CA1084179A - Method for biological purification of waste water - Google Patents
Method for biological purification of waste waterInfo
- Publication number
- CA1084179A CA1084179A CA286,948A CA286948A CA1084179A CA 1084179 A CA1084179 A CA 1084179A CA 286948 A CA286948 A CA 286948A CA 1084179 A CA1084179 A CA 1084179A
- Authority
- CA
- Canada
- Prior art keywords
- sludge
- phase
- flow
- oxygen addition
- stage
- 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.)
- Expired
Links
- 239000002351 wastewater Substances 0.000 title claims abstract description 19
- 238000000746 purification Methods 0.000 title claims abstract description 9
- 238000000034 method Methods 0.000 title claims description 26
- 239000010802 sludge Substances 0.000 claims abstract description 87
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 34
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 34
- 239000001301 oxygen Substances 0.000 claims abstract description 34
- 238000005352 clarification Methods 0.000 claims abstract description 16
- 238000000926 separation method Methods 0.000 claims abstract description 15
- 239000007788 liquid Substances 0.000 claims abstract description 12
- 239000012071 phase Substances 0.000 claims abstract description 12
- 239000007791 liquid phase Substances 0.000 claims abstract description 10
- 239000000126 substance Substances 0.000 claims abstract description 9
- 230000008719 thickening Effects 0.000 claims abstract description 8
- 238000005188 flotation Methods 0.000 claims description 6
- 238000007792 addition Methods 0.000 description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 17
- 238000004062 sedimentation Methods 0.000 description 6
- 239000008213 purified water Substances 0.000 description 4
- 238000005273 aeration Methods 0.000 description 3
- 239000010796 biological waste Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000002028 Biomass Substances 0.000 description 1
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000000855 fermentation Methods 0.000 description 1
- 230000004151 fermentation Effects 0.000 description 1
- 230000035764 nutrition Effects 0.000 description 1
- 235000016709 nutrition Nutrition 0.000 description 1
- 230000000050 nutritive effect Effects 0.000 description 1
- 229960003903 oxygen Drugs 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/38—Treatment of water, waste water, or sewage by centrifugal separation
- C02F1/385—Treatment of water, waste water, or sewage by centrifugal separation by centrifuging suspensions
-
- 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
-
- 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
Abstract
ABSTRACT OF THE DISCLOSURE
In a system for biological purification of waste water, the liquid flow from an oxygen addition stage is fed with a low sludge concentration to a sludge thickening zone within a separation unit, the flow in said zone being di-vided into a sludge phase with a high dry substance concen-tration of at least 2% and a liquid phase substantially free from sludge. At least part of the sludge phase is re-turned to the oxygen addition stage, and the liquid phase is fed to a clarification stage where sludge residue is re-moved from the liquid phase.
In a system for biological purification of waste water, the liquid flow from an oxygen addition stage is fed with a low sludge concentration to a sludge thickening zone within a separation unit, the flow in said zone being di-vided into a sludge phase with a high dry substance concen-tration of at least 2% and a liquid phase substantially free from sludge. At least part of the sludge phase is re-turned to the oxygen addition stage, and the liquid phase is fed to a clarification stage where sludge residue is re-moved from the liquid phase.
Description
~34179 ~ ~
The present invention relates to a method for per-forming biological waste water purification according to the activated sludge method, comprising feeding waste water into at least one oxygen addition stage from which a liquid flow with relatively low sludge concentration is led into a sludge separation unit, separated sludge from the latter unit being returned to the oxygen addition stage, Systems for performing biological waste water purification according to the activated sludge method may be designed in a variety of ways. However, all these sys-tems are provided with one or more stages for the addition of oxygen to the inflowing water in the presence of acti-vated sludge, which thereby grows by utilizing the nutrition present in the waste water, aerobic conditions prevailing, i.e., with an excess of oxygen dissolved in the water. The systems also comprise a sludge separation unit into which the water to which oxygen has been added is led for removing accompanying sludge. The water from which sludge has been removed may be further purified (e.g., chemically purified -;
20 according to any precipitating method) and discharged into ;~
a receiver. Part of the separated sludge, corresponding to the continuous growth in the oxygen addition stage, is re-moved from the system and the remainder is returned to the oxygen addition stage.
Considering the rigid regulations for the quality of the water discharged into receivers from waste water plants, it is as necessary to achieve a high degree of re-duction of the BOD of the waste water as to remove sludge to a high degree in the sludge separation unit to make the outflowing water sufficiently free from suspended matter.
