CO2 and O2 gas exchange in outdoor thin-layer high density microalgal cultures

Two thin layer culture units operated as batch cultures with the algaChlorella kessleri were used in gas exchange experiments. The mass transfer coefficient Kg [g m−2 h−1 kPa−1] of O2 and CO2 desorption from culture surface decreased with increasing culture temperature. Between 60–70% of supplied CO2 was used for algal growth. It was estimated that the length of growth surface may be extended to about 50 m, without additional saturation by CO2. On average 1.35 g CO2 was consumed by the alga per 1 g of produced O2. Net CO2 consumption (RCO2) and O2 production (RO2) were not inhibited by irradiance. RO2 did not decrease (in some cases it even increased) along the culture surface, despite increased accumulation of O2. Measurement of pO2 where the culture leaves the reactor before being pumped back onto the illuminated surface, correlated with O2 production and CO2 consumption and may be used to monitor the reactors growth performance.