Production of a biodiesel additive in a stirred basket reactor using immobilized lipase: Kinetic and mass transfer analysis

Farzaneh Vahabzadeh,Mohamad Hajar 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.4

A laboratory-scale stirred basket reactor (SBR) was constructed to study the synthesis of an n-butyl oleate ester using Novozym 435. An ester yield of approximately 98% was obtained after 6 h using an equimolar substrate ratio, 3.5 g of enzyme, a reaction temperature of 40 oC, and an impeller speed of 200 rpm. The kinetic data were modeled as a ping-pong bi-bi mechanism using a non-linear regression technique. Statistical analysis of the results showed that a model that incorporated the inhibitory effect of n-butanol yielded the best fit with the following parameters: Vmax=24.8mmol L−1 min−1, Km, oleic acid=190.8mM, Km, n-butanol=544.7 mM, and Ki, n-butanol=158.3mM. Mass transfer effects on the enzyme kinetics were also studied, and the absence of internal and external diffusion limitations on the reaction in the SBR was confirmed by considering calculated values of the Thiele modulus and the Damkohler number. Novozym 435 exhibited satisfactory performance in repeated-batch experiments using SBR.

Kinetic Modeling of Cometabolic Degradation of Ethanethiol and Phenol by Ralstonia eutropha

Mahsa Sedighi,Farzaneh Vahabzadeh 한국생물공학회 2014 Biotechnology and Bioprocess Engineering Vol.19 No.2

Cometabolism, as a complex phenomenon inmicrobial world, is a special mechanism for transformationof many compounds of environmental and toxicologicalsignificance. Several models have been proposed to describethe cometabolic transformations of non-growth substratesin the absence or presence of growth substrates. In thisstudy, a model was proposed to simulate the degradationkinetics of phenol and ethanethiol (ET) by a pure culture ofRalstonia eutropha, including the effects of cell growth,endogenous cell decay, loss of transformation activity,competitive inhibition between growth and non-growthsubstrates, and self-inhibition of non-growth substrate. Themodel parameters were determined independently andwere then used for evaluating the applicability of the modelby comparing experimental data with model predictions. The model successfully predicted ET transformation andphenol utilization for a wide range of concentrations of ET(0 ~ 40 mg/L) and phenol (0 ~ 100 mg/L).

Degradation of Formaldehyde in Packed-bed Bioreactor by Kissirisimmobilized Ralstonia eutropha

Alireza Habibi,Farzaneh Vahabzadeh 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.3

The ability of the Ralstonia eutropha cells to utilize formaldehyde (FA) as the only source of carbon and energy was studied in the kissiris-immobilized cell bioreactor (KICB) in batch-recirculation and continuous modes of operation. In batch-recirculation experiments, the test bacterium could tolerate concentrations of FA up to 1,400 mg/L at 30oC and aeration rate equal to 0.75 vvm (rS = 7.25 mg/L/h, qS = 0.019 gFA/gcell/h). However, further increase of initial FA concentration resulted in degradation reaction of FA to stop at 1,600 mg/L. Results of continuous mode experiments showed that the biodegradation performance of the KICB was dependent on both feed flow rate and inlet FA concentration parameters. The optimum feed flow rate which corresponded to the highest biodegradation rate (rS = 240.3 mg/L/h) was observed at Q = 18 mL/min when KICB did not operate under the external mass transfer limiting regime. Substrate inhibition kinetics (Edwards and Luong equations) were used to describe the experimental specific degradation rates data. According to the Luong model, the values of the maximum specific degradation rate (qmax), half-saturation coefficient (KS), the maximum allowable FA concentration (Sm), and the shape factor (n)were 0.178 gFA/gcell/h, 250.9 mg/L, 1,600 mg/L, and 1.86,respectively.

