Strengthening CO2 dissolution with zeolitic imidazolate framework-8 nanoparticles to improve microalgal growth in a horizontal tubular photobioreactor

Abstract

Low dissolution of CO2 in closed tubular photobioreactors results in insufficient carbon source supply, and often limits microalgae growth. An optimized ZIF8-SE medium containing zeolitic imidazolate framework-8 (ZIF-8) nanoparticles was developed for strengthening CO2 mass transfer in the photobioreactor, which improved CO2 dissolution to increase microalgal biomass yield under 15% CO2. The CO2 mass transfer coefficient markedly increased from 1.82 to 3.85, leading to an increased dissolved inorganic carbon concentration. Meanwhile, microalgae biomass accumulation with 0.01 mmol/L ZIF-8 nanoparticles was 25.5% higher than that without ZIF-8 nanoparticles. Furthermore, the average cell size decreased from 2.61 to 2.38 μm and the cell fractal dimension increased from 1.38 to 1.56 when ZIF-8 nanoparticle concentration increased from 0 to 0.2 mmol/L, indicating that potential toxicity might occurred with excess ZIF-8 nanoparticles. Reutilization of ZIF-8 nanoparticles in the recycled culture medium improved microalgal growth by 23%, which was similar to the promotion of fresh ZIF8-SE medium. This new finding provides a new strategy to improve CO2 mass transfer in the horizontal tubular photobioreactor, which makes it a feasible platform for CO2 capture and utilization.