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[Day 4]: Graph it OUT! After the fermentation process, the computer controling the fermentor has given us a analysis graph as shown below.
 Bear with him, he's kinda dragy. Temperature The temperature in the fermenter remains relatively constant throughout the whole process at about 32°C, with slight fluctuations at certain points. This is probably due to the cells’ metabolism that results in the production of heat as a byproduct. In order to keep the temperature as constant as possible, the reactor will try to cool down the temperature slightly, thus, creating the fluctuations PO2 From the history plot, the oxygen level in the fermenter starts high and rapidly decreases to a point where it starts to fluctuate greatly before returning gradually back to its original level and repeat the cycle again. As the bacteria culture was inoculated from a seed culture, there is very short or no lag phase at all, thus the initial dramatic decrease in oxygen level is an indication of the beginning of the log phase. During the log phase, cells actively metabolize and divide, resulting in an increasing demand in oxygen. As the bacteria cell population increases, so does the oxygen required. The fermenter system actively supply air into the fermenter through the sparger, this constant input and consumption of the oxygen is depicted by the great fluctuation on the history plot. As the log phase nears its end as a consequence of high cell density or accumulating waste product, the oxygen level becomes stable, marking the beginning of the stationary phase. During the stationary phase, rate of cell growth equals the rate of cell death and metabolic activity slows, thus the oxygen level remains fairly constant. Death phase begins when the oxygen level, indicated on the graph, starts to rise rapidly. Cell death occurs exponentially at this phase, oxygen level increase rapidly as demand decreases. However, the gradient of the graph decreases before it slope towards the peak, this is probably because the cells have entered a secondary growth (lag) phase in which the cells prepare for the next log phase. Little oxygen is needed at this point thus the continuing increase in oxygen level. The dramatic drop in oxygen level shows that the bacteria have entered the log phase again. Stir Oxygen introduced into the fermenter is to be evenly distributed so as to achieve a homogeneous environment, maximizing efficiency. This is done by an impeller that occupies the central column of the fermenter. The impeller works in coordination to the rate at which oxygen is pumped into the tank, the faster the rate at which oxygen in introduced, the faster the impeller would rotate. Thus, when the oxygen level starts to fluctuate greatly, so does the speed at which the impeller is rotating. pH A constant pH ensures that the bacteria are placed in optimum conditions. Drastic changes in pH would disrupt the structural stability of the bacteria and kill it. The pH, as observed from the graph, remains relatively constant in the beginning and increases slightly. This is due to the release of metabolic waste product by the bacteria into the environment, the slight change in pH does not trigger the system to counteract it . The constant pH is maintained by the fermenting system which automatically adds acid or alkaline when there is a pH change. Hydrochloric Acid (HCl) is not suitable as a correction agent for pH as the Chloride ions (Cl-) would probably kill the bacteria; instead sodium hydroxide (NaOH) and sulphuric acid (H2SO4) are used. We have spoken.
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