Photocatalytic degradation process of antibiotic sulfamethoxazole by ZnO in aquatic systems: a dynamic kinetic model based on contributions of OH radical, oxygenated radical intermediates and dissolved oxygen.

The photocatalytic degradation process of sulfamethoxazole (SMX) using ZnO in aquatic systems has been systematically studied by varying initial SMX concentration from 0 to 15 mgL-1, ZnO dosage from 0 to 4 gL-1 and UV light intensity at the light source from 0 to 18 W(m-lamp length)-1 at natural pH. Almost complete degradations of SMX were achieved within 120 min for the initial SMX concentration ≤15 mgL-1 with ZnO dosage of 3 gL-1 and UV light intensity of 18 W(m-lamp length)-1. The photocatalytic degradation process was found to be interacted with the dissolved oxygen (DO) consumption. With oxygen supply through the gas-liquid free-surface, the DO concentration decreased significantly in the initial SMX degradation phase and increased asymptotically to the saturated DO concentration after achieving about 80% SMX degradation. The change in DO concentration was probably controlled by the oxygen consumption in the formation of oxygenated radical intermediates. A novel dynamic kinetic model based on the fundamental reactions of photocatalysis and the formation of oxygenated radical intermediates was developed. In the modeling the dynamic concentration profiles of OH radical and DO are considered. The dynamics of SMX degradation process by ZnO was simulated reasonably by the proposed model.

Removal of pharmaceutically active compounds (PhACs) by zero-valent iron: quantification of removal mechanisms consisting of degradation, adsorption and co-precipitation.

The removal mechanisms of carbamazepine (CBZ), which is one of pharmaceutically active compounds, using zero-valent iron (ZVI) were quantified by defining three fractions, namely "degradation", "adsorption", and "co-precipitation". The maximum total organic carbon (TOC) removal was obtained at pH 4. The results demonstrate that the adsorption on the ZVI surface is dominant in the TOC removal of CBZ for 4 ≤ pH ≤ 6 while the degradation by oxidative and reductive reactions is efficient exclusively for pH ≤ 3. TOC removal was not obtained for pH ≥ 8. The most dominant mechanism in the removal of CBZ by ZVI is the adsorption onto the iron oxides/hydroxides layer formed on ZVI surface rather than the degradation by oxidative and reductive reactions including Fenton and Fenton-like reactions for pH ≥ 4. A novel kinetic model for removal of CBZ by ZVI was developed to simulate the dynamic concentration profiles of CBZ, TOC, total Fe ions, and dissolved oxygen linked closely with each other and the contributions of degradation, adsorption, and co-precipitation in TOC removal of CBZ. Reasonable agreement between experimental data and model predictions suggests the applicability of the proposed kinetic model to quantitatively analyze the mechanisms of CBZ removal by ZVI.

Biological treatment of non-biodegradable azo-dye enhanced by zero-valent iron (ZVI) pre-treatment.

Zero-valent iron (ZVI) pre-treatment in sequential strategy for removal of non-biodegradable azo-dye Orange II by activated-sludge was quantitatively examined. The decolorization and TOC (total organic carbon) removal of Orange II by ZVI pre-treatment were examined in the ranges of pH from 3 to 11 and ZVI dosage from 500 to 2000 mgL-1. While the decolorization was enhanced with decreasing pH and the optimal pH for decolorization was found at pH 3, the TOC removal rate at pH 3 remained at 22.2% and the maximum TOC removal rate of 78.2% was obtained at pH 4. The decolorization and TOC removal of Orange II were monotonously increased with increasing ZVI dosage. To quantify the ZVI pre-treatment, the contributions of redox degradation, complexation/precipitation and adsorption to TOC removal by ZVI were defined. Novel kinetic models for the ZVI pre-treatment and activated-sludge post-treatment were developed. The proposed kinetic models satisfactorily predicted the transitional behaviors of the ZVI pre-treatment and activated-sludge post-treatment and the contributions of redox degradation, complexation/precipitation and adsorption to TOC removal by the ZVI pre-treatment. The complete removal of non-biodegradable azo-dye Orange II of 300 mgL-1 was accomplished by 78.2% removal after 360 min ZVI pre-treatment with the ZVI dosage of 1000 mgL-1 at pH 4 and subsequently 21.8% removal after 480 min activated-sludge post-treatment. The ZVI pre-treatment integrated with activated-sludge post-treatment was proved to be an effective strategy for treating non-biodegradable pollutants.

