U.S. patent number RE40,565 [Application Number 11/869,357] was granted by the patent office on 2008-11-11 for method and device for purifying waste water comprising an additional sludge treatment by ozonation.
This patent grant is currently assigned to Societe Degremont. Invention is credited to Andre Haubry, Roger Pujol, Eric Thieblin.
United States Patent |
RE40,565 |
Thieblin , et al. |
November 11, 2008 |
**Please see images for:
( Certificate of Correction ) ** |
Method and device for purifying waste water comprising an
additional sludge treatment by ozonation
Abstract
Method for purifying waste water, whereby the waste water is
subjected to a biological treatment producing sludge, part of this
sludge being recycled towards the biological treatment while being
subjected to ozonation combined with mechanical stirring. A
mechanical stirring energy is brought in to attack the walls of the
microorganisms.
Inventors: |
Thieblin; Eric (Plaisir,
FR), Pujol; Roger (Chatou, FR), Haubry;
Andre (Mezy sur Seine, FR) |
Assignee: |
Societe Degremont (Rueil
Malmaison, FR)
|
Family
ID: |
39940955 |
Appl.
No.: |
11/869,357 |
Filed: |
April 14, 2000 |
PCT
Filed: |
April 14, 2000 |
PCT No.: |
PCT/FR98/01647 |
371(c)(1),(2),(4) Date: |
April 14, 2000 |
PCT
Pub. No.: |
WO99/06327 |
PCT
Pub. Date: |
February 11, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09485026 |
Jul 24, 1998 |
06337020 |
Jan 8, 2002 |
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Current U.S.
Class: |
210/627; 210/760;
210/628; 210/173 |
Current CPC
Class: |
Y02W
10/15 (20150501); Y02W 10/10 (20150501) |
Current International
Class: |
C02F
1/34 (20060101); C02F 1/36 (20060101); C02F
1/78 (20060101); C02F 3/02 (20060101); C02F
3/12 (20060101) |
Field of
Search: |
;210/627,173,628,760 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2546756 |
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Apr 1977 |
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DE |
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4407564 |
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Sep 1995 |
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DE |
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0645347 |
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Mar 1995 |
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EP |
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2490208 |
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Mar 1982 |
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FR |
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1116570 |
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Jun 1968 |
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GB |
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2222798 |
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Sep 1990 |
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JP |
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WO 9513990 |
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May 1995 |
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WO |
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Other References
G B. Saayman et al. "Chemical Control of Filamentous Sludge Bulking
in a Full-scale Biological Nutrient Removal Activated Sludge
Plant", Proceedings of the First Australian Conference of the
International Ozone Association, vol. II, pp. III-61-III-81. cited
by other .
Collignon et al, "Treatment of Bulking by Ozonation Mechanisms of
Ozone on Microorganisms", Tribune de l eau, No. 562-12, pp. 46-57.
cited by other .
Kunz et al., "Findings and Experiences from the Practical
Application of Sewage Sludge Disintegration", Schlamme, pp.
1289-1298, (Jul. 1996). cited by other.
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Primary Examiner: Barry; Chester T.
Attorney, Agent or Firm: Miller, Matthias & Hull
Claims
What is claimed is:
1. Method of purifying waste water charged with organic materials,
the method including a step in which the waste water remains in a
biological treatment system, referred to as the main biological
treatment system, in which said organic materials are degraded by
micro-organisms to produce sludge, some of the sludge being
subjected to ozonation combined with mechanical stirring before it
is sent to the main biological treatment system, the sludge
subjected to ozonation in this way being referred to as treated
sludge, wherein during the mechanical stirring step sufficient
mechanical energy is imparted to said treated sludge to attack the
cell walls of the bacteria and other micro-organisms contained in
the treated sludge, this mechanical energy being from 50 kJ/kg to
3,000 kJ/kg of dry material in the treated sludge, and wherein from
0.001 g to .[.0.2 g.]. .Iadd.0.02 g .Iaddend.of ozone per gram of
dry material in the treated sludge are consumed during the
ozonation step.
2. Method according to claim 1, wherein the pH of the treated
sludge is always from 6 to 9.
3. Method according to claim 1, wherein the treated sludge is
mechanically stirred before its ozonation.
4. Method according to claim 1, wherein the treated sludge is
mechanically stirred after its ozonation.
5. Method according to claim 1, wherein the mechanical stirring and
the ozonation of the treated sludge take place in the same reaction
enclosure.
6. Method according to claim 1, wherein a particular flowrate of
treated sludge, referred to as the first flowrate, is taken from
the outlet of an ozonation reactor in which the treated sludge is
subjected to ozonation, this first flowrate is then subjected to
mechanical stirring, and said first flowrate is then sent to the
ozonation reactor with a particular additional flowrate of sludge
from the main biological reactor, referred to as the second
flowrate, the second flowrate being lower than the first
flowrate.
