CA1063264A - Phosphate stripping of sewage - Google Patents
Phosphate stripping of sewageInfo
- Publication number
- CA1063264A CA1063264A CA229,489A CA229489A CA1063264A CA 1063264 A CA1063264 A CA 1063264A CA 229489 A CA229489 A CA 229489A CA 1063264 A CA1063264 A CA 1063264A
- Authority
- CA
- Canada
- Prior art keywords
- phosphate
- sludge
- subnatant
- stripping zone
- anaerobic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/02—Aerobic processes
- C02F3/12—Activated sludge processes
- C02F3/1205—Particular type of activated sludge processes
- C02F3/1215—Combinations of activated sludge treatment with precipitation, flocculation, coagulation and separation of phosphates
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
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- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Microbiology (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- Biodiversity & Conservation Biology (AREA)
- Removal Of Specific Substances (AREA)
- Activated Sludge Processes (AREA)
- Purification Treatments By Anaerobic Or Anaerobic And Aerobic Bacteria Or Animals (AREA)
- Treatment Of Sludge (AREA)
- Separation Of Suspended Particles By Flocculating Agents (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
- Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
- Micro-Organisms Or Cultivation Processes Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Activated sludge sewage treatment process comprising aerating a mixed liquor comprising phosphate-containing influent sewage material to cause the microorganisms present to take up phosphate, separating phosphate-enriched sludge from the mixed liquor, and settling the separated sludge in a phosphate stripping zone to form supernatant liquor and settled sludge. At least part of the settled sludge is maintained under anaerobic conditions to cause release of soluble phosphate and the resulting sludge containing released phosphate is contacted with a lower soluble phos-phate content medium to effect phosphate enrichment of the supernatant liquor in the stripping zone, with at least a portion of the anaerobic sludge being recirculated to the aeration zone.
Activated sludge sewage treatment process comprising aerating a mixed liquor comprising phosphate-containing influent sewage material to cause the microorganisms present to take up phosphate, separating phosphate-enriched sludge from the mixed liquor, and settling the separated sludge in a phosphate stripping zone to form supernatant liquor and settled sludge. At least part of the settled sludge is maintained under anaerobic conditions to cause release of soluble phosphate and the resulting sludge containing released phosphate is contacted with a lower soluble phos-phate content medium to effect phosphate enrichment of the supernatant liquor in the stripping zone, with at least a portion of the anaerobic sludge being recirculated to the aeration zone.
Description
~o63z64 BACKGROUND OF THE INVENTION
Thls invention relates to an activated sludge sewage treatment process ~or treating raw or treated phosphate-containing sewage to obtain a substantially phosphorous-~ree e~fluent which is returned to natural water resources.
~ n the conventional actlvated sludge system in use today, sewage is sub~ected to the usual screening and prelimlnary sedimentation procedures, then mixed with activated sludge recycled ~rom a settling tank to form a mixed liquor which is sub~ected to aeration. During aeratlon o~ the mixed liquorJ the organisms present cause the aerobic decomposition o~ sollds and a high degree of BOD removal is achieved.
Phosphates, which are present in organic wastes and detergents, escape conventional sewage treatment processes and are released with the e~fluent into natural water resources, e.g., lakes, rivers and streams. These phosphates result ln over ~ertilization or eutrophication of waters causing unsightly algal blooms and serious pollution problems.
It is known that aeration of the mixed liquor in an activated sludge sewage treatment process lnitially causes the microorganisms present to take up phosphate.
U.S, Patent ~o. 3,236,766 discloses a process which util-izes this phenomenon for removing phosphates ~rom sewage.
According to the process disclosed in that patent, the pH o~ raw sewage is ad~usted, if necessary, to maintain $~ ' a range of from about 6.2 to about 8.5, the sewage is mixed with activated sludge to form a mixed liquor, the mixed liquor is aerated to maintain a dissolved oxygen content of at least 0.3 mg. per liter in the mixed liquor and a phosphate-enriched sludge is separated from the`
mixed liquor to provide a sùbstantially phosphate-free effluent. The phosphate-enriched sludge is treated to reduce the phosphate content thereof prior to recycling for mixing with the influent sewage. This is accomplished by maintaining the phosphate-enriched sludge in an an-aerobic condition for several hours.
Several other processes have been proposed for reducing the phosphate content of phosphate-enriched sludge following the aeration step in an activated sludge sewage treatment process. Thus~ for example, U.S. Patent No. 3,38S,785 discloses adjusting the pH of phosphate-enriched sludge to between about 3.5 and 6 and agitating the sludge in contact with a low phosphate-containing aqueous medium in a tank for a time sufficient to effect transfer of water-soluble phosphate material from the sludge to the aqueous phase. The low phosphate-containing aqueous medium used in this tank is water added from an external source to leach out the phosphate from the sludge.
After the soluble phosphate has been leached out of the sludge into the aqueous medium, the mixture is passed to a settling tank wherein the phosphate-enriched aqueous medium is separated from the phosphate-depleted sludge.
Since this process requires the addition of considerable quantlties of water from an external source and requires two separate tanks -- i.e., a phosphate leaching tank and a settllng tank, to separate the soluble phosphate rrom the sludge, a large capital lnvestment is required in such a process.
Accordingly, it is an ob~ect o~ thi5 invention to provlde an improved process for reducing the phosphate content of phosphate-contalning sewage in an activated sludge sewage treatment prooess.
It ls a further ob~ect o~ thls invention to provlde such a process whlch includes an improved phos-phate strlpping operation of phosphorous-enriched sludge and which results in lncreased efficiency of the phosphate removal from the sewage.
Other ob~ects and advantages of this invention will be apparent from the ensuing disclosure and claims.
SUMMARY
This invention relates to an activated sludge process for treating raw or treated phosphate-containlng sewage to obtaln a substantially phosphorous-free efflu-ent.
The process of this invention comprises aeratlng a mlxed liquor comprising phosphate-containing in M uent sewage material and activated sludge in an aeration zone to reduce the BOD content o~ the sewage material and to cause the m~croorganlsms present to take up phosphate.
Phosphate-enriched sludge is separated from the mixed llquor to provide a substantially phosphate-free effluent.
106326~
This phosphate-enriched sludge is passed to a phosphate stripping zone and settled to form supernatant liquor in the stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer. The subnatant sludge layer is maintained under anaerobic conditions for a time sufficient to re-lease phosphate to the liquid phase of the subnatant sludge layer. Subnatant anaerobic sludge is contacted with a lower soluble phosphate content medium to trans-fer the soluble phosphate in the subnatant anaerobicsludge liquid phase to said lower soluble phosphate content medium, for phosphate enrichment of supernatant liquor in the stripping zone upper section. At least a portion of the subnatant anaerobic sludge is recycled from the phosphate stripping zone to the aeration zone as the aforementioned activated sludge therefor.
As used herein, the term "sludge" refers to a solids-liquid mixture characterized by a sludge solids phase and an associated liquid phase. The term "lower soluble phosphate content medium" refers to an aqueous or water-containing medium which contains a lower con-centration of soluble phosphate than the subnatnat an-aerobic sludge with which it is contacted.
In accordance with the present invention, phosphate-enriched sludge, in which the phosphate is present in the cells of the sludge microorganisms, i.e., biological solids, is maintained under anaerobic condi-tions in a settled subnatant sludge layer in the phosphate 9~23-~063Z64 strlpping ~one for a tlme sufflclent to cause the micro-organisms to release phosphate to the liquid phase Or the sludge. The resultant subnatant anaerobic sludge ls con-tacted with a lower soluble phosphate content medlum. The purpose of such contacting is to transfer soluble phos-phate out of the subnatant anaerobic sludge and ultimately to the supernatant li~uor in the stripping zoneJ so as to e~ect a phosphate enrlchment Or the supernatant llquor thereln. In accordance wlth the lnvention, the soluble pho~phate ln the subnatant anaerobic sludge may be trans-rerred either directly by contacting the anaerobic sludge with the supernatant liquor or indirectly, as for example by contacting the anaerobic sludge with the phosphate-enriched sludge passed to the stripping zone.
Without the aforementloned contactlng/transfer steps, a conslderable time would be required for the sol-uble phosphate in the subnatant anaerobic sludge to migrate through the supernatant portion of the sludge and into the supernatant liquor in the stripping zone. Under such condi-tions, ir the sludge were withdrawn from the stripping zone and recycled to the aeration zone be~ore a sufficient arnount o~ the soluble phosphate is transferred to the supernatant liquor, an excess amount of soluble phosphate will be re-cycled to the aeration zone and the phosphate removal er~lciency of the overall process will be lowered. The pre~ent invention overcomessuch difficulty and has been demonstrated in actual operation to achieve a high level of pho~phate removal efficiency.
9~23-~063Z64 BRIEF DESCRIPTION OF ~HE DRAWINGS
Figure 1 is a schematlc flowsheet Or an actlvated sludge process accordlng to one embodiment of the inven-tion, wherein subnatant anaerobic ~ludge is contacted wlth the phosphate-enrlched sludge passed to the stripping zone.
Figure 2 is a schematic ~lowsheet Or an activated sludge process accordlng to another embodiment of the in-vention, wherein a portion o~ the supernatant liquor in the phosphate stripping zone iR wlthdrawn therefrom and is reintroduced into the stripping zone underneath the layer Or subnatant anaerobic sludge for contacting there-with.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
~ererring now to the drawings, Figure 1 shows an illustrative process system according to the present inventlon. A raw phosphate-containing sewage influent stream 1 is passed through conventional screenlng and grit-removing units and is optionally sub~ected to primary settling in a primary settling tank 2 ~rom which primary sludge is removed in line 3. The primary ~ettled sewage 1~ mlxed with recycled, activated sludge hereinafter described to form a mixed liquor and is passed by line 4 to the aeration tank 5.
