PROCESS FOR SEPARATION

Abstract: The present invention relates to a method and a device at a biological purification step of waste water in aerated basins, whereby one introduces a non-aeration zone provided with a static stirring of the water passing said zone prior to a precipitation step.

Description: PROCESS FOR SEPARATION • 1- DESCRIPTION Technical Field The present invention relates to a process and device at a bio- logical purification step of waste water in aerated basins. The object of the present invention is to obtain a possibi lity to increase the amount of biological sludge from a so called biostep in a plant for the purification of waste water and to lower the amount of COD (oxygen demanding) compounds in the wa¬ ter (sludge water) which is led on in the purification process and/or to a recipient. Hereby it i s meant to increase and im¬ prove the formation of floes in the precipitation step, and this can thus not only be applied on a biologi cal purifi cation step but can be used after a chemical precipitation step as well. Background of the invention At so called biological purifi cation in a plant for the treat- ment of waste water the water is introduced, after a coarse fi ltration, into large aeration basins through which the water is allowed to pass during a si ultaneous, violent aeration by means of ai r introduced via nozzles in the bottom of the basins before the water (sludge water) is led to a sedimentation basin for precipitation of what i s called, in a dai ly language, the biological sludge. The water from the sedimentation basin i s then Led further on to process steps for chemical precipitation and/or direct to a recipient. Outgoing water from the precipitation basin contains, however, too large amounts of suspended material and particularly at heavy loaded plants, the outgoing water wi ll also contain large amounts of oxygen consuming material. The more pollutants which are brought forward to the chemical precipitation step the more chemicals are needed to reduce the amounts of pollutants to an acceptable level . However, there i s a desi re to reduce to amount of chemicals which are used in a waste water purifi ca- tion plant for several reasons, partly economical, as the che¬ micals is a great cost in the running of the plant, partly for the risk of dissolving undesired side products, or at very aci¬ dic waters, release of dissociated aluminium or iron, which ions can damage biological life. Normally such a risk will not appear but the metal salts used wi ll be precipitated with the so called chemical sludge. Thus one desires an increased sedimentation effect in the bio- logical step and thereby a reduced outgoing amount of suspended material to the chemical precipitation step. Description of the present invention It has now surprisingly been found possible to be able to re- duce the amount of outgoing suspended material by means of the present invention, which is characterized in that one pr or to a sedimentation step introduces a non-aeration zone with a sta¬ tic and/or mechanical stirring of the water containing suspend¬ ed material and passing through the zone. Further character stics are evident from the accompanying clai s. By applying the present invention it is obtained that the amount of suspended material in water from a subsequent pre¬ cipitation step will be reduced with up to 70%. The amount of oxygen consuming material, particularly in heavy loaded plants, have also been able to be reduced with up to 50%. The invention will be described more in detai l below with re¬ ference to the accompanying drawings, wherein FIG. 1 shows schematically a plant for carrying out the method, and FIG. 2 shows an insert device for obtaining a static and mecha- nical stirring FIG. 3 siows a preferred embodiment of an insert device accord¬ ing to the present irvention to obtain s static stirring 1 denotes generally 3 series of aeration basins in the biologi ¬ cal step of a waste water purification plant. The basins have a length of about 10 m and a width of about 3 m in a normal sized plant, but can also be considerably larger at large plants. At the bottom 2 of the basins nozzles 3 are arranged for the in¬ troduction of large amounts of ai r in order obtain an aerobic degradation of the bi o log i ca I /o rgani c material present in the sludge water. Normally several aeration basins are connected in series so that the water is brought further on either via a spi llway or via a bottom channel. Normally the water i s led from the last basin via a spi llway to a precipitation basin 4 provided with a sludge hopper 5 and a chain or wi re transported sludge scraper 6 before the water i s led out via a drainage 7. In the embodiment shown in FIG. 1 , the most simple one accord¬ ing to the present invention, the last nozzles 3 in the basin immediately prior to the precipitation basin have been elimina¬ ted or, more simpLy just been closed off, and in stead, there has been introduced a sti rrer 8 which gives a mechanical sti rr¬ ing of the water in a zone after the aeration and without the add ition of ai r. This sti rring has turned out to be enough to give an acceptable formation of floes wh ch give a reduction of suspended mater al after the precipitation. In the most simple case no mechani cal separation of or diffe¬ rentiation of the aeration and sti rring zones i s needed. If so desired a wooden wall 9 can easily be placed across the basin which wall has sparsely placed boards whi ch allow passage of water from the aeration zone to the sti rring zone. In FIG. 2 there is shown an insert device comprising a tube 10 having a square cross-section intended to be lowered into the basin 1, a spi llway channel 11 with a discharge 12 to a preci¬ pitation basin in order to obtain an increased residence time of the sludge water before the precip tat on step (so cal led intermediate precipitation) in which channel a static stirring is obtained. The device further comprises a stirrer 8 substan¬ tially centrally placed in the tube 10. It has turned out that the stirrer 8 can have different form and effect. Thus it can be made in the form of a paddle stirrer or in the form of an ascending screw placed in a vertical, cir¬ cular tube for vertical stirring, or can comprise a number of smaller screws placed on the same shaft or can comprise fixed devices for static formation of turbulence. The static stirring in the spillway channel 11 can also be im¬ proved by arranging one or more helical means in the channel in order to force the water to a circulation during this passage. In FIG. 3 a preferred embodiment of the present invention is shown which embodiment comprises two concentric cylinders 21 and 22 on a common bottom 23. The cylinders 21 and 22 are in principle open upwardly with the exception of a smaller part of the outer cylinder 21 which is closed with a cover 24. In the upper part of the outer cylinder 21 an inlet 25 is provided. In the inner cylinder 22 at its bottom 23 there is a second open¬ ing 26 arranged which opening has an area which is about 3 ti¬ mes as large as the area of the inlet opening of the inlet 25. Both cylinders 221 and 22 are partly cut down at their upper parts to the formation of an opening 27 which creates a spi ll¬ way over the cover 24. The height of this cut-down 27 is about half of the height of the second opening 26. The outlet opening 27 has a width that corresponds .to the diameter of the inner cylinder 22. In the bottom 23 there is further provided cent¬ rally a smaller drainage 28 through which outlet 28 a smaller drainage of sludge assembled its in centre can be made. The device functions in that way that sludge containing water is introduced through the inlet opening 25 and passes in the slot between the outer cylinder 21 and the inner cylinder 22 with a rotating movement downwardly as the opening of the inner cylinder 22 is arranged at the bottom 23. The water then flows into and upwardly in the inner cylinder 22 and i s spi lled into the opening 27 over the cover 24. The device i s hereby placed in such a way in a precipitation basin that the spi 11 way /open ing 27 is placed in the upper sur¬ face of the precipitation basin, whereby a flow out from the device is created and the floes formed can then slowly fall to the bottom of the precipitation basin during a simultaneous further growth. As the water in the devi ce obtains a rotating movement by the flow in the outer slot between the cylinders 21 and 22 the water wi ll rotate in the inner cylinder as well, which means that more heavy sludge wi ll be gathered on the bot¬ tom in the centre of the inner cylinder. Such sludge i s with- drawn continuously through the opening 28 which has a diameter of 30 to 40 mm when the inner cylinder has a diameter of about 1800 mm and the outer cylinder 22 has a diameter of about 2400 mm. The inner cylinder 22 is, in a further preferred embodi¬ ment, conically downwardly so that the width of the slot bet- ween the cylinders increases downwardly in order to reduce the flowing rates and provide a possibi lity for an even better floe formation. The diameter of the inlet tube should also be equal to the width of the slot between the cylinders in the level with the inlet opening 25. At a test using the present method and device in a waste water plant, whereby one has had the same percolation rate in paral¬ lel basins, uti lizing the present method and device in one of the basins, it was obtained the following results. A denotes a result obtained using the present method and device introduced after the aeration basin in a biological step and B denotes those results obtained in the parallel basin using conventional running operation after the same aeration basin. TABLE Precipitati on Prec ipi tation Reduction A B % COD mgO^/l 122 212 43 P ÷ 1 3.53 52 to * t mg a P/l .68 Susp mg/ I 35.9 122.6 71 B0D ? mgO_/l 40 128 69 (3-days test) As evident from the results above a marked improvement of the purification results are obtained. The results show the mean values over 12 days. The reduction of suspended material has turned out to be inde- pendent of the use of a flocculating agent in the biological step or if the water is untreated without any addition of a fLoccuLation and sludge improving agent .

