GB1563160A - Method for the performance of biological waste water purification - Google Patents
Method for the performance of biological waste water purification Download PDFInfo
- Publication number
- GB1563160A GB1563160A GB37954/77A GB3795477A GB1563160A GB 1563160 A GB1563160 A GB 1563160A GB 37954/77 A GB37954/77 A GB 37954/77A GB 3795477 A GB3795477 A GB 3795477A GB 1563160 A GB1563160 A GB 1563160A
- Authority
- GB
- United Kingdom
- Prior art keywords
- sludge
- oxygen addition
- stage
- waste water
- 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
- 238000000034 method Methods 0.000 title claims description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims description 23
- 238000000746 purification Methods 0.000 title description 4
- 239000010796 biological waste Substances 0.000 title description 2
- 239000010802 sludge Substances 0.000 claims description 108
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 37
- 229910052760 oxygen Inorganic materials 0.000 claims description 37
- 239000001301 oxygen Substances 0.000 claims description 37
- 230000008719 thickening Effects 0.000 claims description 24
- 239000002351 wastewater Substances 0.000 claims description 24
- 238000005352 clarification Methods 0.000 claims description 19
- 238000000926 separation method Methods 0.000 claims description 12
- 239000000126 substance Substances 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 10
- 238000005188 flotation Methods 0.000 claims description 9
- 239000007791 liquid phase Substances 0.000 claims description 9
- 239000008213 purified water Substances 0.000 claims description 8
- 238000004062 sedimentation Methods 0.000 claims description 7
- 239000012071 phase Substances 0.000 claims description 6
- 238000005273 aeration Methods 0.000 claims description 5
- 239000002245 particle Substances 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 1
- 241000237074 Centris Species 0.000 description 1
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 239000000306 component Substances 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
- 235000015097 nutrients Nutrition 0.000 description 1
- 230000035764 nutrition Effects 0.000 description 1
- 235000016709 nutrition Nutrition 0.000 description 1
- 230000001376 precipitating effect Effects 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
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Hydrology & Water Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Mechanical Engineering (AREA)
- Analytical Chemistry (AREA)
- Biodiversity & Conservation Biology (AREA)
- Microbiology (AREA)
- Activated Sludge Processes (AREA)
- Physical Water Treatments (AREA)
- Centrifugal Separators (AREA)
- Treatment Of Sludge (AREA)
Description
(54) METHOD FOR THE PERFORMANCE OF BIOLOGICAL
WASTE WATER PURIFICATION
(71) We, ALFA-LAVAL AB., a Swedish
Corporate Body, of Postfack, S-147 00 Tuba, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of purifying waste water.
Plants for purifying waste water by the so-called activated sludge method are known and may be designed in a variety of ways. All of these known plants are provided, however, with one or more stages for adding oxygen to the inflowing water in the presence of activated sludge, which grows by utilizing the nutrition present in the waste water under robic conditions, i.e. with an excess of oxygen which is dissolved in the water. The plants also comprise a sludge separation unit, into which the water is led after the addition of oxygen for removing the sludge. The water from the sludge separation unit may be further purified, e.g. chemically by any precipitating method, and is discharged into a receiver.
Part of the separated sludge, corresponding to the growth in the oxygen addition stage, is removed from the plant and the remainder is returned to the oxygen addition stage so that the amount of sludge in the plant remains constant.
Because of the rigid regulations for the purity of water that is discharged from waste water plants, it is necessary to achieve a large reduction in the BOD of the waste water and to remove sludge to a high degree to ensure the outflowing water is sufficiently free of suspended matter. This means, that the sludge separation unit, which in most cases comprises one or more sedimentation basins, normally covers a very large area in view of its low specific yield, which is due to the voluminous character of the sludge and its low sedimentation rate. Also, it is not possible to achieve any high dry substance concentration in the sedimented sludge, which means, that the sludge returned to the oxygen addition stage has a dry substance content which is not above 0.8 it and consists of nearly 100% purified water which dilutes the waste water fed to the oxygen addition stage. As a result the concentration of activated sludge in the oxygen addition stage is low and hence has a limited yield.
It follows that both the oxygen addition stage and the sludge separation unit require much space when the hitherto methods are used.
The present invention aims at eliminating, or substantially reducing the drawbacks of the known waste water purifying methods, and accordingly provides a method of purifying waste water with activated sludge comprising the steps of feeding the waste water to an oxygen addition stage in which the water is mixed with the sludge, passing liquid containing sludge from the oxygen addition stage to a sludge thickening device to divide the flow into a sludge phase having a dry substance concentration which is at least 20/,, and a liquid phase which is substantially free of sludge, returning at least part of the sludge phase to the oxygen addition stage, and feeding the liquid phase to a clarification stage where sludge residue is removed from the liquid phase.
