Grantee Research Project Results

2012 Progress Report: BioWinol Technologies: A hybrid green process for biofuel production – Phase 2

EPA Grant Number: SU835171
Title: BioWinol Technologies: A hybrid green process for biofuel production – Phase 2
Investigators: Wilkins, Mark , Atiyeh, Hasan , Huhnke, Raymond , Zhu, Xiaoguang , Dharman, Karthikeyan Ramachandriya , Liu, Kan
Current Investigators: Wilkins, Mark , Dharman, Karthikeyan Ramachandriya , Liu, Kan , Atiyeh, Hasan , Huhnke, Raymond , Zhu, Xiaoguang , Kundiyana, Dimple , Terrill, Jennine
Institution: Oklahoma State University
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2011 through August 14, 2013
Project Period Covered by this Report: August 15, 2011 through August 14,2012
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2011) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Air Quality , Sustainable and Healthy Communities

Objective:

BioWinol Technologies proposes a unique hybrid technology that uses several renewable resources, specifically biomass, wind and solar, to produce hydrogen (H2). This process can also capture carbon-dioxide (CO2) from other industries to produce biofuels. The primary objective for this Phase II project is to develop and optimize a fermentation process using hollow fiber membrane (HFM) technology for cultivation of autotrophic microorganisms.

Progress Summary:

The bacterium Clostridium carboxidivorans was selected based on Phase I results for further testing and scale-up from small serum bottle fermentations to larger lab-scale fermenters with temperature and pH control.  Additionally, we decided to construct a lab-scale hollow fiber membrane (HFM) reactor in order to enhance the mass transfer of CO₂ and H₂ to the bacteria cells.  Enhanced mass transfer will deliver more substrate to the cells and allow the productivity of the cells to increase.  Mass transfer of gases to cells is limited in stirred tank reactors due to the low solubility of most gases in water and the resistance to transfer by the interface between gas bubbles and media.  In a HFM system, gas diffuses through a membrane into the media, which avoids the resistance due to bubble media interface.  A recent study comparing mass transfer coefficients for various fermenter types showed that hydrophobic HFMs have much mass transfer coefficients for gases that are over 4 times greater than hydrophilic membranes (Orgill et al., 2013).  This was due to water not being able to enter the lumen of the membranes, which allowed gaseous diffusion to be the main mechanism of mass transfer as opposed to liquid diffusion.  Also, the hydrophobic HFM reactors achieved mass transfer coefficients that were from 2 to 10 times greater than the maximum mass transfer coefficient observed in a stirred tank reactor (Orgill et al., 2013).

 

Due to the high mass transfer coefficients observed for HFM fermenters, the BioWinol team decided to use this fermenter type to scale up the CO₂/H₂ fermentation.  Several vendors were contacted to supply membranes, and two suppliers were identified, MedArray and Membrana.  MedArray produces hydrophobic polydimethylsiloxane (PDMS) non-porous membranes and Membrana produces hydrophobic polypropylene porous membranes.  Membranes were purchased from both companies and tested for durability, ease of use, and fermentation performance (cell growth and ethanol production).  The PDMS membrane was smaller and more expensive than the PP membranes.  Also, the PDMS membranes developed holes in them under pressure and good cell growth was not obtained.  Additionally, a biofilm was observed to form on the PP membrane, which enables direct transfer of gas to the cells in the biofilm without diffusion into the media.  For these reasons, the Membrana PP membrane was chosen for further study.

A HFM fermenter system was setup as shown in Figure 1.  Gas containing 75% H₂ and 25% CO₂ entered the system through two HFMs at a rate of 20scc/min.  Medium (2.5L) was placed in a 3L stirred vessel equipped with temperature and pH control.  The medium was pumped through the HFMs at 300 mL/min in a direction counter to the gas flow. Medium contained (per L): 30 mL mineral stock solution, 10 mL trace metal solution, 10 mL vitamin solution, 30 g corn steep liquor (CSL), 10 mL of 4% cysteine sulfide solution, and 0.1 mL of 1% resazurin indicator.  A 70g/L NaHSO₃ solution was used to control pH.  Two Aalborg gas flow meters were used to monitor inlet and outlet gas flow.  The pressure in the fermentation system was 110 kPa, which was slightly above atmospheric pressure to prevent gas leaks. 

