The growth of Chlamydomonas reinhardtii as influenced by high CO(2) and low O(2) 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.