Biotransformation of 4-nitrophenol by co-immobilized Geobacter sulfurreducens and anthraquinone-2-sulfonate in barium alginate beads.

Geobacter sulfurreducens and anthraquinone-2-sulfonate (AQS) were used suspended and immobilized in barium alginate during the biotransformation of 4-nitrophenol (4-NP). The assays were conducted at different concentrations of 4-NP (50-400 mg/L) and AQS, either in suspended (0-400 µM) or immobilized form (0 or 760 µM), and under different pH values (5-9). G. sulfurreducens showed low capacity to reduce 4-NP in absence of AQS, especially at the highest concentrations of the contaminant. AQS improved the reduction rates from 0.0086 h-1, without AQS, to 0.149 h-1 at 400 µM AQS, which represent an increment of 17.3-fold. The co-immobilization of AQS and G. sulfurreducens in barium alginate beads (AQSi-Gi) increased the reduction rates up to 4.8- and 7.2-fold, compared to incubations with G. sulfurreducens in suspended and immobilized form, but in absence of AQS. AQSi-Gi provides to G. sulfurreducens a barrier against the possibly inhibiting effects of 4-NP.

Methylene blue biosorption by pericarp of corn, alfalfa, and agave bagasse wastes.

The presence of dyes in effluent is a matter of concern due to their toxicologic and aesthetical effects. In this research, locally available agro-industrial wastes (Zea mays pericarp, ZMP; Agave tequilana bagasse, ATB; and Medicago sativa waste, MSW) were used as alternative low-cost adsorbents for the removal of methylene blue (MB) from aqueous solutions. The adsorbents were characterized physically and chemically by Fourier transform infrared, scanning electron microscopy, potentiometric titrations, and N2 physisorption. MB adsorption experiments were carried out in batch systems and experimental data were used to calculate the adsorption isotherm model parameters (Langmuir, Freundlich, and Temkin) and the adsorption kinetic model parameters (pseudo-first- and pseudo-second-order models). MB-loaded biosorbents were desorbed with deionized water, ethanol (10% and 50% v/v), hydrochloric acid (0.01 and 0.05 N), and sodium hydroxide (0.1 N) at room temperature, and the best eluent was used in various adsorption-desorption cycles. The selected agricultural wastes can be considered as promising adsorbents for dye uptake from water since they exhibit considerable MB adsorption capacity (MSW 202.6 mg g(-1), ATB 156.2mg g(-1), and ZMP 110.9mg g(-1)), but it is lower than that reported for activated carbon; however, the biosorbents show higher adsorption rate than powdered activated carbon. Furthermore, the adsorbents can be economically regenerated with HCl solutions and reused for seven adsorption-desorption cycles.