Three experiments have been completed that have investigated the effect of pH on cell growth, product formation.  A pH of 6.0 has been shown to promote cell growth in our previous work with C. carboxidivorans, while pH values from 4.5 to 5 have been shown to promote alcohol production. The first experiment (E1) controlled pH at 6.0 for 72 h, after which the pH was allowed to decline to pH 5.5.  The second experiment (E2) controlled pH at 6.0 for the entire experiment.  The third experiment (E3) allowed pH to decline from the initial pH of 5.8 to 5.5, and then the pH was controlled at 5.5. Cell growth, ethanol, acetic acid, n-butanol, n-butyric acid, n-hexanol and n-hexanoic acid were measured over time.

The pH value did not have an effect on the initial growth rate of C. carboxidivorans (Figure 2).  Cell growth in E3 was actually sustained longer than E1 and E2.  This is contrary to the expectation that pH control at pH 6 would result in increased growth.  Instead, it appeared cell growth may have been more dependent on the amount on nutrients available in the medium.  The pH did have an effect on alcohol production.  In both E1 and E2, ethanol production was observed in the first 48 to 50 h, and then ethanol was consumed by the cells or stripped from the medium by the gas flow (Figure 3).  In E1 ethanol production resumed at 96 h once pH decreased to 5.5, while in E2, which had pH controlled at pH6, ethanol production resumed after 163 h, but a much lower rate than that observed with E1.  In E3 ethanol was produced from 20 to 141 h.  The pH in E3 had declined to 5.56 at 20 h, so it appears the reduction in pH to ~5.5 coincided with the start of ethanol production in both E1 and E2.  n-Butanol and n-hexanol were also produced in all three fermentations.  The trend for n-butanol production was similar to that of ethanol production for all three pH control schemes with butanol production being greatest for E1 (0.83 g/L), followed by E3 (0.50 g/L) with little butanol being produced in E2 (data not shown).  n-Hexanol production was produced at the same time as ethanol (Figure 4).  Concentration of n-hexanol reached 0.43 g/L in both E1 and E3, which are greater than any n-hexanol concentrations reported in literature.  These concentrations are quite remarkable given the fact that CO₂ and H₂ were the substrates.  n-Hexanol is a potential fuel compound and it can also be converted to jet fuel through catalysis.

Figure 1. BioWinol reactor setup.

Figure 2. Cell growth under various pH control schemes (see text for scheme descriptions).

Figure 3.  Ethanol production under various pH control schemes (see text for scheme descriptions).

Figure 4.  n-Hexanol production under various pH control schemes (see text for scheme descriptions).

Future Activities:

A hollow fiber membrane fermenter can be used to effectively transfer gas to cells.  CO₂ and H₂ can be converted to ethanol, n-butanol and n-hexanol, all of which can be used as biofuels.  The pH in the fermenter greatly affects the products formed with alcohol being produced at pH 5.5 in greater concentrations that at pH 6.0.

References:

Orgill, J.J., Atiyeh, H.K., Devarapalli, M., Phillips, J.R., Lewis, R.S., Huhnke, R.L., 2013. A comparison of mass transfer coefficients between trickle-bed, hollow fiber membrane and stirred tank reactors. Bioresour. Technol., 133, 340-346.

Journal Articles:

No journal articles submitted with this report: View all 6 publications for this project

Supplemental Keywords:

Hexanol, biofuels, butanol, greenhouse gas

Progress and Final Reports:

Original Abstract

Final Report

P3 Phase I:

BioWinol Technologies: A Hybrid Green Process for Biofuel Production  | Final Report