when applying low concentrations of 20 mM MDEA for scrubbing in comparison to CO2 absorbed in a phosphate buffered liquid alone. The CH4 production rate increased until it peaked at 63.6 ± 2.5 NmLCH4 L - 1 culture h -1 with an MDEA concentration of 30 mM. The lower CH4 production rates at 0-20 mM MDEA compared to that at 30-70 mM indicated that too low CO2 concentrations could in fact reduce the metabolic processes due to substrate limitation of the CO2, as was previously seen for the methanogen Methanobacterium congolense . The conversion rate remained at a stable level up to 70 mM MDEA, following a general decline in CH4 production which continued to a MDEA concentration of 400 mM, where the CH4 productivity had been diminished to 2.1 ± 0.4 NmLCH4 L -1 culture h -1 and entirely inhibited at 500 mM MDEA. Regardless of the inhibition of biomethanation at higher MDEA concentrations, the amine assisted biomethanation demonstrated accelerated CH4 productivities up to an MDEA concentration of 170 mM in comparison to the positive control which had a CH4 productivity of 32.8 NmLCH4 L -1 culture h -1 . Thus, the biomethanation conversion rate was increased by 1.77 times by applying a 30 mM N2:CO2 saturated MDEA compared to the control, where gaseous CO2 and H2 was added to the headspace of the reactor without amine solvent, which is a method previously reported for examining biomethanation systems . The gradual decline in CH4 productivity as a response of the increased MDEA concentrations past 30 mM indicate that the aqueous amine possesses certain inhibitory characteristics. In this context, the inhibitory characteristics of the aqueous amine could be attributed to the antimicrobial activities that many alkanolamines have been found to exhibit at higher concentrations . This inhibitory effect may become more profound at the presence of amine degradation products from potential oxidative and microbial degradations of the amines. Additionally, the hydrogenotrophic methanogens for biomethanation have an optimal growth within a pH ranging from 6.5 to 8.5 depending on the specific species , and the alkaline properties of the MDEA solvent solution therefore constituted non-optimal pH conditions for methanogens of 10.63 at 20 mM and 11.08 at 500 mM. A PBS buffer was therefore employed to maintain the isotonicity and reduce the pH to 9.62 and 10.51 respectively. Although reduced, these high pH levels would still render the methanogens inhibited, but as the aqueous amine solutions were saturated with CO2, their pH was reduced from >10 to pH 6.71 (wo. PBS buffer) and 6.67 (w. PBS buffer) at 20 mM MDEA and 7.57 (wo. PBS buffer) and 7.50 (w. PBS buffer) at 500 mM MDEA, which was within the optimal range for methanogenic growth. PBS was the only chemicals applied to the process to demonstrate the simplicity of the system and the methanogenic response to the amines. Accordingly, because of the moderate pH effects caused by the addition of PBS, the results suggested that the system could also be employed even without addition of a buffering agent.