7. Method according to claim 1, wherein the treated sludge is
subjected to aerobic or anaerobic digestion in addition to
ozonation and mechanical stirring.
8. Method according to claim 7, wherein the aerobic or anaerobic
digestion takes place after ozonation and mechanical stirring.
9. Method according to claim 7, wherein a particular flowrate of
the treated sludge is taken from the outlet of a digester in which
the treated sludge undergoes the aerobic or anaerobic digestion and
this flowrate of treated sludge is then subjected to mechanical
stirring and ozonation before it is sent to the digester with a
particular additional flowrate of sludge from the main biological
reactor.
10. Method according to claim 7, wherein the main biological
treatment system is sent only some of the treated sludge that has
been subjected to aerobic or anaerobic digestion and further
treated sludge leaving the digester is evacuated.
11. Method according to claim 1, wherein the ozonation step is
implemented in a ozonation reactor which includes at least one vent
from which exits a gaseous effluent including at least ozone and
oxygen, the method further including a step of collecting this
gaseous effluent and re-using said gaseous effluent to treat the
waste water or other liquid resulting from the treatment of the
waste water.
12. Method according to claim 11, wherein the ozone contained in
the gaseous effluent collected from the outlet of the vent is
destroyed before said gaseous effluent is re-used.
13. Method according to claim 1, wherein the treated sludge is
subjected to ozonation in a pressurized ozonation reactor.
14. Method according to claim 1, wherein the waste water is
subjected to a clarification step after passing through the main
biological treatment system and in which at least the sludge to be
treated by ozonation and mechanical stirring is separated from said
waste water.
Description
The present invention relates to methods and systems for purifying
waste water which include additional sludge treatment by ozonation
or reduce significantly the quantities of sludge produced by a
biological treatment system, in particular to reduce the cost of
treating the sludge resulting from new regulations.
One advantage of said invention is to improve settling of the
sludge after treatment.
The invention relates more particularly to a method of purifying
waste water charged with organic materials, the method including a
step in which the waste water remains in a biological treatment
system, referred to as the main biological treatment system
(consisting of one or more reactors such as aeration pools,
bacteria beds, anaerobic digesters, clarifiers, etc for biological
treatment, possibly in conjunction with physical-chemical
treatment), in which said organic materials are degraded by
micro-organisms to produce sludge, some of the sludge being
subjected to ozonation combined with mechanical stirring before it
is sent to the main biological treatment system, the sludge
subjected to ozonation in this way being referred to as "treated
sludge".
Document EP-A-0 645 347 describes a method of the above kind in
which ozonation takes place after acidifying the treated sludge to
a pH less than 5, mechanical stirring being employed either during
the acidification process to mix the treated sludge with an
acidification reactant or by spraying some of the treated sludge
into the ozonation reactor by means of a pump.
The method described in the above document has the drawbacks of
requiring relatively large quantities of ozone and interfering with
the operation of the main biological treatment system because of
the acidification of the treated sludge.
One particular object of the present invention is to alleviate
these drawbacks.
To this end, the invention proposes a method which is essentially
characterized in that during the mechanical stirring step
sufficient mechanical energy is imparted to said treated sludge to
attack the walls of the micro-organisms contained in the treated
sludge.
This improves the efficiency of the ozonation treatment compared to
the process described in the document mentioned above because the
mechanical stirring energy imparted to the treated sludge is
sufficient to weaken the floc and the cell walls of the
micro-organisms contained in said treated sludge to enable the
ozone to attack the micro-organisms more efficiently. The floc is
destroyed by attacking the exopolymers which account for the
cohesion of said floc and this causes various bacteria and protozoa
to burst.
Quantities of ozone significantly smaller than used in the method
described in the document mentioned above can therefore be
used.
Moreover, correct operation of the main biological treatment system
is not interfered with because it is not necessary to acidify the
treated sludge.
Furthermore, the efficiency of the ozonation process is further
improved because the treated sludge does not have to be
acidified.
Finally, recirculating the sludge to the main biological treatment
system absorbs additional pollution generated when the cell walls
of the micro-organisms are destroyed (increased chemical oxygen
demand [COD], biochemical oxygen demand [BOD] and dissolved organic
carbon), the final result being that the volume and mass of the
sludge are greatly reduced, the indices of the sludge (in
particular the Mohlmann index) are significantly improved and
possible biological disorders (in particular "bulking" due to
filamentary bacteria) are minimized.
