M. Viera

Zinc and cadmium biosorption by untreated and calcium-treated Macrocystis pyrifera in a batch system.

Zinc and cadmium can be efficiently removed from solutions using the brown algae, Macrocystis pyrifera. Treatment with CaCl(2) allowed stabilization of the biosorbent. The maximum biosorption capacities in mono-component systems were 0.91 mmol g(-1) and 0.89 mmol g(-1) and the Langmuir affinity coefficients were 1.76 L mmol(-1) and 1.25 L mmol(-1) for Zn(II) and Cd(II), respectively. In two-component systems, Zn(II) and Cd(II) adsorption capacities were reduced by 50% and 40%, respectively and the biosorbent showed a preference for Cd(II) over Zn(II). HNO(3) (0.1M) and EDTA (0.1M) achieved 90-100% desorption of both ions from the loaded biomass. While HNO(3) preserved the biomass structure, EDTA destroyed it completely. Fourier transform infrared spectra identified the contribution of carboxylic, amine and sulfonate groups on Zn(II) and Cd(II) biosorption. These results showed that biosorption using M. pyrifera-treated biomass could be an affordable and simple process for cadmium and zinc removal from wastewaters.

Biosorption of mercury by Macrocystis pyrifera and Undaria pinnatifida: influence of zinc, cadmium and nickel.

This study investigated the adsorption of Hg(II) on Macrocystis pyrifera and Undaria pinnatifida in monometallic system in the presence of Zn(II), Cd(II) and Ni(II). The two biosorbents reached the same maximum sorption capacity (q(m) = 0.8 mmol/g) for mercury. U. pinnatifida showed a greater affinity (given by the coefficient b of the Langmuir equation) for mercury compared to M. pyrifera (4.4 versus 2.7 L/mmol). Mercury uptake was significantly reduced (by more than 50%) in the presence of competitor heavy metals such as Zn(II), Cd(II) and Ni(II). Samples analysis using an environmental scanning electron microscopy equipped with an energy dispersive X-ray microanalysis showed that mercury was heterogeneously adsorbed on the surface of both biomaterials, while the other heavy metals were homogeneous distributed. The analysis of biosorbents by Fourier transform infrared spectrometry indicated that Hg(II) binding occurred on S = O (sulfonate) and N-H (amine) functional groups.

Biosorption of chromium(III) by two brown algae Macrocystis pyrifera and Undaria pinnatifida: Equilibrium and kinetic study

Two brown algae, Macrocystis pyrifera and Undaria pinnatifida, were employed to remove Cr(III) from aqueous solutions. Both seaweeds were characterized in terms of alginate yields. The alginate contents were 20 and 30% of the dry weight for M. pyrifera and U. pinnatifida, respectively. Kinetics experiments were carried out at different initial pH values. Cr(III) biosorption was affected by the solution pH. The highest metal uptake was found at pH 4 for both biosorbents. Different models were applied to elucidate the rate‐controlling mechanism: pseudo‐first‐order, pseudo‐second‐order, external mass transfer and intra‐particle diffusion. The application of Langmuir, Freundlich and Dubinin–Radushkevich models to the equilibrium data showed a better fitting to the first model. The maximum Cr(III) sorption capacity (qm) and the affinity coefficient (b) were very similar for both biosorbents: 0.77 mmol/g and 1.20 L/mmol for M. pyrifera and 0.74 mmol/g and 1.06 L/mmol for U. pinnatifida. The free energy of the sorption process was estimated using the Dubinin–Radushkevich isotherm. The values indicate that the processes are chemical sorptions. To evaluate the significance of the ion‐exchange mechanism, the light metals (Ca2+, Na+, Mg2+ and K+) and pH were measured during the experiments.

