M. Gómez

Testing a Pseudomonas putida strain for 4-chlorophenol degradation in the presence of glucose

Abstract One of the most studied process for the decomposition of phenolic compounds involves the use of different microbial species or consortia. The main drawback of biological methods is the possible inhibitory effect of high concentrations of phenolic compounds impacting on the microorganisms. To overcome these difficulty bacteria can be acclimated to higher concentrations of phenols and the use of supplemental carbon sources. In this work a Pseudomonas putida strain isolated from a waste treatment plant receiving phenolic waste was tested for 4-chlorophenol removal using 1% (w/v) glucose as a co-substrate. Total removal of 4-chlorophenol concentrations of 50, 150 and 200 mg l−1 were obtained in approximately 27, 53 and 93 h respectively. For a higher 4-chlorophenol concentration of 250 mg l−1, only 22% of degradation was obtained suggesting that at this high concentration, the 4-chlorophenol exerts an inhibitory effect on the bacteria.

Continuous tank reactors in series: an improved alternative in the removal of phenolic compounds with immobilized peroxidase

Immobilized derivatives of soybean peroxidase, covalently bound to a glass support, were used in a continuous stirred tank reactor in series, in order to study the removal of two phenolic compounds: phenol and 4-chlorophenol. The use of two reactors in series, rather than one continuous tank, improved the removal efficiencies of phenol and 4-chlorophenol. The distribution of different amounts of enzyme between the two tanks showed that the relative distributions influenced the removal efficiency reached and the degree of the enzyme deactivation. The highest removal percentages were reached at the outlet of the second tank for a distribution of 50% of the enzyme in each tank. However, with a distribution of 75% in the first tank and 25% in the second, the elimination percentage in the second tank was slightly lower than in the previous case, and the effects of deactivation of the enzyme in the first tank were less pronounced. In all the distributions assayed it was observed that the first tank acts as a filter for the second one, which receives a feed with a smaller load of phenolic compounds, thus diminishing enzyme deactivation in the second tank.

Screening of three commercial plant peroxidases for the removal of phenolic compounds in membrane bioreactors

A comparative study of three plant peroxidases, horseradish (HRP), soybean (SBP) and artichoke (AKPC), was carried out to select the most appropriate one for 4-chlorophenol treatment in an ultrafiltration membrane reactor. Soybean peroxidase showed the highest enzymatic activity, followed by HRP and AKPC. The same tendency was observed in a discontinuous tank reactor, where SBP attained more than 90% of 4-chlorophenol removal within the pH range tested. The optimum temperature was 30 °C, with SBP showing highest thermostability. With the ultrafiltration membrane reactor, SBP attained the highest operational stability, with 4-chlorophenol conversions of around 90% in the permeate stream for up to 200 minutes. Finally, permeate samples were analysed and no significant amount of enzyme was detected, so the observed loss of activity, less pronounced with SBP, was attributed to enzyme adsorption on the polymeric products deposited on the membrane surface. Soybean peroxidase was selected as the most appropriate peroxidase for future research.

Behaviour of RO98pHt polyamide membrane in reverse osmosis and low reverse osmosis conditions for phenol removal

Phenolic compounds and their derivatives are very common pollutants in wastewaters. Among the methods described for their removal, pressure‐driven membrane processes are considered as a reliable alternative. Our research group has previously studied phenol removal in reverse osmosis (RO) conditions and obtained very low rejection percentages. Subsequently, when low reverse osmosis (LRO) conditions were studied, the organic rejection percentages improved. To further our knowledge in this respect, the main objective of this work was to study the behaviour of the polyamide thin‐film composite membrane RO98pHt used for phenol removal in RO and LRO conditions. The influence of different operating pressures, phenol feed concentrations and pH on permeate flux and phenol rejection was studied. Low reverse osmosis conditions led to higher phenol rejection percentages in all the assayed conditions, suggesting that other factors related to the molecular characteristics of the organic molecules, such as solubility, acidity and hydrogen bonding capacity, play an important role in the rejection percentage attained. As expected, permeate flux was greater in RO conditions.

Polyamide nanofiltration membranes to remove aniline in aqueous solutions

Aniline is commonly used in a number of industrial processes. It is known to be a harmful and persistent pollutant and its presence in wastewater requires treatment before disposal. In this paper, the effectiveness of nanofiltration (NF) to remove aniline from aqueous solutions is studied in a flat membrane test module using two thin-layer composite membranes of polyamide (NF97 and NF99HF). The influence of different operational variables (applied pressure, feed concentration and pH) on the removal of aniline from synthetic aqueous solutions was analysed. The experimental NF results are compared with results previously obtained by reverse osmosis. Based on this comparative study, the effective order for aniline rejection is: HR98PP>NF97>DESAL3B>SEPA-MS05>NF99HF.