This means that the sludge separation unit, which in most ' . .
10~4179 cases comprises one or more sedimentation basins, must cover a very large area in view of the low specific yield obtain-able due to the voluminous character of the sludge and its ;
low sedimentation rate. Also, it is not possible to achieve -a high dry substance concentration in the sedimented sludge.
Thus, the sludge which has been returned to the oxygen addi-tion stage ~i.e., the return sludge wherein the dry substance content is not above 0.8%) consists of nearly 100% water that is already purified and which dilutes the waste water fed to the oxygen addition stage for purifying. This will cause the concentration of activated sludge in the oxygen addition stage to be low, with limited yield as a result.
It is obvious that both the oxygen addition stage and the sludge separation unit require much space according to methods hitherto used.
The present invention has for an object to avoid the drawbacks inherent in prior methods of the above-mentioned type for biological purification of waste water, ;
and to provide a method which enables a substantial increase in the capacity of present systems and a substantial reduc-tion of space demand for new systems for such purification.
According to the invention, a method of the above-mentioned type is characterized in that the liquid flow from the oxygen addition stage is fed to a sludge-thickening de-vice within the sludge separation unit, where the liquidflow is divided into two parts. The first of these two parts is a sludge phase with a relatively high dry substance concentration (i.e., at least 2~), at least some of which phase is returned to the oxygen addition stage. The second of these two parts is a liquid phase that is substantially free from sludge, which phase is fed to a clarification 1~84~79 stage where the sludge residue is removed from the liquid phase.
According to one preferred embodiment of the in-vention, the sludge-thickening device consists of a cen-trifugal separator, such as a centrifuge which provides forintermittent periodic or automatic sludge-sensing discharge.
In a further embodiment which has proved especial-ly suitable for the performance of the biological waste water purification, the sludge thickening device comprises .
a coarse screen and a fine screen through which the liquid flow from the oxygen addition stage passes successively be- ~
fore it is fed into the centrifugal separator. The fine ;~ -screen may be of a design disclosed in Swedish Patent Specification No. 357,992, the centrifugal separator being ~i-provided with permanently open nozzles, circumferentially arranged in the rotor, for continuous discharge of sludge. `
A fine screen of the type mentioned is marketed under the trade mark MICROSORTER and is designed for the fractionating of paper pulp. Surprisingly, it solves the problem of pre-separating a fraction of the activated sludge down to a particle size which enables a centrifugal separator with t ~ '~
permanently open circumferential nozzles in the rotor to be utilized for concentrating the activated sludge with the smallest particle size. There is a risk of such centrifugal separators having their nozzles clogged by coarser particles, which means a serious operational disturbance.
In a particularly suitable embodiment of the method according to the invention, the mesh size of the fine ~
screen is within the range 0.1-0.8 mm, and the opening width -of the circumferential nozzles of the centrifugal separator is within the range 0.9-1.5 mm. -.
~10~4179 In an alternative embodiment of the method accord-ing to the invention, the sludge-thickening device consists ~-~
of a flotation system.
The clarification stage may consist of one or more sedimentation basins, which can be designed with a much smaller bottom area as compared with a traditional system with the same amount of waste water fed for biological puri- ~ -fication.
The liquid flow emerging from the sludge-thickening device may also be clarified by flotation.
With the method according to the invention, sludge accompanying the li~uid flow from the oxygen addition stage to the sludge separation unit can be separated and returned to the oxygen addition stage with substantially higher dry substance concentration than has hitherto been possible.
Only minor amounts of sludge will accompany the liquid flow from the centrifugal separator to the clarification stage for final clarification, so that the latter task requires substantially smaller resources for a given waste water load. As the return sludge, compared with the sludge ob-tained from prior methods for active sludge treatment of waste water, is accompanied by a substantially smaller amount of purified water, the yield of the oxygen addition stage is increased due to reduced dilution of waste water fed into the system.
The invention will now be described more in de-tail, reference being made to the attached drawings in which Fig. 1 is a schematic flowsheet of the method according to the invention, and Fig. 2 illustrate$ schematically an em-bodiment of the sludge-thickening device shown in Fig. 1.
