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Horseradish peroxidase (HRP) was immobilized in calcium alginate beads by extruding an alginate/HRP solution through a syringe onto calcium chloride. The aim of this study was to evaluate their use to remove the azo-dye Orange II (OII), under different experimental conditions, such as the number of beads, pH, reuse of the biocatalyst, hydrogen peroxide feeding strategy. A mathematical model that takes into account the diffusion of reactants, products, and HRP throughout the beads and the effect of the enzyme leakage on the observable oxidation rate was also developed. Results indicated that the immobilization efficiency decreased as a function of the incubation time in CaCl2. Although enzyme-containing beads had a low OII adsorption capacity, under the presence of hydrogen peroxide, the dye removal was highly increased due to the catalytic activity of HRP. Besides, the initial OII oxidation rate (RS0) using 3 beads at pH 9 was higher than at pH 7. Also, RS0 increased as a function of the number of tested beads. The developed model was fitted to experimental data obtained at different conditions. Then, the model was validated against a new data set that was not used for the calibration of the model, obtaining a satisfactory agreement between simulation results and these new data. Simulations demonstrate that 70–90% of the total OII removed was due to its oxidation by hydrogen peroxide catalyzed by HRP in the liquid phase.

Nowadays, several advanced oxidation and enzymatic processes are available for the removal of organic compounds. Mathematical models are crucial to optimize the operating conditions and to reduce the costs associated with the studied oxidation process. The present work deals with a procedure to develop COD/DOC balanced models to represent the oxidation process of organic compounds. The procedure is of general nature since no hypothesis is made regarding the identity of the organic compounds or the oxidant employed. Using the developed procedure, proposed oxidation pathways always fulfill elemental and electron balances. Several examples of oxidation pathways were studied to demonstrate the usefulness of the procedure. From the analysis of a particular pathway, several restrictions regarding the range of possible values of the model coefficients can be found. These restrictions can be used to enhance the robustness of the fitting procedure of the model by using different types of data, such as COD, DOC and/or the actual concentration of some relevant species. This work will help researchers in areas related to the removal of organic compounds using any oxidation process. Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

In this work, three xenobiotics (orange II, phenol, and bisphenol A) were oxidized by hydrogen peroxide in the presence of a horseradish peroxidase (HRP) using a fed-batch system. During the experiments, the oxidation-reduction potential (ORP) of the reaction mixture was measured continuously. Results demonstrate that ORP values only increased when both substrates of the enzyme (hydrogen peroxide and the target compound) were present in the reaction mixture. For all of the tested pollutants, the continuous addition of hydrogen peroxide caused an increase in ORP values. When the reducing substrate was depleted, the addition of an excess of hydrogen peroxide caused a decrease of ORP values. The time at which ORP reached a maximum represented the end of the oxidation process. This maximum could be easily detected by means of the derivative of ORP as a function of time. To extend the application of the developed technique, the enzymatic oxidation of a binary mixture of BPA and OII was also followed using ORP measurements. Results were similar to those observed with only one reducing substrate. This work demonstrates that ORP measurements can be useful to maximize hydrogen peroxide efficiency through the controlled addition of the oxidant during the oxidation of OII, phenol, and BPA catalyzed by HRP. This approach allows a minimization of time and process costs since the reaction end-point can be easily detected on a real-time basis. Fil: Morales Urrea, Diego Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Haure, Patricia Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

