Method for producing biodiesel using high-cell-density cultivation of microalga Chlorella protothecoides in bioreactor

Abstract

A method is provided to produce biodiesel from algae using a strain of microalga chlorella protothecoids , by screening a specific strain with characteristics of high yield of biomass and high oil content, cultivating the screened strain for high-cell-density growth for up to 108 grams of dry cell weight per liter of the suspension in a bioreactor using solutions containing carbohydrates as feed, harvesting and drying the high density cultivated algal cells to extract oil from the dried algal cells, and producing the biodiesel by reaction of catalyzed transesterification using the extracted oil as feedstock.

1 . A method for producing biodiesel from algae using microalga  chlorella Protothecoides  in bioreactors, comprising the steps of:
 screening a specific strain of said  chlorella  Protothecoides with characteristics of high yield of biomass and high oil content;   inoculating the strain in a first bioreactor for algal-seed-cells cultivating;   feeding a first solution containing carbohydrates into the first bioreactor;   transferring the cultivated algal-seed-cells into a second bioreactor for high-cell-density cultivation;   feeding a second solution containing carbohydrates into the second bioreactor;   harvesting the high density cultivated algal cells from the second bioreactor;   drying the high density cultivated algal cells;   extracting oil from dried algal cells; and   producing the biodiesel by reaction of transesterification using the extracted oil as feedstock.   
   
   
       2 . The method of  claim 1 , wherein said high-cell-density is between 15 to 108 g/L. 
   
   
       3 . The method of  claim 1 , wherein the high-cell-density cultivation further comprises heterotrophic cultivation of C. Protothecoides with a high oil content 40-61% dry cell weight. 
   
   
       4 . The method of  claim 1 , wherein the screening step further comprises selecting cells with lower gravity and/or higher oil content using a centrifuge. 
   
   
       5 . The method of  claim 1 , wherein said feeding the first solution containing carbohydrates into the first bioreactor and/or said feeding the second solution containing carbohydrates into the second bioreactor further comprises a batch feeding operation. 
   
   
       6 . The method of  claim 1 , wherein said feeding the first solution containing carbohydrates into the first bioreactor and/or said feeding the second solution containing carbohydrates into the second bioreactor further comprises a continuous feeding operation. 
   
   
       7 . The method of  claim 1 , wherein the first or the second sugar solution further comprises at least one of glucose or other monosaccharides, disaccharides, and polysaccharides. 
   
   
       8 . The method of  claim 7 , wherein the concentration of said at least one of glucose or other monosaccharides, disaccharides, and polysaccharides, in the first or the second bioreactor is controlled between 0.01 and 100 g/L. 
   
   
       9 . The method of  claim 1 , wherein the amount of inoculum in the first bioreactor or the second is between 0.01% and 50% by volume. 
   
   
       10 . The method of  claim 1 , further comprising agitating the medium in the first or the second reactor with a preferable speed of agitation between 5 and 1,000 rpm. 
   
   
       11 . The method of  claim 1 , further comprising a step of aerating in the first or the second bioreactor, wherein the dissolved oxygen (DO) in cultivation medium in the first or the second bioreactor is maintained at least 5% of DO saturation. 
   
   
       12 . The method of  claim 1 , wherein the source of carbohydrates fed into the first or the second bioreactor comprises at least one of plants containing glucose, fructose, corn starch hydrolysate, cassaya starch hydrolysate, wheat starch hydrolysate, and juice of broomcorn. 
   
   
       13 . The method of  claim 1 , further comprising feeding organic nitrogen into the first and the second bioreactor. 
   
   
       14 . The method of  claim 13 , wherein the organic nitrogen comprises glycine, yeast powder, yeast extract, or corn syrup. 
   
   
       15 . The method of  claim 1 , wherein pH value in the first or the second bioreactor is maintained between 6.0 and 8.0. 
   
   
       16 . The method  claim 1 , further comprising adding a base to reduce acidity and regulate the pH of the culture medium in the first or the second bioreactor. 
   
   
       17 . The method of  claim 16 , wherein the base comprises KOH. 
   
   
       18 . The method of  claim 1 , wherein the temperature in the first or the second bioreactor is between 25 to 33° C. 
   
   
       19 . The method of  claim 1 , wherein said transesterification further comprises catalyzation by immobilized lipase from  candida  sp. 99-125. 
   
   
       20 . The method of  claim 19 , further comprising adding said lipase and methanol into said feedstock.