Refugio Bernardo García-Reyes

Determining optimal conditions to produce activated carbon from barley husks using single or dual optimization.

When producing activated carbons from agricultural by-products, certain properties, such as yield and specific surface area, are very important for obtaining an economical and promising adsorbent material. Nevertheless, many researchers have not simultaneously optimized these properties and have obtained different optimal conditions for the production of activated carbon that either increases specific surface area but decreases yield or vice versa. In this research, the production of activated carbon from barley husks (BH) by chemical activation with zinc chloride was optimized by using a 2(3) factorial design with replicates at the central point, followed by a central composite design with two responses (the yield and iodine number) and three factors (the activation temperature, activation time, and impregnation ratio). Both responses were simultaneously optimized by using the desirability functions approach to determine the optimal conditions of this process. The findings reveal that after the simultaneous dual optimization, the maximal response values were obtained at an activation temperature of 436 °C, an activation time of 20 min, and an impregnation ratio of 1.1 g ZnCl₂/g BH, although the results after the single optimization of each response were quite different. At these conditions, the predicted values for the iodine number and yield were 829.58 ± 78.30 mg/g and 46.82 ± 2.64%, respectively, whereas experimental tests produced values of 901.86 mg/g and 48.48%, respectively. Moreover, activated carbons from BH obtained at the optimal conditions primarily developed a porous structure (mesopores > 71% and micropores > 28%), achieving a high surface area (811.44 m(2)/g) that is similar to commercial activated carbons and lignocellulosic-based activated carbons. These results imply that the pore width and surface area are large enough to allow the diffusion and adsorption of pollutants inside the adsorbent particles. In summary, two responses were optimized to determine the optimal conditions for the production of activated carbons because it is possible to increase both the specific surface area and yield.

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 156.2 mg g−1, and ZMP 110.9 mg 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.

Decolorization and biogas production by an anaerobic consortium: effect of different azo dyes and quinoid redox mediators

The inhibitory effect of azo dyes and quinoid compounds on an anaerobic consortium was evaluated during a decolorization process and biogas production. In addition, the impact of quinoid compounds such as lawsone (LAW) and anthraquinone-2,6-disulfonate (AQDS) on the rate of decolorization of Direct Blue 71 (DB71) was assessed. The anaerobic consortium was not completely inhibited under all tested dye concentrations (0.1-2 mmol l(-1)), evidenced by an active decolorization process and biogas production. The presence of quinoid compounds at different concentrations (4, 8, and 12 mmol l(-1)) also inhibited biogas production compared to the control incubated without the quinoid compounds. In summary, the anaerobic consortium was affected to a greater extent by increasing the quantity of azo dyes or quinoid compounds. Nevertheless, at a lower concentration (1 mmol l(-1)) of quinoid compounds, the anaerobic consortium effectively decolorized 2 mmol l(-1) of DB71, increasing up to 5.2- and 20.4-fold the rate of decolorization with AQDS and LAW, respectively, compared to the control lacking quinoid compounds.

Phenol and methylene blue adsorption on heat-treated activated carbon: Characterization, kinetics, and equilibrium studies:

A comprehensive study was performed for a thermally treated activated carbon to evaluate the influence of this treatment on the physical and chemical properties of the mineral activated carbon, as well as the adsorption toward phenol and methylene blue. After the heat treatment, surface area decreased and total pore volume diminished about 8.5%, and the total basic groups decreased 18% while the total acid groups increased 8% in comparison with the raw activated carbon. Equilibrium adsorption of phenol and methylene blue was described well with the Freundlich and Langmuir isotherm models, respectively. Adsorption kinetics of phenol and methylene blue was predicted adequately with the empirical pseudo-second-order model, the intraparticle diffusion model, and the homogeneous solid diffusion model, but mass transfer coefficients of the diffusion models help to better understand the adsorption phenomenon. Intraparticle diffusion seems to be the rate-controlling step in the adsorption process, and heat-treated activated carbon in an inert atmosphere was a better adsorbent for both phenol and methylene blue than raw activated carbon.

Mechanism of anaerobic bio-reduction of azo dye assisted with lawsone-immobilized activated carbon

Lawsone redox (LQ) mediator was covalently bound to granular activated carbon (GAC) by Fischer esterification. A high LQ adsorption capacity on GAC was achieved (∼230 mg/g), and desorption studies showed strong chemical stability. Furthermore, kinetic experiments with solid-phase redox mediator (RM) and their controls (soluble RM, GAC and anaerobic sludge) were tested for decolorization of congo red dye at initial concentration of 175 mg/L. Benzidine, a by-product of complete congo red reduction, was also measured by HPLC analysis along the kinetic experiments. The highest percentage of decolorization after 24 h of incubation was achieved in cultures with soluble (77%) and immobilized (70%) LQ. In contrast, low decolorization efficiency was reached in anaerobic bio-reduction assays with unmodified GAC (47%) and anaerobic sludge (28%) after 24 h. Removal of congo red by adsorption onto LQ-GAC was negligible. The rate of benzidine production was slower than decolorization rate, suggesting that one azo bond of congo red is selectively broke and followed by a slower breaking of the second azo bond, consequently, appearance of benzidine in solution. These issues could be attributed to the steric rearrangement and the inhibitory effects of the produced aromatic amines in the biotransformation process.