Enzymatic decolourization of azo-dyes could be a cost-competitive alternative compared to physicochemical or microbiological methods. Stoichiometric and kinetic features of peroxidase-mediated decolourization of azo-dyes by hydrogen peroxide (P) are central for designing purposes. In this work, a modified version of the Dunford mechanism of peroxidases was developed. The proposed model takes into account the inhibition of peroxidases by high concentrations of P, the substrate-dependant catalatic activity of peroxidases (e.g. the decomposition of P to water and oxygen), the generation of oxidation products (OP) and the effect of pH on the decolourization kinetics of the azo-dye Orange II (OII). To obtain the parameters of the proposed model, two series of experiments were performed. In the first set, the effects of initial P concentration (0.01–0.12 mM) and pH (5–10) on the decolourization degree were studied at a constant initial OII concentration (0.045 mM). Obtained results showed that at pH 9–10 and low initial P concentrations, the consumption of P was mainly to oxidize OII. From the proposed model, an expression for the decolourization degree was obtained. In the second set of experiments, the effect of the initial concentrations of OII (0.023–0.090 mM), P (0.02–4.7 mM), HRP (34–136 mg/L) and pH (5–10) on the initial specific decolourization rate (q0) was studied. As a general rule, a noticeable increase in q0 was observed for pHs higher than 7. For a given pH, q0 increased as a function of the initial OII concentration. Besides, there was an inhibitory effect of high P concentrations on q0. To asses the possibility of reusing the enzyme, repeated additions of OII and P were performed. Results showed that the enzyme remained active after six reuse cycles. A satisfactory accordance between the change of the absorbance during these experiments and absorbances calculated using the proposed model was obtained. Considering that this set of data was not used during the fitting procedure of the model, the agreement between predicted and experimental absorbances provides a powerful validation of the model developed in the present work., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Hexavalent chromium becomes in one of the tops internationally concern environmental issues due to its wide usage in several industrial activities. There are two stable oxidation states of chromium in the environment which differ significantly on its toxicity; Cr(III) has lower solubility, mobility and lesser biological toxicity in comparison with Cr(VI). While Cr(VI) is a well-known carcinogen, Cr(III) is an essential dietary element. For this reason, most technologies focus attention on the reduction of Cr(VI) to Cr(III). On this context, the ability of microorganisms to reduce Cr(VI) to Cr (III) has gained attention. The objectives of the present work were to analyze the effect of Cr(VI) on the activated sludge community in a continuous reactor, and to evaluate the differences on the metabolic activity of native (NAS) and Cr(VI)-acclimated activated sludge (CrAAS) using a respirometric method. Results showed that the activated sludge community had the capability to acclimate to the presence of Cr(VI). On the other hand, the increase of the initial Cr(VI) concentration from 0 to 100 mgCr/L leads to a decrease in the specific exogenous respiration rate (qEx) values, but this reduction was more noticeably in the case of NAS in comparison with CrAAS. The respirometric curves were well described by the proposed mathematical model. It was concluded that the CrAAS tolerated a Cr(VI) concentration about one order of magnitudehigher than NAS, which was positively reflected in the respiration rate first-order decay constant (kd), the specific maximum exogenous respiration rate (qExm), and the observed oxidation coefficient (YO/S) values. Fil: Ferro Orozco, Ana Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina. Universidad Nacional de La Plata. Facultad de Ingenierí­a. Departamento de Ingeniería Química; Argentina

As a result of its wide usage in the production of polycarbonate plastics and epoxy resins, bisphenol A (BPA) is commonly detected in wastewaters. Recently, BPA became a major concern because its adverse effects as an endocrine disruptor. In this work, the biodegradation kinetics of BPA and its metabolic intermediates 4-hydroxyacetophenone (4HAP), 4-hydroxybenzaldehyde (4HB) and 4-hydroxybenzoic acid (4HBA) by BPA-acclimated activated sludge was studied using manometric respirometry (BOD) tests. For all the tested compounds, BOD curves exhibited two phases. In the first one, a fast increase of the oxygen consumption (OC) due to the active oxidation of the substrate was obtained. Then, when the substrate was exhausted, the endogenous respiration produced a slower increase of OC. A standard Monod-model with biomass growth was used to represent the OC profiles as a function of time. For all the tested compounds, a good agreement between the proposed model and the experimental data was obtained. According to their biodegradation rates, the tested compounds can be ordered as follows: BPA

Since its recognition as an endocrine disrupting chemical, bisphenol A (BPA) removal processes became not only an engineering issue but also a public health concern. In actual biological treatment systems, alternating periods of presence and absence of BPA may cause a decrease of the BPA degradation ability of activated sludge (AS). The objective of this work was to study the effect of alternating periods of presence and absence of BPA in the BPA degradation ability of AS. Two semi-continuous reactors, with partial (SCR1) or total (SCR2) biomass recycling, were used. In SCR1, five feeding phases were tested, being dehydrated cheese whey (DCW) the carbon source. During phases I, III, and V, BPA was also added. In SCR2, seven feeding phases that consisted of the alternation between DCW and BPA as the sole carbon sources were studied. For both SCRs, specific dissolved organic carbon (qDOC), and BPA (qBPA) removal rates, and metabolic measurements (qO2) were performed. Obtained results demonstrated that qDOC and qO2 values were not affected by the alternation between feeding with and without BPA. Conversely, a noticeable deterioration of qBPA values was observed. Thus, BPA degradation ability of AS would not be stable in actual treatment systems.

