Aysun Ergene

Adsorption of Remazol Brilliant Blue R using ZnO fine powder: Equilibrium, kinetic and thermodynamic modeling studies

Zinc oxide powders with six-sided flake-like particles were prepared by homogeneous precipitation from boiling aqueous solutions that contained excess urea and 0.075 (Z075) and 0.300 (Z300)M Zn(2+). The average sizes of the particles are 37 and 46 microm, while the average sizes of the crystals are approximately 45 for Z075 and Z300 at 1000 degrees C. Equilibrium, kinetic and thermodynamic studies were carried out for the adsorption of RBBR dye from aqueous solution using both types of ZnO in the form of fine powders. The effects of pH, initial dye concentration, contact time and temperature of solution on the adsorption were studied. Langmuir, Temkin and Dubinin-Radushkevich (D-R) isotherm models were used to describe the adsorption of RBBR onto ZnO powders. The Langmuir and D-R isotherm models fit the equilibrium data better than the Temkin isotherm model. The monomolecular adsorption capacity of Z075 and Z300 was determined to be 190 and 345 mg g(-1) for RBBR, respectively. The Lagergren first-order, Ritchie second-order kinetic and intra-particle diffusion models were used for the adsorption of the dye onto ZnO powders. The Ritchie second-order model was suitable for describing the adsorption kinetics for the removal of RBBR from aqueous solution onto Z075 and Z300. Thermodynamic parameters, such as the Gibbs free energy (DeltaG(#)), enthalpy (DeltaH(#)), entropy (DeltaS(#)) and equilibrium constant of activation (K(#)) were calculated. These parameters showed that the adsorption process of RBBR onto Z075 and Z300 was an endothermic process of a chemical nature under the studied conditions.

Reversible immobilization of lipase on phenylalanine containing hydrogel membranes

Poly(2-hydroxyethylmethacrylate-co-methacrylamidophenlyalanine) poly(HEMA-MAPA) membranes were prepared by UV-initiated photopolymerization of HEMA and MAPA. Lipase immobilization onto these membranes from aqueous solutions containing different amounts of lipase at different pH was investigated in a batch system. The lipase adsorption capacity of the membranes was increased as the MAPA ratio increased in the membrane structure. The maximum lipase immobilization capacity of the poly(HEMA-MAPA-3) membrane was 135 μg cm−2. The optimum temperature was 5°C higher than that of the free enzyme and was significantly broader. The storage stability increased with immobilization. The enzyme could be repeatedly adsorbed and desorbed without any significant loss in adsorption capacity.

Production and characterization of biosurfactants produced by microorganisms isolated from milk factory wastewaters

Biosurfactants or surface‐active compounds are produced by microorganisms. These molecules reduce the surface tension of both aqueous solutions and hydrocarbon mixtures. In this study, the isolation and identification of biosurfactant‐producing microorganisms were assessed. The characterization of biosurfactant produced by microorganisms isolated from milk factory wastewaters was investigated. For this purpose, five different microorganisms were isolated and identified. In order to determine the biosurfactant production, the ‘drop‐collapse’ method was applied and it was determined that only three species, Yarrowia lipolytica MFW5 (yeast), Micrococcus luteus MFW1 (cocci) and Burkholderia cepacia MFW2 (bacillus), were able to produce biosurfactant. Biosurfactants produced by Yarrowia lipolytica, Micrococcus luteus and Burkholderia cepacia were coded as BS‐I, BS‐II and BS‐III, respectively. After the initial biosurfactant production and characterization studies were completed, isolates of these three species were incubated with whey wastewaters at 35°C for 10 days for biosurfactant production. At the end of the incubation period, the biosurfactants were extracted and further characterized with biochemical analysis, FTIR spectra, haemolysis test, emulsification test and determination of the surface tension.

Biochemical and Molecular Characterization of Strontium-resistant Environmental Isolates of Pseudomonas fluorescens and Sphingomonas paucimobilis

Strontium resistance was investigated in strains isolated from the river Kızılırmak which has been affected by industrial and agricultural heavy metal pollution from the surrounding facilities and domestic effluents from the city Kırıkkale, Turkey. Strontium-resistant isolates with a minimal inhibitory concentration of 2000 mg L−1 were isolated and identified as Pseudomonas fluorescens and Sphingomonas paucimobilis. Both isolates were shown to be resistant to other heavy metals like aluminum, lithium, barium, nickel and resistance to the antibiotics like aztreonam and pefloxacin. Plasmid DNA analysis, transformation and curing results revealed that the strontium resistance ability of both isolates was chromosome-encoded. Outer membrane and total protein isolation results descriptively showed that not only membrane porins but also other proteins were effective in the strontium resistance in Pseudomonas fluorescens and Sphingomonas paucimobilis.

Preliminary characterization of biosurfactants produced by microorganisms isolated from refinery wastewaters

Some bacterial strains isolated from refinery wastewaters were identified as Pseudomonas aeruginosa RWI, Pseudomonas putida RWII, Pseudomonas fluorescens RWIII and Burkholderia cepacia RWIV, and the biosurfactants produced by these strains were coded as BS‐I, BS‐II, BS‐III and BS‐IV, respectively. The bacterial strains were characterized by the following biochemical methods: Gram stain, oxidase activity, indol, lactose and growth at 42 °C. Biosurfactant production was evaluated by: emulsification activity, surface tension measurement and critical micelle concentration. Chemical characterization of the biosurfactants was done by: FTIR and analysis of carbohydrate, protein and lipid content. The biosurfactants showed good emulsification activity against different hydrocarbon sources. The initial surface tension of culture broth was determined as 67.3 mN/m, and production of BS‐I, BS‐II, BS‐III and BS‐IV lowered this value to 35.9, 49.2, 51.6 and 45.7 mN/m, respectively. The critical micelle concentration of the biosurfactants was found to be in the range 10–50 mg/L. From the results of this study it was observed that the refinery wastewaters are a suitable source for isolation of biosurfactant‐producing bacteria, but are not a substrate for biosurfactant production.

Surface water-borne multidrug and heavy metal-resistant Staphylococcus isolates characterized by 16S rDNA sequencing.

Abstract Four Staphylococcus isolates having both multidrug- and multimetal-resistant ability were isolated from surface water. Further identification of the isolates was obtained through biochemical tests and 16S rDNA gene sequencing. One methicillin-resistant and two methicilin-sensitive isolates were determined as Staphylococcus aureus. The other isolate was identified as Staphylococcus warneri. The antibiotic and heavy metal resistance profiles of the Staphylococcus isolates were determined by using 26 antibiotics and 17 heavy metals. S. aureus isolates displayed resistance to most of the β-lactam antibiotics tested. All Staphylococcus isolates were resistant to heavy metals including silver, lithium, and barium. Due to a possible health risk of these pathogenic bacteria, a need exists for an accurate assessment of their acquired resistance to multiple drugs and metals.