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Switchable solvents with hydrophobicities that can be reversibly changed were evaluated as single solvents for oil extraction from wet biomass. Three switchable solvents, N,N-dimethylcyclohexylamine (DMCHA), N-ethylbutylamine (EBA), and dipropylamine, were used to extract oil from the undisrupted wet paste of harvested Chlorella sp. microalgae. The oil extraction yields for the three solvents were 13.6%, 12.3%, and 7.0%, respectively. However, single hydrophobicity solvents n-hexane and [Bmim][PF6] were unable to extract any oil, achieving yields of 0% and 0.7%, respectively. A parametric study was performed to evaluate the effects of temperature, cell disruption duration, and extraction duration on the effectiveness of oil extraction. The results were used to develop a statistical model to predict oil extraction effectiveness under different conditions. The switchable solvents were also evaluated in simultaneous extraction-reaction systems used to convert the oils extracted from wet microalgae into biodiesel. The use of enzymes was found to enhance the production yield of biodiesel by 33%. The highest biodiesel yield of 47.5% was achieved using DMCHA at 35 °C with a methanol/oil molar ratio of 6:1 and a 30% enzyme loading employing a solvent program comprising 1-h cell disruption, 1-h extraction/reaction, and 1-h phase separation steps. The proposed strategy of using a single solvent for simultaneous extraction and reaction could substantially simplify biodiesel production from wet microalgae.

Lipids, proteins, and carbohydrates are the major constituents found in microalga cells, in varying proportions, and these biomolecules find applications in different industries. During microalga cultivation, to efficiently manipulate, control, and optimize the productivity of a specific compound for a specific application, real-time monitoring of these three cell components is essential. In this study, a method using measurement of electrical capacitance was developed to simultaneously determine the lipid, protein, and carbohydrate content of microalga cells without the requirement for any pre-processing steps. The marine microalga Nannochloropsis oculata was cultivated under nitrogen starvation conditions to induce lipid accumulation over a period of 22 days. The correlation between the electrical capacitance of the microalga culture and the intracellular biomolecule content (determined by standard techniques) was investigated, enabling subsequent deduction of microalga intracellular content from electrical capacitance of the culture. The accuracy and precision of the technique were proven by validating an independent sample. The main advantage of the proposed technique is its capability of quantifying microalga composition within a few minutes, significantly faster than currently available conventional techniques.

Crude proteins and pigments were extracted from different microalgae strains, both marine and freshwater. The effectiveness of enzymatic pre‐treatment prior to protein extraction was evaluated and compared to conventional techniques, including ultrasonication and high‐pressure water extraction. Enzymatic pre‐treatment was chosen as it could be carried out at mild shear conditions and does not subject the proteins to high temperatures, as with the ultrasonication approach. Using enzymatic pre‐treatment, the extracted proteins yields of all tested microalgae strains were approximately 0.7 mg per mg of dry cell weight. These values were comparable to those achieved using a commercial lytic kit. Ultrasonication was not very effective for proteins extraction from Chlorella sp., and the extracted proteins yields did not exceed 0.4 mg per mg of dry cell weight. For other strains, similar yields were achieved by both treatment methods. The time‐course effect of enzymatic incubation on the proteins extraction efficiency was more evident using laccase compared to lysozyme, which suggested that the former enzyme has a slower rate of cell disruption. The crude extracted proteins were fractionated using an ion exchange resin and were analyzed by the electrophoresis technique. They were further tested for their antioxidant activity, the highest of which was about 60% from Nannochloropsis sp. The total phenolic contents in the selected strains were also determined, with Chlorella sp. showing the highest content reaching 17 mg/g. Lysozyme was also found to enhance the extraction of pigments, with Chlorella sp. showing the highest pigments contents of 16.02, 4.59 and 5.22 mg/g of chlorophyll a, chlorophyll b and total carotenoids, respectively.