The objective of the present work was to analyze the interrelationship between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge (AS) in semi-continuous reactors (SCRs). AS were obtained from three SCRs fed with glucose, acetate or peptone. AS from these reactors were used as inocula for three SCRs that were fed with each biogenic substrate, and for three SCRs that were fed with the biogenic substrate and BPA. In all cases, dissolved organic carbon (DOC), BPA, total suspended solids (TSS) and respirometric measurements were performed. Although BPA could be removed in the presence of all the tested substrates, AS grown on acetate exhibited the longest acclimation to BPA. Reactors fed with peptone attained the lowest TSS concentration; however, these AS had the highest specific BPA degradation rate. Specific DOC removal rates and respirometric measurements demonstrated that the presence of BPA had a negligible effect on the removal of the tested substrates. A mathematical model was developed to represent the evolution of TSS and DOC in the SCRs as a function of the operation cycle. Results suggest that the main effect of BPA on AS was to increase the generation of microbial soluble products. This work helps to understand the relationship between the biodegradation of BPA and readily biodegradable substrates., Facultad de Ciencias Exactas, Centro de Investigación y Desarrollo en Criotecnología de Alimentos, Facultad de Ingeniería

In this work the aerobic degradation of phenol (PH), catechol (CA), resorcinol (RE), hydroquinone (HY) and of the binary mixtures PH+CA, PH+RE, PH+HY by phenol-acclimated activated sludge was studied. Single substrate experiments show a Haldane-type dependence of the respiration rate on PH, RE and HY, while CA corresponded to the Monod model. Binary substrate experiments demonstrated that the presence of a second substrate only affected the kinetics, but not the stoichiometry of the oxidation of the compounds tested. While CA inhibited the oxidation of PH, PH inhibited the oxidation of RE and HY. A mathematical model was developed to represent the aerobic biodegradation of the phenolic compounds tested. The agreement between the proposed model and the experimental data indicates that the proposed model can be useful for predicting substrate and dissolved oxygen concentrations in bioreactors treating phenolic wastewaters., Centro de Investigación y Desarrollo en Criotecnología de Alimentos

Most industrial wastewater treatment systems often operate under transient conditions, causing several operational problems. An effective solution is the use of Sequencing Batch Reactors (SBR). In general, a great number of simulations are necessary to solve SBRs mathematical models in order to evaluate the effect of the operational conditions on the performance of the reactor. In this work, a set of analytical equations that represent the effect of the operational parameters on the performance of a SBR was developed. The obtained equations adequately represent the change of the organic substrate, ammonia, biomass, oxygen and soluble microbial products as a function of time within a single operation cycle of the SBR. The equations also predict the steady-state concentrations as a function of several operational parameters, avoiding the problem of performing a great number of simulations. Based on real SBR data, the biomass growth yield and the decay factor for two synthetic wastewaters were obtained. Using these coefficients, the proposed equations adequately predicted the biomass concentration in real cases.

