72 



P. M. COOK 



The supply of nutrients must be provided at the optimum 

 levels within the range of concentration of each nutrient that 

 permits best growth. Carbon dioxide would be supplied to the 

 medium at the proper concentration. Fixed nitrogen as ammo- 

 nium ion or nitrate ion would supply the nitrogen. Ammonium 

 is the most promising, primarily for economic reasons. Other 

 nutrients required are minor and present no problems and so will 

 not be discussed here. 



CONTINUOUS CULTURE TANKS {- 



♦ t t t I i t t t 



FRESH MEDIUM SPENT MEDIUM 



CULTURE 

 HARVEST 



FLOTATION 



AND 



CARBONATION 



STERILIZING 



MINERAL 



NUTRIENTS 



CO; 



BLENDING 



T 



CHLORELLA 



(WET) 



DRYING 



MAKE UP 

 WATER 



CHLORELLA 

 (DRY) 



Fig. 10 — Flow diagram of the continuous culture process. 



Large-Scale Chlorella Culture Process 



The major conditions have been considered and must now 

 be incorporated into a simple, cheap, efficient system. This re- 

 quires not only inexpensive construction, ease of control and 

 operation, but also maximum efficiency. A continuous process is, 

 in our opinion, the only way to obtain such a system. Conditions 

 must always be maintained at the optimum point. Each cell must 

 receive the required nutrients, proper population density must be 

 maintained, and the temperature must be correct. To obtain a 

 continuous system is not difficult but to design the most efficient 

 system requires the consideration of a large number of complex 

 variables. We have studied and experimented with these variables 