Biochemical characterization of Macrocystis pyrifera and Undaria pinnatifida (Phaeophyceae) in relation to their potentiality as biosorbents

Abstract: Undaria pinnatifida and Macrocystis pyrifera from Patagonia were characterized in terms of the alginate, protein, total carbohydrate and organic matter content, cation exchange capacity and acid-base properties to assess the suitability of both species as potential biosorbents of metals. Environmental scanning electron microscopy equipped with an energy dispersive X-ray microanalysis system, Fourier transform infrared spectroscopy (FT-IR) and Brunauer, Emmett and Teller surface area analysis were also applied for characterization. The results showed that U. pinnatifida had a higher percentage of organic matter, alginate and protein and a larger specific surface area than M. pyrifera, although the latter exhibited a higher ionic exchange capacity. The groups with a weak acid behaviour represented 84% and 97% of the total acid groups in M. pyrifera and U. pinnatifida, respectively. FT-IR analysis confirmed the presence of different chemical groups such as sulphonate in both biomaterial M. pyrifera and U. pinnatifida. Besides, Zn(II) adsorption capacity was different among different parts of the thallus of each species. The difference founded in the physicochemical properties of both algae could affect their biosorption capacities.

[11] Development of Thiobacillus biofilms for metal recovery

Publisher Summary This chapter describes the preparation of two types of biofilms: (1) Thiobacillus ferrooxidans, immobilized by the two more widely used techniques—attachment and entrapment—for the production of sulfuric acid and (2) attached Thiobacillus ferrooxidans cells for the ferrous iron oxidation. In both cases, whole and viable cells are used. These bacteria are all gram-negative, mesophilic, autotrophic, and obligately acidophilic. T.ferrooxidans is able to use ferrous iron or reduced sulfur compounds as electron donors, whereas T. thiooxidans is only capable of using reduced sulfur compounds. Ferric iron and sulfuric acid are the final products of these oxidation processes. The ability of acidophilic bacteria to assist in the recovery of metals by the dissolution of sulfide minerals is well known, but the mechanism is not fully understood. The chapter also relates the application of these biofilms to recover metals from the leaching of a sulfide ore.

Recovery of Nickel and Zinc Using Biogenerated Sulphuric Acid

Sludge generated in automotive and related industries often contains heavy metals. Bioleaching is an attractive alternative for the treatment of metal containing solids. Bacteria of the genus Acidithiobacillus are the most important microorganisms applied to metal solubilisation. These microorganisms are able to produce sulphuric acid from the aerobic oxidation of elemental sulphur. The biogenerated sulphuric acid can be applied to the solubilisation of metals from a solid matrix. In this paper we present the results of our experiments aimed at the removal of nickel and zinc from sludge generated in the water treatment plant of an automotive industry. Acidithiobacillus thiooxidans cells were immobilised on sulphur pearls in a column reactor. The effects of sulphur pulp density and the dilution rate on the production of sulphuric acid were studied. In a second stage, sulphuric acid was used to solubilise the nickel and zinc from the sludge. The effects of different sludge pulp densities and initial acid pH were studied. High recoveries of zinc and nickel were obtained when the pH value of the sulphuric acid solution was lower than 2.0 for 1 and 2 % of pulp density.

Efficiency of surfactant-enhanced bioremediation of aged polycyclic aromatic hydrocarbon-contaminated soil: Link with bioavailability and the dynamics of the bacterial community

Shifts in the bacterial-community dynamics, bioavailability, and biodegradation of polycyclic aromatic hydrocarbons (PAHs) of chronically contaminated soil were analyzed in Triton X-100-treated microcosms at the critical micelle concentration (T-CMC) and at two sub-CMC doses. Only the sub-CMC-dose microcosms reached sorbed-PAH concentrations significantly lower than the control: 166±32 and 135±4mgkg-1 dry soil versus 266±51mgkg-1; consequently an increase in high- and low-molecular-weight PAHs biodegradation was observed. After 63days of incubation pyrosequencing data evidenced differences in diversity and composition between the surfactant-modified microcosms and the control, with those with sub-CMC doses containing a predominance of the orders Sphingomonadales, Acidobacteriales, and Gemmatimonadales (groups of known PAHs-degrading capability). The T-CMC microcosm exhibited a lower richness and diversity index with a marked predominance of the order Xanthomonadales, mainly represented by the Stenotrophomonas genus, a PAHs- and Triton X-100-degrading bacterium. In the T-CMC microcosm, whereas the initial surface tension was 35mNm-1, after 63days of incubation an increase up to 40mNm-1 was registered. The previous observation and the gas-chromatography data indicated that the surfactant may have been degraded at the CMC by a highly selective bacterial community with a consequent negative impact on PAHs biodegradation. This work obtained strong evidence for the involvement of physicochemical and biologic influences determining the different behaviors of the studied microcosms. The results reported here contribute significantly to an optimization of, surfactant-enhanced bioremediation strategies for chronically contaminated soil since the application of doses below the CMC would reduce the overall costs.

