DK146362B - PROCEDURE FOR THE REMOVAL OF POLLUTANEOUS POLLUTANTS FROM BIOLOGICAL PROCEDURE AND APPARATUS FOR EXERCISING THE PROCEDURE - Google Patents

Description

in 146362

The present invention relates to a method of the kind set out in the preamble of claim 1 for removing contaminants from wastewater by biological reaction and to an apparatus of the kind set forth in the preamble of claim 3 for carrying out the method.

U.S. Patent No. 3,375,849 discloses a method and apparatus for biological treatment of wastewater comprising a treatment tank having a biological treatment zone in the upper portion and a resting precipitation zone in the lower portion. The biological treatment zone comprises a plurality of parallel rotatable shafts disposed across the upper portion of the tank. Each of these shafts carries a number of biological contact members, typically thin plates. The contact members extend into the wastewater in the tank for less than half the depth of the tank and provide an underlying precipitation zone for loosened solids. Alternatively, the surface of the biological contact members is exposed to the atmosphere and wastewater at appropriate intervals to promote the growth of aerobic biological coatings.

By such a method, contrary to the prior art, it is possible to avoid the use of a post-treatment tank following the treatment tank while maintaining a good purification effect; however, a satisfactory purification effect is not always achieved because the wastewater flowing into the treatment tank can in some cases flow below the surface of the tank without contacting the rotatable contact members in the upper portion of the treatment tank. Thus, it is possible for the wastewater to flow directly to the outlet orifice and thereby not at all reach the precipitation zone which forms the lower part of the tank. This may result in not exposing the entire amount of waste water in the tank to the purification process, which is why optimum purification of the waste water is not always achieved.

The object of the present invention is thus to provide, by further development of the method and apparatus described above, a method and apparatus by means of which an improved purification effect can be obtained.

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This is achieved by the method according to the invention which is characterized by the characterizing part of claim 1 and the apparatus according to the invention which is characterized by the characterizing part of claim 3.

The primary advantage of the treatment tank used according to the invention is that 100¾ of the wastewater supplied is exposed to the aerobic biological effect in the biological treatment zone. In addition, in practice, all, usually 100%, of the biologically treated wastewater is forced through the underlying precipitation zone, which, due to its physical separation from the rotating contact means, is calm and capable of high removal of suspended solids. The process and apparatus of the invention result in uniform removal of carbonaceous contaminants from the wastewater with a minimum overflow of suspended solids, eliminating the need for subsequent solids removal apparatus.

The invention is further illustrated by the embodiments shown in the accompanying drawings, in which fig. 1 schematically shows a vertical section through an apparatus according to the invention along line I-I in FIG. 2, FIG. 2 is a schematic top view of an apparatus according to the invention; FIG. 3 and 4 schematically show vertical sections through alternative embodiments of apparatus according to the invention; and FIGS. 5 is a schematic sectional view taken along line 5-5 of FIG. 3 seen from below.

In FIG. 1 and 2, a tank 10 with a sewage inlet 11 and an effluent outlet 12 is seen. The tank 10 can be either a primary precipitation tank, a secondary precipitation tank or a complete clearing unit in an existing or new wastewater treatment plant. The wastewater directed to the tank 10 can be either untreated or partially treated, ie. decayed household or industrial wastewater containing biochemical-oxidizable contaminants.

The upper portion of the tank 10 contains a biological treatment zone comprising a plurality of parallel biological contact member assemblies 13 shown as thin plates comprising a plurality of rotatably arranged shafts 14. Each shaft 14 carries a plurality of concentrically fixed plates 15 providing a surface area on which to grow biological coatings. The shafts 14 are preferably positioned above the usual level of the wastewater in the tank to simplify the mechanical construction, although the immersion of the plates 15 may vary from approx. 1/3 to 2/3 of their diameter.

Although the rotatable biological contact members of the invention may take various forms, such as drums, cylinders, brushes or thin, closely spaced plates, it is preferred to use contact means having a discontinuous honeycomb structure, as described in Danish Patent No. 143,841.

