The effect of ozonation on natural organic matter removal by alum coagulation

Natural organic matter (NOM) was extracted from a moderately colored, eutrophic surface water source (Forge Pond, Granby, MA), and fractionated into quasi-homogeneous fractions. Fulvic acid (FA) and hydrophilic neutrals (HN) were the two most abundant NOM fractions that were isolated. Adsorption affinity of the isolated NOM fractions on preformed aluminum hydroxide flocs increased with increase in specific organic charge of the fractions, except for the two most highly charged fractions, FA and hydrophilic acids (HAA), which showed less adsorption affinity than expected based on their specific organic charge. Prior ozonation of FA and HN fractions resulted in a decline and an increase, respectively, in their adsorption affinity on aluminum hydroxide surface. Prior ozonation of Forge Pond raw water resulted in a progressive decline in dissolved organic carbon (DOC) removal by alum coagulation with increase in ozone dose. It appeared that ozone applied to raw water reacted preferentially with the humic fraction of NOM, resulting in the detrimental effects of ozonation on subsequent NOM removal by alum coagulation being magnified. Forge Pond raw water was pre-coagulated to remove humic substances. Ozonation of the pre-coagulated water demonstrated the beneficial effects of ozonation on the removal of non-humic NOM through alum coagulation. A strategy for staged coagulation with intermediate ozonation was proposed for waters containing both humic and non-humic NOM for maximum DOC and specific UV absorbance at 254nm (SUVA) removal.     

Elimination of resin acids by advanced oxidation processes and their impact on subsequent biodegradation

Wood pulping and paper production generate a considerable amount of wastewater, containing many pollutants among them resin and fatty acids. Resin acids contribute substantially to effluent toxicity and were identified to be detrimental to microorganisms of activated sludge and in particular to bacteria in anaerobic wastewater treatment system and other forms of aquatic life. The objective of the present study was to check the applicability of the ozone and advanced oxidation processes (AOPs) to eliminate resin acids from aqueous solutions and to determine the ozone dose required. Furthermore, an investigation of the influence of the oxidation methods on subsequent biological destruction of the byproducts was performed. Aqueous solution of the resin acids: abietic, dehydroabietic and isopimaric acids with different initial composition were subjected to ozonation or AOP processes at different ozone doses. After ozonation or advanced oxidation pretreatment the model solutions were biodegraded in aerated vessels containing activated sludge. During ozonation of the resin acids aqueous solutions the resin acids were almost eliminated, however the reduction of chemical oxygen demand (COD) was rather low. The ozone dose required to obtain reduction of resin acids >90% was in the range of 0.1-0.7mgO(3)/mgCOD, depending on the composition and concentration of model solutions. The toxicity of ozonated resin acids solutions decreased with increasing applied ozone dose up to about 0.3-0.5mgO(3)/mgCOD, thereafter increased. Ozonation and other AOP processes did not increase the rate of biodegradation of resin acids model solutions in aerated activated sludge systems compared to not pretreated solutions.     

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD₅/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L⁻¹, 0.48 for BOD₂₁/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS⁻¹ h⁻¹.     

The effect of humic acids on nitrobenzene oxidation by ozonation and O3/UV processes

Three types of commercially available humic acids from different sources were used to simulate natural organic matter in water for the investigation of nitrobenzene oxidation by ozonation and O(3)/UV. Despite the structural differences among the Fluka, Aldrich and Suwanee River humic acids as reflected by the UV absorptivity, their effects on nitrobenzene removal rate was observed to be similar for the two processes. Removal rate of nitrobenzene was hindered by the addition of humic acids in ozonation as well as in O(3)/UV processes. However, the hindrance by the humic acids was more pronounced in O(3)/UV as compared to the ozonation process. The effect of humic acid in O(3)/UV was primarily a UV light screening. Addition of humic acids above a certain concentration did not cause any further retardation on nitrobenzene removal rate by ozonation and O(3)/UV.Accumulation of hydrogen peroxide as well as probable formation of peroxy radicals in the solutions might induce chain promoting reactions to produce hydroxyl radical during the nitrobenzene oxidation. For waters containing high levels of humic acid, ozonation alone might be as effective as O(3)/UV process for the removal of nitrobenzene.     

