Study on degradation process of famotidine hydrochloride in aqueous samples

The kinetics of famotidine (FAM) transformation under the influence of various factors, important from the environmental point of view, was investigated in aqueous solutions. The degradation processes using UV, H₂O₂, UV/H₂O₂, H₂O₂/Fe²⁺, and UV/H₂O₂/Fe²⁺ were studied. Direct photolysis and H₂O₂-assisted photolysis showed a pseudo-first-order kinetics, while the Fenton and the photo-Fenton processes fit second-order kinetics. The provided experiments proved a high resistance of FAM to direct photolysis. Its stability depends highly on the pH of the reaction solutions. The rate of FAM direct photolysis in acidic solutions was almost negligible. The reaction rate of FAM photolysis at pH 8–9 was 3.7 × 10^?3 min^?1 with DT₅₀ about 3 h 7 min. It was found that the presence of H₂O₂ in the reaction environment enhances the rate of photolysis of FAM. The observed rates of reaction were 5.1 × 10^?3 min^?1 and 3.7 × 10^?3 min^?1 in acidic and basic solutions, respectively. The used Fenton systems appeared to be the most efficient in FAM removal. The rate of reaction depends on concentration of Fe²⁺ and H₂O₂. It was observed that the presence of UV-light enhances the reaction rate by two to six times in comparison to the classical Fenton system. Additionally, FAM behavior in natural water under solar irradiation was examined. The irradiation experiments were carried out in batch experiments with simulated sunlight.     

Sonocatalytic degradation of tetracycline antibiotic in aqueous solution by sonocatalysis

Tetracycline (TC), one of the most common antibiotics, is often poorly bio-degraded in conventional wastewater treatment plants. In this study, the sonocatalytic degradation of TC was investigated using TiO₂ nano-particles as catalyst. The effect of pH, initial TC concentrations, reaction times, and H₂O₂ concentrations were evaluated. The efficacy of ultrasonic irradiation alone in the removal of this pollutant was negligible but removal efficiency increased upon addition of TiO₂ up to 250 mg L^?1; increase of pH and initial TC concentration attenuated TC degradation. Addition of H₂O₂ raised the removal efficiency so that complete removal of TC was achieved within 75 min.     

Removal of Eu3+, Ce3+, Sr2+, and Cs+ ions from radioactive waste solutions by modified activated carbon prepared from coconut shells

As a biomass agricultural waste material, coconut shells were used for the preparation of high-quality modified activated carbon. Chemical modification of the surface of the prepared activated carbon is done by oxidation using H₂O₂ and HNO₃, respectively. The surface area and pore volume of the coconut shells activated carbon are increased by the chemical modification, and followingly the removal of the metals is improved. The structural morphology and composition of the modified activated carbon coconut shells (MACCS) were evaluated by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis–differential thermal analysis (TGA-DTA), scanning electron microscope (SEM), X-ray diffraction (XRD), surface area analysis (SAA), X-ray fluorescence (XRF), and carbon, hydrogen, nitrogen, and sulfur (CHNS) elemental analysis. The prepared MACCS has reasonably good chemical stability. The influence of solution pH, contact time, adsorbent dosage, adsorption temperature, initial metal concentrations, and interfering ions on the adsorption performance of the investigated ions onto the prepared sorbent was examined by a batch method. The selectivity sequence for sorption of Eu³⁺, Ce³⁺, Sr²⁺, and Cs⁺ ions on MACCS was found to be Eu^3+?>?Ce^3+?>?Sr^2+?>?Cs⁺. The saturation capacities of MACCS for the studied metal ions were found to be 136.84, 85.55, 69.85, and 60.00?mg?g^?1 for Eu³⁺, Ce³⁺, Sr²⁺, and Cs⁺ ions, respectively. The thermodynamic parameters, ΔH°, ΔS°, and ΔG° were also evaluated.     

Kinetics of the oxidation of endocrine disruptor nonylphenol by ferrate(VI)

The kinetics of the oxidation of endocrine disruptor nonylphenol (NP) by potassium ferrate(VI) (K₂FeO₄) in water as a function of pH 8.0–10.9 at 25°C is presented. The observed second-order rate constants, k _obs, decrease with an increase in pH 269–32 M^?1 s^?1. The speciation of Fe(VI) (HFeO ₄ ^? and FeO ₄ ^2? ) and NP (NP–OH and NP–O^?) species was used to explain the pH dependence of the k _obs values. At a dose of 10 mg L^?1 (50 μM) K₂FeO₄, the half-life for the removal of NP by Fe(VI), under water treatment conditions, is less than 1 min.     

