Gönül Dönmez

A comparative study on heavy metal biosorption characteristics of some algae

The biosorption of copper(II), nickel(II) and chromium(VI) from aqueous solutions on dried (Chlorella vulgaris, Scenedesmus obliquus and Synechocystis sp.) algae were tested under laboratory conditions as a function of pH, initial metal ion and biomass concentrations. Optimum adsorption pH values of copper(II), nickel(II) and chromium(VI) were determined as 5.0, 4.5 and 2.0. respectively, for all three algae. At the optimal conditions, metal ion uptake increased with initial metal ion concentration up to 250 mg l−1. Experimental results also showed the influence of the alga concentration on the metal uptake for all the species. Both the Freundlich and Langmuir adsorption models were suitable for describing the short-term biosorption of copper(II), nickel(II) and chromium(VI) by all the algal species.

Removal of chromium(VI) from saline wastewaters by Dunaliella species

Some industrial wastewaters contain higher quantities of salts besides chromium(VI) ions so the effect of these salts on the biosorption of chromium(VI) should be investigated. The biosorption of chromium (VI) from saline solutions on two strains of living Dunaliella algae were tested under laboratory conditions as a function of pH, initial metal ion and salt (NaCl) concentrations in a batch system. The biosorption capacity of both Dunaliella strains strongly depends on solution pH and maximum. Chromium(VI) sorption capacities of both sorbents were obtained at pH 2.0 in the absence and in the presence of increasing concentrations of salt. Chromium(VI)-salt biosorption studies were also performed at this pH value. Equilibrium uptakes of chromium(VI) increased with increasing chromium(VI) concentration up to 250–300 mg l−1 and decreased sharply by the presence of increasing concentrations of salt for both the sorbents. Dunaliella 1 and Dunaliella 2 biosorbed 58.3 and 45.5 mg g−1 of chromium(VI), respectively, in 72 h at 100 mg l−1 initial chromium(VI) concentration without salt medium. When salt concentration arised to 20% (w/v), these values dropped to 20.7 and 12.2 mg g−1 of chromium(VI) at the same conditions. Both the Freundlich and Langmuir adsorption models were suitable for describing the biosorption of chromium(VI) individually and in salt containing medium by both algal species. The pseudo second-order kinetic model was successfully applied to single chromium(VI) and chromium(VI)-salt mixtures biosorption data.

A COMPARATIVE STUDY ON THE BIOSORPTION CHARACTERISTICS OF SOME YEASTS FOR REMAZOL BLUE REACTIVE DYE

Biosorption capacities and rates of different kinds of dried yeasts (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces marxianus, Candida sp., C. tropicalis, C. lipolytica, C. utilis, C. quilliermendii and C. membranaefaciens) for Remazol Blue reactive dye from aqueous solutions were compared under laboratory conditions as a function of initial pH and initial dye concentration. Optimum initial biosorption pH was determined as 2 for all the yeasts. All the yeast species showed comparable and very high dye sorption at 100 mg/l initial dye concentration. The equilibrium sorption capacity of the biomass increased with increasing initial dye concentration up to 400 mg/l for Candida sp. C. lipolytica and C. tropicalis; up to 300 mg/l for C. quilliermendii and C. utilis and up to 200 mg/l for S. cerevisiae, S. pombe, K. marxianus and C. membranaefaciens while the adsorption yield of dye showed the opposite trend for all the yeasts. Among the nine yeast species, C. lipolytica exhibited the highest dye uptake capacity (Q(0) = 250 mg/g). Both the Freundlich and Langmuir adsorption models were found suitable for describing the biosorption of the dye by all the Candida yeasts (except C. membranaefaciens). The results indicated that the dye uptake process followed the pseudo-second-order kinetics for each dye-yeast system.

The effect of copper(II) ions on the growth and bioaccumulation properties of some yeasts

Abstract The influence of copper(II) ions on the growth and bioaccumulation properties of adapted and growing cells of Saccharomyces cerevisiae , Kluyveromyces marxianus , Schizosaccharomyces pombe and Candida sp. was studied. The level of copper(II) accumulation and microbial growth were dependent on the pH and initial copper(II) concentration. Optimum pH values for maximum copper(II) accumulation were determined as 4.0, 5.0, 4.0 and 4.0 for S. cerevisiae , K. marxianus , S. pombe and Candida sp. , respectively. The results indicated that Candida sp. and K. marxianus are able to accumulate large amounts of copper(II) from feed medium at higher copper(II) concentrations without loosing their biological activities.

Bioaccumulation of copper(ii) and nickel(ii) by the non-adapted and adapted growing CANDIDA SP.

The effect of copper(II) and nickel(II) ions on the growth and bioaccumulation properties of non-adapted and adapted growing cells of a non-pathogenic Candida sp. has been tested under laboratory conditions as a function of initial pH and initial metal ion concentration. Optimum pH value for maximum metal ion accumulation was determined as 4.0 for both the metal ions. Although the copper(II) adapted Candida sp. was capable of removing of copper(II) with the maximum specific uptake capacity of 36.9 mg g-1 at 783.6 mg dm-3 initial copper(II) concentration, non-adapted Candida was only capable of bioaccumulating copper(II) with 23.1 mg g-1 maximum uptake capacity from aqueous solution at 578.7 mg dm-3 initial copper(II) concentration. The non-adapted and nickel(II) adapted Candida cells also showed the highest nickel(II) uptake capacities (46.8 and 30.8 mg g-1, respectively) at 321.5 and 300.6 mg dm-3 initial nickel(II) concentrations, respectively. For both the non-adapted and nickel(II) adapted Candida sp., the growth of cells was totally inhibited by 500 mg dm-3 of nickel(II) ions. The results also indicated that copper(II) adapted Candida sp. has been found to be more efficient to accumulate larger amounts of copper(II) than that of nickel(II) bioaccumulated by nickel(II) adapted Candida at higher initial metal ion concentrations without loosing its biological activity.