Ozonation effect on natural organic matter adsorption and biodegradation - Application to a membrane bioreactor containing activated carbon for drinking water production

More stringent legislation on dissolved organic matter (DOM) urges the drinking water industry to improve in DOM removal, especially when applied to water with high dissolved organic carbon (DOC) contents and low turbidity. To improve conventional processes currently used in drinking water treatment plants (DWTPs), the performances of a hybrid membrane bioreactor containing fluidised activated carbon were investigated at the DWTP of Rennes. Preliminary results showed that the residual DOC was the major part of the non-biodegradable fraction. In order to increase the global efficiency, an upstream oxidation step was added to the process. Ozone was chosen to break large molecules and increase their biodegradability. The first step consisted of carrying out lab-scale experiments in order to optimise the necessary ozone dose by measuring the process yield, in terms of biodegradable dissolved organic carbon (BDOC). Secondly, activated carbon adsorption of the DOC present in ozonated water was quantified. The whole process was tested in a pilot unit under field conditions at the DWTP of Rennes (France). Lab-scale experiments confirmed that ozonation increases the BDOC fraction, reduces the aromaticity of the DOC and produces small size organic compounds. Adsorption tests led to the conclusion that activated carbon unexpectedly removes BDOC first. Finally, the pilot unit results revealed an additional BDOC removal (from 0.10 to 0.15 mg L⁻¹) of dissolved organic carbon from the raw water considered.     

Mechanistic and kinetic evaluation of organic disinfection by-product and assimilable organic carbon (AOC) formation during the ozonation of drinking water

Ozonation of drinking water results in the formation of low molecular weight (LMW) organic by-products. These compounds are easily utilisable by microorganisms and can result in biological instability of the water. In this study, we have combined a novel bioassay for assessment of assimilable organic carbon (AOC) with the detection of selected organic acids, aldehydes and ketones to study organic by-product formation during ozonation. We have investigated the kinetic evolution of LMW compounds as a function of ozone exposure. A substantial fraction of the organic compounds formed immediately upon exposure to ozone and organic acids comprised 60-80% of the newly formed AOC. Based on experiments performed with and without hydroxyl radical scavengers, we concluded that direct ozone reactions were mainly responsible for the formation of small organic compounds. It was also demonstrated that the laboratory-scale experiments are adequate models to describe the formation of LMW organic compounds during ozonation in full-scale treatment of surface water. Thus, the kinetic and mechanistic information gained during the laboratory-scale experiments can be utilised for upscaling to full-scale water treatment plants.     

Treatment of persistent organic compounds by integrated advanced oxidation processes and sequential batch reactor

The objective of this study was to evaluate the extent of improvement in the biodegradability of persistent organic compounds by pre-oxidation by using Sequential Batch Reactors (SBRs). Dichlorodiethyl ether (DCDE), a non-biodegradable compound, was used as a test chemical. Ozonation, Fenton reagent and ultra-violet light coupled with hydrogen peroxide (UV/H₂O₂) were used for oxidation of DCDE at levels of 50-100%. Pre-oxidized DCDE solutions were then subjected to SBR studies using activated sludge to determine the rate and extent of biodegradation of oxidation by-products. The results indicated that the biodegradability of pre-oxidized DCDE increased drastically, reaching an average of 90% for all three oxidation methods versus zero for non-oxidized DCDE. It was concluded that the results of SBR experiments may be better indicators of biodegradability of chemically-oxidized wastewaters due to significant acclimation of microorganisms in SBRs, which cannot be observed in conventional respirometric laboratory studies.     

