LARGE-SCALE CHLORELLA CULTURE 57 



Utilization of sunlight. The growing season is short and sunlight 

 during the remainder of the year is wasted. Young plants inter- 

 cept but a very small portion of light falling on the land. It is only 

 during a short period before harvesting that a substantial portion 

 of light is actually incident upon a surface capable of photosyn- 

 thesis. 



With algae, it is not difficult to visualize a system where con- 

 stant conditions can be maintained in a continuous system per- 

 mitting the most efficient use of land, sunlight, and equipment. 

 By continuously harvesting at the rate at which the algae in- 

 crease, and supplying the necessary raw materials, the optimum 

 conditions may be maintained and the maximum possible pro- 

 duction realized. 



Development of Chlorella Culture Process 



Experimental 



To become familiar with the problems of growing algae, to 

 obtain a simple continuous system, and to maintain accurate 

 control of all variables, a 4-inch diameter pyrex glass column, 

 six feet in height, was constructed. This column (Figure i) is 

 illuminated by three loo-Watt fluorescent lights, placed about 

 % of an inch from die column wall, and spaced 90° apart around 

 the inside of a sheet-metal reflector. A cooling tube is sealed into 

 the top part of the unit and extends almost to the bottom. Tem- 

 perature is maintained by a temperature controller which regu- 

 lates the flow of cooling water. Aeration is provided by means 

 of an inlet tube which enters at the bottom of the column. Two 

 other tubes are sealed into the column near the bottom; one for 

 the introduction of new medium and the other for sampling. 

 Volume is maintained constant by an overflow at a level of 10 

 liters. The population density of Chlorella in the culture is held 

 constant by means of a photoelectric cell with amplifier which 

 activates a solenoid valve allowing the entry of new medium. 

 This medium is supplied from glass bottles as indicated in Fig- 

 ure I. A continuous supply of sterile medium is available from 

 the supply botdes. By this technique, a closed sterile system is 



