A PURIFICATION SYSTEM WITH FILTER FOR SEPARATION OF ACTIVATED SLUDGE AND TREATED WATER IN A PROCESS TANK

Abstract: A purification system with filter for separation of activated sludge and treated water in a process tank. The separation of activated sludge and treated water takes place by filtration in the process tank itself. A hydraulic pressure forces the treated water through the filter units. The activated sludge in the process tank is moved horizontal whereby the suspension flows along the filter units. By this mechanism the filters are partly cleaned. Cleaning of the filters are made further effective by: (1) increasing the velocity of flow by decreasing the cross section of the flow, (2) making the surface of the filter smooth preventing growth of organisms on the filters, (3) return-washing of the filters by water or by air or both water and air, (4) brushing and/or pressure washing of the outer surface of the filters.

Description: A purification system with filter for seperation of activated sludge and treated water in a procestank. The invention concerns a purification system of the type defined in the introductory portion of claim l.It is well-known to perform biological purification using so-called activated sludge.Activated sludge is an ex¬ pression covering colonies of microorganisms which remove organics and nutrients from the liquid which is purified. In an activated sludge treatment plant the mixture of water and activated sludge will be kept in motion and leaves the procestank after a certain time. To avoid pollution of the environment by activated sludge and to keep the useful activated sludge in the procestank,it is necessary to separate treated water and activated sludge.After separation the treated water is discharged to a recipient and the activated sludge is returned to the procestank.Up to now separation and return of activated sludge has been carried out by a sedimentation tank, here microorganisms sedimentates unto the buttom and are scraped to a central pump and returned to the procestank.The treated water is discharged from the surface of the sedi¬ mentation tank to the recipient or to further treament. This procedure usually works satisfactory,but the amount of investment for such a sedimentation tank often is so high that the price dos not corresponds with the benefit. Furthermore such a sedimentationtank may not work satisfactory if high inletflow or gasproduction or bulking slud¬ ge occures.Such events causes oveflow of activated sludge into the en¬ vironment. The pupose of the invention is thus to create an activated sludge treat¬ ment plant whithout a sedimentation tank. By this invention not only the investment for a sedimentation tank and the the dysfunction of a sedimentation tank is avoided but the advantage of increasing the sludgeconcentration in the procestank is achieved.- Thereby the size and the cost of the procestank can be decreased.Thus this invention remarkebly will decrease the investment costs of sewa- getreatment. Till now it has been difficult to integrate a sedimentationunit in a pro¬ cestank,since the water in the procestank typically flows with a velocity of 0,2 - 0,5 m/sec.A danish patent invented by the undersigned concerns integrating a sedementation unit in a procestank,whereas this invention concerns separating treated water and activated sludge by filtration. By filtration the inexpidient function of the sedimentation tank is avoi¬ ded and the sludgeconcentration in the procestank can be increased. The clean water between the activated sludgeflocs is forced through the filter by an all over hydrostatic p eassure.This hydrostatic preassure can be established by installation of an overflowwire for the filtrated water.The wire then controls the hydraulics of the system (fig. 1). Filtration of activated sludge have in the past been impossible because of the fast clugging of the filter.This invention solves the problems with clugging of the filter.The clogging is avoided by the following met¬ hods: A. A horisontal velocity is forced upon the activated sludge,in which the filter is submerged,whereby the filter is cleaned (fig l).This velocity can be created by different machinery but most often by propellermixers,- rotors or turbines.To ensure the mixing of the suspended matter (microor¬ ganisms) the proces most often operates at velocities of 0,2 -0,5 m/sec- By these velocities most of the filtercake will be poured off. B. The velocity of flow along the filter is increased by the displacement of water by the filter and by the reduction of the crosssection area of the flow (fig 3).By submerging a filterunit the velocity of flow along the filter will increase because of the displaced water.The velocity of flow can be further increased by placing several filterunits in a channel with steep walls whereby the crossection area of the flow is reduced (fig 3). C. The filters are provided with smooth sufaces,while a smooth surface prevents the growth of microorganisms on the surface.Further the filters are placed a certain distance under the surface water level to reduce the intensity of light,whereby the growth of algae are inhibited. D. In addition to the "natural" hydraulic cleaning of the filters (A - C) the filters are provided with an artificial cleaning mechanism,consisting of returnwashing of the filter by a liquid or a gas or both,possibly in- termittend.Such a system can be worked out as seen in fig l.The filtrated water runs to a returnwashing basin which is provided with an overflow weir,from where the water runs to the recipient or to further treatment.