No abstract

The need for light intensity has made dye degradation very costly for industry. In this work, Fenton reagent was used for the efficient degradation of an aqueous solution of dye without the need for a light source. The influences of the pH of the media, the initial concentrations of Fe 2+ , H 2 O 2 , and methylene blue (MB) dye; in addition to temperature on the oxidation of MB dye were studied. The optimum amounts of the Fenton reagent were 4mM of Fe 2+ and 70mM of H 2 O 2 at 20 mg/L of dye. The optimum ratio of 0.05 of Fe 2+ /H 2 O 2 was found to give the best result for the decolorization of dye. The Fenton process was effective at pH 3 with a maximum dye decolorization efficiency of 98.8% within 30 min of reaction, corresponding to a COD removal of 85%. The decolorization process was thermodynamically feasible, spontaneous, and endothermic. The activation energy (E a ) was 33.6 kJ/mol suggesting that the degradation reaction proceeded with a low energy barrier.

Polluted water may contain more than one dye species. Consequently, the behavior of a particular dye in a water system may be affected by the presence of the others. In this study, the adsorption of methylene blue (MB) in single dye system (SDS) and in ternary dye system (TDS) comprising of MB, congo red and methyl orange onto formaldehyde-treated melon husk (FMH) was investigated as a function of pH, contact time and species concentrations. Surface studies of FMH were investigated by Fourier transform infrared and scanning electron microscopy. The dye species adsorption equilibria were rapidly attained after 60 (SDS) and 90 min (TDS) of contact times. The adsorption kinetics were analyzed using pseudo first-order, pseudo second-order and intraparticle diffusion models and the adsorption data were well described by the pseudo second-order model. The equilibrium adsorption data were interpreted in terms of the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Harkin-Jura and Halsey isotherm models and the goodness of fittings were inspected using linear regression analysis (R 2 ). Our results indicated that the Langmuir model was best fitted, suggesting monolayer adsorption. Thermodynamic study showed that the adsorptions in SDS and TDS on FMH are favourable. The change in entropy (DS°) and heat of adsorption (DH°) of dye species on FMH in TDS were estimated as 82.2 J/ mol K and 17.95 kJ/mol. respectively while in SDS, they were respectively -43.76 J/mol K and -21.84 kJ/mol. The sorption process in both systems was thermodynamically feasible with negative DG°values.

Modeling of adsorption process establishes mathematical relationship between the interacting process variables and process optimization is important in determining the values of factors for which the response is at maximum. In this paper, response surface methodology was employed for the modeling and optimization of adsorption of phenol onto rice husk activated carbon. Among the action variables considered are activated carbon pretreatment temperature, adsorbent dosage, and initial concentration of phenol, while the response variables are removal efficiency and adsorption capacity. Regression analysis was used to analyze the models developed. The outcome of this research showed that 99.79% and 99.81% of the variations in removal efficiency and adsorption capacity, respectively, are attributed to the three process variables considered, that is, pretreatment temperature, adsorbent dosage, and initial phenol concentration. Therefore, the models can be used to predict the interaction of the process variables. Optimization tests showed that the optimum operating conditions for the adsorption process occurred at initial solute concentration of 40.61 mg/L, pretreatment temperature of 441.46 ∘ C, adsorbent dosage 4 g, adsorption capacity of 0.9595 mg/g, and removal efficiency of 97.16%. These optimum operating conditions were experimentally validated.

Properties of raw sawdust ofParkia biglobosa, as a biosorbent for the removal of Acid Blue 161 dye in single, binary, and ternary dye systems with Rhodamine B and Methylene Blue dyes in aqueous solution, were investigated. The sawdust was characterized using Scanning Electron Microscopy, Fourier Transform Infrared spectrophotometry, X-ray diffraction, and pH point of zero charge. Batch adsorption experiments were carried out to determine the equilibrium characteristics, thermodynamics, and kinetics of the sorption processes. The data obtained were subjected to various isotherm and kinetics equations. The results showed that the adsorption processes were described by different isotherm models depending on the composition of the system; they were all spontaneous (ΔGranges from −0.72 to −5.36 kJ/mol) and endothermic (range ofΔHis 11.37–26.31 kJ/mol) and with increased randomness withΔSvalues of 55.55 and 98.78 J·mol/K for single and ternary systems, respectively. Pseudo-second-order kinetics model gave better fit for all the sorption systems studied irrespective of the differences in composition, with the initial and overall rate constants higher for the mixtures than for the single system (6.76 g·mg−1min−1). The presence of Rhodamine B and Methylene Blue had a synergetic effect on the maximum monolayer capacity of the adsorbent for Acid Blue 161 dye.