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

The aim of this study was to find an inexpensive and environmentally friendly CO 2 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 CO 2 gas mixed with fresh air. After 5 days of growth, the dry biomass per litre algal culture was slightly higher (17 %) at 6.8 % CO 2 as compared to at 1.2 % CO 2 . A further increase to 17.1 % CO 2 decreased the biomass by about 40 %. Then, the flue gas from a silicomanganese smelter was used as a CO 2 source for growing the algae. The flue gas was characterized by a high CO 2 concentration (about 17 % v / v ), low oxygen concentration (about 4 %), about 100 ppm NO x and 1 ppm SO 2 . The culture medium bubbled with undiluted flue gas contained about 490 mg L −1 dissolved CO 2 and 4.0 mg L −1 dissolved O 2 , while the lowest flue gas concentration contained about 280 mg L −1 CO 2 and 7.1 mg L −1 O 2 . Undiluted flue gas (17.4 % CO 2 ) decreased the biomass of the algae by about 40 % as compared with 4.8 % pure CO 2 gas or flue gas diluted to a concentration of 6.3 % CO 2 . Flue gas diluted to give 10.0 % CO 2 gave less reduction in the growth of the algae (22 %). It was concluded that the high CO 2 concentration itself caused the growth reduction and not the air pollutants, and the very low O 2 concentrations in the growth medium could not counteract this negative effect.