Inactivation kinetics of horseradish peroxidase (HRP) by hydrogen peroxide.

In recent years, the peroxidase enzymes have generated wide interest in several industrial processes, such as wastewater treatments, food processing, pharmaceuticals, and the production of fine chemicals. However, the low stability of the peroxidases in the presence of hydrogen peroxide (H2O2) has limited its commercial use. In the present work, the effect of H2O2 on the inactivation of horseradish peroxidase (HRP) was evaluated. Three states of HRP (E0, E2, and E3) were identified. While in the absence of H2O2, the resting state E0 was observed, in the presence of low and high concentrations of H2O2, E2, and E3 were found, respectively. The results showed that HRP catalyzed the H2O2 decomposition, forming the species Ex, which was catalytically inactive. Results suggest that this loss of enzymatic activity is an intrinsic characteristic of the studied HRP. A model from a modified version of the Dunford mechanism of peroxidases was developed, which was validated against experimental data and findings reported by the literature.

Improvement of the Polyhydroxyalkanoates Recovery from Mixed Microbial Cultures Using Sodium Hypochlorite Pre-Treatment Coupled with Solvent Extraction.

The use of mixed microbial cultures (MMC) and organic wastes and wastewaters as feed sources is considered an appealing approach to reduce the current polyhydroxyalkanoates (PHAs) production costs. However, this method entails an additional hurdle to the PHAs downstream processing (recovery and purification). In the current work, the effect of a sodium hypochlorite (NaClO) pre-treatment coupled with dimethyl carbonate (DMC) or chloroform (CF) as extraction solvents on the PHAs recovery efficiency (RE) from MMC was evaluated. MMC were harvested from a sequencing batch reactor (SBR) fed with a synthetic prefermented olive mill wastewaster. Two different carbon-sources (acetic acid and acetic/propionic acids) were employed during the batch accumulation of polyhydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from MMC. Obtained PHAs were characterized by 1H and 13C nuclear magnetic resonance, gel-permeation chromatography, differential scanning calorimetry, and thermal gravimetric analysis. The results showed that when a NaClO pre-treatment is not added, the use of DMC allows to obtain higher RE of both biopolymers (PHB and PHBV), in comparison with CF. In contrast, the use of CF as extraction solvent required a pre-treatment step to improve the PHB and PHBV recovery. In all cases, RE values were higher for PHBV than for PHB.

Digestive proteinases from the marine fish processing wastes of the South-West Atlantic Ocean: Their partial characterization and comparison.

Fish processing generates plenty of waste that is directly discarded in open-air dumps and water sources, or treated in the same way as urban solid waste, causing serious pollution problems. The waste represents a significant source of high-value bioproducts with potential applications in different industrial processes such as the production of feed, fertilizers, biodiesel and biogas, detergent additives and cosmetics. The objective of this study was to characterize and compare specific activities under different pH values and temperature conditions of acid and alkaline proteinases and viscera yield from the following fish species: Argentine hake Merluccius hubbsi, Brazilian flathead Percophis brasiliensis, Brazilian codling Urophycis brasiliensis and Stripped weakfish Cynoscion guatucupa. Individuals were fished off the coast of Mar del Plata (Argentina) by a commercial fleet and the viscera were immediately extracted and kept on ice until use. Stomach proteinases from four species had the highest activity at pH 2, with stability in the range of pH 2-4. The optimum pH was 11.5 from intestinal enzymes of C. guatucupa, M. hubbsi and P. brasiliensis and 9.5 from intestinal enzymes of U. brasiliensis. Alkaline proteinases from all species were highly stable in the range of 7-11.5. The optimum temperature of stomach proteinases from the four species studied were 30 and 50°C, with stability at 10 and 30°C during 150 min. The optimum temperature of intestinal enzymes from the tested species were 50°C with high stability at 10 and 30°C during 150 min. Alkaline proteinase from all species and acid proteinases from C. guatucupa were inactive at 70°C after 150 min, while there was a residual activity lower than 5% at 80°C on pre-incubated stomach enzymes of M.hubbsi, P. brasiliensis and U. brasiliensis after 5, 10 and 20 min, respectively. Digestive proteinases recovered in this study could be appropriate for technological usage, reducing manufacturing costs, obtaining revenue from fishery wastes, and contributing to the reduction of environmental pollution.