~o84~79 In Fig. 1, reference numeral l designates an oxy-gen addition stage, 2 a sludge separation unit, 3 a sludge-thickening device which is part of the unit 2, and 4 a clarification stage. An inlet line 5 is provided for feed 5 of waste water to the system, and a line 6 is provided for r the liquid flow from oxygen addition stage l to sludge-thickening device 3. A line 7 connects the latter to the ;
clarification stage 4, from which a line 8 discharges the purified water from the system. A line 9 connects the 10 sludge-thickening device or zone 3 to oxygen addition stage 1 for returning of separated sludge. Excess sludge may be discharged from the system through a bifurcated line 10, and a line 11 from the clarification stage 4 has the same pur- ~;
pose.
In oxygen addition stage 1, a biomass is main- ;
tained (i.e., activated sludge suspended in water). Oxygen is fed continuously to this stage, generally in the form of air, as shown in the drawing by an arrow 12. Waste water is generally fed continuously to oxygen addition stage 1, and the activated sludge grows by utilizing the nutritives available in the waste water. A liquid flow, generally con-tinuous and containing some sludge, is led through line 6 to sludge-thickening device 3 where the flow is divided into two parts, of which the first is a liquid flow having a 25 small residue of sludge and which passes to clarification -stage 4. The second part is a thickened sludge flow, of which a portion is returned through line 9 to the oxygen addition stage 1, while excess sludge is discharged through bifurcation line 10. Separated sludge is discharged through the line ll from clarification stage 4.
~i084~
Referring to Fig. 2, the sludge-thickening device 3 comprises a pre-screen 13, a fine screen 14 of the type disclosed in Swedish Patent Specification No. 357,992, and - -a centrifugal separator 15 having a rotor (locus of cen-trifugal force) provided with circumferentially arranged, permanently open nozzles for sludge discharge. Line 6 is arranged to convey the liquid flow, emerging with a rela-tively low sludge concentration, from the oxygen addition stage 1 to pre-screen 13. A line 16 connects pre-screen 13 with fine screen 14, and a line 17 connects fine screen 14 to centrifugal separator 15, which in turn is connected via line 7 to clarification stage 4. Lines 18, 19 and 20 from pre-screen 13, fine screen 14 and centrifugal separator 15 are provided to convey sludge phase from the sludge thickener 3 to line 9 for returning sludge to the oxygen addition stage and discharging excess sludge through bifur-cation line 10, -Examples For further elucidation of the present invention, data will now be given, by way of example, from a system for the performance of a conventional biological purifica- ;~
tion method for waste water from a fermentation process, and corresponding data from two different systems constituting two embodiments for the performance of the method according to the invention. The first one (I~ utilizes a centrifugal separator with intermittent sludge discharge combined with a sedimentation basin, while the other one (II) operates with flotation for the sludge thickening and also for the clarification.
Waste water BOD7 = 10,000 mg/l ~ -Flow: 30 m3/h corresponding to 300 kg BOD/h or -7200 BOD/24 h (100 p.e.) System for a conventional wast~
water purification according to the activated sludge method Aeration basin: 2400 m3 ~ -Concentration of activated sludge: 3000 mg/l Load: 3 kg BOD/m3.24 h.
Sludge separation unit i Sedimentation basin, 4m deep, 60 m2 bottom area Sedimented sludge for returning, dry substance conc. 0.4 Residual sludge concentration in discharged puri~
fied water: ca 30 mg/l.
System for performing the method according to invention embodiment I
Oxygen addition stage Aeration basin: 500 m3 ~ -~
Concentration of activated sludge: 15,000 mg/l Load: 15 kg BOD/m3.24 h.
Sludge separation unit ;`
Sludge thickening device ~ -Centrifugal separator with intermittent sludge discharge.
Centrifugated sludge for returning, dry substance concentration: ca 6% -Clarification stage Sedimentation basin, 4m deep, 30 m2 bottom area. ~ !
Residual sludge concentration in discharged puri-fied water: 30 mg/l.
. .
-7- ~ ~ `
~o84~79 System for performing the method according to invention embodiment II
Oxygen addition~st_ge Aeration basin: 750 m3 Concentration of activated sludge: 10,000 mg/l Load: 10 kg BOD/m3.24 h.
Sludge separation unit Sludge thickening device Flotation plant (thickening operation) I ;
3 m deep, 30 m2 bottom area Flotated sludge for returning, dry substance con- ;`
centration: 2%
Clarification stage Flotation plant (clarification operation) II
3 m deep, 6 m2 bottom area Residual sludge in discharged, purified water:
30 mg/l.
