C. Quintelas

Treatment of chromium(VI) solutions in a pilot-scale bioreactor through a biofilm of Arthrobacter viscosus supported on GAC

The aim of this work is to evaluate the applicability of a biofilm to the removal of chromium in solution, at a pilot scale. The effect of the initial concentration of metal on the biosorption behavior of an Arthrobacter viscosus biofilm supported on granular activated carbon, in batch and column essays was also analyzed. Six isotherm equations have been tested in the present study. The best fit was obtained with the Freundlich model. It was observed that as the initial chromium concentration increases, the uptake increases too, but the removal percentage decreases, with values between 95.20% (C(0)=5mg/l) and 38.28% (C(0)=1000 mg/l). The batch adsorption studies were used to develop a pilot bioreactor able to remove chromium from aqueous solutions. Data obtained in a pilot-scale reactor showed an average removal percentage of 99.9%, during the first 30 days, for the initial concentration of 10mg/l and an average removal percentage of 72%, for the same period and for the initial concentration of 100mg/l. Uptake values of 11.35 mg/g and 14.55 mg/g were obtained, respectively, for the initial concentration of 10 and 100mg/l. The results obtained are very promising and encourage the utilization of this biofilm in environmental applications.

The effect of clay treatment on remediation of diethylketone contaminated wastewater: uptake, equilibrium and kinetic studies.

The ability of four different clays to adsorb diethylketone was investigated in batch experiments aiming to treat wastewater with low solvent concentrations. The adsorption performance in terms of uptake followed the sequence: vermiculite>sepiolite=kaolinite=bentonite, for all the adsorbent doses tested (from 0.1 to 1.5 g) in 150 mL of ketone solution (800 mg/L). The equilibrium data in the batch systems were described by Sips and Dubinin-Raduskevich isotherms. The best fits for bentonite and kaolinite clays were obtained with the Sips isotherm and for sepiolite and vermiculite the best fits were obtained with the Dubinin-Raduskevich model. Kinetic data were described by pseudo-first and pseudo-second order kinetics models. The best fit was obtained for the pseudo-first order model which assumed that the interaction rate was limited only by one process or mechanism on a single class of sorbing sites and that all sites were time dependent. The presence of functional groups on the clay surface that might have interacted with the solvent was confirmed by FTIR. XRD analysis was also performed. This study showed that the tested clays are very effective for the removal of diethylketone from industrial effluents.

Removal of chromium(VI) and cadmium(II) from aqueous solution by a bacterial biofilm supported on granular activated carbon

A biofilm of Arthrobacter viscosus, supported on granular activated carbon, removed between 100% and 50% of Cr(VI) and between 100% and 20% of Cd(II) from solutions with initial concentrations between 4–11 mgmetal l−1 and a flow residence time of 1.2 min. For experiments of lower initial concentrations, a steady-state removal of 50% was reached after 71 bed volumes of Cr solution passed through the biosorbent bed and a steady-state removal of 30% was reached after 47 bed volumes of Cd solution passed through a similar bed. Final uptakes of 8.5 mgCr gcarbon−1 and 4.2 mgcd gcarbon−1 were determined for initial concentrations of 10 mgCr l−1 and 11 mgCd l−1, respectively. The influence on the overall process of two different surface treatments of the support was evaluated and compared with the behavior of a support not treated.

Removal of Ni(II) from aqueous solutions by an Arthrobacter viscosus biofilm supported on zeolite: From laboratory to pilot scale

This study discusses the retention of Ni(II) by Arthrobacter viscosus supported on zeolite 13 X in batch mode and in continuous mode, at laboratory scale and at pilot scale. The maximum adsorption capacities of 28.37, 20.21 and 11.13 mg/g were recorded for lab scale batch, for continuous lab scale minicolumns and for pilot scale bioreactors, respectively. The Sips isotherm and pseudo second order kinetics described well the observations registered in batch assays. The Adams-Bohart, Thomas and Yoon-Nelson models were applied to data obtained with the pilot scale bioreactor and a good fit was reached for Adams-Bohart and for Yoon-Nelson models. A fed-batch was performed at lab scale and the applicability of the biofilm in continuous mode for the described purpose was confirmed. The sorption mechanism was investigated in detail through FTIR, SEM and EDX analyses.

Tailored zeolites for the removal of metal oxyanions: Overcoming intrinsic limitations of zeolites

This review aims to present a global view of the efforts conducted to convert zeolites into efficient supports for the removal of heavy metal oxyanions. Despite lacking affinity for these species, due to inherent charge repulsion between zeolite framework and anionic species, zeolites have still received considerable attention from the scientific community, since their versatility allowed tailoring them to answer specific requirements. Different processes for the removal and recovery of toxic metals based on zeolites have been presented. These processes resort to modification of the zeolite surface to allow direct adsorption of oxyanions, or by combination with reducing agents for oxyanions that allow ion-exchange with the converted species by the zeolite itself. In order to testify zeolite versatility, as well as covering the wide array of physicochemical constraints that oxyanions offer, chromium and arsenic oxyanions were selected as model compounds for a review of treatment/remediation strategies, based on zeolite modification.