Mathematical modeling of supercritical extraction of lipids from Scenedesmus sp. microalgae is presented in this study. Broken and intact cells (BIC) model, proposed by Sovova in 1994, was used to predict the extraction curves. The effects of extraction pressure, temperature and fluid flowrate on predicted model parameters and extraction rates were assessed. The results indicates that BIC model represents well the experimental data, and the mass transfer coefficients in the fluid and solid phases changed in ranges of 6.7–30.9 × 10−6 m s−1 and 2.08–13.2 × 10−10 m s−1, respectively. The fluid phase coefficient increased with increasing the flowrate and temperature, but was not affected by the pressure, whereas the solid phase showed a significant decrease with the increase in pressure. According to the external mass transfer coefficient, mass transfer correlations were developed to relate Sherwood number to Reynolds, Schmidt, and Grashof numbers. It was found that when Schmidt exponent was fixed at 1/3 (model 1), the model did not fit the experimental data well, whereas when the power was adjusted and considered as a fitting parameter the coefficients of determination increased significantly exceeding 90%. The natural convection effect was found to be insignificant compared to the forced convection. The validity of the developed correlations with coefficients determined from experimental data collected from a small scale extraction cell was confirmed by predicting the overall extraction curve (OEC's) of a larger scale extraction cell.

Supercritical carbon dioxide (SC-CO 2 ) extraction of lipid from Scenedesmus sp. for biodiesel production was investigated and compared to conventional extraction methods. The effect of biomass pre-treatment prior to extraction and extracting conditions, namely pressure in the range of 200–500 bar, temperatures in the range of 35–65 °C and CO 2 flow rate in the range of 1.38–4.02 g min −1 , on SC-CO 2 extraction yield and quality of lipid were investigated. Three levels full factorial design of experiments and response surface methodology was used to model the system. A second order polynomial model was developed and used to predict the optimum conditions. Scaling up to a laboratory larger scale was also tested. The results indicated that SC-CO 2 extraction was superior to other extraction techniques, but exhibited significant variations in yield with changes in operating parameters. In the developed model, it was found that the linear and quadratic terms of the temperature, as well as the interaction with pressure had a significant effect on lipid yield; whereas, their effect on lipid quality was insignificant. The best operating conditions, in the tested range, were 53 °C, 500 bar and 1.9 g min −1 , in which lipid extraction yield of 7.41% (dry weight basis) was obtained. Negligible differences were observed when the fatty acid composition of SC-CO 2 extracted lipid was compared to that extracted by the conventional methods. At the optimum conditions, SC-CO 2 extraction was successfully scaled-up by eight-folds and the extracted lipid yield dropped by 16%.

The performance of an adsorption column packed with granular activated carbon was evaluated for the removal of phenols from refinery wastewater. The effects of phenol feed concentration (80–182 mg/l), feed flow rate (5–20 ml/min), and activated carbon packing mass (5–15 g) on the breakthrough characteristics of the adsorption system were determined. The continuous adsorption process was simulated using batch data and the parameters for a new empirical model were determined. Different dynamic models such as Adams–Bohart, Wolborsko, Thomas, and Yoon-Nelson models were also fitted to the experimental data for the sake of comparison. The empirical, Yoon–Nelson and Thomas models showed a high degree of fitting at different operation conditions, with the empirical model giving the best fit based on the Akaike information criterion (AIC). At an initial phenol concentration of 175 mg/l, packing mass of 10 g, a flow rate of 10 ml/min and a temperature of 25 °C, the SSE of the new empirical and Thomas models were identical (248.35) and very close to that of the Yoon–Nelson model (259.49). The values were significantly lower than that of the Adams–Bohart model, which was determined to be 19,358.48. The superiority of the new empirical model and the Thomas model was also confirmed from the values of the R 2 and AIC, which were 0.99 and 38.3, respectively, compared to 0.92 and 86.2 for Adams–Bohart model.

Phenol-degrading bacterial strains have been extracted from oil-sludge samples collected from a local refinery. A selective medium was used to isolate the active strain capable of utilizing phenol as a sole carbon source, which was identified as Ralstonia pickettii. The growth kinetics of mixed and isolated R. pickettii suspensions were investigated using different initial concentrations of phenol in the range of 25 to 200 g m−3 at 35°C and pH of 8.5. The results were compared to those of a commercially available mixed bacterial suspension, which was either acclimatized to 100 g m−3 phenol concentration, extracted from PVA particles that were subjected to real petroleum refinery wastewater containing phenol, or an isolated active strain grown on a selective medium that was identified as Pseudomonas putida. The effect of substrate inhibition was observed using all bacterial suspensions, and the growth results were used to determine the parameters of a suitable kinetic model. It was found that the phenol bi...

