SK151299A3 - Method and apparatus for biological removal of nitrogen compounds from water - Google Patents

Abstract

Method of removing nitrogen and its compounds from water using biological process in activated sludge suspension. The nitrogen in the form of nitrates and nitrites is removed by means of a denitrification proceeding in a fluidized layer of sludge blanket, the layer being formed by a suspension of biological sludge and being kept in a fluidized condition. Apparatus for performing the method comprises an upwards widening denitrification zone (5), into the lower part of which an admission for the water containing nitrates, an admission for the activated sludge and an admission for the substrate, which has been biologically oxidized during the denitrification, mouth.

Description

The invention relates to a process for the removal of nitrogen and its compounds from the biological process in an activated sludge suspension and to an apparatus for carrying out the process.

BACKGROUND OF THE INVENTION

In the biological removal of nitrogen compounds from water, a denitrification process is used to remove nitrates. Nitrates and nitrites serve as a source of oxygen for microorganisms during denitrification and are reduced by their metabolism to nitrogen gas. At the same time, the microorganisms consume a suitable biodegradable substrate which oxidizes the oxygen obtained. As a substrate for denitrification, the microorganisms themselves can also temporarily serve in the so-called process. endogenous respiration when, for example, the delivery of the biodegradable substrate is irregular.

In order for denitrification to occur, anoxic conditions are necessary, i.e., there must be a lack of molecular oxygen in the environment. If molecular oxygen is available in the environment, the microorganisms are oriented towards its consumption and pass on denitrification only after depletion of oxygen. Therefore, anoxide conditions are generally achieved in such a way that, at a sufficient concentration of microorganisms, oxygen supply is prevented and the microorganisms themselves create anoxide conditions by consuming the oxygen present.

In general, biological processes can be carried out either with microorganisms attached to a solid support or with microorganisms that are in suspension of activated sludge ("attached - growth process" and "suspended - growth process" - see Metcalf and Eddy, Wastewater Engineering, McGraw-Hill (New York, 1985). For reasons of convenience, processes with microorganisms in activated sludge suspension are more commonly used.

In the denitrification process in the activated sludge suspension, the suspension is carried along with the purified water, from which it must be separated and returned to the denitrification process. The separation of the suspension is complicated by the bubbles of excreted nitrogen which adhere to it. Removal of these bubbles is accomplished by vigorous mechanical movement of the suspension, which is generally accomplished by aeration in known processes.

In wastewater treatment, aeration simultaneously serves to aerobically activate water purification and to create conditions for the nutrification of ammonia and organic nitrogen, i. to convert any residual nitrogen pollution into nitrates. Water with these

The nitrates and activated sludge are then returned to the denitrification process where these nitrates are removed. Thus, the coupling of denitrification and nitrification results in biological removal of all nitrogen compounds from the water. Activated sludge, separated from the effluent, is also usually returned to the denitrification.

However, this denitrification has a number of disadvantages. In biological processes in the activated sludge suspension, the suspension must be suspended. During aerobic activation, suspension suspension is ensured automatically by aeration. During denitrification, the suspension is usually carried out by mechanical agitation. The disadvantage here is that a mechanical stirrer requires a stirrer and a source of movement - e.g. electric motor with gears. These mechanical parts increase the investment costs and in the event of failure, due to their storage in the denitrification area, the repair is complicated. Another disadvantage of the described denitrification is the limitation of the concentration of activated sludge in the denitrification to only the values given by mixing the individual components entering the denitrification, which limits the rate of denitrification per unit of volume of denitrification space.

SUMMARY OF THE INVENTION

The above-mentioned disadvantages are eliminated by the process according to the invention, which is based on the fact that nitrogen in the form of nitrates or nitrites is removed by denitrification, which takes place in a fluidized layer of a flocculent cloud formed by a slurry of biological sludge and maintained in a fluidized state.

The activated biological sludge suspension is fed to the denitrification region by a bottom-up flow, wherein the down-stream flow rate slows down at least at the bottom of the denitrification.

It is important to carry out the process according to the invention that excess activated sludge is removed from the top of the denitrification area in the form of a slurry, which is subsequently subjected to aeration, separated from water and returned to the bottom of the denitrification area.

