Design of an experimental bioreactor for measurements of microbial photosynthetic carbon dioxide fixation
Atmospheric CO2 concentrations have risen from 280 ppmv in 1800-1890 to 376 ppmv in 2004, due to human-induced interactions with the environment. This change in CO2 concentration has increased the efficiency of the greenhouse effect on the planet, and it has been implicated for increasing global temperatures by 0.82°C since 1866. The international community has reacted to this global warming by drafting the Kyoto protocol agreement. An objective of the Kyoto Protocol is to create new technologies capable of capturing and sequestering atmospheric CO2. The objective of this thesis research was to design and construct an experimental bioreactor for quantifying the conversion CO2 into organic matter by photosynthetic bacteria. This bioreactor used light emitting diodes to supply light energy, measured media pH and electrical conductivity, and controlled CO2 gas intake. The bioreactor was equipped with a gas-sampling chamber that allowed measurements of humidity, gas pressure and the gas outflow from the reactors. Data collected during a series of incubation experiments, ranging from two days to seven days, were used to estimate bacterial photosynthetic CO2 fixation. Photosynthetic rates were measured for 'Rhodopseudomonas palustris', a purple, non-sulfur bacteria, and for 'Rhodobacter capsulatus', a green non-sulfur bacteria. For 'Rhodopseudomonas palustris', the CO2 uptake rates ranged from 0.543 g CO2 g-1 cell mass h -1 to 1.038 g CO2 g-1 cell mass h -1; and for 'Rhodobacter capsulatus' the CO2 uptake was 0.359 g CO2 g-1 cell mass h-1 . These rates of CO2 consumption were similar to those reported for bacterial growth under natural conditions.