LARGE-SCALE CHLORELLA CULTURE 55 



from waste combustion gases, from fermentation processes, lime 

 calcination, or even from carbon dioxide wells. The supply of 

 carbon dioxide is ample, therefore, and the cost low. Water, of 

 course, is necessary to supply the hydrogen and oxygen in the 

 organic synthesis. Mineral nutrients and possibly some other 

 micro-nutrients have to be added to the water to provide 

 the optimum conditions for most rapid growth To conserve 

 on costs, it was planned to reuse the spent culture medium 

 by recycling the solution after the Chlorella had been separated 

 from it, and after fresh nutrients and make-up water had been 

 added. Fixed nitrogen can be supplied at the concentration neces- 

 sary to control the synthesis for high protein or high fat, as 

 desired. 



Light, of course, is the source of energy which makes the 

 process possible. Sunlight is always available and calculations 

 showed that no consideration was warranted of any other source 

 of light at present. 



In addition to the raw materials required for the growth of 

 Chlorella, certain environmental conditions must be maintained 

 to achieve rapid growth. Chlorella will grow under wide vari- 

 ations in temperature but the optimum condition is from 20° to 

 25° C. The temperature should go no higher than this upper 

 limit, but when no photosynthesis is taking place lower temper- 

 atures are no detriment. Agitation was also considered as a neces- 

 sary condition because the density of Chlorella is higher than 

 water and the cells will settle out if agitation of some type is not 

 employed. The last necessary factor considered was that of main- 

 taining sterile conditions. The importance of maintaining pure 

 cultures was unknown, although evidence was available that con- 

 tamination lowered the growth rate of Chlorella. The use of an 

 open system was considered but without many years of study and 

 research, it could not be determined satisfactorily whether con- 

 ditions could be maintained that would permit exposure to all 

 types of contamination and still permit rapid growth rates and 

 a suitable final product. 



Several important concepts were considered in order to visual- 

 ize and develop an actual system or process for the most efficient 



