Efficient storage and utilization of CO2 in open raceway ponds for cultivation of microalgae

Abstract

For efficient storage and utilization of CO2 in open raceway ponds, the effects of cultural and operational parameters were studied. A 10 m2 indoors raceway pond was operated to determine CO2 storage capacity, average rate of absorbed CO2 losses and mass transfer coefficient for CO2 outgassing from various pH, salinity and alkalinity regimes of culture medium; mixing velocities and culture depths. Average rate of CO2 outgassing for saltwater (35 ppt salinity) at 40 meq/L alkalinity was 40-fold higher than seawater (35 ppt salinity and 2.3 meq/L alkalinity) at pH 8. Operating at lower pHs or salinities aggravated CO2 outgassing. An empirical equation for CO2 outgassing average mass transfer coefficient, \(\bar K_L \), was developed as a function of mixing velocity and depth. Nannochloropsis sp. PTCC6016 was cultivated in the pond for 14 days. Due to higher amount of outgassing, CO2 utilization efficiency declined as the productivity in the pond decreased.