg C (contact time = 10 min). The ozone/peroxide system yielded lower BDOC values than ozone alone, a phenomenon related to differences in byproducts generated by the two oxidative systems. Moreover, reduction of the concentration of DOC was higher with ozone/hydrogen peroxide than with ozone alone. For both oxidant systems, BDOC formation occurred during the first minute of treatment.     

Formation Of Aldehydes During Ozonation

This study investigated the formation of aldehydes after ozonation of three real and three model waters reconstituted from hydrophobic organic material. The four main aldehyde species formaldehyde, acetaldehyde, glyoxal, and methyl glyoxal were analyzed. Formaldehyde was the dominant species formed as a result of ozonation. The different waters varied greatly with respect to aldehyde production under similar treatment conditions. Studies conducted with model waters allowed for exploring aldehyde formation as a function of various water quality parameters. Overall, the hydrophobic organic extracts appeared to have greater aldehyde formation potential than the hydrophilic organics. Aldehydes were formed in direct proportion to the total organic carbon (TOC) concentration of the water at a 1:1 ozone-to-TOC ratio. Greater aldehyde formation was observed at lower ozonation pH values. Bromide ion and inorganic carbon added to model waters appeared to have no effect on aldehyde production. Finally, Assimilable Organic Carbon (AOC) measurements exhibited a strong correlation between aldehyde production and AOC production.     

Formation and Removal of Biodegradable Ozonation By-Products during Ozonation-Biofiltration Treatment: Pilot-Scale Evaluation

An ozonation-biological filtration pilot-scale study was performed to evaluate the formation and removal of biodegradable ozonation by-products. The formation of aldehydes and ketoacids was found to be proportional to the DOC concentration and ozone dosage, and a strong relationship between the formation of aldehydes, ketoacids, and biodegradable dissolved organic carbon (BDOC) was observed. Four types of granular activated carbon (GAC) and one nonadsorbing medium, biolite, were employed to evaluate the performance of biofiltration for removing ozonation by-products. It was observed that GAC filters developed biological activity sooner than the biolite filter. Once developed, biofilters, either GACs or biolite, were particularly effective in the removal of aldehydes, ketoacids and BDOC.     

Parameters Affecting the Formation of Bromate Ion During Ozonation

Batch type ozone experiments conducted on aquatic humic substances solutions spiked with bromide ion were developed to evaluate the importance of various parameters that may affect the formation of bromate ion during ozonation. The nature of the NOM, the alkalinity, the bromide ion content and the presence of ammonia were found to significantly affect the bromate ion production. Temperature and pH can be considered as minor factors. The ozonation of a clarified surface water using a continuous flow ozone contactor have shown that the addition of a low quantity of ammonia (0.05 to 0.1 mg/L NNH₄ ⁺) appeared to be an interesting option for controlling the bromate formation. On the contrary, the addition of hydrogen peroxide may enhance or reduce the bromate ion production, depending on the applied hydrogen peroxide/ozone ratio.     

Effects Of Ozone On The Production Of Biodegradable Dissolved Organic Carbon (BDOC) During Water Treatment

This article deals with the oxidation effect of ozone on the increasing fraction of biodegradable organic matter with the “ozotest” method, a laboratory technique which simulates the effect of ozonation and allows a complete oxidation assessment. Ozone treatment was performed on river water samples and sand filter effluent samples. Ozone consumption, reduction of UV absorbance and BDOC formation were monitored with applied ozone doses from 0 to 10 mg/L and with contact times from 0 to 60 min. The BDOC formation was optimum at an applied ozone dose of 0.25-0.5 mg O₃ per mg DOC (contact time = 5 min) corresponding to apparition of traces of residual ozone and maximum UV reduction. Maximum ozone consumption, UV reduction and BDOC formation occurred simultaneously during the first two minutes of treatment. Concerning BDOC formation, applied ozone dose showed a greater effectiveness than contact time. For the same quantity of consumed ozone, a short contact time associated with a high ozone dose was preferable to a long contact time and a low ozone dose.     

Kinetics of Natural Organic Matter as the Initiator,Promoter, and Inhibitor,and Their Influences on the Removal of Ibuprofen in Ozonation

Natural organic matter (NOM) can simultaneously act as the initiator, promoter and inhibitor in water ozonation. This study presents an explicit method that can be used to determine these rate constants via the integration of the transient steady-state hydroxyl radical (?OH) model, the R_ct concept and the pseudo first-order ozone decomposition model. The theoretical background of this method was provided, and the method was validated with model compounds. The rate constants of three NOM isolates were determined using the developed method. With these rate constants, the influences of NOM on the degradation of ibuprofen, an ?OH-reactive pharmaceutical compound, can be quantitatively described. [Supplementary materials are available for this article. Go to the publisher's online edition of Ozone Science &; Engineering for the following free supplemental resources: tables, figures, and equations.]     

Effect of Ozone on Removal of Dissolved Organic Matter and its Biodegradability and Adsorbability in Biotreated Textile Effluents

A study was conducted on the efficacy of ozonation in removing dissolved organic matter (DOM) in biotreated textile effluents and effects on its biodegradability and adsorbability. Results showed the efficient removal of color and fluorescence compounds were achieved through ozonation, due to increasing hydrophilicity and lowering molecular weight of DOM. A significant biodegradability improvement was also observed, and DOM adsorbability on activated carbon was highly dependent on ozone dosage. As the key parameter, consumed 3.8 g O₃/?g TOC₀ was the optimal dosage in the hybrid process combining ozonation with biological activated carbon (BAC) for wastewater reclamation.     

