A hollow fiber membrane photo-bioreactor for CO2 sequestration from combustion gas coupled with wastewater treatment: a process engineering approach.

BACKGROUND: In the presence of light, micro-algae convert CO 2 and nutrients to biomass that can be used as a biofuel. In closed photo-bioreactors, however, light and CO 2 availability often limit algae production and can be difficult to control using traditional diffuser systems. In this research, a hollow fiber membrane photo-bioreactor (HFMPB) was investigated to: (1) increase the interfacial contact area available for gas transfer, (2) treat high nutrient strength (412 mg NO 3 - -N L -1 ) wastewater, and (3) produce algal biomass that can be used as a biofuel. RESULTS: A bench scale HFMPB was inoculated with Spirulina platensis and operated with a 2-15% CO 2 supply. A mass transfer model was developed and found to be a good tool to estimate CO 2 mass transfer coefficients at varying liqu id velocities. Overall mass transfer coefficients were 1.8 × 10 -6 , 2.8 × 10 -6 , 5.6 × 10 -6 m s -1 at Reynolds numbers of 38, 63, and 138, respectively. A maximum CO 2 removal efficiency of 85% was observed at an inlet CO 2 concentration of 2% and a gas residence time (membrane-lumen) of 8.6 s. The corresponding algal biomass concentrations and NO 3 removal efficiencies were 2131 mg L -1 and 68%, respectively. CONCLUSION: The results show that the combination of CO 2 sequestration, wastewater treatment and biofuel production in an HFMPB is a promising alternative for greenhouse gas mitigation.