Oxygen supply Surface aeration

The rate of water flow is also most important. This determines the supply of oxygen to the rusting surface, and may remove corrosion products that would otherwise stifle further rusting. A plentiful oxygen supply to the cathodic areas will stimulate corrosion, but so may smaller supplies at a slow rate of flow, if this leads to the formation of differential aeration cells (see Section 1.6). 

Simple aeration of groundwater in surface installations cannot meet the demand for oxygen supply in most bioremediation projects. This is illustrated in the following example (adapted from Reference 10). 

Aeration basins are wastewater ponds or lagoons that have air introduced by mechanical action. Aeration may be performed to assist aerobic bioremediation and/or to remove volatile organic compounds. In an aeration basin, oxygen is usually supplied by surface aerators or by diffused aeration units. The action of the aerators and that of the rising air bubbles from the diffuser is used to keep the contents of the basin in suspension. Aeration is widely used in wastewater treatment and can be adapted to treat groundwater. 

For surface aeration of static cultures, in a closed system, a void volume 10 times larger than the culture medium volume is necessary for adequate oxygen supply. In agitated cultures with surface aeration, oxygen transfer is dependent on agitation rate and impeller geometry. 

Mechanical surface aerator is used to supply air/oxygen to the aerobic pond. In aerobic systems it is important to ensure that enough oxygen is supplied to the aerobic microorganisms to do the job. 

With Cj = 10 and = 1.5, Tj = 0.76 at 15 to 20 C. Disregarding the two other parameters, the corrected amount of oxygen becomes 2 358 kg day b. Correction factor F related to the shape of the aeration tank and to hydraulic conditions. Depending on the type of surface aerator and the shape of the tank, the second F fector 12 = Fi can be calculated (shape of the tank) x F2 (ratio between width and depth) x F3 (specific stirring power) char can be 0.9 for example. A nominal net specific aerator input measured at the shaft of 2 kg kWh of O2 becomes a real input of 1.8. Four aerators, with 20 kW of absorbed power, therefore supply 4 x 20 x 1.8= 144 leg of O2 per hour for a total of 74 that are required on the average. They can be run intermittently and still ensure a maximum stirring power of 37 W m of tank. 

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