David A. Rubinos

Ex Situ Treatment of Hydrocarbon-Contaminated Soil Using Biosurfactants from Lactobacillus pentosus

The utilization of biosurfactants for the bioremediation of contaminated soil is not yet well established, because of the high production cost of biosurfactants. Consequently, it is interesting to look for new biosurfactants that can be produced at a large scale, and it can be employed for the bioremediation of contaminated sites. In this work, biosurfactants from Lactobacillus pentosus growing in hemicellulosic sugars solutions, with a similar composition of sugars found in trimming vine shoot hydrolysates, were employed in the bioremediation of soil contaminated with octane. It was observed that the presence of biosurfactant from L. pentosus accelerated the biodegradation of octane in soil. After 15 days of treatment, biosurfactants from L. pentosus reduced the concentration of octane in the soil to 58.6 and 62.8%, for soil charged with 700 and 70,000 mg/kg of hydrocarbon, respectively, whereas after 30 days of treatment, 76% of octane in soil was biodegraded in both cases. In the absence of biosurfactant and after 15 days of incubation, only 1.2 and 24% of octane was biodegraded in soil charged with 700 and 70,000 mg/kg of octane, respectively. Thus, the use of biosurfactants from L. pentosus, as part of a well-designed bioremediation process, can provide mechanisms to mobilize the target contaminants from the soil surface to make them more available to the microbial population.

Interaction of Hg(II) with kaolin-humic acid complexes

Abstract The adsorption and desorption of Hg(II) by humic acid (HA) previously adsorbed on kaolin was studied. In the range of HA concentration investigated (0.0 -26.9 mg g-1), the Hg(II) adsorption capacity of kaolin at pH 4 is enhanced by the presence of HA. For the complexes with the highest HA concentration and for low Hg(II) initial concentrations, adsorption was lower, i.e. as HA concentration on the complexes increases, Hg(II) equilibrium concentration also increases. This behaviour is due to the increasing presence of dissolved organic matter as the HA concentration on the complexes increases. The dissolved organic matter is able to form a soluble complex with Hg, thus decreasing adsorption. Hg(II) adsorption from a 2.5 × 10-5MHg(II) solution was influenced by pH. For kaolin, a pHmax (pH where maximum adsorption occurs) of 4.5 was observed. At pH values >pHmax retention decreased with increasing pH. This same behaviour was observed for the kaolin-HA complex containing the lowest HA concentration (6.6 mg g-1). For the other kaolin-HA complexes there was little effect of pH on Hg(II) adsorption between pH 2.5 and pH 6.5. The presence of HA increased the adsorption of Hg(II) on kaolin all along the pH range studied. Desorption experiments showed that the amount of Hg(II) desorbed was quite low (<1%) for all the HA and Hg(II) concentration range studied, except for the kaolin at acid pH (pH 2.5) where the Hg(II) released was >50% of Hg(II) previously adsorbed. The presence of HA dramatically reduced this percentage of desorption to values of <3%, indicating reduced risk of toxicity problems in surface and subsurface waters. The addition of Cu(II) did not favour any Hg(II) desorption, even though Cu exhibits a strong affinity for organic matter.

Undrained shear strength of clays as modified by pH variations

The undrained shear strength of clays is an important geotechnical parameter used during construction processes. Several laboratory tests were performed on kaolinite and smectite mixed with pore fluids with different pH values. Vane shear tests were carried out and it was found that the undrained shear resistance for clays increased considerably if the pore fluid had a high or a low pH. A possible explanation could be the dissolution of Al3+ which acts as a coagulant, increasing the internal shear resistance. Geochemical computations, Al measurements and ζ-potential experiments were performed to confirm this theory. The research suggests varying the pH may make a useful contribution to soil improvement techniques.RésuméLa résistance au cisaillement non drainé des argiles est un paramètre géotechnique important utilisé en phase de construction d’ouvrages. Plusieurs essais de laboratoire ont été mis en œuvre sur des kaolinites et des smectites préparées avec des fluides de différents pH. Des essais de cisaillement au scissomètre ont été réalisés et l’on a trouvé que la résistance au cisaillement non drainé des argiles augmente considérablement si le fluide interstitiel a un pH faible ou fort. Pour un pH faible, une explication possible pourrait venir de la dissolution des Al3+ qui agissent comme des coagulants, augmentant la résistance au cisaillement. Des calculs géochimiques, des mesures de teneur en Al et de potentiel ζ ont été réalisés pour confirmer cette théorie. Les résultats de cette recherche suggèrent que le fait de faire varier le pH de l’eau interstitielle peut contribuer utilement à l’amélioration de la résistance des sols.

