Influence of design and operational parameters of a Taylor flow reactor on the bioconversion of methane to ectoines

Abstract

Ectoine is one of the most attractive bioproducts due to its high market price and applications. Methanotrophic bacteria can synthesize ectoine from biogas. In this work, key design and operating parameters were optimised to maximise the bioconversion of methane to ectoine in a novel Taylor Flow bioreactor. This bioreactor configuration is characterized by higher gas-liquid mass transfer coefficients compared to conventional bubble column bioreactors. Thus, the influence of the internal gas recirculation flow rate (1.0 L·min−1, 2.5 L·min−1, 4.0 L·min−1, 5.5 L·min−1) at 60 and 120 min of gas residence time (GRT), the liquid recirculation flow rate (0 L·h−1, 141 L·h−1, 165 L·h−1, 395 L·h−1, 434 L·h−1) and the capillary length (1.50 and 0.75 m) was evaluated using a mixed methanotrophic consortium. Process operation at 120 min of GRT and 5.5 L·min−1 of gas recirculation flow rate enhanced methane bioconversion, resulting in a maximum efficiency of 83.8 ± 2.7 %. The decrease in capillary length from 1.5 to 0.75 m did not enhance methane bioconversion. Intracellular ectoine and hydroxyectoine reached maximum contents of 105.1 ± 8.6 mgEC·gTSS−1 and 33.4 ± 11.7 mgHE·gTSS−1, respectively. Nitratireductor was the dominant genus, while Methylomicrobium and Methylophaga were the main methanotrophic bacteria detected in the consortium. This study confirmed the feasibility of bioconverting novel renewable feedstocks such biogas into high-added value bio-products, boosting the circular and carbon neutral economy in bio-based industries.