Completely-mixed aerated system

Shivaraman N, Kumaran P, Pandey RA, et al. 1985. Microbial degradation of thiocyanate, phenol and cyanide in a completely mixed aeration system. Environ Pollut, Ser A 39 141-150. 

Completely-mixed aerated system (Figure 11.4) High rate activated sludge... 

The oxygen requirements for an activated sludge system with aeration and agitation for complete mixing are shown by mathematical model as the rate of oxygen transferred is... 

Determine the amount of benzene that can be stripped in a complete-mix activated-sludge reactor equipped with a diffused-air aeration system. Assume the following conditions apply ... 

A completely mixed system allows a more uniform aeration of wastewater in the aeration tank. This system can sustain shock and toxic loads. 

Different types of activated sludge systems are used in treating pharmaceutical waste water. Some sludge systems include conventional, complete mix, contact stabilization, extended aeration, and step aeration. 

Complete Mix—The influent and the RAS are introduced at several points in the center of the aeration basin from a header or central channel. Effluent fi om the aeration basin is collected from both sides of the basin by means of two effluent channels. A clarifier is used to separate the solids in the basin effluent before the sludge is recycled back to the head of the system. Excess sludge is sent to the sludge handling facility of the treatment plant. Aeration can be accomplished by diffused air or mechanical aeration. 

In order to achieve simultaneous suspension of solid particles and dispersion of gas, it is necessary to define the state when the gas phase is well dispersed. Nienow (1975) defined this to be coincident with the minimum in Power number, Ne, against the aeration number, 1VA, relationship (see Fig. 12 [Sicardi et al., 1981]). While Chapman et al. (1981) accept this definition, their study also showed that there is some critical particle density (relative to the liquid density) above which particle suspension governs the power necessary to achieve a well-mixed system and below which gas dispersion governs the power requirements. Thus, aeration at the critical stirrer speed for complete suspension of solid particles in nonaerated systems causes partial sedimentation of relatively heavy particles and aids suspension of relatively light particles. Furthermore, there may be a similar (but weaker) effect with particle size. Wiedmann et al. (1980), on the other hand, define the complete state of suspension to be the one where the maximum in the Ne-Ren diagram occurs for a constant gas Reynolds number. 

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