Graduate Thesis Or Dissertation
 

Some aspects of the biological metabolism of a partially colloidal substrate

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  • An investigation was conducted to ascertain if certain concepts of microbial metabolism, derived from studies using simple soluble substrates, are applicable to the biological assimilation of complex, partially colloidal suspensions. A mixture containing one gram of Carnation dry-skim milk is considered to be a complex, partially colloidal substrate and was used as the medium for analysis throughout this inquiry. The metabolism of the milk suspension was followed by means of a biological oxygen demand test (BOD test). The test was performed in such a manner that the point of maximum net cell growth was observed on the BOD curve through the occurrence of an inflection point called a plateau. Experimental evidence shows that at the plateau 43 percent of the ultimate BOD of the milk suspension has been exerted through respiration and the remaining 57 percent is accounted for as new cell growth. Formulations were derived in the text showing that the biological oxygen demand encountered during the respiration phase of assimilation is directly related to the chemical oxygen demand of the milk suspension. These formulations when combined with experimental evidence yield the equation: Plateau BOD = 0.49 COD, where the Plateau BOD is the amount of oxygen (mg/1) removed from solution at the plateau, and COD is the initial chemical oxygen demand of the milk waste in mg/1. Two activity indices were developed and used to determine plateau characteristics: and 1. The slope of the endogenous curve of the seed organisms used in the BOD test, 2. an activity coefficient defined as the slope of the endogenous curve times 10³ divided by the initial cell concentration of the BOD bottles. It was shown that these activity indices are very closely related to the geometry of BOD curves. Experimental evidence was recorded which shows that, under the constraints of this study, at least ten hours of metabolism time were required before a plateau could appear. It was also noted that the time required for maximum cell growth to occur is related to the logarithm of the slope of the seed organisms' endogenous curve. Relative activity coefficients multiplied by the slope of the seed organisms' endogenous curve were calculated. When this product was plotted against the time required for plateau appearance it was found that the product is optimum at about -0.01 mgO₂/1 per hour.
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