Arsenic release from river sediments in a gold-mining area (Anllóns River basin, Spain): effect of time, pH and phosphorous concentration

The release of arsenic (As) from As-rich riverbed sediments (Anllons River, Spain) was studied. In this area As is associated with pyrite and arsenopyrite and its mobilization has been favoured by past gold-mining activities. The effect of pH and phosphorous (P) concentrations, as well as the kinetics of the As release process were studied. Also, As species in solution were determined as a function of pH and time. The release of As was greatly influenced by pH and it was between 10 and 45 times higher at pH stat 10 than at pH stat 4 for all the sediments studied. The percentages of As released were between 0.1 and 0.8 % of total As at pH stat 4 but increased to values between ~7 and 11 % of total As at pH stat 10. The sediment containing the highest concentration of As released the highest amount of As (~18 mg/kg at pH stat 10). The As release kinetics was also greatly influenced by pH, mostly at alkaline pH. At pH stat 10, the amount of released As increased progressively with time. In contrast, at pH stat 4 only small differences were observed after 24 h in the amounts of As released. At alkaline pH As was released along with Fe and Al, and accompanied by organic matter dissolution. This suggests a determining role of organic matter in the As release behaviour in alkaline media. In contrast, at weakly acid pH, the release of these components was very low, suggesting that As release is controlled mainly by desorption. The speciation of As was influenced by the pH and the release time. At pH stat 4 the major species in solution were As(III) and As(V) (representing 45–69 % and 51–29 % of As released, respectively). In contrast, at pH stat 10 almost all the released As was As(V) (~99 %). The amount of As released from sediments increased with the increase in initial P concentration in solution and it experienced a dramatic increase at added P concentrations above 1 mM. Namely, the percentage of As released by 10 mM P reached ~6 % of total As for the sediments richer in As. The results obtained let us conclude that changes in pH, especially alkalinization, and inputs of P to the river markedly enhanced As mobilization from the Anllons River sediments, thus increasing health risks.

Speciation of adsorbed arsenic(V) on red mud using a sequential extraction procedure

Abstract The distribution of sorbed arsenic(V) among different geochemical fractions for arsenic(V)-loaded red mud, an oxide-rich residue from bauxite refining that has been proposed as an adsorbent for arsenic, was studied as a function of sorbed arsenic(V) concentration using a sequential extraction procedure. The release of previously sorbed arsenic(V) was also studied as a function of pH and arsenic(V) concentration. Most sorbed arsenic(V) (0.39-7.86 mmol kg-1) was associated with amorphous and crystalline Al and Fe oxides (24.1-43.8% and 24.7-59.0% of total sorbed arsenic, respectively). Exchangeable arsenic was the smallest fraction (0.4-5.2% of total sorbed arsenic). The distribution of sorbed arsenic(V) was related to the arsenic surface coverage. For arsenic surface coverages >~30% the percentage of arsenic(V) associated with the amorphous Al oxide fraction increased and that associated with the crystalline oxide fraction decreased. The arsenic(V) exchangeable fraction increased from 1.4 to 756 μmol kg-1 as surface coverage increased from 388 to 7855 μmol kg-1. The release of sorbed arsenic(V) from red mud was greater at alkaline pH values (maximum release of ~33% of previously sorbed arsenic at pH = 12), but for high arsenic(V) initial concentration (0.2 mM arsenic) considerable amounts of arsenic (6.5% of previously sorbed arsenic) were released at pH 4, in accordance with the dissolution of amorphous Al oxides in the red mud. The results obtained suggest a greater mobility of sorbed arsenic(V) as its surface concentration approaches saturation.

Assessment of bauxite refining residue (red mud) as a liner for waste disposal facilities

Red mud (RM), a waste arising from the bauxite refining, was studied to assess its suitability as a compacted liner material. The geotechnical and hydraulic conductivity (K) characteristics of the RM, as well as the effect of desiccation, were evaluated. RM has index properties satisfying the requirements to achieve low K. The compaction–permeability studies showed that RM may be compacted to a dense homogeneous mass using a moderate compactive effort, while lowest K (⩽1 × 10−7 cm/s) was achieved for RM compacted slightly (0.4–4%) wet of optimum. Shear strength test revealed high values of friction angle and cohesion for compacted RM, and its tight structure was also evidenced by its low compressibility and maximum settlement under load. Desiccation adversely affected the permeability of compacted RM, but to a lesser extent than generally observed for clays. These results suggest that RM could be potentially utilised as a low-permeability barrier to be laid down under engineered landfill sites.