In the aeration tank, the mixed liquor ls aerated at a rate sufficient to maintain it ~erobic --i.e., so that there is a measurable amount of dissolved ~063264 oxygen present in the mlxed liquor in at least a part of the aeration tank, for a period o~ 1 to 8 hours. During aeratlon, the microorganlsms present take up phosphate and consume organic matter present in the sewage. A hl~h degree o~ BOD removal ls obtained durlng aeration.
A~ter aeratlon, the mixed liquor is fed lnto a secondary settling tank 6. In the secondary settllng tank 6) phosphate-enrlched sludge settles and thereby 3eparates ~rom the llquor. The sludge contains a substan-tial portlon of the phosphate present in the sewage The substantlally phosphate-free e~luent ls discharged for dlsposal ln a conventlonal manner by line 7.
The phosphate-enrlched sludge ls removed from the settllng tank 6 by llne 8. A portlon of the sludge may be dellvered to waste and the remalnder contacts and mixes wlth recycled, subnatant, anaeroblc sludge from the phosphate strlpper whlch contains a high concentration o~
soluble phosphate and the mlxture ls passed to the phos-phate stripper 9. In the phosphate stripper 9, the phosphate-enrlched sludge is settled to ~orm supernatant liquor ln the upper sectlon o~ the strlpplng zone, and settled sludge comprlsing a supernatant sludge layer and a subnatant sludge layer. The subnatant sludge layer ls maintalned under anaeroblc conditions ~or a tlme suf~lclent to cause the microorganlsms in the subnatant anaeroblc sludge to release phosphate to the llquld pha~e of the subnatant sludge layer. The phosphate leaks out of the sludge sollds lnto the llquld phase. ~he mechanlsm o~
thls treatment will be descrlbed ln more detail hereinbelow.
-~ 9923-1 ~063264 A phosphate-enrlched supernatant ll~uor is produced in the phosphate strlpper 9 and is passed by llne 10 to the phosphate preclpitator 11. A phosphate precipitant, such as alumlnum or lron salts or lime, is mixed with the phosphate-enriched supernatant liquor in the phosp~late precipitator 11 to precipitate phosphate.
The precipitated phosphate is passed by line 12 for mixing with raw sewage in line 1.
In the phosphate stripper 9, sludge solids, contalnlng a high amount of phosphate ln the cells of the organisms in the sludge, separate from the aqueous phase of the sludge and settle toward the bottom of the phosphate stripper. Thus, the solld particles in the sludge contain intracellular phosphate and these partlcles settle into the subnatant anaeroblc layer of sludge in the phosphate stripper 9. A density gradient exists in the layer of settled sludge, the density of the sludge being greater at the bottom of the sludge layer than at the top. As the sollds in the sludge containing intra- -cellular phosphate mlgrate to the bottom of the sludge layer, because of the anaerobic conditions existing in this portion of the sludge layer, the organisms release phosphate to the liquid phase of the sludge in the form of water-~oluble phosphate ions. Preferably, the residence time of the sludge in the phosphate stripper is from 2 to 30 hours. The concentration of soluble phosphate is initially greatest in the lower portion of the sludge layer. As discussed earlier herein, a considerable time -` 9923-ls requlred rOr the soluble phosphate to mlgrate through the less dense and lower solids containing supernatant portion of the sludge and into the supernatant llquor.
If the sludge ls withdrawn and recycled to the aeration zone be~ore a su~icient amount o~ the soluble phosphate is trans~erred to the supernatant llquor, an excess amount o~ ~oluble phosphate wlll be recycled to the aeration tank and the phosphate removal e~riciency o~ the overall pro-ce~s wlll be lowered. It ls pre~erred that no more than 75% o~ the soluble phosphate which is relea~qed in the phos-phate stripper be recycled to the aeration tank with the recycle activated sludge.
Accordlng to one embodiment o~ the invention, subnatant, anaerobic sludge containing a substantlal portion o~ the ~oluble phosphate which ls released in the phosphate 3trlpper 9 is withdrawn from the phosphate stripper and split lnto two portions. One portlon Or this high soluble phosphate-containing sludge ls recycled through line 13 for mixing with the raw sewage which is being red to the aeration tank in line 4, and the other portion of anaerobic, high soluble phosphate-containing sludge ls recycled through llne 14 for contacting and mix-ing wlth aeroblc sludge from the secondary ~ettling tank 6 as it is being passed to the phosphate stripper 9. Since the sludge withdrawn from the secondary settling tank 6 contains lntracellular phosphate in the solids phase thereor and since the liquid phase, which may comprise 98 to 99~ o~ the sludge, contains little or no soluble 10~3Z64 phosphate, the llquld portion of thls aerobic sludge leaches or elutriates the soluble phosphate from the high soluble phosphate-contalnlng anaeroblc sludge por-tion from line 14. It is preferred that each Or the high soluble phosphate-contalnlng anaeroblc sludge portlonQ
wlthdrawn from the strlpper and passed through llnes 13 and 14 comprlse from about 25 to 75~ o~ the total amount o~ high soluble phosphate-containlng sludge wlthdrawn ~rom the stripper and that at least 25% of the soluble phosphate released in the strlpper be removed from the stripper along wlth the supernatant`llquor ln line 10.
The portion of the hlgh soluble phosphate-contalning sludge ln llne 14 may also be introduced dir-ectly into the phosphate strlpper 9 above the sludge layer contalned therein so that the soluble phosphate will come in contact with the supernatant ln the phosphate sbrlpper and be dlsso'ved by the supernatant.
In the embodlment of the invention shown in Fig. 2, phosphate-containing influent sewage material is introduced to the sewage treatment system by line 15 and mixed wlth the phosphate-depleted supernatant liquor from line 34, to be described more fully hereina~ter. The in-~luent sewage and recycle sludge in line 24 are pas~ed into aeration zone 16 wherein the mixed llquor formed ~rom the sewage material and the recycled activated sludge are aerated to reduce the BOD content of the sewage and to cause the microorganisms present to take up phosphate.
In practlce, the aeration zone may be Or a conventional type wherein atmospheric air is used as the oxidant in open aeration chambers. Alternatively, the aeration may be conducted in a manner as taught by U.S. Patent No~.3,547,813 - 3,547,815 to J.~. McWhlrter et al ~n ~hlch at least one enclosed covered aeration chamber i~ employed wherein the llquid undergoing treat-ment is lntimately contacted in the presence of activ-ated sludge with oxygen enrlched gas ~rom an overlying gas space to dissolve the oxygen necessary for aeroblc biological activity. Such oxygenation systems are able to operate at biological suspended æolids levels se~reral times ~reater and aeration detentlon periods several times less than those Or conventional alr aeration systems while maintaining comparable or higher overall levels o~ treat-ment, and have been found to be hlghly e~fective in the practice of the present invention.
The aerated mixed liquor is conducted from the aeration zone in line 17 and passed to the secondary settling zone 18. In the settling zone, phosphate-enriched sludge is separated from the mixed liquor to provide a substantially phosphate-free effluent which is discharged Irom the system in line 19. The separated phosphate-enriched sludge is passed from the secondary settllng zone by line 20 to the phosphate strlpping zone 21. In the stripping zone, the phosphate-enriched sludge is settled to rorm supernatant liquor in the upper section 22 Or the si~ripping zone, and settled sludge comprising a supernatant sludge layer and a ~ubnatant æludge layer.
The subnatant sludge layer ln the stripplng zone is main-tained under anaerobic conditions in the same manner pre-viously descrlbed for a time sufrlcient to release phos-phate to the liquid phase of the subnatant ~ludge layer.
The subnatant anaerobic sludge contacting step is conducted in this system by withdrawing supernatant liquor from the stripping zone upper section in line 25 and dlverting a portlon thereof into line 26, having pump means 27 disposed therein, for reclrculation to the stripping zone lower section, The dlverted supernatant liquor ln line 26 is reintroduced lnto the phosphate stripplng zone by the sparging means 28, whlch may for example co~prise multiple stationary nozzles. In thls manner a countercurrent elutriation of the ~oluble phos-phate in the subnatant anaeroblc sludge ls established, as the soluble phosphate is trans~erred to the upflowing recirculated supernatant liquor and subsequently to the bulk liquid volume of the supernatant liquor in the strlpplng zone upper section.
The portion of the supernatant liquor withdrawn from the stripping zone ln line 25 whlch is not diverted as recycle contacting medium in line 26 is flowed to quick mix tank 29. In this tank, the undiverted super-natant liquor is rapldly mlxed (by means not shown) with a phosphate precipitant, e.g., lime, lntroduced to the tank by me~ns of line 30. The supernatant liquor-phos-phate preclpitant mixture is then passed by line 31 to flocculator tank 32 in which the precipitated phosphate is settled and removed from the system as waste chemlcal sludge in line 33. The overflow phosphate-depleted super-natant from the flocculator tank 32 is recycled in line 34 for ~oining with the sewage influent entering the process in line 15.
