The two-step bubble column-photobioreactor
photosynthetic biogas
upgrading system can enable simultaneous production of biomethane
and value-added products from microalgae. However, due to the influence
of a large number of variables, including downstream processes and
the presence of microalgae, no unanimity has been reached regarding
the performance of bubble column reactors in photosynthetic biogas
upgrading. To investigate this further, the present work documents
in detail, the design and commissioning of a lab-scale bubble column
reactor capable of treating up to 16.3 L/h of biogas while being scalable.
The performance of the bubble column was assessed at a pH of 9.35
with different algal densities of
Spirulina platensis
at 20 °C in the presence of light (3–5 klux or 40.5–67.5
μmol m
–2
s
–1
). A liquid/gas
flow (L/G) ratio of 0.5 allowed consistent CO
2
removal
of over 98% irrespective of the algal density or its photosynthetic
activity. For lower concentrations of algae, the volumetric O
2
concentration in the upgraded biomethane varied between 0.05
and 0.52%, thus providing grid quality biomethane. However, for higher
algal concentrations, increased oxygen content in the upgraded biomethane
due to both enhanced O
2
stripping and the photosynthetic
activity of the microalgae as well as clogging and foaming posed severe
operational challenges.