The present invention relates to a method for per-forming biological waste water purification according to the activated sludge method, comprising feeding waste water into at least one oxygen addition stage from which a liquid flow with relatively low sludge concentration is led into a sludge separation unit, separated sludge from the latter unit being returned to the oxygen addition stage, Systems for performing biological waste water purification according to the activated sludge method may be designed in a variety of ways. However, all these sys-tems are provided with one or more stages for the addition of oxygen to the inflowing water in the presence of acti-vated sludge, which thereby grows by utilizing the nutrition present in the waste water, aerobic conditions prevailing, i.e., with an excess of oxygen dissolved in the water. The systems also comprise a sludge separation unit into which the water to which oxygen has been added is led for removing accompanying sludge. The water from which sludge has been removed may be further purified (e.g., chemically purified -;
20 according to any precipitating method) and discharged into ;~
a receiver. Part of the separated sludge, corresponding to the continuous growth in the oxygen addition stage, is re-moved from the system and the remainder is returned to the oxygen addition stage.
Considering the rigid regulations for the quality of the water discharged into receivers from waste water plants, it is as necessary to achieve a high degree of re-duction of the BOD of the waste water as to remove sludge to a high degree in the sludge separation unit to make the outflowing water sufficiently free from suspended matter.
This means that the sludge separation unit, which in most ' . .
10~4179 cases comprises one or more sedimentation basins, must cover a very large area in view of the low specific yield obtain-able due to the voluminous character of the sludge and its ;
low sedimentation rate. Also, it is not possible to achieve -a high dry substance concentration in the sedimented sludge.
Thus, the sludge which has been returned to the oxygen addi-tion stage ~i.e., the return sludge wherein the dry substance content is not above 0.8%) consists of nearly 100% water that is already purified and which dilutes the waste water fed to the oxygen addition stage for purifying. This will cause the concentration of activated sludge in the oxygen addition stage to be low, with limited yield as a result.
It is obvious that both the oxygen addition stage and the sludge separation unit require much space according to methods hitherto used.
The present invention has for an object to avoid the drawbacks inherent in prior methods of the above-mentioned type for biological purification of waste water, ;
and to provide a method which enables a substantial increase in the capacity of present systems and a substantial reduc-tion of space demand for new systems for such purification.
According to the invention, a method of the above-mentioned type is characterized in that the liquid flow from the oxygen addition stage is fed to a sludge-thickening de-vice within the sludge separation unit, where the liquidflow is divided into two parts. The first of these two parts is a sludge phase with a relatively high dry substance concentration (i.e., at least 2~), at least some of which phase is returned to the oxygen addition stage. The second of these two parts is a liquid phase that is substantially free from sludge, which phase is fed to a clarification 1~84~79 stage where the sludge residue is removed from the liquid phase.
According to one preferred embodiment of the in-vention, the sludge-thickening device consists of a cen-trifugal separator, such as a centrifuge which provides forintermittent periodic or automatic sludge-sensing discharge.
In a further embodiment which has proved especial-ly suitable for the performance of the biological waste water purification, the sludge thickening device comprises .
a coarse screen and a fine screen through which the liquid flow from the oxygen addition stage passes successively be- ~
fore it is fed into the centrifugal separator. The fine ;~ -screen may be of a design disclosed in Swedish Patent Specification No. 357,992, the centrifugal separator being ~i-provided with permanently open nozzles, circumferentially arranged in the rotor, for continuous discharge of sludge. `
A fine screen of the type mentioned is marketed under the trade mark MICROSORTER and is designed for the fractionating of paper pulp. Surprisingly, it solves the problem of pre-separating a fraction of the activated sludge down to a particle size which enables a centrifugal separator with t ~ '~
permanently open circumferential nozzles in the rotor to be utilized for concentrating the activated sludge with the smallest particle size. There is a risk of such centrifugal separators having their nozzles clogged by coarser particles, which means a serious operational disturbance.
In a particularly suitable embodiment of the method according to the invention, the mesh size of the fine ~
screen is within the range 0.1-0.8 mm, and the opening width -of the circumferential nozzles of the centrifugal separator is within the range 0.9-1.5 mm. -.
~10~4179 In an alternative embodiment of the method accord-ing to the invention, the sludge-thickening device consists ~-~
of a flotation system.
