Activated sludge dissolved oxygen

Activated sludge Sludge particles produced in raw or settled wastewater (primary effluent) by the growth of organisms (including zoogleal bacteria) in aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that... 

The activated sludge process has been found to be the most efficient treatment for various categories of pharmaceutical wastewater [14,15,19,42-46]. It has also been reported that this process can be successfully employed for the removal of tert-butanol, a common solvent in pharmaceutical wastewater that cannot be degraded by anaerobic treatment [44]. At a volumetric loading rate of 1.05 kg COD/m day, HRT (hydraulic retention time) of 17 hours, and mixed liquor dissolved oxygen concentration of 1 mg/dm, the tert-butanol can be completely removed by the activated sludge process. 

Dissolved oxygen (DO) concentration is a key variable in the operation. It affects the economy and is also closely related to the biological activity of the organisms in the sludge. The main emphasis in this paper is to show how the DO concentration distribution in a non-homogeneous aerator can be used for the estimation of the activity of both heterotrophic and nitrifying organisms. 

Olsson, G. Andrews, J.F. "The dissolved oxygen profile - a valuable tool for control of the activated sludge process Water Res., 1978, 12, 985-1004. 

Flanagan, M.J. Bracken, B.D. "Design procedures for dissolved oxygen control of activated sludge processes" USEPA, 600/2-77-032, June 1977. 

Oxygen is a necessary nutrient. In suspended-growth processes, such as the activated sludge process, air must be literally forced into the liquid. The air, thus, dissolved provides the necessary oxygen nutrient for the microorganism stabilizing the wastewater. 

Consider ihe contents inside an activated sludge reactor laden with dissolved oxygen and pollutants subjected to aeration. Also, consider the sedimentation basin that follows the reactor and all the associated pipings. For the purpose of performing the material balance, let the boundaries of these items encompass the control volume. According to the Reynolds transport theorem, the total rate of increase of the concentration of dissolved oxygen is equal to its partial (or local) rate of increase plus its convective rate of increase. 

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