Search

Enzymatic transesterification of triglycerides to produce biodiesel has been gaining increasing attention owing to its advantages over chemical processes. Being catalysts, enzymes are not consumed during the processes in which they are used. Therefore, a successful technique to allow their repeated use can significantly enhance the economic feasibility of the process. The most common approach to allow easy separation of the enzymes and to eliminate their wastage is immobilization on a support matrix. Recently, Metal-Organic Frameworks (MOFs) have been suggested as preferable support for enzyme immobilization, owing to their high-order structure and high porosity and specific surface area. This thesis presents a study on the use of lipase encapsulated inside hexagonal ZIF-8 for enhance biodiesel production. It was shown that the lipase encapsulation did not have a significant effect on the morphology, surface properties and crystallinity of the ZIF-8 crystals. The effects of methanol ratio, temperature, oil concentration and water content, on the biodiesel production yield and rate of reaction, were tested. The highest yield was obtained at a methanol ratio and temperature of 6:1 and 40℃, respectively. It was also shown that the yield decreased with the increase in water content. The activity and stability of the immobilized lipase in ZIF-8 by encapsulation were compared to that immobilized by surface adsorption. Although the adsorbed lipase on ZIF-8 showed higher activity. At a methanol ratio of 12:1, the encapsulated lipase in ZIF-8 maintained 83% residual activity after 5 cycles, compared to only 34% attained by the adsorbed lipase at the same conditions. The experimental results were used to determine the kinetics parameters of the modified Ping Pong Bi Bi model, and the accuracy of the prediction was compared to those obtained by the Michaelis Menten model. To gain a better insight into how the reaction occurs inside the ZIF-8 crystal with encapsulated lipase

For the economical application of enzymatic processes in biodiesel production, lipase enzyme has to be used in immobilized form to allow easy retention and reuse. The main challenges facing the industrialization of the enzymatic process are the high mass transfer resistance, the tendency to adsorb the by-product glycerol onto the support matrix and poor operational stability. These problems can be solved by a good selection of supports of favourable surface characteristics and pore sizes. In that regard, increasing interest has recently been in Metal-Organic Frameworks (MOFs) as a new kind of porous support for enzyme immobilization. Physical adsorption, which is a fast and easy method of enzyme immobilization ensures limited enzyme denaturation and does not affect the enzyme activity, native structure, and active sites. However, the physically adsorbed enzyme is prone to leaching resulting in low stability, owing to the weak interaction between the enzyme and the support. As an alternative, chemisorption in which the nucleophiles of the enzymes are covalently bonded to the organic linkers of MOFs to form peptide bonds. However, physically immobilized lipase is generally more active reached than chemically immobilized ones, owing to the negative effect of the chemical bonds on the structure of the enzyme. However, enzyme attachment into the internal pores of MOFs may not be efficient, as part of the enzymatic activity may be lost due to conformational changes during diffusion into small cavities. In this process, the enzyme is caged inside the pores of the MOFs during the crystallization process. In addition, enzymes immobilized by this approach exhibit mass transfer limitations and their diffusion are restricted as the substrate may not be able to access the entire active sites. Kinetics and thermodynamics studies of the adsorption process, which are scarce in the literature, could provide invaluable information to explain the different performance of surface ad

Crude petroleum oil spills are among the most important organic contaminations, which result from uncontrolled releases and spillages during transportation or storage. The separated oils on that accumulate on top of the water can be removed by various conventional skimming methods. However, the emulsified portions that remain within the water phase are more difficult to remove and pose significant threats to the environment and could tamper the tertiary treatment in a wastewater treatment plant. Biological treatment, using bacteria, have proven to be an effective method in the removal of the emulsified oils. However, the biomass produced in this case does not have any significant remunerative value, and in most cases the used bacteria are pathogenic. In this work, microalgae have been proposed to be used, instead of bacteria, to combine the emulsified oil remediation with the microalgae potential as biofuel feedstock, which enhances the economic and environmental benefit of the process. A freshwater strain of Chlorella vulgaris was grown in water containing different concentrations of emulsified crude oil, up to 275 mg/L, at different temperatures. To enhance the removal of the emulsified oils, chemotrophic cultivation conditions was applied keeping the emulsified oils as a sole carbon source. The degradation was monitored by measuring the total organic carbon in the water. The specific growth rate of the microalgae at each initial oil concentration was determined and the results were fitted to a modified Monod kinetics model that takes specific interfacial area as the influential substrate, rather than the actual concentration. The microalgae growth was found to increase with the increase in temperature, in tested range, with μmax increasing from 1.17-1.48 day−1 as the temperature increased from 30oC and 40oC, and the activation energy was found to be 19.05 kJ/mol. However, the increase in the microalgae growth with temp

