Refugio B Garcia Reyes

Within their complex structure, agro-waste materials such as sorghum straw (SS), oats straw (OS) and agave bagasse (AB) have functional groups (i.e. carboxyl and phenolic) that play a major role in metals sorption. The advantages of these materials include availability, low-cost, and a reasonable metal sorption capacity. These agro-waste materials were chemically characterized by acid-base titrations and ATR-FTIR analyses in order to determine their functional groups, equilibrium constants, and surface charge distribution. Batch experiments were conducted at pH 3 and 4, at 25 degrees C and 35 degrees C to determine the biosorbents chromium (III) sorption capacity. Partially saturated biosorbents were desorbed with HNO3, NaOH, and EDTA at different concentrations and temperatures (25 degrees C, 35 degrees C, and 55 degrees C). Finally, the chromium (III) sorption mechanism was discussed. Agro-waste materials functional groups are associated, in part, to carboxyl and hydroxyl groups: these oxygen-containing sites play an important role in the chromium (III) removal. The maximum chromium (III) sorption capacity was 6.96, 12.97, and 11.44 mg/g at pH 4 for acid-washed SS, OS, and AB, respectively. The chromium (III) sorption capacity decreased at pH 3 because H+ ions competed for the same functional groups. On the other hand, an increase in temperature enhanced both the biosorbents chromium (III) sorption capacity and their desorption by EDTA. The most probable chromium (III) sorption mechanisms were ion exchange and complexation. The agro-waste materials studied herein efficiently remove chromium (III) from aqueous solution and, most importantly, EDTA can efficiently desorb Cr (III) from agro-waste materials at 55 degrees C.

The capacity of a heat-treated sludge (HTS) to produce hydrogen from the mono- and co-digestion of corn (NW, pH 13.1) and brewery (BW, pH 3.8) wastewater was evaluated. The co-digestion of NW and BW was conducted with ratios (NW/BW) from 40/60 to 80/20 (vol/vol) at pH 6 and under different initial pH values (from 5.8 to 12.3) according to the substrates mixtures. With the initial pH adjusted to 6, the highest production (302 mL) occurred for the mono-digestion of NW, but hydrogen was produced in all incubations. For incubations under variable pH values, the highest hydrogen production was obtained with the ratio 60/40 (270 mL), followed by the ratio 65/35 (260 mL) with pH values of 10.8 and 10.4, respectively. The initial pH influenced the kinetic parameters, especially on maximum production and lag phase. For the ratio 60/40, with an alkaline pH value (10.4), the lag phase was delayed up to 122 h, but the highest volume of hydrogen was obtained with this condition. The Clostridium ...

- 4:45 PM 168d. Chromium (III) Sequestration by Oats Straw and Agave Baggasse: Sorption Mechanism. Refugio Bernardo García Reyes, División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica, AC, Camino a la Presa San José 2055, Col. ...

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.

Within their complex structure, agro-waste materials such as sorghum straw (SS), oats straw (OS) and agave bagasse (AB) have functional groups (i.e. carboxyl and phenolic) that play a major role in metals sorption. The advantages of these materials include availability, low-cost, and a reasonable metal sorption capacity. These agro-waste materials were chemically characterized by acid-base titrations and ATR-FTIR analyses in order to determine their functional groups, equilibrium constants, and surface charge distribution. Batch experiments were conducted at pH 3 and 4, at 25 degrees C and 35 degrees C to determine the biosorbents chromium (III) sorption capacity. Partially saturated biosorbents were desorbed with HNO3, NaOH, and EDTA at different concentrations and temperatures (25 degrees C, 35 degrees C, and 55 degrees C). Finally, the chromium (III) sorption mechanism was discussed. Agro-waste materials functional groups are associated, in part, to carboxyl and hydroxyl groups: these oxygen-containing sites play an important role in the chromium (III) removal. The maximum chromium (III) sorption capacity was 6.96, 12.97, and 11.44 mg/g at pH 4 for acid-washed SS, OS, and AB, respectively. The chromium (III) sorption capacity decreased at pH 3 because H+ ions competed for the same functional groups. On the other hand, an increase in temperature enhanced both the biosorbents chromium (III) sorption capacity and their desorption by EDTA. The most probable chromium (III) sorption mechanisms were ion exchange and complexation. The agro-waste materials studied herein efficiently remove chromium (III) from aqueous solution and, most importantly, EDTA can efficiently desorb Cr (III) from agro-waste materials at 55 degrees C.

BACKGROUND: Agro-waste materials can be used as biosorbents of heavy metals in aqueous solution. However, it is necessary to further study the contribution of agro-waste materials components (i.e. hemicelluloses, cellulose, and lignin) to the heavy metal ions removal from aqueous solution to better understand the biosorption mechanism, and also based on the biosorbents main components, to predict their potential to remove heavy metals.RESULTS: Cellulose is contained in major proportion (greater than 46%) in the agro-waste materials reported herein compared with hemicelluloses (from 12% to 26%), lignin (varying from 3% to 10%), and other compounds (22% to 30%) that were removed after the neutral detergent fiber procedure. The identified functional groups in agro-waste materials and their fractions included hydroxyl, carboxyl, and nitrogen-containing compounds. Lignin contributed in higher proportion than hemicelluloses to Cr (III) adsorption capacity in both sorghum straw and oats straw. On the other hand lignin was the main fraction responsible for Cr (III) adsorption in agave bagasse.CONCLUSION: Hemicelluloses and lignin were the main contributors to Cr (III) removal from aqueous solution, and cellulose contained in the agro-waste adsorbents studied did not seem to participate. Copyright © 2009 Society of Chemical Industry