Fe-pillared bentonite,a stable Fenton catalyst for treatment of petroleum refinery wastewater

Fe-pillared bentonite (Fe-Bent) was prepared by ion exchange as heterogeneous catalyst for degradation of organic contaminants in petroleum refinery wastewater. X-ray diffraction analysis showed the existence of α-Fe₂O₃. The effects of pH, H₂O₂ concentration, and catalyst dosage on the rate of lowering the chemical oxygen demand (COD) were investigated in detail. Removal efficiency of COD can be up to 92% under the following conditions: dosage of Fe-Bent 7 g L^?1, pH value 3, and H₂O₂ concentration 10 mmol L^?1. Fe-Bent showed good stability for the degradation of organics in petroleum refinery wastewater for five cycles. The adsorption of organics in wastewater onto Fe-Bent could be well described by a pseudo-second-order kinetic model.     

Removal of olive mill waste water phenolics using a crude peroxidase extract from onion by-products

Olive mill waste water (OMWW) originating from a two-phase olive oil-producing plant was treated with a crude peroxidase extract prepared from onion solid by-products. The treatments were based on a 3 × 3 factorial design, employing a series of combinations of pH and H₂O₂, in order to identify optimal operational conditions. The treatment performance was assessed by estimating the removal percentage of total polyphenols. The model established produced a satisfactory fitting of the data (R ² = 0.94, p = 0.0158), while the second-order polynomial equation used to describe the process indicated that peroxidase-catalysed polyphenol removal in diluted OMWW is facilitated at relatively low pH and intermediate H₂O₂ values. A predicted value of 50.7 ± 9.5% removal was calculated under optimal operational conditions (pH 2.76, [H₂O₂] = 3.56 mM). Analysis of an untreated and an optimally treated sample by high performance liquid chromatography revealed that enzyme treatment brought about alteration in the original OMWW polyphenolic profile. The use of peroxidase from onion solid by-products is proposed as an alternative means that could have a prospect in bioremediation applications.     

Decomposition of perfluorooctanoic acid by microwaveactivated persulfate: Effects of temperature, pH, and chloride ions

Microwave-hydrothermal treatment of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S₂O ₈ ^2? ) has been found effective. However, applications of this process to effectively remediate PFOA pollution require a better understanding on free-radical scavenging reactions that also take place. The objectives of this study were to investigate the effects of pH (pH = 2.5, 6.6, 8.8, and 10.5), chloride concentrations (0.01?C0.15 mol·L^?1), and temperature (60°C, 90°C, and 130°C) on persulfate oxidation of PFOA under microwave irradiation. Maximum PFOA degradation occurred at pH 2.5, while little or no degradation at pH 10.5. Lowering system pH resulted in an increase in PFOA degradation rate. Both high pH and chloride concentrations would result in more scavenging of sulfate free radicals and slow down PFOA degradation. When chloride concentrations were less than 0.04 mol·L^?1 at 90°C and 0.06 mol·L^?1 at 60°C, presence of chloride ions had insignificant impacts on PFOA degradation. However, beyond these concentration levels, PFOA degradation rates reduced significantly with an increase in chloride concentrations, especially under the higher temperature.     

Removal of acid yellow 36 using Box–Behnken designed photoelectro-Fenton: a study on removal mechanisms

Photoelectro-Fenton was applied for the removal of acid yellow 36 (AY36) from synthetic aqueous solution using iron electrodes. A Box–Behnken design was used for optimization of the effects of pH, H₂O₂ concentration, current density, and reaction time. Individual effects of these variables were more important than their interaction effects. The derived model was in good agreement with the experimental results. Total organic carbon was determined in solution and sludge in order to clarify the removal mechanism. Increase of H₂O₂ concentration and current density led to domination of oxidation and coagulation mechanisms, respectively. The effects of scavenging and inhibiting agents were also investigated: (1) presence of alcohols can reduce the efficiency through competition with dye for reaction with hydroxyl radicals; (2) anions (NO₃^?, HCO₃^?, and H₂PO₄^?) scavenged hydroxyl radicals and reduced decolorization of AY36.     