Optimization of production of extracellular polymeric substances by Arthrobacter viscosus and their interaction with a 13X zeolite for the biosorption of Cr(VI)

In this work we aimed to optimize the production of extracellular polymeric substances (EPS) by an Arthrobacter viscosus biofilm supported on 13X zeolite to be used in the biosorption of Cr(VI). The optimization parameters were agitation rate, work volume, pH and glucose concentration. Following the optimization of EPS production, the biofilm was used in the biosorption of hexavalent Cr from liquid solutions. Differences between the use of dead or active biomass and between the performance of zeolite in powder or in pellet form were also studied. The optimized EPS production allowed values of metal uptake between 2.72 mg/gbiosorbent and 7.88 mg/gbiosorbent for initial Cr(VI) concentrations of 20–60 mg/L. For an initial concentration of 20 mg/L, the optimal conditions of EPS production allowed an increase of 10% on the removal percentage of total Cr, and the use of zeolite as a powder rather than the pelleted form produced an increase of 46.5% in the removal percentage. For the initial concentration of 60 mg/L, the use of active biomass compared to dried biomass allowed a reduction of the time required for the total removal of Cr(VI) from 20 to 13 days.

Near-infrared spectroscopy for the detection and quantification of bacterial contaminations in pharmaceutical products.

Accurate detection and quantification of microbiological contaminations remains an issue mainly due the lack of rapid and precise analytical techniques. Standard methods are expensive and time-consuming being associated to high economic losses and public health threats. In the context of pharmaceutical industry, the development of fast analytical techniques able to overcome these limitations is crucial and spectroscopic techniques might constitute a reliable alternative. In this work we proved the ability of Fourier transform near infrared spectroscopy (FT-NIRS) to detect and quantify bacteria (Bacillus subtilis, Escherichia coli, Pseudomonas fluorescens, Salmonella enterica, Staphylococcus epidermidis) from 10 to 10(8) CFUs/mL in sterile saline solutions (NaCl 0.9%). Partial least squares discriminant analysis (PLSDA) models showed that FT-NIRS was able to discriminate between sterile and contaminated solutions for all bacteria as well as to identify the contaminant bacteria. Partial least squares (PLS) models allowed bacterial quantification with limits of detection ranging from 5.1 to 9 CFU/mL for E. coli and B. subtilis, respectively. This methodology was successfully validated in three pharmaceutical preparations (contact lens solution, cough syrup and topic anti-inflammatory solution) proving that this technique possess a high potential to be routinely used for the detection and quantification of bacterial contaminations.

Iron and Chromium Removal from Binary Solutions of Fe(III)/Cr(III) and Fe(III)/Cr(VI) by Biosorbents Supported on Zeolites

The removal of metallic ions from binary aqueous solutions of Fe(III)/Cr(III) and Fe(III)/Cr(VI) by an Arthrobacter viscosus biofilm supported on NaY zeolite was investigated. Experiments were repeated with suspended biomass for comparison purposes. Batch assays were performed using different concentrations (10, 25 and 40 mg/L), for both metals in solution. Results indicated that Arthrobacter viscosus is able to retain the metallic ions, although not totally. The removal efficiencies were improved when the biofilm was supported on the zeolite, for all the initial concentrations of Cr(III), for the intermediate and higher concentration of Cr(VI) and for all range of initial concentrations of Fe(III), in the presence of Cr(III). The bacteria reduce Cr(VI) to Cr(III) and, only then, this cation may be entrapped in the framework zeolite by ion exchange. Suspended bacteria had higher affinity for Fe(III), than for Cr(VI) or Cr(III), while the conjugated system was selective to Fe(III) when in the presence of Cr(VI). For solutions of Fe(III)/Cr(III), very high removals were achieved by the supported system, ranging from 94 to 100 % for Cr(III) and from 98 to 100 % for Fe(III). The conjugated system also reached the highest removal ratio of Cr(VI), 36 %, for the initial concentration of 40 mg/L. The materials in study were characterized by techniques such as FTIR, SEM and chemical analyses.

Comparative study between natural and artificial zeolites as supports for biosorption systems

This study aims the definition of a new material that may act as a robust and yet cost effective biosorbent for treatment of wastewater with low concentration of heavy metals. A comparative study was made between two biosorption systems composed of an Arthrobacter viscosus biofilm supported on Cuban natural zeolites and on prepared NaY and NaX, in terms of their ability to retain ionic chromium. The bacterium is able to reduce Cr(VI) to Cr(III) and, only then, this smaller and positive ion may be entrapped in the zeolite cages by ion exchange. The first support was tested in a continuous flow semi-packed bed column. The highest removal ratio, 42%, was achieved for initial chromium concentration of 10 mg/L, but the best up-take, 5.5 mg/gzeolite, was obtained for initial concentration of 70 mg/L. Biosorbents prepared with the same biofilm supported in NaY and NaX zeolites were also considered in batch studies, with a typical kinetics of biosorption processes, reaching 20% of initial chromium removal within an initial range of Cr(VI) concentration between 50 and 250 mg/L. These last structures were characterized by spectroscopic methods (FTIR and ICP-AES), surface analysis (DRX) and thermal analysis (TGA). All these techniques indicated that the biosorption process does not modify the morphology and structure of the FAU-zeolites.

Monitoring biological wastewater treatment processes: Recent advances in spectroscopy applications

Biological processes based on aerobic and anaerobic technologies have been continuously developed to wastewater treatment and are currently routinely employed to reduce the contaminants discharge levels in the environment. However, most methodologies commonly applied for monitoring key parameters are labor intensive, time-consuming and just provide a snapshot of the process. Thus, spectroscopy applications in biological processes are, nowadays, considered a rapid and effective alternative technology for real-time monitoring though still lacking implementation in full-scale plants. In this review, the application of spectroscopic techniques to aerobic and anaerobic systems is addressed focusing on UV–Vis, infrared, and fluorescence spectroscopy. Furthermore, chemometric techniques, valuable tools to extract the relevant data, are also referred. To that effect, a detailed analysis is performed for aerobic and anaerobic systems to summarize the findings that have been obtained since 2000. Future prospects for the application of spectroscopic techniques in biological wastewater treatment processes are further discussed.