High cell density submerged membrane photobioreactor (SMPBR) for microalgae cultivation

Abstract

Microalgae have been extensively studied as a potentially sustainable biomass resource. However, its cultivating and harvesting system faces many challenges due to the low cell density of microalgae. Recently, membrane technology in microalgae cultivation is believed to improve the CO2 gas-liquid mass transfer. It could generate more uniform microbubbles to prolong the gas retention time in the culture solution. This study used a submerged membrane photobioreactor (SMPBR) based on a hydrophobic polypropylene membrane as a CO2 diffuser for producing high cell density microalgae. The SMPBR performance during Chaetoceros calcitrans batch cultivation in a modified f/2 (Guillard) medium was investigated. Results show that Chaetoceros calcitrans growth follows a sigmoid mode without a lag phase until it reaches the stationary and death phase. Cultivation using SMPBR also intensified the biomass concentration, initially from 7.0 x 106 cells/mL up to 4.8 x 108 cells/mL. In 7 days of cultivation under 3% of CO2 and 1.8 L/min of inlet gas flow rate, a maximum biomass concentration of 2.1 g/L was achieved with a maximum specific growth rate of 2.1 day1. Results show that the SMPBR configuration effectively supplies CO2 to a microalgae culture due to the high CO2 transfer in the medium. Moreover, it has the potential application for producing high cell density microalgae.