A water-sediment screening tool for measuring biodegradation of organic chemicals

A water-sediment screening tool (WSST) was developed based on OECD guideline 301 C (MITI I; Ministry of International Trade and Industry, Japan) to generate biodegradation data. The WSST and experimental procedures were tested and validated using aniline (CAS No. 62-53-3) and benzoic acid (CAS No. 65-85-0) as reference substances. In the presence of sediment components a higher endogenous respiration rate in the control vessels without test substance was measured compared to the water-only MITI test system, particularly due to organic constituents. However, it could be demonstrated that a distinct biodegradation in the presence of sediment can be determined and that there is no influence of the sediment pre-treatment on the biological oxygen demand in the WSST. Experiments resulted in biodegradation rates > 60% after approximately six days for both compounds. However, degradation of benzoic acid resulted in a shorter lag-phase and a higher degree of degradation compared to aniline. Differences in results between the MITI test system and the WSST observed for aniline can be explained by adsorption to constituents of the sediment and assimilation by activated sludge. In comparison with literature data the results obtained for aniline in the MITI test system and the WSST showed reproducibility and were within the expected range. In conclusion, the WSST is a suitable screening tool to determine kinetic biodegradation data required to predict the biodegradation behaviour of organic chemicals in water-sediment systems and the data might be used to improve quantitative structure-property relationships (QSPRs).     

Evaluation of the prediction of trace organic compound removal during ozonation of secondary effluents using tracer substances and second order rate kinetics

The application of the R_CT-concept for predicting the removal of trace organic compounds (TrOCs) in organic rich WWTP effluents is often problematic due to the fast ozone depletion with instantaneous ozone demand in the range of typically applied ozone dosages. In this study, the determination of OH-radical and ozone exposure from second order rate kinetics with two internal tracer substances was evaluated as alternative approach for these waters. Results from batch and semi-batch experiments showed a linear correlation of OH-radical exposure with ozone consumption, characterized by its slope indicating the formation efficiency of OH-radicals and a lag ozone consumption without significant formation of OH-radicals. Evaluation of data from the project PILOTOX on ozonation of secondary effluent confirmed reasonable prediction of ozone resistant compound removal from relative residual concentration of an internal tracer substance. In contrast, predicting the reduction of TrOCs by direct reactions with ozone from internal tracers was not feasible. Similar removal efficiencies for fast reacting compounds with different rate constants from k_O3 = 10⁴ M⁻¹ s⁻¹ to k_O3 = 10⁶ M⁻¹ s⁻¹ were observed indicating a limitation of the reaction by mass transfer. This effect was observed at low ozone dosages in semi-batch and pilot experiments as well as in batch experiments, where mass transfer from gas to liquid phase is not limiting. It is assumed that consumption of low ozone dosages is faster than sample homogenization in the batch reactors used. Thus, prediction of compound removal by direct reaction with ozone always needs to consider reactor design and geometry.     

Removing of fulvic acids by ozonation and biological active carbon filtration

It was studied the effect of the content of biodegradable organic carbon (BDOC) after the processes of aeration and ozonation of the fulvic acid (FA) solutions on the efficiency of its adsorption and biofiltration. It was found that the change of free energy of adsorption of the FA oxidation products correlated with the part of biodegradable organic carbon in total organic carbon content. Predicting the effectiveness of NOM solutions ozonation before filtration through BAC is more appropriate by determining the value of the free adsorption energy. It was established that ozonation of FA solutions with high initial BDOC content by ozone doses that are economically and technologically acceptable, leads to a decrease in the BDOC value. Ozonation of FA solutions leads to equalization of the adsorption ability of FA fractions and increases the adsorption energy of FA in most investigated systems with a high initial BDOC content.     

Lincomycin solar photodegradation, algal toxicity and removal from wastewaters by means of ozonation

Antibiotic molecules have been reported among the xenobiotics present at trace levels in sewage treatment plant (STP) effluents and aquatic environment. Lincomycin, one of the most used in clinical practices whose presence in the STP effluents has been often documented, is submitted to an extensive investigation to assess its persistence in the environment and toxicity towards different algal strains. The possibility to remove the lincomycin from water by means of ozonation is demonstrated and a reduction of toxicity of ozonated solutions on S. leopoliensis, with respect to untreated solutions containing this compound, is obtained even just for 1h of treatment. Kinetic constants for the attack to lincomycin of ozone (from 1.53 x 10(5) M(-1)s(-1) at pH = 3.0 and 4.93 x 10(5) M(-1)s(-1) at pH = 6.7) and OH radicals (4.37 x 10(9) M(-1)s(-1) at pH = 5.5 and 4.59 x 10(9) M(-1)s(-1) at pH = 7.5) are also evaluated.     

