What is the importance of microalgae harvesting? Before we discuss about the importance, first we need to understand the position of microalgae harvesting especially in the production of biofuels.
Sustainable production of biofuels is being debated worldwide because it is increasingly understood that biofuels produced from food and crops and lignocellulosic sources are limited in their ability to accomplish goal for biofuel production, climate change mitigation, and economic growth. Biofuels production from microalgae offers great opportunity in the development of biofuels.
Existing steps for biodiesel production from microalgae involve a production unit where microalgae is cultivated, followed by separation of the microagla biomass from the growing media and subsequent downstream processing, such as dewatering, drying, and lipid extraction. After that biodiesel or other biofuels are produced in similar methods to existing processes and technologies used for other biofuels feedstock. Figure below is a diagram representation of microalgae biomass production step, starting from the selection of microalgae species, followed by the Microalgae harvesting, processing and oil extraction to supply the biodiesel production unit.
Microalgae harvesting is the concentration of diluted algae suspension, typically 0.02%-0.06% total suspended solids (TSS) into a thick microalgae paste with concentration of 15%-25% TSS or depending on the target process objective. Table below shows that it is possible to obtain the desired microalgae concentration by a one or two step Microalgae harvesting step, which includes a primary harvesting that form slurry followed by a secondary dewatering step that produces an algal cake.
One of a main difficulty in the integrated microalgae harvesting of biofuels is harvesting the microagae from the growth medium efficiently in an economical way. Microagae harvesting can be a considerable problem because of the small size (3-30 micrometer in diameter) of microalgal cells. Culture broth are relatively dilute (less than 0.5 kg/m3 dry biomass in some commercial production system) and thus large volumes of culture need to be processed to recover the biomass. In addition, microalgae harvesting a a major bottleneck to microalgae bioprocess engineering owing to its high operating cost. Thus reducing the cost of microalgae harvesting step is very essential. If microalgae can be concentrated about 30-50 times by coagulation – flocculation and gravity sedimentation prior to sedimentation, the energy demand for microalgae harvesting could be significantly reduced.
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