By means of the above-describéd subnatant sludge contacting scheme, a significant amount of the phosphate which is released in the subnatant anaerobic sludge layer is transferred to the supernatant liquor in the stripping zone upper section, whereby the subnatant sludge withdrawn from the bottom of the stripping zone in line 23 and re-circulated to the aeration zone in line 24 has a suffic-iently lowered phosphate content to permit high removal of phosphate from the sewage to be achieved in the aeration zone.
Means other than those illustratively described hereinabove may be used in the broad practice of the pres-ent invention to maximize the contact between the subnatant anaerobic sludge portion containing a high soluble phos-phate content and the supernatant liquor in the phosphate stripper so that the soluble phosphate will be eluted into the supernatant liquor. For example, two or more phosphate stripping tanks may be used. While one tank is maintained in a relatively unagitated state and the sludge is main-tained under anaerobic conditions so that the microorgan-isms will release their phosphate content, another tank, in which the microorganisms have already released their phosphate content is agitated to cause the subnatant, anaerobic layer of sludge containing the soluble phosphate 9~23-1 to mix wi~h the supernatant liquor. Arter the supernatant liquor has eluted substantlally all of the soluble phos-phate from the sludge sollds, the vigorous agitation is stopped and the solids are permltted to settle. After the solids have settled, the supernatant llquor, whlch then contains substantlally all Or the soluble phosphate in the tank, ls removed and passed to a phosphate preciplta~
tor and the phosphate-depleted sludge is recycled for mixing with raw sewage which 1~ being ~ed to the aeration tank. The tank is then ~illed with sludge from the secondary settling tank, the sludge is permltted to settle and become anaerobic and is maintained under anaerobic conditions while the previously descrlbed process of vigor-ously stirrlng the subnatant anaerobic sludge and super-natant liquor, settllngJ and removing a phosphate-enriched supernatant is repeated with the first tank. In other words, the two tanks are maintained 180 out of phase with each other.
Another means for effecting transfer o~ the soluble phosphate from the subnatant anaerobic sludge is to introduce rresh sludge from the secondary settling tank into the bottom of the stripping zone so that it diffuses up through the anaerobic layer and elutes the soluble phosphate contained in this layer.
Another means for maximizing the contact between the supernatant liquor and the subnatant anaerobic sludge layer containing a high concentration of soluble phosphate i~ the phosphate stripper is to intermittently 9923-~
and vigorously stir the contents o~ the phosphate stripper so that the anaerobic layer of sludge will be dispersed into the supernatant. The supernatant will thereby elute the phosphate from the slud~e solids The contents of the phosphate stripper are then permitted to settle. Dur-ing agitation and settling, no recycle sludge would be re-moved rrom the bottom of the phosphate stripper. Agitation may be accomplished by introduction Or a non-oxygen con-taining gas at the bottom of the stripper 9. Different portions of the anaerobic sludge layer may also be raised above the sludge layer and then permitted to settle again.
During settling, the soluble phosphate is eluted by the supernatant. While this i9 being done, another portion of the anaerobic sludge layer may be withdrawn from the phosphate stripping for recycle to the aeration tank.
Any o~ these processes may be conducted either continuously or intermittently. Thus, sufficient elutria-tion of phosphatemay be obtained in the Fig. 1 system if, ~or example, the anaerobic sludge withdrawn ~rom the phosphate stripper is recycled through line 14 one hour out Or every five hours of operation.
The following examples illustrate the specific advantages of the present invention in acheiving high overall removals of phosphate from phosphate-containing sewage relative to the prior art process systems lacking the subnatant sludge contacting feature of the instant process.
~(323-1 EXAMRLE I
In this test, a process system of a type simllar to that shown in Figure 2 herein was operated inltially ln the manner of the prior art wlthout the subnatant sludge contacting ~eature Or the present invention and subse-quently was operated ln accordance with the present ln-vention, using supernatant llquor wlthdrawn ~rom the strlpplng zone upper sectlon a~ the lower soluble phos-phate content contacting medlum, ln a manner substan-tially simllar to that described herelnabove in connec-tlon with Figure 2.
In both phases the comparative evaluatlon test, inrluent sewage was mixed with recycle activated sludge to form a mixed liquor which was then aerated in the aera-tion zone to cause the mlcroorganisms present to take up phosphate. Phosphate-enriched sludge was then separated from the mixed liquor in the secondary clarifier to pro-vide a substantlally phosphate-rree e~fluent. The sep-arated phosphate-enriched sludge was passed to the phos-phate stripping zone and settled therein to form a super-natant liquor in the stripping zone upper section, and settled sludge comprislng a supernatant sludge layer and a subnatant sludge layer. The subnatant sludge layer wa~
maintalned under anaerobic conditions rOr a time sufric-lent to release phosphate to the liquid phase o~ the sub-natant sludge and to provide a phosphate-enrlched super-natant llquor. This phosphate-enriched supernatant liq-uor was withdrawn rr~m the phosphate stripping zone, mixed with phosphate precipitant (lime) in a qulc~ mix tank; the resulting precipitated phosphate was removed as waste chemical sludge in a flocculation tank and phosphate-depleted supernatant liquor was recirculated to the influent sewage llne. Settled sludge was withdrawn frorn the phosphate stripping zone and recirculated to the influent sewage line as the aforementioned activated sludge.
Tn the first phase of the comparative evalua-tion test, operated in accordance with the prior art teachings, none of the supernatant liquor withdrawn from the stripping zone upper section was recirculated or re-introduced into the stripplng zone. All of the withdrawn supernatant liquor was treated with phosphate precipitant and recirculated to the influent sewage line. As des-cribed in terms of the Figure 2 system,the recycle pump 27, schematically shown as disposed in the recycle line 26 which is connected to the phosphate stripping zone supernatant liquor discharge line 25 and which terminates in the lower portion of the stripping zone, was not ac-tuated and no flow was conducted through the recycle line.
In the second phase of the comparative evalua-tion test, operated in accordance with the present inven-tion, the process system was operated as above, except that the aforedescribed recycle pump was actuated so as to d~vert a portion of the lower soluble phosphate con-tent supernatant liquor from the stripping zone super-natant llq~or discharge line and to introduce same into 9~23-the phosphate strirping zone beneath the subnatant anaer-obic sludge. In this manner a countercurrent elutriation of the soluble phosphate ~n the subnatant anaerobic sludge was established whereby the phosphate was transferred to the elutrlant surernatant liquor and subsequently into the supernatant liquor in the stripping zone upper section, ~or ~hosphate enrichment thereof. ~he duration o~ the first phase test, without subnatant sludge contacting, was 8 days o~ contlnuous operation and the second ~hase test, wherein subnatant sludge contacting was employed, was contlnuously o~erated ~or 10 days.
The data which were taken during the comparatlve evaluation test of the above described systems is set rorth in the Table below. These data demonstrate the substantial improvement in phosphate removal efficiency which is achieved by the proGess of this invention (data shown in column A) over the system whlch is taught by the prior art (data shown in column B). As shown by the data, the ~rocess ~arameters in the respective systems, includ-lng influent sewage ~low rate, phosphate-enriched sludge recycle rlow rate, strip~ing zone underflow rate, stripping zone over~low rate, mlxed liquor suspended solid~ under aeration, mixed liquor volatile suspended solids under aeration, influent blochemical oxygen demand (BOD5), and effluent blochemical oxygen demand (BODs) all had closely corresponding measured numerical value~. Acco~dingly, the entries in tAe Table relating to measured phosphate con-centrations in selected process streams in the two systems, ~ 9923-1 ~063264 .. . ...
TABLE
''A~ B'' Process ~eaturing Process w~thout subnatant slud~e subnatant sludge Proces~ Par~meter contacting contact~ng INFLUENT FLOW RATE,GPM12.1 12.0 PHOSPHATE-ENRICHED SLUDGE
RECYCLE F~OW RATE (SLUDGE
FROM SECONDARY SETTLING ZONE
PASSED TO STRIPPER), GPM 3.0 3.0 STRIPPING ZONE UNDE~FLOW
RA~E, aPM 1.~ 1.4 STRIPPING ZONE OVERFLOW
RATE, GPM 1.6 1.6 MIXED LIQUOR SUSPENDED SOLIDS
IN AERATION ZONE, MG-/L-2929 3448 MIXED LIQUOR VOLATILE SUS-PENDED SOLIDS IN AERATION
ZONE, MG./L. 2324 2454 INFLUENT BOD5, MG./L. 7 51 EFFLUENT BODs, MG-/L- 10 16 INFLUENT PHOSPHATE* MG./L. 5.3 4.2 LUENT PHospHATE* MG-/L- -7 PERCENTAGE OVERALL
PHOSPHATE*REMOVAL 87% 16.7%
PHOSPHATE*IN STRIPPER
UNDERFLOW, MG./~. 468 685 PHOSPHATE*IN STRIPPER
SUPERNATANT. M~.~L- 35 9 * Measured as total phosphorous content ~063Z64 vis.~ phos~hate in the in~luent sewage, phosphate in the efrluent sewage, phosphate overall percentage removal, ~hosphate in the stripper under~low, and phosphate in the stripper supernatant llquor, clearly demonstrate that the proceQs Or this invention, wherein the subnatant anaeroblc sludge i9 contacted with a lower soluble phosphate content medium to effect an ultimate transfer to and enrlchment of the supernatant liquor ln the stripping zonè, provldes a sub~tantlally enhanced overall removal of phosphate (87%
v. 16.7~) from the sewage~being treated relative to the prior art process, which dld not employ such 9ubnatant anaerobic sludge contactlng tep.