Artificial Neural Network for predicting biosorption of methylene blue by Spirulina sp.

An artificial neural network (ANN) was used to predict the biosorption of methylene blue on Spirulina sp. biomass. Genetic and anneal algorithms were tested with different quantity of neurons at the hidden layers to determine the optimal neurons in the ANN architecture. In addition, sensitivity analyses were conducted with the optimised ANN architecture for establishing which input variables (temperature, pH, and biomass dose) significantly affect the predicted data (removal efficiency or biosorption capacity). A number of isotherm models were also compared with the optimised ANN architecture. The removal efficiency or the biosorption capacity of MB on Spirulina sp. biomass was adequately predicted with the optimised ANN architecture by using the genetic algorithm with three input neurons, and 20 neurons in each one of the two hidden layers. Sensitivity analyses demonstrated that initial pH and biomass dose show a strong influence on the predicted removal efficiency or biosorption capacity, respectively. When supplying two variables to the genetic algorithm, initial pH and biomass dose improved the prediction of the output neuron (biosorption capacity or removal efficiency). The optimised ANN architecture predicted the equilibrium data 5,000 times better than the best isotherm model. These results demonstrate that ANN can be an effective way of predicting the experimental biosorption data of MB on Spirulina sp. biomass.

Quinone-functionalized activated carbon improves the reduction of congo red coupled to the removal of p-cresol in a UASB reactor

In this research was immobilized anthraquinone-2-sulfonate (AQS) on granular activated carbon (GAC) to evaluate its capacity to reduce congo red (CR) in batch reactor and continuous UASB reactors. The removal of p-cresol coupled to the reduction of CR was also evaluated. Results show that the immobilization of AQS on GAC (GAC-AQS) achieved 0.469mmol/g, improving 2.85-times the electron-transferring capacity compared to unmodified GAC. In batch, incubations with GAC-AQS achieved a rate of decolorization of 2.64-fold higher than the observed with GAC. Decolorization efficiencies in UASB reactor with GAC-AQS were 83.9, 82, and 79.9% for periods I, II, and III; these values were 14.9-22.8% higher than the obtained by reactor with unmodified GAC using glucose as energy source. In the fourth period, glucose and p-cresol were simultaneously fed, increasing the decolorization efficiency to 87% for GAC-AQS and 72% for GAC. Finally, reactors efficiency decreased when p-cresol was the only energy source, but systems gradually recovered the decolorization efficiency up to 84% (GAC-AQS) and 71% (GAC) after 250 d. This study demonstrates the longest and efficient continuous UASB reactor operation for the reduction of electron-accepting contaminant in presence of quinone-functionalized GAC, but also using a recalcitrant pollutant as electron donor.

Artificial neural networks for modeling the reverse osmosis unit in a wastewater pilot treatment plant

AbstractThis paper presents experimental and modeling data from a membrane-based wastewater treatment (WWT) pilot plant. The effluents from various upstream steps of a can-manufacturing plant were combined and subjected to a pretreatment process, which consisted of coalescing filters, coagulation and gravity settling, and sand activated carbon and polishing filtration, and a pressure-driven membrane process, such as reverse osmosis (RO). The performance of the RO membrane was evaluated and experiments were conducted using continuous wastewater flow. The complete membrane separation scheme was validated with a closed loop cell through several experiments, in which the concentration of the antiscaling agent and the pH were varied to determine the optimal operational conditions. Detailed parametric studies for these continuous flow experiments were conducted, and the permeate flow rates in the RO membrane system were experimentally measured. The experimental flow data were correlated and analyzed using an ar...

A mass transfer model for the fixed-bed adsorption of ferulic acid onto a polymeric resin: axial dispersion and intraparticle diffusion.

ABSTRACT In this study, amberlite XAD-16 (XAD-16) bed column system was used to remove ferulic acid (FA) from aqueous solutions. Laboratory-scale column experiments were conducted in downflow fixed bed at initial FA concentration of 1 g/L, initial pH 3, and 25°C. The performance of the adsorbent bed under different flow rates (1.3–7.7 mL/min) was studied. The bed utilization efficiency was in the range of 64.64–72.21% at the studied flow rates. A mass transfer model considering both axial dispersion and intraparticle diffusion was developed to predict the breakthrough curves of FA adsorption on XAD-16. This model predicted the experimental data better than Bohart–Adams model and Thomas model, based on the low deviation between predicted and experimental data. The axial dispersion coefficient value varied from 6.45 × 10−6 to 1.10 × 10−6 m2/s at flow rate from 1.3 to 7.7 mL/min, whereas the intraparticle diffusion coefficient was 1.04 × 10−10 m2/s, being this last resistance the rate-limiting step. In conclusion, axial dispersion and intraparticle diffusion phenomena play the major role in predicting the adsorption of FA onto XAD-16 in fixed-bed columns. GRAPHICAL ABSTRACT

Erratum to: Biosorption of Cu(II) and Pb(II) from aqueous solutions by chemically modified spent coffee grains

The original version of this article unfortunately contained mistakes. The presentations of Figs. 1 and 2 were incorrect. The correct versions of the figures are given in following page.