Bulent Keskinler

Biodiesel production from sunflower, soybean, and waste cooking oils by transesterification using lipase immobilized onto a novel microporous polymer.

This study aims at carrying out lipase-catalyzed synthesis of fatty acid methyl esters (biodiesel) from various vegetable oils using lipase immobilized onto a novel microporous polymeric matrix (MPPM) as a low-cost biocatalyst. The research is focused on three aspects of the process: (a) MPPM synthesis (monolithic, bead, and powder forms), (b) microporous polymeric biocatalyst (MPPB) preparation by immobilization of lipase onto MPPM, and (c) biodiesel production by MPPB. Experimental planning of each step of the study was separately carried out in accordance with design of experiment (DoE) based on Taguchi methodology. Microporous polymeric matrix (MPPM) containing aldehyde functional group was synthesized by polyHIPE technique using styrene, divinylbenzene, and polyglutaraldehyde. Thermomyces lanuginosus lipase was covalently attached onto MPPM with 80%, 85%, and 89% immobilization efficiencies using bead, powder, and monolithic forms, respectively. Immobilized enzymes were successfully used for the production of biodiesel using sunflower, soybean, and waste cooking oils. It was shown that immobilized enzymes retain their activities during 10 repeated batch reactions at 25 degrees C, each lasting 24h. Since the developed novel method is simple yet effective, it could have a potential to be used industrially for the production of chemicals requiring immobilized lipases.

An amperometric biosensor based on multiwalled carbon nanotube-poly(pyrrole)-horseradish peroxidase nanobiocomposite film for determination of phenol derivatives

An amperometric biosensor based on horseradish peroxidase (HRP) and carbon nanotube (CNT)/polypyrrole (PPy) nanobiocomposite film on a gold surface has been developed. The HRP was incorporated into the CNT/PPy nanocomposite matrix in one-step electropolymerization process without the aid of cross-linking agent. Amperometric response was measured as a function of concentration of phenol derivatives, at a fixed bias voltage of -50 mV. Optimization of the experimental parameters was performed with regard to pH and concentration of hydrogen peroxide. The linear range, sensitivity and detection limit of the biosensor were investigated for eighteen phenol derivatives. The sensitivity in the linear range increased in this order: 4-methoxyphenol>2-aminophenol>guaiacol=m-cresol>2-chlorophenol=4-chlorophenol=hydroquinone=pyrocatechol>2,6-dimethoxyphenol>3-chlorophenol>p-cresol>p-benzoquinone=4-acetamidophenol>catechol>phenol=pyrogallol=2,4-dimethylphenol. CNTs was shown to enhance the electron transfer as a mediator and capable to carry higher bioactivity owing to its intensified surface area. The biosensor exhibited low detection limits with a short response time (2s) for the tested phenolics compared to the reported working electrodes. It retained 70% of its initial activity after using for 700 measurements in 1 month.

Sorption of Ni(II) ions from aqueous solution by Lewatit cation-exchange resin

Ion-exchange is an alternative process for uptake of heavy metals from aqueous solutions. In the present study, the sorption of nickel(II) ions from aqueous solution was investigated by using Lewatit MonoPlus SP 112 (strongly acidic, macroporous cation-exchange resin) in a batch adsorption system as a function of pH (2.0-8.0), initial nickel concentration (50-200 mg/L), resin dosage (0.5-2.0 g/L), contact time (0.5-3h), and temperatures (298-318K). The data were analyzed on the basis of Lagergren pseudo-first order, pseudo-second order (Types 1-5), Elovich and external, Weber-Morris intraparticle, pore-surface mass diffusion models. The experimental data showed that the maximum pH for efficient sorption of nickel(II) was 6.0. At the optimal conditions, nickel(II) ions sorption on the resin was decreased when the initial metal concentration increased. The results indicated that the resin dosage strongly affected the amount of nickel(II) ions removed from aqueous solution. The adsorption process was very fast due to 80% of nickel(II) sorption was occurred within 30 min and equilibrium was reached at about 90 min. Freundlich and Langmuir adsorption isotherm models were used for sorption equilibrium data and the maximum adsorption capacity (171 mg/g) of Lewatit MonoPlus SP 112 was obtained from Langmuir isotherm. The thermodynamic parameters (DeltaG degrees, free energy change; DeltaS degrees, enthalpy change; and DeltaH degrees, entropy change) for sorption of nickel(II) ions were evaluated. The rise in temperature caused a partly increase in the value of the equilibrium constant (K(c)) for the sorption of nickel(II) ions. Moreover, column flow adsorption study was also studied. Breakthrough curves were obtained from column flow studies by using both synthetic solution and rinsing bath water of filter industry. The column regeneration was carried out for two sorption-desorption cycles. The eluant used for regeneration of the cation-exchange resin was 7% (w/w) HCl. The experimental results demonstrated that Lewatit MonoPlus SP 112 cation-exchange resin could be used effectively for the removal of nickel(II) ions from aqueous medium.

