Two-stage process for producing oil from microalgae

Abstract

A process for production of biofuels from algae can include cultivating an oil-producing algae by promoting sequential photoautotrophic and heterotrophic growth. The method can further include producing oil by heterotrophic growth of algae wherein the heterotrophic algae growth is achieved by introducing a sugar feed to the oil-producing algae. An algal oil can be extracted from the oil-producing algae, and can be converted to form biodiesel.

What is claimed is: 
     
         1 . A process for production of biofuels from algae, comprising:
 a) cultivating an oil-producing algae by photoautotrophic growth;   b) producing algal oil by heterotrophic growth of the oil-producing algae wherein the heterotrophic growth is fed by introducing a sugar feed to the oil-producing algae; and   c) extracting an algal oil from the oil-producing algae.   
     
     
         2 . The method of  claim 1 , further comprising converting the oil to biodiesel. 
     
     
         3 . The process of  claim 1 , wherein the oil-producing algae includes a member selected from the group consisting of diatoms (bacillariophytes), green algae (chlorophytes), blue-green algae (cyanophytes), golden-brown algae (chrysophytes), haptophytes, and combinations thereof. 
     
     
         4 . The process of  claim 3 , wherein the oil-producing algae includes  Amphipleura, Amphora, Chaetoceros, Cyclotella, Cymbella, Fragilaria, Hantzschia, Navicula, Nitzschia, Phaeodactylum, Thalassiosira, Ankistrodesmus, Botryococcus, Chlorella, Chlorococcum, Dunaliella, Monoraphidium, Oocystis, Scenedesmus, Tetraselmis, Oscillatoria, Synechococcus, Boekelovia , or combinations thereof. 
     
     
         5 . The process of  claim 4 , wherein the oil-producing algae includes  Chlorella, Dunaliella , or combinations thereof. 
     
     
         6 . The process of  claim 1 , further comprising introducing a nitrogen-fixing algae to the oil-producing algae to provide nitrogen as a nutrient. 
     
     
         7 . The process of  claim 6 , wherein the oil-producing algae is the nitrogen-fixing algae. 
     
     
         8 . The process of  claim 6 , wherein the nitrogen-fixing algae includes blue-green algae or cyanobacteria. 
     
     
         9 . The process of  claim 1 , wherein the sugar feed is the primary source of both carbon and energy in the heterotrophic growth stage. 
     
     
         10 . The process of  claim 1 , wherein introducing the sugar feed further includes cultivating algae and extracting the sugar feed therefrom. 
     
     
         11 . The process of  claim 1 , wherein the heterotrophic growth stage is initiated using a stress induction mechanism. 
     
     
         12 . The process of  claim 11 , wherein the stress induction mechanism includes at least one of light deprivation, nutrient deprivation, injection of a reactive oxygen source, a lipid trigger, and chemical additives. 
     
     
         13 . The process of  claim 1 , wherein the photoautotrophic growth stage and the heterotrophic growth stage overlap in time. 
     
     
         14 . The process of  claim 1 , wherein the photoautotrophic growth stage and the heterotrophic growth stage are performed substantially simultaneously. 
     
     
         15 . A biodiesel product formed by the process of  claim 2 . 
     
     
         16 . The biodiesel product of  claim 15 , wherein the biodiesel product is substantially free of sulfur. 
     
     
         17 . The biodiesel product of  claim 15 , wherein the biodiesel product is a fatty acid ethyl ester or an alkane.