Bioelectrochemical synthesis of caproate through chain elongation as a complementary technology to anaerobic digestion

Abstract

Chain elongation is one of the common anaerobic fermentation processes in which bacteria convert ethanol and short chain fatty acids (SCFA) into medium chain fatty acids (MCFA). These are single carboxylic acids having six to twelve carbon atoms, with several applications, such as biofuels. Caproate is a promising MCFA, and several technologies were proposed for the valorization of waste to obtain it. Bioelectrochemical systems (BESs) are technologies that are capable of converting the chemical energy of organic/inorganic wastes into value‐added products, using in situ generated H2 or electricity as energy sources. To convert waste biomass into caproate, an electron donor in the form of hydrogen or ethanol should be supplemented within the anaerobic fermentation, which can be used as the electron donor in the cathodic compartment for the conversion of acetate into caproate. This review highlights recent anaerobic and bioelectrochemical processes for the production of caproate. The discussion will also cover the potential applications of this technology, together with obstacles to its use, compared with the conventional anaerobic digestion (AD) process, and considers whether it could be a standalone technology or a complementary one for AD. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Medium Chain Carboxylic Acids from Complex Organic Feedstocks by Mixed Culture Fermentation

“…While the operational conditions that select for other MMC fermentation products such as volatile fatty acids (VFAs) [47] and hydrogen (H 2 ) [48] have been reviewed, the operational conditions or process set-up that allow MCC to be steered towards MCCA formation have to be further evaluated. A recent review is available regarding the use of bio-electrochemical systems for MCCA production as a complementary technology to AD [49]. Certain other reviews include a section on MCCAs as potential MMC fermentation products, either in the context of operational control applied in AD [50], or the contexts of a biorefinery [51], wastewater treatment [11] or food waste treatment [21,52,53,54].…”

Electro-fermentation and redox mediators enhance glucose conversion into butyric acid with mixed microbial cultures

“…Over the last years, the ever-increasing attention towards the implementation of a bio-based economy has rapidly spurred the scientific interest towards the development of sustainable bioprocesses targeting the production of VFA from renewable resources [3][4][5][6]. However, in spite of the substantial economic value of VFA, acidogenic fermentation is not yet developed as a stand-alone technology at the industrial scale, mostly due to difficulties in implementing long-term operational strategies which allow tuning and regulating the product spectrum (i.e., the composition of produced VFA), particularly when waste organic substrates of undefined composition are used as feedstock materials and mixedmicrobial cultures (MMC) are employed as biocatalysts [7,8]. Indeed, to date, acidogenic fermentation is mainly exploited as one of the key steps of anaerobic digestion (AD), a well-established bioprocess, widely implemented at the industrial scale, whereby biogas (i.e., a gaseous mixture rich in methane and carbon dioxide) is ultimately generated from the treatment of an organic waste by means of at least four interdependent phases (hydrolysis, acidogenesis, acetogenesis and methanogenesis) [9].…”

Microbial electrosynthesis from CO2: Challenges, opportunities and perspectives in the context of circular bioeconomy

“…Hence, such production and extraction system developed out of MES would be relevant in supporting circular bioeconomy. Even though the caproate production rate in MES is yet slower than that in AD through chain-elongation (Jourdin et al, 2018), MES could serve as a complementary technology to AD in the future, if it fully utilizes its anode compartment for wastewater treatment and increases its profitability (Reddy et al, 2018).…”