Effects of Ozonation on Molecular Weight Distribution of Humic Substances and Coagulation Processes – A Case Study: The Úzquiza Reservoir Water

In this article the influence of preozonation on the effectiveness of NOM removal via coagulation processes will be studied (focusing on the influence of the calcium hardness) as well as changes in MW (molecular weight) distribution of humic substances caused by ozonation. Additionally, THMFP removal in both ozonation and preozonation-coagulation processes is assessed. Three different types of water have been used in this study: a natural water from the Úzquiza Reservoir (Burgos, Spain), a synthetic water prepared using natural fulvic acids extracted from the Úzquiza Reservoir and a synthetic water prepared using a commercially supplied humic acid. Molecular weights of humic substances were determined using high-performance size exclusion chromatography (HPSEC); average molecular weights calculated for the unozonated humic substances are 4500 Da for the commercial humic acids and 1000 Da for the natural fulvic acids extracted from the Úzquiza Reservoir. Preozonation shifted the molecular weight distribution of humic substances (both humic and fulvic acids) towards lower average molecular weight values. For the natural water from the Úzquiza Reservoir (with low levels of calcium hardness and hydrophobic fraction (humic substances) being the main fraction of NOM), preozonation has a negative effect on the effectiveness of the coagulation process for NOM removal: the percentages of TOC removal via coagulation decrease with increasing ozone dosage; the maximum TOC removal (33%) is achieved for the unozonated water. Also for this water, ozonation reduced 5–25% of THMFP with ozone doses varying from 0.25 to 2.5 mg O₃/L. A preferential THMFP removal, that is to say, higher reduction in THMFP (43%) relative to TOC (28%) is achieved by the coagulation-flocculation process; this also occurs when preozonation is used, independently of ozone dosage.     

Toward Elucidating Mechanism And Kinetics Of Ozone Decolorization And Dechlorination Of Pulp Mill Effluents

This study elucidated the mechanism and kinetics of ozone decolorization and dechlorination of composite wastewaters obtained from various pulp mill effluents by means of ultrafiltration and freeze drying. These raw samples had similar initial true color but varied color intensity (C.I.) and biodegradability. Both raw and ozone-treated samples were separated into four components to assess the effects of ozonation on individual components. Analytical HPSEC was employed to determine the changes induced by ozonation in molecular weight distribution of lignins and their derivatives.     

Ozonation of humic acid in water

BACKGROUND: Humic acids (HAs) are heterogeneous macromolecules widely dispersed in natural waters, which display significant resistance to biodegradation. Removal of HA by ozone and its related reaction mechanisms are investigated. RESULTS: Ozonation of HA showed a significant reduction of UV₂₅₄, Color₄₃₆ and had the capability of mineralizing the TOC to CO₂ and improving the biodegradability. Fourier trandform infrared (FT‐IR) spectra, elemental composition analysis and high performance size exclusion chromatography (HPSEC) revealed that ozonation could not only change the structure characteristics but modify the molecular size distribution of HA. Volatile compounds detected by gas chromatography‐mass spectroscopy (GC‐MS) showed that ozonation brought out 43 different organics, which were identified as mainly: aldehydes, ketones, aromatics, carboxylic acids and alcohols. CONCLUSION: Ozonation of HA could be elucidated by the followed mechanism: ozonation with its direct and indirect pathway hydroxylated the HA in water, and polyhydroxy HA was further oxidized to bond rupture leading to the change of molecular structure and size distribution of HA, trimming out a series of small molecular volatile compounds. The volatile compounds with electron denoting group could be further oxidized to acids and esters, and even totally mineralized to CO₂. Copyright © 2007 Society of Chemical Industry     

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.     

Ozonation of Humic Substances: Effects on Molecular Weight Distributions of Organic Carbon and Trihalomethane Formation Potential

Four different sources of humic substances were studied to determine the effects of ozonation on molecular weight-distributions, based on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP). Solutions of two soil-derived fulvic acids and a one soil-derived humic acid, as well as dissolved organic matter (DOM) associated with a natural water source were studied. Both gel permeation chromatography (GPC) and ultrafiltration (UF) were employed to define apparent molecular weight (AMW). Applied ozone doses ranged from 2.0 to 2.5 mg O₃/mg DOC. Overall samples of untreated and ozonated waters, as well as individual molecular weight fractions, were characterized according to DOC, UV absorbance, and THMFP. Ozonation resulted in a significant disappearance of higher AMW material with a corresponding increase in lower AMW material. Although little overall reduction in DOC concentration was observed, significant overall reductions in UV absorbance and THMFP levels were observed.     

