GCRIS

3 Biological methods for removing heavy metals are in competition with chemical and physical techniques such as precipitation, ion exchange, electrochemical treatment and evaporative recovery, especially, when the concentration of the heavy metal ion is low, between 1.0 and 100 mg/L. In order to qualify for industrial applications, biosorbents have to be produced at low cost. The use of biomass from various production stages; e.g. from the pharmaceutical or the food industries, is one way to minimize the costs. This study is concerned with the binding of nickel ions onto waste biomass of Saccharomyces cerevisiae genus, obtained from the food industry. Since the biomass employed is a waste material, biosorption process described in this study may represent a cheap alternative to conventional methods.Biomass cell walls, consisting mainly of polysaccharides, proteins and lipids, offer many functional groups which can bind metal ions such as carboxylate, hydroxyl, phosphate and amino groups.The objective of this study was to investigate the adsorption of nickel on wastebaker.s yeast as a function of several factors, i.e. pretreatment, pH, temperature, biomass concentrations and initial metal concentrations, in order to determine the optimum adsorption conditions of a batch process.Pretreatment of waste yeast biomass using sodium hydroxide, formaldehyde, nitric acid and ethanol decreased the sorption of nickel (II) ions compared with live biomass. Optimum initial pH for nickel (II) ions was 5.0 at the optimum temperature of 25o C. The uptake values increased with the increasing initial nickel (II) ion concentrations up to 150 mg/L. The optimum biomass concentration for this process was determined as 1.0 g/L.The biosorption isotherms were developed at various initial pH and temperature values. The equilibrium values were expressed with the Langmuir model while nickel sorption did not fit the Freundlich plot. The Langmuir parameters qmax (14.30 mg/L) and b (0.0069 L/mg) have been calculated."qmax" increased from 7.8 to 14.30 mg/L with the increase in pH from 3.0 to 5.0. Similar trend was observed for the "b" values; an increase from 0.0025 to 0.0069 L/mg were obtained when the pH of the solution was raised from 3.0 to 5.0. Both Langmuir model parameters were found to be the highest values at pH 5.0 which is consistent with the results of the optimization studies as described above.Temperature also affected the phase equilibria of nickel (II)/S.cerevisiae system.The highest capacity for biosorption system was obtained at 25o C with the qmax and b values of 14.3 mg/L and 0.0069 L/mg at pH 5.0, respectively. The enthalpy change for the biosorption process have been evaluated by using the Langmuir constant "b", which is related to the energy of adsorption. Nickel (II) biosorption is considered to be an exothermic process since low binding occurs when the temperature increases from 25 to 45o C.The uptake of nickel (II) ions by the yeast biomass was also investigated with respect to time under optimum operating conditions. Biosorption kinetics were rapid within the first few minutes. After the initial rapid uptake, further biosorption by yeast cells continued slowly and reached an equilibrium after 2 hours at all pH values of 3.0, 4.0 and 5.0. On the other hand, the rate of adsorption was found to be the fastest at pH 5.0 with an initial rate of around 3.59 mg Ni (II) / g-min.

Boron is a versatile element distributed in every part of the environment but most of its deposit reserves are localized in a few countries, Turkey being one of the most prominent. Boron is known to be an essential micronutrient for plants and some animals. Like any other essential element it has toxicity in high concentrations. Herein the mechanism of toxicity and the elements of the boron stress response were investigated in Saccharomyces cerevisiae with a proteomics approach. Boron is believed to have played a role in the evolution of life on earth. It has strongly electrophile organic compounds, the most important physiological form being boric acid. Boric acid has a capacity to bind cis-located hydroxl groups and some amino groups. Some of these groups are located at the active sites of some enzymes and at the carbohydrates with five-membered furanose rings. The riboses of some metabolically important molecules like S-adenosyl methionine, diadenosine phosphate family members and 3'end of RNAs are prone to be affected. The yeast cells subjected to boron in this study expressed higher amounts of carbohydrate metabolic enzymes, proteins involved in protein synthesis, protein folding and catabolism, redox homeostasis and nucleotide synthesis. All of these proteins are common to metal stress responses in yeasts. Some of them involve in other stress responses like peroxide, salt or herbicide stresses showing complex interplay between responses.

Master Degree / Yüksek Lisans Tezleri

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