Impact of heterotrophic and mixotrophic growth of microalgae on the production of future biofuels

Currently, many different feedstocks and processes for biofuel production, either physicochemical, biochemical or thermochemical, are under discussion and research. One of these options is the production of biodiesel from algae oil. Algae are the most diverse group of plants on earth; they have a much higher specific yield than land-based crops and another significant difference to other plants is their ability to grow heterotrophically, mixotrophically or photoautotrophically. For the first two metabolisms listed, additional organic nutrition (e.g., glucose) is needed. The theoretical efficiency of the production of biodiesel from heterotrophic algae fed with glucose is up to 75%. However, since glucose or other organic nutrients also have to be produced (in most cases produced from land-based crops), the photosynthetic efficiency of this production has to be added to the overall efficiency of the process. This suppresses most advantages of photoautotrophic algae and degrades it to a refinement process. Nevertheless, mixotrophic growth should be investigated further with regard to the mass production of algae because it might be a way of keeping the features of photoautotropic growth and enhancing it by the partial use of organic nutrients.