Single and Combined Application of Ozonation and Coagulation/Flocculation for Humic Acid Removal

Humic acids are often found in surface and ground waters as a result of organic matter decay. In this study, water samples containing 50 mgL^?1 humic acid were treated by conventional application of coagulation/flocculation technique. The results showed 70% ±10 turbidity, ≥82% ±10 UV₂₅₄ absorbance and 85% ±10 total organic carbon removal under pH 5–9 and above 5 mgL^?1 Fe³⁺ coagulant doses. Application of post-ozonation significantly increased the UV₂₅₄ absorbance and turbidity removal under low dose Fe³⁺ application. On the other hand ozonation prior to coagulation/flocculation process altered the structure of HA and caused no significant improvement in removal efficiencies.     

Removal of phosphate by adsorption onto oyster shell powder—kinetic studies

Kinetic studies on the removal of phosphate by adsorption onto oyster shell powder have been investigated at 24 °C. The results showed that the equilibrium occurred in 10 min and the equilibrium data followed the Freundlich isotherm. Freundlich constants were found to be k_f, 1.4 × 10^?2, and n, 0.71. The phosphate removal was not influenced by pH over the range 5.0–10.5. Continuous agitation studies at 24 °C and 530 rpm reached equilibrium after 7.7 days, when 24 g dm^?3 of oyster shell powder reduced the phosphate concentration from 50 to 7.0 mg dm^?3. The Lagergren rate constant for the slow adsorption process was observed to be 3.81 × 10^?4 dm³ min^?1. Comparison with calcium carbonate, GR grade, showed that oyster shell powder and CaCO₃ behave more or less in the same way. Copyright © 2004 Society of Chemical Industry     

Towards the design of non-amyloidogenic proteins

Glucose oxidase was immobilized onto poly(2-hydroxyethyl methacrylate) (pHEMA) membranes by two methods: by covalent bonding through epichlorohydrin and by entrapment between pHEMA membranes. The highest immobilization efficiency was found to be 17.4% and 93.7% for the covalent bonding and entrapment, respectively. The K_m values were 5.9 mmol dm^?3, 8.8 mmol dm^?3 and 12.4 mmol dm^?3 for free, bound and entrapped enzyme, respectively. The V_max values were 0.071 mmol dm^?3 min^?1, 0.067 mmol dm^?3 min^?1 and 0.056 mmol dm^?3 min^?1 for free, bound and entrapped enzyme. When the medium was saturated with oxygen, K_m was not significantly altered but V_max was. The optimum pH values for the free, covalently-bound and entrapped enzyme were determined to be 5, 6, and 7, respectively. The optimum temperature was 30°C for free or covalently-bound enzyme but 35°C for entrapped enzyme. The deactivation constant for bound enzyme was determined as 1.7 × 10^?4 min^?1 and 6.9 × 10^?4 min^?1 for the entrapped enzyme.     

Modelling of Cr(VI) removal from polluted groundwaters by ion exchange

This work reports the viability and modelling of the removal of Cr(VI) from polluted groundwaters by means of ion exchange using the resin Lewatit MP‐64. Feed groundwaters that contained Cr(VI) at an average concentration of 2431 mg dm^?3 and 1187 mg dm^?3 of chloride and 1735 mg dm^?3 of sulfate as main anions were acidified to a pH of 2.0 prior to the removal process. Dynamic experiments were carried out in a fixed bed column with feed waters at flow rates in the range of 2.78 × 10^?7 m³ s^?1 to 5.55 × 10^?7 m³ s^?1. Regeneration was achieved with NaOH (2 mol dm^?3). From the experimental results, the equilibrium of the ion exchange reaction was successfully modelled, obtaining an equilibrium constant (K′_AB) = 44.90. Finally, a mass balance that included mass transfer resistances in the liquid and solid phases was developed and from the comparison between simulated and experimental data the value of the effective intraparticle diffusivity (D_s) was determined as 1.43 × 10^?12 m² s^?1. Copyright © 2004 Society of Chemical Industry     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

Photoelectrocatalytic bleaching of p-nitrosodimethylaniline using Ti/TiO2 nanostructured electrodes deposited by means of a pulsed laser deposition process

