Lipid Extraction From Spirulina sp. and Schizochytrium sp. Using Supercritical CO2 With Methanol

Microalgae are one of the most promising feedstocks for biodiesel production due to their high lipid content and easy farming. However, the extraction of lipids from microalgae is energy intensive and costly and involves the use of toxic organic solvents. Compared with organic solvent extraction, supercritical CO2 (SCCO2) has demonstrated advantages through lower toxicity and no solvent-liquid separation. Due to the nonpolar nature of SCCO2, polar organic solvents such as methanol may need to be added as a modifier in order to increase the extraction ability of SCCO2. In this paper, pilot scale lipid extraction using SCCO2 was studied on two microalgae species: Spirulina sp. and Schizochytrium sp. For each species, SCCO2 extraction was conducted on 200 g of biomass for 6 h. Methanol was added as a cosolvent in the extraction process based on a volume ratio of 4%. The results showed that adding methanol in SCCO2 increased the lipid extraction yield significantly for both species. Under an operating pressure of 4000 psi, the lipid extraction yields for Spirulina sp. and Schizochytrium sp. were increased by 80% and 72%, respectively. It was also found that a stepwise addition of methanol was more effective than a one-time addition. In comparison with Soxhlet extraction using methylene chloride/methanol (2:1, v/v), the methanol-SCCO2 extraction demonstrated its high effectiveness for lipid extraction. In addition, the methanol-SCCO2 system showed a high lipid extraction yield after increasing biomass loading fivefold, indicating good potential for scaling up this method. Finally, a kinetic study of the SCCO2 extraction process was conducted, and the results showed that methanol concentration in SCCO2 has the strongest influence on the lipid extraction yield

Investigation of Electrolytic Flocculation for Microalga Scenedesmus sp Using Aluminum and Graphite Electrodes

Electrolytic flocculation using non-sacrificial electrodes with flocculants added was studied on harvesting Scenedesmus sp. In order to optimize the operating conditions of the electrolytic flocculation process and to quantify the amount of flocculants added, aluminum electrodes were first used in the process. It was found that under optimal conditions, the microalgae removal efficiency using aluminum electrodes could reach 98.5%, while 34.2 mg L-1 of aluminum ions were released during the process. Different metal electrodes were also studied, but high microalgae removal efficiency was witnessed only using aluminum electrodes, indicating the influence of the aluminum ion in flocculation. When non-sacrificial graphite electrodes were used in the electrolytic flocculation process, the corresponding amount of aluminum sulfate was added so that the aluminum ion concentration in water was also equal to 34.2 mg L-1. The result showed that the microalgae removal efficiency of graphite electrodes could reach above 90% after aluminum sulfate was added. In contrast, using graphite electrodes alone and using the metal salt alone only yielded 22.9% and 7.1% of microalgae removal efficiency, respectively. These results indicated that the presence of metal ions is necessary in the electrolytic flocculation process. The energy consumption of the process was found to be 0.3 kW h m-3 or 0.88 kW h kg-1, which is considered to be low energy consumption. The total cost of the process, including energy and chemicals, was found to be $ 0.21 m-3, proving a cost competitive method in microalgae harvesting

Mechanistic studies on enzymatic nitroarene reduction and implications for the fate of nitroarene mixtures in redox-stratified biofilm

At military bases and munitions factories, 2,A,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (24DNT), and 2,6-dinitrotoluene (26DNT) are persistent soil and groundwater contaminants. Although the reduction of nitro groups in these compounds has been extensively investigated, few researchers have studied the link between the reduction rates and the electrochemical properties of these compounds. In this work, the standard one-electron redox potentials at pH 7 (E1°′) for TNT and related nitroorenes were measured for the first time by pulse rodiolysis. The reduction kinetics were investigated using a bacterial nitroreduclase. Contrary to most whole cell studies wherein amino group formation has been observed, nitro group reduction halted at the level of the hydroxylamino group. A linear free energy relationship was observed between the enzymatic reduction rates and the E1°′ values. Enzymatic TNT reduction did not obey simple Michoelis-Menten kinetics, and clear evidence of enzyme inactivation during TNT transformation was obtained. ^ Batch experiments were conducted to test whether 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, and 2,4-diamino-6-nitrotoluene, potential TNT degradation products, were aerobically transformed by a mixed culture that mineralizes DNTs. None of the compounds were degraded to any extent when provided as sole carbon and nitrogen sources or when DNTs were provided as primary substrate. 26DNT degradation was inhibited in the presence of 4-amino-2,6-dinitrotoluene. ^ As a first step in testing the feasibility of using a redox-stratified biofilm for simultaneous DNT and TNT mineralization, a comprehensive biofilm model was developed. A novel model form was derived to depict nitroarene reduction as a function of the compound E1°′ and the intracellular NADH concentration, an indicator for solution redox potential. Using the comprehensive biofilm model, several reactor types (fluidized bed, hollow fiber membrane, and extractive membrane) were investigated. Model results suggested that membrane biofilm reactors are most effective because they promote thicker biofilm growth and redox stratification. A sensitivity analysis demonstrated that additional investigation of aminodinitrotoluene mineralization, oxygen limitation, and ozoxy dimer production ore necessary to better predict this technology. This model will guide application of this treatment process, as more mechanistic detail becomes available. However, these model results are preliminary due to several assumptions that require more stringent validation.

