The conventional scheme involves two bioreactors (stirred tanks) in series, the first one being the aerobic tank in which carbon removal (organic matter destruction) and nitrification occur, while in the second denitrification is performed anoxically. Nevertheless, all the schemes employ stirred tank bioreactors. A comprehensive survey of the same has been presented by Rao and Subramanyam. Since the process is anoxic in nature, this bioreactor does not need supply of atmospheric air from outside.Īs stated earlier, many modifications of activated sludge process have been proposed by different researchers during the past. During denitrification, the nitrates formed during nitrification are reduced to nitrogen gas and thus is expelled from the bioreactor. Denitrification, being an anoxic process, is conducted in a separate bioreactor. Nitrification is accomplished in the aerobic tank itself (simultaneously with carbon removal), during which the dissolved ammonia in wastewater is converted to nitrates. This high operating cost of air compressors forms the major economic limitation of this process, though the system is simple to design and install.Īpart from the oxidation of the dissolved organic matter (to carbon dioxide and water), nitrification and denitrification processes could also be conducted here. Since the volume of the aerobic tank is usually quite large and the solubility of atmospheric oxygen in water or aqueous solutions is very low, huge air compressors would have to be deployed to sparge in significant amount of air so as to meet the oxygen requirement of the microbes and that of the aerobic process. Air is sparged under high pressure from the bottom to provide sufficient dissolved oxygen in the medium. Here, suspended growth of microbes occur. The conventional activated sludge process employs an aerobic tank which is an agitated vessel (stirred tank bioreactor) seeded with an inoculum of microbial sludge (usually the recycled portion of active sludge). It is also the process that has been subjected to the maximum number of modifications and diversifications. Still this process is popular in spite of some of its inherent limitations. Activated sludge process, which involves aerobic treatment of industrial effluents in stirred tank bioreactors, is one among the very old industrial applications of biotechnology.
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