This study investigated the potential use of oxidation in a photoelectrocatalytic cell for bleaching p-nitrosodimethylaniline. The Ti/TiO₂ used as photo-anode was prepared by a pulsed laser deposition method. The TiO₂ coatings were found to have rutile and anatase structures consisting of approximately 10 and 15 nm in diameter, respectively. A relatively high degradation rate of p-nitrosodimethylaniline was recorded using the photoelectrocatalytic cell, compared to those measured during conventional electrochemical oxidation, direct photolysis and photocatalysis processes. The influence of different parameters such as crystallographic structure of Ti/TiO₂, type of cathode, potential applied, electrolysis time, UV irradiation and initial pH were investigated. The photoelectrocatalytic cell using Ti/TiO₂ (anatase structure) as photo-anode and vitreous carbon as cathode operated at a current intensity of 0.1 A for 120 min with 254 nm of UV irradiation was found to have the best conditions to remove high amounts of p-nitrosodimethylaniline (22.6 × 10^?3 mM h^?1).     

The Fenton Chemistry and Its Combination with Coagulation for Treatment of Dye Solutions

Abstract

Aqueous solutions of Acid Blue 74, Acid Orange 10, and Acid Violet 19 were subjected to Fenton/Fenton‐like oxidation and its combination with lime coagulation. The analysis indicated no dependence of chemical oxidation efficacy on dye concentration in the range of 0.1–1 g L^?1. Complete or nearly complete (higher than 95%) color removal of all treated samples was observed. Dye:H₂O₂ weight ratio of 1∶2 proved optimal for treatment of all dye solutions by means of Fenton/Fenton‐like oxidation. Moderate doses of hydrogen peroxide led to the improvement of biodegradability of dye solutions. No formation of any toxic intermediates during the oxidation of Acid Orange 10 and Acid Violet 19 was detected. Only a slight toxicity increase was observed after Acid Blue 74 degradation by Fenton chemistry. H₂O₂/Fe³⁺ system with pH adjusted to 3 proved the most effective oxidation process. The combination of Fenton chemistry and subsequent lime coagulation was the most feasible treatment method of removing COD and UV₂₅₄ and UV_max absorbance of dye solutions. Combined oxidation and coagulation was more effective for Acid Blue 74 and Acid Orange 10 elimination than for Acid Violet 19.     

Effect of pre‐treatments based on UV photocatalysis and photo‐oxidation on toluene biofiltration performance

BACKGROUND: The integration of UV photocatalysis and biofiltration seems to be a promising combination of technologies for the removal of hydrophobic and poorly biodegradable air pollutants. The influence of pre‐treatments based on UV_{254 nm} photocatalysis and photo‐oxidation on the biofiltration of toluene as a target compound was evaluated in a controlled long‐term experimental study using different system configurations: a standalone biofilter, a combined UV photocatalytic reactor‐biofilter, and a combined UV photo‐oxidation reactor (without catalyst)‐biofilter. RESULTS: Under the operational conditions used (residence time of 2.7 s and toluene concentrations 600–1200 mg C m^?3), relatively low removal efficiencies (6–3%) were reached in the photocatalytic reactor and no degradation of toluene was found when the photo‐oxidation reactor was operated without catalyst. A noticeable improvement in the performance of the biofilter combined with a photocatalytic reactor was observed, and the elimination capacity of the biological process increased by more than 12 g C h^?1 m^?3 at the inlet loads studied of 50–100 g C h^?1 m^?3. No positive effect on toluene removal was observed for the combination of UV photoreactor and biofilter. CONCLUSIONS: Biofilter pre‐treatment based on UV_{254 nm} photocatalysis showed promising results for the removal of hydrophobic and recalcitrant air pollutants, providing synergistic improvement in the removal of toluene. Copyright © 2011 Society of Chemical Industry     

Photocatalytic degradation of humic acid in the presence of montmorillonite

Humic acids (HA) representing the major fraction of the naturally occurring humic substances (HS) are composed of highly functionalized carbon rich polydisperse organic fractions. Clay minerals which are responsible for the transport of inorganic and organic contaminants constitute the main component of the dispersed inorganic material in natural waters. The understanding of interactions between humic substances and clay minerals is an important task for the achievement of an effective water treatment performance. The aim of this research was to investigate the influence of montmorillonite as a representative clay mineral on the TiO₂ photocatalytic removal of humic acids as the model compound of natural organic matter. The interactions prevailing between humic acid, montmorillonite and TiO₂ surface were assessed prior to the application of photocatalysis in order to address the adsorptive and photolytic behavior of humic acids. The changes attained in humic acid were described by UV–vis spectroscopic i.e. color forming moieties (Color₄₃₆) and UV absorbing centers (UV₃₆₅ and UV₂₅₄), and dissolved organic carbon (DOC) contents. Application of the pseudo first order kinetic model revealed both an enhancement and retardation with respect to the applied montmorillonite dose. The overall effect of montmorillonite on the photocatalytic degradation of humic acid was also evaluated in terms of molecular size distribution profiles (0.45 μm filtered fraction, 100 kDa fraction, 30 kDa fraction and 3 kDa fraction) described by the specified and DOC normalized specific UV–vis parameters.     