Application of Integrated Microbial Processes for Heavy Metal Recovery from Industrial Wastes of Buenos Aires, Argentina

To allow the final disposal of galvanic sludge from a wastewater treatment plant of automotive factory, integrated microbial processes were performed to release and recover nickel and zinc contained in the solid residue. The metals were successfully leached using sulfuric acid continuously produced by Acidithiobacillus thiooxidans biofilm on elemental sulfur. The best condition using a sludge pulp density of 1 % w/v and a dilution rate of 0.22 h−1 100 % allowed more than 90 % of nickel and zinc dissolution, respectively; higher values of dilution rate and/or pulp density decreased the percentages of metal dissolution. The recovery of metals from the leachates was performed by continuous adsorption on Undaria pinnatifida biomass after raising the pH up to 4. Adsorption processes allowed great recoveries of nickel and zinc from monometallic solutions at the lowest flow rate (100 and 90 %); the recoveries from the leachates were not so good and to increase them three fixed bed columns in series were used reaching approximately 50 and 80 % of nickel and zinc recovery respectively, even at high dilution rates (more than 1.5 h−1). This integrated process could be applied on a higher scale.

Isolation of Mesophilic Sulphate-Reducing Bacteria from a Microbial Community: Comparative Study of the Effect of pH and Dissolved Heavy Metals on the Reduction of Sulphate

Metallurgical processes and mining are the main source of heavy metal contamination of water sources, rivers and lakes. There are a large number of physicochemical processes that can be applied for the immobilization of heavy metals from a liquid matrix. However, many of them are not particularly desirable because their low selectivity and inefficiency when high volumes of low metal concentration liquids must be treated. In such conditions, alternative biological processes have shown to be more useful than traditional physicochemical processes. One of those processes, bioprecipitation of metal sulphides is relevant due to the possibility of forming stable solids (very low solubility) with small volumes compared with other solids. This process is mediated by a broad group of organisms called sulphate reducers that are able to catalyze, under anaerobic conditions, the reduction of sulphate with organic compounds as electron donors. In this paper, we study the effect of the presence of various heavy metals and the pH on the ability to reduce sulphate by sulphate-reducing bacteria. We compare the reduction of sulphate by a microbial community obtained from the effluent of a tannery with a strain isolated from that community. Our results showed that sulphate reduction was significantly affected by pH changes whereas the presence of heavy metals did not show a significant effect. In addition, metal precipitation by the isolated strain was similar than that produced by the community.

Cadmium and Zinc Biosorption by Macrocystis Pyrifera: Changes in the Biomass

Macrocystis pyrifera was used for the recovery of Zn2+ and Cd2+ from slightly acidic solutions (i.e., pH 4). Sorption isotherms were obtained from mono- and bi-component solutions. For the study of metal desorption, EDTA, HNO3 and Ca(NO3)2 were used as eluents. Metal release (Ca2+, Mg2+, K+ and Na+) was monitored in order to evaluate ion exchange mechanisms. After metal sorption/desorption steps the sorbent was characterized using SEM-EDAX analysis. SEM-EDAX analysis also allowed identifying the presence of elements such as Si, Al, Co, Ag, S, P, and Fe in the cell wall. Zinc desorption was almost complete when using 0.1 M nitric acid solution and the sorbent was not significantly damaged by the acidic treatment. Cadmium was completely removed from loaded sorbent when using EDTA, but at the expense of a partial degradation of the biomass as evidenced by the decrease in the intensity of the C and O peaks (SEM-EDAX).