How effective is microalgae treatment of different wastewaters for simultaneous nutrient removal and lipid production for bio-fuel?

[Abstract]: Nutrient removal from wastewaters has been traditionally achieved by activated sludge. In recent years, research has focused on the use of microalgae to simultaneously achieve nutrient removal from wastewaters and lipid production for use as bio-fuel. The effluent that has been polished by algae treatment can be recycled for different beneficial uses. If carbon taxes are introduced, bio-diesel production through algae can potentially become lucrative as this process is virtually carbon neutral when used in conjunction with CO2 mitigation. There are studies available on algae production using piggery, dairy and municipal wastewater but the optimisation of lipid production is yet to be carried out. In addition, the growth rates of algae in different wastewaters and potential lipid production have not been fully established. Hence, in this dissertation, the aim was to investigate the rates of nutrient removal, algal growth and lipid production using the wastewater collected from a leafy vegetable nursery, a wastewater reclamation facility and a dairy. Experiments were conducted using a batch reactor, having a capacity of 3.5L. The reactor was filled with the wastewater and inoculated with Chlorella vulgaris microalgae. Both compressed air and CO2 were supplied to provide the carbon necessary for the algal growth. The required illumination for growth was provided by florescent light. Both pH and DO were monitored every minute and the pH was controlled at a set-point of 7.5 ± 0.5. Data acquisition of the analogue signals from the pH and DO sensors was processed by a personal computer equipped with Labview software. The algal growth rate was monitored by measuring suspended solid concentration and optical density using a spectrophotometer. When the growth entered the death phase, the algae were harvested for lipid measurement. Experimental results indicated that algae can indeed remove nitrogen from nursery, municipal and dairy wastewater at rates of 2.64 mg/L/d, 1.59 mg/L/d and 1.73 mg/L/d respectively. However, nitrification was also detected in all three wastewaters. Phosphorous removal rates from nursery and municipal wastewater were 0.27 mg/L/d and 0.51 mg/L/d which resulted in a N:P utilisation ratio of 49:5 and 3:1 respectively. Lipid production was found to be most successful in nursery wastewater with a maximum total lipid content of 25.5% of the algal dry weight, followed by municipal wastewater with a maximum of 12.8% total lipids of the algal dry weight. The total lipid content benchmark was 20-30% for Chlorella vulgaris. These results obtained from the batch experiments are very promising whereby Chlorella vulgaris microalgae can be successfully utilised for nutrient removal and lipid production from different wastewater. This research will give insight into the feasibilities of using small scale effluent cleaning via algal growth in decentralised businesses, which have the potential to have their own on-site algae farm for producing bio-fuels and CO2 mitigation