Photocatalytic degradation of 17α‐ethynylestradiol in environmental samples by ZnO under simulated solar radiation

BACKGROUND: Recently, the fate of emerging micro‐contaminants in environmentally relevant samples has attracted considerable attention. Semiconductor photocatalysis may offer an appealing methodology to treat such contaminants; in this respect, the degradation of synthetic estrogen 17α‐ethynylestradiol (EE2) employing simulated solar radiation and ZnO as the photocatalyst was investigated. RESULTS: A factorial design approach was adopted to evaluate the effect of estrogen concentration (100–500 µg L^?1), ZnO concentration (50‐500 mg L^?1 in suspension), treatment time (2‐10 min), photon flux (4.93 × 10^?7–5.8 × 10^?7 einstein L^?1 s^?1) and the water matrix (ultrapure water and treated wastewater) on EE2 removal. The first four variables had a statistically important, positive effect on degradation, while the water matrix introduced a negative effect presumably due to the competition between EE2 and the effluent organic and inorganic matter for hydroxyl radicals and other oxidizing species. Moreover, second‐order interactions of estrogen concentration with time and the water matrix were also significant. EE2 degradation follows first‐order kinetics with the respective rate constants in wastewater and water being 9.2 ± 0.7 × 10^?2 and 41 ± 8 × 10^?2 min^?1 at the maximum ZnO concentration and photon flux. On the other hand, the removal rate of effluent's overall estrogenicity (as assessed by the yeast estrogen screening bioassay) was an order of magnitude lower than that of EE2, implying the presence of persistent estrogenic compounds in the photocatalyzed effluent. CONCLUSIONS: An effective treatment process is demonstrated which benefits from the use of renewable energy and a stable and highly active photocatalyst. Copyright © 2012 Society of Chemical Industry     

Photocatalytic degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the layer of TiO2 particles in the batch mode plate film reactor

The photocatalytic degradation of diuron in aqueous solution on TiO₂ layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0·8–8·0×10⁻⁵ mol dm⁻³) and on the light intensity (0·8–2·7×10⁻⁹ einstein cm⁻² s⁻¹) but independence on the flow rate (2·5–3·6 dm³ min⁻¹) were found. A reaction scheme was proposed following the main identified primary [3-(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methylurea] and secondary [3-(3,4-dichlorophenyl)-1-formylurea and 3,4-dichlorophenylurea] products. © 1998 SCI     

Oxidation of Esculetin,a Model Pollutant Present in Cork Processing Wastewaters,by Chemical Methods

The ozonation of esculetin (6,7-dihydroxycoumarin), a major pollutant present in the wastewater generated in the cork industry, was accelerated at high pH, with apparent second-order rate constants in the range from 3.3 × 10⁴ L/(mol·s) at pH=2 to 8.4 × 10⁷ L/(mol·s) at pH=9. The acid-base equilibrium of esculetin was studied, resulting in a pK_a value of 7.37. Taking into account this pK_a, the rate constants for the reaction between ozone and the un dissociated and dissociated forms of esculetin were 3.0 × 10⁴ and L/(mol·s) 6.67 × 10⁸ L/(mol·s), respectively. Apparent first-order rate constants for the photolysis by UV irradiation were also evaluated, with values between 0.12 × 10^?2 min^?1 at pH=2 and 1.15 × 10^?2 min^?1 at pH=9, while the quantum yields for this photo-degradation reaction varied from 0.99 × 10^?2 mol/Eins to 11.1 × 10^?2 mol/Eins at these pHs. The Fenton's reagent system was used for the generation of hydroxyl radicals, and the rate constant for the reaction between esculetin and these radicals was determined to be 1.06 × 10¹⁰ L/(mol·s). Finally, several chemical oxidation systems were used in the degradation of this pollutant: single oxidants (ozone, UV irradiation) and advanced oxidation processes (Fenton's reagent, UV/H₂O₂, O₃/H₂O₂, O₃/UV, O₃/H₂O₂ /UV, and photo-Fenton system). The results revealed that the most efficient methods in terms of esculetin removal were ozonation among the single oxidants, and the photo-Fenton system among the combined processes.     