It is also essential that nitrogen in the form of nitrates and nitrites is removed by denitrification, which takes place in a fluidized layer of flocculent cloud consisting of a slurry of biological sludge and maintained in a fluidized state by flowing from the bottom up, at least at the bottom of the fluidized layer. and nitrate-containing water, activated sludge, and a substrate that is biologically oxidized during denitrification are fed to the bottom of the fluidized bed.

For better removal of nitrogen from purified water, it is beneficial that nitrogen in the form of nitrates and nitrites is removed by denitrification, which is carried out in a fluidized

- a flake cloud layer consisting of a slurry of biological sludge and maintained in a fluidized state by a bottom-up flow, wherein at least in the bottom fluidized layer the upward flow rate decreases, and water containing nitrates and nitrites, activated sludge and substrate are fed; which is biologically oxidized during denitrification.

To close the nitrogen removal cycle from purified water, it is beneficial that during aeration, nitrogen in the form of ammonia and organic nitrogen is biologically oxidized to nitrates and the water with these nitrates, together with the activated sludge, returns to the denitrification process.

The principle of the device according to the invention is that during aeration, nitrogen in the form of ammonia and organic nitrogen is biologically oxidized to nitrates and the water with these nitrates is returned to the denitrification process together with the activated sludge.

For the reliability of the method, it is important that the denitrification space (5) is in its upper part connected to the activation space (8), which contains aeration elements (20) and is connected to the separation space (7), in the upper part of which the circuit is arranged (10) denitrified water, wherein the separation space (7) is associated with a withdrawal of separated sludge, provided with a source of forced movement and opens to the bottom of the denitrification space.

BRIEF DESCRIPTION OF THE DRAWINGS

The device according to the invention for the treatment of domestic waste water is shown in the drawings, where FIG. 1 is a cross-sectional view of the device, and FIG. 2 device in plan view.

DETAILED DESCRIPTION OF THE INVENTION

The device consists of a vertical cylindrical tank with a jacket 1 and a bottom 2 in which the vertical partition wall 3, the first conical wall 4 and the part 2 'of the bottom 2 between the lower edges of the partition wall 3 and the first semi-conical wall 4 are formed upwardly extending denitrification space 5 On the other side of the cylindrical tank, a separating space 7 is formed by a vertical partition wall 3 and a second semi-conical wall 6. An activation space 8 is defined between the housing 1 and the two semi-conical walls 4 and 6. In the upper part of the separation space 7 there is arranged a withdrawal inlet 9 of purified water with outlet 10. The water level 11 is determined by the position of the withdrawal inlet 9 of purified water. In the upper part of the first first half-conical wall 4, a connection 12 is made between the denitrification space 5 and the activation space 8. This connection 12 is formed by two circular

- holes whose upper edges are above the surface of the water and the lower edges below it. However, the connection 12 may also be formed by other means, for example by recesses in the upper edge of the first half-conical wall 4 or by otherwise performing an overflow by lowering the upper edge of the first half-conical wall 4. An opening 13 is formed at the bottom of the second half-conical wall 6. 7 and activation space 8. In the denitrification space S, there is a vertical semicircular line 14 at the vertical partition 3, which forms a common supply of biodegradable substrate, activated sludge and nitrates to the bottom of the denitrification space 5. A basket 15 is located at the top of semicircular line 14. over which there is a waste water inlet 16. In the lower part of the separation space 7, opposite the opening IX, in the partition wall 3 there is a discharge opening 17 of the separated suspension, which is led into the mammoth pump 18. The mammoth pump 18 is essentially inserted into the semicircular pipe 14 and led under the basket 15 (FIG. 1). At the bottom of the pump 18 is a compressed air supply 19. Aeration elements 20 are located at the bottom of the activation space 8 at the bottom 2. At the bottom of the denitrification space 5 at the bottom part 2 'there is a coarse-bubble auxiliary aeration element 21.

The method according to the invention and the functions of the described apparatus are described in the following.

Waste water containing nitrogen compounds such as urea, ammonia, nitrogen in organic substances, and various other biodegradable substances, which will hereinafter be referred to as a substrate in its entirety, flows through the wastewater 16 into the basket 15. Larger pieces are retained in the basket 15, such as paper. Through the air coming from the mammoth pump 18 under the basket 15, these pieces are constantly floated, preventing the basket 15 from clogging. If these pieces are biodegradable, they will gradually biodegradate under the influence of the air and activated sludge supplied by the pump 18. Non-biodegradable pieces, such as polyethylene bags and the like, remain in the basket 15 and are removed therefrom when periodically inspected.

