Anaerobic-Aerobic Fermentation

FIGURE 4.3 Effects of temperature and duration on changes of GABA in tea leaves under anaerobic conditions. 

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A commercial technology (69), the SABRE process, treats contaminated water and soil ia a two-stage process by adding a readily degradable carbon and an inoculum of anaerobic bacteria able to degrade the contaminant. An initial aerobic fermentation removes oxygen so that the subsequent reduction of the contaminant is not accompanied by oxidative polymerization. 

Ensio-Fenox A process for removing chlorinated phenols from pulp-bleaching effluents. It combines anaerobic and aerobic fermentation processes. 

Two major types of fermentors are widely used in industry. The stirred tank, with or without aeration (e.g., air sparging) is most widely used for aerobic and anaerobic fermentations, respectively. The bubble column (tower fermentor) and its modifications, such as airlifts, are used only for aerobic fermentations, especially of a large scale. The important operating variables of the sparged (aerated)... 

The existence of mitochondrial DNA, ribosomes, and tRNAs supports the hypothesis of the endosymbiotic origin of mitochondria (see Fig. 1-36), which holds that the first organisms capable of aerobic metabolism, including respiration-linked ATP production, were prokaryotes. Primitive eukaryotes that lived anaerobically (by fermentation) acquired the ability to carry out oxidative phosphorylation when they established a symbiotic relationship with bacteria living in their cytosol. After much evolution and the movement of many bacterial genes into the nucleus of the host eukaryote, the endosymbiotic bacteria eventually became mitochondria. 

The most traditional application of the fermentor is in batch mode. In anaerobic fermentations the reactor looks like a normal batch reactor, since gas-liquid contact is not an important design consideration. Depending on the reaction, the microbes may or may not be considered as a separate phase. For aerobic fermentations, oxygen is bubbled through the media, and mass transfer between phases becomes one of the major design factors. 

Vitamin B12 (cyanocobalamine) is produced by bacteria from glucose, corn, and cobalt salts in anaerobic (3 days) and then an aerobic fermentation (also 3 days). 

The value for Kk, the saturation coefiicient or growth-limiting substrate concentration at which organism growth rate is one-half its maximum value, varies considerably with the reaction, the species mediating the reaction, and environmental conditions. In anaerobic methane fermentations, Kk tends to be much larger, at least with acetate and propionate, than for aerobic oxidations. Values of 10" moles/liter seem appropriate for the former and 10" for the latter. Kk also tends to increase with decrease in temperature. 

Aerobic fermentation Microbial/ Anaerobic fermentation BiochemicaH Biophotolysis Composting Enzymic... 

Table 2 Common TEAs used for aerobic, anaerobic, and fermentation respiration...

Explain how the CO2 content and pH of natural waters is affected by processes and reactions including the dissolution of C02(g), photosynthesis and respiration, aerobic decay, anaerobic decay (fermentation), nitrate reduction, and denitrification and sulfate reduction. 

Fluid mixing is essential in fermentation processes. Usually the most critical steps in which mixers are used are in the aerobic fermentation process. However, mixers are also used in many auxiliary places in the fermentation process and there are places also for agitation in anaerobic fermentation steps. 

Fig. 3-4 The biochemical pathway of glycolysis, which obtains energy from the breakdown of 6-carbon sugars to a pair of 3-carbon pyruvate molecules. The enzymes at each reaction in the sequence are in italics. The energy generated is stored in the form of ATP (see Fig. 3-5). Pyruvate can be further transformed to lactate or ethanol under anaerobic conditions (fermentation), or, under aerobic conditions, it can enter the TCA cycle (see Fig. 3-10).

Distillation residue from recovery of orange oil has been used as substrate for production of cobalamin (Vitamin B ) by Propionibacterium freudenreichii and Propionibacterium shermanii fermentation (25). By filtration of the distillation residue, pH adjustment to 7.0 with NaOH, and use of a two-stage, anaerobic to aerobic fermentation, nearly 6.35 mg/L of cobalamin were produced in 192 hours of fermentation (Table II). 

A cancer cell is also described by Dr. Ali as a metabolic two-timer, but with the difference that it (merely) smvives in the presence of oxygen, but proliferates in its absence. The presence of oxygen denotes an aerobic condition, and its absence denotes an anaerobic or fermentative condition. Whereas Dr. Ali is in full agreement with the Warburg theory of cancer metabolism, he diverges with Warburg s viewpoint that cancer is irreversible. 

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