Bisphenol A (BPA) has been described as a estrogenic compound. However, it is used in the production of polycarbonate, epoxy resins and other plastics. Mixed microbial cultures, such as activated sludge, have been proposed as a feasible methodology to achieve the decontamination of wastewater containing BPA. Several studies on the biodegradation of BPA have demonstrated the presence of 4-hydroxyacetophenone (4HAP), 4-hydroxybenzaldehyde (4HB) and 4-hydroxybenzoic acid (A4HB) as the main metabolic intermediates. The objective of the present work was to study the kinetics and stoichiometric characteristics of the aerobic degradation of BPA and its metabolic intermediates by activated sludge. The effect of the sludge age (SA), and the concentration of each compound was analyzed. The biodegradation of the compounds was analyzed by an open respirometer. The kinetics of the biodegradation of all the tested compounds was influenced by the SA, the acclimation process, and the concentration of the tested compound. The stoichiometry of the reactions was not affected by the studied conditions. The oxidation coefficient (YO/S) was 10.0 ± 0.5, 5.2 ± 0.2, 3.7 ± 0.2, and 3.0 ± 0.1 molO2 molS-1 for BPA, 4HAP, 4HB, and 4HBA, respectively. Based on the obtained YO/S values, the aerobic biodegradation pathway of the tested compounds by BPA-acclimated activated sludge is discussed. Fil: Ferro Orozco, Ana Micaela. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina Fil: Zaritzky, Noemi Elisabet. Universidad Nacional de La Plata. Facultad de Ingenieria; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina

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., Centro de Investigación y Desarrollo en Criotecnología de Alimentos, Facultad de Ingeniería

Polyethoxylated nonylphenols (NPEOx) are widely used in various domestic and industrial applications. These commercial products are mixtures of oligomers that affect aquatic ecosystems, acting as endocrine disruptors. In the present work a simple high-performance liquid chromatography-ultraviolet method to quantify single oligomers of nonylphenol ethoxylates was developed. The following NPEOx commercial mixtures were analyzed: Igepal CO-520, Igepal CO-630, and Igepal CO-720. Obtained results demonstrate that the absorbance of each oligomer was not a function of the ethoxyl chain length. This result allowed the comparison between experimental molecular distribution functions of NPEOx mixtures with molecular distributions predicted by the Poisson's equation. In all cases, good agreement was obtained. The method was validated by quantifying NPEOx samples with different molecular size distributions. Fil: Arturi, Tatiana Sonia. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina. Universidad Nacional de La Plata. Facultad de Ingenieria; Argentina Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentina

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 >> PY RE > HY. Also, they exhibited the following degree of toxicity to their own degradation: PY >> CA RE >> 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 molCA1 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 Fil: Lobo, Cintia Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigaciones En Criotecnología de Alimentos (i); Argentina Fil: Bertola, Nora Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigaciones En Criotecnología de Alimentos (i); Argentina Fil: Contreras, Edgardo Martin. Universidad Nacional de la Plata. Facultad de Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina

In this study the oxidation–reduction potential (ORP) and the proton production (Hp) profiles as a function of time were proposed as indicators to monitor the ozonation of phenol solutions at const...

The objectives of this work were: (a) to analyze the effect of alkalinity, pH and initial Fe:P molar ratio (Fe0:P0) 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 NaHCO3; when 1gL-1 NaHCO3 was added, orthophosphate removals higher than 97% and pH above 6.2 were obtained using Fe0:P0=1.9. Precipitation assays at constant pH showed that Fe(III) hydrolysis and FePO4 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 Fe0:P0 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. Fil: Caravelli, Alejandro Horacio. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Contreras, Edgardo Martin. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería; Argentina Fil: Zaritzky, Noemi Elisabet. Universidad Nacional de La Plata. Facultad de Ingeniería; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina

The aim of this work was to study the effect of the initial sulfite concentration on the stoichiometric coefficient of sulfite oxidation. A combined method based on the oxidation of sulfite by oxygen in the presence of cobalt(II) (0.5 mM) as catalyst was used to determine the volumetric mass transfer coefficient (kLa) and the oxygen consumption (OC) due to sulfite oxidation. Results demonstrated that the dissolved oxygen (DO) probe response constant (ksensor) was not dependent on the DO concentration or the agitation speed; obtained ksensor values were high enough to not interfere with DO or OC measurements. Using the reaction time to sulfite depletion method, volumetric mass transfer coefficient (kLa) yielded a linear increase as a function of the initial sulfite concentration. On the contrary, from the saturation phase of DO curves, an almost constant k La. value was obtained in accordance to constant air flow rate and agitation conditions that were used in the experiments. The observed stoichiometric coefficient (OC/S0) at high initial sulfite concentrations or low kLa values was lower than the theoretical one, suggesting that the formation of elemental sulfur becomes significant at these conditions. Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

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.