One or more of the following features can be used in preferred
embodiments of the invention: the pH of the treated sludge is
always from 6 to 9; the treated sludge is mechanically stirred
before its ozonation; the treated sludge is mechanically stirred
after its ozonation; the mechanical stirring and the ozonation of
the treated sludge take place in the same reaction enclosure; a
particular flowrate of treated sludge, referred to as the first
flowrate, is taken from the outlet of a treated sludge ozonation
reactor, this first flowrate then being subjected to mechanical
stirring, said first flowrate being then sent to the ozonation
reactor with a particular additional flowrate of sludge from the
main biological reactor, referred to as the second flowrate, the
second flowrate being lower than the first flowrate; the treated
sludge is subjected to aerobic or anaerobic digestion in addition
to ozonation and mechanical stirring; the aerobic or anaerobic
digestion takes place after ozonation and mechanical stirring; a
particular flowrate of the treated sludge is taken from the outlet
of a digester in which the treated sludge undergoes the aerobic or
anaerobic digestion, this flowrate of treated sludge then being
subjected to mechanical stirring and ozonation before it is sent to
the digester with a particular additional flowrate of sludge from
the main biological reactor; the main biological treatment system
is sent only some of the treated sludge that has been subjected to
aerobic or anaerobic digestion and further treated sludge leaving
the digester is evacuated; the ozonation step is implemented in an
ozonation reactor which includes at least one vent from which exits
a gaseous effluent including at least ozone and oxygen, the method
further including a step of collecting this gaseous effluent and
re-using said gaseous effluent to treat the waste water or other
liquid resulting from the treatment of the waste water; the ozone
contained in the gaseous effluent collected from the outlet of the
vent is destroyed thermally or catalytically before said gaseous
effluent is re-used; the mechanical stirring energy is from 10 kJ
to 20,000 kJ per kg of dry material of the treated sludge; the
mechanical stirring energy is from 50 kJ to 3,000 kJ per kg of dry
material of the treated sludge.
The invention also provides a system for implementing a method as
defined hereinabove, the system including a pressurized ozonation
reactor in which the treated sludge is subjected to ozonation.
Other features and advantages of the invention will become apparent
in the course of the following description of several embodiments
of the invention given by way of non-limiting example and with
reference to the accompanying drawings.
IN THE DRAWINGS
FIG. 1 is a diagrammatic view of an installation for treating waste
water using one embodiment of a method in accordance with the
invention,
FIGS. 2 to 4 are diagrams showing in more detail the content of the
box 9 in FIG. 1,
FIGS. 5 to 8 are diagrammatic views showing in more detail the
content of the box 10 from FIGS. 2 to 4, in which ozonation and
mechanical stirring of the treated sludge are combined, and
FIG. 9 is a view similar to FIG. 1 for a different embodiment of
the invention.
In the various figures, the same reference symbols designate
identical or similar elements.
FIG. 1 is a highly diagrammatic representation of a station 1 for
purifying waste water, the station including: an inlet 2 for waste
water charged with organic material, one or more biological
treatment reactors, for example an aeration pool 3 in which said
organic materials are degraded by micro-organisms to produce
sludge, the aeration pool 3 possibly being associated with or
replaced by one or more other biological treatment systems such as
fixed culture reactors, anaerobic digesters, etc., a clarifier 4,
or any other solids-liquids separator system, which receives the
waste water after it has passed through the aeration pool 3 and
which separates the water and the sludge, a treated water outlet 5
which collects the water from the outlet of the clarifier 4, a
sludge outlet 6 which collects the sludge from the outlet of the
clarifier 4, a first recycling loop 7 which collects some of the
sludge from the outlet 6 and recycles it to the inlet of the
aeration pool 3, this first recycling loop 7 possibly being
dispensed with (this loop can carry a flowrate representing from
50% to 300% of the nominal flowrate of the urban or industrial
effluent treated by the purifying station, for example), and a
second sludge degrading loop 8 which also collects some of the
sludge from the outlet 6 and feeds it to the inlet of the aeration
pool 3 via a sludge treatment system 9 in which said sludge is
subjected to at least one combined treatment of ozonation and
mechanical stirring.
As shown in FIGS. 2 to 4, the sludge treatment system 9 can
include: only an ozonation and mechanical stirring system 10 (FIG.
2), or an aerobic or anaerobic digester 11 downstream of an
ozonation and mechanical stirring system 10 (FIG. 3), some of the
sludge leaving the digester 11 possibly being evacuated rather than
recycling all of the sludge to the inlet of the aeration pool 3, or
an anaerobic digester 11 including a recirculation loop 12 (FIG. 4)
into which an ozonation and mechanical stirring system 10 is
integrated, the flowrate Q4 of sludge at the sludge outlet 6 being
generally less than the flowrate Q3 of the sludge in the recycling
loop 12 between the inlet and the outlet of the digester 11 (as in
the case of FIG. 3, some of the sludge leaving the digester 11 can
be evacuated rather than recycling all of the sludge to the inlet
of the aeration pool 3).
