Activated sludge process for sewage purification

Details Activated sludge process for sewage purification Activated sludge process for sewage purification

1994-02-03

1995-09-05

Upton, Christopher

Liquid purification or separation

Processes

Treatment by living organism

210624, 210626, 210903, C02F 330

Patent

active

054476330

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to an activated sludge process for sewage purification in which the sewage is introduced into a first, partially aerated activation stage, is then submitted to intermediate clarification, is then introduced into a second, partially aerated activation stage, is subjected to post-clarification and is then removed, in which sludge is fed back from the intermediate clarification into the first activation stage and from the post-clarification into the second activation stage, and in which excess sludge is removed from at least one activation stage is removed from the sludge circuit.
The usual two-stage activated sludge process (Doctor W. Lindner, "The Two-Stage Activation Process in Sewage Purification" (Kempten 1957), Thomas-Verlag) is a known process. In this process, substrate breathing where the micro-organisms consume oxygen through the oxidation of organic compounds and where the biological decomposition of carbon compounds is therefore most conspicuous takes full effect in the first activation stage with high sludge load. The second activation stage in this known process is generally carried out with lower sludge load so that a decomposition of the remaining carbon compounds and the oxidation of nitrate compounds (nitrification) takes place.
Normally the known, two-stage activation process is carried out with a sludge proportion of 0.8 to 2.0 kg BO.sub.5 (biochemical oxygen requirement in 5 days)/kg dry substances and per day in the first stage and from 0.15 to 0.5 kg BOR.sub.5 /kg dry substance and per day in the second activation stage (Lehr- und Handbuch der Abwassertechnik [Instructions and Handbook for Sewage Technology], published by the Abwassertechnischen Vereinigung (Sewage Technology Association) e.V. in St. Augustin, Berlin Ernst Verlag, page 426, vol. IV, 3rd edition, 1985). In the method which is typical for this process, the major part of carbon decomposition takes place as described in the first stage, and extensive nitrification in the second stage. Denitrification is no longer possible in the second stage due to the absence of easily decomposed carbon substrate. The withdrawal of excess sludge from the overall plant takes place either during pre-clarification before the first stage or, in the absence of preclarification, from the sludge circuit of the first stage The excess sludge of the second stage is withdrawn together with the sludge of the first stage without giving rise to a controlled removal of nitrogen because no anoxic conditions exist in the first stage.
In a process known from AT-PS 318.503 for the elimination of organically and inorganically attached nitrogen from domestic and industrial sewage, nitrified sewage is taken from the sedimentation basin of the second process stage and is fed into a conduit through which sewage is conveyed from the aeration basin of the first stage into the post-clarification basin of the first stage for the denitrification of the ammonium nitrified in the second process stage, and thereby for the elimination of nitric nitrogen from the sewage to be purified. In the process known from AT-PS 318.503 only denitrification takes place in the first process stage (aeration basin and sedimentation basin) and only nitrification takes place in the second process stage.
In the process known from DE-OS 31 36 409, two plants, i.e. two stages of equal rank are parallel-connected for nitrification. According to the DE-OS 31 36 409 particularly favorable conditions for the nitrification are to be maintained in the auxiliary nitrification stage so that no interruption of nitrification may occur in case of disturbances in the main nitrification stage but that biology held in reserve in the auxiliary nitrification stage may be introduced from same into the main stage if necessary to ensure that nitrification can be continued therein substantially without interruption once a disturbance has occurred.
WO 83/00856 describes a sludge treatment process in which only carbon compounds are to be decomposed and in which ne

REFERENCES:
patent: 3957632 (1976-05-01), Knopp et al.
patent: 3964998 (1976-06-01), Barnard
patent: 4173531 (1979-11-01), Matsch et al.
patent: 4183809 (1980-01-01), Klopwijk et al.
patent: 4460470 (1984-07-01), Reimann
patent: 4552663 (1985-11-01), Spector et al.
patent: 4780208 (1988-10-01), Bohnke et al.
patent: 5252214 (1993-10-01), Lorenz et al.

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