Thin sheets are also advantageous biological contact means, since they allow a high concentration of surface area per unit area. volume unit in the biological treatment zone and can be used to induce a pumping effect on the wastewater.

Suitable biological contact means may be constructed of many available materials, although preferred are plastic materials and light metals.

Drive means not shown are used to rotate the shafts 14 to produce a predetermined peripheral speed of the plates 15. The drive means is advantageously capable of applying rotational forces varying in size and direction to the shafts 14. This allows for adaptation to varying amounts of flowing wastewater through the tank 10 and enables mechanical removal of excessive sludge growth from the surface of the plates 15, if desired. Preferably, the directional component of the peripheral velocity of the plates in their lower part is in the same direction as the wastewater flow through the biological treatment zone.

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The tank 10 is divided into two vertically adjacent treatment zones physically separated by a partition wall in the form of a horizontal baffle 16. The upper portion of the tank unit 10 comprising the rotating plate assemblies 13 is arranged to perform the biological function. The lower portion of the tank 10 between the baffle 16 and the bottom of the tank is an underlying precipitation zone, generally designated 17, for settling excess sludge from the effluent stream during treatment. Typically, a sludge collection means 18 is provided at the bottom of the tank to remove the precipitated sludge to a collection means 19 from which it is removed for subsequent laying or disposal. Sludge collection means 18 may be selected from the conventional types.

In a particular embodiment of the invention, the horizontal baffle 16 forming a false floor in the biological treatment zone extends over the entire width of the tank and along substantially the whole, typically 85-95%, of the length of the tank. A sufficient gap is provided between the end of the baffle 16 and the farthest wall of the tank 10 to allow the biologically treated wastewater to change direction and flow through the underlying precipitation zone countercurrent with the flow direction through the biological treatment zone. The velocity of the wastewater downward as it flows from the upper to the lower zone should be approx. 0.9-5 m / minute.

The distance between the lower edge of the plates 15 and the horizontal baffle 16 is typically between approx. 5 cm and approx. 0.9 to 1.2 m, depending on the composition of the wastewater which is fed through the inlet 11. When supplied with precipitated wastewater which is substantially free of sludge and solid contaminants, the baffle 16 may be placed very tightly, usually approx. . 5-15 cm from the bottom of the plates, since the accumulation of solids on the top of the baffle will be minimal. By further rotating the plates so that their lower portion has a velocity component in the same direction as the wastewater stream as shown by the arrows in FIG. 1, accumulated solids are forced over the edge of the baffle 5 and down into the underlying treatment zone where they are collected and removed through the collecting means 19. When untreated wastewater is added to the biological treatment zone, a larger gap must be provided between the bottom edge of the plates 15 and the baffle 16 to prevent precipitated solids from significantly influencing flow through the biological treatment zone. When treating untreated wastewater to the biological treatment zone, a solid removal means similar to the means shown in the precipitation zone of the tank 10 and designated by the number 18. Advantageously, is provided when such a body is desired in the biological treatment zone, the distance between the plates 15 and the baffle 16 at least be approx. 1 meter.

According to the invention, the horizontal baffle 16 may advantageously be provided with regular or randomly distributed perforations 27, as shown in FIG. 5. Such perforations allow settable solids, typically sand, in the incoming wastewater to pass from the biological treatment zone to the settling zone, without accumulating significant amounts on the top of the plate 16. Perforations 27 remove the need for a solid removal means below the plates 15 and allow that the baffle 16 is spaced at a distance of approx. 5-15 cm from the plates when treating solid wastewater. In this embodiment, the perforations 27 are approx. 2.5-30 cm in diameter, preferably approx. 7.5-15 cm, and comprises a total cross section of approx. 2-5 / 0 of the cross-section of the wastewater flow area through the biological treatment zone, i. the product of the tank width and the immersion depth of the plates 15.

In FIG. 3 and 4 are shown embodiments of apparatus according to the invention. Containers 20 and 20a are typical existing primary or secondary precipitation tanks in a wastewater treatment plant comprising an overflow member 21 and an outlet pipe 22 for removal of treated wastewater.