NAD(P)H:Flavin Mononucleotide Oxidoreductase Inactivation during 2,4,6-Trinitrotoluene Reduction

Bacteria readily transform 2,4,6-trinitrotoluene (TNT), a contaminant frequently found at military bases and munitions production facilities, by reduction of the nitro group substituents. In this work, the kinetics of nitroreduction were investigated by using a model nitroreductase, NAD(P)H:flavin mononucleotide (FMN) oxidoreductase. Under mediation by NAD(P)H:FMN oxidoreductase, TNT rapidly reacted with NADH to form 2-hydroxylamino-4,6-dinitrotoluene and 4-hydroxylamino-2,6-dinitrotoluene, whereas 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene were not produced. Progressive loss of activity was observed during TNT reduction, indicating inactivation of the enzyme during transformation. It is likely that a nitrosodinitrotoluene intermediate reacted with the NAD(P)H:FMN oxidoreductase, leading to enzyme inactivation. A half-maximum constant with respect to NADH, K(N), of 394 μM was measured, indicating possible NADH limitation under typical cellular conditions. A mathematical model that describes the inactivation process and NADH limitation provided a good fit to TNT reduction profiles. This work represents the first step in developing a comprehensive enzyme level understanding of nitroarene biotransformation

Investigation Of Electrolytic Flocculation For Microalga: Scenedesmus Sp. Using Aluminum And Graphite Electrodes

© 2018 The Royal Society of Chemistry. Electrolytic flocculation using non-sacrificial electrodes with flocculants added was studied on harvesting Scenedesmus sp. In order to optimize the operating conditions of the electrolytic flocculation process and to quantify the amount of flocculants added, aluminum electrodes were first used in the process. It was found that under optimal conditions, the microalgae removal efficiency using aluminum electrodes could reach 98.5%, while 34.2 mg L-1 of aluminum ions were released during the process. Different metal electrodes were also studied, but high microalgae removal efficiency was witnessed only using aluminum electrodes, indicating the influence of the aluminum ion in flocculation. When non-sacrificial graphite electrodes were used in the electrolytic flocculation process, the corresponding amount of aluminum sulfate was added so that the aluminum ion concentration in water was also equal to 34.2 mg L-1. The result showed that the microalgae removal efficiency of graphite electrodes could reach above 90% after aluminum sulfate was added. In contrast, using graphite electrodes alone and using the metal salt alone only yielded 22.9% and 7.1% of microalgae removal efficiency, respectively. These results indicated that the presence of metal ions is necessary in the electrolytic flocculation process. The energy consumption of the process was found to be 0.3 kW h m-3 or 0.88 kW h kg-1, which is considered to be low energy consumption. The total cost of the process, including energy and chemicals, was found to be $ 0.21 m-3, proving a cost competitive method in microalgae harvesting

Lipid Extraction From Spirulina Sp. And Schizochytrium Sp. Using Supercritical Co 2 With Methanol

© 2018 Shihong Liu et al. Microalgae are one of the most promising feedstocks for biodiesel production due to their high lipid content and easy farming. However, the extraction of lipids from microalgae is energy intensive and costly and involves the use of toxic organic solvents. Compared with organic solvent extraction, supercritical CO 2 (SCCO 2 ) has demonstrated advantages through lower toxicity and no solvent-liquid separation. Due to the nonpolar nature of SCCO 2 , polar organic solvents such as methanol may need to be added as a modifier in order to increase the extraction ability of SCCO 2 . In this paper, pilot scale lipid extraction using SCCO 2 was studied on two microalgae species: Spirulina sp. And Schizochytrium sp. For each species, SCCO 2 extraction was conducted on 200 g of biomass for 6 h. Methanol was added as a cosolvent in the extraction process based on a volume ratio of 4%. The results showed that adding methanol in SCCO 2 increased the lipid extraction yield significantly for both species. Under an operating pressure of 4000 psi, the lipid extraction yields for Spirulina sp. And Schizochytrium sp. Were increased by 80% and 72%, respectively. It was also found that a stepwise addition of methanol was more effective than a one-time addition. In comparison with Soxhlet extraction using methylene chloride/methanol (2:1, v/v), the methanol-SCCO 2 extraction demonstrated its high effectiveness for lipid extraction. In addition, the methanol-SCCO 2 system showed a high lipid extraction yield after increasing biomass loading fivefold, indicating good potential for scaling up this method. Finally, a kinetic study of the SCCO 2 extraction process was conducted, and the results showed that methanol concentration in SCCO 2 has the strongest influence on the lipid extraction yield