(674e) Effects of CO2 On South African Fresh Water Microalgae Growth

South Africa obtains over 80% of its energy needs from fossil fuels. Latest research indicate that South Africa emits over 222 000 000 tones of carbon dioxide (CO2) per year and it is ranked number eight as the world's CO2 emitter. Unabated or controlled emission of CO2 and other green house gases has largely contributed to detrimental global warming and adverse climatic change. Microalgae are capable to convert the hazardous CO2 into valuable biomass. A high CO2 tolerating microalgae was collected from Johannesburg Zoo Lake. Batch cultures were grown on 1000 ml Erlenmeyer flasks. CO2 was bubbled into microalgae culture media. The media contained optimal nutrients and under optimal photoperiod and light intensity and controlled pH. Concentrations of 100 %, 50 %, 25 %, 10 %, and 5 % CO2 and total gas flow rates of 20, 50 and 100 ml/min were used. Final concentrations were made up to 100 % by mixing with nitrogen gas. The aim of this study is to find out the effective CO2 concentrations that gives optimal microalgae growth. Microalgae have at 50% carbon in its dry mass and when all the other nutritional and environmental conditions are not limiting carbon is the main limiting factor. When atmospheric air was supplied at 50 ml/minute the growth rate was 0.1151 per day and it increased drastically by almost 5 folds when 100% CO2 was supplied at 50 ml per minute. At a gas flow rate of 20 ml/min 10 % CO2, growth rate optimal growth rate was 1.42 per day and a dry biomass yield of 809.96mg/l after 12 days. At a gas flow rate 50 ml/min 5% CO2 and the highest growth rate was 1.993 per day and an overall biomass yield of 1200mg/l and the average pH was 6.36, at 100% CO2 the growth rate was 1.265 per day and dry biomass yield of 469.81 mg/l and the average pH was 5.12. When gas flow rate was increased to 100 ml/minute 5 % CO2 the growth rate slightly reduced to 1.30 per day and dry biomass yield of 1000 mg/l, while at 100% the growth rate was 0.34 and dry biomass yield of 279.47 mg/l and the average pH was 5.09. Higher flow rates and higher concentrations resulted in slightly reduced growth due to low pH. These investigations indicate that the species under study is CO2 tolerant.