The performance of pumice as a filter bed material under rapid filtration conditions

Abstract Deep bed sand filters are used extensively in drinking water and wastewater treatment. In this study, sand and pumice were used as a filtration media under rapid filtration conditions and performance results for both were compared. Turbidity removal performance and head losses were investigated as functions of filtration rate, bed depth and particle size. Under the same experimental conditions such as 750 mm bed depth, 7.64m 3 /m 2 .h flow rate and, 0.5−1.0 mm grain size, turbidity removal rates for sand and pumice were found to be 85–90% and 98–99%, respectively. Furthermore, the head loss for sand and pumice were found to be 460 mm and 215 mm, respectively. The results obtained have shown that pumice has a high potential for use as a filter bed material.

Covalent attachment of microbial lipase onto microporous styrene–divinylbenzene copolymer by means of polyglutaraldehyde

A novel method for immobilization of Thermomyces lanuginosus lipase onto polyglutaraldehyde-activated poly(styrene-divinylbenzene) (STY-DVB), which is a hydrophobic microporous support has been successfully developed. The copolymer was prepared by the polymerization of the continuous phase of a high internal phase emulsion (polyHIPE). The concentrated emulsion consists of a mixture of styrene and divinylbenzene containing a suitable surfactant and an initiator as the continuous phase and water as the dispersed phase. Lipase from T. lanuginosus was immobilized covalently with 85% yield on the internal surface of the hydrophobic microporous poly(styrene-divinylbenzene) copolymer and used as a biocatalyst for the transesterification reaction. The immobilized enzyme has been fully active 30 days in storage and retained the activity during the 15 repeated batch reactions. The properties of free and immobilized lipase were studied. The effects of protein concentration, pH, temperature, and time on the immobilization, activity, and stability of the immobilized lipase were also studied. The newly synthesized microporous poly(styrene-divinylbenzene) copolymer constitutes excellent support for lipase. It given rise to high immobilization yield, retains enzymatic activity for 30 days, stable in structure and allows for the immobilization of large amount of protein (11.4mg/g support). Since immobilization is simple yet effective, the newly immobilized lipase could be used in several application including oil hydrolysis, production of modified oils, biodiesel synthesis, and removal of fatty acids from oils.

Effect of presence of ions on surface characteristics of surfactant modified powdered activated carbon (PAC)

Modification of surface characteristics of solids using surfactants has practical implications in industrial and environmental applications. Extensive research has been conducted to explore the mechanism of surfactant sorption to different solid surfaces. However, a clear understanding yet to be found especially for heterogeneous surfaces in which pores and structure show local differences. The main objective of this study was to determine the effects of ions on the surface potential of surface modified activated carbon. In order to achieve the objective, anionic and cationic surfactants were selected and adsorptions of these surfactants to powdered activated carbon (PAC) were investigated. Then, zeta potential measurements were conducted for the surface modified PAC and finally, the effects of mono- and di-valent anions and cations on the zeta potentials of PAC surface were investigated. The results showed that even at very low cetyl trimethyl ammonium bromide (CTAB) concentrations charge reversal was observed and substantial increase was observed in zeta potential. However, linearalkyl benzene sulfonate (LABS) showed somewhat gradual decrease in zeta potential, reaching maximum when maximum sorption capacity was attained. Presence of anions in addition to CTAB effected the change of zeta potential. Similar effects were also observed for LABS modified PAC in the presence of mono- and di-valent cations. The change of zeta potential of with the valance of cations and anions were linear.

Determination of the apparent rate constants of the degradation of humic substances by ozonation and modeling of the removal of humic substances from the aqueous solutions with neural network.