Acute toxicity of arsenic to Aliivibrio fischeri (Microtox® bioassay) as influenced by potential competitive–protective agents

In this study, we investigated the effect of some potential alleviative compounds against the acute toxicity of arsenic (AsV, AsIII and DMAV) on Aliivibrio fischeri (formerly Vibrio fischeri), a bioluminescent model bacterium, through the Microtox® bioassay. The compounds studied differed in their mechanism of action, and they included the following: phosphate and glycerol, as chemical analogues (and potential competitors) of AsV or AsIII, respectively; citrate, a weak natural organic ligand; and the antioxidant ascorbic acid. Special attention was paid to phosphate effects, a widespread pollutant in natural environments. AsV was found to be more acutely toxic than AsIII to A. fischeri, in accordance with its higher interaction with the bacteria. Both AsV and AsIII were found to be much more acutely toxic than DMAV, which was essentially non-acutely toxic even at very high concentrations. Phosphate presence (at equimolar P/As ratios or higher) resulted in the almost total suppression of bioluminescence inhibition, suggesting it exerts an alleviative effect against AsV acute toxicity on A. fischeri. Interestingly, the uptake and the percentage of extracellular AsV were not affected by the addition of phosphate, suggesting that such protective effect does not result from the competition for their common transporters. In contrast, the acute toxicity of AsIII was essentially unaffected by phosphate. Glycerol did not decrease the acute toxicity or the uptake of AsIII by A. fischeri, denoting the likely occurrence of an additional mechanism for AsIII uptake in such bacteria. Similarly, citrate and ascorbic acid essentially did not caused alleviation of AsV or AsIII acute toxicity. As for environmental and operational implications, P could beneficially protect aquatic microorganisms against acute detrimental effects of AsV, whilst its presence could mask the toxicity due to AsV when assessed using the Microtox® bioassay, thus leading to seriously underestimate the actual ecological and health risks.

Arsenate Retention by Epipsammic Biofilms Developed on Streambed Sediments: Influence of Phosphate

Natural geological conditions together with the impact of human activities could produce environmental problems due to high As concentrations. The aim of this study was to assess the role of epipsammic biofilm-sediment systems onto As (V) sorption and to evaluate the effect of the presence of equimolar P concentrations on As retention. A natural biofilm was grown on sediment samples in the laboratory, using river water as nutrient supplier. Sorption experiments with initial As concentrations 0, 5, 25, 50, 100, 250, and 500 μg L−1 were performed. The average percentage of As sorbed was 78.9 ± 3.5 and 96.9 ± 6.6% for the sediment and biofilm-sediment systems, respectively. Phosphate decreased by 25% the As sorption capactity in the sediment devoid of biofilm, whereas no significant effect was observed in the systems with biofilm. Freundlich, Sips, and Toth models were the best to describe experimental data. The maximum As sorption capacity of the sediment and biofilm-sediment systems was, respectively, 6.6 and 6.8 μg g−1 and 4.5 and 7.8 μg g−1 in the presence of P. In conclusion, epipsammic biofilms play an important role in the environmental quality of river systems, increasing As retention by the system, especially in environments where both As and P occur simultaneously.

ADSORPTION OF METHYLENE BLUE BY RED MUD, AN OXIDE­ RICH BYPRODUCT OF BAUXITE REFINING

The use of organic basic dyes for the determination of the surface adsorption in different materials is one of the oldest ways of measuring the adsorption capacity or the amount of exchange sites of small-size particles and colloidal material (Makitie and Ervio, 1966). Methylene blue (MB) is an organic cationic dye with formula C16H18N3SCI.3H20. The molecule can be regarded approximately as a rectangular volume of dimensions 17.0 x 7.6 x 3.3 A. The projected area of the molecule has been given by several authors (quoted in Hang and Brindley, 1970; Taylor, 1985). Estimated values ranged between 130-135 A2.

Utilization of waste products as alternative landfill liner and cover materials – A critical review

ABSTRACT Landfill sealing technologies comprise low hydraulic conductivity engineered layers as part of covers and bottom liners, for which clays and geosynthetic materials are conventionally used. In last decades, an increasing number of diverse wastes have been suggested as alternative landfill barrier materials. A comprehensive critical review on the different wastes proposed in the literature as components of landfills barriers is presented. The geotechnical and hydraulic properties, the advantages and disadvantages of the studied wastes are discussed, while their environmental impact issues are emphasized. Overall, several wastes were identified as technically suitable to be used in landfill barriers, nonetheless it is worth to mention that some of them also show concerning leaching of hazardous contaminants that could restrict their practical application in real landfills.