- The overflow weir controls the surface water level in the procestank.In the returnwashing basin the returnwashing pump is pumping treated water backwards through the filters when the filters need cleaning.This return- washing can be supplemented by blowing air backwards through the filters by a blower. ashing water and washing air can be supplied at the same time or inter ittend.The system is equipped by the necessary valves and controlers. E. The filter can be designed with a hydraulic suction at a part of the surface,or at the whole suface,of the filter( fig. 2).By designig the filter with a hydraulic suck - that means a negative hydrostatic preas- sure - this suck will remove the microorganisms from the filter and ther¬ eby prevent clogging of the filter. F. The pores in the filtermedia can be carried out in such a way that the pores will open further by returnwashing.Hereby suspended matter which is catched in the pores can be released and washed out.This can pos¬ sibly be done by performing an elastic filtermedia. The procestank can be equipped with one or more filterunits.At bigger plants more units will be necessary.The filterunits can be installed in different ways.A favourable installation of the filterunits is shown in fig 3.In fig 3 the filterunits are installed side by side between 2 ver- tical walls in the procestank.Hereby the velocity of flow is increased because of the reduction of the crosssection area of the flow.It is an advantage too that the filterunits easily can bee connected by pipes for filtrated water and for returnwashing by water and air.At even bigger plants several rows of filterunits can be installed behind each other between 2 vertical walls in a procestank ( fig 4 ) . The filters can have arbitrary geometry.On fig 5 the favourable geometri¬ es of the filter is shown. hich geometry at a given purpose is most op¬ timal depends on a combination of the selfcleaning of the filter and the production- and installation costs.A favourable combination of selfclea¬ ning and costs is shown on fig 6. The filters can be constructed in different ways.Important is the filter- membrane.The filter can be constructed either as a shell or as a uniform unit (fig 7 ).If the filter is constructed as a shell this can be done by different numbers of materials.A favorable design is to construct a stiff framework of steel with perforated plates covered with a filterme brane. A uniform filter can probably consist of foamed plastics with small po¬ res. Returnwashing can bee operated with some filters beeing washed while the other filters are still filtrating.Hereby more constant hydralic flows are maintained. The invention is explained further below with references to the figures 1 - 7.: Fig. 1 is a top view and sectional view of a treatment plant according to the invention with a filterunit installed in the procestank. Fig. 2 is a sectional view of the flow along 2 different geometries of a filter. Fig. 3 is a top view of the flow along a filterunit consisting of several filters. fig. 4 shows the installation of several filters arranged in 2 rows. fig. 5 shows top views of 6 examples of filtergeometry. fig. 6 shows top view and sectional views of a favourable filter-con¬ struction. fig.7 shows a plan section of a filter constructed as a shell and as a uniform body. Fig. 1 is a top view and a sectional view of a treatment plant consisting of a procestank (1) with a filterunit (2) and a returnwashing basin (3)- .The raw sewage is fed to the procestank at (4) and the cleaned water runs out of the returnwashing basin at (5).The activated sludge is aera¬ ted by the aggregate (6) and is moved forward by the mixers (7).The ac¬ tivated sludge flows along several filters (8),whereby the purified water is filtrated through the filters by a hydraulic gradient from the water surface level (9) in the procestank till the overflowweir (10) in the returnwashing basin.In the returnwashing basin returnwashing pumps (11) are installed and probably a blower (12) for returnwashing by air is also installed.The returnwashing pumps cleans the filters by pumping purified sewage from the returnwashing basin through the filters into the pro¬ cestank.The filters can be looked after and maintained from the service- bridge (13). Fig. 2 is a top view of the flow (12) along 2 different filters (13).It can be seen that the velocity of flow is increased (14) along the fil¬ ters,and that a hydraulic suck (15) is created along the filters. Fig. 3 is a top view of the velocity of flow (16) along several filters (17).It can be seen that the velocity of flow is increased between the filters.Further it can be seen how the water filtrates through the fil¬ ters (18) and runs out through the outlet pipe (19). Fig. 4 is a top view of several filters arranged in 2 rows (20) and with 2 outletpipes (21) with connected returnwashing pumps (22). Fig. 5 shows top views of 6 different gemetries of filters: (23) prism,- (24) drop, (25) lens, (26) double airoplane wing, (27)rectangular, (28) cir- cular.The filter (27) has opposite the rest of the filters no hydraulic suck along the filter.On the other hand (27) is a favourable simple and cheap geometry of the filter. Fig. 6 shows as an example a top view (29) and a sectional view (30) of a more detailed drawing of the filter (23).The sides of the filter consists of a perforated plate (24) covered by a filtermembrane (25).The filter is connected with other filters by the outletpipe (25).Through this pipe (25) also the returnwashing takes place.The filters are hanged by the hangingirons(26) .The perforated plates (24) are fixed to a framework (27). Fig. 7 is a top section of 2 types of filters: - (28) which is a shell (29) covered by a filtermembrane (30) and cleaned water (31) inside the filter, -(32) which is a uniform filter (33) with an internal pipe (34) used for collecting cleaned water.