In recent years the application of partial nitrification techniques has been denoted as very promising. These methods are based on the oxidation of ammonia to nitrite and the inhibition of the nitratation using different strategies. In most cases, this inhibition causes an increase in the concentration of nitrite. However, the effect of high nitrite concentrations under low dissolved oxygen (DO) conditions on the nitrification process is not well understood. In this paper, the effect of ammonia, nitrite, and nitrate concentrations on the nitrification process under low dissolved oxygen concentrations were studied using respirometric techniques. Results showed that the specific oxygen uptake rate (SOUR) followed a Monod-type equation with respect to the DO concentration. The coefficient SOURm was constant with respect to the ammonia, nitrite, and nitrate within the tested concentrations; in addition, KO was constant with respect to ammonia and nitrate but it increased linearly with the nitrite concentratio...

The carbonate buffer system plays a fundamental role in the biological treatments of wastewaters. In this work, the CO2 volumetric mass transfer coefficient (kLac) in a bubbled column was determined using the conventional titration method for different column volumes and air flow rates. In addition, a simple method to determine k Lac based on the interpretation of the changes in the pH level due to the CO2 stripping was developed. Results show that the apparent CO2 volumetric mass transfer coefficient (k Lac-app was strongly affected by the pH level; however, the actual CO2 volumetric mass transfer coefficient, k Lac = kLac-app/aα 0«, was constant within the tested pH conditions. In addition, kLac increased with higher air flow rates and lower column volumes; the obtained kLac values ranged between 20.0 and 71,9 h-1. For all the tested conditions, kLac values obtained using the noncontrolled pH method were similar to the values measured using the titrimetric method. The proposed mathematical model represented adequately the changes on the pH level and total inorganic carbon species concentration as a function of time. The model was extended to take into account the effect of phosphates. Simulation results showed that, although phosphates buffered the changes of pH, the losses of total inorganic carbon were faster than in the case of a nonbuffered solution; thus, the rise in the pH level prevented the stripping of CO2. Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

In this work, the simultaneous degradation of BPA and cheese whey (CW) in semi-continuous activated sludge reactors was studied. The acclimation process and microbial growth on BPA, CW and BPA + CW were analyzed. In addition, the effect of increasing CW concentration on the BPA degradation by acclimated activated sludge was also studied. In order to reduce the factors involved in the analysis of the simultaneous degradation of BPA and CW, the effect of bisphenol A (BPA) on activated sludge not previously exposed to BPA (native activated sludge) was studied. Results demonstrate that BPA concentrations lower than 40 mg l⁻¹ had a negligible effect on the growth of native activated sludge. In the semi-continuous reactors, the presence of CW increased the acclimation time to 40 mg l⁻¹ of BPA. Once the capability of degrading BPA was acquired, the removal of BPA was not affected by the presence of CW. Increasing the CW concentration did not affect the removal of BPA by the acclimated activated sludge. Additionally, the CW consumption was not modified by the presence of BPA. Kinetic and stoichiometric coefficients reported in the present work can be useful in developing mathematical models to describe the simultaneous aerobic biodegradation of a biogenic substrate, such as CW, and BPA by activated sludge., Facultad de Ciencias Exactas, Centro de Investigación y Desarrollo en Criotecnología de Alimentos, Facultad de Ingeniería

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.

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.

Growth kinetics of Sphaerotilus natans and Acinetobacter anitratus (strain E932) in pure and mixed cultures were analysed. In order to determine mixed cultures biomass composition, a quantitative image analysis technique was developed. Pure culture studies showed that for dilution rates less than 0.188 h−1, the filamentous micro-organism will predominate leading to bulking phenomena. By using the developed technique to determine biomass composition, mixed culture experiments showed that changes in the dilution rate modify the microbial composition of the biomass determining which micro-organisms predominate. The stated equations that predict the predominance of S. natans at low dilution rates agree satisfactorily with the obtained results.