Degradation and Transformation of Organic Compounds in Songhua River Water by Catalytic Ozonation in the Presence of TiO2/Zeolite

This paper presents experimental results of the catalytic ozonation of Songhua River water in the presence of nano-TiO₂ supported on Zeolite. The removal efficiency of TOC and UV₂₅₄, the variation of AOC and molecular weight distribution of organics was studied. Results showed that TOC and UV₂₅₄ removal efficiency by ozone was improved in the presence of TiO₂/Zeolite, and increased by 20% and 25%, respectively. The part of organic compounds less than 1000 Da increased in ozonation, but decreased in catalytic ozonation. The AOC of water increased in catalytic ozonation, and the increase of AOC was particularly obvious when ozone dose increased from 28.8 mg·L^?1 to 46.6 mg·L^?1. The degradation and transformation of organic compounds was analyzed by means of GC-MS. The total number of organic compounds was reduced from 50 in the untreated water to 36 and 20, respectively, in ozonation and catalytic ozonation. The removal efficiency of the total organic compounds peak area in ozonation and catalytic ozonation were 23.5% and 62.5%, respectively. Most of the hydrocarbons could be removed easily in ozonation and catalytic ozonation. The organic compounds having hydroxyl, carboxyl or carbonyl groups were hard to be removed in ozonation, but could be removed efficiently in the presence of TiO₂/Zeolite.     

Optimisation of the biological treatment of hypersaline wastewater from Dunaliella salina carotenogenesis

The reutilisation of Dunaliella salina carotenogenesis medium, after microalgal biomass separation by centrifugation, was assessed. The wastewater had an NaCl concentration between 174 g dm^?3 and 254 g dm^?3 and an average total organic matter concentration of 1540 mg dm^?3 ash‐free dry weight, of which 41% (w/v) was glycerol. The biological treatment was established at laboratory scale and batch operations used halophilic bacteria from the wastewater itself. The wastewater was supplemented with NH₄⁺,PO₄^3?, K⁺ and Mg²⁺ ions to enhance growth. The effect of each ion added per se was initially investigated and a response surface methodology (RSM) used to identify the optimal conditions for maximisation of glycerol removal from the wastewater, which was considered to be the main objective. Addition of NH₄⁺ ions alone achieved 79% glycerol removal compared with only 59% in the absence of supplement, after 8 days incubation. The combined addition of ions ([NaCl] = 214 g dm^?3, [Mg²⁺] = 114 mg dm^?3, [K⁺] = 131 mg dm^?3, [NH₄⁺] = 113 mg dm^?3, [PO₄^3?] = 40 mg dm^?3) increased glycerol removal from the wastewater such that, after 2 days incubation, no residual glycerol was apparent in cultures. These ion combinations enabled the halophilic bacteria to efficiently remove glycerol from the wastewater and consequently reduce organic matter. This treated wastewater should be appropriate for reutilisation as a carotenogenesis medium for β‐carotene production from D salina. © 2001 Society of Chemical Industry     

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.     

The application of reticulated vitreous carbon rotating cylinder electrodes to the removal of cadmium and copper ions from solution

The removal of cadmium and cupric ions from 0.50 mol dm^?3 Na₂SO₄ at pH 2 and 298 K was studied using a reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The cathode was a 100 pores per linear inch porosity grade with a radius of 0.5 cm, a height of 1.2 cm and a volume of 0.94 cm 3 . The cathode was rotated a constant speed of 1500 rev min^?1. A rate enhancement of approximately three times is reported for the removal of cupric ions from a chloride solution (0.05 mol dm^?3 cupric ions in 0.1 mol dm^?3 NaCl at pH 7) when compared with the analogous reaction in acid sulfate solutions (0.50 mol dm^?3 Na₂SO₄ at pH 2). SEM images of the metal deposit morphology allow the morphology of the metal deposits to be characterised. The deposits showed incomplete coverage of the RVC surface and appreciable roughness developed with time due to dendritic growths. Copyright © 2004 Society of Chemical Industry     

