Methane is a valuable substrate for production of PHB.

Improving superficial gas velocity enhanced PHB production yield.

Internal gas recirculation saved methane.

Reactor geometry affected PHB production yield.

To parity of aspect ratio, larger volumes increased PHB production yield.

The pressing problem posed by plastic pollution has led to other, environmentally friendly alternatives, such as polyhydroxyalkanoates. This work proposes an innovative process to produce poly(3-hydroxybutyrate) by replacing expensive substrates, such as sugars, with methane. A two-step process was simulated: a first fermentation is performed in a continuous mode for 20 days to grow a strain belonging to the genus Methylocystis, while a second semi-continuous and nitrogen-limited fermentation is employed to induce the poly(3-hydroxybutyrate) accumulation within 12 days. The effects of the superficial gas velocity on the mass transfer and the poly(3-hydroxybutyrate) production yields were evaluated. Several scenarios were analyzed to optimize the geometry of the reactors and the methane utilization. The working volume of the reactors, as well as the presence of gas recycling stream, were shown to affect the global yields positively, while improving the aspect ratio from 8 to 19, with equal volume, lowered the fraction of poly(3-hydroxybutyrate) into the biomass by up to 37.5%.

empty bed residence time

methane utilization capacity

biomass produced after growth cycle

PHB produced after accumulation cycle

Polyhydroxyalkanoates

Poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

production of PHB for unit of substrate

production of PHB for unit of reactor volume

virtual residence time

velocity of small bubbles

Biopolymers

Bioplastics

Poly(3-hydroxybutyrate)

Methane

Methanotrophs

Process optimization

© 2022 The Author(s). Published by Elsevier B.V.