Potentials of Exploiting Heterotrophic Metabolism for Biodiesel Oil Production by Microalgae

Abstract

The current prices of microalgae oils are much higher than oils from higher plants (vegetable oils) mainly due to the high cost of photoautotrophic cultivation of microalgae. However, many strains of microalgae can also grow and produce oil using organic carbons, as the carbon source under dark (heterotrophy) or light conditions (mixotrophy). Lipid productivities of most strains of microalgae are higher in culture systems that incorporate heterotrophic metabolisms (presence of organic carbon source) than under photoautotrophic conditions. This is because for many strains, cell growth rates and final cell concentrations are higher in heterotrophic cultures than in photoautotrophic cultures. Furthermore, in some cases, the oil contents of the cells are also higher in cultures incorporating heterotrophic metabolisms. It has also been reported for some strains that the quality of oil produced in the presence of organic carbon sources are more suitable for biodiesel oil production than those produced under photoautotrophic conditions. Thus, heterotrophy can be used to reduce the cost of biodiesel oil production, but the effectiveness of the various organic carbons in supporting cell growth and oil accumulation depends on the strain and other culture conditions. Use of wastewaters for cultivation of microalgae can further substantially reduce the cost of production (since they contain carbon, nitrogen, and other nutrients) and also reduce the requirement for freshwater. Generally, many factors such as nitrogen limitation, phosphate limitation, silicon limitation, control of pH, and low temperature can be used to increase oil accumulation, although their effectiveness depends on the strain and other culture conditions.

Evaluation of Oil Producing Potential of a New Isolate—<i>Chlorella lewinii</i> SUB3545914 for Biodiesel Production under Heterotrophic Cultivation

“…Under heterotrophic cultivation, biomass concentrations were higher for both glucose and glycerol-supplemented media than those obtained in photoautotrophic cultures. This supports the argument that heterotrophic cultures yield more biomass than their autotrophic counterparts [9] [15]. Another major advantage of heterotrophic cultures over the photoautotrophic culture is that it is simpler and cheaper to construct and operate large scale heterotrophic reactors than photobioreactors since light supply and distribution is a big constraint in photobioreactor design and scale up [35].…”

“…[10] [11] [14] [15] [34]. Similarly, lipid accumulation in heterotrophic cultures was significantly higher than the values obtained in photoautotrophic cultures.…”

“…Besides, some heterotrophically cultivated microalgae produce higher oils than their photoautotrophic counterparts [9] [12] [13] [14] [15]. Consequently, heterotrophic microalgal cultivation could offer a better prospect for biodiesel production.…”

Effects of Carbon Source on Growth Characteristics and Lipid Accumulation by Microalga <i>Dictyosphaerium</i> sp. with Potential for Biodiesel Production

“…This attribute is vital since the heterotrophic cultivation of algae has been recommended for biofuel production in terms of the cost of production. It has been pointed out previously that one major challenge of the use of algae for bioenergy is that many species cannot grow heterotrophically [9] [10].…”

“…Not all oils are suitable for biodiesel production de novo. Ogbonna and McHenry [9] and Ogbonna and Moheimani [10] reported that oil quality of heterotrophically cultivated algal cells is better than those under photoautotrophic…”