Modeling of bromate formation by ozonation of surface waters in drinking water treatment

The main objective of this paper is to try to develop statistically and chemically rational models for bromate formation by ozonation of clarified surface waters. The results presented here show that bromate formation by ozonation of natural waters in drinking water treatment is directly proportional to the "Ct" value ("Ctau" in this study). Moreover, this proportionality strongly depends on many parameters: increasing of pH, temperature and bromide level leading to an increase of bromate formation; ammonia and dissolved organic carbon concentrations causing a reverse effect. Taking into account limitation of theoretical modeling, we proposed to predict bromate formation by stochastic simulations (multi-linear regression and artificial neural networks methods) from 40 experiments (BrO(3)(-) vs. "Ctau") carried out with three sand filtered waters sampled on three different waterworks. With seven selected variables we used a simple architecture of neural networks, optimized by "neural connection" of SPSS Inc./Recognition Inc. The bromate modeling by artificial neural networks gives better result than multi-linear regression. The artificial neural networks model allowed us classifying variables by decreasing order of influence (for the studied cases in our variables scale): "Ctau", [N-NH(4)(+)], [Br(-)], pH, temperature, DOC, alkalinity.     

Analysis of the mechanism of sludge ozonation by a combination of biological and chemical approaches

Using the practical sludge obtained from municipal sewage treatment plants, the mechanism of the sludge ozonation process was systematically investigated by a combination of biological and chemical approaches, including analysis of the changes in biological response by CFU and PCR-DGGE, bio-macromolecular activity and radical scavenging activity. The results indicated that after the sludge was exposed to ozone at less than 0.02 g O₃/g TSS, the DGGE fingerprint remained constant and there was still some enzyme activity, indicating that the sludge solubilization was the main process. At greater than 0.02 g O₃/g TSS, the bacteria began to be broken down and ozone was used to oxidize the bio-macromolecules such as proteins and DNA released from the sludge. Bacteria belonging to ‘G-Bacteria’ were able to conserve their DNA in the presence of less than 0.08 g O₃/g TSS. At levels higher than 0.10 g O₃/g TSS, the disintegration of the sludge matrix became slow and the microbes lost most of their activity, and ozone was used to transform the bio-macromolecules into small molecules. However, at levels higher than 0.14 g O₃/g TSS, the ozone failed to oxidize the sludge efficiently, because several radical scavengers such as lactic acid and SO₄²⁻ were released from the microbial cells in the sludge.     

Comparison of 2-chlorobenzoic acid biodegradation in a membrane bioreactor by B. cepacia and B. cepacia bearing the bacterial hemoglobin gene

Degradation of 2-chlorobenzoic acid (2-CBA), a model recalcitrant chlorinated organic compound, by pure cultures of Burkholderia cepacia strain DNT with (transformed B. cepacia) and without (untransformed B. cepacia) the bacterial hemoglobin (Vitreoscilla hemoglobin, VHb) gene, vgb, was investigated in parallel membrane bioreactors (MBRs). This was done aseptically to prevent contamination during the operation of the MBRs. The objective was to determine whether the degradation of 2-CBA by cometabolism, using acetate as a primary carbon source, under hypoxic conditions might be enhanced for vgb-bearing cells in MBRs. The 2-CBA removal efficiency of transformed B. cepacia (97-99%) was slightly higher than that of untransformed B. cepacia (95-99%) at all stages. The average amount of chloride released from 2-CBA by transformed cells was also higher than for untransformed cells, 92-96% compared to 64-84% of the maximum theoretical amount, the exact value depending on the operating conditions. These results indicate that 2-CBA degradation/transformation is not accompanied by the stoichiometric release of chloride for the untransformed strain. The difference between percentages of 2-CBA removal and chloride release by untransformed cells was attributed to persistence, under hypoxic conditions, of the 2-CBA chlorine atom in 2-CBA metabolites. Growth of transformed cells was also significantly enhanced under hypoxic conditions compared to untransformed cells. For varying media compositions, the transformed cells reached higher cell densities (3.2-5.4 g/L) relative to untransformed cells (2.8-4.7 g/L) at food to microorganism ratios ranging from 0.44-0.59 to 0.38-0.49 g COD/g biomass-d The observed yields thus ranged from 0.16-0.20 and 0.15-0.18 g TSS/g COD for untransformed and transformed cells, respectively. The value of the yield depended on medium composition. The MBR system using vgb-containing B. cepacia maintained a high biomass concentration without oxygen limitations and provided cell-free effluent. Hence, it may be useful for treating high volumes of water contaminated with low levels of recalcitrant organics.     

