Abstract
Microalgae have been currently recognized as one group of the most potential feedstocks for biodiesel production due to high productivity potential, efficient biosynthesis of lipids and less competition with food production. Moreover, utilization of microalgae with environmental purposes (CO2 fixation, NOX and wastewater treatment) and biorefinery have been reported. However, there are still challenges that need to be addressed to ensure stable large-scale production with positive net energy balance. This review gives an overview of the current status of the application of microalgae in biodiesel production and environmental protection. The practical problems not only facing the microalgae biodiesel production but also associated with microalgae application for environmental pollution control, in particular biological fixation of greenhouse gas (CO2 and NOX) and wastewater treatment are described in detail. Notably, the synergistic combination of various applications (e.g. food, medicine, wastewater treatment and flue gas treatment) with biodiesel production could enhance the sustainability and economics of the algal biodiesel production system.
Highlights
Current trends in energy supply and use are unsustainable – economically, socially, and environmentally (International Energy Agency, 2013a)
Fossil fuels are at the core of energy demand in the transport and electricity generation sectors and account for most – over 80% – of global total primary energy supply (TPES) (International Energy Agency, 2013b)
Growing energy demand for fossil fuels comes from worldwide economic growth and development resulting in the sharp accumulation in CO2 and nitrogen oxides (NOx) emissions, responsible for the majority of greenhouse gas (GHG) emissions worldwide, which bring some irreversible changes to the climate system including global warming
Summary
Current trends in energy supply and use are unsustainable – economically, socially, and environmentally (International Energy Agency, 2013a). This mode of cultivation possesses a number of drawbacks that need to be resolved: (1) the limited number of available heterotrophic algal species, (2) potential contamination by bacteria, (3) inhibition of growth by soluble organic substrates at low concentrations, and (4) the inability to produce some lightinduced products, such as pigments (Chen, 1996) The former three problems can be resolved by screening microalgae strains, which have strong pollution tolerance and are able to grow in heterotrophic condition and adapt to a wide range of organic carbon. The low biomass productivity at field level is its fatal drawback considering the competition of land for traditional crops when commercial developments of microalgae biofuel are promoted (Chen et al, 2013) They are strongly limited by contamination (by other algae, bacteria), the degree of which depends on climatic conditions (for example, it is very difficult to maintain an open algal culture in the tropics during the rainy season). When considering commercial-scale processes for dewatering and recovering algal biomass for further downstream processes, a traditional harvesting method may involve up to two steps:
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