The catalytic wet peroxide oxidation of phenol (1 g/L) was performed in a laboratory batch reactor using the cupro-Fenton homogeneous reaction. At 70 °C and using 200 mg/L of Cu (II) complete phenol removal, high TOC reduction (ca. 85%) and efficient use of hydrogen peroxide were achieved. A lumped kinetic model that accounts for organics mineralization and peroxide consumption was developed to predict reactants and total organic carbon profiles. After the reaction step, Cu(II) was recovered by precipitation with NaOH; Cu(II) concentration in the discharged liquid was always less than the 1 mg/L. The sludge was reused in subsequent reaction steps with minor fluctuations in the catalytic activity. The combination of the cupro-Fenton reaction with an alkaline precipitation procedure allows lower operational costs and helps to reduce the toxicity of the treated wastewater. Fil: Inchaurrondo, Natalia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina Fil: Haure, Patricia Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina

This work deals with the calculation of the uncertainty of the exogenous respiration rate (Rex) and the total oxygen consumed (OCT) derived from a single open respirometric profile. Uncertainties were evaluated by applying a linear error propagation method. Results show that standard deviations (SD) of Rex and OCT depend not only on the SD of the dissolved oxygen (C) and kLa (kLa), but also on the SD of the derivative term (dC/dt) of the oxygen mass balance equation (b). A Monte Carlo technique was employed to assess b; a power law expression for the dependence of sb as a function of sC, the time window (tw) and the sampling rate (δt) was proposed. The equations obtained in the present work are useful to calculate suitable conditions (e.g., biomass concentration, kLa) that minimize the coefficient of variation corresponding to Rex and OCT., Centro de Investigación y Desarrollo en Criotecnología de Alimentos

In this work the aerobic degradation of phenol by acclimated activated sludge was studied. Results demonstrate that while the phenol removal rate by acclimated activated sludge follows the Monod model, the oxygen uptake rate obeys a Haldane-type equation. The phenol oxidation coefficient obtained at different intial phenol concentrations ranged from 1.9 to 2.6 mol O2 · mol-1 phenol. A mathematical model based on a simplified version of the catalytic mechanism of the enzyme phenol 2-monooxygenase was developed to predict transient phenol concentrations and oxygen requirements by phenol-acclimated activated sludge in batch reactors under different initial phenol concentrations. The proposed model not only adequately represents the experimental results of the present paper, but also those reported by other authors. Particular cases of the proposed model are discussed., Centro de Investigación y Desarrollo en Criotecnología de Alimentos

In this work the effect of (a) the sludge age (SA) and the acclimation strategy on the acclimation process of activated sludge (AS) to bisphenol A (BPA), (b) the presence of biogenic substrates on the degradation of BPA, and (c) the acclimation on the degradation of biogenic substrates was studied. AS samples from reactors operated at SA of 30 and 45d were acclimated to BPA using two strategies: constant or increasing the initial BPA concentration. Although acclimation to BPA was achieved using both strategies, no net biomass growth was detected. Specific BPA degradation rate of acclimated AS ranged between 65 and 90mgBPAgTSS-1d-1. BPA degradation was not affected by the biogenic substrates cheese whey or acetate; acclimation to BPA did not cause a negative effect on the biodegradation of these substrates. During the degradation of cheese whey, specific mean oxygen uptake rate (qo2mean) and specific mean substrate consumption rate (qSmean) of non-acclimated AS were similar to those corresponding to acclimated ones. When acetate was tested, qo2mean and qSmean values corresponding to acclimated AS were about twofold the values of the non-acclimated ones. This enhancement could occur because acetate is an intermediate of the metabolism of BPA. Fil: Ferro Orozco, Ana Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Lobo, Cintia Cecilia. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Contreras, Edgardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina

The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (μobs), biomass yield (YX/S), and specific growth substrate consumption rate (qS) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (μobs, YX/S, qS). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process. Fil: Ferro Orozco, Ana Micaela. Provincia de Buenos Aires. Gobernación. Comision de Invest.científicas. Centro de Investigación y Desarrollo En Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Investigación y Desarrollo En Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Cs.exactas. Centro de Investigación y Desarrollo En Criotecnología de Alimentos; Argentina Fil: Contreras, Edgardo Martin. Provincia de Buenos Aires. Gobernación. Comision de Invest.científicas. Centro de Investigación y Desarrollo En Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Investigación y Desarrollo En Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Cs.exactas. Centro de Investigación y Desarrollo En Criotecnología de Alimentos; Argentina Fil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comision de Invest.científicas. Centro de Investigación y Desarrollo En Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Investigación y Desarrollo En Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Cs.exactas. Centro de Investigación y Desarrollo En Criotecnología de Alimentos; Argentina