Bezafibrate removal by means of ozonation: primary intermediates, kinetics, and toxicity assessment

Bezafibrate (BZF) is a lipid regulator largely used for the treatment of hyperlipidaemia. As a result of its wide use, unmetabolized BZF is released in the environment with potential toxic effects for aquatic living organisms. The results obtained in this work show that ozonation is an efficient method to degrade BZF: after 10 min of treatment (corresponding to a dose of 0.73 mmol L(-1) of ozone), the complete BZF abatement is achieved, starting from an initial concentration of 0.5 mmol L(-1). However, only a small part of the substrate is mineralized. Two different experimental approaches (absolute and competition method) are adopted to estimate the second-order kinetic constants for the ozone attack at pH=6.0, 7.0 and 8.0. A good agreement was observed between the two kinetic methods adopted. The identification of main intermediates, attempted by high-performance liquid chromatograph (HPLC)-MS technique, indicates that the oxidation of BZF develops through both the hydroxylation of the aromatic ring and the attack of ozone on the unchlorinated aromatic one. The assessment of by-products biodegradability and acute toxicity demonstrates that ozonation is a suitable technique to improve the biodegradability and reduce the toxicity of waters containing BZF.     

Surfactant-coated aluminum hydroxide for the rapid removal and biodegradation of hydrophobic organic pollutants in water

The removal of hydrophobic organic pollutants in water to surfactant-coated aluminum hydroxide [surfactant-Al(OH)₃] was investigated. Anionic surfactants such as sodium dodecyl sulfate (SDS), sodium bis(2-ethylhexyl)sulfosuccinate (AOT), and sodium oleate were sorbed on positively charged aluminum hydroxide at pH 7 and formed hydrophobic aggregates that can incorporate hydrophobic organic pollutants in water. Because of the hydrophobic interaction and decrease in the positive charge, surfactant-Al(OH)₃ was coagulated into precipitates that can readily be separated from water. Hydrophobic organic pollutants such as alkylphenols, polycyclic aromatic hydrocarbons, estrogens, chlorinated antifungals, and pesticides were well collected to the precipitates and thus efficiently removed from water. The collection of hydrophobic organic pollutants was correlated to their aqueous-octanol distribution coefficient. The decomposition of hydrophobic organic pollutants was examined using a bacterial agent (Bacillus subtilis). Hydrophobic organic compounds collected to AOT-Al(OH)₃ or sodium oleate-Al(OH)₃ were insufficiently decomposed. On the other hand, nonylphenol, octylphenol, and pendimethalin collected to SDS-Al(OH)₃ were decomposed within 1 week. The decomposition was accelerated by the collection to SDS-Al(OH)₃.     

Occurrence of emerging pollutants in urban wastewater and their removal through biological treatment followed by ozonation