A phenomenological reaction kinetic model for Cu removal from aqueous solutions by zero-valent iron (ZVI).

Zero-valent iron (ZVI) being an inexpensive and eco-friendly catalyst has drawn great attention in removal of heavy metals from wastewaters. However, quantitative understandings of ZVI processes are significantly deficient. To compensate for the lack of quantitative analyses of removal of heavy metals by ZVI, a phenomenological reaction kinetic model was newly developed for removal of Cu chosen as a typical heavy metal from acidic aqueous solutions by ZVI. The novel kinetic model is based on the adsorption of Cu2+ and H+ onto ZVI surface and subsequent Cu2+ reduction on ZVI surface and Fe2+ elution from ZVI. Batch experiments were conducted to elucidate effects of pH and Cu loading on Cu removal by ZVI in acidic aqueous solutions and to validate the proposed phenomenological reaction kinetic model. The quick and complete removals of 1.57 mM Cu were established in the rage of pH 2-5. Although the maximum Cu removal rate was obtained at pH 4, effects of pH were insignificant. In the range of Cu loading from 0.393 to 4.72 mM, almost complete Cu removals were obtained at pH 4 within 35 min. The changes in concentrations of Cu2+, Fe2+, H+ and dissolved oxygen were strongly linked with each other. They could be successfully simulated by the proposed model with the average correlation coefficient of 0.979. The capability of the phenomenological reaction kinetic model for dynamic simulation of Cu removal by ZVI under acidic conditions was confirmed.

Removal of antibiotic sulfamethoxazole by zero-valent iron under oxic and anoxic conditions: Removal mechanisms in acidic, neutral and alkaline solutions.

Removal of antibiotic sulfamethoxazole (SMX) by zero-valent iron (ZVI) was examined in the range of pH from 3.0 to 11.0 under oxic and anoxic conditions to clarify mechanisms of SMX removal in acidic, neutral and alkaline solutions. SMX removal was affected by solution pH and related to the speciation of SMX. Under the oxic condition, the maximums of SMX removal efficiency and rate were obtained at pH 3.0. The SMX removal efficiency decreased from 100 to 32% with increasing pH in the acidic solutions (3 â‰¦ pH â‰¦ 5) and increased to 88% in neutral and moderately alkaline solutions (6 â‰¦ pH â‰¦ 10). In highly alkaline solution (pH = 11), the SMX removal was significantly suppressed due to the formation of passive layer on ZVI surface. The removal rate of SMX under the oxic condition significantly declined with increasing pH. Under the anoxic condition, SMX removal was completed within 300 min in the acidic solutions and remained to less than 70% after 300 min in neutral and moderately alkaline solutions. For pH â‰§ 10, no SMX removal practically occurred. The removal rate of SMX under the anoxic condition approximately remained constant in the acidic solution and largely decreased in neutral and moderately alkaline solutions. SMX removal by ZVI was found to be dominated by the reductive degradation and adsorption under both the oxic and anoxic conditions. It was concluded that ZVI has the potential for effective removal of antibiotic SMX under the oxic and anoxic conditions. A kinetic model could reasonably simulate the dynamic profiles of SMX removal.

Removal of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) from wastewaters by zero-valent iron (ZVI): predominant removal mechanism for effective SDBS removal.

