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 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 mu mol 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 NO (x) 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 O-2, while the lowest flue gas concentration contained about 280 mg L-1 CO2 and 7.1 mg L-1 O-2. 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 O-2 concentrations in the growth medium could not counteract this negative effect.