M.A. Sanromán

Decontamination of soils containing PAHs by electroremediation: A review

During the last years, the anthropogenic sources have contributed to organic compound penetration into the environment. One large group of persistent and toxic contaminants is the hydrophobic organic contaminants. Among them, polycyclic aromatic hydrocarbons (PAHs) have been recognized as a representative group of these pollutants with low solubility. In this paper, it is showed the electroremediation of soil contaminated with PAHs as an alternative, to organic compound removal. This technique, mainly used for heavy metal extraction, applies the electric current to promote the movement of contaminants. Nowadays the application of this technique alone or combined with other techniques as for example Fenton or bioremediation is taking fine results to PAHs removal. Although the PAHs soil decontamination by means of the electric field is in an initial stage, many researchers have demonstrated the treatment effectiveness. This paper describes the foremost principles to carry out the electroremediation of soils contaminated with PAHs, just like the different alternatives to improve the electroremediation of PAHs and also the new methodologies of PAHs removal by using hybrid technologies.

Decolourisation of dyes under electro-Fenton process using Fe alginate gel beads.

This study focuses on the application of electro-Fenton technique by use of catalytic activity of Fe alginate gel beads for the remediation of wastewater contaminated with synthetic dyes. The Fe alginate gel beads were evaluated for decolourisation of two typical dyes, Lissamine Green B and Azure B under electro-Fenton process. After characterization of Fe alginate gel beads, the pH effect on the process with Fe alginate beads and a comparative study of the electro-Fenton process with free Fe and Fe alginate bead was done. The results showed that the use of Fe alginate beads increases the efficiency of the process; moreover the developed particles show a physical integrity in a wide range of pH (2-8). Around 98-100% of dye decolourisation was obtained for both dyes by electro-Fenton process in successive batches. Therefore, the process was performed with Fe alginate beads in a bubble continuous reactor. High color removal (87-98%) was attained for both dyes operating at a residence time of 30 min, without operational problems and maintaining particle shapes throughout the oxidation process. Consequently, the stable performance of Fe alginate beads opens promising perspectives for fast and economical treatment of wastewater polluted by dyes or similar organic contaminants.

Efficient PAHs biodegradation by a bacterial consortium at flask and bioreactor scale

In this work, the biodegradation of three polycyclic aromatic hydrocarbons (PAHs) such as Phenanthrene (PHE), Pyrene (PYR) and Benzo[a]anthracene (BaA) has been investigated. A bacterial consortium consisting of two strains was used for the first time based on preliminary promising biodegradation data. They were tentatively identified as Staphylococcus warneri and Bacillus pumilus. Degradation values higher than 85% were obtained for each single PAH when operating at flask scale, whereas minimum levels of 90% of PAHs removal were obtained after just 3 days of cultivation at bioreactor scale. The operation in cometabolic conditions led to maximum levels about 75% and 100% at flask and bioreactor scale, respectively. All the experimental data were analyzed in the light of logistic and Luedeking and Piret type models, with the purpose to better characterize the biodegradation process by S. warneri and B. pumilus. Finally, the metabolic pathway followed to degrade each PAH was ascertained.

Study of the degradation of dyes by MnP of Phanerochaete chrysosporium produced in a fixed-bed bioreactor.

The production of ligninolytic enzymes by the fungus Phanerochaete chrysosporium in a fixed-bed tubular bioreactor, filled with cubes of nylon sponge, operating in semi-solid-state conditions, was studied. Maximum individual manganese-dependent peroxidase (MnP) and lignin peroxidase (LiP) activities of 1293 and 225 U/l were detected. The in vitro decolourisation of two structurally different dyes (Poly R-478, crystal violet) by the extracellular liquid obtained in the above-mentioned bioreactor was monitored in order to determine its degrading capability. The concentration of some compounds (sodium malonate, manganese sulphate) from the reaction mixture was optimised in order to maximise the decolourisation levels. A percentage of Poly R-478 decolourisation of 24% after 15 min of dye incubation was achieved. On the other hand, a methodology for a long treatment of these dyes based on the continuous addition of MnP enzyme and H(2)O(2) was developed. Moreover, this enzymatic treatment was compared with a photochemical decolourisation process. The former allowed to maintain the degradation rate almost constant for a long time, resulting in a decolourisation percentage of 70% and 30% for crystal violet and Poly R-478, respectively, after 2 h of treatment. As for the latter, it was not able to degrade Poly R-478, whereas crystal violet reached a degradation of 40% in 2 h.

Decolorization of dye Reactive Black 5 by newly isolated thermophilic microorganisms from geothermal sites in Galicia (Spain)

In this study, thermophilic microbial strains from thermal spots in northwestern Spain displaying excellent decolorization capability were isolated. The research work tackled: (i) the ability of consortia to degrade a model di-azo dye Reactive Black at different pHs in flask cultures, obtaining that just neutral pHs licensed degradation levels near to 70%, (ii) the isolation of tree of the bacteria, which rendered possible reaching high levels of decolorization (80%) after just 24 h in aerobic conditions, and which were identified through 16S rRNA sequencing to possess high homology (99%) with Anoxybacillus pushchinoensis, Anoxybacillus kamchatkensis and Anoxybacillus flavithermus, and (iii) the cultivation of the isolates in a bench-scale bioreactor, which led to a decolorization rate two-fold higher than that obtained in flask cultures. Therefore, this work makes up the first time that a decolorization process of an azo dye by thermophilic microorganisms in aerobic conditions is investigated.

