Inmovilización de un mediador redox en carbón activado y su aplicación en la reducción biológica de colorantes azo

"El presente estudio reporta por primera vez la inmovilización de un catalizador con capacidad para transferir electrones (mediador redox) en carbón activado (CA). El CA granular estudiado presentó una gran capacidad de adsorción del mediador redox antraquinona-2,6-disulfonato (AQDS), logrando una adsorción máxima de 1500 mg AQDS/g CA. La AQDS inmovilizada se probó como catalizador en procesos de decoloración de diferentes compuestos azo tanto en cultivo en lote como en reactores anaerobios de flujo ascendente (UASB). En cultivos en lote, la AQDS inmovilizada aumentó 2.4 veces la tasa de decoloración del compuesto azul directo 71 (AD71) con respecto al control sin AQDS. Además, el reactor UASB operado en presencia de AQDS inmovilizada presentó una mayor eficiencia de decoloración de diferentes colorantes azo, incluyendo AD71, anaranjado de metilo (AM) y negro ericromo (NE). La eficiencia de decoloración en el reactor UASB operado sin AQDS fue de 76.5%, 70.1% y 80.3% para los colorantes AD71, AM y NE, respectivamente; mientras que en el reactor UASB en el que se inmovilizó la AQDS en CA, las eficiencias de decoloración fueron de 86.7%, 81.4% y 86.7%, respectivamente, para los mismos colorantes. No se detectó desprendimiento de la AQDS durante los procesos de decoloración indicando que la inmovilización de la AQDS en CA es robusta. Los resultados indican que la aplicación de mediadores redox inmovilizados en CA en reactores anaerobios permite obtener procesos de decoloración más eficientes y estables con respecto a reactores operados sin catalizador. La información presentada podría ser considerada para acelerar la biodegradación de contaminantes recalcitrantes comúnmente encontrados en efluentes industriales.

Maximizing hydrogen production and substrate consumption by Escherichia coli WDHL in cheese whey fermentation

"Fermentative hydrogen production is strongly affected by pH. In order to maximize hydrogen production and substrate consumption in Escherichia coli ΔhycA, ΔlacI (WDHL) cheese whey fermentation, the influence of pH control at values of 5.5, 6, and 6.5 was studied in batch stirred-tank bioreactors. From the conditions evaluated, pH 6.5 was the best condition, at which the highest cumulative hydrogen production and yield (1.78 mol H2/mol lactose) were obtained. Moreover, at this pH, all carbohydrates from the cheese whey were consumed, and a mix of ethanol and organic acids, mainly lactate, were produced from glucose, whereas galactose yielded acetate, ethanol, and succinate. Operating the reactor at pH 5.5 resulted in the highest maximum specific production rate, but smaller hydrogen yield because only glucose was metabolized and galactose was accumulated. At pH 6, not all cheese whey carbohydrates were consumed, and it was not favorable for hydrogen production. Lactose consumption and growth kinetics were not affected by the pH. The results show the importance of controlling pH to maximize hydrogen production and substrate consumption using cheese whey as substrate.

Hydrogen production by Escherichia coli ΔhycA ΔlacI using cheese whey as substrate

"This study reports a fermentative hydrogen production by Escherichia coli using cheese whey as substrate. To improve the biohydrogen production, an E. coli ΔhycA ΔlacI strain (WDHL) was constructed. The absence of hycA and lacI genes had a positive effect on the biohydrogen production. The strain produced 22% more biohydrogen in a shorter time than the wild-type (WT) strain. A Box-Behnken experimental design was used to optimize pH, temperature and substrate concentration. The optimal initial conditions for biohydrogen production by WDHL strain were pH 7.5, 37 °C and 20 g/L of cheese whey. The specific production rate was improved from 3.29 mL H2/optical density at 600 nm (OD600nm) unit-h produced by WDHL under non-optimal conditions to 5.88 mL H2/OD600nm unit-h under optimal conditions. Using optimal initial conditions, galactose can be metabolized by WDHL strain. The maximum yield obtained was 2.74 mol H2/mol lactose consumed, which is comparable with the yield reached in other hydrogen production processes with Clostridium sp. or mixed cultures.