In this work, a mathematical model for the biological reduction of Cr(VI), carbon and nitrogen sources consumption, and biomass growth under fully aerobic conditions was developed. The model comprises three types of aerobic heterotrophic cells (non-growing cells, growing cells with chromate reductase activity, and growing cells that have lost the chromate reductase activity), and five soluble compounds (organic substrate, ammonia nitrogen, non-metabolizable soluble products, dissolved oxygen, and hexavalent chromium). Two processes are considered responsible for the reduction of Cr(VI). The first one is the reduction of Cr(VI) coupled with growth, the second process is coupled with the endogenous decay of the biomass. The model was calibrated using the results obtained in batch cultures in the absence of carbon and nitrogen sources, using different initial Cr(VI) concentrations (0–100 mgCr L −1 ), two carbon sources (cheese whey and lactose), and different initial nitrogen to carbon ratio (0–50 mgN gCOD −1 ). The calibrated model was used to calculate steady-state values of TSS, soluble COD, TAN and Cr(VI) in continuous systems, obtaining a good agreement with the experimental data. The model also accurately predicted the transient concentration of Cr(VI) as a function of time in response to step changes of the inlet Cr(VI) concentration in continuous systems.

The objectives of the present work were: (i) to analyze the capacity of activated sludge to reduce hexavalent chromium using different carbon sources as electron donors in batch reactors, (ii) to determine the relationship between biomass growth and the amount of Cr(VI) reduced considering the effect of the nitrogen to carbon source ratio, and (iii) to determine the effect of the Cr(VI) acclimation stage on the performance of the biological chromium reduction assessing the stability of the Cr(VI) reduction capacity of the activated sludge. The highest specific Cr(VI) removal rate (qCr) was attained with cheese whey or lactose as electron donors decreasing in the following order: cheese whey ≈ lactose > glucose > citrate > acetate. Batch assays with different nitrogen to carbon source ratio demonstrated that biological Cr(VI) reduction is associated to the cell multiplication phase; as a result, maximum Cr(VI) removal rates occur when there is no substrate limitation. The biomass can be acclimated to the presence of Cr(VI) and generate new cells that maintain the ability to reduce chromate. Therefore, the activated sludge process could be applied to a continuous Cr(VI) removal process. Fil: Ferro Orozco, Ana Micaela. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Contreras, Edgardo Martin. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina

The objective of this study was to evaluate the effect of powdered activated carbon (PAC) on the growth kinetics of activated sludge; in addition, a kinetic model for this system was developed. Adsorption kinetic experiments of the growth substrate (cheese whey) in the absence of activated sludge were carried out in conical flasks (20 °C, pH 7). Substrate adsorption attained the equilibrium within the first hour. The Langmuir adsorption equation adequately fitted the specific adsorption capacity (qC) as a function of the soluble COD (CODS). Activated sludge batch growth experiments in the presence of different PAC concentrations were also performed. Specific growth rate (μobs) and specific oxygen uptake rate (qO2) decreased as PAC concentration increased; however, stoichiometric coefficients YX/S and YO/S were almost constant. A mathematical model was developed to represent the effect of PAC on the microbial growth kinetics. The model combined biochemical processes (biomass growth, substrate consumption and product generation) with the adsorption kinetics of the substrate onto PAC. A good agreement between the proposed model and the experimental data was obtained. Simulations show that PAC acts as a buffer of substrate, yielding slower responses to changes of the substrate concentration. Fil: Ferro Orozco, Ana Micaela. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Contreras, Edgardo Martin. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina

