Integration of Gas Enhanced Oil Recovery in Multiphase Fermentations for the Microbial Production of Fuels and Chemicals

Abstract

In multiphase fermentations where the product forms a second liquid phase or where solvents are added for product extraction, turbulent conditions disperse the oil phase as droplets. Surface-active components (SACs) present in the fermentation broth can stabilize the product droplets thus forming an emulsion. Breaking this emulsion increases process complexity and consequently the production cost. In previous works, it has been proposed to promote demulsification of oil/supernatant emulsions in an off-line batch bubble column operating at low gas flow rate. The aim of this study is to test the performance of this recovery method integrated to a fermentation, allowing for continuous removal of the oil phase. A 500 mL bubble column is successfully integrated with a 2 L reactor during 24 h without affecting cell growth or cell viability. However, higher levels of surfactants and emulsion stability are measured in the integrated system compared to a base case, reducing its capacity for oil recovery. This is related to release of SACs due to cellular stress when circulating through the recovery column. Therefore, it is concluded that the gas bubble-induced oil recovery method allows for oil separation and cell recycling without compromising fermentation performance; however, tuning of the column parameters considering increased levels of SACs due to cellular stress is required for improving oil recovery.

Methyl ketones: a comprehensive study of a novel biofuel

“…This is especially true for bulk products like biofuels. 70,71 Additionally, 2-undecanone has a log P of 4.1. This is in the lower range of the log P values that most microorganisms can tolerate for growth.…”

Impact of flocculant addition in oil recovery from multiphasic fermentations

“…The highest oil recovery was observed for F4 (88% clear oil release), yet this cannot be fairly compared against the other cases, since the early CaCl 2 addition had an impact on fer-mentation performance and oil emulsification. Surprisingly, the results showed that F4 had higher protein concentration (see Table 7), which has been reported to increase emulsion stability (Heeres et al, 2014;Heeres et al, 2015;Pedraza-de la Cuesta et al, 2017). Studies reported CaCl 2 as a cross linking agent (Hariyadi et al, 2014;Ye and Singh, 2000) which can promote protein bridging making the emulsion more susceptible to the shear by centrifugation and promoting oil recovery.…”

“…The impact of flocculants in enhancing oil recovery by GEOR was assessed in the aforementioned fermentations and synthetic emulsion. The reproducibility of fermentations allows to exclude important parameters, such as oil fraction and biomass concentration, that can influence GEOR's performance and results (Heeres et al, 2016;Pedraza-de la Cuesta et al, 2017). The same cannot be held for fermentation F4.…”

“…Low-cost and mild alternatives for oil recovery during fermentation, such as gravity separation and gas enhanced oil recovery (GEOR), have recently been proposed and successfully tested in-line with a bioreactor at laboratory (Dolman et al, 2017;Heeres et al, 2016;Pedraza-de la Cuesta et al, 2017) and at pilot scale (Steinbusch, 2019). The in-line gravity separator proposed by Dolman et al (2017) makes use of the density difference between product and medium to create a concentrated emulsion.…”

“…It was observed that when an emulsion had the capacity to cream, oil recovery by GEOR could be achieved. However, the oil recovery achieved during the fermentation process is generally low (10-30% oil recovery) due to small oil droplet size, back-mixing and SACs (Da Costa Basto et al, 2019;Pedraza-de la Cuesta et al, 2017). In contrast, mechanical methods combined with de-emulsifiers and temperature swings, such as centrifugation, have been reported to recover 90% of the oil in fermentation broth emulsion (Tabur and Dorin, 2012).…”