Fourier-transform infrared assay of bile salt-stimulated lipase activity in reversed micelles

A Fourier-transform infrared (FT-IR) spectroscopic method has been developed for assaying the bile salt-stimulated human milk lipase (BSSL, EC3.1) catalyzed hydrolysis of triolein in AOT reversed micelles in iso-octane. At 37°C in 50 mmol dm^?3 AOT the molar absorbtivities for the carbonyl stretching frequencies for triolein (at 1751 cm^?1) and oleic acid (at 1714 cm^?1) were 1646 dm³ mol^?1 cm^?1 and 743 dm^?3 mol^?1 cm^?1, respectively. The rate was linearly dependent upon the concentration of enzyme in the water pool up to 10 mg cm^?3 and maximum activity was observed at a ratio (w₀) of [H₂O]:[AOT] = 16·7. Using these conditions, and in the presence of 10 mmol dm^?3 sodium taurocholate (TC), the derived Michaelis–Menten parameters V_max and K_m were 57·5 μmol min^?1 mg^?1 and 5·53 mmol dm^?3, respectively. These results are compared with those obtained in an oil-in-water microemulsion system and are discussed in terms of the relative partitioning of the enzyme and the substrate in the aqueous and oil phases and the interfacial concentration of the substrate in the two systems.     

Sonophotocatalytic degradation of eriochrome black-T dye in water using Ti grafted SBA-15

Here in, a series of titanium-modified mesoporous silica (Ti-SBA-15) was prepared by grafting titanium isopropoxide. The as-synthesized Ti-SBA-15 nanocatalysts were characterized through N₂-adsorption–desorption, XRD, TGA/DSC, TEM and EDX techniques. Sonocatalytic and sonophoto-catalytic degradation of Eriochrome Black T (EBT) dye were investigated. 88.7 % removal was achieved in 70 min by using 5 % Ti-SBA-15 through sonophotocatalytic degradation under visible light irradiation. The kinetic study revealed that photo-degradation of EBT follows pseudo-first order reaction mechanism, where the rate constant was 27.4 × 10^?3 min^?1.     

Post-Treatment of Pulp and Paper Industry Wastewater by Advanced Oxidation Processes

The aim of this study was to investigate the effectiveness of chemical oxidation by applying ozonation, combination of ozone and hydrogen peroxide and Fenton's processes for decolorization and residual chemical oxygen demand (COD) removal of biologically pretreated pulp and paper industry effluents. The batch tests were performed to determine the optimum operating conditions including pH, O₃, H₂O_2, and Fe²⁺ dosages. H₂O₂ addition reduced the reaction times for the same ozone dosages; however combinations of ozone/hydrogen peroxide were only faintly more effective than ozone alone for COD and color removals. In the Fenton‘s oxidation studies, the removal efficiencies of COD, color and ultraviolet absorbance at 254 nm (UV₂₅₄) for biologically treated pulp and paper industry effluents were found to be about 83, 95, and 89%, respectively. Experimental studies indicated that Fenton oxidation was a more effective process for the reduction of COD, color, and UV₂₅₄when compared to ozonation and ozone/hydrogen peroxide combination. Fenton oxidation was found to have less operating cost for color removal from wastewater per cubic meter than the cost for ozone and ozone/hydrogen peroxide applications.     

Ozonation of Two Commercially Important Biocidal Finishing Agents

Ozonation of 2 commercially important textile biocidal finishing agents (called BI and BII herein) in aqueous solution was studied in a semi-batch bubble column reactor at different ozone feed rates (500, 750, and 900 mg/h) and pH (pH=7 and 12). Ozonation efficiency and kinetics were assessed in terms of COD, TOC and UV absorbance at 280 nm (UV₂₈₀) and 254 nm (UV₂₅₄), representing the aromaticity and unsaturated moieties of the studied textile biocides, respectively. Due to its chlorinated aromatic content, the fate of Adsorbable Organic Halogens (AOX) of BI was also followed during the ozonation experiments. At alkaline pH, appreciably higher COD and TOC removals were achieved, speaking for a free radical (^?OH) dominated degradation pathway for both tested biocides. AOX, UV₂₈₀ and TOC abatement rates obtained for BI ozonation at optimized reaction conditions indicated that the degradation of BI followed a sequential path of dechlorination, dearomatization, oxidation and mineralization, respectively.