LARGE-SCALE CHLORELLA CULTURE 61 



Pilot Plant 



Results from data obtained in the above experiments indicated 

 the optimum conditions necessary for maximum yield. These re- 

 sults were evaluated in terms of the best system for maximum 

 production and minimum cost. A small pilot plant w^as then 

 designed and constructed. The pilot plant is shovi^n diagrammat- 

 ically in Figure 5. It consists of four horizontal culture tanks four 

 feet u^ide by ten feet long. The depth of the tanks is six inches. 

 Each tank is maintained at constant conditions in the same man- 

 ner as our other equipment. Barrels coated v^^ith non-toxic paint 

 are used for medium supply and overflow storage. Tap water is 

 constantly circulated through cooling coils welded to the under- 

 side of the tank. Temperature of the culture is maintained con- 

 stant by a thermoswitch controlling a solenoid valve allowing 

 steam to enter the cooling coils. A supply of carbon dioxide can 

 be added to the medium or aerated into the tanks by means of 

 six jet orifices in each tank. Constant population density is main- 

 tained by a photoelectric cell circuit in conjunction with a by- 

 pass in the system through which culture is constantly pumped. 

 As new medium is allowed to enter, the overflow passes into the 

 storage barrels thus maintaining a constant depth or volume of 

 ■culture in the tanks. The overflow barrels are directly piped to a 

 Sharpies centrifuge for separation of the cells. 



This pilot plant should serve two purposes: (i) to obtain 

 •substantial daily production of Chlorella; (2) to determine opti- 

 mum conditions of growth in the type of system visualized for 

 large-scale production. 



Experiments are proposed employing the same conditions in 

 each tank, except that the depth of the culture is varied. There- 

 fore, the important variables of depth versus population densities 

 during the same conditions of sunlight can be studied. The four 

 tanks would be operated at culture depths of i5/2> 3? 4j and 5 

 inches. By maintaining the same population densities in each 

 tank, data of growth rates and yields versus depth of culture can 

 be obtained for the same sunlight conditions. 



Another phase of this research program has had the objective 