This work reports a systematic survey of over seventy individual pollutants in a Sewage Treatment Plant (STP) receiving urban wastewater. The compounds include mainly pharmaceuticals and personal care products, as well as some metabolites. The quantification in the ng/L range was performed by Liquid Chromatography-QTRAP-Mass Spectrometry and Gas Chromatography coupled to Mass Spectrometry. The results showed that paraxanthine, caffeine and acetaminophen were the main individual pollutants usually found in concentrations over 20 ppb. N-formyl-4-amino-antipiryne and galaxolide were also detected in the ppb level. A group of compounds including the beta-blockers atenolol, metoprolol and propanolol; the lipid regulators bezafibrate and fenofibric acid; the antibiotics erythromycin, sulfamethoxazole and trimethoprim, the antiinflammatories diclofenac, indomethacin, ketoprofen and mefenamic acid, the antiepileptic carbamazepine and the antiacid omeprazole exhibited removal efficiencies below 20% in the STP treatment. Ozonation with doses lower than 90 μM allowed the removal of many individual pollutants including some of those more refractory to biological treatment. A kinetic model allowed the determination of second order kinetic constants for the ozonation of bezafibrate, cotinine, diuron and metronidazole. The results show that the hydroxyl radical reaction was the major pathway for the oxidative transformation of these compounds.     

The ozonation of organic halide precursors: effect of bicarbonate

A laboratory study of the effect of bicarbonate on the ozonation of organic halide precursors in fulvic acid solutions and in a raw drinking water was conducted. The experimental variables were bicarbonate concentration, ozone dose and pH of chlorination. Results are expressed in terms of trihalomethane (THM), total organic halide (TOX), trichloracetic acid, dichloroacetic acid, trichloroacetone and dichloroacetonitrile precursor concentrations. Kinetic studies showed that bicarbonate slowed the decomposition of ozone in the presence of fulvic acid, and thereby, led to a greater degree of destruction of u.v.-absorbing substances. Similarly, precursor destruction increased with increasing bicarbonate concentrations in the range of 10⁻⁴spd 10⁻² M. Precursor destruction was greatest when chlorination was performed at low pH. At high pH's of chlorination, some precursor enhancement was noted, especially in the absence of bicarbonate. Results are interpreted both from a mechanistic standpoint and with respect to their applicability to water treatment practice.     

Removal and transformation of recalcitrant organic matter from stabilized saline landfill leachates by coagulation-ozonation coupling processes

The Bordo Poniente sanitary landfill in Mexico City currently receives 11,500 ton/day of solid wastes. The landfill has been in operation since 1985, in what was formerly Texcoco Lake, now a dried-up lakebed. The physico-chemical characteristics of the leachate generated by this particular landfill are altered by the incorporation of freatic saline water present in the area. This paper reports the results from a study evaluating coagulation and ozonation as alternative processes for removing and transforming recalcitrant organic matter from stabilized saline landfill leachate. Coagulation with ferric sulfate was found to remove up to 67% of COD and 96% of leachate color. The remaining 33% COD was removed with ozone. Recalcitrant organic matter removal by ozonation is limited by the reaction kinetic due mainly to ozone's low reactivity with the organic compounds present in the leachates (amines, amides, alcohols, aliphatic compounds, and carboxylic acids). However, ozone contributes greatly to changing the recalcitrant characteristics of organic matter. Leachate biodegradability was found to be significantly enhanced through ozonation: BOD(5) values reach 265%, and the BOD(5)/COD ratio increases from 0.003 to 0.015. Infrared analysis of ozonated leachates shows that the main by-products of recalcitrant organic matter ozonation are an increase in the hydroxyl and carboxylic groups, and the presence of aldehydes groups.     

Assessment of enhancement in biodegradation of dichlorodiethyl ether (DCDE) by pre-oxidation

The objective of this study is to assess the enhancement in biodegradation of dichlorodiethyl ether (DCDE) by ozonation and Fenton treatment. Acclimated and non-acclimated sludge cultures were used to test the biodegradability of the preoxidized DCDE solutions by three different tests: Short-term and long-term respirometry through continuous monitoring of oxygen consumption, and the mid-term test in which the amount of remaining organic matter was measured by TOC and COD tests. These tests were applied to solutions of DCDE preoxidized at the levels of 25%, 50%, 75%, and 100%. The results indicated that the biodegradability of oxidized DCDE solutions improved substantially compared to non-oxidized solutions. Fenton-treated DCDE exhibited toxicity to microorganisms under long-term exposure. Higher levels of preoxidation of DCDE led to mineralization of larger amounts of organic matter during subsequent biodegradation. There was no significant difference in the rate of biodegradation of oxidized products by either acclimated or non-acclimated bacteria.