Pseudomonas putida, immobilized in polyvinyl alcohol (PVA) particles, has been successfully utilized for the bioremoval of phenol from simulated wastewater, using two immobilization techniques and two types of bioreactors. The biodegradation efficiency of P. putida immobilized within the PVA gel before the cross-linking stage of the polymer (T1) was compared to that of the same bacteria immobilized by soaking blank PVA particles in bacterial suspension (T2), a procedure that avoids subjecting the bacteria to sub-freezing temperature during the cross-linking stage. The effects of nutrient deprivation and exposure to high phenol concentrations on the activity of P. putida were also evaluated. The experimental results indicated that the immobilized bacteria remained active for a period of 72 h, even without the addition of nutrients. Subsequently the activity gradually decreased, but the bacteria easily regained their original activity with the addition of nutrients. Sudden exposure to high phenol concentrations resulted in immediate decline in the biodegradation activity, but the bacteria adapted to the new concentrations and regained their activity within 24 h. The biodegradation experiments were carried out in two types of bioreactors namely, bubble column and spouted bed bioreactor (SBBR). Both reactor configurations and both immobilization techniques proved to be effective in the biodegradation of phenol.

The feasibility of enzymatic production of biodiesel from waste animal fats using supercritical fluid technology for the extraction and reaction has been investigated. The operating conditions that resulted in the optimum extraction and biodiesel production yields were identified. The effects of extraction temperature, pressure and supercritical CO2 (SC-CO2) flow rate were investigated in the ranges of 35–55 °C, 300–500 bar and of 3–5 ml min−1, respectively, and optimized using response surface methodology (RSM). In addition, the effects of reaction temperature, methanol:fat molar ratio and enzyme loading on biodiesel production yield were investigated in the ranges of 35–60 °C, 3:1–6:1 and 10–50%, respectively. The optimum conditions for supercritical fluid extraction (SFE) were determined to be 45 °C, 500 bar and 3 ml min−1; at which, 87.4% of total fat content was extracted from freeze dried meat. The statistical analysis however, showed that pressure has negligible effect on the extraction yield, which is extremely important, as it allows saving energy by using lower pressure. On the other hand, biodiesel yield of 40% was obtained using extracted fat as feedstock in SC-CO2 medium at 50 °C, 200 bar, 4:1 methanol:fat molar ratio and 30% loading of lipase enzyme, after 24 h of reaction. The experimental results were used to fit a suitable reaction kinetic model using non-linear regression analysis to estimate the model parameters.

Experiments were carried out to evaluate the batch adsorption of phenol from petroleum refinery wastewater on a locally prepared date-pit activated carbon (DP-AC). Adsorption equilibrium and kinetics data were determined for the uptake of phenol from real refinery wastewater and from synthetically prepared aqueous phenol solution. The data were fitted to several adsorption isotherm and kinetics models. Sips as well as Langmuir models gave the best fit for equilibrium isotherms, whereas the kinetics data were best fitted by the pseudo-second order model. The enthalpy of adsorption showed an exothermic nature of the adsorption process. Several chemical and thermal techniques were tested for the regeneration of saturated activated carbon; using ethanol was found to be the most effective with more than 86% regeneration efficiency after four regeneration cycles.

Experiments were carried out to evaluate the continuous biodegradation of phenol using Pseudomonas putida, immobilized in polyvinyl alcohol (PVA) gel matrices in a specially designed spouted bed bioreactor (SBBR) at different conditions. The plexiglas reactor had a total volume of 1.1 l and was equipped with a surrounding jacket for temperature control. The mean residence time in the SBBR was determined experimentally by tracking the concentration of a tracer compound in a continuous effluent stream. The effects of initial phenol concentration, air flow rate, liquid flow rate and PVA particle size, on the rate of phenol biodegradation, were investigated. It was found that the rate of continuous biodegradation increased with increasing the initial phenol concentration and decreased with increasing the liquid flow rate. Mass transfer and hence the accessibility of the biomass to phenol was enhanced by decreasing the PVA particle size and increasing the air flow rate, which had a positive effect on the rate of biodegradation.