Claims: Patent claims : 1. A purification system including a procestank with an inlet and an out ¬ let,where polluted water containing organic matter,nutrients and others are purified during circulation in the procestank,the purification being performed biological or biological-chemical in the procestank by so-cal¬ led activated sludge with microorganisms,which absorb the organics and the nutrients,the purified water is separated from the activated sludge through a filter, nd the filtrated water is discharged and the activated sludge remains in the procestank,except for the surplus sludge which is pumped for sludge treatment, characterized by a relative smooth filter submerged in the procestank and arranged in such a manner that the ' mixture of activated sludge and puri¬ fied water circulates in the procestank along the the filter, and the velocity of flow is increased along the filter by displacing the fluid and decreasing the cross-section -area of the the flow, nd that the fil¬ trating system is carried out in such a way,that a hydraulic preaεεure is created,and that devices for returnwashing of the filter are installed in connection with the filter. 2.A purification system according to claim 1,characterized by the geo- metry of the filter wich ensures the creation of a hydraulic suck at a part of or at the whole filter by wich the filter is further cleaned. 3.A purification system according to claim 1 and designed as an endless channel characterized in that the filterunits are placed between 2 wa- 11s,in such a way that the filterunits causes a decrease of the cross- section-area of the waterflow and thereby creates an increase of the flo- wvelocity along the filters. 4.A purification system according to claim 1,characterized in that the filtration-device consists of a number of filters installed side by side in the direction of the flow. 5.A purification system according to claim 1,characterized in that the geometry of the plan of the filter is carried out as one of the following geometries : -prism -drop -lens -double "airoplane wing" -rectangular -circular 6.A purification system according to claim 1,characterized in that a num¬ ber of filters are connected to the same system of pipes for outlet of purified water,inlet of returnwash-water and returnwash-air. 7.A purification system according to claim 1,characterized in that the water level is regulated by an overflowweir in a tank,through which the purified water runs. 8.A purification system according to claim 1,characterized in that the filters are carried out with filtermembranes,flexible filtermembranes or plasticfoame. 9.A purification system according to claim 1,characterized in that the pores of the filtermembrane are carried out in such a way,that they are enlarged at returnwashing,probably by making the filtermembrane elastic. AMENDED CLAIMS [received by the International Bureau on 30 March 1994 (30.03.94); original claims 1-4 replaced by amended claims 1-11 (2 pages)] 1. A purification system including a procestank with an inlet and an out- let, here polluted water containing organic matter, utrients and others are purified during circulation in the procestank,the purification being performed biological or biological-chemical in the procestank by so-cal¬ led activated sludge with microorganisms,which absorb the organics and the nutrients,the purified water is separated from the activated sludge through a filter,and the filtrated water is discharged and the activated sludge remains in the procestank,except for the surplus sludge which is pumped for sludge treatment, characterized by a relative smooth filter submerged in the procestank and arranged in such a manner that the mixture of activated sludge and puri¬ fied water circulates in the procestank along the the filter, and the velocity of flow is increased along the filter by displacing the fluid and decreasing the cross-section -area of the the flow,and that the fil¬ trating system is carried out in such a way,that a hydraulic preassure is created,and that devices for returnwashing of the filter are installed in connection with the filter. 2. A purification system according to claim 1 characterized in that au¬ tomatic brushing and/or automatic preassure washing of the outer surface of the filters take place while the filters are submerged. 3. A purification system according to claim 1,characterized by the geo¬ metry of the filter wich ensures the creation of a hydraulic suck at a part of or at the whole filter by wich the filter is further cleaned. 4. A purification system according to claim 1 and designed as an endless channel characterized in that the filterunits are placed between 2 wa¬ lls,in such a way that the filterunits causes a decrease of the cross- section-area of the waterflow and thereby creates an increase of the flo- wvelocity along the filters. 5. A purification system according to claim 1,characterized in that the filtration-device consists of a number of filters installed side by side in the direction of the flow. 6. A preferred distance between the filters is from 10 mm to 150 mm.A smaller distance creates a risk for clogging of the filters, hile a big¬ ger distance causes a too small increase of velocity along the filters. 7. A purification system according to claim 1,characterized in that the geometry of the plan of the filter is carried out as one of the following geometries : -prism -drop -lens -double "airoplane wing" -rectangular -circular 8. A purification system according to claim 1,characterized in that a number of filters are connected to the same system of pipes for outlet of purified water,inlet of returnwash-water and returnwash-air. 9. A purification system according to claim 1,characterized in that the water level is regulated by an overflowweir in a tank,through which the purified water runs. 10. A purification system according to claim 1,characterized in that the filters are carried out with filtermembranes,flexible filtermembranes or plasticfoame. 11. A purification system according to claim 1,characterized in that the pores of the filtermembrane are carried out in such a way,that they are enlarged at returnwashing, robably by making the filtermembrane elastic.

Inventors: ANDERSEN KARSTEN KROGH, ANDERSEN, KARSTEN, KROGH
Applicants: ANDERSEN KARSTEN KROGH, ANDERSEN, KARSTEN, KROGH
Application year: 1993
Main classification: C02F3
IPC codes: B01D29, C02F3