Photocatalytic activity of tungsten-doped TiO2 with hydrothermal treatment under blue light irradiation

Tungsten doping and hydrothermal treatment were found to significantly improve the visible-light photoactivity of TiO(2) synthesized by the sol-gel method. It was observed that TiO(2) doped with a 0.5% W:Ti mole ratio and treated with 4 h of hydrothermal curing showed photoactivity under blue light irradiation equal to 74% of the commercial Degussa P-25 under UV irradiation, i.e., 0.01 mM 2-chlorophenol was completely removed in 120 and 90 min, respectively. Light absorptivity and photocatalytic activity under blue light irradiation were not dependent on the crystallite structure of the TiO(2). The oxidation kinetics under blue light irradiation can be effectively explained by the Langmuir-Hinshelwood model with an apparent reaction rate constant and a Langmuir constant of 3.60 × 10(-4) mM min(-1) and 206.53 mM(-1), respectively.     

Removal of cobalt(Ⅱ) ion from aqueous solution by chitosan-montmorillonite

Montmorillonite （MMT） modified with chitosan （CTS, molecular weight = S x 104） was applied to remove heavy metal cations by using Co2＋ as a model ion. An increase in MMT interlayer distance observed from X-ray diffraction indicates the intercalation of CTS into MMT. Together with the results of scanning electron microscopy and Fourier transform infrared spectroscopy, it was concluded that the composite material of CTS and MMT （CTS-- MMT） was prepared successfully. The mass ratio of CTS to MMT had a strong influence on the adsorption performance of CTS-MMT. The highest adsorption value of 150 mg/g was obtained over the composite material with CTS to MMT mass ratio of 0.25, which is much higher than those reported in other studies. The adsorption isotherms and kinetic results indicated that Co2＋ was adsorbed over CTS-MMT in a multilayer model, and the chemical sorption of Co2＋ was determined to be the rate-limiting step.     

Effect of surfactant on phenanthrene metabolic kinetics by Citrobacter sp. SA01

To attain a better understanding of the effects of surfactants on the metabolic kinetics of hydrophobic organic compounds, the biodegradation of phenanthrene by Citrobacter sp. SA01 was investigated in a batch experiment containing Tween 80, sodium dodecyl benzene sulfonate and liquid mineral salt medium. The Monod model was modified to effectively describe the partition, phenanthrene biodegradation and biopolymer production. The results showed that Tween 80 and sodium dodecyl benzene sulfonate （each at 50 rag/L） enhanced phenanthrene metabolism and poly-β-hydroxybutyrate production as indicated by the increasing amounts of intermediates Coy 17.2% to 47.9%）, and percentages of poly-β- hydroxybutyrate （by 107.3% and 33.1%） within the cell dry weight when compared to their absence. The modified Monod model was capable of predicting microbial growth, phenanthrene depletion and biopolymer production. Furthermore, the Monod kinetic coefficients were largely determined by the surfactant-enhanced partition, suggesting that partitioning is a critical process in surfactant-enhanced bioremediation of hydro- phobic organic compounds.     

Determination of growth kinetics of microorganisms linked with 1,4-dioxane degradation in a consortium based on two improved methods

● Evaluated three methods for determining the consortia’s growth kinetics. ● Conventional method is flawed since it relies on the total biomass concentration. ● Considering only selected bacterial taxa improved the accuracy. ● Considering oligotrophs and copiotrophs further improved the accuracy. The conventional method for determining growth kinetics of microbial consortia relies on the total biomass concentration. This may be inaccurate for substrates that are uncommon in nature and can only be degraded by a small portion of the microbial community. 1,4-dioxane, an emerging contaminant, is an example of such substrates. In this work, we evaluated an improved method for determining the growth kinetics of a 1,4-dioxane-degrading microbial consortium. In the improved method, we considered only bacterial taxa whose concentration increase correlated to 1,4-dioxane concentration decrease in duplicate microcosm tests. Using PEST (Parameter Estimation), a model-independent parameter estimator, the kinetic constants were estimated by fitting the Monod kinetics-based simulation results to the experimental data that consisted of the concentrations of 1,4-dioxane and the considered bacterial taxa. The estimated kinetic constants were evaluated by comparing the simulation results with experimental results from another set of microcosm tests. The evaluation was quantified by the sum of squared relative residual, which was four orders of magnitude lower for the improved method than the conventional method. By further dividing the considered bacterial taxa into oligotrophs and copiotrophs, the sum of squared relative residual further decreased.     

