Oxygen requirements

Normal air at sea level contains approximately 21% oxygen. As mentioned in Section 2.2.1, reducing the oxygen content of an environment reduces the chances of combustion and explosion. In personnel, however, it also can cause serious physiological damage or death. 

When the oxygen concentration is more than 35%, an individual may suffer from oxygen toxicity. However, the primary hazard is one of fire or explosion. Many materials not normally combustible will burst into flames in oxygen-rich environments. In an oxygen-rich environment, care must be taken to reduce the inventory of combustible materials, eliminate sources of static electricity, and prohibit smoking. 

For cultivation of fermentative species such as LAB, low-oxygen environments are relatively easily created by use of either stab cultures or agar 

The use of sugars as sole carbon source is dealt with under oxygen requirements and end products. 

If the agar in the above test is semi-sloppy, then the test may, in competent 

Liquid media may also be used for testing oxidative/fermentative reactions (Hugh and Leifson s O/F test), and if this is done then a small inverted test tube known as a Durham tube is added. This allows the reaction to be examined for the formation of gas as well as acid. Tubes are again prepared in duplicate, and sterile liquid paraffin or mineral oil is again added to one tube to accentuate the anaerobic reaction. A few organisms may produce an alkaline reaction due to the conversion of peptones in the medium to amines. 

Organisms may be divided into three groups depending on their temperature requirements, psychrophiles, mesophiles, and thermophiles. The division is arbitrary, but is generally regarded as below 10 °C, 10-45 °C, and above 45 °C. 

There are a number of reactions used in identification for which the temperature is critical, e.g. the growth of thermotolerant coliforms at 44 °C in various media is used as a diagnostic test, especially in water samples. Other species in which temperature is important are those which can grow at low temperatures in refrigerators, thus causing problems such as spoilage and food poisoning, e.g. Listeria. 

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This equation indicates that every molecule of urea requires 9/2 molecules of oxygen for complete oxidation. The oxygen required for the reactions depletes the receiving water of oxygen, causing the death of aquatic life. 

The oxygen transfer rate for aerators is normally reported at standard conditions. Thus, ia order to make meaningful comparisons, the ORT under working or field conditions should be adjusted to standard conditions oxygen requirement for treatment (SORT) by means of... 

Temperature. The temperature for combustion processes must be balanced between the minimum temperature required to combust the original contaminants and any intermediate by-products completely and the maximum temperature at which the ash becomes molten. Typical operating temperatures for thermal processes are incineration (750—1650°C), catalytic incineration (315—550°C), pyrolysis (475—815°C), and wet air oxidation (150—260°C at 10,350 kPa) (15). Pyrolysis is thermal decomposition in the absence of oxygen or with less than the stoichiometric amount of oxygen required. Because exhaust gases from pyrolytic operations are somewhat "dirty" with particulate matter and organics, pyrolysis is not often used for hazardous wastes. 

Onaverage, it takes 1.4 kg oxygen to oxidize 1 kg cells as VSS. Therefore, for each kilogram of VSS substracted from the sludge yield, 1.4 kg oxygen must be added to the oxygen required. 

Biochemical Oxygen Demand. The biochemical oxygen demand (BOD) test is an empirical determination of the oxygen requirement of a sample. It is most often appHed to wastewaters, industrial effluents, and poHuted waters. The decrease in the dissolved oxygen concentration resulting primarily from biological action is measured after storage for 5 d at 20°C. 

Characteristics of moving-bed gasifiers are low gasification temperatures, relatively low oxygen requirements, relatively high methane content in... 

Because there does not appear to be sufficient MTBE capacity to satisfy the oxygen requirements for the 1990 CAA revision, there has been a general upward movement ia MTBE market prices that should provide the iacentive for additional capacity to be built (27). 

A definitive determination of the waste sludge production and the oxygen requirement can be obtained using the pseudo constants referred to previously. The ultimate BOD in the waste will be accounted for by the sum of the oxidation and sludge synthesis (Eq. 25-20). 

Waste BOD = Oxygen required -t- BOD of sludge produced (25-20) where BOD of sludge = (Ynet)(1.42)(Waste BOD )... 

Ignition will occur when both combustible gases and oxygen are available in sufficient quantity above the ignition temperature. The amount of oxygen required for ignition varies from one polymer to another. For example, in tin... 

The design basis is the most important eonsideration when determining the size of a biologieal reaetor. Other pertinent faetors are the final produet, the mieroorganism used, its growth rate and oxygen requirement, the produet eoneentration (e.g., expressed in mg/L broth for proteins or 100 mg/L for organie aeids), and the type of produet (intereellular or extraeellular). 

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