As shown in FIG. 5, the ozonation and mechanical stirring system 10
includes a mechanical stirrer 13 generally consisting of an
enclosure 14 including one or more turbines 15, or possibly dynamic
mixers, hydro-ejectors, kneaders or any other mechanical stirring
system.
Note that ultrasound is regarded as a physical phenomenon
(generation of acoustic waves) and therefore is not included in the
category of "mechanical" phenomena in the context of the present
invention, using moving systems.
The power of the mechanical stirring system is chosen so that the
sludge treatment system 9 preferably dissipates a mechanical
stirring energy from 10 kJ/kg to 2,000 kJ/kg of dry material of the
treated sludge (typically 600 kJ/m.sup.3 to 3,600 kJ/m.sup.3 of
treated sludge), which energy can be as high as 20,000 kJ/kg of dry
material (typically 14,000 kJ/m.sup.3 of treated sludge). The
preferred range of mechanical energy runs from 50 kJ/kg to 3,000
kJ/kg of dry material.
Also, the ozonation and mechanical stirring system 10 includes an
ozonation reactor 16 which generally consists in a closed enclosure
17 which receives the sludge to be treated and into which ozone
from an ozoner 18 is injected via injection nozzles 19 (which can
be replaced with porous diffusers, hydro-ejectors or the like),
these nozzles being coupled to static or dynamic mixers if
necessary.
The overall consumption of ozone is preferably from 0.001 g to 0.02
g of ozone per gram of dry material in the treated sludge passing
through the sludge treatment system 9 (if the treated sludge were
passed several times through the ozonation reactor 16, the
above-mentioned ozone consumption would be the total consumption
for all passes of the sludge through the ozonation reactor).
The enclosure 17 can be pressurized, if required, in which case it
is the subject of appropriate structural design calculations.
Moreover, the enclosure 17 includes a vent 20 from which exits a
gaseous effluent containing at least oxygen and ozone not consumed
by treating the sludge. If necessary, the vent 20 can be connected
to a system 21 for destroying the ozone by heating it or by passing
it over activated carbon, or said gaseous effluent can instead be
re-used at any point of the purifying station. For example, it can
be injected into the waste water at the inlet of the aeration pool
3 or brought into contact with any other liquid resulting from the
treatment of the waste water (waste water at the outlet from the
aeration pool or at the outlet from the clarifier, etc.).
The mechanical stirrer 13 and the ozonation reactor 16 are
generally fed with sludge by a pump 22 which can if necessary
contribute to the mechanical stirring of the sludge, in which case
the pump 22 is advantageously a centrifugal pump.
In this case, the mechanical stirring energy imparted to the sludge
by the stirrer 13 can if necessary be less than 10 kJ/kg of dry
material in the treated sludge (600 kJ/m.sup.3 of treated sludge),
provided that the sum of this mechanical stirring energy plus the
mechanical energy imparted to the sludge by the pump 22 is from 10
kJ/kg to 2,000 kJ/kg of dry material in the treated sludge (600
kJ/m.sup.3 to 14,400 kJ/m.sup.3 or treated sludge).
Of course, the mechanical stirrer 13 and the ozonation reactor 16
are not necessarily disposed as shown in FIG. 5; instead, as shown
in FIGS. 6 to 8: the ozonation reactor 16 could be upstream of the
mechanical stirrer 13 (FIG. 6), the turbine 15 or other mechanical
stirring system could be in the ozonation reactor 33 itself (FIG.
7), this reactor having characteristics similar to the ozonation
reactor 16 previously described, the mechanical stirrer 13 could be
installed on a recirculation loop 24 which takes a flowrate Q1 of
sludge from the outlet of the ozonation reactor 16 and feeds that
flowrate Q1 back to the inlet of said reactor, the flowrate Q2 of
sludge taken from the sludge outlet 6 and joining the flowrate Q1
at the inlet of the ozonation reactor generally being less than the
flowrate Q1 and the recirculation loop 24 generally being provided
with a pump 25 which can if necessary contribute to the mechanical
stirring of the sludge, as previously described for the pump
22.
Finally, as shown in FIG. 9, the ozonation treatment system 9,
along with all its variants previously described, could take sludge
from the aeration pool 3 and return the treated sludge to the same
aeration pool.
More generally, the sludge treatment system 9 could take sludge to
be treated from anywhere in the purifying station after at least
one biological treatment of the waste water and return at least
some of the treated sludge to that biological treatment.
Finally, note that the treated sludge is not subjected to
acidification at any time, the pH of the sludge always remaining
greater than 5, and preferably from 6 to 9, so that re-injecting
the sludge into the biological treatment stage of the purification
station does not interfere with said biological treatment.
* * * * *