Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2002-05-22
2004-03-16
Prince, Fred G. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S623000, C210S626000, C210S195300, C210S259000, C210S906000
Reexamination Certificate
active
06706185
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application corresponds to JP 2000-385659, filed Dec. 19, 2000, and to JP 2000-398231, filed Dec. 27, 2000, the subject matter of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Technical Field
The invention concerns a method and apparatus for the biological removal of phosphorus from raw water, and in particular a method and apparatus for the biological removal of phosphorus which has a sludge-reducing solubilizing means, in which phosphorous removal is carried out biologically by means of an anaerobic/aerobic method.
2. Related Art
In an active sludge treatment process where waste water which contains phosphorus is subjected to a biological treatment with active sludge, the amount of phosphorus is reduced along with the degradation of the organic compounds in the raw water. In the metabolism of materials by microorganisms, phosphorus is also included in ATP and nucleic acids (DNA, RNA), and it is an essential element for biomass synthesis. Generally, about 2.3% phosphorus is present in activated sludge, and the removal of the phosphorus with the progress of biomass synthesis can be expected. However, the amount of phosphorus removed in activated sludge treatment, if the average retention time of the sludge is held constant, is roughly proportional to the organic material concentration in the waste water, and so the amount of phosphorus which can be removed is limited.
On the other hand, under certain specified conditions, a large amount of phosphorus other than the phosphorus required for growth and metabolism of the biomass is accumulated in the biomass, and the phosphorus concentration in such activated sludge can reach from 6 to 8%. The phenomenon is called excess uptake or luxury uptake. That is to say, sludge where the environment of the activated sludge has been rendered anaerobic and which has forcibly released phosphorus subsequently exhibits a marked increase in the amount of phosphorus which is taken up.
In an apparatus for the biological removal of phosphorus, use is made of the luxury uptake phenomenon such that return sludge is introduced into an anaerobic tank into which the raw water is introduced and phosphorus is released from the sludge, and the raw water which contains the phosphorus-deficient sludge is subjected to an aerobic treatment and the phosphorus is taken up in excess by the sludge and phosphorus is removed.
In an apparatus for the biological removal of phosphorus of this type, the phosphorus is taken up in the sludge and separated from the water along with the excess sludge, but there is a disadvantage in that a large amount of sludge is formed.
Thus, an apparatus for the biological removal of phosphorus, in which some of the return sludge is left to stand in an anaerobic tank and phosphorus is released and then this is subjected to solid/liquid separation, the solid fraction is solubilized and the amount of sludge is reduced in volume, has been proposed (Japanese Unexamined Laid Open Patent Application H11-188383). Furthermore, an apparatus for the biological removal of phosphorus, in which the return sludge is solubilized and the sludge is reduced in volume and at the same time the phosphorus-containing water which is discharged from the sludge in the anaerobic tank is subjected to a crystallization type phosphorus removal treatment, has been proposed by the present applicant (Japanese Unexamined Laid Open Patent Application H11-57773).
A schematic representation of the phosphorus-removing apparatus of Japanese Unexamined Laid Open Patent Application H11-188383 is shown in
FIG. 5
, where the raw water
31
is introduced into the anaerobic tank
33
of the biological phosphorous-removal activated sludge treatment process
32
along with return sludge
38
from the settling tank
35
and ozone-oxidized sludge
49
which is discharged from the ozone oxidation tank
48
, and BOD elimination and absorption of phosphorus by the phosphorus-removing bacteria are carried out in the anaerobic tank
33
and the aerobic tank
34
which is connected thereto in the process
32
. Some of the sludge in the same process is sent to the settling tank
35
and the supernatant water in the settling tank
35
is taken out as treated water
36
, and most of the settled sludge
37
which has settled out is recycled to the anaerobic tank
33
as the returned sludge
38
.
A part of the sludge is divided off from the aforementioned settled sludge
37
and is poured into the sludge anaerobic tank
40
as the branched or divided sludge
39
and phosphorus is released from the phosphorus-containing sludge on being left to stand here under anaerobic conditions. The sludge in the sludge anaerobic tank
40
is then subjected to solid/liquid separation by means of a membrane separating tank
41
, and then the separated sludge
43
obtained by solid/liquid separation is introduced into an ozone-oxidation tank
48
and subjected to oxidative degradation with ozone, and soluble organic material is dissolved out. The ozone-oxidized sludge
49
produced in this ozone-oxidation tank
48
is returned to the anaerobic tank
33
of the biological phosphorous removal activated sludge treatment process
32
and then flows into the aerobic tank
34
, and the ozone-oxidized sludge
49
(of which the biodegradability by microorganisms has been improved) is degraded to carbon dioxide gas and water microbiologically.
The activated sludge which has been propagated by elimination of the BOD of the raw water in this way is degraded to carbon dioxide gas and water by circulation through the sludge anaerobic tank
40
, the ozone-oxidation tank
48
and the biological phosphorus-removing activated sludge treatment process
32
, and so it should be discharged out of the system and the amount of excess sludge is more or less zero.
Moreover, soluble organic matter (BOD) is included in abundance in the ozone-oxidized sludge
49
as a result of the oxidative degradation of the activated sludge with ozone and so, if this is added to the anaerobic tank
33
, the phosphorus release from the phosphorus-removing bacteria can be made to occur actively. Furthermore, if the sludge is left to stand anaerobically beforehand in the sludge anaerobic tank
40
, the solubilization rate of the sludge is improved in the ozone-oxidation of sludge in the ozone-oxidizing tank
48
.
On the other hand, metal compounds which bring about chemical precipitate-forming reactions with phosphorus, such as calcium, magnesium, aluminum or iron compounds for example, are added in the phosphorus chemical-removal process
45
to the solid/liquid separated water
42
from the membrane separating tank
41
and the phosphorus is precipitated and separated and recovered as a calcium phosphate compound, such as hydroxyapatite, magnesium ammonium phosphate (MAP), aluminum phosphate or iron phosphate. In the case of
FIG. 5
, calcium hydroxide
44
is used for the metal compound and the hydroxyapatite
47
is produced.
The biological phosphorus-removing apparatus of the aforementioned Japanese Unexamined Laid Open Patent Application No. H11-57773 is an apparatus for the biological removal of phosphorus by means of an anaerobic/aerobic method, in which there is provided a sludge solubilizing process to which some return sludge is introduced, a means of returning sludge which has been solubilized in said sludge solubilizing device to the anaerobic tank, and a phosphorus-removal reaction column into which the liquid from the anaerobic tank is introduced.
In that apparatus for the biological removal of phosphorus, the volume of sludge can be reduced by solubilizing at least some of the return sludge and subjecting it to biological treatment once again. Furthermore, by removing and recovering the phosphorus which is included in the solubilized sludge obtained by solubilizing the returned sludge as MAP (magnesium ammonium phosphate) by way of the anaerobic tank and the phosphorus-removing column (MAP reaction column), it is possible to remove the phosphorus from t
Goel Rajeev
Yasui Hidenari
Burns Doane Swecker & Mathis L.L.P.
Kurita Water Industries Ltd.
Prince Fred G.
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