The rea~on for such striking difference in phos-phate removal levels between the respective systems is readlly apparent based on a comparison Or the phosphate concentrations in the phosphate strlpper underflow and supernatant in these systems. In the process conducted in accordance with the present (data tabulated in column A), the phosphate stripper underflow phosphate concentra-tion was 468 milligrams/liter and the phosphate stripper supernatant liquor concentration was 35 milligrams/liter, whereas in the prior art process corresponding phosphate concentrations were 685 milligrams/liter in the stripper underflow and only 4.9 milligrams/liter in the stripping zone supernatant liquor. These data lndicate that in the prior art process, the phosphate released by the subnatant anaerobic ~ludge was retained in the settled sludge layer and was not significantly transferred to the supernatant 1063Z64 9923~1 liquor in the stripping zone, whereas in the process according to the present invention a substantial transfer of the phosphate, concommitant with significantly higher overall phosphate removals than the prior art process, were achieved.
EXAMPLE II
Raw sewage (about 1,000,000 gallons per day --g.p.d.) containing about 100 parts per million (p.p.m.) of solids and about 10 p.p.m. of total phosphate is passed through conventional screening and grit-removing units and is mixed with recycle activated sludge (about 100,000 g.p.d.) containing about 50 p.p.m. of soluble phosphate.
The mixed liquor is fed to an aeration zone and is aerated at a rate of 2 cubic feet of air per gallon of sewage for 6 hours. The effluent mixed liquor from the aeration zone is fed to a secondary settling tank. Clarified waste liquor which is substantially free of phosphate is dis-charged to the effluent outflow after chlorination at a rate of about 1,000,000 g.p.d. The settled mixture of phosphate-enriched sludge is withdrawn from the secondary settling tank at a rate of about 210,000 g.p.d. A por-tion of this sludge (about 10,000 g.p.d.) is passed to waste sludge, and the remainder is passed to an anaerobic phosphate stripper wherein it is held under anaerobic conditions for about 10 hours. The conditions existing in the stripper induce considerable quantities of intra-cellular phosphate to be released by the microorganisms.
The sludge is permitted to thicken and settle under slow 9~23-mechanical stirrlng, which stlrring ls not su~flcient to infuse the phosphate secreted by the sludge layer into the supernatant liquor at a fast enough rate to render the process satisfactorily e~icient. Thus, the soluble phos-phate which is released by the microorgani9ms tends to remain ln the anaerobic, subnatant sludge. The anaerobic subnatant ~iquor is removed ~rom the bottom o~ the phos-phate stripper at a rate of 200,000 g.p.d. A portion of this anaerobic sludge (100,000 g.p.d.) is recycled for mlxing with lncoming raw sewage and the remainder (100,000 g.p.d ) is recycled for mixlng with aerobic sludge wlth-drawn from the secondary settling tank as lt is being passed to the phosphate stripper. The soluble phosphate contained in the anaerobic sludge portion is thus dis-solved by the liquor portion o~ the aerobic sludge, and the soluble phosphate is thereby distributed into the supernatant liquor in the stripper tank. Phosphate-enriched supernatant liquor containing about 50 p.p.m.
Or soluble phosphate (100,000 g.p.d.) is wlthdrawn ~rom the stripper tan~ and red to a chemical precipitation tank where llme ls added and mlxed to form a phosphate precipitate. The precipitated phosphorous is recycled and mlxed wlth influent raw sewage. In the aeration zone, the soluble phosphate introduced along with the recycled sludge from the phosphate stripper is taken up by the microorganisms present in the sludge along with the phos-phate contained in the influent sewage.
9~23-Although illustratlve embodiments of the lnven-tlon have been set forth above which variously employ supernatant liquor and phosphate-enriched sludge as a lower soluble phosphate content medium, it is apparent that other such media, as for example a portion of the substantially phosphate free ef~luent from the process, may be used in the contacting of the subnatant anaerobic step in accordance wlth the process of this invention.
Thus, although preferred embodiments of this invention have been descrlbed in detail it will be appreciated that other embodiments are contemplated only with modi-fication of the disclosed ~eatures, as being within the scope of the invention.
Thls invention relates to an activated sludge sewage treatment process ~or treating raw or treated phosphate-containing sewage to obtain a substantially phosphorous-~ree e~fluent which is returned to natural water resources.
~ n the conventional actlvated sludge system in use today, sewage is sub~ected to the usual screening and prelimlnary sedimentation procedures, then mixed with activated sludge recycled ~rom a settling tank to form a mixed liquor which is sub~ected to aeration. During aeratlon o~ the mixed liquorJ the organisms present cause the aerobic decomposition o~ sollds and a high degree of BOD removal is achieved.
Phosphates, which are present in organic wastes and detergents, escape conventional sewage treatment processes and are released with the e~fluent into natural water resources, e.g., lakes, rivers and streams. These phosphates result ln over ~ertilization or eutrophication of waters causing unsightly algal blooms and serious pollution problems.
It is known that aeration of the mixed liquor in an activated sludge sewage treatment process lnitially causes the microorganisms present to take up phosphate.
U.S, Patent ~o. 3,236,766 discloses a process which util-izes this phenomenon for removing phosphates ~rom sewage.
According to the process disclosed in that patent, the pH o~ raw sewage is ad~usted, if necessary, to maintain $~ ' a range of from about 6.2 to about 8.5, the sewage is mixed with activated sludge to form a mixed liquor, the mixed liquor is aerated to maintain a dissolved oxygen content of at least 0.3 mg. per liter in the mixed liquor and a phosphate-enriched sludge is separated from the`
mixed liquor to provide a sùbstantially phosphate-free effluent. The phosphate-enriched sludge is treated to reduce the phosphate content thereof prior to recycling for mixing with the influent sewage. This is accomplished by maintaining the phosphate-enriched sludge in an an-aerobic condition for several hours.
Several other processes have been proposed for reducing the phosphate content of phosphate-enriched sludge following the aeration step in an activated sludge sewage treatment process. Thus~ for example, U.S. Patent No. 3,38S,785 discloses adjusting the pH of phosphate-enriched sludge to between about 3.5 and 6 and agitating the sludge in contact with a low phosphate-containing aqueous medium in a tank for a time sufficient to effect transfer of water-soluble phosphate material from the sludge to the aqueous phase. The low phosphate-containing aqueous medium used in this tank is water added from an external source to leach out the phosphate from the sludge.
After the soluble phosphate has been leached out of the sludge into the aqueous medium, the mixture is passed to a settling tank wherein the phosphate-enriched aqueous medium is separated from the phosphate-depleted sludge.
Since this process requires the addition of considerable quantlties of water from an external source and requires two separate tanks -- i.e., a phosphate leaching tank and a settllng tank, to separate the soluble phosphate rrom the sludge, a large capital lnvestment is required in such a process.
Accordingly, it is an ob~ect o~ thi5 invention to provlde an improved process for reducing the phosphate content of phosphate-contalning sewage in an activated sludge sewage treatment prooess.
It ls a further ob~ect o~ thls invention to provlde such a process whlch includes an improved phos-phate strlpping operation of phosphorous-enriched sludge and which results in lncreased efficiency of the phosphate removal from the sewage.
Other ob~ects and advantages of this invention will be apparent from the ensuing disclosure and claims.
SUMMARY
This invention relates to an activated sludge process for treating raw or treated phosphate-containlng sewage to obtaln a substantially phosphorous-free efflu-ent.
The process of this invention comprises aeratlng a mlxed liquor comprising phosphate-containing in M uent sewage material and activated sludge in an aeration zone to reduce the BOD content o~ the sewage material and to cause the m~croorganlsms present to take up phosphate.
Phosphate-enriched sludge is separated from the mixed llquor to provide a substantially phosphate-free effluent.
106326~
This phosphate-enriched sludge is passed to a phosphate stripping zone and settled to form supernatant liquor in the stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer. The subnatant sludge layer is maintained under anaerobic conditions for a time sufficient to re-lease phosphate to the liquid phase of the subnatant sludge layer. Subnatant anaerobic sludge is contacted with a lower soluble phosphate content medium to trans-fer the soluble phosphate in the subnatant anaerobicsludge liquid phase to said lower soluble phosphate content medium, for phosphate enrichment of supernatant liquor in the stripping zone upper section. At least a portion of the subnatant anaerobic sludge is recycled from the phosphate stripping zone to the aeration zone as the aforementioned activated sludge therefor.
As used herein, the term "sludge" refers to a solids-liquid mixture characterized by a sludge solids phase and an associated liquid phase. The term "lower soluble phosphate content medium" refers to an aqueous or water-containing medium which contains a lower con-centration of soluble phosphate than the subnatnat an-aerobic sludge with which it is contacted.
In accordance with the present invention, phosphate-enriched sludge, in which the phosphate is present in the cells of the sludge microorganisms, i.e., biological solids, is maintained under anaerobic condi-tions in a settled subnatant sludge layer in the phosphate 9~23-~063Z64 strlpping ~one for a tlme sufflclent to cause the micro-organisms to release phosphate to the liquid phase Or the sludge. The resultant subnatant anaerobic sludge ls con-tacted with a lower soluble phosphate content medlum. The purpose of such contacting is to transfer soluble phos-phate out of the subnatant anaerobic sludge and ultimately to the supernatant li~uor in the stripping zoneJ so as to e~ect a phosphate enrlchment Or the supernatant llquor thereln. In accordance wlth the lnvention, the soluble pho~phate ln the subnatant anaerobic sludge may be trans-rerred either directly by contacting the anaerobic sludge with the supernatant liquor or indirectly, as for example by contacting the anaerobic sludge with the phosphate-enriched sludge passed to the stripping zone.
