Oxygen transfer mechanisms in the gluconic acid fermentation by Pseudomonas ovalis

The oxygen uptake rate to suspended cells of Pseudomonas ovalis was measured in two ways using the same cell suspension. Initially the rate was found by measuring the rate of production of gluconic acid by cells suspended in a nitrogenfree, aerated medium. Then, an oxygen electrode was used to measure the rate of transfer of dissolved oxygen to cells suspended in a liquid that was being agitated but not sparged. These rates were markedly different. It was found that agitation affected the oxygen transfer rates in aerated solutions at dissolved oxygen concentrations well above the critical level, but had no affect on the oxygen uptake rates by cells suspended in an unsparged but agitated medium. The data suggested that an additional path existed for oxygen transfer. This alternate route, parallel to the conventional pathway of oxygen transfer, becomes operative when the liquid films surrounding the cells and bubbles merge. The resulting shorter path presents a mechanism for direct transfer of oxygen which increases in importance as the gas−liquid interfacial area increases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37878/1/260060309_ftp.pd

Kinetics of the conversion of glucose to gluconic acid by Pseudomonas ovalis

The concept of a “critical oxygen concentration” is conventionally considered to hold for the submerged aerobic fermentation of glucose to gluconic acid. Above the critical level the fermentation rate is supposedly independent of oxygen concentration. In this work it is shown that, at a given agitation rate, the fermentation is independent of dissolved oxygen when above the critical. However, an increase in the agitation rate results in an increase in the fermentation rate. This increase was shown to be accompanied by an increase in the gluconolactone concentration in the broth. Gluconolactone, an intermediate in the reaction pathway, is hydrolyzed nonenzymatically to gluconic acid. Evidence is presented to suggest that the increased gas-liquid interfacial area brought about by increased agitation causes an increased net rate of lactone formation. This in turn results in an increased rate of hydrolysis of the lactone to gluconic acid. A model is presented hypothesizing that negatively charged cells adsorb at the gas-liquid interface. These cells attract hydrogen ions, causing a lowering of the pH in the film around the bubbles. It is this lowered pH which is considered to bring about increased fermentation rates when the interfacial area is increased. Supporting evidence is presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37880/1/260120208_ftp.pd

The Economics of Antifoulant Application

The performance of heat integration systems is normally quantified in terms of the amount of heat that is recovered. In an effort to mitigate the usual decrease in heat recovery with time due to fouling of the heat transfer surface, various chemical additives can be utilized. Using the "Total Fouling Related Expense (TFRE)" approach, the economics of antifoulant application are evaluated based on the optimum exchanger cleaning interval. Sensitivities to antifoulant effectiveness are calculated and procedures which can be used to evaluate the economic optimum use of antifoulants are described

Optimization of Heat Exchanger Cleaning

The performance of heat integration systems is quantified in terms of the amount of heat that is recovered. This decreases with time due to increased fouling of the heat exchange surface. Using the "Total Fouling Related Expenses (TFRE)" approach, economic incentives for heat exchanger cleaning are evaluated using linear, exponential, and exponential finite decrease models of the heat recovery decay. A mathematical comparison of mechanical and chemical cleaning of heat exchangers has identified the most significant parameters which affect the choice between the two methods