Advanced Materials Research Vols. 71-73

Abstract: Eichhornia spp. biomass collected from Chandola lake, Ahmedabad, Gujarat, India. Point of zero charge of the biomass was pH 7.3. Flask study showed pH 5 and 2 to 3 h contact time as optimum conditions for copper sorption. In 24 h of contact time, as high as 85% of copper was removed from 100 ppm copper containing solution. In first 2 h of the contact time the removal reached to 67.25%. Copper loading capacity of the biomass ranged between 2.85 to 1.0 g per 100 g of biomass. Influence of pH, temperature, nickel and zinc was studied by 24 factorial experiments. Under the experimental conditions pH and interactions between pH-nickel, temperature-pH and temperature-pH-nickel-zinc were found to be significant with 60 to 74.7% copper removal. As high as 95% of sorbed copper was desorbed with 0.1 N HNO3. Langmuir and Freundlich isotherms were also studied. Reactor study showed 90% overall copper removal from 25 L of copper containing waste and sulfatereducing bacteria played a significant role. Treatment of actual waste also showed 61% of copper removal. SEMquant element analysis showed presence of 12.39% w/w of copper in the biomass exposed to the waste, where as only 0.0018% of copper was detected in unexposed biomas

Abstract: The aim of the work was the comparison between a selected reactive mixture containing organic matter for SRB and other electron donors, such as ethanol and polysaccharides. The comparison was performed in order to select the best operating conditions in terms of organic sources for SRB. A continuously operating fixed-bed column was filled with a batch-optimised solid reactive mixture (6% leaves, 9% compost, 3% zero valent iron, 30% silica sand, 30% perlite, 22% limestone) and inoculated by SRB. At steady state 50±10% sulphate abatement was reached and metals were totally removed. Batch tests with ethanol showed the ability of SRB to grow on this substrate efficiently. Experimentation using ethanol was performed using two different column reactors filled with perlite, one inoculated by SRB and the other used as blank. Sulphate abatements of the inoculated column were 70±10% against 10±5% of the blank column. Preliminary batch tests with polysaccharides showed the ability of bacteria to grow on these substrates.

Abstract: Sulfate reducing bacteria (SRB) can be used as an alternative biotechnology to promote passive treatment of industrial effluents. Treatment efficiency however depends on pH and metals content of the effluent and also on the quantity of organic matter available. As COD/sulfate ratio varies, sulfate consumption changes. It is commonly assumed that the ideal COD/sulfate ratio is around 0.67. The aim of this work was to optimize the growth and sulfate reduction capacity of mixed bacterial cultures. Samples were cultured using modified Postgate C medium. Metals (Cu, Mn and Ni) were added to the medium in order to study bacterial resistance. Maximum sulfate reducing (98%) was achieved for lactate containing medium, pH 7.0. However, with ethanol containing medium sulfate removal was of about 50%. Acetate production was observed in all cases. Results shown that lactate was more efficient than ethanol for sulfate biological reduction and pH neutralization.

Abstract: The aim of this study was to find cheap, solid substrate material for sulphate reducing bacteria (SRB) to be used in permeable reactive barrier (PRB) and infiltration beds to treat acidic, nickel-, copper- and iron-rich mine drainage. Laboratory experiments were carried out to examine the reactivity and utilisation of different substrate materials. The materials of interest were peat, sawdust, cucumber compost and cellulose. Limestone, phosphorus and nitrogen were added to the mixture to create optimum growth conditions for SRB. Based on a batch tests, cucumber compost was chosen to be examined in larger-scale column tests. Results from the column tests were promising. Nickel (43 mg L-1), copper (24 mg L-1) and iron (95 mg L-1) were precipitated almost completely and the concentration of sulphate was decreased approximately 20 %. pH values increased from 2.7 to 8. Based on laboratory tests results it appears that cucumber compost was suitable substrate material for SRB in PRBs and infiltration beds treating AMD.

Abstract: The main environmental problems associated with the mining activities are related to the production of large amounts of wastes; Different pathways are responsible for heavy metals dispersion, by air due to wind action, by water mediated by acid mine drainage and erosion, and the metals could be mobilized in the soil by different transport mechanisms. Different remediation alternatives have been studied and reported in literature. In situ stabilization is a cheaper method. The heavy metals stabilization enables the decrease of metal mobility, reactivity and toxicity in the soil, decreasing heavy metals availability and phytoavailability. Sulphate reducing bacteria (SRB) have been successfully utilized in groundwater bioprecipitation of heavy metals. In this study, this biological agent has been used in the immobilization of heavy metal in the subsurface of the soil due to its dissimilative metabolism. SRB produces hydrogen sulfide that reacts with soluble metals present in the media, generating as final product low soluble metal compounds (metal sulfides). The bio-stabilization was studied at pilot scale to determine the stabilization efficiency using biological agent, SRB. The metals studied were Fe, Cu, Pb and Zn in the contaminated smelter soil. Bioaugmentation and biomagnification were applied. After 4 months, the metal stabilization efficiency was determined by leaching with acid solution at different pH to stimulate the metal mobility. The remediation pilot scale system showed that copper, lead and iron were much more stable at pH 3.0, with only 3.7% and 1% of total metal eluted, and compared with the system without biological agent. In the case of zinc, the elution was similar with or without remediation. The metal stabilization using biological agent was successful in the contaminated smelter soil and these results are promising antecedents for full scale in situ remediation strategy.