Without the aforementloned contactlng/transfer steps, a conslderable time would be required for the sol-uble phosphate in the subnatant anaerobic sludge to migrate through the supernatant portion of the sludge and into the supernatant liquor in the stripping zone. Under such condi-tions, ir the sludge were withdrawn from the stripping zone and recycled to the aeration zone be~ore a sufficient arnount o~ the soluble phosphate is transferred to the supernatant liquor, an excess amount of soluble phosphate will be re-cycled to the aeration zone and the phosphate removal er~lciency of the overall process will be lowered. The pre~ent invention overcomessuch difficulty and has been demonstrated in actual operation to achieve a high level of pho~phate removal efficiency.
9~23-~063Z64 BRIEF DESCRIPTION OF ~HE DRAWINGS
Figure 1 is a schematlc flowsheet Or an actlvated sludge process accordlng to one embodiment of the inven-tion, wherein subnatant anaerobic ~ludge is contacted wlth the phosphate-enrlched sludge passed to the stripping zone.
Figure 2 is a schematic ~lowsheet Or an activated sludge process accordlng to another embodiment of the in-vention, wherein a portion o~ the supernatant liquor in the phosphate stripping zone iR wlthdrawn therefrom and is reintroduced into the stripping zone underneath the layer Or subnatant anaerobic sludge for contacting there-with.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
~ererring now to the drawings, Figure 1 shows an illustrative process system according to the present inventlon. A raw phosphate-containing sewage influent stream 1 is passed through conventional screenlng and grit-removing units and is optionally sub~ected to primary settling in a primary settling tank 2 ~rom which primary sludge is removed in line 3. The primary ~ettled sewage 1~ mlxed with recycled, activated sludge hereinafter described to form a mixed liquor and is passed by line 4 to the aeration tank 5.
In the aeration tank, the mixed liquor ls aerated at a rate sufficient to maintain it ~erobic --i.e., so that there is a measurable amount of dissolved ~063264 oxygen present in the mlxed liquor in at least a part of the aeration tank, for a period o~ 1 to 8 hours. During aeratlon, the microorganlsms present take up phosphate and consume organic matter present in the sewage. A hl~h degree o~ BOD removal ls obtained durlng aeration.
A~ter aeratlon, the mixed liquor is fed lnto a secondary settling tank 6. In the secondary settllng tank 6) phosphate-enrlched sludge settles and thereby 3eparates ~rom the llquor. The sludge contains a substan-tial portlon of the phosphate present in the sewage The substantlally phosphate-free e~luent ls discharged for dlsposal ln a conventlonal manner by line 7.
The phosphate-enrlched sludge ls removed from the settllng tank 6 by llne 8. A portlon of the sludge may be dellvered to waste and the remalnder contacts and mixes wlth recycled, subnatant, anaeroblc sludge from the phosphate strlpper whlch contains a high concentration o~
soluble phosphate and the mlxture ls passed to the phos-phate stripper 9. In the phosphate stripper 9, the phosphate-enrlched sludge is settled to ~orm supernatant liquor ln the upper sectlon o~ the strlpplng zone, and settled sludge comprlsing a supernatant sludge layer and a subnatant sludge layer. The subnatant sludge layer ls maintalned under anaeroblc conditions ~or a tlme suf~lclent to cause the microorganlsms in the subnatant anaeroblc sludge to release phosphate to the llquld pha~e of the subnatant sludge layer. The phosphate leaks out of the sludge sollds lnto the llquld phase. ~he mechanlsm o~
thls treatment will be descrlbed ln more detail hereinbelow.
-~ 9923-1 ~063264 A phosphate-enrlched supernatant ll~uor is produced in the phosphate strlpper 9 and is passed by llne 10 to the phosphate preclpitator 11. A phosphate precipitant, such as alumlnum or lron salts or lime, is mixed with the phosphate-enriched supernatant liquor in the phosp~late precipitator 11 to precipitate phosphate.
The precipitated phosphate is passed by line 12 for mixing with raw sewage in line 1.
In the phosphate stripper 9, sludge solids, contalnlng a high amount of phosphate ln the cells of the organisms in the sludge, separate from the aqueous phase of the sludge and settle toward the bottom of the phosphate stripper. Thus, the solld particles in the sludge contain intracellular phosphate and these partlcles settle into the subnatant anaeroblc layer of sludge in the phosphate stripper 9. A density gradient exists in the layer of settled sludge, the density of the sludge being greater at the bottom of the sludge layer than at the top. As the sollds in the sludge containing intra- -cellular phosphate mlgrate to the bottom of the sludge layer, because of the anaerobic conditions existing in this portion of the sludge layer, the organisms release phosphate to the liquid phase of the sludge in the form of water-~oluble phosphate ions. Preferably, the residence time of the sludge in the phosphate stripper is from 2 to 30 hours. The concentration of soluble phosphate is initially greatest in the lower portion of the sludge layer. As discussed earlier herein, a considerable time -` 9923-ls requlred rOr the soluble phosphate to mlgrate through the less dense and lower solids containing supernatant portion of the sludge and into the supernatant llquor.
If the sludge ls withdrawn and recycled to the aeration zone be~ore a su~icient amount o~ the soluble phosphate is trans~erred to the supernatant llquor, an excess amount o~ ~oluble phosphate wlll be recycled to the aeration tank and the phosphate removal e~riciency o~ the overall pro-ce~s wlll be lowered. It ls pre~erred that no more than 75% o~ the soluble phosphate which is relea~qed in the phos-phate stripper be recycled to the aeration tank with the recycle activated sludge.
Accordlng to one embodiment o~ the invention, subnatant, anaerobic sludge containing a substantlal portion o~ the ~oluble phosphate which ls released in the phosphate 3trlpper 9 is withdrawn from the phosphate stripper and split lnto two portions. One portlon Or this high soluble phosphate-containing sludge ls recycled through line 13 for mixing with the raw sewage which is being red to the aeration tank in line 4, and the other portion of anaerobic, high soluble phosphate-containing sludge ls recycled through llne 14 for contacting and mix-ing wlth aeroblc sludge from the secondary ~ettling tank 6 as it is being passed to the phosphate stripper 9. Since the sludge withdrawn from the secondary settling tank 6 contains lntracellular phosphate in the solids phase thereor and since the liquid phase, which may comprise 98 to 99~ o~ the sludge, contains little or no soluble 10~3Z64 phosphate, the llquld portion of thls aerobic sludge leaches or elutriates the soluble phosphate from the high soluble phosphate-contalnlng anaeroblc sludge por-tion from line 14. It is preferred that each Or the high soluble phosphate-contalnlng anaeroblc sludge portlonQ
wlthdrawn from the strlpper and passed through llnes 13 and 14 comprlse from about 25 to 75~ o~ the total amount o~ high soluble phosphate-containlng sludge wlthdrawn ~rom the stripper and that at least 25% of the soluble phosphate released in the strlpper be removed from the stripper along wlth the supernatant`llquor ln line 10.
The portion of the hlgh soluble phosphate-contalning sludge ln llne 14 may also be introduced dir-ectly into the phosphate strlpper 9 above the sludge layer contalned therein so that the soluble phosphate will come in contact with the supernatant ln the phosphate sbrlpper and be dlsso'ved by the supernatant.
In the embodlment of the invention shown in Fig. 2, phosphate-containing influent sewage material is introduced to the sewage treatment system by line 15 and mixed wlth the phosphate-depleted supernatant liquor from line 34, to be described more fully hereina~ter. The in-~luent sewage and recycle sludge in line 24 are pas~ed into aeration zone 16 wherein the mixed llquor formed ~rom the sewage material and the recycled activated sludge are aerated to reduce the BOD content of the sewage and to cause the microorganisms present to take up phosphate.
In practlce, the aeration zone may be Or a conventional type wherein atmospheric air is used as the oxidant in open aeration chambers. Alternatively, the aeration may be conducted in a manner as taught by U.S. Patent No~.3,547,813 - 3,547,815 to J.~. McWhlrter et al ~n ~hlch at least one enclosed covered aeration chamber i~ employed wherein the llquid undergoing treat-ment is lntimately contacted in the presence of activ-ated sludge with oxygen enrlched gas ~rom an overlying gas space to dissolve the oxygen necessary for aeroblc biological activity. Such oxygenation systems are able to operate at biological suspended æolids levels se~reral times ~reater and aeration detentlon periods several times less than those Or conventional alr aeration systems while maintaining comparable or higher overall levels o~ treat-ment, and have been found to be hlghly e~fective in the practice of the present invention.
The aerated mixed liquor is conducted from the aeration zone in line 17 and passed to the secondary settling zone 18. In the settling zone, phosphate-enriched sludge is separated from the mixed liquor to provide a substantially phosphate-free effluent which is discharged Irom the system in line 19. The separated phosphate-enriched sludge is passed from the secondary settllng zone by line 20 to the phosphate strlpping zone 21. In the stripping zone, the phosphate-enriched sludge is settled to rorm supernatant liquor in the upper section 22 Or the si~ripping zone, and settled sludge comprising a supernatant sludge layer and a ~ubnatant æludge layer.
