초록
<P><B>Abstract</B></P> <P>The limited gas–liquid mass transfer represents the main challenge in the operation of cost-effective bioreactors devoted to the treatment of poorly soluble gas pollutants such as methane (CH<SUB>4</SUB>). This study evaluates the influence of internal gas-recycling strategies on the enhancement of CH<SUB>4</SUB> abatement in a bubble column bioreactor inoculated with the methanotroph <I>Methylocystis hirsuta</I>. Maximum CH<SUB>4</SUB> removal efficiencies of 72.9 ± 0.5% (corresponding to elimination capacities of 35.2 ± 0.4 g m<SUP>−3</SUP> h<SUP>−1</SUP>) were recorded under process operation at an empty bed residence time of 30 min and 0.50 m<SUP>3</SUP> <SUB>gas</SUB> m<SUP>−3</SUP> <SUB>reactor</SUB> min<SUP>−1</SUP> of internal gas-recycling rate. The accumulation of poly-3-hydroxybutyrate (PHB) in <I>M. hirsuta</I> was evaluated batchwise under limitations of potassium, manganese, nitrogen, and nitrogen with excess of iron. Nitrogen starvation resulted in the highest PHB content (28 ± 1%). Likewise, the implementation of sequential N starvation cycles in a continuous bubble column reactor operated at a gas residence time of 30 min and an internal gas-recycling rate of 0.50 m<SUP>3</SUP> <SUB>gas</SUB> m<SUP>−3</SUP> <SUB>reactor</SUB> min<SUP>−1</SUP> supported a PHB content of up to 34.6 ± 2.5%, with a volumetric PHB productivity of 1.4 ± 0.4 kg m<SUP>−3</SUP> d<SUP>−1</SUP> and elimination capacities of 16.2 ± 9.5 g m<SUP>−3</SUP> h<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Internal gas-recycling resulted in enhanced CH4 EC at low concentration of 4% in a bubble column bioreactor. </LI> <LI> Continuous bioconversion of CH4 into PHB under long-term operation was feasible. </LI> <LI> N limitation was the most effective nutrient limitation to induce PHB synthesis. </LI> </UL> </P>