Ozonation of Several Organic Compounds Having Low Molecular Weight under Ultraviolet Irradiation

Ozonation of several low molecular weight organic compounds under ultraviolet irradiation was studied. Nine compounds were identified as reaction products of the ozonation of phenol which was promoted by the simultaneous use of ozone and ultraviolet irradiation. In the case of several organic compounds having carbon numbers from one to six, the removal of total organic carbon (TOC) by this simultaneous use was higher than by either the ozone oxidation method or the ultraviolet irradiation method for all the compounds.     

Improvement of Biodegradability of Oil Field Drilling Wastewater Using Ozone

The possibility of improving the biodegradability of drilling wastewater using ozone was investigated following coagulation pretreatment. The biodegradability of wastewater was improved significantly following the start of ozonation, and the molecular weight of organic compounds decreased continuously with the progress of oxidation. It is interesting that minimum biochemical oxygen demand, total organic carbon (BOD/TOC) ratio (0.4 g/g) was observed when wastewater was treated with ozone continuously for 15 min. The combination of ozonation for 5 min (ozone consumption ratio of 2.6 g ozone/g TOC) followed by biological degradation produced a total TOC removal rate of 54.3%, which was comparable to direct ozonation for 30 min under the same conditions (TOC removal rate of 54.9%; ozone consumption ratio of 8.7 g ozone/g TOC). It is clear that biological treatment following short-term ozonation was very efficient in TOC removal. A process of successive coagulation-precipitation, ozone oxidation, and biodegradation seemed to be a good option for drilling wastewater treatment.     

Ozone Oxidation of Pulp and Paper Wastewater and its Impact on Molecular Weight Distribution of Organic Matter

The impact of ozone oxidation on removing high molecular weight (HMW) organics in order to improve the biodegradability of alkaline bleach plant effluent was investigated using a semi-batch reactor under different initial pH (12 and 7). After the ozonation process, the ratio of BOD₅/COD increased from 0.07 to 0.16 and 0.22 for initial pH 12 and 7, respectively. Also, the effluent color decreased by 48% and 61% at initial pH 12 and pH 7, respectively. These changes were primarily driven by reductions of the HMW fractions of the effluent during ozonation.     

Combined ozone pretreatment and biological processes for removal of colored and biorefractory compounds in wastewater from molasses fermentation industries

BACKGROUND: The use of ozone combined with biological treatment was investigated for molasses fermentation wastewater containing highly concentrated, brown and biorefractory compounds. These persistent compounds, known as melanoidins, generate disposal issues: in the environment, the color is problematic for aquatic life; and in municipal wastewater treatment plants, the molecules are biorefractory. RESULTS: This paper aims to evaluate the impact of ozone pretreatment, applied in the range 0.1 to 1 g g^?1 consumed ozone doses, on both macroscopic physico‐chemical parameters such as chemical oxygen demand (COD), total organic carbon (TOC), color and UV absorbance, and batch aerobic biodegradability. Then, performances of ozone pretreatment are assessed in terms of biodegradability improvement in batch and semi‐continuous anaerobic processes and, also, in semi‐continuous denitrification as a potential carbon source. Ozonation applied at the ozone dose of 0.5 g O₃ g^?1 COD led to an increase in biodegradability in all bioreactors. On average, the pretreatment resulted in an increased biodegradable fraction from zero to 33% without noticeable toxicity on biomass. This ozone dose also achieved 45% nitrogen removal by biological denitrification. CONCLUSION: Ozone pretreatment is a suitable technique for the biodegradability improvement of molasses fermentation wastewater, in aerobic, anaerobic and anoxic conditions. The pretreatment should be optimized in order to maximize the subsequent biodegradability. Copyright © 2010 Society of Chemical Industry     

Acceleration of Ozone Decomposition and ·OH Generation by Hydroxylamine

Most of protonated amines show very low reactivity with ozone in the process of generating hydroxyl radical (·OH). This study proved that protonated hydroxylamine (HA) can accelerate the decomposition of ozone and promote the yield of ·OH. Benzoic acid (BA) was used as ·OH probe, the stimulation of ozone decomposition and ·OH generation by HA in the condition of pHs ranging from 3.0 to 8.0 were studied. The results revealed the effect of HA, especially the protonated form of HA, on the ozone decomposition. Moreover, two reaction pathways of the reactive oxidant formation in O₃/HA process were proposed: (1) protonated HA reacted with ozone by the way of direct electron transfer to produce O₃^·-; (2) unprotonated HA reacted directly with ozone to form O₂^·- and O₂^·- later reacted with O₃ to form O₃^·- .     

Treatment of Humic Waters By Ozone

Two different generators for ozone were tested, a traditional electrical discharge generator and a generator based upon UV–irradiation of air at 150–180 nm. It was demonstrated that the traditional generator gave slightly higher reductions in levels of color for equivalent ozone dosages. Both gases affected the molecular weight distribution in the way that the bigger molecules were broken down to smaller ones. No significant difference between the molecular weight reduction efficiency of the gases was found.     

