WANG+Ling　ZHU+jing

【Abstract】Culturing of microalgae has be established as an alternative feedstock for biofuel production due to their fast growth rate and ability to accumulate high quantity of lipid and carbohydrate respectively. However， using this bioresource is still limited duo to low productivity and higher cultivation cost. Genetic and metabolic engineering，photobioreactors play significant role in algal biomass production. Hence， this review is focused on these， aiming at providing useful informations.

【Key words】Microalgae； Biofuel； Bioresource

0 Introduction

Rapid population and industrialization growth result in increase of Global energy demand[1]. At present， the current use of fossil fuels is unsustainable due to its associated global warming and climate changes[2-3].To confront energy shortage and mitigate climate change， more attention has be paied to algal biofuel. Microalgae recognized as one of the oldest microorganisms can convert sunlight to biochemical energy efficiently[5]， and accumulate large quantity of high energy molecules[6]. Base on above， microalgae have been established as one of the most promising alternative for biofuel production.

Currently， the potential and prospect of microalgae for biofuel have received growing interes. However， Culturing of microalgae at industrial scale for biofuels production is still not a huge success[7]. This paper critically assesses the literature on transgenics and metabolic engineering， photobioreactors， aiming at providing useful information.

1 Genetic and metabolic engineering

In order to profoundly impact the viability of algal biofuel production， microalgaes characteristiced by high rate of growth， producing higher yields of lipids/carbohydrates， coaxing the cells to excrete the oil[5]. Fortunately， the requirement can be addressed by genetic and metabolic engineering. Such as improving algal growth rate， reducing the size of the light harvesting chlorophyll antenna. On the other hand， it is important to easy biomass and oil recover. For example， Algae are known to be able to autoflocculate under certain conditions. So it is possible to engineer a cell age triggered autoflocculation mechanism to facilitate recovery of the cells.

2 Photobioreactors（PBRs）

The algal biomass must be produced inexpensively for algal biofuel production. There are two main alternatives for cultivating photoautotrophic algae： open pond systems and PBRs. Currently， the commercial productivity of algal biomass cultured mainly in open ponds. However， the applications of these systems are limited due to lack of precise control， contamination， loss of water by evaporation.

In comparison to open pond， closed PBRs are established as the most promising culturing system. According to reactor geometry， PBRs are classified in to vertical column， tubular and flat panel PBRs. Based on these different PBR configurations， a variety of different technologies have been developed to improve biomass productivity and lower construction cost. However， using this kind of reactors is still limited duo to higher construction cost and energy consumption. Hence， it is necessary to develop cost-effective PBR， such as bag PBR.

3 Using byproducts after lipid extraction

Actually， the retained microalgae biomass also has a huge potential for biofuel production. Recent studies have depicted that some microalgae strains contain high concentration of carbohydrate used as carbon source[8]. Base on this， algae cultivation will become more realistic with diversified products. Consequently， high energy input to operate PBRs can be offset. In fact， there are other potential green technologies that can help to minimize the dependency of fossil fuel in microalgae farm， such as solar panel and wind turbines. Integration of these renewable energies has yet to be discovered to revitalize a truly sustainable algal biofuel production.

4 Conclusion

The production of biofuels using lipid-/carbohydrate-rich microalgae is a very promising alternative to conventional biofuel production approaches. To significantly improve the feasibility of microalgal biofuel production， engineering strategies increasing both growth and lipid/carbohydrate content must be developed and cost-energy effective photobioreactor should be developed.

【References】

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[4]Maity， J.P.， et al.， Microalgae for third generation biofuel production， mitigation of greenhouse gas emissions and wastewater treatment：Present and future perspectives A mini review. Energy， 2014.78：p.104-113[Z].

[5]Stephenson， P.G.， et al.， Improving photosynthesis for algal biofuels：toward a green revolution. Trends in Biotechnology， 2011.29（12）：p.615-623[Z].

[6]Leite， G.B.， A.E.M. Abdelaziz and P.C. Hallenbeck， Algal biofuels：Challenges and opportunities. Bioresource Technology， 2013.145：p.134-141[Z].

[7]Ho， S.， et al.， Perspectives on engineering strategies for improving biofuel production from microalgae—A critical review. Biotechnology Advances， 2014.32（8）：p.1448-1459[Z].

[8]Lu， X.， A perspective： Photosynthetic production of fatty acid-based biofuels in genetically engineered cyanobacteria. Biotechnology Advances， 2010.28（6）：p.742-746[Z].

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