In this study, the degradation rate constants of humic substances by ozonation under the different empirical conditions such as ozone-air flow rate, ozone generation potential, pH, temperature, powdered activated carbon (PAC) dosage and HCO(3)(-) ions concentration were determined. The ozonation of humic substances in the semi-batch reactor was found to fit pseudo-first-order reaction. The values of apparent rate constant of humic substances degradation increased with the increase of initial ozone-air flow rates, ozone generation potential, pH, temperatures and PAC dosage, but decreased with the increase of HCO(3)(-) concentration of the solution. Using Arrhenius equation, the activation energy (E(a)) of the reaction was found as 1.96 kJ mol(-1). The reaction of ozonation of humic substances under the different temperatures was defined as diffusion control according to E(a). The model based on artificial neural network (ANN) could predict the concentrations of humic substances removal from aqueous solution during ozonation. A relationship between the predicted results of the designed ANN model and experimental data was also conducted. The ANN model yielded determination coefficient of (R(2)=0.995), standard deviation ratio (0.065), mean absolute error (4.057) and root mean square error (5.4967).

Water softening in a crossflow membrane reactor

Abstract This paper presents an investigation on the removal of hardness by using a crossflow membrane reactor. Lime soda (LS) and caustic soda (CS) were added to hard water as softening chemical agents. The effect of the LS-CS dosage, specific cake resistances (α) and transmembrane pressure drop ( ΔP ) on steady-state rejection and flux was investigated. Also, flux declines were evaluated with respect to various flux decline models. It was found that hardness rejections decrease for LS and increase for CS with increasing LS and CS dosage, respectively. As ΔP increases, it was observed that while steady-state fluxes rise for both additives, hardness rejections were decreased for CS and remained constant for LS. A maximum of 97.5% hardness removal was achieved for 100% stochiometric dosages of CS. Obtained steady-state flux values varied between 224 to 881 L/m 2 h, depending on added chemical dosages and applied ΔP . It was determined that the reason for the flux decline at the beginning of the filtration (i.e., in the rapid flux decline period, RPD) was due to an intermediate pore blocking mechanism. As filtration progressed to the slow flux decline period (SDP), it was concluded that cake filtration occurred for all experiments. If solid matter concentration in the feed solution and applied ΔP are relatively low, the experiments showed that flux decline is due to the intermediate pore blocking mechanism. However, it was determined that if solid matter concentration in the feed solution and applied ΔP are relatively high, the flux decline model fits well with the cake filtration model.

Biodegradation characteristics and size fractionation of landfill leachate for integrated membrane treatment.

The fate of organics and nitrogen during the biological treatment with MBR and subsequent membrane filtration processes (nano filtration, NF; reverse osmosis, RO) were investigated for a landfill leachate. The chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal performances of membrane bioreactor (MBR) were obtained to be around 89% and 85%, respectively. The effluent COD of MBR was measured to be 1935 mg/L (30 kDa) which is much lower than experimentally determined soluble inert COD of 3200 mg/L using 0.45 μm filter. The readily and slowly biodegradable COD fractions were estimated to be 17% and 52% of raw influent COD, respectively. The respirometry based modeling test performed on raw leachate exhibited much slower degradation kinetics compared to municipal wastewater. A unique subset of model parameters was extracted from batch respirometry by using acclimated MBR sludge. The sequential ultrafiltration (UF) experiments (particle size distribution, PSD) revealed that most of the organics was below 2 nm filter mesh size. In addition, NF/RO post treatment after MBR system was required to increase COD and total nitrogen (TN) removal performances up to 99%. Relatively lower salt rejection rates around 94% was obtained for RO system as a post treatment of MBR system.

Techno-economic investigation of water recovery and whey powder production from whey using UF/RO and FO/RO integrated membrane systems

AbstractAs a by-product of dairy industry with high pollutant capacity, uncontrolled discharges of cheese whey result in serious pollution problems in the environment. Besides, recovery of water and whey powder in a whey stream has come to the fore as an important one of whey control strategies in environmental pollution. In that sense, the feasibility of water recovery and whey powder production from whey using integrated membrane processes was techno-economically investigated in this study. The study was focused on three case studies including different process scenarios were executed with laboratory-scale experiments in order to determine the technical performances of processes. The process scenarios were selected as following: the ultrafiltration/reverse osmosis (UF/RO), the forward osmosis/reverse osmosis (FO/RO) with NaCl draw solution and forward osmosis/reverse osmosis including thermolysis (FO/T/RO) at 60°C for concentrating NH4HCO3 draw solution. The real-scale costs for the processes were estim...