A.M. Hidalgo

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.

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.

Removal of 4-chlorophenol in a continuous membrane bioreactor using different commercial peroxidases

Abstract Three commercial plant peroxidases, the commonly used soybean (SBP) and horseradish (HRP) and a cheap alternative, artichoke (AKPC), have been tested for the removal of 4-chlorophenol in a continuous tank reactor associated to an ultrafiltration membrane module. An important conversion fall over time was observed both in the reactor and permeate samples with AKPC. For the other peroxidases, this conversion decrease occurred in the reactor only, as a result of the enzyme retention on the membrane, and was rather insignificant in the case of SBP. Supplementary addition of enzyme in the feed stream allowed maintaining high conversions in the case of HRP. Consequently, SBP and HRP were selected as the most appropriate peroxidases. Using them, it was observed that conversion values increased when higher substrate concentrations were used and that the influence of the molar ratio H2O2:chlorophenol and the spatial time was negligible. In all cases, higher 4-chlorophenol conversions were attained with SB...

Removal of anilinic compounds using the NF-97 membrane: Application of the solution-diffusion and SKK models

ABSTRACT In the present work, the characterization of the polyamide membrane NF-97 has been carried out studying its behaviour in the treatment of effluents that contain anilinic compounds. High rejection coefficients with a maximum value of 94.72% for aniline, 79.83% for 4-chloroaniline, and 63.63% for 4-nitroaniline were obtained with operating pressures of about 30 bar and pH values between 3 and 4. The fouling parameter based on solute permeate flux was higher than that for the solvent permeate flux and higher for magnesium chloride. Lastly, experimental data were fitted to the Solution-Diffusion model and to the simplified model of Spiegler–Kedem–Katchalsky.

Removal of 4-chloro-2-methylphenol from aqueous solutions by nanofiltration and reverse osmosis

AbstractChloromethylphenols are typical phenolic pollutants frequently found in wastewater treatment plants and industrial landfill leachates, while pressure-driven membrane processes have been demonstrated to be a practical and competitive alternative for their removal. The performance of two membranes (an NF99 nanofiltration membrane and an RO99 reverse osmosis membrane) for removing 4-chloro-2-methylphenol (4C2MP) from synthetic solutions at different pressures, feed concentrations and feed pH values is compared in this paper using permeate flux and rejection as representative parameters. Higher permeate fluxes were obtained with the NF99 membrane but higher rates of 4C2MP rejection were obtained with the RO99 membrane. There was a substantial increase in 4C2MP rejection as the pH was increased from 8 to 11 in the case of the NF99 membrane. The results are explained by the different chemical structures of the active layers of both membranes.