LARGE-SCALE CHLORELLA CULTURE 73 



at some length. The tentative plant design I should like to de- 

 scribe is one we believe to be the most efficient and most econom- 

 ical we have constructed thus far. Certainly, the basic principles 

 will apply to any design. The details of the engineering are not 

 important and will not be discussed. 



In Figure lo is shown a simple block flow diagram illustrating 

 the major ideas involved. There are two major parts of the plant: 

 i) the culture farm; 2) the processing plant. Growth takes place 

 in long, flat, horizontal, glass-covered tanks. Conditions for 

 growth are maintained at optimum by introducing fresh medium 

 at frequent intervals along the tank. Because growth is constant 

 in all portions of the tank it is necessary to provide an equal flow 

 of fresh media into each inlet of the tank, thus maintaining con- 

 stant population density. When each interval is equally diluted and 

 culture is removed only at the end of the tank, the flow rate of 

 the culture is necessarily low near the head and rapid near the 

 end. To obtain proper agitation, the culture is recycled in enough 

 quantity to obtain a condition of turbulent rather than stream- 

 lined flow in the tanks. The necessary nutrients, including carbon 

 dioxide as carbonate and bicarbonate, are introduced with the 

 fresh medium. An atmosphere of carbon dioxide and air is main- 

 tained over the culture. The harvested culture flows to the proc- 

 essing plant where the cells are separated from the medium by 

 flotation. Waste combustion gases from the sterilization and de- 

 hydration processes supply enough carbon dioxide for growth 

 requirements. Some of these gases are absorbed in solution during 

 the same flotation process for removal of cells. Make-up water to 

 which the necessary nutrients have been added, will be sterilized 

 and incorporated with the spent medium for return to the culture 

 farm. 



One particular design for the tanks is shown in Figure 11. The 

 tanks operate by gravity flow. Each tank extends to the end of the 

 farm, turns, and returns to its origin at a slightly lower level. 

 Here the recycled portion is pumped up to the head of the tank. 

 A pipe carrying new medium extends most of the length of the 

 tank and introduces the new medium at equal intervals in the 

 tanks. Thus, we have a simple, continuous system. It provides for 



