A mutant strain of microalga Chlorella sp. for the carbon dioxide capture from biogas

To upgrade biogas produced from the anaerobic digestion of swine wastewater, an outdoor photobioreactor was established in this study. A mutant strain of microalga Chlorella sp. MM-2 was firstly isolated by ethyl methane sulfonate-induced random mutagenesis. The Chlorella sp. MM-2 grew in the presence of gas containing H ₂S < 100 ppm, and the growth capacity of the microalgal culture aerated with 80% CH ₄ was ∼70% that of the control culture (0% CH ₄). In the field study, CO ₂ capture efficiency of the Chlorella cultures, at a biomass concentration of 1.2 g L ^-1, from the desulfurized biogas (∼20% CO ₂, ∼70% CH ₄ and H ₂S < 100 ppm) was approximate 70% on cloudy days and 80% on sunny days. CH ₄ concentration in the effluent biogas from the Chlorella cultures was increased to approximate 84% on cloudy days and 87% on sunny days from its original 70%. The established outdoor photobioreactor system using a gas cycle-switching operation could be used as a CO ₂ capture model for biogas upgrading.