Aeration design

Aerators designed to faciHtate the transfer of oxygen from air to water increase interfacial area by producing Hquid turbulence and circulation. There are four basic types of aerators summarized in Table 1. 

Dykman, M. and B. J. Michel, Comparing Mechanical Aerator Designs, Chem. Engineering March 10, 1960, p. 117. 

A four-stage aeration design with four shower heads and a pressure drop of 10 psi achieved 99.9% VOC removal. 

Mechanical Aerators. Mechanical aerators are modular ia design and built usiag electric motors. This type of aerator is also known as a surface splasher because it pumps water vertically iato the air. During this process the water is broken up iato small droplets allowiag exchange of oxygen from the air to the water. One type of mechanical aerator is shown ia Figure 3e. 

The effective saturation depth,, represents the depth of water under which the total pressure (hydrostatic plus atmospheric) would produce a saturation concentration equal to for water ia contact with air at 100% relative humidity. This can be calculated usiag the above equation, based on a spatial average value of T, measured by a clean water test. For design purposes,, can be estimated from clean water test results on similar systems, and it can range from 5 to 50% of tank Hquid depth. Effective depth values for coarse bubble diffused air, fine bubble diffused air, and low speed surface aerators are 26 to 34%, 21 to 44%, and 5 to 7%, of the Hquid depth, respectively. 

Flooding. When a stable rathole forms in a bin and fresh material is added, or when material falls into the channel from above, a flood can occur if the bulk sohd is a fine powder. As the powder falls into the channel, it becomes entrained in the air in the channel and becomes fluidized (aerated). When this fluidized material reaches the outlet, it is likely to flood from the bin, because most feeders are designed to handle sohds, not fluids (see Eluidization). Fimited Discharge Kate. Bulk sohds, especially fine powders, sometimes flow at a rate lower than required for a process. This flow rate limitation is often a function of the material s air or gas permeabihty. Simply increasing the speed of the feeder does not solve the problem. There is a limit to how fast material... 

The BPT is defined as the level of treatment that has been proven to be successful for a specific industrial category and that is currendy in fuU-scale operation. Sufficient data exist for this level of treatment so that it can be designed and operated to achieve a level of treatment consistendy and with rehabUity. For example, in the pulp and paper industry, BPT has been defined as biological treatment using the aerated lagoon or the activated sludge process with appropriate pretreatment. 

FIG. 14-32 Aeration factor for pressure drop calculation, sieve plates. [Bolles and Fair, Encyclopedia of Chemical Processing and Design, vols. 16, 86. J. M. McKetta (ed.), Marcel Dekker, New Yoik, J9S2.]... 

Boermaand Lankester [Chem. E/ig. Sci., 23, 799 (1968)] have measured the surface aeration of a six-bladed disk-type turbine (note A well-designed pitched-blade turbine will give equal or better perfor-... 

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