Low Cost Microalgal Production for Biofuels: A Review

Background: Autotrophic microalgae carry out the photosynthetic conversion from light into organic compounds. Microalgal cultivation brings environmental advantages, highlighting the capability of nutrient recycling from wastewater combined with C02 fixation from flue gases towards a wide range of 3G biofuels and bioproducts. These micro-organisms have been widely recognized as having huge potential as feedstock for food and feed industries, as "nutraceutical" agents (carotenoids, antioxidants, polyunsaturated fatty acids, single-cell proteins (SCP), phycobiliproteins, polysaccharides, vitamins, phytosterols, minerals), for the cosmetic industry, bioplastics, agriculture biofertilizers and recently as an energetic vector towards the production of a wide range of biofuels. Microalgae exhibit clear advantages when compared with higher plants, such having a higher photosynthetic efficiency, higher areal biomass productivities, higher C02 biofixation rates from flue gases emitting plants, higher 02 production rates, non-competition for agricultural areas (marginal lands such as deserts, rocky areas and salt pans can be used), non-competition for drinking waters (saltwater, brackish water and wastewaters can be used), harvesting routines can be carried out daily with better equipment and better resource management lowering storage costs. Objective: A brief introduction will be presented on microalgal biotechnology with a special emphasis on economics and production costs to date. The key factors which have strongly affected microalgal biomass and/or their product costs will be analyzed and critically discussed, especially concerning biofuels. Results: Several constraints should be overcome in order to achieve a cost-effective microalgal biofuel production, such as the high energy inputs and the still prohibitive production costs (currently around 5000 /ton, far above the desired threshold target of 500 /ton). The attempts carried out by researchers in the last decades in order to decrease microalgal production costs either by increasing productivities and/or product yields or by cutting production factors (low cost bioreactors, cheap culture media formulations, wastewater treatment, greenhouse gases biofixation and low cost downstream processing) will be revised and discussed.