Mechanisms for removal of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in wastewaters by zero-valent iron (ZVI) were systematically examined. The contributions of four removal mechanisms, i.e., reductive degradation, oxidative degradation, adsorption, and precipitation, changed significantly with solution pH were quantified and the effective removal of SDBS by ZVI was found to be attributed to the adsorption capability of iron oxides/hydroxides on ZVI surface at nearly neutral pH instead of the degradation at acidic condition. The fastest SDBS removal rate and the maximum TOC (total organic carbon) removal efficiency were obtained at pH 6.0. The maximum TOC removal at pH 6.0 was 77.8%, and the contributions of degradation, precipitation, and adsorption to TOC removal were 4.6, 14.9, and 58.3%, respectively. At pH 3.0, which is an optimal pH for oxidative degradation by the Fenton reaction, the TOC removal was only 9.8% and the contributions of degradation, precipitation, and adsorption to TOC removal were 2.3, 4.6, and 2.9%, respectively. The electrostatic attraction between dodecyl benzene sulfate anion and the iron oxide/hydroxide layer controlled the TOC removal of SDBS. The kinetic model based on the Langmuir-Hinshelwood/Eley-Rideal approach could successfully describe the experimental results for SDBS removal by ZVI with the averaged correlation coefficient of 0.994. ZVI was found to be an efficient material toward the removal of anionic surfactant at nearly neutral pH under the oxic condition.

Hydroxyl radical generation in electro-Fenton process with a gas-diffusion electrode: Linkages with electro-chemical generation of hydrogen peroxide and iron redox cycle.

The hydroxyl radical generation in an electro-Fenton process with a gas-diffusion electrode which is strongly linked with electro-chemical generation of hydrogen peroxide and iron redox cycle was studied. The OH radical generation subsequent to electro-chemical generations of H2O2 was examined under the constant potential in the range of Fe2+ dosage from 0 to 1.0 mM. The amount of generated OH radical initially increased and gradually decreased after the maximum was reached. The initial rate of OH radical generation increased for the Fe2+ dosage <0.25 mM and at higher Fe2+ dosages remained constant. At higher Fe2+ dosages the precipitation of Fe might inhibit the enhancement of OH radical generation. The experiments for decolorization and total organic carbon (TOC) removal of azo-dye Orange II by the electro-Fenton process were conducted and the quick decolorization and slow TOC removal of Orange II were found. To quantify the linkages of OH radical generation with dynamic behaviors of electro-chemically generated H2O2 and iron redox cycle and to investigate effects of OH radical generation on the decolorization and TOC removal of Orange II, novel reaction kinetic models were developed. The proposed models could satisfactory clarify the linkages of OH radical generation with electro-chemically generated H2O2 and iron redox cycle and simulate the decolorization and TOC removal of Orange II by the electro-Fenton process.

Adsorption capacities of poly-γ-glutamic acid and its sodium salt for cesium removal from radioactive wastewaters.

Cesium removal from radioactive wastewaters was examined using water-insoluble poly-γ-glutamic acid (γ-PGA) and water-soluble sodium salt form poly-γ-L-glutamic acid (γ-PGANa) as biosorbents. The maximum adsorption capacities at equilibrium of γ-PGA and γ-PGANa for Cs were 345 mg-Cs(g-γ-PGA)-1 at pH 6.0 and 290 mg-Cs(g-γ-PGANa)-1 at pH 9.0, respectively. At lower pH < pKa, the carboxyl groups of γ-PGA primarily remained in the protonated form and adsorption of Cs only slightly occurred. At higher pH > pKa, the adsorption of Cs was significantly facilitated due to ionization of carboxyl groups to carboxylate ion. Adsorption of Cs at pH > 9.0 was inhibited due to the hydrolysis of Cs. The Langmuir model could successfully describe the isotherm data. For γ-PGA and γ-PGANa, the maximum adsorption capacities at equilibrium in the Langmuir model were 446 and 333 mg-Cs(g-adsorbent)-1, respectively. The high adsorption capacities confirmed a potential utilization of γ-PGA and γ-PGANa for Cs removal. The adsorption of Cs by both γ-PGA and γ-PGANa attained the equilibrium within 0.5 min. The very quick equilibration is a benefit from the viewpoint of practical application. The spectra of FT-IR and XPS before and after adsorption confirmed the adsorption of Cs onto γ-PGA and γ-PGANa via electrostatic interaction with carboxylate anions.

Zero-valent iron treatment of dark brown colored coffee effluent: Contributions of a core-shell structure to pollutant removals.