The subnatant sludge layer ln the stripplng zone is main-tained under anaerobic conditions in the same manner pre-viously descrlbed for a time sufrlcient to release phos-phate to the liquid phase of the subnatant ~ludge layer.
The subnatant anaerobic sludge contacting step is conducted in this system by withdrawing supernatant liquor from the stripping zone upper section in line 25 and dlverting a portlon thereof into line 26, having pump means 27 disposed therein, for reclrculation to the stripping zone lower section, The dlverted supernatant liquor ln line 26 is reintroduced lnto the phosphate stripplng zone by the sparging means 28, whlch may for example co~prise multiple stationary nozzles. In thls manner a countercurrent elutriation of the ~oluble phos-phate in the subnatant anaeroblc sludge ls established, as the soluble phosphate is trans~erred to the upflowing recirculated supernatant liquor and subsequently to the bulk liquid volume of the supernatant liquor in the strlpplng zone upper section.
The portion of the supernatant liquor withdrawn from the stripping zone ln line 25 whlch is not diverted as recycle contacting medium in line 26 is flowed to quick mix tank 29. In this tank, the undiverted super-natant liquor is rapldly mlxed (by means not shown) with a phosphate precipitant, e.g., lime, lntroduced to the tank by me~ns of line 30. The supernatant liquor-phos-phate preclpitant mixture is then passed by line 31 to flocculator tank 32 in which the precipitated phosphate is settled and removed from the system as waste chemlcal sludge in line 33. The overflow phosphate-depleted super-natant from the flocculator tank 32 is recycled in line 34 for ~oining with the sewage influent entering the process in line 15.
By means of the above-describéd subnatant sludge contacting scheme, a significant amount of the phosphate which is released in the subnatant anaerobic sludge layer is transferred to the supernatant liquor in the stripping zone upper section, whereby the subnatant sludge withdrawn from the bottom of the stripping zone in line 23 and re-circulated to the aeration zone in line 24 has a suffic-iently lowered phosphate content to permit high removal of phosphate from the sewage to be achieved in the aeration zone.
Means other than those illustratively described hereinabove may be used in the broad practice of the pres-ent invention to maximize the contact between the subnatant anaerobic sludge portion containing a high soluble phos-phate content and the supernatant liquor in the phosphate stripper so that the soluble phosphate will be eluted into the supernatant liquor. For example, two or more phosphate stripping tanks may be used. While one tank is maintained in a relatively unagitated state and the sludge is main-tained under anaerobic conditions so that the microorgan-isms will release their phosphate content, another tank, in which the microorganisms have already released their phosphate content is agitated to cause the subnatant, anaerobic layer of sludge containing the soluble phosphate 9~23-1 to mix wi~h the supernatant liquor. Arter the supernatant liquor has eluted substantlally all of the soluble phos-phate from the sludge sollds, the vigorous agitation is stopped and the solids are permltted to settle. After the solids have settled, the supernatant llquor, whlch then contains substantlally all Or the soluble phosphate in the tank, ls removed and passed to a phosphate preciplta~
tor and the phosphate-depleted sludge is recycled for mixing with raw sewage which 1~ being ~ed to the aeration tank. The tank is then ~illed with sludge from the secondary settling tank, the sludge is permltted to settle and become anaerobic and is maintained under anaerobic conditions while the previously descrlbed process of vigor-ously stirrlng the subnatant anaerobic sludge and super-natant liquor, settllngJ and removing a phosphate-enriched supernatant is repeated with the first tank. In other words, the two tanks are maintained 180 out of phase with each other.
Another means for effecting transfer o~ the soluble phosphate from the subnatant anaerobic sludge is to introduce rresh sludge from the secondary settling tank into the bottom of the stripping zone so that it diffuses up through the anaerobic layer and elutes the soluble phosphate contained in this layer.
Another means for maximizing the contact between the supernatant liquor and the subnatant anaerobic sludge layer containing a high concentration of soluble phosphate i~ the phosphate stripper is to intermittently 9923-~
and vigorously stir the contents o~ the phosphate stripper so that the anaerobic layer of sludge will be dispersed into the supernatant. The supernatant will thereby elute the phosphate from the slud~e solids The contents of the phosphate stripper are then permitted to settle. Dur-ing agitation and settling, no recycle sludge would be re-moved rrom the bottom of the phosphate stripper. Agitation may be accomplished by introduction Or a non-oxygen con-taining gas at the bottom of the stripper 9. Different portions of the anaerobic sludge layer may also be raised above the sludge layer and then permitted to settle again.
During settling, the soluble phosphate is eluted by the supernatant. While this i9 being done, another portion of the anaerobic sludge layer may be withdrawn from the phosphate stripping for recycle to the aeration tank.
Any o~ these processes may be conducted either continuously or intermittently. Thus, sufficient elutria-tion of phosphatemay be obtained in the Fig. 1 system if, ~or example, the anaerobic sludge withdrawn ~rom the phosphate stripper is recycled through line 14 one hour out Or every five hours of operation.
The following examples illustrate the specific advantages of the present invention in acheiving high overall removals of phosphate from phosphate-containing sewage relative to the prior art process systems lacking the subnatant sludge contacting feature of the instant process.
~(323-1 EXAMRLE I
In this test, a process system of a type simllar to that shown in Figure 2 herein was operated inltially ln the manner of the prior art wlthout the subnatant sludge contacting ~eature Or the present invention and subse-quently was operated ln accordance with the present ln-vention, using supernatant llquor wlthdrawn ~rom the strlpplng zone upper sectlon a~ the lower soluble phos-phate content contacting medlum, ln a manner substan-tially simllar to that described herelnabove in connec-tlon with Figure 2.
In both phases the comparative evaluatlon test, inrluent sewage was mixed with recycle activated sludge to form a mixed liquor which was then aerated in the aera-tion zone to cause the mlcroorganisms present to take up phosphate. Phosphate-enriched sludge was then separated from the mixed liquor in the secondary clarifier to pro-vide a substantlally phosphate-rree e~fluent. The sep-arated phosphate-enriched sludge was passed to the phos-phate stripping zone and settled therein to form a super-natant liquor in the stripping zone upper section, and settled sludge comprislng a supernatant sludge layer and a subnatant sludge layer. The subnatant sludge layer wa~
maintalned under anaerobic conditions rOr a time sufric-lent to release phosphate to the liquid phase o~ the sub-natant sludge and to provide a phosphate-enrlched super-natant llquor. This phosphate-enriched supernatant liq-uor was withdrawn rr~m the phosphate stripping zone, mixed with phosphate precipitant (lime) in a qulc~ mix tank; the resulting precipitated phosphate was removed as waste chemical sludge in a flocculation tank and phosphate-depleted supernatant liquor was recirculated to the influent sewage llne. Settled sludge was withdrawn frorn the phosphate stripping zone and recirculated to the influent sewage line as the aforementioned activated sludge.
Tn the first phase of the comparative evalua-tion test, operated in accordance with the prior art teachings, none of the supernatant liquor withdrawn from the stripping zone upper section was recirculated or re-introduced into the stripplng zone. All of the withdrawn supernatant liquor was treated with phosphate precipitant and recirculated to the influent sewage line. As des-cribed in terms of the Figure 2 system,the recycle pump 27, schematically shown as disposed in the recycle line 26 which is connected to the phosphate stripping zone supernatant liquor discharge line 25 and which terminates in the lower portion of the stripping zone, was not ac-tuated and no flow was conducted through the recycle line.
In the second phase of the comparative evalua-tion test, operated in accordance with the present inven-tion, the process system was operated as above, except that the aforedescribed recycle pump was actuated so as to d~vert a portion of the lower soluble phosphate con-tent supernatant liquor from the stripping zone super-natant llq~or discharge line and to introduce same into 9~23-the phosphate strirping zone beneath the subnatant anaer-obic sludge. In this manner a countercurrent elutriation of the soluble phosphate ~n the subnatant anaerobic sludge was established whereby the phosphate was transferred to the elutrlant surernatant liquor and subsequently into the supernatant liquor in the stripping zone upper section, ~or ~hosphate enrichment thereof. ~he duration o~ the first phase test, without subnatant sludge contacting, was 8 days o~ contlnuous operation and the second ~hase test, wherein subnatant sludge contacting was employed, was contlnuously o~erated ~or 10 days.
The data which were taken during the comparatlve evaluation test of the above described systems is set rorth in the Table below. These data demonstrate the substantial improvement in phosphate removal efficiency which is achieved by the proGess of this invention (data shown in column A) over the system whlch is taught by the prior art (data shown in column B). As shown by the data, the ~rocess ~arameters in the respective systems, includ-lng influent sewage ~low rate, phosphate-enriched sludge recycle rlow rate, strip~ing zone underflow rate, stripping zone over~low rate, mlxed liquor suspended solid~ under aeration, mixed liquor volatile suspended solids under aeration, influent blochemical oxygen demand (BOD5), and effluent blochemical oxygen demand (BODs) all had closely corresponding measured numerical value~. Acco~dingly, the entries in tAe Table relating to measured phosphate con-centrations in selected process streams in the two systems, ~ 9923-1 ~063264 .. . ...
