RESUMO
BACKGROUND: Sawdust from Parkia biglobosa was prepared as an adsorbent for the adsorption of dye from aqueous solution. OBJECTIVES: The ability of sawdust to adsorb Congo red in a single dye system and binary dye system was examined. METHODS: Effects of several variables (pH, contact time, initial dye concentration and adsorbent dose) were investigated and optimum conditions were established. The equilibrium data were subjected to kinetic and isotherm models. RESULTS: Equilibrium time was observed at 600 mins while the optimum dose was 0.2 g and there was an increase in adsorption at low pH. The equilibrium data fitted the Freundlich isotherm model in both systems (coefficient correlation (R2) > 0.9). Harkin-Jura was the worst-fitted (R2 < 0.8). The qm in the single system (21.65) was lower than in BDS (27.17; 34.01). The values of 1/n show the heterogeneity on the surface of sawdust which reduced in the BDS. The increase in qm in the binary system showed that the presence of another dye (Reactive black 5) had a synergistic effect on the adsorption of Congo red. The kinetics of the process followed the pseudo-second-order model both in the single system and one of the binary systems. The dynamics of the process showed that the single system was non-spontaneous at low temperatures, endothermic and increased randomness on the surface of the adsorbent, while in the binary system, the process was exothermic and had little affinity for the adsorbent. CONCLUSIONS: Sawdust from Parkia biglobosa is a potential adsorbent for removing Congo red dye from aqueous solution in single and binary systems. COMPETING INTERESTS: The authors declare no competing financial interests.
RESUMO
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 Fe2+, H2O2, 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 Fe2+ and 70mM of H2O2 at 20 mg/L of dye. The optimum ratio of 0.05 of Fe2+/H2O2 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 (Ea) was 33.6 kJ/mol suggesting that the degradation reaction proceeded with a low energy barrier.
