A systematic comparison of two empirical gas-liquid mass transfer determination methodologies to characterize methane biodegradation in stirred tank bioreactors

Abstract

This study aimed at systematically comparing the potential of two empirical methods for the estimation of the volumetric CH₄ mass transfer coefficient (k_la_CH4), namely gassing-out and oxygen transfer rate (OTR), to describe CH₄ biodegradation in a fermenter operated with a methanotrophic consortium at 400, 600 and 800 rpm. The k_la_CH4 estimated from the OTR methodology accurately predicted the CH₄ elimination capacity (EC) under CH₄ mass transfer limiting conditions regardless of the stirring rate (∼9% of average error between empirical and estimated ECs). Thus, empirical CH₄-ECs of 37.8 ± 5.8, 42.5 ± 5.4 and 62.3 ± 5.2 g CH₄ m^-3 h^-1vs predicted CH₄-ECs of 35.6 ± 2.2, 50.1 ± 2.3 and 59.6 ± 3.4 g CH₄ m^-3 h^-1 were recorded at 400, 600 and 800 rpm, respectively. The rapid Co²⁺-catalyzed reaction of O₂ with SO₃^-2 in the vicinity of the gas-liquid interphase during OTR determinations, mimicking microbial CH₄ uptake in the biotic experiments, was central to accurately describe the k_la_CH4.

Keywords: Biological gas treatment; CH(4); Greenhouse gas; Suspended growth bioreactor; Volumetric mass transfer coefficient.