The growth of Chlamydomonas reinhardtii as influenced by high CO2 and low O2 in flue gas from a silicomanganese smelter

Abstract

The aim of this study was to find an inexpensive and environmentally friendly CO2 source for growing the hydrogen-producing microalgae Chlamydomonas reinhardtii. The effect of different flue gas concentrations from a silicomanganese smelter on the growth of these algae at a photon flux density of 200 μmol photons m−2 s−1 applied 24 h day−1 was studied. First, the algae were grown in a laboratory at 1.2, 6.8 and 17.1 % (v/v) pure CO2 gas mixed with fresh air. After 5 days of growth, the dry biomass per litre algal culture was slightly higher (17 %) at 6.8 % CO2 as compared to at 1.2 % CO2. A further increase to 17.1 % CO2 decreased the biomass by about 40 %. Then, the flue gas from a silicomanganese smelter was used as a CO2 source for growing the algae. The flue gas was characterized by a high CO2 concentration (about 17 % v/v), low oxygen concentration (about 4 %), about 100 ppm NOx and 1 ppm SO2. The culture medium bubbled with undiluted flue gas contained about 490 mg L−1 dissolved CO2 and 4.0 mg L−1 dissolved O2, while the lowest flue gas concentration contained about 280 mg L−1 CO2 and 7.1 mg L−1 O2. Undiluted flue gas (17.4 % CO2) decreased the biomass of the algae by about 40 % as compared with 4.8 % pure CO2 gas or flue gas diluted to a concentration of 6.3 % CO2. Flue gas diluted to give 10.0 % CO2 gave less reduction in the growth of the algae (22 %). It was concluded that the high CO2 concentration itself caused the growth reduction and not the air pollutants, and the very low O2 concentrations in the growth medium could not counteract this negative effect.