Thermal treatment of plasma-synthesized goethite improves Fenton-like degradation of orange II dye

Various iron oxides are used for Fenton reactions to degrade organic pollutants. The degradation efficiency may be improved by transforming an iron oxide phase to another. Here, we report on the transformation of goethite into hematite by thermal treatment at 400 °C. The products were analyzed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and N₂-physisorption. The catalytic activities were measured for orange II bleaching at initial concentration of 25 mg L^?1, pH 3, catalyst concentration of 0.2 g L^?1; 5 mM H₂O₂, 30 °C. Results show that the synthesized goethite was successfully transformed into hematite, and the specific surface area of the material increased from 134 to 163 m² g^?1. The bleaching efficiency of the orange II dye reached 100 % for the hematite product, versus 78 % for goethite. Therefore, a moderate thermal treatment of a plasma-synthesized goethite improves the catalytic oxidation of organic pollutants.     

Catalytic hydrolysis of gaseous HCN over Cu–Ni/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst: parameters and conditions

To decompose efficiently hydrogen cyanide (HCN) in exhaust gas, g-Al₂O₃-supported bimetallicbased Cu–Ni catalyst was prepared by incipient-wetness impregnation method. The effects of the calcination temperature, H₂O/HCN volume ratio, reaction temperature, and the presence of CO or O₂ on the HCN removal efficiency on the Cu–Ni/g-Al₂O₃ catalyst were investigated. To examine further the efficiency of HCN hydrolysis, degradation products were analyzed. The results indicate that the HCN removal efficiency increases and then decreases with increasing calcination temperature and H₂O/HCN volume ratio. On catalyst calcined at 400°C, the efficiency reaches a maximum close to 99% at 480 min at a H₂O/HCN volume ratio of 150. The HCN removal efficiency increases with increasing reaction temperature within the range of 100°C–500°C and reaches a maximum at 500°C. This trend may be attributed to the endothermicity of HCN hydrolysis; increasing the temperature favors HCN hydrolysis. However, the removal efficiencies increases very few at 500°C compared with that at 400°C. To conserve energy in industrial operations, 400°C is deemed as the optimal reaction temperature. The presence of CO facilitates HCN hydrolysis andincreases NH₃ production. O₂ substantially increases the HCN removal efficiency and NO _x production but decreases NH₃ production.

Open image in new window

     

Bioreduction of nitrate in groundwater using a pilot-scale hydrogen-based membrane biofilm reactor

A long-term pilot-scale H₂-based membrane biofilm reactor (MBfR) was tested for removal of nitrate from actual groundwater. A key feature of this second-generation pilot MBfR is that it employed lower cost polyester hollow fibers and still achieved high loading rate. The steady-state maximum nitrate surface loading at which the effluent nitrate and nitrite concentrations were below the Maximum Contaminant Level (MCL) was at least 5.9 g·N·(m²·d)^?1, which corresponds to a maximum volumetric loading of at least 7.7 kg·N·(m³·d) ^?1. The steady-state maximum nitrate surface area loading was higher than the highest nitrate surface loading reported in the first-generation MBfRs using composite fibers (2.6 g·N·(m²·d)^?1). This work also evaluated the H₂-utilization efficiency in MBfR. The measured H₂ supply rate was only slightly higher than the stoichiometric H₂-utilization rate. Thus, H₂ utilization was controlled by diffusion and was close to 100% efficiency, as long as biofilm accumulated on the polyester-fiber surface and the fibers had no leaks.     

Coupled electrocoagulation–electro-Fenton for efficient domestic wastewater treatment

This article reports the first use of coupled electrocoagulation and electro-Fenton (EF-EC) to clean domestic wastewater. Domestic wastewater contains high amounts of organic, inorganic and microbial pollutants that cannot be usually treated in a single step. Here, to produce an effluent suitable for discharge in a single process step, a hybrid process combining electrocoagulation and electro-Fenton was simultaneously used to decrease chemical oxygen demand (COD), turbidity and total suspended solids (TSS) from domestic wastewater. The electrocoagulation–electro-Fenton process was firstly tested for the production of H₂O₂ using Ti–IrO₂ and vitreous carbon- or graphite electrodes arranged at the anode and the cathode, respectively. The concentration of H₂O₂ recorded at 1.5 A of current intensity during 60 min of electrolysis using vitreous carbon- and graphite electrodes at the cathode was 4.18 and 1.62 mg L^?1, respectively. By comparison, when the iron electrode was used at the anode, 2.05 and 1.06 mg L^?1 of H₂O₂ were recorded using vitreous carbon and graphite, respectively. The H₂O₂ concentration decrease was attributed to hydroxyl radical formation generated by the Fenton reaction. Electro-Fenton using iron electrode at the anode and vitreous carbon at the cathode with a current density imposed of 0.34 A dm^?2 ensures the removal efficiency of 50.1 % COD_T, 70.8 % TSS and 90.4 % turbidity. The electrocoagulation–electro-Fenton technique is therefore a promising secondary treatment to simultaneously remove organic, inorganic and microbial pollutants from domestic, municipal and industrial wastewaters.     