An artificial neural network approach to determine the rheological behavior of pickering-type diesel-in-water emulsion prepared with the use of β-cyclodextrin

Alireza Monazzami,Farzaneh Vahabzadeh,Abdolreza Aroujalian,Azadeh Mogharei 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.4

With the use of β-cyclodextrin (β-CD), Pickering-type diesel-in-water emulsions were prepared based on the inclusion complex formed between diesel and β-CD which acted as an emulsifier. By using the artificial neural network (ANN), the rheological behavior of the emulsions was characterized using three input variables: diesel-to-water ratio, β-CD concentration, and shear rate and one-output variable as shear stress. Gradient descent (GD), conjugate gradient (CG), and quasi Newton (QN) were used as three different methods in the feed-forward back-propagation algorithm for network training. Hyperbolic tangent sigmoid and pure linear were the transfer functions used for transforming information between input and output through one hidden layer containing ten neurons. By dividing the experimental data into three sets of training, validation, and testing, the QN method in predicting shear stress was found to have performed better than the other two network learning techniques (R2=0.994 and MSE=0.006).

Ethanethiol Degradation by Ralstonia eutropha

Mahsa Sedighi,Farzaneh Vahabzadeh,Seyed Morteza Zamir,Abbas Naderifar 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.4

In the present study, a pure culture of Ralstonia eutropha was used to degrade gaseous ethanethiol. Ethane thiol at various initial concentrations ranging from 115 to 320 mg/m3 was degraded almost completely within 120 ~168 h, while at higher concentrations up to 452 mg/m3,removal efficiency declined. It was likely that ethanethiol was used as the source of energy by R. eutropha, since no clear increase in the biomass concentration was observed. Kinetic data of ethanethiol bidegradation could be fitted using the Monod model. The kinetic parameters were qm =0.23 (mg ethanethiol/g biomass/h), and Ks = 1.379 (mg/L). The mineralization pathway of ethanethiol through sulphate,as the detected product, and the energy production were discussed in some detail.

Rheological characterization of ferrous sulfate-containing water-in-oil-in-water (W/O/W) double emulsions

Mozhgan Keyvani,Farzaneh Vahabzadeh,Leila Davarpanah 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.9

With use of response surface methodology (RSM), the W1/O/W2 emulsions containing ferrous sulfate asthe inner phase were optimized in terms of stability (ES) and apparent viscosity (µapp). Curvature display of the responsesaround their optimal settings was appropriately described using the quadratic polynomial regression model. The non-Newtonian behavior of the test W1/O/W2 emulsions was characterized using the power-law model and change fromnon-Newtonian to Newtonian (n1) was seen in the case of W1/O :W2 ratio equal 20 : 80 when the level of Tween-80 was 1 v%. Results of the size distribution pattern showed 60% of the particles were less than 5 µm. Rheologicalproperties of the test W1/O/W2 emulsions as the viscoelastic liquids were analyzed and the results of oscillatory ex-periments considering shear stress and frequency dependency of G' and G'' moduli were discussed in terms of the internalmicrostructure of the emulsions.

Bioelectrochemical treatment of olive oil mill wastewater using an optimized microbial electrolysis cell to produce hydrogen

Anis Askari,Milad Taherkhani,Farzaneh Vahabzadeh 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.8

A single chamber microbial electrolysis cell (MEC) was constructed to treat olive oil mill wastewater(OOMW) biologically and produce hydrogen simultaneously. To characterize the optimal MEC condition, the MECwas fed with synthetic wastewater (SW) having a phenol concentration of 250mg l1. Therefore, the influence of differentapplied voltages and cathode materials was explored and the optimum condition for MEC was determined, whichwas when the stainless steel cathode was implemented and the external voltage of 0.6 V was supplied. Chemical oxygendemand (COD) removal of 62% and current density of 362 mA m2 were obtained for OOMW treatment, whileCOD removal of 73% and the current density of 274.4mA m2 were attained for SW treatment in this MEC at 0.6 V. Hydrogen production rate was 0.045m3 H2 m3d1 for SW and 0.053m3 H2 m3d1 for OOMW. Furthermore, the coulombicefficiency and cathodic hydrogen recovery were 23% and 81%, respectively. Finally, MEC performance in termsof electrical current generation, wastewater treatment and hydrogen production was compared to some similar reportedstudies.

