Enhanced selectivity to butyrate and caproate above acetate in continuous bioelectrochemical chain elongation from CO2: Steering with CO2 loading rate and hydraulic retention time. (September 2019) - Jourdin, Ludovic
Abstract: The selective and high-rate microbial electrosynthesis of a valuable molecule is favoured from an economic perspective. We demonstrate here that increasing selectivity towards n-butyrate and n-caproate over acetate, while maintaining high production rate and electron recovery, is achievable by adjusting the CO2 feeding strategy and hydraulic retention time. We show that high CO2 loading rate (173 L d − 1 ) and long hydraulic retention time (14 days) triggers bioelectrochemical chain elongation to n-butyrate and n-caproate (53.6 ± 4.1%C), whereas lower CO2 loading rate (8.6 L d − 1 ) does not, even with increasing HRT (96.4 ± 2.4%C into acetate). Moreover, temporarily detaching and re-attaching the biofilm allowed to obtain high-rate n-caproate production of 2.0 ± 0.1 g L − 1 d − 1 (max 3.1 g L − 1 ), while producing 3.3 ± 0.2 g L − 1 d − 1 n-butyrate (max 9.3 g L − 1 ), at an increased 63.6 ± 5.0%C into both. This was achieved with 69.8 ± 2.8% total electron recovery at −100.8 A m − 2 . Highlights: Continuous bioelectrochemical chain elongation of CO2 to organics was investigated. Impacts of CO2 feeding strategy and hydraulic retention time were evaluated. 63.6 ± 5.0%C was recovered into n-butyrate and n-caproate, over acetate. n-Caproate production rate of 2.0 ± 0.1 g L − 1 d − 1 was achieved (max 3.1 g L − 1 ). Enhanced selectivity to medium-chain fatty acids, at high rate, can be obtained.