Abstract: A process for the precipitation of trivalent arsenic sulphide in sulphate-reducing condition at low pH would be very attractive due to the high arsenic content (60%) in the final precipitate. A bacterial consortium able to reduce sulphate at pH 4.5 served to inoculate column bioreactors that were continuously fed with As(V) or As(III), glycerol and/or hydrogen, at pH values between 2 and 5. The diversity, functionality and evolution of the consortium colonizing the bioreactors were characterized by means of biomolecular tools, in relation with operating parameters (pH, As, sulphide, acetate). The highest As removal rate obtained during these experiments was close to 3 mg.l-1.h-1 using As(V) as the initial arsenic form, while precipitation rates were improved using As(III). When glycerol was replaced by hydrogen in a bioreactor containing a mature biofilm, sulphate-reducing activity increased roughly. Organisms related to Desulfosporosinus were the only sulphate-reducing bacterium (SRB) detected in the bioreactor. arrA genes, involved in As(V) dissimilatory reduction, were also detected and suggested that As(V) was reduced by a Desulfosporosinus-like organism. Molecular fingerprints evidenced an evolution of the bacterial population structure according to changes in operating conditions.

Abstract: Five species of algae (Lessonia nigrescens Bory, Prionitis decipiens, Grateloupia doryphora, Lessonia trabeculata and Macrocystis integrifolia) collected from Peruvian coast have been tested for mercury recovery from synthetic solutions. Preliminary experiments showed that optimum sorption occurred at pH 6-7 and that Lessonia algae were the most efficient sorbents for Hg(II). The biomass was cross-linked with calcium chloride. Stabilized biosorbent showed sorption capacity as high as 267 mg g-1 at pH 6. The sorption isotherm was described by the Langmuir equation, while the pseudo-second order equation was used for modeling uptake kinetics. Salt addition strongly affected mercury sorption following the sequence: NaNO3 << Na2SO4 <<< NaCl.

Abstract: Fundamental investigation on adsorption of Cu2+ and Ni2+ ions on Sargassum sp. was performed in fixed-bed column. The Langmuir isotherm fitted well the biosorption equilibrium and the maximum Cu2+ and Ni2+ uptake capacities were 1.35 and 1.06 mmolg- 1, respectively. Mappings of copper and nickel in the algae surface using energy dispersive X-ray spectroscopy indicated a homogeneous distribution of Cu- and Niadsorbent sites. Fourier-transform infrared analysis revealed that the main chemical groups involved in the copper and nickel biosorption were carboxyl, ether, alcoholic, amino, and sulphonic groups.

Abstract: The present study is focused on the investigation of hexavalent chromium uptake by the yeast S. cerevisiae UCM Y–1968 and its protoplasts. For the first time the ability of S. cerevisiae protoplasts to accumulate Cr (VI) ions was shown. Under the influence of various concentrations of Cr (VI) ions, the proportion of the surviving yeast cells and protoplasts decreased as treatment time extended. During 0.5 – 1h of treatment, yeast protoplasts demonstrated a significant level of Cr (IV) ion accumulation, 44 – 47 % of the supplied Cr ions, whereas the initial strain S. cerevisiae UCM Y-1968 accumulated 9 – 10 %. The isotherms for S. cerevisiae UCM Y-1968 were related to L2 types and for yeast protoplasts isotherms were related to L3 types. Cr (VI) sorption/uptake parameters (Qmax, b) for living cells were found for S. cerevisiae UCM Y–1968 (Qmax = 890 μmol/g) and its protoplasts (Qmax = 1335 μmol/g) at the initial Cr (VI) ions concentration of 25 mg/l. The results showed that hexavalent chromium uptake by living yeasts biomass mainly depended on intracellular accumulation. Chromium uptake by protoplasts cells was characterized by simultaneous metabolism-dependent bioaccumulation with prevalence of the intracellular accumulation of Cr (VI) ions.

Abstract: This paper deals with arsenic and lead biosorption by different waste biomasses coming from the marine environment. Shoreline seaweeds and seagrasses were used to adsorb metals from aqueous solutions, under different pH. Experimental tests were performed in order to study the equilibrium of biosorption with suspended biomass. The obtained results confirmed the possibility of using marine macrophyte biomass for heavy metal biosorption and evidenced a strong dependence of lead and arsenic uptake on the macrophyte structure. Brown algae were found to be the best sorbents for lead with a maximum observed lead uptake of 140 mg/g; green algae showed a maximum lead uptake in the range 50-70 mg/g; red algae were the worst lead sorbent, in the investigated experimental conditions, with a maximum lead uptake in the range 10-40 mg/g. As concerns arsenic, the macrophytes had in general good sorption abilities when compared with those of activated carbon. Furthermore red algae, that for lead were not effective, resulted to be the best sorbents for arsenic. This was explained by a different speciation in aqueous solution of lead (II), that is cationic with respect to arsenic(V), that is anionic.