The clarification stage may consist of one or more sedimentation basins, which can be designed with a much smaller bottom area as compared with a traditional system with the same amount of waste water fed for biological puri- ~ -fication.
The liquid flow emerging from the sludge-thickening device may also be clarified by flotation.
With the method according to the invention, sludge accompanying the li~uid flow from the oxygen addition stage to the sludge separation unit can be separated and returned to the oxygen addition stage with substantially higher dry substance concentration than has hitherto been possible.
Only minor amounts of sludge will accompany the liquid flow from the centrifugal separator to the clarification stage for final clarification, so that the latter task requires substantially smaller resources for a given waste water load. As the return sludge, compared with the sludge ob-tained from prior methods for active sludge treatment of waste water, is accompanied by a substantially smaller amount of purified water, the yield of the oxygen addition stage is increased due to reduced dilution of waste water fed into the system.
The invention will now be described more in de-tail, reference being made to the attached drawings in which Fig. 1 is a schematic flowsheet of the method according to the invention, and Fig. 2 illustrate$ schematically an em-bodiment of the sludge-thickening device shown in Fig. 1.
~o84~79 In Fig. 1, reference numeral l designates an oxy-gen addition stage, 2 a sludge separation unit, 3 a sludge-thickening device which is part of the unit 2, and 4 a clarification stage. An inlet line 5 is provided for feed 5 of waste water to the system, and a line 6 is provided for r the liquid flow from oxygen addition stage l to sludge-thickening device 3. A line 7 connects the latter to the ;
clarification stage 4, from which a line 8 discharges the purified water from the system. A line 9 connects the 10 sludge-thickening device or zone 3 to oxygen addition stage 1 for returning of separated sludge. Excess sludge may be discharged from the system through a bifurcated line 10, and a line 11 from the clarification stage 4 has the same pur- ~;
pose.
In oxygen addition stage 1, a biomass is main- ;
tained (i.e., activated sludge suspended in water). Oxygen is fed continuously to this stage, generally in the form of air, as shown in the drawing by an arrow 12. Waste water is generally fed continuously to oxygen addition stage 1, and the activated sludge grows by utilizing the nutritives available in the waste water. A liquid flow, generally con-tinuous and containing some sludge, is led through line 6 to sludge-thickening device 3 where the flow is divided into two parts, of which the first is a liquid flow having a 25 small residue of sludge and which passes to clarification -stage 4. The second part is a thickened sludge flow, of which a portion is returned through line 9 to the oxygen addition stage 1, while excess sludge is discharged through bifurcation line 10. Separated sludge is discharged through the line ll from clarification stage 4.
~i084~
Referring to Fig. 2, the sludge-thickening device 3 comprises a pre-screen 13, a fine screen 14 of the type disclosed in Swedish Patent Specification No. 357,992, and - -a centrifugal separator 15 having a rotor (locus of cen-trifugal force) provided with circumferentially arranged, permanently open nozzles for sludge discharge. Line 6 is arranged to convey the liquid flow, emerging with a rela-tively low sludge concentration, from the oxygen addition stage 1 to pre-screen 13. A line 16 connects pre-screen 13 with fine screen 14, and a line 17 connects fine screen 14 to centrifugal separator 15, which in turn is connected via line 7 to clarification stage 4. Lines 18, 19 and 20 from pre-screen 13, fine screen 14 and centrifugal separator 15 are provided to convey sludge phase from the sludge thickener 3 to line 9 for returning sludge to the oxygen addition stage and discharging excess sludge through bifur-cation line 10, -Examples For further elucidation of the present invention, data will now be given, by way of example, from a system for the performance of a conventional biological purifica- ;~
tion method for waste water from a fermentation process, and corresponding data from two different systems constituting two embodiments for the performance of the method according to the invention. The first one (I~ utilizes a centrifugal separator with intermittent sludge discharge combined with a sedimentation basin, while the other one (II) operates with flotation for the sludge thickening and also for the clarification.
Waste water BOD7 = 10,000 mg/l ~ -Flow: 30 m3/h corresponding to 300 kg BOD/h or -7200 BOD/24 h (100 p.e.) System for a conventional wast~
water purification according to the activated sludge method Aeration basin: 2400 m3 ~ -Concentration of activated sludge: 3000 mg/l Load: 3 kg BOD/m3.24 h.