Claims: CLAIHS. 1. A method at a biologi cal purifi cation step of waste water in aerated basins, characterized in that one introduces a non- aeration zone provided with a static sti rring of the water passing said zone prior to a precipitation step. 2. Method according to claim 1, characterized in that one uti¬ lizes vertical sti rring. 3. Method according to claim 1 , characterized in that one uti¬ lizes a fixed device for stati c turbulence formation. 4. Devi ce for carrying out the method according to claims 1-3, character zed in that it comprises a tube (10) to be lowered into a basin, a spi llway channel (11) and a sti rrer (8) arr¬ anged substantially centrally in the tube. 5. Device according to claim 4, characterized in that a helical sti rrer for static sti rring is provided in the spi llway channel (11) . 6. Device for carrying out the method according to claims 1-3, characterized in that it comprises two, substantially concent¬ ric cylinders (21,22) provided with a common bottom (23) and further provided with an inlet opening (25) in the outer cy¬ linder (21) and arranged in the upper part of thi s cylinder (21), as well as an inlet opening (26) arranged in the inner cylinder (22) and arranged in the lower part of this cylinder (22), and that the cylinders (21,-22) are provided with a spi ll- way (27) and an outlet opening (28) arranged centrally in its bottom. 7. Device according to claim 6, characterized in that the inner cylinder (22) is coni cally tapering downwardly. 8. Device according to claim 6, characterized in that the slot between the outer (21) and the inner (22) cylinders has a width which corresponds to the diameter of the inlet opening (25). 9. Device according to claim 6, characterized in that the spillway (27) has a width corresponding to the diameter of the inner cylinder (22).

Inventors: HELGESSON IVAN, HELGESSON, IVAN
Applicants: K Z HANDELS AB, K.Z. HANDELS AKTIEBOLAG
Application year: 1989
Main classification: C02F3
IPC codes: C02F3