Sustainable production of renewable energy is being hotly debated globally since it is increasingly understood that first generation biofuels, primarily produced from food crops and mostly oil seeds are limited in their ability to achieve targets for biofuel production, climate change mitigation and economic growth. These concerns have increased the interest in developing second generation biofuels produced from non-food feedstocks such as microalgae, which potentially offer greatest opportunities in the longer term. This paper reviews the current status of microalgae use for biodiesel production, including their cultivation, harvesting, and processing. The microalgae species most used for biodiesel production are presented and their main advantages described in comparison with other available biodiesel feedstocks. The various aspects associated with the design of microalgae production units are described, giving an overview of the current state of development of algae cultivation systems (photo-bioreactors and open ponds). Other potential applications and products from microalgae are also presented such as for biological sequestration of CO 2 , wastewater treatment, in human health, as food additive, and for aquaculture.

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Microalgae for biodiesel production and other applications: A review

Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.

/pdf/biofuels-from-microalgae-a-review-of-technologies-for-1t1wwr5e69.pdf

Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: A critical review

The potential of sustainable algal biofuel production using wastewater resources

This paper provides an analysis of the potential environmental impacts of biodiesel production from microalgae. High production yields of microalgae have called forth interest of economic and scientific actors but it is still unclear whether the production of biodiesel is environmentally interesting and which transformation steps need further adjustment and optimization. A comparative LCA study of a virtual facility has been undertaken to assess the energetic balance and the potential environmental impacts of the whole process chain, from the biomass production to the biodiesel combustion. Two different culture conditions, nominal fertilizing or nitrogen starvation, as well as two different extraction options, dry or wet extraction, have been tested. The best scenario has been compared to first generation biodiesel and oil diesel. The outcome confirms the potential of microalgae as an energy source but highlights the imperative necessity of decreasing the energy and fertilizer consumption. Therefore contr...

http://pubs.acs.org/doi/pdf/10.1021/es900705j

Life-cycle assessment of biodiesel production from microalgae.

Thirty microalgal strains were screened in the laboratory for their biomass productivity and lipid content. Four strains (two marine and two freshwater), selected because robust, highly productive and with a relatively high lipid content, were cultivated under nitrogen deprivation in 0.6-L bubbled tubes. Only the two marine microalgae accumulated lipid under such conditions. One of them, the eustigmatophyte Nannochloropsis sp. FM102: 100–112. © 2008 Wiley Periodicals, Inc.

http://biodiesel.persiangig.com/Cultivation/(1)22033_ftp.pdf

Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor.

Fresh olive mill waste deprived of polyphenols as feedstock for hydrogen photo-production by means of Rhodopseudomonas palustris 42OL

Dephenolization of stored olive-mill wastewater, using four different adsorbing matrices to attain a low-cost feedstock for hydrogen photo-production.

Hydrogen photo-evolution by Rhodopseudomonas palustris 6A using pre-treated olive mill wastewater and a synthetic medium containing sugars

Polyhydroxyalkanoates (PHAs) are a family of biopolyesters produced by many bacteria as intracellular storage carbon and energy source. Poly-β-hydroxybutyrate (PHB) is probably the most common type of PHA. It is biodegradable and renewable, with relevant thermoplastic properties along with adjustable thermal and mechanical properties. The thermoplastic properties of PHB and its biodegradability make it a potential alternative to petroleum-based plastics. Several microorganisms growing in the dark and/or in the light produce PHB. The polymer is mainly accumulated in the cytoplasm of cells when microorganisms are growing under conditions of stress. If purple non-sulfur photosynthetic bacteria (PNSB) are grown under nitrogen starvation conditions, a photoevolution of molecular hydrogen occurs as well. The PHB amount increases when carbon and energy sources are in excess, but the growth is limited, for example, by the lack of a nitrogen, phosphorous or sulfur source. This work deals the possibility of producing PHAs by photosynthetic microorganisms belonging to cyanobacteria and PNSB. Different culture broths, with and without organic carbon sources, were investigated to maximize PHA production by photosynthetic microorganisms. An unbalanced agro-industrial wastewater has been also investigated in the present study. It concerns the olive mill wastewater (OMW) containing significant reusable carbon fractions suitable for an eco-efficient valorization by feeding photosynthetic processes. The maximum PHA concentration in a cyanobacterium drybiomass was 317 mg/L, when growing cells in a medium with a low content of acetic acid (LAC). In PNSB drybiomass the maximum PHB content was 215 mg/L, when growing PNSB in a synthetic medium. A simultaneous H2 co-production (1,295 mL/L of culture) was cumulated as well, at the end of the process.

Giulia Padovani

Papers

Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor.

Fresh olive mill waste deprived of polyphenols as feedstock for hydrogen photo-production by means of Rhodopseudomonas palustris 42OL

Dephenolization of stored olive-mill wastewater, using four different adsorbing matrices to attain a low-cost feedstock for hydrogen photo-production.

Hydrogen photo-evolution by Rhodopseudomonas palustris 6A using pre-treated olive mill wastewater and a synthetic medium containing sugars

Phb-rich Biomass and Bioh2 Production by Means of Photosynthetic Microorganisms