Biodiesel Production from Mixed Culture Algae Via a Wet Lipid Extraction Procedure

With world crude oil reserves decreasing and energy prices continually increasing, interest in developing renewable alternatives to petroleum-based liquid fuels has increased. An alternative that has received consideration is the growth and harvest of microalgae for the production of biodiesel via extraction of the microalgal oil or lipids. However, costs related to the growth, harvesting and dewatering, and processing of algal biomass have limited commercial scale production of algal biodiesel. Coupling wastewater remediation to microalgal growth can lower costs associated with large scale growth of microalgae. Microalgae are capable of assimilating inorganic nitrogen and phosphorous from wastewater into the biomass. By harvesting the microalgal biomass these nutrients can be removed, thus remediating the wastewater. Standard methods of oil extraction require drying the harvested biomass, adding significant energetic cost to processing the algal biomass. Extracting algal lipids from wet microalgal biomass using traditional methods leads to drastic reductions in extraction efficiency, driving up processing costs. A wet lipid extraction procedure was developed that was capable of extracting 79% of the transesterifiable lipids from wet algal biomass (16% solids) without the use of organic solvents while using relatively mild conditions (90 °C and ambient pressures). Ultimately 77% of the extracted lipids were collected for biodiesel production. Furthermore, the procedure was capable of precipitating chlorophyll, allowing for the collection of algal lipids independently of chlorophyll. The capability of this procedure to extract lipids from wet algal biomass, to reduce chlorophyll contamination of the algal oil, and to generate feedstock material for the production of additional bio-products provides the basis for reducing scale-up costs associated with the production of algal biofuels and bioproducts

Evaluation of syngas mass transfer and its impact on syngas fermentation and development of a novel enhanced gas to liquid mass transfer bioreactor

The ability to utilize lignocellulosic biomass, an abundantly available renewable material, provides an immense opportunity to produce significant quantities of renewable bio-based fuels and chemicals. However, challenges in processing this material have limited the scale and commercial feasibility of this production pathway. Syngas fermentation provides an avenue that combines thermochemical processing (gasification) of lignocellulosic biomass with the biological process of fermentation to potentially utilize all the carbon contained in lignocellulosic biomass to generate liquid fuels. The biological conversion of syngas generated from the gasification of lignocellulosic biomass has several advantages including the relatively mild conditions required by biological catalysts, specificity of product compounds, and the inherent robustness of biological systems with contaminating compounds in syngas. A limiting factor in this technology is the low gas to liquid mass transfer rates of syngas components, specifically CO and H2, which leads to low microbial productivity and product yields. Research present in this study explored the impacts of gas to liquid mass transfer on syngas fermentation at a fundamental metabolic level within the cell as well as its impact on the distribution of products generated. Additionally, this research was extended at an engineering level to develop a novel syngas fermentation bioreactor to achieve significantly higher gas to liquid mass transfer rates and production rates over traditional fermentation systems. Fundamental studies on the impact of mass transfer resulted in a deeper understanding of how syngas is assimilated in the cell’s metabolism and mass transfer impacts on different stages of the culture’s metabolism, specifically the critical step of alcohol production. At the engineering scale, a bioreactor capable of reaching mass transfer rates (KLa) of 2.28 sec-1 using oxygen as a model gas and up to 0.5 – 0.8 sec-1 with an integrated packed bed region was developed. Production rates of ethanol achieved were measured at 746 mg/L/hr within the immobilized biofilm region of the reactor. These results provide a deeper understanding of the syngas fermentation process and provide an opportunity to further develop the unique bioreactor developed in this study to create a more effective and efficient process to produce biofuels via syngas fermentation.</p

A novel bulk-gas-to-atomized-liquid reactor for enhanced mass transfer efficiency and its application to syngas fermentation

Syngas fermentation for fuels and chemicals is limited by the low rate of gas-to-liquid mass transfer. In this work, a unique bulk-gas-to-atomized-liquid (BGAL) contactor was developed to enhance mass transfer. In the BGAL system, liquid is atomized into discrete droplets, which significantly increases the interface between the liquid and bulk gas. Using oxygen as a model gas, the BGAL contactor achieved an oxygen transfer rate (OTR) of 569 mg·L−1·min−1 and a mass transfer coefficient (KLa) of 2.28 sec−1, which are values as much as 100-fold greater than achieved in other kinds of reactors. The BGAL contactor was then combined with a packed bed to implement syngas fermentation, with packing material supporting a biofilm upon which gas saturated liquid is dispersed. This combination avoids dispersing these gas-saturated droplets into the bulk liquid, which would significantly dilute the dissolved gas concentration. Although this combination reduced overall KLa to 0.45–1.0 sec−1, it is still nearly 20 times higher than achieved in a stirred tank reactor. The BGAL contactor/packed bed bioreactor was also more energy efficient in transferring gas to the liquid phase, requiring 8.63–26.32 J mg−1 O2 dissolved, which is as much as four-fold reduction in energy requirement compared to a stirred tank reactor. Fermentation of syngas to ethanol was evaluated in the BGAL contactor/packed bed bioreactor using Clostridium carboxidivorans P7. Ethanol productivity reached 746 mg·L−1·h−1 with an ethanol/acetic acid molar ratio of 7.6. The ethanol productivity was two-fold high than the highest level previously reported. The exceptional capability of BGAL contactor to enhance mass transfer in these experiments suggests its utility in syngas fermentation as well as other gas-liquid contacting processes.This is a manuscript of an article published as Sathish, Ashik, Ashokkumar Sharma, Preston Gable, Ioannis Skiadas, Robert Brown, and Zhiyou Wen. "A novel bulk-gas-to-atomized-liquid reactor for enhanced mass transfer efficiency and its application to syngas fermentation." Chemical Engineering Journal 370 (2019): 60-70. DOI: 10.1016/j.cej.2019.03.183. Posted with permission.</p

A novel bulk-gas-to-atomized-liquid reactor for enhanced mass transfer efficiency and its application to syngas fermentation

Syngas fermentation for fuels and chemicals is limited by the low rate of gas-to-liquid mass transfer. In this work, a unique bulk-gas-to-atomized-liquid (BGAL) contactor was developed to enhance mass transfer. In the BGAL system, liquid is atomized into discrete droplets, which significantly increases the interface between the liquid and bulk gas. Using oxygen as a model gas, the BGAL contactor achieved an oxygen transfer rate (OTR) of 569 mg·L−1·min−1 and a mass transfer coefficient (KLa) of 2.28 sec−1, which are values as much as 100-fold greater than achieved in other kinds of reactors. The BGAL contactor was then combined with a packed bed to implement syngas fermentation, with packing material supporting a biofilm upon which gas saturated liquid is dispersed. This combination avoids dispersing these gas-saturated droplets into the bulk liquid, which would significantly dilute the dissolved gas concentration. Although this combination reduced overall KLa to 0.45–1.0 sec−1, it is still nearly 20 times higher than achieved in a stirred tank reactor. The BGAL contactor/packed bed bioreactor was also more energy efficient in transferring gas to the liquid phase, requiring 8.63–26.32 J mg−1 O2 dissolved, which is as much as four-fold reduction in energy requirement compared to a stirred tank reactor. Fermentation of syngas to ethanol was evaluated in the BGAL contactor/packed bed bioreactor using Clostridium carboxidivorans P7. Ethanol productivity reached 746 mg·L−1·h−1 with an ethanol/acetic acid molar ratio of 7.6. The ethanol productivity was two-fold high than the highest level previously reported. The exceptional capability of BGAL contactor to enhance mass transfer in these experiments suggests its utility in syngas fermentation as well as other gas-liquid contacting processes