Monitoring and modeling 4-chlorophenol biodegradation kinetics by phenol-acclimated activated sludge by using open respirometry.

The aim of this study was to analyze the mechanisms, stoichiometry, and stability of 4-chlorophenol (4CP) biodegradation kinetics by phenol-acclimated activated sludge using open respirometry. While the removal of 4CP was higher than 98%, the removal of chemical oxygen demand (COD) ranged between 69 and 79% due to the accumulation of an intermediate metabolite. The value obtained from respirometric profiles for the stoichiometric ratio of O2 to 4CP (YO2/4CP) was 1.95 ± 0.04 mol of oxygen consumed per mol of 4CP removed. This YO2/4CP value reflected the action of the oxygenases responsible for the first steps of the aerobic oxidation of 4CP. The 4CP degradation activity decreased noticeably when successive pulses of 4CP were added to the respirometer. A mathematical model was developed to represent the aerobic biodegradation of 4CP. The fitted model adequately predicted the oxygen consumption rate, total phenols, and soluble COD concentrations as a function of time. The results presented could help to predict the dynamic of biodegradation of chlorophenols in a biological wastewater treatment system.

Stoichiometry and kinetic of the aerobic oxidation of phenolic compounds by activated sludge.

The aerobic degradation of phenol (PH), catechol (CA), resorcinol (RE), pyrogallol (PY), and hydroquinone (HY) by phenol-acclimated activated sludge was investigated. A Haldane-type dependence of the respiration rate on PH, RE, and HY was observed; CA and PY exhibited a biphasic respiration pattern. According to the initial biodegradation rate, tested compounds were ordered as follows: CA>PH>>PYRE>HY. Also, they exhibited the following degree of toxicity to their own degradation: PY>>CARE>>PH>HY. Oxidation coefficients for PH, PY, RE, and HY were constant as a function of the consecutive additions of the compound. Conversely, an increase of YO/S from 1 to 1.5 molO2 molCA(-1) was observed during repeated additions of CA. The role of some enzymes involved in the aerobic degradation pathways of the tested compounds is discussed and related to the obtained results.

Phosphorous removal in batch systems using ferric chloride in the presence of activated sludges.

The objectives of this work were: (a) to analyze the effect of alkalinity, pH and initial Fe:P molar ratio (Fe(0):P(0)) on the precipitation of orthophosphate using ferric chloride in the presence of activated sludge in order to represent conditions of simultaneous precipitation, and in exhausted wastewater to simulate conditions of post-precipitation, (b) to compare the experimental results with predictions obtained from a chemical equilibrium model, and (c) to propose a mechanistic model to determine the dose of coagulant required to achieve a given orthophosphate removal degree at constant pH. Results showed that the presence of biomass did not affect the orthophosphate precipitation; however, addition of ferric chloride caused a drop of pH to values not compatible with the normal activity of activated sludges. For this reason, the wastewater was supplemented with NaHCO(3); when 1gL(-1) NaHCO(3) was added, orthophosphate removals higher than 97% and pH above 6.2 were obtained using Fe(0):P(0)=1.9. Precipitation assays at constant pH showed that Fe(III) hydrolysis and FePO(4) precipitation reaction compete with each other. Calculations using a chemical equilibrium model (CHEAQS) predicted that ferric phosphate precipitation should not take place if pH is higher than about 7.8. However, experimental results showed that ferric phosphate precipitation occurred even at pH 9. For this reason, a mechanistic model was proposed to predict orthophosphate concentrations as a function of Fe(0):P(0) at constant pH. The model can be applied to calculate the minimum Fe(III) concentration required to achieve a given discharge limit for orthophosphate as a function of its initial concentration and pH.

Modelling phenol biodegradation by activated sludges evaluated through respirometric techniques.