The decolorization and total organic carbon (TOC) removal of dark brown colored coffee effluent by zero-valent iron (ZVI) have been systematically examined with solution pH of 3.0, 4.0, 6.0 and 8.0 under oxic and anoxic conditions. The optimal decolorization and TOC removal were obtained at pH 8.0 with oxic condition. The maximum efficiencies of decolorization and TOC removal were 92.6 and 60.2%, respectively. ZVI presented potential properties for pollutant removal at nearly neutral pH because of its core-shell structure in which shell or iron oxide/hydroxide layer on ZVI surface dominated the decolorization and TOC removal of coffee effluent. To elucidate the contribution of the core-shell structure to removals of color and TOC at the optimal condition, the characterization of ZVI surface by scanning electron microscopy (SEM) with an energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) was conducted. It was confirmed that the core-shell structure was formed and the shell on ZVI particulate surface and the precipitates formed during the course of ZVI treatment consisted of iron oxides and hydroxides. They were significantly responsible for decolorization and TOC removal of coffee effluent via adsorption to shell on ZVI surface and inclusion into the precipitates rather than the oxidative degradation by OH radicals and the reduction by emitted electrons. The presence of dissolved oxygen (DO) enhanced the formation of the core-shell structure and as a result improved the efficiency of ZVI treatment for the removal of colored components in coffee effluents. ZVI was found to be an efficient material toward the treatment of coffee effluents.

Linkage of iron elution and dissolved oxygen consumption with removal of organic pollutants by nanoscale zero-valent iron: Effects of pH on iron dissolution and formation of iron oxide/hydroxide layer.

The iron elution and dissolved oxygen (DO) consumption in organic pollutant removal by nanoscale zero-valent iron (nZVI) was examined in the range of solution pH from 3.0 to 9.0. Their behaviors were linked with the removal of organic pollutant through the dissolution of iron and the formation of iron oxide/hydroxide layer affected strongly by solution pH and DO. As an example of organic pollutants, azo-dye Orange II was chosen in this study. The chemical composition analyses before and after reaction confirmed the corrosion of nZVI into ions, the formation of iron oxide/hydroxide layer on nZVI surface and the adsorption of the pollutant and its intermediates. The complete decolorization of Orange II with nZVI was accomplished very quickly. On the other hand, the total organic carbon (TOC) removal was considerably slow and the maximum TOC removal was around 40% obtained at pH 9.0. The reductive cleavage of azo-bond by emitted electrons more readily took place as compared with the cleavage of aromatic rings of Orange II leading to the degradation to smaller molecules and subsequently the mineralization. A reaction kinetic model based on the Langmuir-Hinshelwood/Eley-Rideal approach was developed to elucidate mechanisms for organic pollutant removal controlled by the formation of iron oxide/hydroxide layer, the progress of which could be characterized by considering the dynamic concentration changes in Fe(2+) and DO. The dynamic profiles of Orange II removal linked with Fe(2+) and DO could be reasonably simulated in the range of pH from 3.0 to 9.0.

Removal of cationic dye methylene blue by zero-valent iron: Effects of pH and dissolved oxygen on removal mechanisms.

Effects of pH and dissolved oxygen on mechanisms for decolorization and total organic carbon (TOC) removal of cationic dye methylene blue (MB) by zero-valent iron (ZVI) were systematically examined. Decolorization and TOC removal of MB by ZVI are attributed to the four potential mechanisms, i.e. reduction, degradation, precipitation and adsorption. The contributions of four mechanisms were quantified at pH 3.0, 6.0 and 10.0 in the oxic and anoxic systems. The maximum efficiencies of decolorization and TOC removal of MB were found at pH 6.0. The TOC removal efficiencies at pH 3.0 and 10.0 were 11.0 and 17.0%, respectively which were considerably lower as compared with 68.1% at pH 6.0. The adsorption, which was favorable at higher pH but was depressed by the passive layer formed on the ZVI surface at alkaline conditions, characterized the effects of pH on decolorization and TOC removal of MB. The efficiencies of decolorization and TOC removal at pH 6.0 under the anoxic condition were 73.0 and 59.0%, respectively, which were comparable to 79.9 and 55.5% obtained under the oxic condition. In the oxic and anoxic conditions, however, the contributions of removal mechanisms were quite different. Although the adsorption dominated the decolorization and TOC removal under the oxic condition, the contribution of precipitation was largely superior to that of adsorption under the anoxic condition.