Bacterial biotreatment has gained a lot of attention in recent years as an alternative method for the removal of phenol from wastewater. Under aerobic conditions, Pseudomonas putida utilize phenol as a source of carbon and energy. In this work, P. putida was immobilized in Polyvinyl Alcohol (PVA) gel particles and used in a spouted bed bioreactor to remove phenol from wastewater. The effects of initial phenol concentration and air flow rate on the rate of aerobic phenol removal were investigated. The experimental results were used to develop a dynamic model to describe the utilization of phenol for the bacterial growth in spouted bed bioreactor.

The applications of lipase immobilized on ceramic beads and entrapped in sol-gel matrix, in the production of bio-diesel from waste cooking oil, are compared to that of free lipase. Experimental determination of the effect of molar equivalent of methanol, to moles of ester bond in the triglyceride, on the rate of the enzymatic trans-esterification was experimentally determined. It was found that for the same weight of lipase used, the production of bio-diesel was much higher using lipase immobilized on ceramic beads in comparison to that using lipase entrapped in sol-gel and in free form. Substrates inhibition effect was observed in all cases, which agrees with previous results found in literature. The optimum methanol:oil molar ratio was found to be 0.87 for immobilized lipase from yeast source, C. antartica and 1.00 for free lipase from the same yeast source and immobilized lipase from bacterial source, P. cepacia. On the other hand, it was shown that biodieasel can be produced in considerable amounts, with yield reaching 40%, in absence of organic solvent using immobilized lipase, from P. cepacia, on ceramic beads. The results of this study can be used to determine the kinetics parameters of mathematical models which describe the system.

Lipase catalysed reactions take place at the interface between the aqueous phase containing the enzyme and the oil phase. The reaction starts with the adsorption of the enzyme at the oil-water interface. In a mechanically agitated reactor, the total free interfacial area is limited and hence, there would be a critical enzyme concentration at which the interfacial area is saturated with the adsorbed enzyme. In this paper, an unsteady-state dynamic model is developed from Ping Pong Bi Bi mechanism, modified to take into consideration the effect of available interfacial area. The model is validated against experimental results from the hydrolysis of palm oil using lipase from Candida rugusa in a mechanically agitated batch bioreactor. It is shown that the model presented the experimental data better than previous models found in literature. The fraction of the enzyme, available in the aqueous phase, which is contributing in the coverage of oil-water interface in a stirred batch bioreactor, is determined at different agitation speeds. This fraction is found to increase as agitation speed increases, which is assumed to be a result of the increase in desorption to adsorption ratio of the enzyme at the interface with agitation. � 2007 Elsevier B.V. All rights reserved.

The hydrolysis of oil by lipase takes place at the interface between the oil and the aqueous solution containing the enzyme. For such systems, interfacial area between the oil phase and the aqueous phase influences the rate of hydrolysis. In this study, to enhance the hydrolysis rates of lipids, ultrasonication instead of mechanical agitation was used for interfacial area generation. By ultrasonication, larger interfacial area with much narrower distribution of oil droplet diameter could be produced as compared to by mechanical agitation. Experiments carried out to assess the hydrolysis rate of lipids showed that it was significantly enhanced by ultrasonic emulsification and the interfacial area saturation with enzyme was also not observed due to large interfacial area generated.

The kinetics of the production of biodiesel by esterification of butyric acid with methanol, catalysed by lipase from Mucor miehei, was studied in two types of systems, namely, n-hexane microaqueous and biphasic (n-hexane/water) containing different amounts of water. The experimental results were fit to a Ping-Pong mechanism and the constants found in the rate expression were determined. The results have shown that in a microaqueous media, butyric acid does not inhibit the reaction in the range of initial concentrations considered. The effect of water content on the initial rate of reaction and conversion were illustrated. It was shown that the initial rate of reaction increased as the initial water content increased up to 25% (v/v). However, the conversion was found to be higher at low initial water concentrations.