Biosorption of Co(II) ions from aqueous solution using Chrysanthemum indicum: Kinetics,equilibrium and thermodynamics

The present study investigates the adsorption potential of Chrysanthemum indicum flower in its raw (CIF-R) and biochar (CIF-BC) form for the removal of cobalt ions from aqueous solution. The adsorbents were characterized for their surface area using BET analysis, surface morphology and elemental composition with SEM-EDAX and for the presence of functional groups by FTIR analysis. Batch adsorption experiments were carried out to evaluate the effect of process parameters, viz. pH, adsorbent dosage, initial metal ion concentration, contact time, stirring speed, presence of interfering ions and temperature on the adsorption of Co(II) ion using both the adsorbents. The optimum conditions for maximum removal of Co(II) ion was ascertained to be pH 5 for both adsorbents, adsorbent dose of 4 g/L and 3 g/L, equilibrium time of 60 min and 45 min, respectively, for CIF-R and CIF-BC. The maximum adsorption capacity of CIF-R and CIF-BC was found to be 14.84 mg/g and 45.44 mg/g, respectively, for the removal of Co(II) ion. The mechanism of adsorption was studied using different models of adsorption kinetics, isotherms and thermodynamics. It was inferred that Co(II) adsorption on both CIF-R and CIF-BC followed pseudo-second order kinetics and Langmuir isotherm model with the process being spontaneous and endothermic in nature.     

Comparison studies of adsorption properties of MgO nanoparticles and ZnO–MgO nanocomposites for linezolid antibiotic removal from aqueous solution using response surface methodology

In this investigation, the adsorption measure of linezolid antibiotic onto MgO nanoparticles and ZnO–MgO nanocomposites were performed. The adsorbents were characterized by different techniques such as XRD, SEM, TEM and BET. The parameters influence such as the pH, adsorbent dosage and temperature was tested and evaluated by Box–Behnken Design combined with response surface methodology. Performing adsorption tests at optimal conditions set as 0.5 g L⁻¹ of adsorbent, pH 10 and 308 K make admit to obtain high adsorption turnover (123.45 and 140.28 mg g⁻¹ for MgO nanoparticles and ZnO–MgO nanocomposites, respectively). A good compromise between predicted and experimental data in this research was observed. The experimental equilibrium data fitting to Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich models indicate that the Langmuir model is a best model for evaluation of adsorption behavior. Kinetic evaluation of experimental data indicated that the adsorption operations followed well pseudo-second-order models. The adsorption capacity of ZnO–MgO nanocomposites is higher than MgO nanoparticles that because of the ZnO–MgO nanocomposites have high specific surface area.     

Semi-continuous anaerobic co-digestion of orange peel waste and residual glycerol derived from biodiesel manufacturing

The manufacturing of orange juice generates high volumes of orange peel waste which should not be deposited in landfill according to current recommendations. Furthermore, glycerol is a compound co-generated in biodiesel manufacturing, but the volume generated is higher than the current demand for pure glycerol. The anaerobic co-digestion of orange peel waste with residual glycerol could reduce the inhibitory effect of some compounds and provide a correct nutrient balance. Under mesophilic temperature and semi-continuous conditions, a mixture of orange peel waste-residual glycerol of 1:1 (in COD) operated favorably for organic loads up to 2.10 g VS/L. At higher organic loads, the accumulation of volatile fatty acids (VFA) and a decrease in the pH caused process destabilization. The methane yield coefficient was quite constant, with a mean value of 330 ± 51 mL_STP/g VS_added, while the organic loading rate (OLR) reached a mean value of 1.91 ± 0.37 kg VS/m³ d (17.59 ± 2.78 kg mixture/m³ d) and the hydraulic retention time (HRT) varied in a range of 8.5–30.0 d.     

