Heterotrophic Algae Products
Currently, the world market trades a slightly increasing amount of 20’000 tons of dried microalgae per year. Microalgae are mostly manufactured in pills or pelletized form for food supplement or as functional ingredient in food in extracted or concentrated form. Cosmetic and pharmaceutical applications of microalgae are possible.
Algae production today
Photobioreactors produce just a small percentage of the current worldwide algae production. 
The major part of the traded algae is produced in open systems, so-called open raceway ponds. The open construction of the ponds allows contaminants from the environment to enter the algae culture and hence causes frequent quality fluctuations. In addition, the areal productivity is low due to the high depth of the algae suspension. There are only a few spots worldwide, which provide sufficiently clean environmental conditions for valuable biomass from open systems. The spots can mostly be found in very dry and warm regions causing enormous water consumption through evaporation and chilling. Investment and operating costs have forbidden a phototrophic breakthrough until today.
A proven economic success of an algae production at industrial scale has not occurred yet. Researchers discuss time frames of twenty years or more they will need to develop technologies with proven economic feasibility. This is why phototrophic microorganisms are produced heterotrophic for some specific products.
Unsaturated omega-three fatty acids (e.g. DHA)
The PUFA docosahexaenoic acid (DHA) is produced in large scale with heterotrophic cultivation of Schizochytrium, which is an alga from coastal marine origin. The DHA can be extracted from the harvested algae and be sold for high prices after a purification process. The algae can also be added to fish feed in aquaculture or to other livestock feed in unprocessed or dried form. This sensitive alga requires a very clean environment as it is not very fast-growing.
Colorants (e.g. Astaxanthine)
Algae produce many different colorants when growing on light. The colorants aim on absorbing the light energy or protect the algae cells against damage from the UV-percentage of sunlight. The green alga Haematococcus pluvialis produces e.g. the deep red carotenoid Astaxanthine, when exposed to strong sunlight or another source of stress. Various blue algae additionally produce the yellow-gold Xanthophyll Lutein or the deep blue Phycocyanine. Specific colorants can be produced in economically relevant amounts without light in heterotrophic production systems. World market prices of the mentioned colorants from classical plant ressources have recently increased a lot and cause an increasing number of related algae projects.
Plant cell cultivation
Plant cells are a resource which has been sorted into agriculture by the biotechnology for a long time. But the huge variety of novel opportunities from the cultivation of isolated specific plant cells currently moves into the focus of research and industry. Recent publications from the Columbian University of Medellin show an orange juice from orange cells which have been produced in a sterile bioreactor. The juice could not be distinguished from a pressed one except the missing orange flesh. The cultivation of cells from the yew tree, which belongs to the conifers, is more common and established. These evergreen bushes form Taxanes, which are an active agent in anti-cancer preparations.
The high requirements for purity and the sensitive organisms demand for controlled productions under sterile conditions with both of the mentioned products. Concerning the yew tree, the biotechnological yew cell production prevents deforestation of the rare yew forests.
Inoculum for algae production
Many algae production facilities may need high-quality biomass for inoculation. Larger amounts of inoculum biomass can be supplied by heterotrophic algae production due to its sterile cultivation conditions. Start-up phases can be skipped and the related risk of contamination is reduced close to zero. After finishing a phase with light sensitivity phototrophic organisms can proceed under phototrophic conditions. The heterotrophic start-up biomass production is already established with some economically relevant species like e.g. Chlorella vulgaris (Glucose as carbon source) or with the genetic researcher’s favorite Chlamydomonas rheinhardtii (Acetate as carbon source). Due to the fact that some fast-growing bacteria can metabolize the mentioned carbon sources as well, the process has to be kept as sterile as possible.
Biofuel from algae
The public financial support of biofuel from algae has led to an interesting development in the USA. A leading company of the algae biofuel sector has a business model which is based on heterotrophic algae production. These are processed with an adapted refinery technology to biofuel, which is then sold on the market but mainly to the US Navy and the US Air Force. The original idea of the program has been to support the development of crude-oil replacement products from sunlight and CO2. But the former idea is missed with that business model, as the carbon sources for heterotrophic algae cultivation must be supplied by agriculture or industry. This concept has only proven the general technological feasibility of biofuel from algae.