Carbon Capture Using The Microalgae Chlorella Vulgaris in a Packed Bubble Column Photobioreactor

Abstract

In response to increasing pressure to reduce carbon emissions, algae photobioreactors have become central to finding environmentally-sustainable mitigation strategies for carbon capture. Although a good number of photobioreactors have been proposed, only a few of them can be practically used for large-scale algal Co₂ sequestration and for that matter mass production of algae. One of the major factors that limit their practical application with algal mass cultures is mass transfer. Against this background, the purpose of this research was to test a scalable bench scale photobioreactor with a capacity to enhance the mass transfer of Co₂ (gas) into a fresh water Chlorella vulgaris algal culture (liquid) phase. To achieve this, a packed vertical column being referred to as a Packed Bubble Column Photobioreactor (PBCP) was used to increase gas-liquid contacting surface area enhancing the mass transfer of the gas into the liquid phase. The dynamics of the PBCP showed more moles of Co₂ were transferred with higher composition of inlet Co₂ at same algal culture composition. Higher algal culture concentration showed lower composition of Co₂ in the outlet gas from of the reactor. Co₂ increased in outlet gas composition with increasing rate of moles of Co₂ into the reactor. During 45 minutes of steady state semi-continuous experimental test runs with 350 mL of algal culture at 0.21 and 0.35 g/L and Co₂ (of 5.0 -- 9.5% composition at flow rate of 25.0 mL/min to 112 mL/min); Co₂ transferred into the algal culture phase was typically in the range of 10 to 30%. These results have shown that the PBCP is able to significantly enhance the transfer of Co₂, and reductions of carbon dioxide greater than 30% are achievable with higher algal cultures and Co₂ composition in the reactor.