The treatment of industrial wastewater contaminated with phenols is among the main challenges in the chemical, and particularly the petrochemical industry. Phenols, which present in considerable amounts in industrial wastewater, are toxic even at low concentrations. Therefore, it is essential to reduce their concentrations in water to harmless levels before being discharged. On the other hand, the dependence on the conventional fossil sources of energy, which is non-renewable, is not sustainable and can cause harmful environmental impacts. Therefore, in this work, the dual utilization of microalgae as a cheap and efficient means to remove phenolic compounds commonly found in refinery wastewater and as a sustainable source for oils for biodiesel production has been proposed. Most conventional bacteria used in the treatment of phenolics are pathogenic and the collected biomass after treatment is considered a secondary waste that does not have an evident commercial value. Microalgae, however, are promising, sustainable and renewable sources of oils that can be used for biodiesel production. In addition, they contain important compounds, such as proteins and pigments, which have large applications in the food and pharmaceutical industries. Combining the production of these valuable products with wastewater treatment renders the cultivation of microalgae very attractive and economically feasible. In this work, two freshwater microalgae stains, namely Chorella sp. and Tetraselmis sp., were used to remove several phenolic compounds commonly found in refinery wastewater (phenol, 4-nitrophenol and 2,4- dinitrophenol). These compounds were selected since they are very toxic and may cause serious threats for the ecosystem. In addition, the removal of 4-nitrophenol and 2, 4-dinitrophenol is challenging, and there is no previous study conducted their removal using microalgae. The effect of initial concentrations of the phenols on the biomass growth and pheno

In this study, a thermo-responsive switchable solvent (TSS), with a tunable hydrophobicity by simply changing the temperature (between 25 to 45oC) was used for simultaneous lipids extraction from wet microalgae and biodiesel production. By manipulating the hydrophobicity of the solvent, the cell wall disruption, lipid extraction and transesterification, and product separation steps were all carried out in a single pot, while eliminating the need for the energy intensive and time-consuming drying step. To overcome the problems currently encountered by using conventional alkaline catalysts in the transesterification of lipids, immobilized enzyme has been used. The proposed TSS consisted of an ionic liquid (N,N diethyl-Nmethylammonium methane sulfonate), a polymer poly (propylene) glycol (PPG) and water. The effectiveness of the proposed process was compared to that using conventional organic solvent, n-hexane, and other CO₂ triggered amine based switchable solvents, namely 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)-1-hexanol and DBU-Mono-ethanolamine (MEA). At the same conditions and solvent switching program, using immobilized lipase as a biocatalyst, the biodiesel yields were 45.5 ± 0.38 %, 37.8 ± 1.03 % and 5.9 ± 1.50 %, using TSS, DBU-hexanol, and DBU-MEA respectively. Using n-hexane resulted in insignificant yield of 3.1 ± 0.43 %. Furthermore, a reusability of the TSS-immobilized lipase system was investigated, and it was shown that the reusability biodiesel yield dropped from 50 ± 1.46 % in the first cycle to 20.4 ± 0.60 % in the fourth. A parametric study was performed, using response surface methodology (RSM) to evaluate the effects of cell disruption and extraction/reaction durations in the range of 0-3 h, and methanol amount used in the range of 0.02 – 0.2 mL on the biodiesel production yield from 1 g of wet biomass. The results were used to develop a statistical model to predict the biodiesel yield under different conditions and to optimi

