Biosorption of nickel(II) and copper(II) ions from synthetic and real effluents by alginate-based biosorbent produced from seaweed Sargassum sp.

In this study, the alginate-based biosorbent produced from seaweed Sargassum sp. was used in biosorption of Ni2+ and Cu2+ ions from synthetic solutions and real electroplating effluents. Biosorption kinetics, isotherms, pH effect, thermodynamic parameters, and sorption/desorption cycles were also evaluated. Kinetic studies show the sorption equilibrium can be obtained within 180 min for Ni2+ ions and 360 min for Cu2+ ions, and the adsorption kinetics data are well described by the pseudo-second order and diffusion in spherical adsorbents. Langmuir model can be well used to describe the biosorption isotherm data. The maximum sorption capacity (qmax) and Langmuir constant (b) were up to 1.147 mmol g-1 and 1.139 L mmol-1 for Ni2+ ions and 1.640 mmol g-1 and 4.645 L mmol-1 for Cu2+ ions. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) showed that the biosorption of Ni2+ and Cu2+ ions are predominantly a chemical phenomenon of endothermic nature, favorable, and spontaneous at the temperature ranges of 293-313 K. Partial desorption of the Ni2+ and Cu2+ ions on the biosorbent was achieved using acidic and saline eluents, allowing the biosorbent to be used in new sorption/desorption cycles. EDX analysis suggests an ion exchange mechanism between calcium ions on the biosorbent and target metals. Biosorption of Ni2+ and Cu2+ from real electroplating effluents with high concentrations of light metals becomes highly competitive, decreasing the amount of Ni2+ and Cu2+ ions biosorbed due to the ionic strength effect.

Kinetics and thermodynamics studies of silver ions adsorption onto coconut shell activated carbon.

The presence of silver in the natural water environment has been of great concern because of its toxicity, especially when it is in the free ion form (Ag(+)). This paper aims to study the adsorption kinetics of silver ions from an aqueous solution onto coconut shell activated carbon using batch methods. Batch kinetic data were fitted to the first-order model and the pseudo-second-order model, and this last equation fits correctly the experimental data. Equilibrium experiments were carried out at 30°C, 40°C, and 50°C. The adsorption isotherms were reasonably fit using Langmuir model, and the adsorption process was slightly influenced by changes in temperature. Thermodynamic parameters (ΔH°, ΔG°, and ΔS°) were determined. The adsorption process seems to be non-favorable, exothermic, and have an increase in the orderness.

Zinc(II) desorption by Sargassum filipendula biomass in batch and in fixed-bed column for multiple sorption-regeneration cycles.

The reusability of the alga Sargassum filipendula was studied in batch reactor and in fixed-bed column in order to investigate Zn(II)-laden biomass regeneration. Four types of desorbing solutions at two different concentrations were tested and the results obtained to the desorption efficiencies were higher than 90% for three of the agents. Ten consecutive sorption-regeneration cycles at a flow rate of 8 mL/min were carried in fixed bed column with the feed concentration of 50 mg/L and using two eluent solutions: H(2)SO(4) (0.1 M) and MgSO(4) (3.5% at pH 3), which showed the best ability to elution tests in batch system. The column was used for a period of 30 days. The adsorption capacity decreased the passing of cycles, but the total amount of zinc removed after 10 cycles was approximately 8 times greater than if the biomass had been used for only one time, for both agents tested. Therefore, the regeneration in the Sargassum filipendula column through the two desorbing agents tested showing high efficient use of biomass and facilitating the process of treatment of wastewater containing metals that has successive exchanges of biomass.

Treatment of sewage sludge generated in municipal wastewater treatment plants.

This study was designed to evaluate the performance of a cylindrical anaerobic digester in treating secondary sewage sludge. A series of three independent batch experiments was performed for a total operation time of 60 d. The system of anaerobic digestion showed stability conditions, with no noticeable scum or foaming problems. The chemical oxygen demand reduction reached 29,21, and 45% in sludge and 95,85, and 82% in supernatant for the three experiments, respectively. Total coliform bacteria levels in the digester ranged from 10(4) to 10(5) in influent sludge and from 10(4) to 10(3) in effluent sludge, with an average reduction of 90%. Fecal coliforms of the order of 10(4) were enumerated in influent sludge and those of the order of 10(0) were enumerated in effluent sludge, with an average reduction of 99.9%. The studied system had satisfactory results, showing that both organic matter and indicator bacteria levels substantially decrease when the sludge is submitted to anaerobic digestion.