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

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.