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Aerobic Denitrification in Sewage Treatment |
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Aerobic
Denitrification
in
Sewage
Treatment - In denitrification facultatively aerobic heterotrophs like Pseudomonas spp. can use nitrate as terminal electron acceptor in the absence of dissolved oxygen.
Denitrification which occurs in secondary sedimentation tanks is inefficient and replaces the nitrate problem with that of a turbid effluent. The major problem in effecting complete denitrification of a well nitrified effluent with low BOD is the scarcity of respiratory substrates available to donate electrons to nitrate.
Thus denitrification process requires the addition of an endogenous carbon source as a substrate unless complex recycle systems are used. Methanol is used as the most economically efficient substrate.
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Activated sludge process has been modified so that biologica1 denitrification can be effected without the need for additional substrate input. In one such modified system an anoxic zone is included between the aeration and final sedimentation stage. In another modification a four-stage system incorporating alternate anaerobic and aerobic reactors with multiple cell and effluent recycle systems is employed.
Incorporation of a high rate of effluent recycle to the beginning of the process has been found to be a most successful system. In this system the incoming wastewater provides respiratory substrates for denitrification in anoxic zone followed by an aerobic zone for nitrification of ammonia in the incoming waste water. It appears that the nitrifiers are not inhibited to any significant extent by exposure to anoxic conditions for a few hours.
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