A mathematical model to predict the hydrolysis rate of oils by lipase, from a proposed kinetic mechanism of the reaction is derived. The model predicts interfacial saturation at high enzyme concentration. It is used to determine, under different operating conditions, the critical enzyme concentration, i.e., the enzyme concentration at which the interface between the oil and the aqueous phase containing the enzyme is saturated. To verify the model predictions, experimental results of the hydrolysis of palm oil and sunflower oil are used. The model predictions closely agree with the experimental results for sun flower oil. The sensitivity of the model predictions to the values of the kinetic parameters is also investigated.

An unsteady-state kinetic model has been proposed for the hydrolysis of palm oil by lipase in a stirred batch bioreactor. The hydrolysis model was derived from a reaction mechanism and simplified for conditions of low enzyme concentration. From it, the regions where the quasi-steady-state assumption for the intermediates is applicable is identified and verified experimentally. The experimental results showed that the hydrolysis of palm oil by lipase in a well-stirred reactor has a short induction time for the penetration of enzyme at the interface and for the formation of the enzyme–substrate complex. This indicates that the quasi-steady-state assumption for the intermediates is applicable under the operating conditions used in this study. It is also shown that increasing the agitation speed results in reduced induction time.

The kinetics of the enzymic hydrolysis of palm oil using lipase in a batch reactor has been investigated. The lipase enzyme used was not ester bond position selective and its activity at the interface was higher compared to that in the bulk. A mathematical model taking into account the mechanism of the hydrolysis reaction and the effect of interfacial area between the oil phase and the aqueous phase containing the enzyme was developed. A correlation between the interfacial area and the operating conditions including agitation speed and oil volume fraction was established experimentally. The kinetic parameters were estimated by fitting the data to the model and comparing with previously reported values. The kinetic model represented the experimental data accurately.

Most conventional techniques for the determination of microalgae lipid content are time consuming and in most cases are indirect and require excessive sample preparations. This work presents a new technique that utilizes radio frequency (RF) for rapid lipid quantification, without the need for sample preparation. Tests showed that a shift in the resonance frequency of a RF open-ended coaxial resonator and a gradual increase in its resonance magnitude may occur as the lipids content of microalgae cells increases. These response parameters can be then calibrated against actual cellular lipid contents and used for rapid determination of the cellular lipids. The average duration of lipid quantification using the proposed technique was of about 1 minute, which is significantly less than all other conventional techniques, and was achieved without the need for any time consuming treatment steps.

Experiments were carried out to evaluate the batch adsorption of COD from petroleum refinery wastewater on a locally prepared date-pit activated carbon (DP-AC), and its adsorption effectiveness was compared to that of commercially available BDH activated carbon (BDH-AC). Adsorption equilibrium and kinetic data were determined for both adsorbents and fitted to several adsorption isotherm and kinetics models, respectively. The Langmuir monolayer isotherm fitted well the equilibrium data of COD on both adsorbents; whereas, the kinetics data were best fitted by the pseudo-second order model. Modeling of the controlling mechanisms indicated that both intrinsic kinetics and mass transfer contributed to controlling the adsorption process. Mass transfer seemed to be the dominant mechanism at low COD content, while intrinsic kinetics dominates at high concentrations. In general, the adsorption effectiveness of locally prepared DP-AC was proven to be comparable to that of BDH-AC. Therefore, DP-AC can be utilized as an effective and less expensive adsorbent for the reduction of COD in refinery wastewater.

A kinetic model is devised, from the reaction mechanism steps, to predict the rate of reducing sugar production by hydrolysis of two types of cellulose, namely, amorphous carboxymethylcellulose (CMC) and highly crystalline wood shavings, using Aspergillus niger cellulase. Experimental results in a stirred batch reactor at 40 degrees C show that the production of reducing sugar reduced at much shorter times for wood shavings in comparison to CMC at the same initial substrate concentration. The experimental results are used to determine the kinetic parameters of the model equations. The significance of crystallinity was determined using inert fraction coefficient, which is assumed to be constant and equals 0.05 and 0.98 for CMC and wood shavings, respectively. It is shown there is a good agreement between the experimental results and proposed kinetic model predictions. The effect of the inert fraction coefficient on the production of reducing sugar by the enzymatic hydrolysis of cellulose is also determined. It is found that the cellulase used extracted from A. niger is much more sensitive towards the substrate structure in comparison to that extracted from Trichoderma reesei.