TABLE
''A~ B'' Process ~eaturing Process w~thout subnatant slud~e subnatant sludge Proces~ Par~meter contacting contact~ng INFLUENT FLOW RATE,GPM12.1 12.0 PHOSPHATE-ENRICHED SLUDGE
RECYCLE F~OW RATE (SLUDGE
FROM SECONDARY SETTLING ZONE
PASSED TO STRIPPER), GPM 3.0 3.0 STRIPPING ZONE UNDE~FLOW
RA~E, aPM 1.~ 1.4 STRIPPING ZONE OVERFLOW
RATE, GPM 1.6 1.6 MIXED LIQUOR SUSPENDED SOLIDS
IN AERATION ZONE, MG-/L-2929 3448 MIXED LIQUOR VOLATILE SUS-PENDED SOLIDS IN AERATION
ZONE, MG./L. 2324 2454 INFLUENT BOD5, MG./L. 7 51 EFFLUENT BODs, MG-/L- 10 16 INFLUENT PHOSPHATE* MG./L. 5.3 4.2 LUENT PHospHATE* MG-/L- -7 PERCENTAGE OVERALL
PHOSPHATE*REMOVAL 87% 16.7%
PHOSPHATE*IN STRIPPER
UNDERFLOW, MG./~. 468 685 PHOSPHATE*IN STRIPPER
SUPERNATANT. M~.~L- 35 9 * Measured as total phosphorous content ~063Z64 vis.~ phos~hate in the in~luent sewage, phosphate in the efrluent sewage, phosphate overall percentage removal, ~hosphate in the stripper under~low, and phosphate in the stripper supernatant llquor, clearly demonstrate that the proceQs Or this invention, wherein the subnatant anaeroblc sludge i9 contacted with a lower soluble phosphate content medium to effect an ultimate transfer to and enrlchment of the supernatant liquor ln the stripping zonè, provldes a sub~tantlally enhanced overall removal of phosphate (87%
v. 16.7~) from the sewage~being treated relative to the prior art process, which dld not employ such 9ubnatant anaerobic sludge contactlng tep.
The rea~on for such striking difference in phos-phate removal levels between the respective systems is readlly apparent based on a comparison Or the phosphate concentrations in the phosphate strlpper underflow and supernatant in these systems. In the process conducted in accordance with the present (data tabulated in column A), the phosphate stripper underflow phosphate concentra-tion was 468 milligrams/liter and the phosphate stripper supernatant liquor concentration was 35 milligrams/liter, whereas in the prior art process corresponding phosphate concentrations were 685 milligrams/liter in the stripper underflow and only 4.9 milligrams/liter in the stripping zone supernatant liquor. These data lndicate that in the prior art process, the phosphate released by the subnatant anaerobic ~ludge was retained in the settled sludge layer and was not significantly transferred to the supernatant 1063Z64 9923~1 liquor in the stripping zone, whereas in the process according to the present invention a substantial transfer of the phosphate, concommitant with significantly higher overall phosphate removals than the prior art process, were achieved.
EXAMPLE II
Raw sewage (about 1,000,000 gallons per day --g.p.d.) containing about 100 parts per million (p.p.m.) of solids and about 10 p.p.m. of total phosphate is passed through conventional screening and grit-removing units and is mixed with recycle activated sludge (about 100,000 g.p.d.) containing about 50 p.p.m. of soluble phosphate.
The mixed liquor is fed to an aeration zone and is aerated at a rate of 2 cubic feet of air per gallon of sewage for 6 hours. The effluent mixed liquor from the aeration zone is fed to a secondary settling tank. Clarified waste liquor which is substantially free of phosphate is dis-charged to the effluent outflow after chlorination at a rate of about 1,000,000 g.p.d. The settled mixture of phosphate-enriched sludge is withdrawn from the secondary settling tank at a rate of about 210,000 g.p.d. A por-tion of this sludge (about 10,000 g.p.d.) is passed to waste sludge, and the remainder is passed to an anaerobic phosphate stripper wherein it is held under anaerobic conditions for about 10 hours. The conditions existing in the stripper induce considerable quantities of intra-cellular phosphate to be released by the microorganisms.
The sludge is permitted to thicken and settle under slow 9~23-mechanical stirrlng, which stlrring ls not su~flcient to infuse the phosphate secreted by the sludge layer into the supernatant liquor at a fast enough rate to render the process satisfactorily e~icient. Thus, the soluble phos-phate which is released by the microorgani9ms tends to remain ln the anaerobic, subnatant sludge. The anaerobic subnatant ~iquor is removed ~rom the bottom o~ the phos-phate stripper at a rate of 200,000 g.p.d. A portion of this anaerobic sludge (100,000 g.p.d.) is recycled for mlxing with lncoming raw sewage and the remainder (100,000 g.p.d ) is recycled for mixlng with aerobic sludge wlth-drawn from the secondary settling tank as lt is being passed to the phosphate stripper. The soluble phosphate contained in the anaerobic sludge portion is thus dis-solved by the liquor portion o~ the aerobic sludge, and the soluble phosphate is thereby distributed into the supernatant liquor in the stripper tank. Phosphate-enriched supernatant liquor containing about 50 p.p.m.
Or soluble phosphate (100,000 g.p.d.) is wlthdrawn ~rom the stripper tan~ and red to a chemical precipitation tank where llme ls added and mlxed to form a phosphate precipitate. The precipitated phosphorous is recycled and mlxed wlth influent raw sewage. In the aeration zone, the soluble phosphate introduced along with the recycled sludge from the phosphate stripper is taken up by the microorganisms present in the sludge along with the phos-phate contained in the influent sewage.
9~23-Although illustratlve embodiments of the lnven-tlon have been set forth above which variously employ supernatant liquor and phosphate-enriched sludge as a lower soluble phosphate content medium, it is apparent that other such media, as for example a portion of the substantially phosphate free ef~luent from the process, may be used in the contacting of the subnatant anaerobic step in accordance wlth the process of this invention.
Thus, although preferred embodiments of this invention have been descrlbed in detail it will be appreciated that other embodiments are contemplated only with modi-fication of the disclosed ~eatures, as being within the scope of the invention.
Claims (19)
1. An activated sludge sewage treatment process which comprises aerating a mixed liquor comprising phos-phate-containing influent sewage material and activated sludge in an aeration zone to reduce the BOD content of said sewage material and to cause the microorganisms present to take up phosphate; separating the phosphate-enriched sludge from the mixed liquor to provide a sub-stantially phosphate-free effluent; passing said phos-phate enriched sludge to a phosphate stripping zone and settling said phosphate-enriched sludge to form super-natant liquor in said stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer; maintaining said subnatant sludge layer under anaerobic conditions for a time suf-ficient to release phosphate to the liquid phase of said subnatant sludge layer; contacting the subnatant an-aerobic sludge with a lower soluble phosphate content medium to transfer the soluble phosphate in the subnatant anaerobic sludge liquid phase to said lower soluble phos-phate medium, for phosphate enrichment of supernatant liquor in said stripping zone upper section; and re-cycling at least a portion of said subnatant anaerobic sludge from said phosphate stripping zone to said aera-tion zone as said activated sludge.
2. A process as defined in Claim 1 wherein the residence time of the sludge in said phosphate stripping zone is from 2 to 30 hours.
3. A process as defined in Claim 1 wherein no more than 75% of the soluble phosphate which is released in said phosphate stripping zone is recycled to said aeration zone in said subnatant anaerobic sludge recycled from said phosphate stripping zone to said aeration zone as said activated sludge.
4. A process as defined in Claim 1 wherein said lower soluble phosphate content medium comprises supernatant liquor.
5. A process as defined in Claim 1 wherein said lower soluble phosphate content medium comprises said phosphate-enriched sludge passed to said phosphate stripping zone.
6. A process as defined in Claim 1 wherein subnatant sludge somprising phosphate-depleted sludge solids is withdrawn from said phosphate stripping zone and reintroduced thereto in said supernatant liquor.
7. A process as defined in Claim 1 wherein phosphate-enriched supernatant liquor is withdrawn from said phosphate stripping zone and mixed with a phosphate precipitant to precipitate phosphate therefrom.
8. A process as defined in Claim 3 wherein the contents of said phosphate stripping zone are con-tinuously or intermittently agitated after the micro-organisms in said anaerobic sludge have released their phosphate to cause the subnatant anaerobic layer contain-ing the soluble phosphate to mix with the supernatant liquor, thereafter permitting said sludge solids to settle, whereby the soluble phosphate content of said subnatant, anaerobic sludge is transferred to the super-natant liquor in said phosphate stripping zone.
9. A process as defined in Claim 3 wherein a portion of the supernatant liquor in said phosphate stripping zone is withdrawn therefrom and is reintroduced into said phosphate stripping zone underneath the layer of subnatant, anaerobic sludge, whereby a countercurrent elutriation of the soluble phosphate in said subnatant, anaerobic sludge is established.
10. A process as defined in Claim 3 wherein at least a portion of said phosphate-enriched sludge which is passed to said phosphate stripping zone is introduced into said phosphate stripping zone beneath said subnatant, anaerobic sludge, whereby a countercurrent elutriation of the soluble phosphate in said subnatant, anaerobic sludge is established.
11. A process as defined in Claim 3 wherein the contents of said phosphate stripping zone are intermittent-ly agitated by the introduction of a non-oxygen contain-ing gas underneath said subnatant, anaerobic sludge layer.
12. A process as defined in Claim 3 wherein a portion of said subnatant, anaerobic sludge is raised above said sludge layer and is then permitted to resettle.