Mechanisms for removal of p-nitrophenol from aqueous solution using zero-valent iron.

Batch experiments were conducted to examine mechanisms for removal of p-nitrophenol (PNP) from aqueous solution using zero-valent iron (ZVI). Removal of PNP using ZVI was mainly attributed to three mechanisms: degradation, precipitation and adsorption. A complete removal of 30 mg L(-1) PNP with ZVI dosage of 1000 mg L(-1) achieved within 30 min at pH 3. The PNP removal rate in the acidic solutions was significantly suppressed at higher pH. The modified Langmuir-Hinshelwood kinetic model could successfully describe the PNP removal process using ZVI at different pH conditions. Total organic carbon (TOC) removal efficiencies were found to be almost independent of pH. While the TOC removal at lower pH was profoundly affected by the reductive and/or oxidative degradation, the adsorption was favorable at higher pH. The effect of dissolved oxygen on PNP removal was investigated at pH 3 where a maximum contribution of oxidative degradation could be expected. The PNP removal in the anoxic system purged with nitrogen gas was quick as well as that in the system being open to the air. However, the TOC removal under the anoxic condition was negligible as compared with that in the oxic system. The profiles of the intermediates formed during the PNP degradation indicated that the reductive degradation was predominant in the initial phase of the removal and subsequently the oxidative degradation occurred.

Simultaneous removal of nitrate, hydrogen peroxide and phosphate in semiconductor acidic wastewater by zero-valent iron.

The zero-valent iron (ZVI) wastewater treatment has been applied to simultaneous removal of nitrate, hydrogen peroxide and phosphate in semiconductor acidic wastewaters. The simultaneous removal occurs by the reactions performed due to the sequential transformation of ZVI under the acidic condition. Fortunately the solution pH of semiconductor acidic wastewaters is low which is effective for the sequential transformation of ZVI. Firstly the reduction of nitrate is taken place by electrons generated by the corrosion of ZVI under acidic conditions. Secondly the ferrous ion generated by the corrosion of ZVI reacts with hydrogen peroxide and generates ·OH radical (Fenton reaction). The Fenton reaction consists of the degradation of hydrogen peroxide and the generation of ferric ion. Finally phosphate precipitates out with iron ions. In the simultaneous removal process, 1.6 mM nitrate, 9.0 mM hydrogen peroxide and 1.0 mM phosphate were completely removed by ZVI within 100, 15 and 15 min, respectively. The synergy among the reactions for the removal of nitrate, hydrogen peroxide and phosphate was found. In the individual pollutant removal experiment, the removal of phosphate by ZVI was limited to 80% after 300 min. Its removal rate was considerably improved in the presence of hydrogen peroxide and the complete removal of phosphate was achieved after 15 min.

Decolorization of dark brown colored coffee effluent using zinc oxide particles: the role of dissolved oxygen in degradation of colored compounds.

The degradation of model dark brown colored coffee effluent using photocatalyst zinc oxide (ZnO) has been systematically studied by varying ZnO dosage from 0 to 4000 mg L(-1), coffee loading from 0 to 90 mg L(-1) and intensity of UV light having the radiation peak at 352 nm from 0 to 18 W(m-lamp length)(-1). Almost complete decolorization was achieved after 180 min for the initial coffee concentration of 50 mg L(-1) with ZnO dosage of 3000 mg L(-1) and three UV lamps. The dissolved oxygen (DO) largely affected the photodecolorization process. Without air sparging or with oxygen supply only through the free-surface, the DO concentration significantly decreased during the initial decolorization process and then increased to the saturated DO concentration after about 80% decolorization was achieved. Under the anoxic condition with nitrogen gas sparging, the efficient color removal was not obtained unlike the decolorization without air sparging or under the oxic condition with air sparging. These findings suggest that the change in DO concentration was controlled by the oxygen consumption for the formation of oxygen adduct intermediates such as organoperoxy radicals. The mineralization rate of model coffee effluent was rather slow as compared with the decolorization rate and it was insignificantly affected by anoxic and oxic conditions. The present results indicate that ZnO photocatalyst has potential for treatment of coffee processing wastewaters.