In this paper respirometric techniques were used to study the effect of pH, phenol and dissolved oxygen (DO) concentrations on the phenol biodegradation kinetics by activated sludges. In addition, a mathematical model was developed to interpret the obtained respirometric curves. Closed respirometer experiments showed that phenol inhibited the respiration rate of unacclimated sludges. On the contrary, oxygen uptake rate (OUR) of phenol acclimated sludges exhibiting the typical Haldane's substrate inhibition curve. The Monod equation adequately represented the relation between OUR of acclimated biomass and DO concentration. Within the tested pH range (4-12) the oxygen saturation coefficient was independent of pH. On the contrary, the maximum OUR was strongly affected by the pH, being its maximum between 9.5 and 10.5. Open respirometer experiments shows that as pH decreased from 10.2 to 5.8, the maximum OUR also decreased, in accordance with the trend observed in the closed respirometer experiments. Although the respiration rate of phenol degrading bacteria was strongly affected by pH, a constant phenol oxidation coefficient was observed within the studied pH interval. A mathematical model was proposed to interpret the open respirometry curves. The coefficients of the model were estimated using both pseudo steady state and dynamic conditions for different biomass concentrations. The model adequately predicted the whole OUR and DO profiles as a function of time during the biodegradation of phenol under different DO conditions. The mathematical model proposed in the present work is useful for predicting transient responses such as substrate concentration and DO concentrations as a function of time in bioreactors treating phenolic wastewaters under an overload of phenolic compounds.

Modelling Cr(VI) removal by a combined carbon-activated sludge system.

The combined carbon-activated sludge process has been proposed as an alternative to protect the biomass against toxic substances in wastewaters; however, the information about the effect of powdered-activated carbon (PAC) addition in activated sludge reactors for the treatment of wastewaters containing Cr(VI) is limited. The objectives of the present study were: (a) to evaluate the removal of hexavalent chromium by (i) activated sludge microorganisms in aerobic batch reactors, (ii) powdered-activated carbon, and (iii) the combined action of powdered-activated carbon and biomass; (b) to propose mathematical models that interpret the experimental results. Different Cr(VI) removal systems were tested: (S1) biomass (activated sludge), (S2) PAC, and (S3) the combined activated carbon-biomass system. A Monod-based mathematical model was used to describe the kinetics of Cr(VI) removal in the system S1. A first-order kinetics with respect to Cr(VI) and PAC respectively, was proposed to model the removal of Cr(VI) in the system S2. Cr(VI) removal in the combined carbon-biomass system (S3) was faster than both Cr(VI) removal using PAC or activated sludge individually. Results showed that the removal of Cr(VI) using the activated carbon-biomass system (S3) was adequately described by combining the kinetic equations proposed for the systems S1 and S2.

Degradación biológica de fenol utilizando técnicas respirométricas

Los objetivos del trabajo fueron analizar la degradación biológica del fenol, utilizando barros activados aclimatados y no aclimatados a ducho sustrato y determinar los parámetros cinéticos y estequiométricos correspondientes, utilizando medidas respirométricas. Por otra parte se realizaron ensayos utilizando un respirometro abierto para obtener el coeficiente de oxidación del fenol

Degradación biológica de fenol utilizando técnicas respirométricas

Los objetivos del trabajo fueron analizar la degradación biológica del fenol, utilizando barros activados aclimatados y no aclimatados a ducho sustrato y determinar los parámetros cinéticos y estequiométricos correspondientes, utilizando medidas respirométricas. Por otra parte se realizaron ensayos utilizando un respirometro abierto para obtener el coeficiente de oxidación del fenol

Efecto de la concentración inicial de biomasa y de distintos sustratos en la reducción de Cr(VI) por barros activados

Las industrias metalúrgicas, curtiembre y químicas, descargan aguas residuales con gran contenido de cromo y deben ser tratados para evitar problemas ambientales. El uso de cultivos mixtos como por ej. barros activados, para la remoción de cromo hexavalente, parece ser una tecnología económicamente viable y prometedora. El artículo analiza el efecto de diferentes sustratos dadores de electrones, sobre la remoción de cromo hevalente en barros activados e investigar el efectos de la concentración de biomasa sobre la remoción de Cr(VI)

Efecto de la concentración inicial de biomasa y de distintos sustratos en la reducción de Cr(VI) por barros activados

Las industrias metalúrgicas, curtiembre y químicas, descargan aguas residuales con gran contenido de cromo y deben ser tratados para evitar problemas ambientales. El uso de cultivos mixtos como por ej. barros activados, para la remoción de cromo hexavalente, parece ser una tecnología económicamente viable y prometedora. El artículo analiza el efecto de diferentes sustratos dadores de electrones, sobre la remoción de cromo hevalente en barros activados e investigar el efectos de la concentración de biomasa sobre la remoción de Cr(VI)

Use of image analysis in the study of competition between filamentous and non-filamentous bacteria.

