Proof-of-concept of a hollow biofilm photobioreactor using engine exhaust gases

The aim of this work was to study the performance of a perfused biofilm system based on hollow biofilm photobioreactors (HB-PBR) at a pilot plant scale using engine exhaust gases over a year. Biomass productivity, rate of biofilm growth, biofilm composition and tightness against CO2-enriched air leakage were assessed in a pilot plant of fifteen HB-PBR panels (90 m2 biofilm surface area in all) inside a polycarbonate greenhouse. A mixture of four microalgae (Chlorella sp., Scenedesmus sp., Chlamydomonas sp. and Ankistrodesmus sp.) was used as a starter medium for biofilm growth. Mean biomass productivity over a year of continuous operation of the pilot plant amounted to 3.07 g center dot m-2 center dot day-1 for an indoor mean PAR irradiance of 16.85 mol center dot m-2 center dot day-1, considering the footprint of the system. The rate of biofilm growth, assessed as the slope of the linear regression function between monthly mean vertical biomass productivity and monthly mean vertical PAR irradiance, was 0.1802 g center dot mol-1 over a year. Biofilm composition varied with the time but overall, Chlorella sp. was the dominant species. Tests of tightness proved that engine exhaust gases can be safety supplied into the HB-PBR inner chamber for biofilm growth without leakage to greenhouse ambient air. Finally, considerations for integrating HB-PBRs with carbon emitting industries were made.