In this process, high-purity oxygen is used in lieu of air as the oxygen source. The process is typically carried out in a closed tank similar to the activated sludge process for wastewater using pure oxygen. High-purity oxygen atmosphere is maintained in the space above the liquid surface, and oxygen is transferred into the sludge via mechanical aerators. The process can also be performed in open tanks, in which case oxygen is introduced to the sludge in minute bubbles with special diffusers. The bubbles dissolve before they reach the liquid surface. Because of the high cost of generating pure oxygen, it is cost-effective only when used in conjun ction with a pure oxygen activated sludge system. The principal advantage of the system is that it is relatively insensitive to changes in ambient temperatures when closed tanks are used because of the increased rate of biological activity and the exothermic nature of the process; consequently, it is particularly applicable in cold weather climates. High temperatures resulting from the exothermic process increase the rate of volatile solids destruction.
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