The sludge thickening device preferably consists of a centrifugal separator, e.g. with timed intermittent discharge or automatic sludge discharge initiated by sludge sensing means.
In a preferred embodiment, the sludge thickening device comprises a coarse screen and a fine screen through which liquid from the oxygen addition stage is passed successively before being fed into the centrifugal separator.
The fine screen can be of the design disclosed in the Swedish Patent Specification No.
357 992, and the rotor of the centrifugal separator may be provided with permanently open nozzles around its circumference for continuously discharging sludge. A fine screen of the type mentioned is marketed under the trade mark Microsorter, and is designed for fractionating paper pulp. Surprisingly, it pre separates a fraction of the activated sludge down to a particle size which enables a centri fugal separator with permanently open circum ferential nozzles to be utilized for concentrat ing the activated sludge particles of smaller size. There is a danger of the sludge discharge nozzles of such centrifugal separators becoming clogged by coarse particles, leading to serious interruptions in operation of the plant.
Suitably the mesh size of the fine screen is within the range of 0.1 to 0.8 mm and the opening width of the sludge discharge nozzles of the centrifugal separator is within the range of 0.9 to 1.5 mm.
In an alternative embodiment of the invention the sludge thickening device consists of a flotation plant.
The clarification stage may consist of one or more sedimentation basins, which can be much smaller in area, compared with those of previously used water purifying plants.
The liquid from the sludge thickening device may also be clarified by flotation.
The method according to the invention enables sludge accompanying the liquid flow- ing from the oxygen addition stage to the sludge separation unit to 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 from the centrifugal separator to the clarification stage for final clarification, which means the latter step requires substantially less resources for a given waste water load. As the returned sludge is accompanied by a substantially smaller amount of purified water than in previous plants the yield of the oxygen addition stage is increased due to reduced dilution of the waste water.
An embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which:
Figure 1 shows a schematic flowsheet of a
water purifying plant, and
Figure 2 illustrates schematically a com- ponent in the plant.
Shown schematically in Figure 1 are an
oxygen addition stage 1, a sludge separatior unit 2 including a sludge thickening device 3 and a clarification stage 4. An inlet line 5 is provided for feeding waste water to the plant and a line 6 is provided for passing liquid from oxygen addition stage 1 to the 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 plant. A line 9 returns separated sludge from the sludge thickening device 3 to the oxygen addition stage 1. Excess sludge may be discharged from the plant through a branch line 10 and a line 11 from the clarification stage.
A biomass, i.e. an activated sludge suspended in water, is maintained in the oxygen addition stage 1. Oxygen is fed continuously to the stage, generally in the form of air, as indicated in the drawing by an arrow 12.
Waste water is fed continuously to the oxygen
addition stage 1 through the line 5 and the
activated sludge grows by utilizing the nutrients
in the waste water. A continuous liquid flow, containing some sludge is led to sludge thick
ening device 3, from which a liquid flow with
a small residue of sludge is discharged through
line 7 to clarification stage 4. A thickened
sludge flow is discharged from sludge thicken
ing device 3 and a part of this flow is returned
through line 9 to the oxygen addition stage,
while excess sludge is discharged through the
branch line 10. Separated sludge is discharged
through the line 11 from the clarification
stage 4.
One form of sludge thickening device shown
schematically in Figure 2, comprises a coarse,
prescreen 13, a fine screen 14 of the type disclosed in the Swedish Patent Specification No.
357 992 and a centrifugal separator 15 having permanently open sludge discharge nozzles, arranged around the circumference of the rotor.
Line 6 is arranged to convey the flow from the oxygen addition stage to prescreen 13, while a line 16 connects the prescreen 13 with the fine screen 14, and a line 17 connects the fine screen 14 to the centrifugal separator 15.
Line 7 connects the separator 15 to clarification stage 4. Lines 18, 19 and 20 from prescreen 13, fine screen 14 and centrifugal separator 15 are provided to convey sludge from the apparatus to line 9 for part of the sludge to be returned to the oxygen addition stage and excess sludge to be discharged through the branch line 10.
To elucidate further the present invention two specific examples of waste water purification by the method of the invention will now be given. In the example of water purified was waste water from a fermentation process and in the first a centrifugal separator with intermittent sludge discharge combined with a sedimentation basin was used, whereas in the second flotation was used for the sludge thickening as well as for clarification.
Waste water to be purified
BOD,=10 000 mg/l
Flow: 30 m3/h corresponding to 300 kg
BOD/h or 7200 BOD/24 h (100 p.e.)
Plant for a conventional waste water purifica
tion according to the activated sludge
method (for comparison)
Aeration basin: 2400 m3
Concentration of activated sludge: 3000
mg/l
Load: 3 kg BOD/m3. 24 h.
Sludge separation unit
Sedimentation basin, 4 m deep, 60 m2 bottom area.