Remediation of polluted soil by a two-stage treatment system: desorption of phenanthrene in soil and electrochemical treatment to recover the extraction agent.

In this study, the feasibility of a two-stage treatment process for the remediation of soil contaminated with phenanthrene as a model polycyclic aromatic hydrocarbon (PAH) has been assessed at laboratory scale. The initial stage of the process involved contacting contaminated soil with a solution of Tween 80 to enhance the desorption of phenanthrene from soil. In order to simulate a flushing process this initial stage was carried out in a washing packed-bed soil column. At the optimised conditions the total phenanthrene removal attained a value of almost 65% after 3 days. The second stage of the suggested treatment involved regeneration of the washing solution via phenanthrene degradation. The use of an electrochemical treatment was proposed for surfactant recovery and degradation of contaminants present in the solution collected. This oxidation was accomplished via an electrochemical cell by using graphite as electrode material. The phenanthrene was almost totally degraded in 3 days, reaching a degradation of about 96%. In addition, a test in which this regenerated solution was employed in the washing process was carried out in shake flask and washing column. The results demonstrate that selective degradation of pollutants by electrochemical treatment is potentially effective in reusing surfactant in another polluted soil treatment.

Electrokinetic remediation of PAH mixtures from kaolin

Because of increased industrialisation and new manufacturing processes, elevated amounts of organic pollutants are released into the environment. Hydrophobic organic contaminants, including polycyclic aromatic hydrocarbons (PAHs), are toxic and persistent contaminants that are not treatable by natural attenuation. In this work, electroremediation is proposed for cleaning soil contaminated by organic compounds. Model samples of kaolin clay polluted with a mixture of PAHs (fluoranthene, pyrene, and benzanthracene) were treated. Electroremediation of kaolin contaminated with a mixture of these three PAHs was carried out using a solution of 1% Tween 80 and 0.1 M Na(2)SO(4) as the processing fluid. Under these conditions, low removal was obtained. However, by using the same processing fluid and controlling the pH at 7 in the anode chamber, high electro-osmotic flow was detected. After the treatment, removal of around 40% of the PAHs was achieved. The created environment inside the soil during the electrokinetic treatment greatly influenced the process. The results of this work reveal the high potential for the application of the electroremediation process on soil polluted with different PAHs.

Technoeconomic assessment of phenanthrene degradation by Pseudomonas stutzeri CECT 930 in a batch bioreactor.

Polycyclic aromatic hydrocarbons (PAHs) are among the most persistent pollutants that accumulate in natural environment mainly as a result of anthropogenic activities. Therefore, the improvement of the available bank of microbial resources and information is crucial to the proper management of PAHs-polluted sites and effluents. In this work, Pseudomonas stutzeri CECT 930 was selected for aerobically degrading an aqueous effluent containing phenanthrene (PHE). Maximum PHE degradation of 90% was obtained both at flask and stirred tank bioreactor scale. All the experimental data were fitted to logistic and Luedeking and Piret models, and licensed to quantitatively ascertain a stronger dependence on the biomass of the metabolites triggering the bioremediation process. In addition, PHE degradation via protocatechuate pathway was elucidated through GC-MS data. Finally, based on the promising results of biodegradation, a preliminary economic evaluation of this process at industrial scale was approached by means of simulation data obtained with SuperPro Designer.

A two-stage process using electrokinetic remediation and electrochemical degradation for treating benzo[a]pyrene spiked kaolin

An innovative process that combines soil electrokinetic remediation and liquid electrochemical oxidation for the degradation of organic compounds present in a polluted soil was developed and evaluated by using benzo[a]pyrene spiked kaolin. In order to increase benzo[a]pyrene solubility during electrokinetic treatment, the addition of a co-solvent or surfactant, such as ethanol or Brij 35, as flushing solution was tested. The research carried out demonstrated the influence of the desorption agent employed on benzo[a]pyrene remediation from the kaolin matrix. Thus, if the flushing solution was ethanol at 40%, there was no presence of contaminant in either chamber. On the contrary, when a solution of surfactant Brij 35 was used, benzo[a]pyrene was transported towards the cathode chamber, where it was collected. Moreover, the extent of this recovery depends on the pH profile on the soil. When no pH control was used, around 17% of initial contaminant was detected in the cathode chamber; however, when pH control was applied, the recovery of benzo[a]pyrene could be higher than 76%, when the pH control in the anode chamber was set at 7.0. In order to obtain the total degradation of mobilised benzo[a]pyrene from the contaminated soil, the liquid collected by electrokinetic remediation was oxidised by electrochemical treatment. This oxidation was accomplished via an electrochemical cell with a working volume of 0.4 L, and graphite as electrode material. The benzo[a]pyrene was almost totally degraded in 1d, reaching a degradation of about 73% in 16 h.

Hydrogen peroxide biosensor with a supramolecular layer-by-layer design.

A new sensor design is reported for the construction of an amperometric enzyme biosensor toward H (2)O(2). It was based in the supramolecular immobilization of alternating layers of horseradish peroxidase (either modified with 1-adamantane or beta-cyclodextrin-branched carboxymethylcellulose residues) on Au electrodes coated with polythiolated beta-cyclodextrin polymer. The analytical response of the electrodes, using 1 mM hydroquinone as an electrochemical mediator, increases when the number of enzyme layers increases. The biosensor having three enzyme layers showed a sensitivity of 720 microA/M cm (2) and a detection limit of 2 microM and retained 96% of its initial activity after 30 days of storage. The host-guest supramolecular nature of the immobilization method was confirmed by cyclic voltammetry.