The addition of powdered activated carbon (PAC) has been proposed as a suitable technique to protect activated sludge against toxic wastewaters. However, the literature data describing the combined effect of PAC addition on Cr(VI) removal using activated sludge are scarce. The objectives of this study were to investigate the effect of the initial Cr(VI) concentration, PAC and an electron donor addition on Cr(VI) removal using aerobic activated sludge batch reactors. The following Cr(VI) removal systems were tested: activated sludge alone; activated sludge with an external electron donor (5 g/ℓ of lactose); activated sludge with PAC addition (4 g/ℓ); activated sludge with both PAC and lactose; and PAC alone. The results reported here showed that activated sludges are capable of removing Cr(VI) via its reduction to Cr(III) only if a suitable electron donor (such as lactose) is available. For initial Cr(VI) concentration lower than 10 mg/ℓ, biomass alone can remove 100% of the Cr(VI). However, for higher initial Cr(VI) concentrations, removal efficiencies (RE) of the system with PAC were higher than RE corresponding to the system without PAC. In addition, as the initial Cr(VI) concentration increased, the rate of Cr(VI) removal and RE values decreased reflecting loss of metabolic activity of the activated sludge due to the toxicity of Cr(VI); however, this inhibition was less in systems with PAC. Whereas the removal of Cr(VI) using powdered activated carbon (PAC) alone is negligible, the addition of PAC can improve the biological reduction of Cr(VI) due to the stimulating or protective effect against the Cr(VI) toxicity. This protective effect was also observed in respiratory activity of the biomass., Centro de Investigación y Desarrollo en Criotecnología de Alimentos

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.

A simple technique to determine biomass concentration as chemical oxygen demand (COD) was developed as an alternative to the standard volatile suspended solid (VSS) method. The proposed technique for biomass measurement as COD is based on the determination of the biomass COD (CODB) as the difference between total COD (CODT) and the soluble COD (CODS) of the sample. The obtained results show that this technique was quicker and simpler than the traditional VSS method. The validity of the proposed methods was tested with pure cultures of a filamentous micro-organisms (Sphaerotilus natans), a floc-forming bacteria and activated sludges. The method was also used for estimating the conversion factor (fCV) from VSS to COD units. A modification of the standard VSS technique was also proposed using two membranes in the filtration device; this technique allowed the biomass determination in 1 μm size bacteria cultures that cannot be detected by the standard VSS method because cells are not retained by the 1.5 μm diameter pore glass-fibre filter., Facultad de Ingeniería, Centro de Investigación y Desarrollo en Criotecnología de Alimentos

Bulking by Sphaerotilus natans has been attributed to several factors such as low dissolved oxygen in the aeration basin, wastes with high C:N ratios and phosphorus limitation; however, the occurrence of bulking has been reported in fruit, vegetable, meat and poultry wastewaters in which the ratio C:N is variable. Growth of S. natans was analyzed in a model system of a food industry wastewater (potato processing waste) that was characterized by HPLC determining that citric acid was the most important identified component. The effect of several carbon sources on S. natans growth was also studied; different C:N ratios were tested in a continuous culture system (chemostat). This strain grew in a mineral medium with citric acid as a sole carbon source, in spite of the contradictory results found in literature. Chemostat studies showed that the medium was carbon-limited when C:N ratios

The effects of pH (5.0, 5.2, 5.4, 5.6, and 5,8) and concentration of potassium sorbate (10.0 and 16.6 mM) at two water activity values (0.90 and 0.92) on the aerobic growth and decline of Staphylococcus aureus ATCC 6538P, 196-E, and FDA-C243 were studied using brain-heart infusion broth. The inoculum was approximately 4 to 5 log CFU/ml, and the incubation temperature was 30 degrees C. Samples were periodically enumerated on tryptic soy agar. The Gompertz model was used to obtain microbial growth parameters, specific growth rate was obtained as a derived parameter, and the inhibition index was calculated. A linear model was fitted in cases of bacteriostatic or bactericidal action of the treatment. The ATCC 6538P strain showed the highest resistance in the range of tested conditions. Microbial behavior was modeled considering the main controlling factors, and a response surface methodology was used to determine the effects of undissociated acid concentration and pH. These results can be used to establish treatment conditions for microorganism growth or inhibition., Centro de Investigación y Desarrollo en Criotecnología de Alimentos, Comisión de Investigaciones Científicas de la provincia de Buenos Aires