Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr Amarjeet Bassi

Abstract

Two challenging problems facing our world are the exhaustion of fossil fuels and climate change. Microalgae are eukaryotic phototrophs or prokaryotic cyanobacteria (blue green algae) that are able to capture CO2 and produce lipids suitable for biodiesel, thus can mitigate these challenges. The potential application of microalgae biomass for biofuel production is a clean and sustainable approach to replace fossil fuels. An important consideration for reducing the cost of biofuel is the economical production of algal biomass with high lipid yields. In this study, the marine microalgae Nannochloropsis gaditana were investigated for biomass and lipid production using two wastewater streams, i.e., road salt run-off and vegetable Greenhouse industry effluents as the growth media using batch or fed-batch cultivation. The recovery of biomass was also investigated using coagulants or pH change.

In the first phase of the research the effect of salinity on biomass concentration and lipid production was examined in the batch cultures. Increasing the concentration of salt in the nutrient road salt growth media increased the lipid content from 17% to 21.6% (w/w dry weight) which had the 70%(w/w) of long chain fatty acid, which are suitable for the biofuel production.

The fed-batch cultivation system was next applied to provide the nutrition sufficient, depletion and repletion conditions. Three different feeding strategies were examined: continuous, pulse and stage feeding for the effect on biomass and lipid yields. The best condition of the feeding regime was identified as pulse feeding based on the substrate to biomass conversion and lipid yield, which resulted the biomass of 2.08+/-0.03g. The increased light intensity doubled the lipid yields with the maximum of 58% (w/w) lipid content and the lipid productivity of 47mg/L/day was obtained.

The final phase of the study evaluated the flocculation methods to harvest the biomass from the growth media using two approaches: coagulant chemical addition and pH change. The pH values of 11-threshold pH for the alkaline flocculation of cells above, which the cells flocculate at the faster rate and the harvesting efficiencies over 90%, were achieved. The harvesting efficiency of 95% was achieved with ferric chloride with concentration factor of 23.5. The bio-coagulant chitosan was not effective to coagulate the cells.


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