UV light photo-Fenton degradation of polyphenols in oolong tea manufacturing wastewater.

The UV light photo-Fenton degradation of oolong tea polyphenols in tea manufacturing effluent that color the wastewater to a dark brown has been examined. In order to elucidate the photo-Fenton degradation mechanism of oolong tea polyphenols and find the optimal dosages of the Fenton reagents, systematic study has been conducted. For the UV light photo-Fenton degradation of oolong tea effluent being 70 mg-(polyphenol) L(-1), the optimum dosages of Fenton reagents were found to be 20 mgL(-1) of total Fe and 500 mgL(-1) of H2O2. The polyphenol degradation could be divided into two stages. The polyphenols concentration rapidly decreased to around 30% of the initial concentration within 2 min and the degradation rate significantly slowed down in the subsequent stage. After 60 min of UV light irradiation, 97% polyphenol removal was obtained. The initial quick degradation of oolong tea polyphenols suggests that hydroxyl radical generated by the photo-Fenton process might preferentially attack polyphenols having high antioxidant activity by scavenging hydroxyl radicals. Almost complete decolorization of the oolong tea effluent was achieved after 80 min. About 96% mineralization of 63 mgL(-1) TOC loading was achieved within 60 min and then further mineralization was rather slow. The complete COD removal of 239 mgL(-1) COD loading was obtained after 100 min. The present results indicate that the UV light photo-Fenton degradation process can treat tea manufacturing wastewaters very effectively.

Solar photo-Fenton process for the treatment of colored soft drink wastewater: decolorization, mineralization and COD removal of oolong tea effluent.

The decolorization and mineralization of dark-brown-colored oolong tea effluent by the solar photo-Fenton process has been examined. The solar photo-Fenton process for a fine day achieved 92% decolorization after 60 min and 94% mineralization after 80 min. For a cloudy day, about 88% decolorization and 85% mineralization were obtained after 290 min. For reference the UV light photo-Fenton process was also conducted. Very similar degradation efficiencies were found between the solar and UV light photo-Fenton processes. However, the intrinsic low cost associated with abundant solar energy turned out to be more efficient in treating oolong tea effluent as compared with UV light. The decolorization and mineralization profiles under the different light intensities could be unified with the accumulated light energy instead of with irradiation time. This implies that the solar photo-Fenton process should be designed and operated on the basis of the accumulated energy rather than the reaction time. The COD removal was 99.3% after 75 min under the fine condition. This removal rate for a fine day was approximately twice as fast than that for a cloudy day and comparable to that by the UV light irradiation. The results obtained in this study suggest that the solar photo-Fenton process offers a promising technology for decolorization and degradation of oolong tea effluent.

Photo-Fenton degradation of non-ionic surfactant and its mixture with cationic or anionic surfactant.

The oxidative degradation of non-ionic surfactants by the photo-Fenton process has been examined. The photo-Fenton degradation kinetics of mixtures of non-ionic surfactant and other type surfactants has been also investigated since mixtures of non-ionic and ionic surfactants are commonly used to utilize their synergistic effects in many practices. Effects of operating parameters such as dosages of Fenton reagents (iron and hydrogen peroxide) and UV light intensity on the degradation of commercial non-ionic surfactant Sannonic SS-90 (polyoxyethylene alkyl ether) were studied. Although the dosages of the Fenton reagents increased the degradation rate up to the optimum dosages, further addition of the reagents could not enhance the degradation rate. Excess dosages of Fe and H(2)O(2) caused excess OH radicals which could be a scavenger of OH radicals and as a result could not enhance the degradation of the surfactant. The increase in UV light intensity resulting in the faster photo-Fenton process or the enhancement of OH radical formation rate led to the increase in degradation rate of non-ionic surfactant. Although the existence of the anionic surfactant (sodium dodecylbenzene sulphonate) would inhibit the degradation of the non-ionic surfactant due to the formation of complex with Fe ion, the existence of cationic surfactant (dodecyltrimethyl ammonium chloride) affected insignificantly the photo-Fenton degradation process of the non-ionic surfactant.

