Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-04-04
2001-09-18
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S620000, C210S630000, C210S903000
Reexamination Certificate
active
06290849
ABSTRACT:
The present invention relates to a method for biological purification of waste water by the activated sludge method, wherein the waste water is continuously passed through at least two treatment zones in which the waste water is successively subjected to nitrification and denitrification, and an optional clarification zone for dividing the treated waste water into a water fraction and a sludge fraction, using an apparatus comprising four treatment zones (I, II, III, IV), wherein alternating anoxic and aerobic conditions and optionally sedimentation are established, said treatment zones being arranged around a central supply zone for waste water to be purified.
It is known to remove nitrogen from waste water by subjecting it to nitrification for conversion of ammonia into nitrate, and to denitrification for conversion of nitrate into free nitrogen, optionally supplemented with an anaerobic treatment for removal of phosphorous.
Danish patent No. 131 297 discloses a method for biological removal of nitrogen (the biodenitro method), whereby the waste water is passed through two treatment zones under alternating anoxic and aerobic conditions so as to obtain suitable nitrogen removal. If supplemented with an anaerobic zone, an additional reduction of the phosphorous content is obtained (the biodenipho method).
This method has been further developed to comprise three treatment zones (triple channel), where the waste water is passed through a denitrification zone and then through one or two nitrification zones, waste water being in periods passed through two of the three zones. This means that the content of ammonia and nitrate in the waste water is reduced as compared with treatment in two zones.
This method can also be combined with an anaerobic treatment zone for reducing the phosphorous content in the waste water.
There are, however, still some concentration fluctuations in the effluent from the last treatment zone which it would be desirable to even out in order to achieve a more homogeneous effluent quality.
Consequently, it has been considered to increase the number of treatment zones to four so as to obtain improved flexibility. The triple channel system is, however, usually carried out in a plant consisting of three successive tanks, which as compared with the denitro method, which usually is carried out in only two tanks, is more expensive, and an extension so as to comprise four separate tanks will only make the initial costs even higher, for which reason this is of no commercial interest.
An example of a system comprising four tanks is disclosed in WO 96/02468. Since this system is designed specifically for operating with sedimentation, with inlet of waste water into only two of the four tanks, combined with outlet from the two other tanks, the method described is not very flexible.
EP 218 289 describes a method using a tank comprising four compartments operated in a way, where the inlet is shifted from compartment to compartment in a circular pattern, always with an outlet opposite to the inlet. In this way the waste water is always passed through 3 compartments and is subjected to simultaneous nitrification and denitrification. By using this prior art method and apparatus, a fully satisfactory removal of nitrate cannot be obtained.
It has now surprisingly turned out that by the method according to the invention an effective purification of the waste water is obtainable using a commercially acceptable plant.
The method according to the invention is characterized in that only two treatment zones (I, IV) are provided with means for discharging treated water, that the untreated waste water from the central supply zone alternatingly is passed into a first of the four treatment zones (I, II, III or IV), operated under anoxic conditions, and following an optional treatment in one or two additional treatment zones (II and/or III) is passed into a last treatment zone (I, IV) from which treated waste water is discharged.
Naming the four zones I, II, III and IV is merely to demonstrate that untreated waste water can be supplied to any of the particular treatment zones, and that treated waste can be discharged only from two of the four treatment zones. This arrangement establishes basis for various types of operation which can be used according to need, since the waste water optionally can be passed through two or more treatment zones, comprising anoxic and/or aerobic treatment. This flexibility ensures that the time during which the waste water is subjected to either nitrification or denitrification can be adjusted according to the composition of the waste water to be treated.
By operating one of the compartments as a sedimentation zone, it is possible to increase the capacity of the system, which can be useful at times with e.g. heavy raining.
By this method an effective removal of nitrogen from the waste water is obtained, and the abovementioned concentration fluctuations in the effluent from the tank are significantly reduced. At the same time improved exploitation of carbon is achieved, as the waste water is always supplied to an anoxic phase. Thus, a better adaptation to the load and the BOD/N ratio of the waste water is made possible.
The method according to the invention may be carried out in an apparatus comprising a tank which by means of partition walls is divided into at least four compartments positioned around supply means for central supply of waste water, and with means for alternatingly connecting the supply means with each of the four compartments, and means for removal of treated waste water from two compartments.
In the following the invention will be described in more detail with reference to the drawings, where:
FIG. 1
is a flow chart which illustrates a known (triple channel) method for purification of waste water.
FIG. 2
is a flow chart which illustrates an embodiment of the method according to the invention for use in normal operation.
FIG. 3
is a flow chart which illustrates an embodiment of the method according to the invention for use in modified operation with internal clarification.
FIG. 4
illustrates an apparatus for carrying out the method according to the invention.
FIG. 5
illustrates an additional embodiment of an apparatus for carrying out the method according to the invention.
FIG. 6
illustrates suitable treatment patterns according to the invention.
REFERENCES:
patent: 3964998 (1976-06-01), Barnard
patent: 4304863 (1981-12-01), Collins et al.
patent: 4663044 (1987-05-01), Goronszy
patent: 5354471 (1994-10-01), Timpany et al.
patent: 131279 (1975-06-01), None
patent: 0218289 (1987-04-01), None
patent: 0363718 (1990-04-01), None
patent: 9602468 (1996-02-01), None
Petersen Gert
Rykaer Søren
Barry Chester T.
Dykema Gossett PLLC
Kruger A/S
Prince Fred
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