The potential of algae biodiesel in Hong Kong

Abstract

Biofuel production from renewable sources is regarded as one of the most sustainable substitution of fossil fuels, and a feasible solution to achieve environmental and economic sustainability. Biofuels derived from microalgae are regarded as third generation biofuels. Microalgae has rapid growth rate, CO2 fixation ability, high biomass productivity and high yield of lipid, and they can be cultivated on non-arable land or in brackish water, thus avoiding competitions for limited arable lands and water resources, especially the land resources in Hong Kong are particularly limited. Maximum production of microalgae can be achieved under subtropical conditions in Hong Kong. A pilot scale experiment was conducted to produce biodiesel using algae as feedstock. Spirulina platensis, Chlorella vulgaris and Isochrysis galbana were selected to be cultivated for biodiesel production. S. platensis and I. galbana were cultivated in glass tanks in the laboratory using Zarrouk medium and F/2 medium respectively as culture media, covered by transparent plastic film to prevent contamination, and have LED light with 14:12 light and dark cycle. C. vulgaris was cultivated using modified Zarrouk medium as culture media, in open tank on the rooftop and exposed to direct sunlight. Air pump was used to provide CO2 to the culture. In harvesting process, S. platensis was harvested by filtration, while C. vulgaris and I. galbana were harvested by CTAB-aided foam flotation and flocculation, followed by sedimentation and filtration. In oil extraction, hexane and methanol (2:1 v/v) were used as solvent for Soxhlet extraction for 8 hours. Transesterification was carried out to convert extracted oil into biodiesel, by mixing extracted oil with methanol (60:1 molar ratio) as base and NaOH (1.25 % w/w) as catalyst under 65 °C with constant shaking at 250 rpm for 3 hours in an incubator. GC-MS was used to analyse the presence of different fatty acids methyl esters. The results show that I. galbana derived biodiesel has FAME content rich in monosaturated fatty acids and monounsaturated fatty acids from C14 to C22, and I. galbana has the highest oil content with 60.6 % dry cell weight and highest biomass productivity of 0.77 g/L among other microalgae species, which is a promising potential candidate as biodiesel feedstock. In terms of the potential of mass production of algae biodiesel in Hong Kong, urban wastewater in Hong Kong has relatively high salinity because of the use of seawater for the toilet flushing system, which provides a suitable condition for cultivating marine algae species. The algae-based wastewater treatment coupled with the cultivation of microalgae for biodiesel production has the potential to greatly enhance the economic efficiency of biomass production, and reduce the environmental and economic cost, which is a win-win approach. The supports from the government are critical to the development of the algae biodiesel industry in Hong Kong. The government can provide financial funding to establish an algae biodiesel research and development programme with industry-university-government collaboration in the form of public-private partnership, coupled with different biofuel policies such as mandatory requirement and target of biofuel use, subsidy for biodiesel, and carbon tax.