Enhancing dilute methane treatment through liquid phase alteration in a capillary bioreactor

Abstract

This study aimed to maximize the treatment of dilute methane emissions (<5% v/v) using a capillary bioreactor (CBR) to overcome the mass transfer limitations commonly encountered in biological technologies. Three universally used non-ionic surfactants (BRIJ 58, TWEEN 60 and SDBS) were tested for their ability to enhance methane bioavailability when combined with a non-aqueous liquid (silicone oil). The study evaluated each surfactant’s effectiveness in increasing methane bioavailability, enhancing the cell hydrophobicity of a mixed culture of methane oxidizing bacteria, and improving the oil-in-water emulsion capacity at a concentration low enough to eliminate the risk of microbial inhibition. BRIJ 58 was selected and showed in combination with silicone oil potential to enhance gas–liquid mass transfer by >50 % in a capillary channel under segmented (Taylor) flow regime. The optimised liquid phase in the CBR supported stable removal of the methane (∼4500 ppm_v = 0.45 % v/v) with elimination capacities over 200 g m^-3h⁻¹ at an empty capillary channel gas contact time of 23 s, which is one order of magnitude lower than the empty bed gas contact time of conventional biological gas treatment methods treating dilute methane. The improved emulsification of the oil-in-water emulsion combined with enhanced cell hydrophobicity appeared to be the main mechanism. Internal gas recirculation was applied to decouple the optimal gas–liquid turbulence conditions inside the capillary channel from the actual gas retention time. The study demonstrated that the addition of 20 % silicon oil and 160 mg L^-1 BRIJ 58 significantly improved the overall methane abatement performance.