A New Kinetic Model for 4-Chlorophenol Adsorption on Expanded Clay

The adsorption of 4-chlorophenol on an expanded commercial clay used in water purification has been studied. Experiments using 4-chlorophenol concentrations of 50, 100, 250, 500, 750, 1000, 1250 and 1500 mg L-1 were carried out in column reactors at 25ºC.A new adsorption kinetics equation has been developed based on the equation for the variation in solute concentration in the liquid phase, representing the difference between the adsorption rate minus the desorption rate that at equilibrium represents the Langmuir isotherm. This was used to derive a new finite equation for the development of the adsorption curve.

Modelling and experimental checking of the influence of substrate concentration on the first order kinetic constant in photo-processes

Most photoprocesses follow a pseudo first order kinetic law and, commonly, the kinetic parameter depends on the initial concentration of the substrate. In this work, a kinetic model, which explains this dependence on the substrate concentration and on the other operational variables, has been developed. In the model, mass transfer of substrate from the bulk solution to the wall of the photoreactor was assumed as the step determining the rate of the process. To check the model, methylene blue (MB) has been used as model substrate and photodegradation experiments have been carried out in an exciplex KrCl flow-through photoreactor, It was observed that the methylene blue conversion improved with a decrease in its initial concentration, in good agreement with the model. Also, by fitting the experimental data to the model, high correlation coefficients and a high degree of agreement between experimental and calculated conversion was obtained, which validates the model.

Photodegradation of 2-methyl-4-chlorophenol in a KrCl exciplex flow-through photoreactor: a kinetic study

AbstractThe removal of 2-methyl-4-chlorophenol (MC), the main photoproduct from 4-chloro-2-methylphenoxyacetic acid oxidation, has been studied with an advanced oxidation treatment and, for this purpose, a KrCl exciplex flow-through photoreactor was tested. Preliminary results show that the use of UV treatment leads to practically total MC degradation in 10, 60 or 90 min for the initial concentrations of 0.2, 1.0 or 2.0 mM, respectively. However, to attain higher elimination of the main photoproducts, 2-MH and 2-MB, addition of an oxidizing agent, such as hydrogen peroxide, is necessary. With molar ratios H2O2/MC/1 or higher, smaller concentrations of photoproducts are obtained after the treatment. Additional chemical analysis, such as chemical oxygen demand (COD) suggests that although COD is smaller after the treatment than before, for the highest H2O2 concentrations an excess of H2O2 remains in the medium, which increases this parameter, being required longer treatment times. Total phenols, pH, and res...

Application of a diffusion-reaction kinetic model for the removal of 4-chlorophenol in continuous tank reactors

A continuous tank reactor was used to remove 4-chlorophenol from aqueous solutions, using immobilized soybean peroxidase and hydrogen peroxide. The influence of operational variables (enzyme and substrate concentrations and spatial time) on the removal efficiency was studied. By using the kinetic law and the intrinsic kinetic parameters obtained in a previous work with a discontinuous tank reactor, the mass-balance differential equations of the transient state reactor model were solved and the theoretical conversion values were calculated. Several experimental series were used to obtain the values of the remaining model parameters by numerical calculation and using an error minimization algorithm. The model was checked by comparing the results obtained in some experiments (not used for the determination of the parameters) and the theoretical ones. The good concordance between the experimental and calculated conversion values confirmed that the design model can be used to predict the transient behaviour of the reactor.

Application of the solution-diffusion model for the removal of atrazine using a nanofiltration membrane

Abstract The solution-diffusion model was used to predict the behaviour of four nanofiltration membranes, two were made of polyamide (NF-99 and NF-97) and the other two were made of polypiperazineamide (DL and DK), when used for the removal of atrazine from aqueous solutions. The mass transfer model applied is very simple and its linearization facilitates rapid calculation of the relevant parameters. The two main parameters, permeate concentration and volumetric permeate flux, are obtained from three different coefficients: water permeability, A w, solute permeability, B s, and osmotic pressure coefficients, Ψ. Good agreement between the experimental and the predicted atrazine concentrations was obtained for the NF-99, DL and DK membranes when the concentration was low. However, only the NF-99 membrane provided accurate values for the two main parameters in the whole range of concentrations studied, which suggests that the solution-diffusion model can only be applied to this membrane.