Serdar S. Çelebi

Performance of immobilized glucoamylase in a magnetically stabilized fluidized bed reactor (MSFBR)

Abstract Glucoamylase (EC 3.2.1.3. from Aspergillus niger) was immobilized onto the magnetic polystyrene particles including active groups. These particles were used in a magnetically stabilized fluidized bed reactor, and performance of this reactor was investigated. Magnetically stabilized fluidized bed reactor was made of a jacketed glass column and a coaxial selenoid covering the whole column as the magnetic field source. An axial and homogeneous magnetic field was introduced to the column by using direct current. The effects of flow rate and magnetic field intensity on the particle behaviour in the column were investigated. The optimum operational conditions for magnetically stabilized fluidized bed reactor were determined and the activity performance of the immobilized glucoamylase in the reactor was researched. Higher activities were obtained at low magnetic field intensities because of no additional diffusion problems coming from particle agglomeration occured in the column when the magnetic field intensity was high. It was found that the fluid flow rate in the column must be as low as possible because higher flow rates require higher magnetic field intensities to keep the particles in the column.

Effects of magnetic field on activity of activated sludge in wastewater treatment

Abstract In this study, the effects of magnetic field on activity of activated sludge in wastewater treatment were investigated in a batch reactor system containing synthetic wastewater. The medium pH and the direct current (DC) magnetic field strength were changed in the ranges of 6.0 to 8.5 and 8.9 to 46.6 mT, respectively. Experiments were also conducted operating at pulsed DC and alternating current. The changes in the substrate (i.e. glucose) and microorganism concentrations were followed. The highest substrate removal and microorganisms growth rates were observed at pH 7.5. The difference between the substrate removal rates of experiments performed with magnetic field and without it was the maximum at this pH, which was about 44%. The substrate removal rate was first increased by increasing the magnetic field strength, and reached the maximum at 17.8 mT, and decreased with further increase. Application of pulsed DC magnetic field did not change significantly the activity of system, hereas using alternating current magnetic field instead of DC form even caused slight decrease in the activity.

Characterization of glucoamylase immobilized on magnetic poly(styrene) particles

Abstract Glucoamylase (EC 3.2.1.3. from Aspergillus niger) which is widely used in industry was immobilized directly in one step onto low-cost magnetic poly(styrene) particles including active groups. Glucoamylase in both free and immobilized forms was used to hydrolyze maltose. For both forms, the temperature of 50°C and pH 4.5 were found as the optimum conditions in the aspects of activity and stability. Kinetic parameters were determined for the hydrolysis of maltose by free and immobilized glucoamylase at the same conditions in the batch reactor. The maximum activity obtained with immobilized glucoamylase is approximately 70% of the free one. The activity half lives for native and bound states of enzyme were found as 33.8 h and 190 h, respectively.

Amperometric enzyme electrode for aerobic glucose monitoring prepared by glucose oxidase immobilized in poly(vinylferrocenium)

Abstract A simple, sensitive, stable and low-cost glucose sensor with a fast response that operates under aerobic solution conditions is described. The electrode consists of a polyvinylferrocenium-perchlorate-coated Pt surface onto which the enzyme is attached. The current response of the electrode was determined by measuring either cyclic voltammetric peak current values or steady state current values obtained after a constant-potential step. The effects of glucose concentration, the amount of enzyme immobilized, the thickness of the polymeric layer and the operating temperature on the response of the enzyme electrode were studied. The effects of two common physiological sources of interference were also investigated. A mechanism for the operation of the electrode is also proposed.

Amperometric enzyme electrode for sucrose determination prepared from glucose oxidase and invertase co-immobilized in poly(vinylferrocenium)

Abstract Co-immobilization of two enzymes, glucose oxidase and invertase, in polyvinyl(ferrocenium) perchlorate (PVF + ClO − 4 ) film led to the development of a simple, sensitive, stable and low-cost sucrose sensor. Invertase catalyses the conversion of sucrose to α-glucose and β-fructose. Phosphate ions used in the medium catalyse the conversion of α-glucose to β-glucose, eliminating the need for the commonly used third enzyme, mutarotase, for mutarotation. Glucose oxidase catalyses the oxidation of β-glucose to gluconic acid, producing H 2 O 2 . Current due to H 2 O 2 oxidation catalysed by PVF + centres was measured, in contrast to most existing sucrose electrodes, which rely on measurement of the O 2 reduction current.

