(138b) Effects of Nitrogen Ions Concentration On South African Fresh Water High CO2 Tolerant Microalgae Growth

South Africa and the world at large are in a dire need to abate unprecedented CO2 levels that are believed to be causing unstable environment, phenomena generally called climate change. Microalgae are photosynthetic aquatic microorganism. They are promising to be a sustainable means of mitigating green house gas emissions and their biomass has valuable uses ranging from biofuels, organic fertilizers, stock feeds and natraceuticals. They are several factors affecting microalgae growth which includes nitrogen, phosphate, carbon, light, temperature and micronutrients. A thorough understanding of the microalgae growth limiting factors is important to give information to engineers to design efficient green house gas emission abatement strategies. The amount of nitrogen ions required to achieve optimal growth rate and maximum biomass yields need to be investigated and quantified. In this study an unknown green microalgae was collected and isolated from Johannesburg Zoo Lake, South Africa. Batch experiments to determine the effect of nitrogen ions species and concentration were carried in Phytotron growth chambers with fixed light intensity and temperature at 6000 lux and 25°C respectively for 12 hours photoperiod. Microalgae growth was assessed by measuring the optical density at 680nm. The nitrogen ion species used were NH4Cl, KNO3 and NH4NO3.Various nitrogen ions concentrations were prepared using the Beijerick medium in 1000ml Erlenmeyer flasks. The results show that the microalgae have no preferential utilization of nitrogen ion species. However the ammonium nitrate appears to have promoted slightly higher specific growth rates and dry biomass yields followed by ammonium chloride and lastly potassium nitrate though the difference was statistically insignificant. When the microalgae was cultured with a medium of nitrogen ions concentrations of 0 mg/l, 18.75 mg/l and 37.5 mg/l the overall biomass after 12 days was 76.05 mg/l, 130.17 mg/l and 179.90 mg/l respectively, on the 12th day 150 mg/l of nitrogen ions concentration were added to these nitrogen depleted cultures and there was a sudden increase in both growth rate and biomass yields in all experiments. Generally, an increase in nitrogen ion concentration resulted in increased specific growth rates and maximum dry biomass yields and 300 mg/l of nitrogen ion concentration was the maximum point and further increase in concentration resulted in a slightly reduced growth rates. When no nitrogen ions were added the specific growth rate and overall biomass yields were 0.10 per day and 76.05 mg/l respectively and reached reached a maximum of 0.55 per day and 624 mg/l respectively at nitrogen ion concentration of 300 mg/ l. The obtained results indicate the importance of nitrogen ions in developing microalgae culturing system since nitrogen constitute at least 6.5% of the microalgae dry biomass.