Sludge separation unit i Sedimentation basin, 4m deep, 60 m2 bottom area Sedimented sludge for returning, dry substance conc. 0.4 Residual sludge concentration in discharged puri~
fied water: ca 30 mg/l.
System for performing the method according to invention embodiment I
Oxygen addition stage Aeration basin: 500 m3 ~ -~
Concentration of activated sludge: 15,000 mg/l Load: 15 kg BOD/m3.24 h.
Sludge separation unit ;`
Sludge thickening device ~ -Centrifugal separator with intermittent sludge discharge.
Centrifugated sludge for returning, dry substance concentration: ca 6% -Clarification stage Sedimentation basin, 4m deep, 30 m2 bottom area. ~ !
Residual sludge concentration in discharged puri-fied water: 30 mg/l.
. .
-7- ~ ~ `
~o84~79 System for performing the method according to invention embodiment II
Oxygen addition~st_ge Aeration basin: 750 m3 Concentration of activated sludge: 10,000 mg/l Load: 10 kg BOD/m3.24 h.
Sludge separation unit Sludge thickening device Flotation plant (thickening operation) I ;
3 m deep, 30 m2 bottom area Flotated sludge for returning, dry substance con- ;`
centration: 2%
Clarification stage Flotation plant (clarification operation) II
3 m deep, 6 m2 bottom area Residual sludge in discharged, purified water:
30 mg/l.
Claims (5)
1. A method for performing biological purifica-tion of waste water according to the activated sludge method wherein waste water is fed into an oxygen addition stage from which a liquid flow with a relatively low sludge con-centration is led into a sludge separation unit, separated sludge being returned to the oxygen addition stage from the sludge separation unit, said method being characterized by feeding said liquid flow from the oxygen addition stage to a sludge thickening zone within said separation unit, divid-ing the flow in said thickening zone into two phases of which the first is a sludge phase with a relatively high dry substance concentration of at least 2%, at least part of said sludge phase being returned to the oxygen addition stage, the second of said two phases being a liquid phase substantially free from sludge, and feeding said liquid phase to a clarification stage and there removing sludge residue from the liquid phase.
2. The method of claim 1, in which said flow is divided into said sludge phase and said liquid phase by centrifuging.
3. The method of claim 2, in which said flow, prior to said centrifuging thereof, is passed through a coarse screen and then through a fine screen to separate part of the sludge, said centrifuging being effected in a locus of centrifugal force from which sludge is discharged continuously through permanently open, circumferential nozzles.
4. The method of claim 3, in which the mesh size of said fine screen is within the range 0.1-0.8 mm., the opening width of said nozzles being within the range 0.9-1.5 mm.
5. The method of claim 1, in which said flow is divided into said sludge phase and said liquid phase by flo-tation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7610325-8 | 1976-09-17 | ||
| SE7610325A SE7610325L (en) | 1976-09-17 | 1976-09-17 | PROCEDURE FOR CARRYING OUT BIOLOGICAL WASTE WATER TREATMENT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084179A true CA1084179A (en) | 1980-08-19 |
Family
ID=20328905
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA286,948A Expired CA1084179A (en) | 1976-09-17 | 1977-09-16 | Method for biological purification of waste water |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1084179A (en) |
| DE (1) | DE2741021A1 (en) |
| FR (1) | FR2364861A1 (en) |
| GB (1) | GB1563160A (en) |
| IT (1) | IT1087506B (en) |
| SE (1) | SE7610325L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4452699A (en) * | 1981-05-07 | 1984-06-05 | Shinryo Air Conditioning Co., Ltd. | Method of improving the SVI of mixed liquor in aeration tank |
-
1976
- 1976-09-17 SE SE7610325A patent/SE7610325L/en unknown
-
1977
- 1977-09-12 GB GB37954/77A patent/GB1563160A/en not_active Expired
- 1977-09-12 DE DE19772741021 patent/DE2741021A1/en not_active Withdrawn
- 1977-09-12 IT IT2745777A patent/IT1087506B/en active
- 1977-09-16 FR FR7727986A patent/FR2364861A1/en active Granted
- 1977-09-16 CA CA286,948A patent/CA1084179A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2741021A1 (en) | 1978-03-23 |
| SE7610325L (en) | 1978-03-18 |
| GB1563160A (en) | 1980-03-19 |
| FR2364861B1 (en) | 1980-04-30 |
| FR2364861A1 (en) | 1978-04-14 |
| IT1087506B (en) | 1985-06-04 |
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