Aqueous photoreduction of oxidized mercury species in presence of selected alkanethiols

Mercury is a global environmental contaminant with severe toxicity impact. The chemical processes resulting in the transformation of oxidized mercury species (Hg²⁺) to elemental mercury (Hg⁰), greatly affects the fate and transport of mercury in the natural environment. We hereby provide the first study on the photochemistry of Hg²⁺ with selected alkanethiols (R-SH) as model compounds to represent thiols and thiol-type binding sites on humic substances in natural waters because of the common sulfhydryl functional group (-SH). Kinetic studies were performed using cold vapor atomic fluorescence spectroscopy (CVAFS), the formation of Hg²⁺-thiol complexes (Hg(SR)₂) were confirmed by UV-visible spectrometry and Atmospheric Pressure Chemical Ionization-Mass Spectrometry (APCI-MS), and the reaction products were analyzed using Electron Impact-Mass Spectrometry (EI-MS) and Solid Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (SPME/GC-MS). Our results indicated that the photoreduction of Hg²⁺ by selected alkanethiols may be mediated by Hg²⁺-thiol complexes to produce Hg⁰. Under our experimental conditions, the apparent first order rate constants obtained for 1-propanethiol, 1-butanethiol, and 1-pentanethiol were (2.0 ± 0.2) × 10⁻⁷ s⁻¹, (1.4 ± 0.1) × 10⁻⁷ s⁻¹, (8.3 ± 0.5) × 10⁻⁸ s⁻¹, respectively. The effects of ionic strength, dissolved oxygen or chloride ion on reaction rates were found to be minimal under our experimental conditions. The identified products of the reaction between oxidized mercury species with selected alkanethiols (C₃-C₅) were Hg⁰ and disulfides (RS-SR). The potential environmental implications are herein discussed.     

Uptake of PAHs into polyoxymethylene and application to oil-soot (lampblack)-impacted soil samples

Polyoxymethylene (POM) is a polymeric material used increasingly in passive sampling of hydrophobic organic contaminants such as PAHs and PCBs in soils and sediments. In this study, we examined the sorption behavior of 12 PAH compounds to POM and observed linear isotherms spanning two orders of magnitude of aqueous concentrations. Uptake kinetic studies performed in batch systems for up to 54 d with two different volume ratios of POM-to-aqueous phase were evaluated with coupled diffusion and mass transfer models to simulate the movement of PAHs during the uptake process and to assess the physicochemical properties and experimental conditions that control uptake rates. Diffusion coefficients of PAHs in POM were estimated to be well correlated with diffusants' molecular weights as D(POM) proportional, variant(MW)(-3), descending from 2.3 x 10(-10) cm(2) s(-1) for naphthalene to 7.0 x 10(-11) cm(2) s(-1) for pyrene. The uptake rates for PAHs with log K(ow)<5.8 were controlled by the POM phase and the hydrophobicity of PAH compounds. For more hydrophobic PAH compounds, the aqueous boundary layer played an increasingly important role in determining the overall mass transfer rate. The POM partitioning technique was demonstrated to agree well with two other procedures for measuring PAH soil-water distribution coefficients in oil-soot (lampblack) containing soil samples.     

Sn(Ⅳ)掺杂纳米TiO2/AC降解橙黄G的动力学与机理研究

采用溶胶凝胶法制备了掺杂Sn(Ⅳ)的TiO2/AC光催化剂,以生物染料橙黄G为目标降解物,研究了多相光催化降解橙黄G的动力学规律.研究表明,该反应符合Langmuir-Hinshelwood动力学方程,速控步为吸附反应.同时,利用GC/MS联用仪探讨了橙黄的中间产物及其降解机理:橙黄G在强氧化性自由基·OH、·OOH、·O2-的作用下逐渐分解氧化为小分子有机醛、酮、酸,最后转化为CO2、NH4 、NO3-、NO2-、SO42-和H2O等无机小分子.