Bioaccumulation of the reactive textile dyes by Candida tropicalis growing in molasses medium

Bioaccumulation of the reactive textile dyes, Remazol Blue, Reactive Black and Reactive Red, by the yeast species Candida tropicalis growing in molasses medium was studied in a batch system as a function of initial pH and initial dye concentration. The optimum pH value for bioaccumulation was determined as 3.0 for all the dyes tested. The maximum specific bioaccumulation capacity of C. tropicalis was 111.9 mg g−1 for Remazol Blue, 101.9 mg g−1 for Reactive Black and 79.3 mg g−1 for Reactive Red at approximately 700 mg l−1 initial dye concentration. Higher bioaccumulation percentages were observed at lower concentrations of all the dyes. In general, the increase in dye concentration inhibited the growth of yeast and caused a long lag period. Remazol Blue dye gave a considerably higher dye bioaccumulation percentage by the yeast among the dyes tested.

Effective bioremoval of reactive dye and heavy metals by Aspergillus versicolor.

In this study, bioaccumulation of heavy metal and dye by Aspergillus versicolor was investigated. Optimum pH values of the maximum heavy metal bioaccumulation was found as 6 for 50mg/L Cr(VI), Ni(II) and 5 for Cu(II) ions with the 99.89%, 30.05% and 29.06% removal yield, respectively. The bioremoval of the dye up to 800 mg/L at pH 5 and 6 was investigated and 27.15% and 28.95% removal rates were measured respectively. The presence of Cr(VI) with dye, decreased the uptake yield for both pollutants. In the medium with Cu(II) and dye, dye removal was not affected by Cu(II), but Cu(II) removal rate increased from 29.06% to 37.91% by the existence of the dye. When Ni(II) and dye were combined, neither pollutant affected the others removal yield. These results indicate that the isolated A. versicolor strain deserves attention as a promising bioaccumulator of heavy metal ions and reactive dyes in wastewater effluents.

Improving the lipid accumulation properties of the yeast cells for biodiesel production using molasses

In this article the high lipid accumulation potential of Candida lipolytica, Candida tropicalis and Rhodotorula mucilaginosa cells were shown in molasses medium. Four different pH values were examined (4-7) to discover the optimum lipid accumulation medium. Varied concentrations of (NH₄)₂SO₄ (0.5, 1.0, 1.5 g/L) and molasses (6%, 8%, 10%) were tested to find the optimum carbon and nitrogen amounts for the highest cellular lipid production. It is shown that the maximum lipid content could be achieved in the medium containing 8% molasses solution and 1.0 g/L (NH₄)₂SO₄ at pH 5 after four days of incubation time. The maximum lipid contents and methyl ester yields were measured as 59.9% and 84.9% for C. lipolytica, 46.8% and 93.2% for C. tropicalis, 69.5% and 92.3% for R. mucilaginosa. Because of the dominant fatty acids were C16 and C18 in the lipids of yeast cells, these crude lipids could be promising feedstock for biodiesel production.

Proteomic changes in response to chromium(VI) toxicity in Pseudomonas aeruginosa.

A proteomic approach was used to identify proteins involved in Cr(VI) stress response of Pseudomonas aeruginosa to toxic Cr(VI). Cytosolic and membrane fractions from bacteria exposed to 300 mg l(-1) Cr(VI) were prepared, 2D gel electrophoresis in combination with MALDI-TOF MS and LC-MS/MS was used to identify proteins whose expression level increased or decreased upon exposure to Cr(VI). Overexpressed proteins include stress proteins, proteins involved in protein biosynthesis, proteins responsible for energy production, proteins involved in free radicals detoxification by the glutathione system, outer membrane proteins, MucD, while downregulated proteins were isocitrate dehydrogenase and 30S ribosomal protein S1. Under Cr(VI) exposure, upregulation of MucD (role in exopolysaccharide production) and outer membrane proteins concluded that bacteria have access to more than one resistance mechanism against toxic metal ions. We propose that the mechanisms of Cr(VI) resistance include production of exopolysaccharide and complexing of metal ions outside the cell.

Single and binary chromium(VI) and Remazol Black B biosorption properties of Phormidium sp.

Wastewaters of textile and leather dying industries may contain significant quantities of chromium(VI) ions besides anionic and water-soluble dyes. Moreover the temperature of these wastewaters may be a controlling parameter affecting the biosorption efficiency. In this study biosorption of chromium(VI) and Remazol Black B reactive dye by dried Phormidium sp., a thermophilic cyanobacterium, was studied as a function of initial chromium(VI) concentration and temperature in no dye and 100 mg l(-1) dye-containing media at an initial pH value of 2.0 at which the biomass exhibited the maximum chromium(VI) and dye uptakes. The decrease of both metal and dye uptakes with temperature indicated that the uptakes were exothermic in nature. Equilibrium uptake of chromium(VI) enhanced considerably with both chromium(VI) and 100 mg l(-1) dye concentrations. Moreover the presence of chromium(VI) also increased the uptake of dye. At 25 degrees C, 22.8 mg g(-1) chromium(VI) and 91.3 mg g(-1) dye were sorbed by the biomass in binary 100 mg l(-1) chromium(VI) and 100 mg l(-1) dye-containing medium. The Langmuir was the best suitable adsorption model for describing the biosorption of chromium(VI) individually and in dye-containing medium. The pseudo-second-order kinetic model described both the chromium(VI) and dye biosorptions kinetics accurately.