Biological hydrogen production: trends and perspectives

"Biologically produced hydrogen (biohydrogen) is a valuable gas that is seen as a future energy carrier, since its utilization via combustion or fuel cells produces pure water. Heterotrophic fermentations for biohydrogen production are driven by a wide variety of microorganisms such as strict anaerobes, facultative anaerobes and aerobes kept under anoxic conditions. Substrates such as simple sugars, starch, cellulose, as well as diverse organic waste materials can be used for biohydrogen production. Various bioreactor types have been used and operated under batch and continuous conditions; substantial increases in hydrogen yields have been achieved through optimum design of the bioreactor and fermentation conditions. This review explores the research work carried out in fermentative hydrogen production using organic compounds as substrates. The review also presents the state of the art in novel molecular strategies to improve the hydrogen production.

Fermentation of lactose and its constituent sugars by Escherichia coli WDHL: impact on hydrogen production

"Fermentations of lactose, glucose and galactose using Escherichia coli WDHL, a hydrogen over producer strain, were performed. With glucose as substrate pyruvate was mainly routed to the lactate pathway, resulting in hydrogen production and yield of 1037 mL and 0.30 mol H2/mol of glucose, respectively. When galactose was the substrate, the pyruvate formate lyase pathway was the main route for pyruvate and a fermentation yield of 1.12 mol H2/mol of galactose and a hydrogen production of 2080 mL were obtained. The fermentation of lactose or glucose plus galactose showed a similar yield of 1.02 mol H2/mol of hexose consumed. This work clearly demonstrated that the kinetics of hydrogen and metabolites production as well as the hydrogen yield were affected by the type of sugar used as substrate as reflected by the deviations from the metabolic hydrogen-production pathway.

Bioreactors packed with activated carbon fibers as redox mediators in the anaerobic biotransformation of 4-Nitrophenol to 4-Aminophenol

The role of functional groups on the surface of activated carbons is of great interest in biological redox processes because they could improve the rate of biotransformation of toxic compounds and reduce costs of water treatment. In this study, we used activated carbon fibers (ACFs) as biological supports and redox mediators for the continuous biotransformation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Different ACFs were prepared from the original material (AW), including HNO3-treated ACF (AW-OX), and redox-active anthraquinone-2,6- disulfonate anchored on ACF surface (AW-AQDS). These ACFs were characterized by potentiometric titrations (point of zero charge and Boehm), FT-IR, and N2-adsorption (BET method). The ACF-packed bed bioreactors (AW, AW-OX and AW-AQDS) with anoxic granular biomass were evaluated for their ability to reduce 4-NF to 4-AP under continuous conditions, and compared to a control bioreactor with only anoxic granular biomass. Our results show that ACFs with a higher concentration of carbonyl groups AW-OX > AW-AQDS > AW (1.3 > 1.0 > 0.8 meq/g) improved the biotransformation of 4-NF by 2.11 > 1.97 > 1.47 – fold, respectively, as compared to the control bioreactor.La función de los grupos funcionales superficiales sobre los carbones activados es de gran interés en procesos biológicos con actividad redox porque tales grupos pueden incrementar la eficiencia de biotransformación de compuestos tóxicos y con esto reducir los costos del tratamiento de aguas. En este estudio se usaron fibras de carbón activado (FCAs) como soportes biológicos y mediadores redox para la biotransformación contínua de 4-nitrofenol (4-NF) hacia 4-aminofenol (4-AF) en condiciones anaerobias. Diversas FCAs se prepararon a partir del material original (AW) incluyendo FCAs tratadas con ácido nítrico (AW-OX) y modificadas con antraquinina- 2,6-disulfonato (AW-AQDS). Éstas FCAs fueron caracterizadas por titulaciones potenciométricas (punto de carga cero ó PCC, Boehm), FT-IR, y adsorción de N2 a bajas temperaturas (método BET). Los reactores empacados con FCAs (AW, AW-OX y AW-AQDS) y con biomasa granular anaerobia fueron evaluados por su capacidad para reducir continuamente el 4-NF a 4-AF. Estos resultados se compararon con el reactor control que carecía de FCAs en su interior y sólo contenía biomasa anaerobia granular. Los resultados muestran que las FCAs con una alta concentración de grupos carbonilo AW-OX > AW-AQDS > AW (1.3 > 1.0 > 0.8 meq/g) mejoraron la biotransformación de 4-NF por 2.11 > 1.97 > 1.47 – veces, respectivamente, comparando con el reactor control

