A novel porous nickel-foam filled CO2 absorptive photobioreactor system to promote CO2 conversion by microalgal biomass

Abstract

In order to solve problems associated with a short residence time and low conversion efficiency when CO₂ gas is aerated directly into raceway ponds, a novel porous nickel-foam filled CO₂ absorptive photobioreactor system was developed to promote CO₂ conversion to NaHCO₃ in a short time to improve photosynthesis of microalgal cells. Numerical simulation showed that the porous nickel-foam promoted the Na₂CO₃ solution radial velocity and CO₂ volume fraction in the CO₂ absorption reactor, which enhanced the reaction rate of CO₂ gas and soluble Na₂CO₃. The conversion efficiency of CO₂ gas to soluble NaHCO₃ gradually increased with an increasing nickel-foam pore diameter and a decreasing CO₂ gas outflow rate, while it first increased and then decreased with an increasing relative nickel-foam height in the CO₂ absorption reactor. The conversion efficiency from soluble NaHCO₃ to microalgal biomass first increased and then decreased with an increasing nickel-foam pore diameter (peaking at 2 mm) and relative height (peaking at 0.24); and CO₂ gas outflow rate (peaking at 2 L/min). The chlorophyll fluorescence measurements showed that a sufficient HCO₃^- supply promoted the quantum ratio used for electron transfer (from 0.19 to 0.23) and the maximum photochemical efficiency (from 0.48 to 0.52), resulting in an increased biomass growth rate (by 1.1 times) when the nickel-foam pore diameter increased from 0.1 to 2 mm.

Keywords: CO(2) conversion efficiency; CO(2) volume fraction; Electron transfer; Maximum photochemical efficiency; Na(2)CO(3) radial velocity; Photobioreactor system.