Integrated System for Simultaneous Removal of Nitrogen and Phosphorus by Ulva Lactuca and Its Subsequent Utilization for Biogas Production (Published)
Biogas is a combustible mixture of gases produced by microorganisms when livestock manure and other biological wastes are allowed to ferment in the absence of air in closed containers or reactor. This process design proposes an integrated biogas production system that aims to remove nitrogen and phosphorus from polluted seawater using U. lactuca and consequently utilize this as a feedstock for biogas production. Anaerobic digestion is done in the process which accomplished in three stages: (1) hydrolysis of insoluble polymers, (2) fermentation of monomeric breakdown products and (3) fermentation of acetate and hydrogen from volatile fatty acids and (4) generation of methane. The basis of the design is 1,000 metric tons of purified biogas per year which is intended for kitchen stove application. It can promote utilization of endemic U. lactuca for seawater treatment and at the same time provide livelihood to communities and save the aquatic environment from pollution. In addition, utilizing purified biogas as an additional source of fuel can save the dwindling natural gas and oil reserves in the world. This purified biogas can be an alternative to the conventional LPG (liquefied petroleum gas) used for kitchen stoves since their energy value and price are comparable.
The main aim of this project was to undertake a feasibility study of microalgae biodiesel production from the Cambois peninsular, Northumberland England. This particular project site was chosen for its potential to support microalgae growth i.e. close proximity to both water and CO2 source. Microalgae chlorella specie was chosen for this analysis because of its good productivity (22g m-2 day-1) as well as high lipid content (50% dry weight). The analysis considers 150 days farm production (March to August) due to low temperature in the winter. A comparative analysis of foam column microalgae harvesting process followed by oil extraction through in-situ transesterification was undertaking against the conventional centrifugation-harvesting route followed by conventional tranesterification. Lastly a hybrid of the 2 processes of centrifugation followed by in-situ transesterification was also analysed side by side.
The 3 different biodiesel processing routes were examined based on final biodiesel yield, cost and energy consumption. The centrifugation route provides high biodiesel yield of 115 L ha-1 day-1 but with associated high energy and centrifuge installation cost. Foam column separation yield 110 L ha-1 day-1 with optimum power consumption and installation cost. The hybrid system yield 100 L ha-1 day-1 with minimum power consumption but may suffer set back due to high cost of centrifuge cost and maintenance. The best-case scenario of foam column separation process was further evaluated to validate its economic potential for large-scale biodiesel production as against the current price of fossil diesel. The outcome confirms the potential of microalgae biodiesel to be cost competitive with diesel if the harvesting process is substituted with the foam column separation technique, while the traditional oil transesterification be substituted with the in-situ transesterification technique.