Anaerobic Digestion

Use of micro-bubbles has beneficial effects on the methanogenesis phase of Anaerobic Digestion. Using pure carbon dioxide, microbubbles linger in the reactor due to their small size (20 micron) providing a reservoir of CO₂ to facilitate efficient conversion. The microbubbles also strip methane from the liquid so shifting the equilibrium towards completion. Use of pure CO₂ microbubbles has produced over 100% increase in methane production over other techniques. The open access journal article below reports on this lab-bench scale study:

Al-Mashhadani MKH, Wilkinson SJ, Zimmerman WB, Carbon dioxide rich microbubble acceleration of biogas production in anaerobic digestion. Chemical Engineering Science 156 (2016) 24–35.

The journal article speculated that it was the fraction of microbubbles less 100 microns in size that is responsible for the acceleration of biogas production. Logically, seeding nearly all of the microbubbles around ~20 microns in size would give much greater acceleration. In an InnovateUK Energy Catalyst Feasibility Grant, Perlemax and the University of Sheffield tested this hypothesis, as well as upscaled to large lab / pilot plant AD operations for seeding ~20micron pure CO₂ microbubbles for 5 minutes daily. The optimisation study showed 4-6 fold increase in biogas production rates.

The Anaerobic Digestion and Biogas Association and World Biogas Association recognized the work in the 2018 Industry Awards as Highly Commended (2nd out of 200 nominees) for Best Project