Energy Efficiency and Productivity Enhancement of Microbial Electrosynthesis of Acetate

Abstract

It was hypothesized that a lack of acetogenic biomass (biocatalyst) at the cathode of a microbial electrosynthesis system, due to electron and nutrient limitations, has prevented further improvement in acetate productivity and efficiency. In order to increase the biomass at the cathode and thereby performance, a bioelectrochemical system with this acetogenic community was operated under galvanostatic control and continuous media flow through a reticulated vitreous carbon (RVC) foam cathode. The combination of galvanostatic control and the high surface area cathode reduced the electron limitation and the continuous flow overcame the nutrient limitation while avoiding the accumulation of products and potential inhibitors. These conditions were set with the intention of operating the biocathode through the production of H2. Biofilm growth occurred on and within the unmodified RVC foam regardless of vigorous H2 generation on the cathode surface. A maximum volumetric rate or space time yield for acetate production of 0.78 g/Lcatholyte/h was achieved with 8 A/Lcatholyte (83.3 A/m2projected surface area of cathode) supplied to the continuous flow/culture bioelectrochemical reactors. The total Coulombic efficiency in H2 and acetate ranged from approximately 80–100%, with a maximum of 35% in acetate. The overall energy efficiency ranged from approximately 35–42% with a maximum to acetate of 12%.

Critical Biofilm Growth throughout Unmodified Carbon Felts Allows Continuous Bioelectrochemical Chain Elongation from CO2 up to Caproate at High Current Density

“…To date, mainly acetate or methane has been produced in MESs from CO2. Other products such as n-butyrate, propionate, ethanol, butanol, and isopropanol were also produced in relatively small amounts and rates in MESs from CO2 (Ganigue et al, 2015;Arends et al, 2017;Batlle-Vilanova et al, 2017;LaBelle and May, 2017). n-Caproate formation in MES occurred incidental (at concentration of 0.739 g L −1 ) from acetate (Van Eerten-Jansen et al, 2013) or was reported as a non-quantified trace compound (Sharma et al, 2013;Batlle-Vilanova et al, 2017).…”

“…The use of electrodes without a biofilm but relying on bacteria in suspension has achieved lower rates (Blanchet et al, 2015). Recently, LaBelle and May (2017) enhanced acetate volumetric productivity up to 18.7 g L −1 day −1 (when normalizing to catholyte volume) by optimizing the cathode to catholyte volume ratio (LaBelle and May, 2017).…”

“…An opportunity for practical implementation of MES is to produce continuously longer carbon-chain (>C2) organic compounds like n-caproate from CO2 which have higher values than acetate (Jourdin and Strik, 2017;LaBelle and May, 2017). To date, MCFA production has been achieved by chain elongation fermentation with open cultures (i.e., reactor microbiome) or pure cultures, using organics as both electron and carbon sources (Angenent et al, 2016).…”

Bioelectrochemical systems and synthetic biology: more power, more products

“…Microbial electrosynthesis, where microorganisms are employed to convert CO 2 to a range of useful products by behaving as catalysts for conversion of electrons, received directly or via electron transfer mediators into stable bonds of organic chemicals. For example, microbial electrosynthesis of acetate from CO 2 and electrons has been demonstrated using both pure cultures and mixed microbial communities and has generally been dependent on hydrogen generation at the electrode where hydrogen serves as an electron transfer mediator to cells (Nevin et al ., ; Marshall et al ., , ; LaBelle and May, ). More recently, interesting progress has been made to develop photosynthetic autotrophs for microbial electrosynthesis applications (Guzman et al ., ).…”

Bioelectrochemical Systems for Energy Valorization of Waste Streams

“…VFA are the most studied group of chemicals synthesized in MES These slightly reduced organic compounds can be produced from CO 2 by a wide variety of microorganisms following different metabolic pathways. Homoacetogens in particular are responsible for acetate production, and recent studies have reported acetic acid production rates above 0.78 g•L −1 •d −1 , product titers of up to 13.5 g•L −1 , and current-to-acetate conversion efficiencies of 99% [42,43]. Butyric acid is the second most reported VFA on MES systems.…”