Phenol removal using zero-valent iron powder in the presence of dissolved oxygen: roles of decomposition by the Fenton reaction and adsorption/precipitation.

The mechanism for removal of phenol by zero-valent iron (ZVI) was quantitatively evaluated in the presence of dissolved oxygen by varying the pH from 2 to 8.1 (natural). The measurement of OH radical concentration suggests that the removal of phenol by ZVI was occurred due to the decomposition by the Fenton reaction besides the adsorption/precipitation to the iron surface. From the measurements of dissolved organic carbon (DOC) in the filtrate with the 0.45 µm syringe filter and the solution obtained from acidification of suspended precipitates, the roles of decomposition by the Fenton reaction and adsorption/precipitation were separately evaluated. At solution pH 3, 91% of phenol removal was achieved and 24% of TOC (total organic carbon) decreased. The contribution of the Fenton reaction was found to be 77% of overall TOC reduction. When the pH values were 4 and 5, the overall TOC removal was found to be mainly due to the adsorption/precipitation. At pH 2 and 8.1, the reduction of TOC was very small. The pH and dissolved oxygen significantly affected the dissolution of iron and the production of OH radicals and changed the roles of phenol removal by the Fenton reaction and adsorption/precipitation.

Hydroxyl radical concentration profile in photo-Fenton oxidation process: generation and consumption of hydroxyl radicals during the discoloration of azo-dye Orange II.

Dynamic behaviors of hydroxyl (OH) radical generation and consumption in photo-Fenton oxidation process were investigated by measuring OH radical concentration during the discoloration of azo-dye Orange II. The effects of operating parameters for photo-Fenton discoloration, i.e. dosages of H(2)O(2) and Fe, initial dye concentration, solution pH and UV irradiation, on the generation and consumption of OH radicals playing the main role in advanced oxidation processes were extensively studied. The scavenger probe or trapping technique in which coumarin is scavenger of OH radical was applied to estimate OH radical concentration in the photoreactor during the photo-Fenton discoloration process. The OH radical generation was enhanced with increasing the dosages of Fenton regents, H(2)O(2) and Fe. At the initial stage of photo-Fenton discoloration of Orange II, the OH radical concentration rapidly increased (Phase-I) and the OH radical concentration decreased after reaching of OH radical concentration at maximum value (Phase-II). The decrease in OH radical concentration started when the complete discoloration of Orange II was nearly achieved and the H(2)O(2) concentration became rather low. The dynamic behavior of OH radical concentration during the discoloration of Orange II was found to be strongly linked with the change in H(2)O(2) concentration. The generation of OH radical was maximum at solution pH of 3.0 and decreased with an increase of solution pH. The OH radical generation rate in the Fenton Process was rather slower than that in the photo-Fenton process.

Modeling of p-nitrophenol biodegradation by Ralstonia eutropha via application of the substrate inhibition concept.

In this study, the capability of Ralstonia eutropha H16 to degrade p-nitrophenol with or without a supplementary substrate (glucose or yeast extract) was investigated. Using PNP as the sole energy and carbon source, the biodegradation behavior of the bacterium was modeled by applying a modified form of the Monod equation that considers substrate inhibition, as suggested in the literature (mu=(mu(m)S/k(s) +S)(1-(S/S(m)(n)). PNP at a 6 mg/L initial level was degraded within 20h under the defined incubation conditions (shaking at the reciprocal mode, pH 7 and temperature of 30 degrees C) however the biodegradation was enhanced when yeast extract included in the test medium (50% reduction in the time for complete degradation). When glucose was used instead of yeast extract in the test medium R. eutropha growth was not supported by this carbohydrate and PNP was degraded in about 14h indicating degradation time reduced by 1/3. Comparison of R. eutropha growth pattern showed that biomass formation was insignificant when the bacterium grew in the test medium containing only PNP or PNP plus glucose. But by use of yeast extract considerable biomass formation was observed (OD(546)=0.35 versus 0.1). The presence of organic pollutants in natural ecosystems at low levels frequently occurs in form of mixture with other compounds. The findings of the present work were discussed in terms of secondary substrate utilization for R. eutropha at low PNP level.