Soil Fulvic Acid Degradation By Ozone In Aqueous Medium

Armadale Armadale soil fulvic acid (SFA) was found to contain several loosely bound organic impurities which could be removed by ethyl acetate extraction. The ozonation of purified Armadale SFA at a variety of dosages was characterized by monitoring the UV absorbance, weight loss, pH changes, total acidity, molecular weight and elemental composition. SFA could only be partially degraded even under ozone dosages as high as SFA/O₃ (w/w) of 1:6. At high ozone dosages (SFA/O3 1:6) mostly aliphatic compounds rich in oxygen were produced, whereas at low ozone dosages (SFA/O₃ < 1:0.5) mainly benzene polycarboxylic acids and polyhydroxy benzene polycarboxylic acids were found. The solid material bisolated from the chlorination (0.5 mg/L residual level) of residues from the ozonation (SFA/O₃ 1:0.2 to 1:0.5) of Contech SFA did not contain any chlorinated products.     

Identification of Oxidation Intermediates in Humic Acid Oxidation

The effects of using ultraviolet irradiation (UV), ozone (O₃) and the combined O₃-UV advanced oxidation process (AOP) on humic acid (HA), which is regarded as the main disinfection by-products (DBPs) precursor, have been evaluated and compared. In particular, aromatic acids, short-chain aldehydes and carboxylic acids were measured. The purpose of this study was to determine the different classes and yields of oxidation intermediates, compare O₃, UV and O₃-UV for HA removal, as well as investigate the effects of O₃, irradiation time, UV intensity on the mineralization of HA. Based on that, the knowledge gap of DBPs generation was made up. The results showed that by UV irradiation and O₃ oxidation, HA broke down into smaller molecules that were more hydrophilic, namely formaldehyde, acetaldehyde, propaldehyde, butyraldehyde, glyoxal, methyl-glyoxal, formic, acetic, fumaric, benzoic, phthalic, protocatechuic and 3-hydroxybenzoic acids. Meanwhile, unsaturated conjugated double bonds in the structure of HA were destroyed, which lead to UV₂₅₄ a slight decrease. Due to the synergistic effect of O₃-UV, DOC and UV₂₅₄ significantly decreased and remained stable after the reaction of 10 min, indicating that O₃-UV system had stronger potential of mineralization and lower nonselectivity. Besides, the kinds and concentration levels of the intermediates were obviously reduced with light intensity increasing. Hydroxyl radical (^.OH) could mineralize some organics that could not be mineralized by O₃.     

Integrated Wet Air Oxidation and Biological Treatment of Polyethylene Glycol-Containing Wastewaters

The treatment of a model wastewater containing polyethylene glycol (PEG) of molecular weight 10000 in an integrated wet air oxidation–aerobic oxidation process was investigated. Partial wet air oxidation under mild operating conditions was capable of converting the original polymer to lower molecular weight compounds, such as oligomers and short-chain organic acids. The effect of molecular weight on the aerobic biodegradability of polyethylene glycol was assessed by performing shake flasks experiments with various polyethylene glycols in a molecular weight range from 200–35000 and it was found that biodegradability generally decreased with increasing molecular weight. Aqueous solutions of PEG 10000 were subjected to continuous wet air oxidation at a temperature of 423 K and a residence time of 30 min and the oxidised effluents were then subjected to subsequent continuous aerobic oxidation at residence times varying between 0·5 and 4 days. Simultaneously, continuous aerobic oxidation experiments on solutions of PEG 10000 were performed and used to compare the efficiency of the integrated treatment process with that of the direct biological treatment. Partial pretreatment by wet air oxidation under mild operating conditions resulted in effluents whose biodegradation rates were significantly higher than those of the original, unoxidised wastewater, as assessed by total organic carbon (TOC) removal rates. The original wastewater was practically non-biodegradable at a 0·5-day residence time with direct biological treatment, while an 80% TOC removal was achieved when biological treatment was coupled with a preceding wet air oxidation step. Conversely, with a 4-day residence time for the direct biological treatment the original wastewater was only partially degradable with 60–70% TOC removal recorded; with the integrated treatment process at a 4-day residence time in the bioreactor the overall TOC removal was greater than 90%. © 1997 SCI     

Decomposition of Ethylene Glycol by the Combined Use of Ozone Oxidation and Electrolytic Methods

Decomposition of ethylene glycol by the combined use of an ozone oxidation and an electrolytic method was studied. The overall order of reaction was 0.8 with respect to the concentration of ethylene glycol, and 0.7 to that of ozone in the feed gas. Glycolaldehyde, glyoxal, glyoxylic acid, and formaldehyde were detected as reaction products, and the removal of total organic carbon (TOC), which was not attained by either of the two methods alone, was attained at the same time. The reaction pathway was estimated, and it was considered that the removal of TOC via formic acid was more important than that via oxalic acid. The synergistic effect of the combined use was considered to be caused by reactive radicals formed during the process of a reaction. The removal of TOC was greatly affected by the quality and quantity of salt added.     

