Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

Constraints to commercialization of algal fuels.

Potential use of algae for heavy metal bioremediation, a critical review.

a b s t r a c t This paper primarily presents an overall review of the use of microalgae as a biofuel feedstock. Among the microalgae that have potential as biofuel feedstock, Chlorella, specifically, was thoroughly discussed because of its ability to adapt both to heterotrophic and phototrophic culture conditions. The lipid content and biomass productivity of microalgae can be up to 80% and 7.3 g/l/d based on the dried weight of biomass, respectively, making microalgae an ideal candidate as a biofuel feedstock. The set-up of the system and the biomass productivity of microalgae cultivated in an open pond and a photobioreactor were also compared in this work. The effect of the culture condition is discussed based on the twostage culture period. The issues that were discussed include the light condition and the CO2, DO and N supply. The microalgal productivities under heterotrophic and phototrophic culture conditions were also compared and highlighted in this work. The harvesting process and type of flocculants used to aid the harvesting were highlighted by considering the final yield of biomass. A new idea regarding how to harvest microalgae based on positive and negative charges was also proposed in this work. The extraction methods and solvents discussed were primarily for the conventional and newly invented techniques. Conversion processes such as transesterification and thermochemical processes were discussed, sketched in figures and summarized in tables. The cost–benefit analysis of heterotrophic culture and the cultivation system was highlighted at the end of this work. Other benefits of microalgae are also mentioned in this work to give further support for the use of microalgae as a feedstock for biofuel production.

Conversion of microalgae to biofuel

Catalytic deoxygenation of microalgae oil to green hydrocarbons

First test flights using blends with algae oil are already carried out and expectations by the aviation and other industries are high. On the other hand technical data about performance of cultivation systems, downstream processing, and suitability of algae oil as fuel are still limited. The existing microalgae growing industry mainly produces for the food and feed market. Energy efficiency is so far out of scope but needs to be taken into account if the product changes to biofuel. Energy and CO2 balances are used to estimate the potential of algae oil to fulfil the EU sustainability criteria for biofuels. The analysis is supported by lab tests as well as data gained by a pilot scale demonstrator combined with published data for well-known established processes. The algae oil composition is indicator of suitability as fuel as well as for economic viability. Approaches attaining high value fractions are therefore of great importance and will be discussed in order to determine the most intended market.

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Rosa Rosello-Sastre

Papers

Composition of Algal Oil and Its Potential as Biofuel

Biofuels from microalgae: photoconversion efficiency during lipid accumulation.

Effects of nitrate and oxygen on photoautotrophic lipid production from Chlorococcum littorale.