Sedimented sludge for returning, dry sub
stance conc. 0.4%
Residual sludge concentration in discharged
purified water: ca 30 mg/l.
Example 1
Plant:
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.
Centrifuged sludge for returning, dry sub
stance concentration: ca 6", Clarification stage
Sedimentation basin, 4 m deep, 30 m bottom area.
Residual sludge concentration in discharged
purified water: 30 mg/l.
Example 2
Plant:
Oxygen addition stage
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
concentration: 2 % Clarification stage
Flotation plant (clarification operation) II
3 m deep, 6 m bottom area
Residual sludge in discharged, purified
water: 30 mg/l.
WHAT WE CLAIM IS:
1. A method of purifying waste water with activated sludge comprising the steps of feeding the waste water to an oxygen addition stage in which the water is mixed with the sludge, passing liquid containing sludge from the oxygen addition stage to a sludge thickening device to divide the flow into a sludge phase having a dry substance concentration which is at least 2:;, and a liquid phase which is substantially free of sludge, returning at least part of the sludge phase to the oxygen addition stage, and feeding the liquid phase to a clarification stage where sludge residue is removed from the liquid phase.
2. A method according to claim 1, wherein the thickening devices divides the flow by
centrifugal separation.
3. A method according to claim 2, wherein
the flow from the oxygen addition stage is passed through a coarse screen and then a fine screen to separate part of the sludge before being centrifugally separated by a centrifugal separator provided with permanently open,
circumferential sludge discharge nozzles, the fine screen being as disclosed in Swedish
Patent Specification No. 357,992.
4. A method according to claim 3, wherein the fine screen has a mesh size within the range of 0.1 to 0.8 mm, and the sludge discharge nozzles of the centrifugal separator have an opening width within the range of 0.9 to
1.5 mm.
5. A method according to claim 1, wherein thickening devices divides the flow by flotation.
6. A method of purifying waste water substantially as herein described.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (6)
- **WARNING** start of CLMS field may overlap end of DESC **.Example 1 Plant: 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.Centrifuged sludge for returning, dry sub stance concentration: ca 6", Clarification stage Sedimentation basin, 4 m deep, 30 m bottom area.Residual sludge concentration in discharged purified water: 30 mg/l.Example 2 Plant: Oxygen addition stage 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) I3 m deep, 30 m2 bottom area Flotated sludge for returning, dry substance concentration: 2 % Clarification stage Flotation plant (clarification operation) II3 m deep, 6 m bottom area Residual sludge in discharged, purified water: 30 mg/l.WHAT WE CLAIM IS: 1. A method of purifying waste water with activated sludge comprising the steps of feeding the waste water to an oxygen addition stage in which the water is mixed with the sludge, passing liquid containing sludge from the oxygen addition stage to a sludge thickening device to divide the flow into a sludge phase having a dry substance concentration which is at least 2:;, and a liquid phase which is substantially free of sludge, returning at least part of the sludge phase to the oxygen addition stage, and feeding the liquid phase to a clarification stage where sludge residue is removed from the liquid phase.
- 2. A method according to claim 1, wherein the thickening devices divides the flow by centrifugal separation.
- 3. A method according to claim 2, wherein the flow from the oxygen addition stage is passed through a coarse screen and then a fine screen to separate part of the sludge before being centrifugally separated by a centrifugal separator provided with permanently open, circumferential sludge discharge nozzles, the fine screen being as disclosed in Swedish Patent Specification No. 357,992.
- 4. A method according to claim 3, wherein the fine screen has a mesh size within the range of 0.1 to 0.8 mm, and the sludge discharge nozzles of the centrifugal separator have an opening width within the range of 0.9 to 1.5 mm.
- 5. A method according to claim 1, wherein thickening devices divides the flow by flotation.
- 6. A method of purifying waste water substantially as herein described.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7610325A SE7610325L (en) | 1976-09-17 | 1976-09-17 | PROCEDURE FOR CARRYING OUT BIOLOGICAL WASTE WATER TREATMENT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1563160A true GB1563160A (en) | 1980-03-19 |
Family
ID=20328905
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB37954/77A Expired GB1563160A (en) | 1976-09-17 | 1977-09-12 | Method for the performance of biological waste water purification |
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 CA CA286,948A patent/CA1084179A/en not_active Expired
- 1977-09-16 FR FR7727986A patent/FR2364861A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2364861B1 (en) | 1980-04-30 |
| SE7610325L (en) | 1978-03-18 |
| IT1087506B (en) | 1985-06-04 |
| CA1084179A (en) | 1980-08-19 |
| DE2741021A1 (en) | 1978-03-23 |
| FR2364861A1 (en) | 1978-04-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed [section 19, patents act 1949] | ||
| PCNP | Patent ceased through non-payment of renewal fee |