Ozonation of Non-Biodegradable Mixtures of Phenol and Naphthalene Derivatives in Tanning Wastewaters

The decomposition of non-biodegradable mixtures of phenol and naphthalene derivatives in aqueous solution by ozonation is investigated. The toxic water pollutants are the intermediate synthesis products obtained via the sulfonation reaction of naphthalene and phenol. These organic compounds are phenol (PH), p-phenol sulfonic acid (p-PSA), and 2-naphthalene sulfonic acid (2-NSA). The kinetic study of ozonation is realized by the pH variation in the range of 2–12. The pH-dependence of the ozone reactivity for different organics is observed. The intermediates and final products determination is measured by UV absorbency and HPLC technique. It is shown that the main sub-products are muconic, fumaric, maleic and malonic acids and catechol. The final products are basically oxalic acid and formic acids as well as formaldehyde. In the initial stage of ozonation, hydroxylation and desulfuration of p-PSA and 2-NSA is detected. The effect of the preliminary ozonation on the biodegradability of the contaminants is estimated by BOD₅/COD-ratio variation, which significantly increases from 0.15 to 0.88.     

Photoelectrochemical degradation of lignin

We have evaluated the efficient of degradation of lignin by an photoelectrochemical process. Using a Ti/Ru_0.1Sn_0.6Ti_0.3O₂ electrode, a quartz reaction device and an artificial ultraviolet light, decoloration ratios higher than 70%, and reductions of 51% and 83% in TOC and total phenol products, respectively, were observed for a reaction time of 6 h. Comparing these values with the sum of the decoloration ratios (or TOC and total phenol reductions) obtained by separate measuring of electrochemical and photochemical procedures, a significant synergetic effect between these two processes was observed. Furthermore, the degradation capacity of the photoelectrochemical process increases as the SnO₂ content is increased.     

Reaction of Water–soluble Dyes with Ozone

Reaction of various kinds of water–soluble dyes with ozone was examined. It was found that the reaction of dyes with ozone improved their biodegradability, and the values of biochemical oxygen demand (BOD} and total organic carbon (TOC) of the ozonation products correlated with those of the theoretical TOC of the original dyes. In addition, the azo dyes had a tendency to be easily decomposed with ozone, and the decomposition of dyes was markedly accelerated when ozonation was accompanied by ultra–violet irradiation.     

Effects of Ozonation on Natural Organic Matter Reactivity in Adsorption and Biodegradation Processes – A Case Study: The Úzquiza Reservoir Water

In this paper the influences of preozonation on the effectiveness of NOM adsorption and biodegradation processes are studied. Three different types of water have been used in this study: A natural water from the Úzquiza Reservoir (Burgos, Spain), synthetics waters prepared using natural humic substances (fulvic and humic acids extracted from the Úzquiza Reservoir) and a synthetic water prepared using a commercially supplied humic acid. The effect of preozonation on NOM adsorption by activated carbon is evaluated: adsorption of humic acids (hydrophobic, high molecular weight compounds) is improved following preozonation; however, for the fulvic acids (hydrophilic, low molecular weight compounds), no net appreciable effect of preozonation on adsorption was observed. Preozonation increases the biodegradability of NOM: biodegradable dissolved organic carbon (BDOC), which was determined using two different bioassays (Billen-Servais method and Joret-Lévi method), increases with increasing ozone dosage. A characterization of humic substances based on their adsorption and biodegradability properties is also reported, showing the effect of ozone.     

The Effect of Ozonation on the Removal of Organics by Coagulation – Flocculation

We present here some works which take place in the particular framework of the study of drinking water treatment of reservoir waters which contain high concentrations of organics, mainly humic substances. Previous studies on coagulation of fulvic acid solutions have proved that the optimal removal of organic matter was reached at acidic pH with 2 mg of ferricion per mg or organic carbon (summarized in this paper). The main question in this study is to know what is the impact of preozonation on the removal of organics by iron (III) coagulation.

The study of the behavior of organics, in terms of UV-absorbance and TOC measurements was made on three aquatic fulvic acids and on two raw waters. The experiments carried out with fulvic acids showed that preozonation (at 0.5 mg O₃/mg C) of fulvic acid appeared to have shifted the region of the optimal DOC removal towards the higher coagulant dose. Furthermore, increasing ozone doses led to a slight decreasing of coagulation efficiency at constant coagulant dose. With two raw waters, preozonation at low ozone doses (0.2 mg 0₃/mg C) was found to improve very slightly the elimination of organic matter, while high ozone doses (0.9 mg O₃/mg C) led to a disturbance of TOC elimination by iron coagulation.