Demand oxygenates

The main reason for the importance of aeration Hes in the limited solubiUty of oxygen in water, a value which decreases in the presence of electrolytes and other solutes and as temperature increases. A typical value for the solubiUty of oxygen (the equiUbrium saturation concentration) in water in the presence of air at atmospheric pressure at 25°C is about 0.008 kg 02/m (= Sparts per million = 0.25 mmol/L). Thus, for a yeast or bacterial bioreaction demanding oxygen at the rates given in Table 1, all oxygen is utilized in about 10 to 40 s (3,7). 

The goal of treatment is to prevent myocardial hypoxia either by raising blood flow (oxygen supply) or by lowering myocardial blood demand (oxygen demand) (A). 

Barriers to the production of industrial enzymes include economic factors, the availability of optimal enzymes and safety issues. Common fermentation and purification processes are described in Figs. 2-1 to 2-3. The process differs for extracellular and intracellular enzymes, liquid and solid culture, and enzyme application. The fermentation conditions are computer-controlled for optimization, e. g. of temperature, pH, agitation speed, aeration, demand oxygen etc. 

Chemical Oxygen Demand—Oxygen demand if a substance is chemically oxidized. 

The amount of oxygen used in the degradation process is called the biochemical oxygen demand (BOD). A standard test has been devised to measure BOD in which the oxygen utilized by microorganisms in contact with the wastewater over a 5-day period at 20°C is measured. 

Another test is the total oxygen demand (TOD) test, which oxidizes the waste in the presence of a catalyst at 900°C in a stream of air. Under these harsh conditions, all the carbon is oxidized to CO2. The oxygen demand is calculated from the difference in oxygen content of the air before and after oxidation. The resulting value of TOD... 

If the composition of the waste stream is known, then the theoretical oxygen demand can be calculated from the appropriate stoichiometric equations. As a first level of approximation, we can assume that this theoretical oxygen demand would be equal to the COD. Then, experience with domestic sewage indicates that the average ratio of COD to BOD will be on the order 1.5 to 2. The following example will help to clarify these relationships. 

Solution First, calculate the theoretical oxygen demand from the equation that represents the overall oxidation of the acetone ... 

Natural occurring oxygen 18 is stable and available commercially, as is water (H20 with 15% 180). Commercial oxygen consumption in the U.S. is estimated at 20 million short tons per year and the demand is expected to increase substantially. 

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