Phenol-acclimated activated sludge and Ralstonia eutropha in a microbial fuel Cell for removal of olive oil from mill wastewater

Mahboobeh Bagheri,Reza Daneshvar,Azadeh Mogharei,Farzaneh Vahabzadeh 한국화학공학회 2020 Korean Journal of Chemical Engineering Vol.37 No.7

The fuel acclimation process offers flexibility in microbial fuel cell (MFC) power generation behavior. Different concentrations (50-200mg/L) of phenol were used for adapting the activated sludge (AS), obtained from a local petroleum wastewater treatment plant and Ralstonia eutropha pure culture. Anodic biomass capable of oxidizing phenol substrate, using either AS inoculum microbial consortium or R. eutropha in the MFC system, has been a reflection of growth supportive functionality of phenol and 150mg/L as initial concentration was used in the experiments. For both types of inocula. The results of phenol and COD removals obtained for closed system configuration were compared with those under open circuit condition. The current production by AS and R. eutropha was improved through phenol acclimation process. The highest power density (PD) using either AS or R. eutropha was 11 and 5.8mW/m2, respectively. In terms of using olive oil mill wastewater as the anodic substrate, the behavior of phenol-acclimated R. eutropha was better than that of the synthetic type of wastewater, and the PD value was 7.8mW/m2.

Optimization of Operational Conditions for Adipate Ester Synthesis in a Stirred Tank Reactor

Naz Chaibakhsh,Mohd Basyaruddin Abdul Rahman,Mahiran Basri,Farzaneh Vahabzadeh,Suraini Abd-Aziz,Abu Bakar Salleh 한국생물공학회 2010 Biotechnology and Bioprocess Engineering Vol.15 No.5

Esterification of adipic acid and oleyl alcohol in a solvent-free system featuring a stirred tank reactor containing commercially immobilized Candida antarctica lipase B was performed. The process was carried out using an artificial neural network (ANN) trained by the Levenberg-Marquardt (LM) algorithm. The effects of four operative variables, temperature, time, amount of enzyme,and impeller speed, on the reaction yield were studied. By examining different ANN configurations, the best network was found to consist of seven hidden nodes using a hyperbolic tangent sigmoid transfer function. The values of the coefficient of determination (R2) and root mean squared error (RMSE) between the actual and predicted responses were determined to be 1 and 0.0058178 for training and 0.99467 and 0.622540 for the testing datasets,respectively. These results imply that the developed model was capable of predicting the esterification yield. The operative variables affected the yield, and their order of contribution was as follows: time > amount of enzyme >temperature > impeller speed. A high percentage of yield (95.7%) was obtained using a low level of enzyme (2.5%w/w), and the temperature, time, and impeller speed were 66.5°C, 354 min (about 6 h), and 500 rpm, respectively. A simple protocol for efficient substrate conversion in a solvent-free system evidenced by high enzyme stability is indicative of successful ester synthesis.

Experimental Study and Kinetic Modeling of Cometabolic Degradation of Phenol and p-nitrophenol by Loofa-immobilized Ralstonia eutropha

Mohammad Maleki,Mahdi Motamedi,Mahsa Sedighi,Seyed Morteza Zamir,Farzaneh Vahabzadeh 한국생물공학회 2015 Biotechnology and Bioprocess Engineering Vol.20 No.1

In the present study, phenol-adapted cells ofRalstonia eutropha were used to degrade p-nitrophenol(PNP) in the presence of phenol. PNP at initial concentrationsranging from 5 to 15 mg/L was degraded almost completelyby free cells of R. eutropha. The use of loofa-immobilizedcells increased the complete removal of PNP up to 30 mg/L. Kinetic data for PNP biodegradation by immobilized cellsof R. eutropha best fitted the Haldane model. The kineticparameters were ks = 0.0006 (mg PNP/mg biomass.h), Ks =8.83 (mg/L) and Ki = 30.77 (mg/L). The degradation pathwaysof PNP through the metabolites, 4-nitro-catechol (4-NC)and hydroquinone (HQ), were investigated using HPLC.