Using Reverse Osmosis Membranes to Couple Direct Ethanol Fuel Cells with Ongoing Fermentations

Abstract

Separations in biological systems remain a challenging problem and can be particularly so in the case of biofuels, where purification can use a significant fraction of the energy content of the fuel. For small-molecule biofuels like ethanol, reverse osmosis (RO) membranes show promise as passive purifiers, in that they allow uncharged small molecules to pass through while blocking most other components of the growth medium. Here, we examine the use of RO membranes in developing biohybrid fuel cells, closely examining the case where a direct ethanol fuel cell (DEFC) is coupled with an ongoing yeast fermentation across an RO membrane. We show that, contrary to initial good performance, the acetic acid produced by the DEFC readily diffuses back across the RO membrane and kills the fermentation after a few days. We introduce an amelioration chamber where the acetic acid is converted to acetate ions. The RO membrane rejects the acetate ions due to their charge, preventing acetic acid buildup in the fermentation. We also show that some small, charged components of the fermentation such as amino acids are imperfectly rejected by RO membranes. Because of the high sensitivity of DEFCs to low concentrations (10s of μM) of amino acids, even a very slow diffusion of amino acids across the RO membranes can limit biohybrid fuel cell lifetimes.

Vapor-fed bio-hybrid fuel cell

“…Having characterized the vapor-fed FC, its long-term potential is demonstrated by operating it for 5 months in combination with a yeast fermentation to supply the ethanol. This study shows that a vapor-fed FC has the potential to be operated in continuous mode over long periods of time, in contrast to previous work [ 63 ]. In addition, the ethanol production rate is increased, presumably by preventing ethanol from reaching concentrations that retard fermentation.…”

“…4 ) that is in excellent agreement with the flow rate current densities. At high flow rates (≥250 mL/min), the current densities were comparable to currents achieved with batch liquid-fed operation [ 39 , 48 , 63 ]. At low flow rates, the current drops substantially, since the effective ethanol concentration in the FC is lower due to conversion of the ethanol to acetic acid and other products.…”

Modeling control and transduction of electrochemical gradients in acid-stressed bacteria

“…Lastly, multi-component model extensions are required for eukaryotes such as yeast, which encounter acid-stress in many renewable and industrial bioprocesses. 105 , 106 , 107 , 108 , 109 In this case, multiple cellular components (e.g., vacuole and plasma membrane) must be modeled in tandem, because of the combined effect of vacuolar and plasma membrane ATPases in maintaining cytosolic pH under acid-stress. 109 , 110 For the wide range of extracellular conditions and cellular physiologies, the increasing availability of kinetic and expression data for transport systems will aid in extending the theoretical framework developed herein.…”

Silica-Based RO Membranes for Separation of Acidic Solution

“…The separation of the acid solution by using a membrane has been mainly investigated for acetic acid (AcOH) solutions for industrial applications [10,11,12,13,14], membrane reactors [15], and microorganisms [16,17]. Polymeric membranes such as polyvinyl alcohol (PVA) membranes [11,13,15] or commercialized polymer membranes [10,17] had been applied for AcOH separation. H 2 SO 4 separation performances were investigated by using commercialized polymer membranes [18,19,20].…”