were used to supply a gas stream of N2 and CO2 in an 80:20 ratio at a total rate of 150 mL min -1 . The gas stream was bubbled through the aqueous amine solutions with a cylindrical aquarium bubble stone diffuser to increase the bubble surface area and attain a rapid and adequate scrubbing of the CO2. Concurrently with the CO2 scrubbing, the pH would decrease as a result of the CO2 absorption and its conversion into carbamate compounds. Thus, the pH was measured before and during the CO2 scrubbing with a pH meter (Mettler-Toledo, Five Easy), and the scrubbing was continued until the pH had remained stable for at least 5 minutes to confirm that the amine scrubbing liquid was fully saturated with CO2. The fresh inoculum was supplied from a 1200 m 3 thermophilic manure-based anaerobic digester (Foulum, Denmark), and the batch bottles were inoculated a few hours after the extraction to maintain a high microbial activity. The fresh inoculum was screened with a 1 mm mesh-sized sieve to remove coarse biomass residues, and hereafter transferred to the batch bottles, where it constituted 4.3% of the total liquid volume (2 mL). For tests with C12-DMAPA inoculum concentrations of 4.3 wt%, 8.3 wt% and 20.3 wt% of the total liquid were applied. The headspace of the batch reactors was flushed with bottled H2 (Air Liquide) and afterwards pressurized to an average total pressure of 1.56 ± 0.06 bar with mass flow controllers. The overall gas to liquid volume ratio thereby constituted 1.55 (Vgas/Vliquid) in the batch reactors at the beginning of the inoculation.