Removal of Color and Organic Matter in Industrial Phosphoric Acid by Ozone: Effect on Activated Carbon Treatment

Industrial phosphoric acid at 42-45% P₂O₅ and containing organic matter (OM) in the range of 220 mg/L to 300 mg/L is treated by combined ozonation and activated carbon. Ozonation alone removes the initial dark color of the acid and eliminates the organic content. Adsorption on activated carbon alone can reduce OM levels by 80% for more than 25 g/kg P₂O₅. We find that a preozonation noticeably enhances activated carbon efficiency and reduces its specific consumption. Isoconversion curves are plotted in specific ozone and activated carbon ratio space.     

Two-Stage Optimization of Coliforms,Helminth Eggs,and Organic Matter Removals from Municipal Wastewater by Ozonation Based on the Response Surface Method

In this study, a set of municipal wastewater (MWW) samples from an actual residual water treatment plant was treated by ozone. The residual water was characterized in terms of organic load and biological contaminants: total coliforms (TC), fecal coliforms (FC) and helminth eggs (HE). Initial values of these parameters were 2.8 × 10⁷ MPN/100 mL, 8.48 × 10⁶ MPN/100 mL, and 470 L^?1, respectively. The experimental setup considered the modification of pH and ozone dose as independent variables. Three different initial pH values (4.0, 7.0, and 11.0) and three different ozone concentrations (6, 15, and 30 mg/L) were used to investigate the pH ozone dose effect. The efficiency of ozone-based treatment was determined by the reduction of the microbiological indicators (TC, FC, and HE) and physicochemical parameters (COD and turbidity). The response surface method was used to determine suboptimal reaction conditions. These conditions were obtained using a two-stage procedure. The conditions under which both microbiological and organics were better removed corresponded to pH 7.8 and ozone concentration of 15.5 mg/L. A decline of biological indicators of 99% for TC, 99% for FC, and 99% for HE was obtained under the same reaction conditions. The reduction of chemical oxygen demand (COD) and turbidity was 75% and 85% under the same operation conditions, respectively.     

Examining the Role of Effluent Organic Matter Components on the Decomposition of Ozone and Formation of Hydroxyl Radicals in Wastewater

The impact of wastewater derived effluent organic matter (EfOM) on the decomposition of ozone and formation of hydroxyl radicals (HO^●) was evaluated for four wastewaters (sites A, B, C1 and C2). The reactivity of EfOM was assessed by fractionation into four apparent molecular weight (AMW) fractions (<10 kDa, <5 kDa, <3 kDa, and <1 kDa). The R_CT, defined as the ratio of HO^● exposure to ozone exposure (∫HO^●dt?/?∫O₃dt), was measured for all fractions and bulk waters (at times greater than 5 seconds), with an initial ozone dose equal to the total carbon concentration of EfOM (ozone:DOC ratio of 1). The R_CT of all the samples and ozone first-order decay rates of two of the waters increased significantly (95% confidence) from the bulk sample to the <10 kDa fraction, and decreased with AMW. This indicates that the intrinsic capacity of different molecular weight fractions of the EfOM have different reactivity with ozone.     

Removal Mechanism of Natural Organic Matter and Organic Acid by Ozone in the Presence of Goethite

The oxidations of natural organic matter (NOM) and a model compound (p-chlorobenzoic acid) were characterized using ozonation and catalytic ozonation processes. In general, the catalytic ozonation showed better performance in the removal of organics tested in the study. The hydrophobic, transphilic, and hydrophilic NOM fractions were isolated using XAD-8 and -4 resins to evaluate the reaction characteristics. The catalytic ozonation in the presence of goethite accomplished the higher removal of NOM with simultaneous reduction of the three fractions than the ozonation which removed the hydrophobic portion only. The analysis of discrete size distributions of NOM revealed that ozonation yielded a removal of >1,000MW and an increase of <1,000MW, whereas all molecular weight fractions reduced after catalytic ozonation. The concentrations of model compound and aqueous and gaseous ozone were monitored during the oxidations, and efficiencies were compared for cases in the absence and presence of iron oxide (FeOOH).     

Ozone Consumption in Natural Waters: Effects of Background Organic Matter,pH and Carbonate Species

It was demonstrated that, in natural waters, the overall kineticsof dissolved ozone consumption can be characterized by the “specific ozone utilization rate”, w[time ^?1]. The dependency of w on the chemical quality of the raw water was analyzed. And, the variation of w values measured in different water samples was explained in terms of the pH, alkalinity, and total organic carbon content of the solution matrix.     

Improving the Biodegradation of Organic Pollutants with Ozonation during Biological Wastewater Treatment

Pre-ozonation is often used to enhance the biodegradability of recalcitrant compounds prior to biological treatment of wastewater. A usual shortcoming of such an approach is wasting ozone on other compounds that are already biodegradable. This research followed a groundbreaking approach of degrading a recalcitrant substance with ozone during biological treatment. Two parallel bench-top activated sludge processes were fed a synthetic wastewater containing typical biodegradable substances and also methylene blue at 5 mg/L. Ozone was applied continuously and directly into one of the activated sludge units at 17 mg/L based on inflow rate. The methylene blue was removed by 95%?in the ozonated process compared with just 40%?removal in the non-ozonated control. The removal in the activated sludge without ozonation was demonstrated to be mainly due to biosorption. The ozone oxidation reaction by-products were analyzed using GC-MS on volatile substances collected in the headspace above ozonated samples of methylene blue and most found to be biodegradable. These by-products are expected to be degraded and assimilated in the same process unit together with the other biodegradables in the feed stream by the activated sludge process. The reaction rate with organic substances depleted the dissolved ozone at such a rate that the inactivation of the treatment bacteria (and protozoa) was minimal, mostly affecting the filamentous bacteria. A concern that ozone, as a powerful disinfectant, could inhibit or kill the beneficial bacteria in the activated sludge process was proven to be incorrect.