Removal of toluene from air streams by cobalt-copper bimetallic catalysts supported on sepiolite

Abstract

Oxidative removal of toluene using copper and cobalt bimetallic catalysts with varying molar ratios supported on sepiolite was investigated. The catalysts prepared by a deposition precipitation method and were characterized using X-ray diffraction, nitrogen adsorption-desorption, field emission scanning electron microscopy, H₂-temperature-programmed reduction, transmission electron microscope, and inductive coupled plasma atomic emission spectroscopy. The species supported on sepiolite are Co₃O₄, CuO, and CuCo₂O₄. The activities of the tested catalysts increased in the order 0Co-4Cu/Sep <1Co-3Cu/Sep <4Co-0Cu/Sep <1Co-1Cu/Sep <3Co-1Cu/Sep. The latter exhibiting 90% toluene oxidative degradation at 288?°C within 15?h, having high selectivity towards CO₂, and being stable at 300?°C up to 15?h. In conclusion, this study showed that sepiolite has excellent properties as a support.     

Ackee apple (Blighia sapida) seeds: a novel adsorbent for the removal of Congo Red dye from aqueous solutions

The ability of ackee apple (AA) seeds to remove Congo Red (CR) dye from aqueous solution was investigated. AA was characterised using thermo gravimetric analyser, scanning electron microscopy, Braunauer Emmett Teller, pH_pzc, elemental analysis and Boehm titration. The effects of operational parameters such as adsorbent dosage, contact time, initial dye concentration and solution pH were studied in a batch system. pH has a profound influence on the adsorption process. Maximum dye adsorption was observed at pH 3.0. The reaction was fast, reaching equilibrium in 90 min. Adsorption data were best described by Langmuir isotherm and the pseudo-second-order kinetic model with a maximum monolayer coverage of 161.89 mg·g^?1. Both boundary layer and intraparticle diffusion mechanisms were found to govern the adsorption process. Thermodynamic parameters such as standard free energy change (Δ G ⁰), standard enthalpy change (Δ H ⁰), and standard entropy change (Δ S ⁰) were studied. Values of Δ G ⁰ varied between?30.94 and?36.56 kJ·mol^?1, Δ H ⁰ was 25.61 kJ·mol^?1, and Δ S ⁰ was 74.84 kJ·mol^?1·K^?1, indicating that the removal of CR from aqueous solution by AA was spontaneous and endothermic in nature. Regeneration and reusability studies were carried out using different eluents. AA gave the highest adsorption efficiency up to four cycles when treated with 0.3 M HCl. AA was found to be an effective adsorbent for the removal of CR dye from aqueous solution.     

Wet oxidation of recalcitrant lignin water solutions: experimental and reaction kinetics

The purpose of the research was to study the behavior of lignin degradation under different conditions (T 110–190°C, pO₂ 0.5–1.5 MPa, pH 5, 9 and 12) and to develop a predictive model. Temperature increase improved lignin removal from 75% at 110°C to 100% at 190°C (experimental). Increasing the pH enhanced the lignin removal efficiency from 30 to 97% (experimental). The developed model predicted the lignin degradation and changes in COD, BOD and TOC. The model agreed well with the experimental data (R ² = 0.93 at pH 5 and 12).     

UV-C light-enhanced photo-Fenton oxidation of methyl parathion

The photodegradation of aqueous solutions containing 0.2 mM methyl parathion has been studied through the optimization of the [H₂O₂]/[Fe³⁺] ratio in a Fe³⁺/H₂O₂/UV-C flow system of 1.3 L capacity. The decay kinetics and TOC abatement have been analyzed for the experiments performed at pH 3.0 and room temperature. All experiments lead to the total methyl parathion destruction after a few minutes, following a pseudo-first-order decay kinetics. Total mineralization can be reached after 120 min at the optimum ratio found, due to the synergistic effect of the very oxidizing hydroxyl radical (^·OH) produced via the Fenton reagent and the effective photodecarboxylation at 253.7 nm.     