Competencia por sustrato durante el desarrollo de biomasa sulfatorreductora a partir de un lodo metanogénico en un reactor UASB

"En este trabajo se estudió la competencia entre microorganismos metanogénicos y sulfatorreductores utilizando un reactor anaerobio de lecho de lodo granular con flujo ascendente (UASB) a escala laboratorio, el cual fue usado para el enriquecimiento de biomasa sulfatorreductora a partir de un lodo granular de origen metanogénico. El reactor se alimentó con una mezcla de etanol y acetato, la carga orgánica se incrementó de 0.5 a 2 g de demanda química de oxígeno (DQO)/L–d a pH de 7.0. El consumo de DQO fue mayor a 90 % y la alcalinidad producida por la oxidación del sustrato incrementó el pH en el efluente hasta 8.0. A partir de los 50 días de operación, el reactor se alimentó con lactato y sulfato para promover la sulfatorreducción. La carga orgánica se aumentó de 1 a 3 g DQO/L–d con una relación DQO/Sulfato de 0.67 a un tiempo de retención hidráulico de un día. A los 194 días de operación del reactor el máximo consumo de DQO y sulfato obtenido fue de 94 y 22 %, respectivamente. La concentración total del sulfuro alcanzada fue de 310 mg S2–/L y la actividad sulfatorreductora de la biomasa fue de 0.29 g DQO–H2S/g SSV–d, lo que mostró el desarrollo de biomasa sulfatorreductora. La actividad metanogénica que se obtuvo fue de 0.35 g DQO–CH4/g SSV–d, estos resultados mostraron que los organismos metanogénicos no fueron desplazados por las bacterias sulfatorreductoras, coexistiendo ambos tipos de microorganismos en el lodo granular anaerobio al final de la operación del reactor.""In this work the competition between methanogenic and sulfate –reducing microorganisms was studied using a laboratory scale up–flow anaerobic sludge blanket reactor (UASB), which was used for the enrichment of sulfate–reducing biomass from a methanogenic granular sludge. The reactor was fed with a mixture of ethanol and acetate and the organic loading rate was increased from 0.5 to 2 g chemical oxygen demand (COD)/L–d at pH of 7.0. The COD consumed was greater than 90 % and the alkalinity produced by the oxidation of the substrate increased the pH in the effluent up to 8.0. After 50 days of operation, the reactor was fed with lactate and sulfate to promote sulfate–reduction. The organic loading rate was increased from 1 to 3 g COD/L–d with a COD/sulfate ratio of 0.67 at a hydraulic retention time of one day. At 194 days of reactor operation, the maximum consumption of COD and sulfate obtained was 94 and 22%, respectively. Total sulfide concentration reached 310 mg S2–/L and the sulfate–reducing activity of the biomass was 0.29 g COD–H2S/g VSS–d, which demonstrated the development of sulfate reducing biomass. The methanogenic activity obtained was 0.35 g COD–CH4/g VSS–d, these results indicated that the methanogenic organisms were not displaced by the sulfate reducing bacteria, and both types of microorganisms coexisted in the anaerobic granular sludge at the end of reactor operation.

Mediadores redox inmovilizados para tratamiento de aguas contaminadas y emisiones de gas

"The present invention relates to a treatment process applicable to degrade or transform organic and inorganic pollutants, commonly found in industrial wastewaters, contaminated aquifers and gas emissions, in which reduction or oxidation reactions (e.g. redox reactions) are involved. The treatment concept comprises reactors in which catalysts, with redox mediating properties, have been immobilized on ion exchange resins in order to improve and accelerate the transformation of priority pollutants by chemical or biological means.""La presente invención se relaciona con un proceso de tratamiento aplicable para degradar o transformar contaminantes orgánicos e inorgánicos, comúnmente encontrados en aguas residuales industriales, acuíferos contaminados y emisiones de gas, en el cual se involucran reacciones de reducción u oxidación (por ej. reacciones redox). El concepto de tratamiento comprende reactores en los cuales los catalizadores, con propiedades mediadas por redox, han sido inmovilizados en resinas de intercambio iónico para mejorar y acelerar la transformación de contaminantes prioritarios por medios químicos o biológicos.