13. An activated sludge sewage treatment process which comprises aerating a mixed liquor comprising phos-phate-containing influent sewage material and activated sludge in an aeration zone to reduce the BOD content of said sewage material and to cause the microorganisms present to take up phosphate; separating the phosphate-enriched sludge from the mixed liquor to provide a sub-stantially phosphate-free effluent; passing said phos-phate-enriched sludge to a phosphate stripping zone and settling said phosphate-enriched sludge to form super-natant liquor in said stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer; maintaining said subnatant sludge layer under anaerobic conditions for a time suf-ficient to release phosphate to the liquid phase of said subnatant sludge layer; withdrawing subnatant anaerobic sludge from said phosphate stripping zone, recycling a portion thereof to said aeration zone as said activated sludge and mixing another portion thereof with the phosphate-enriched sludge being passed to said phosphate stripping zone, to thransfer the soluble phosphate in the liquid phase of said subnatant anaerobic sludge another portion to the liquid phase of said phosphate-enriched sludge, for phosphate enrichment of supernatant liquor in said stripping zone upper section.
14. A process as defined in Claim 13 wherein the residence time of the sludge in said phosphate stripping zone is from 2 to 30 hours.
15. A process as defined in Claim 13 wherein no more than 75% of the soluble phosphate which is released in said phosphate stripping zone is recycled to said aeration zone in said subnatant anaerobic sludge recycled from said phosphate stripping zone to said aeration zone as said activated sludge.
16. A process as defined in Claim 13 wherein from 25 to 75% of said withdrawn subnatant anaerobic sludge is recycled to said aeration zone as said activ-ated sludge and from 25 to 75% of said withdrawn sub-natant anaerobic sludge is mixed with the phosphate-enriched sludge being passed to said phosphate stripping zone.
17. A process as defined in Claim 16 wherein at least 25% of the soluble phosphate released in said phos-phate stripping zone is removed from said phosphate stripping zone dissolved in the phosphate-enriched super-natant liquor.
18. An activated sludge sewage treatment process which comprises aerating a mixed liquor comprising phos-phate-containing influent sewage material and activated sludge in an aeration zone to reduce the BOD content of said sewage material and to cause the microorganisms present to the up phosphate; separating the phosphate-enriched sludge from the mixed liquor to provide a sub stantlally phoshpate-free effluent; passing said phosphate-enriched sludge to a phosphate stripping zone and settling said phosphate-enriched sludge to form supernatant liquor in said stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer; maintaining said subnatant sludge layer under anaerobic conditions for a time sufficient to release phosphate to the liquid phase of said subnatant sludge layer; contacting the subnatant anaerobic sludge with supernatant liquor to transfer the soluble phosphate in the subnatant sludge liquid phase to said supernatant liquor for phosphate enrichment of supernatant liquor in said stripping zone upper section; and recycling at least a portion of said subnatant anaerobic sludge from said phosphate stripping zone to said aeration zone as said activated sludge,
19. An activated sludge sewage treatment process which comprises aerating a mixed liquor comprising phos-phate-containing influent sewage material and activated sludge in an aeration zone to reduce the BOD content of said sewage material and to cause the microorganisms present to take up phosphate; separating the phosphate-enriched sludge from the mixed liquor to provide a sub-stantially phosphate-free effluent; passing said phosphate-enriched sludge to a phosphate stripping zone and settling.
said phosphate-enriched sludge to form supernatant liquor in said stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer; maintaining said subnatant sludge layer under anaerobic conditions for a time sufficient to re-lease phosphate to the liquid phase of said subnatant sludge layer; contacting the subnatant anaerobic sludge with said phosphate-enriched sludge passed to said stripping zone, to transfer the soluble phosphate in the liquid phase of said subnatant anaerobic sludge to the liquid phase of said phosphate-enriched sludge, for phos-phate enrichment of supernatant liquor in said stripping zone upper section, and recycling at least a portion of said subnatant anaerobic sludge from said phosphate stripping zone to said aeration zone as said activated sludge.
said phosphate-enriched sludge to form supernatant liquor in said stripping zone upper section, and settled sludge comprising a supernatant sludge layer and a subnatant sludge layer; maintaining said subnatant sludge layer under anaerobic conditions for a time sufficient to re-lease phosphate to the liquid phase of said subnatant sludge layer; contacting the subnatant anaerobic sludge with said phosphate-enriched sludge passed to said stripping zone, to transfer the soluble phosphate in the liquid phase of said subnatant anaerobic sludge to the liquid phase of said phosphate-enriched sludge, for phos-phate enrichment of supernatant liquor in said stripping zone upper section, and recycling at least a portion of said subnatant anaerobic sludge from said phosphate stripping zone to said aeration zone as said activated sludge.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US48179374A | 1974-06-21 | 1974-06-21 | |
| US58195175A | 1975-06-04 | 1975-06-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1063264A true CA1063264A (en) | 1979-09-25 |
Family
ID=27047049
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA229,489A Expired CA1063264A (en) | 1974-06-21 | 1975-06-17 | Phosphate stripping of sewage |
Country Status (19)
| Country | Link |
|---|---|
| JP (1) | JPS5929320B2 (en) |
| AR (1) | AR206820A1 (en) |
| BR (1) | BR7503861A (en) |
| CA (1) | CA1063264A (en) |
| CH (1) | CH609652A5 (en) |
| DE (1) | DE2527588C2 (en) |
| DK (1) | DK281875A (en) |
| EG (1) | EG11772A (en) |
| FI (1) | FI62275C (en) |
| FR (1) | FR2275408A1 (en) |
| GB (1) | GB1512693A (en) |
| IE (1) | IE41385B1 (en) |
| IL (1) | IL47536A (en) |
| IN (1) | IN144405B (en) |
| IT (1) | IT1040676B (en) |
| NL (1) | NL171568C (en) |
| NO (1) | NO148260C (en) |
| SE (1) | SE410306B (en) |
| TR (1) | TR18849A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3729127A1 (en) * | 1987-09-01 | 1989-03-09 | Taetzner Wolfgang | Process and apparatus for biologically purifying waste waters of their phosphate impurities |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3236766A (en) * | 1964-03-31 | 1966-02-22 | Hazleton Lab Inc | Sewage treatment process |
| US3385785A (en) * | 1966-05-04 | 1968-05-28 | Fmc Corp | Method of controlling phosphate concentration in sewage treatment systems |
| US3681235A (en) * | 1971-03-11 | 1972-08-01 | Biospherics Inc | Internal precipitation of phosphate from activated sludge |
-
1974
- 1974-06-20 TR TR1884974A patent/TR18849A/en unknown
-
1975
- 1975-01-01 AR AR25928175A patent/AR206820A1/en active
- 1975-06-17 CA CA229,489A patent/CA1063264A/en not_active Expired
- 1975-06-18 SE SE7507013A patent/SE410306B/en unknown
- 1975-06-19 FI FI751833A patent/FI62275C/en not_active IP Right Cessation
- 1975-06-20 JP JP50074558A patent/JPS5929320B2/en not_active Expired
- 1975-06-20 BR BR7504965D patent/BR7503861A/en unknown
- 1975-06-20 FR FR7519419A patent/FR2275408A1/en active Granted
- 1975-06-20 CH CH806475A patent/CH609652A5/en not_active IP Right Cessation
- 1975-06-20 NO NO752207A patent/NO148260C/en unknown
- 1975-06-20 IL IL4753675A patent/IL47536A/en unknown
- 1975-06-20 IT IT5015775A patent/IT1040676B/en active
- 1975-06-20 DK DK281875A patent/DK281875A/en not_active Application Discontinuation
- 1975-06-20 NL NLAANVRAGE7507418,A patent/NL171568C/en not_active IP Right Cessation
- 1975-06-20 DE DE2527588A patent/DE2527588C2/en not_active Expired
- 1975-06-20 GB GB26229/75A patent/GB1512693A/en not_active Expired
- 1975-06-21 EG EG35475A patent/EG11772A/en active
- 1975-06-23 IN IN1237/CAL/1975A patent/IN144405B/en unknown
- 1975-06-23 IE IE1394/75A patent/IE41385B1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| CH609652A5 (en) | 1979-03-15 |
| FI62275C (en) | 1982-12-10 |
| SE7507013L (en) | 1975-12-22 |
| NO752207L (en) | 1975-12-23 |
| SE410306B (en) | 1979-10-08 |
| JPS5114757A (en) | 1976-02-05 |
| AR206820A1 (en) | 1976-08-23 |
| IL47536A (en) | 1978-07-31 |
| IE41385L (en) | 1975-12-21 |
| DE2527588C2 (en) | 1985-09-19 |
| NL171568B (en) | 1982-11-16 |
| NO148260B (en) | 1983-05-30 |
| NO148260C (en) | 1983-09-07 |
| FI751833A (en) | 1975-12-22 |
| FI62275B (en) | 1982-08-31 |
| GB1512693A (en) | 1978-06-01 |
| FR2275408A1 (en) | 1976-01-16 |
| IL47536A0 (en) | 1975-08-31 |
| NL171568C (en) | 1983-04-18 |
| NL7507418A (en) | 1975-12-23 |
| IN144405B (en) | 1978-04-29 |
| EG11772A (en) | 1977-10-31 |
| JPS5929320B2 (en) | 1984-07-19 |
| AU8232675A (en) | 1976-12-23 |
| IE41385B1 (en) | 1979-12-19 |
| BR7503861A (en) | 1976-07-06 |
| FR2275408B1 (en) | 1982-07-16 |
| DK281875A (en) | 1975-12-22 |
| DE2527588A1 (en) | 1976-01-15 |
| IT1040676B (en) | 1979-12-20 |
| TR18849A (en) | 1977-11-01 |
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