Immobilization of glucoamylase on Magnetic poly(styrene) particles

Magnetic poly(styrene) particles including active groups were prepared for enzyme immobilization without any activation process. Glucoamylase, which is widely used in industry, was immobilized onto these particles. The effects of pH, buffer concentration, and temperature on immobilization were investigated; moreover, the effect of immobilization temperature on immobilized glucoamylase activity was determined for the hydrolysis of maltose. The acetate buffer with the concentration of 6 × 10 -4 M at pH 4 and 20-30°C was found as the most suitable medium for the immobilization of the glucoamylase. The amount of bound protein is 8 mg/g particle with the immobilization yield of 70%. The maximum activity obtained with immobilized glucoamylase is approximately 70% of the free one.

Amperometric enzyme electrode for organic peroxides determination prepared from horseradish peroxidase immobilized in poly(vinylferrocenium) film

Organic peroxides, t-butyl hydroperoxide, 2-butanone peroxide, cumene hydroperoxide and t-butyl peracetate, were determined by an amperometric enzyme electrode. The enzyme electrode was prepared through electrostatic immobilization of horseradish peroxidase (HRP) in a polyvinylferrocenium (PVF) film. A PVF(+)ClO(4)(-) film was coated on a Pt foil at +0.70 V by electrooxidation of polyvinylferrocene in methylene chloride with 0.1 M tetrabutylammonium perchlorate (TBAP). The enzyme modified electrode PVF(+)HRP(-) was prepared by anion-exchange in a solution of HRP(-) in 0.05 M phosphate buffer at pH 8.5. FTIR spectroscopy was used to identify PVF, PVF(+)ClO(4)(-), and PVF(+)HRP(-). The immobilized amount of the enzyme in the film was determined by UV spectroscopy. The effects of the polymeric film thickness, bulk enzyme concentration used in the immobilization treatment and the temperature on the performance of enzyme electrode were investigated. The inhibitory effect of oxygen was also examined. Linearities, lower detection limits, active life times and sensitivities of the electrode were determined for each peroxide.

Effects of phase vector and history extension on prediction power of adaptive-network based fuzzy inference system (ANFIS) model for a real scale anaerobic wastewater treatment plant operating under unsteady state.

A conceptual neural fuzzy model based on adaptive-network based fuzzy inference system, ANFIS, was proposed using available input on-line and off-line operational variables for a sugar factory anaerobic wastewater treatment plant operating under unsteady state to estimate the effluent chemical oxygen demand, COD. The predictive power of the developed model was improved as a new approach by adding the phase vector and the recent values of COD up to 5-10 days, longer than overall retention time of wastewater in the system. History of last 10 days for COD effluent with two-valued phase vector in the input variable matrix including all parameters had more predictive power. History of 7 days with two-valued phase vector in the matrix comprised of only on-line variables yielded fairly well estimations. The developed ANFIS model with phase vector and history extension has been able to adequately represent the behavior of the treatment system.

Preparation of photooxidized magnetic polystyrene beads for enzyme immobilization

Abstract Magnetic polystyrene beads were synthesized by a modified suspension polymerization technique. The beads consisted of iron powder entrapped in the polymer backbone. The photooxidation of the magnetic polystyrene beads was achieved under UV irradiation in order to obtain functionalized solid support matrices to be used for the immobilization of urease (EC 3.5.1.5). Enzyme immobilization experiments revealed that unirradiated beads were not suitable for direct coupling reactions. Under similar immobilization conditions, direct covalent linkage of enzyme occurred on photooxidized magnetic polystyrene beads. It is found that this immobilized enzyme is efficient in catalyzing decomposition of urea and the photooxidized magnetic polystyrene beads might bring several interesting applications to downstream separations processes.

Biofilm formation on magnetic polystyrene particles

In this study, magnetic polystyrene particles were prepared by using a solvent evaporation technique. Particles 500–595 μm in size were used as a biofilm carrier in a fluidized bed for the biodegradation of an organic carbon source in wastewater. Activated sludge seeds were used as a mixed culture of microorganisms to obtain biofilms on the magnetic polystyrene particles. Fluidized bed experiments were performed at constant dissolved oxygen concentration, pH and temperature. The magnetic particles allowed operation of the column in a magnetic field at high liquid flow rates; hence, external diffusion limitations on biofilm surfaces were lowered. Biofilm formation on the suspended particles was quite successful and allowed effective removal of the substrate.