Biodiesel produced from microalgae biomass has been pursued as a possible replacement to petroleum diesel. Among the main steps in microalgae biodiesel production are the drying and cell walls disruption, which are energy intensive and/or time consuming, and oil extraction, which is conventionally done using toxic organic solvents that contaminate the left over biomass and require additional solvent recovery. Therefore, these steps are considered the major obstacles facing the commercialization of microalgae biodiesel. In this work, switchable solvents (SSs), which can reversibly alter their hydrophobicities, have been tested for oil extraction and biodiesel production. Three switchable solvents, namely N, N-dimethylcyclohexylamine (DMCHA), nethylbutylamine (EBA), and dipropylamine, were used to extract oil from wet microalgae, while avoiding the drying step. Their effectiveness was compared to that of conventional organic solvent, n-hexane, and hydrophobic ionic liquid (IL), 1- Butyl-3-methylimidazolium hexafluorophosphate [Bmim] [PF6]. The optimum extraction protocol was determined for the switchable solvent that showed the highest performance. The switchable solvent was also used for simultaneous extraction-reaction process, in which oils are extracted from wet microalgae and enzymatically converted to biodiesel using the same solvent in the same reaction cell. The successful use of a single solvent for extraction-reaction from wet biomass has never been reported in lite A parametric study was performed using the response surface methodology (RSM) to evaluate the effects of temperature (in the range of 15-55°C) and solvent program, consisted of cell disruption and extraction periods (in the range of 0-3 hrs.) on the oil extraction yield. The results were used to develop a statistical model to predict the oil yield under different conditions and to optimize the process. In addition, effects of the solvent program and methanol t

Excessive use of desalination, due to the increase in freshwater demand, results in large productions of reject brine. Therefore, the development of an efficient treatment process of the reject brine becomes vital. The Solvay process is one of the main treatment technologies, wherein NH3 is introduced to convert soluble Na+ into insoluble NaHCO3. However, in this process, Cl- is not removed and NH4+ is introduced, and therefore electrocoagulation has been proposed for their removal. The experiment was designed using Minitab with different initial concentrations of chloride (7400 – 32600 mg/l), current densities (0.033 - 0.2 A/cm2), and temperatures (3.2 - 36.8°C). It was found that both percentage and rate of removal increased with the increase in temperature and current density, and the decrease in initial concentration of the ions. For example, at 20°C and initial concentrations of 14250 mg/l and 20000 mg/l for NH4+ and Cl-, respectively, increasing the current density from 0 to 0.2 A/cm2 resulted in an increase in the removal percentages from 12.5 to 66.7% and from 3.55 to 28.4% for NH4+ and Cl-, respectively. At 0.1167 A/cm2 and initial concentrations of 14250 mg/l and 20000 mg/l for NH4+ and Cl-, respectively, increasing the temperature from 3.2 to 36.8°C, resulted in an increase in the removal from 42.9 to 72.4% and from 21.8 to 29.8% for NH4+ and Cl-, respectively. However, at 0.1167 A/cm2 and 20°C, increasing the initial concentration of Cl- from 7400 to 32600 mg/l resulted in decreasing in the removal from 56.9 to 45.3% and from 30.3 to 25.6% for NH4+ and Cl-, respectively. The results were fitted into model equations (14 and 15), which were validated against an independent

Chlorinated phenolic compounds represent a major class of hazardous pollutants commonly encountered in wastewater generated by the petroleum and petrochemical industries. In this regard, biological treatment, as an economical and green technology, has been shown to be one of the most promising approaches for the removal of many organic water pollutants such as chlorophenols. Under aerobic conditions, bacteria utilize chlorophenols as a source of carbon and energy. This study aimed at developing an integrated system for biodegradation of 2, 4 dichlorophenol (DCP) in a specially designed spouted bed bioreactor (SBBR), characterized by systematic intense mixing, resulting in enhanced biodegradation rates. The system utilizes microbial immobilization of an effective commercial bacterial consortium, consisting mainly of Pseudomonas putida, in order to retain the biomass within the reactor. The bacteria were immobilized in polyvinyl alcohol (PVA) gel particles and used in the SBBR to remove DCP from the wastewater. The role of glucose, which has often been included as a carbon source during initial biomass acclimatization, was investigated and found not to be significant enough to justify its inclusion in the acclimatization process. In addition, the effects of several operating parameters were investigated in the batch mode operation, then modeled and optimized for maximum degradation rate by response surface methodology. The process was further tested in a continuous mode in order to evaluate the SBBR hydrodynamics in terms of stability and sustainability to shock loads. Total removal of the contaminant was achieved in the batch process at every initial concentration up to 200 mg/l, whereas a combined 80% removal at a throughput of 1400 g/m3day was obtained during Continuous operation. Additionally, the process was mathematically modeled using a dynamic modeling approach in order to assess reaction and mass transfer limitations. The results supported th