Adsorptive features of banana (Musa paradisiaca) stalk-based activated carbon for malachite green dye removal

Chemically prepared activated carbon derived from banana stalk (BSAC) was used as an adsorbent to remove malachite green (MG) dye from aqueous solution. BSAC was characterised using thermogravimetric analyser, Brunauer Emmett Teller, Fourier transform infrared spectrometry, scanning electron microscopy, pH_pzc, elemental analysis and Boehm titration. The effectiveness of BSAC in adsorbing MG dye was studied as a function of pH, contact time, temperature, initial dye concentration and repeated desorption–adsorption processes. pH_pzc of BSAC was 4.5 and maximum dye adsorption occurred at pH 8.0. The rate of dye adsorption by BSAC was very fast initially, attaining equilibrium within 120 min following a pseudo-second-order kinetic model. Experimental data were analysed by Langmuir, Freundlich and Dubinin–Raduschevich isotherms. Equilibrium data fitted best into the Langmuir model, with a maximum adsorption capacity of 141.76 mg·g^?1. Δ G ⁰ values were negative, indicating that the process of MG dye adsorption onto BSAC was spontaneous. The positive values of Δ H ⁰ and Δ S ⁰ suggests that the process of dye adsorption was endothermic. The regeneration efficiency of spent BSAC was studied using 0.5 M HCl, and was found to be in the range of 90.22–95.16% after four cycles. This adsorbent was found to be both effective and viable for the removal of MG dye from aqueous solution.     

Solar-induced generation of singlet oxygen and hydroxyl radical in sewage wastewaters

Singlet oxygen (¹O₂) and hydroxyl radical (·OH) play an important role in the degradation of pollutants in surface waters. However, the mechanism underlying the photochemical generation of ¹O₂ and ·OH in wastewaters is poorly known. Here we studied the photo-induced generation of ¹O₂ and ·OH in different sewage treatment plant units. The correlation between the generation of ¹O₂ and ·OH and the water constituents was discussed. Our results show that in sewage units the ¹O₂ formation rate ranges from 2.19 × 10^?8 to 6.74 × 10^?8 mol L^?1 s^?1, and the ·OH formation rate ranges from 1.7 × 10^?11 to 3.06 × 10^?10 mol L^?1 s^?1. The average ¹O₂ formation rates in the various sewage units are similar to those in wetland and estuarine waters containing rich dissolved organic matter and 2–4 times higher than those in lake and seawater samples. The average ·OH formation rates of the sewage units are 5–50 times higher than for other water samples reported. The ·OH generation rate increased with the iron content with a correlation coefficient of 0.85, which indicates that the photo-Fenton reaction plays a dominant role in ·OH generation in sewage wastewater.     

Removal of elemental mercury by KI-impregnated clay

This study described the use of clay impregnated by KI in gas phase elemental mercury (Hg^o) removal in flue gas. The effects of KI loading, temperature, O₂, SO₂ and H₂O on Hg^o removal were investigated using a fixed bed reactor. The Hg^o removal efficiency of KI-clay with 3% KI loading could maintain at a high level (approximately 80 %) after 3 h. The KI-clay demonstrated to be a potential adsorbent for Hg^o removal when compared with activated carbon based adsorbent. O₂ was found to be an important factor in improving the Hg^o removal. O₂ was demonstrated to assist the transfer of KI to I₂ on the surface of KI-clay, which could react with Hg^o directly. NO and SO₂ could slightly improve Hg^o removal, while H₂O inhibited it greatly. The results indicated that after adsorption, most of the mercury escaped from the surface again. Some of the mercury may have been oxidized as it left the surface. The results demonstrated that the chemical reaction primarily occurred between KI and mercury on the surface of the KI-clay.     

Cloud point extraction of trace cyanide from environmental waters for indirect flame atomic absorption spectrometric determination

A method has been developed for indirect determination of cyanide in environmental waters based on cloud point extraction (CPE), preconcentration and determination by flame atomic absorption spectrometry (FAAS). The method was based on reduction of Cu(II) to Cu(I) in the presence of cyanide and complexation of the produced Cu(I)(CN)₂^? with gallocyanin (GC⁺) as an ion-pairing reagent at pH 4.0, followed by its extraction into polyethyleneglycol mono-p-nonylphenylether (Ponpe 7.5). Selectivity was improved with the use of suitable masking agents. Various factors influencing separation and preconcentration of cyanide have been investigated, and conditions were optimized, allowing determination of cyanide in the range of up to 1.2 mg L^?1 with a detection limit of 0.00045 mg L^?1. The method has been applied to the determination of cyanide in environmental waters, the results being in agreement with those obtained by a reference method.