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As shown in FIG. 3 and 4, a vertical shield plate 24 is disposed against the overflow member 21 to provide a vertical separation between the biological treatment zone and the settling zones in tanks 20 and 20a. The horizontal baffle 25 horizontally separates the upper biological treatment zone from the underlying precipitation zone and extends along the full width of tanks 20 and 20a longitudinally for approx.

85 - approx. 95% of the distance from the vertical screen plate 24 to the opposite side. A sludge removal means 18 and a collecting means 19 are arranged in the precipitation zones of tanks 20 and 20a for collecting and removing precipitated solids.

In the treatment tank 20, wastewater inlet and outlet means 23, 22 are disposed on the same side of the tank, resulting in a countercurrent wastewater flow in the biological treatment zone and the underlying precipitation zone as shown by the arrows in FIG. 3. The tank 20 functions in the same way as the tank 10 of FIG. 1 and 2 and represents an adaptation of the principles of the invention to provide an existing precipitation tank with a biological treatment function.

Similarly, the tank 20a of FIG. 4 is an existing precipitation tank modified in accordance with the principles of the invention to substantially increase the efficiency of pollution removal. In the tank 20a, the waste water outlet 23 is disposed on the opposite side of the tank relative to the outlet means 21. The horizontal baffle 25 is disposed at a sufficient distance, typically approx. 30 cm - 1 m from the bottom of the plates 15 to allow a backflow of sewage as shown by the arrows in FIG. 4. The plates 15 of the tank 20a rotate so that they have a velocity component in their lower part in the same direction as the wastewater flow through the plate assemblies 13. An inlet shield plate 26 is arranged to direct the incoming wastewater through the plate assemblies 13. As in the tanks 10 and 20, the effluent flow below the plates 15 is countercurrent with the effluent flow in the underlying precipitation zone.

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It is preferred to limit the immersion depth of the plates 15 to less than half the depth of the processing tanks 10, 20 and 20a. For practical purposes, the diameter of the plates 15 is approx. 1.8 - 5 m and the dip depth less than half the diameter.

In order to increase the growth of biological coatings on the plate assemblies 13 by alternately immersing them in the wastewater and exposing them to the atmosphere, the plate assemblies 13 are rotated at an appropriate predetermined rate. From a practical point of view, the peripheral speed of the plates should not exceed approx. 1 m / sec and must be high enough to avoid excessive immersion of the biological coatings.

To provide the microorganisms in the sludge with sufficient oxygen to satisfy their metabolic processes, the immersion time of the coating should typically not exceed 10 seconds. As the wastewater becomes progressively clear, the immersion time of the coating can be gradually increased to approx. 30 seconds. For smaller plates, the peripheral velocity can be significantly reduced without avoiding excessive immersion times, while the larger plates generally require the rotational speed to be substantially increased to avoid excessive immersion time. Therefore, in normal operation, the peripheral velocity of the plates 15 must be between approx. 15 cm and 1 m per per second, preferably approx. 22 - 46 cm per second.

The plates 15 should be positioned as close as practicable to the shaft 14 to provide the maximum concentration of plate surface area per unit area. unit of volume in the plate assembly. However, sufficient contact time between the wastewater and that between approx. 1.5 and 7 mm thick layers that develop on the oil surface. In view of this, plates 5 should be separated by at least approx. 13 mm at their centers. A plate spacing of approx. 18 - 38 mm at the centers have proved suitable for the treatment of normal household wastewater. In operation, it must be taken into account that wastewater treatment plants are subject to daily variations in the quantity supplied. In the early morning hours from approx. pm.

2 to 6, the wastewater flow to the plant usually represents a small portion of the daytime supply. In order to adapt the biological treatment plant to these variations in the wastewater flow, an automatic control system can be provided to control the peripheral velocity of the plates, taking into account changes in the flow rate without excessive recycling.

