Carboxylates and alcohols production in an autotrophic hydrogen‐based membrane biofilm reactor
Diana C. Calvo, Aura Ontiveros‐Valencia, Rosa Krajmalnik‐Brown, César I. Torres, Bruce E. Rittmann
Abstract
Abstract Microbiological conversion of CO 2 into biofuels and/or organic industrial feedstock is an excellent carbon‐cycling strategy. Here, autotrophic anaerobic bacteria in the membrane biofilm reactor (MBfR) transferred electrons from hydrogen gas (H 2 ) to inorganic carbon (IC) and produced organic acids and alcohols. We systematically varied the H 2 ‐delivery, the IC concentration, and the hydraulic retention time in the MBfR. The relative availability of H 2 versus IC was the determining factor for enabling microbial chain elongation (MCE). When the H 2 :IC mole ratio was high (>2.0 mol H 2 /mol C), MCE was an important process, generating medium‐chain carboxylates up to octanoate (C8, 9.1 ± 1.3 mM C and 28.1 ± 4.1 mmol C m −2 d −1 ). Conversely, products with two carbons were the only ones present when the H 2 :IC ratio was low (<2.0 mol H 2 /mol C), so that H 2 was the limiting factor. The biofilm microbial community was enriched in phylotypes most similar to the well‐known acetogen Acetobacterium for all conditions tested, but phylotypes closely related with families capable of MCE (e.g., Bacteroidales, Rhodocyclaceae, Alcaligenaceae, Thermoanaerobacteriales, and Erysipelotrichaceae) became important when the H 2 :IC ratio was high. Thus, proper management of IC availability and H 2 supply allowed control over community structure and function, reflected by the chain length of the carboxylates and alcohols produced in the MBfR.