One of the most common problems in the operation of activated sludge plants is the inability to separate solids from treated effluents in the clarifiers caused by the overgrowth of filamentous micro-organisms (FM) with respect to floc-forming bacteria. In order to develop kinetic models that help to predict bulking events, growth kinetics of the FMs and non-filamentous bacteria (NFB) should be known. This paper addresses the competition of a FM and a NFB in a continuous stirred tank reactor. Experimental observations of the effect of the dilution rate on the composition of the mixed culture were compared to simulated results. Image analysis was used to measure NFB and FM fractions in order to evaluate the proposed mathematical model. Experimental results and numerical simulations showed that low D values favored the growth of FM; on the contrary, when high D values were applied a rapid overgrowth of the NFB were observed. Thus, high D values favored the growth of NFB minimizing the risk of filamentous bulking.

Determinación de parámetros cinéticos microbianos mediante respirometria abierta

El objetivo de este trabajo es determinar la velocidad específica máxima de consumo sustentable, velocidad específica máxima de consumo de oxígeno, constante de saturación y el coeficiente de oxidación del sustrato correspondiente a bacterias heterótrofas y autótrofas utilizando un repirómetro abierto. Para los cultivos heterotróficos se determinaron parámetros cinéticos y estequiométricos que caracterizan la biodegradación de glucosa, lactosa y galactosa. En el caso de cultivos autótrofos se empleó sulfato de amonio como sustrato oxidable. A partir de los resultados obtenidos se puede concluir que la respirometría abierta permite la determinación de los parámetros cinéticos de biodegradación de diferentes compuestos en forma rápida y precisa

Determinación de parámetros cinéticos microbianos mediante respirometria abierta

El objetivo de este trabajo es determinar la velocidad específica máxima de consumo sustentable, velocidad específica máxima de consumo de oxígeno, constante de saturación y el coeficiente de oxidación del sustrato correspondiente a bacterias heterótrofas y autótrofas utilizando un repirómetro abierto. Para los cultivos heterotróficos se determinaron parámetros cinéticos y estequiométricos que caracterizan la biodegradación de glucosa, lactosa y galactosa. En el caso de cultivos autótrofos se empleó sulfato de amonio como sustrato oxidable. A partir de los resultados obtenidos se puede concluir que la respirometría abierta permite la determinación de los parámetros cinéticos de biodegradación de diferentes compuestos en forma rápida y precisa

Modeling of chlorine effect on floc forming and filamentous micro-organisms of activated sludges.

Chlorination is the most economical, non-specific method to control the excessive growth of filamentous micro-organisms causing bulking in activated sludge systems in the treatment of food industrial wastewaters; it was one of the first methods used to control filamentous bulking and is still widely employed. Considering that chlorination affects both floc-forming and filamentous micro-organisms and leaves undesirable disinfection by-products, it is necessary to define the adequate doses to control bulking, minimizing the effect on floc-forming bacteria. In the present work the effect of biomass concentration and type of micro-organism on chlorine decay kinetics was evaluated; the inactivation of either a filamentous (Sphaerotilus natans) or a floc-forming (Acinetobacter anitratus) micro-organism due to chlorination was also analyzed. For chlorine decay assays, the samples were treated in a batch system with sodium hypochlorite ranging between 9.8 and 56.6 mg Cl(2) (gVSS)(-1). Respirometric assays were used to evaluate the effect of chlorine on micro-organisms respiratory activity; in these cases, sodium hypochlorite doses ranged between 2.5 and 18 mgCl(2) (gVSS)(-1).A model that allowed to predict simultaneously chlorine consumption and respiratory activity decay for both micro-organisms as a function of time was proposed. The model includes three coupled differential equations corresponding to respiratory inhibition, readily organic matter oxidation by chlorine and chlorine decay. The rate of chlorine decay depended on both, type and concentration of the micro-organisms in the system. Chlorine consumption rate due to S. natans was 2-4 times faster than A. anitratus. Using the proposed model initial critical chlorine doses (the lowest initial dose that leads to a total inhibition of the respiratory activity) were calculated for both micro-organisms and values of 11.9 mgCl(2) (gVSS)(-1) for S. natans and 4.5 mgCl(2) (gVSS)(-1) for A. anitratus were obtained. These critical doses indicated that in non flocculated pure cultures, floc-former bacteria A. anitratus was more susceptible to chlorine action than S. natans.