The method and apparatus according to the invention provide a relatively inexpensive and practical possibility for a substantial increase in the effect of wastewater treatment plants. The invention can be used in connection with primary sedimentation tanks which remove only the precipitated solids from the untreated wastewater. Much of the BOD that will remain can be removed at relatively low cost. Treatment plants that currently remove approx. 30-60¾ of BOD in wastewater can be economically improved to remove approx. 80-99¾ of the BOD contaminants by introducing the principles of the invention into the plant.

The removal of carbonaceous contaminants is a function of the 2 load amount, that is, liters / day / m of the area of the contact means, as well as the composition of the waste water. The wastewater removed from the precipitation zone is biologically treated to remove up to approx. 95¾ of the carbonaceous material measured as BOD (biological oxygen demand), depending on the available surface of the contact members per volume of wastewater, and is substantially free of suspended solids and is suitable for direct discharge into an aqueous recipient, e.g. lakes, rivers and streams. For example, a 90¾ BOD removal can be achieved at a load of 82-204 liters / day / m contact body surface for normal wastewater and 80¾ BOD removal with a load of approx. 164-408 liters / day / m. When an oxygen-enriched atmosphere is provided over the biological treatment zone, i.e. ca. 40-70¾ oxygen, a 90¾ BOD removal can be achieved at a load of 164-408 liters / day / m.

In addition to significantly improving existing wastewater treatment plants, the method and apparatus can

Claims (3)

146362 according to the invention form the basis for designing new plants. A single-tank wastewater treatment plant capable of removing over 90? Of BOD from wastewater can be constructed for a fraction of the cost of a conventionally activated sludge or sand filter plant that produces the same purification rate. The method and apparatus according to the invention are not limited to the above illustrative indications. Thus, for example, the term "horizontal baffle" should be construed to include any horizontally disposed baffle that divides the effluent stream through a biological treatment zone and an underlying precipitation zone. Furthermore, the principles of the invention can also be adapted to a round tank with an upper treatment zone and an underlying precipitation zone separated by a horizontal plate. Patent claims: A method for removing contaminants from wastewater by biological reaction, whereby the wastewater is fed into a treatment tank which is equipped with a biological treatment zone in the upper part of the tank and below it separated from it by a wall device a precipitation zone and whereby the biological treatment zone is provided. with rotatable biological contact means placed across the tank and perpendicular to the direction of flow of the wastewater, which is displaced by rotation at such a peripheral speed that biological coatings can grow on the surface of the contact members, while at the same time the waste water is displaced in the opposite direction in the biological treatment zone respectively and in the underlying precipitation zone, characterized in that a separating wall extending over the entire tank width is arranged horizontally between the precipitation zone and the biological treatment zone, that the entire amount of waste water supplied to the tank is substantially passed through the tank. the treatment zone, in which substantially all of the amount of wastewater located at one end of the tank is directed from the biological treatment zone around the horizontal partition to the underlying precipitation zone and substantially all of the wastewater is passed through the precipitation zone. before discharging from the opposite end of the tank. Process according to claim 1, characterized in that the wastewater is introduced into the biological treatment zone and removed from the precipitation zone at the same end of the treatment tank. Apparatus for carrying out the method according to claim 1 or 2, comprising a tank structure with predetermined length and width dimensions, a biological treatment zone located in the upper part of the tank, a settling zone located in the lower part of the tank, which lies below and has approximately the same extent as the biological treatment zone, a guide member located between the biological treatment zone and the precipitation zone, inlets for introducing wastewater into the tank structure, outlets for removing wastewater from the tank structure, and scraping and transport means for removing precipitated material from the precipitation zone, and rotatable biological contact members in it. biological treatment zone, which contact members are mounted with their shafts located across the tank and across the flow direction of the wastewater, characterized in that the guide means comprises a horizontal guide plate (16,25) immediately below the contact members and extending over the entire width of the tank. the tank (10.20) and in length extending from the inlet (11,23) to at least below the last downstream contact means, the baffle (16,25) dividing the tank into an upper biological treatment zone and a lower precipitation zone (17) which are connected to each other at downstream of the biological treatment zone, the guide means directing the effluent stream from the inlet (11,23), through the biological treatment zone, into the precipitation zone, through the precipitation zone and up to the outlet (12,22).