Waste water, i.e. water with a biodegradable substrate, is mixed with water containing nitrates and returned activated sludge after flowing through the basket 15 and which is fed through the pump 18 below the basket 15. The water mixture with biodegradable substrate, nitrates and activated sludge is fed through a semicircular pipe 14 into the lower part of the denitrification chamber 5, where its direction of flow changes so that the mixture flows upwards in the denitrification chamber 5. As the denitrification space 5 widens upwards, the flow velocity therein decreases upwards. This results in the activated sludge suspension retaining in the denitrification chamber 5 under the influence of gravitational forces, forming a fluidized layer of flocculent cloud through which water with nitrates and biodegradable water flows.

-5substrátom. The oxygen present in the water is rapidly consumed by the microorganisms already at the bottom of the denitrification space, thereby creating anoxic conditions throughout the denitrification space 5 or at least in the predominant part thereof. As a result of the anoxide conditions, denitrification takes place in the denitrification chamber 5 in which nitrates present in the water are reduced to nitrogen gas. A portion of the biodegradable substrate is consumed. Another part of the substrate is collected by activated sludge and consumed later in the period when the substrate is not fed from outside. The nitrate-free water and most of the biodegradable substrate flows by interconnecting 12 from the denitrification space 5 to the activation space 8. Activated sludge suspension particles having trapped nitrogen bubbles in the denitrification space 5 are discharged from the fluidized bed in the denitrification space 5 As the operation of the mammoth pump 18 is continuously fed to the lower part of the denitrification space 5 through the semicircular piping 14, an additional sludge is continuously activated, after the entire denitrification space 5 has been filled with a fluidized layer of flocculent cloud, the excess activated sludge also falls through the interconnection 12 into the activation space 8. Compressed air is supplied to the aeration elements 20, which bubbles up through the activation space 8 and creates turbulence, which releases nitrogen bubbles from the activated sludge suspension particles. At the same time, the water in the activation space 8 is saturated with oxygen and a flow is generated which floats the activated sludge suspension and mixes it evenly throughout the volume of the activation space 8. Likewise the water which has passed from the denitrification space 5 through the connection 12 to the activation space 8 in it gradually mix. The mixed activated sludge in the presence of oxygen oxidizes all the present nitrogen compounds to nitrates, thereby removing residual dissolved biodegradable substances from the water. At the same time, the activated sludge is aerobically stabilized.

Compressed air is blown into the mammoth pump 18 through the inlet 19, which passes through the mammoth pump 19 upwards, thereby creating a known mammoth pump effect. As a result, an activation mixture consisting of nitrate-containing water and mixed activated sludge is sucked through the opening 13 through the opening 13 from the adjacent part of the activation space 8 and fed under the basket 15 and via the semicircular pipe 14 to the lower part of the denitrification space 5. higher. The mammoth pump 18 thus serves as a source of forced movement, which creates a closed circulation circuit, by which the nitrates formed in the activation space 8 are returned to the denitrification space 5.

-6Waste water flows through the inlet 16 in a sudden and irregular manner. In the period when the waste water does not flow, the nitrates of the activation space 8 are introduced into the denitrification space 5, where they are removed by denitrification. The biodegradable substrate for denitrification is preferably the substrate previously trapped in the activated sludge in the fluidized bed of the flocculent cloud in the denitrification space 5. If the trapped substrate is exhausted, further denitrification is then carried out on account of the endogenous respiration of the activated sludge. By these processes, the nitrate concentration in the activation space 8 is constantly reduced to a very low value.

When a certain volume of wastewater flows through the inlet 16, this water expels the same volume of water from the denitrification space 5 by interconnecting 12 into an adjacent part of the activation space. This water then pushes through the opening 13 from the adjacent part of the activation space 8 the same volume of the activation mixture into the lower part of the separation space 7 into the inlet 9 of purified water from where this water flows through the outlet. and separates from water.

If the wastewater inflow lasts for a longer period of time through the inlet 16, the activation mixture flows through the formed fluidized bed of the flake cloud, and the activated sludge slurry is collected and packed into the flake cloud. The large flakes formed then sink in the separation space 7 downwards and are sucked through the orifice 17 through a mammoth pump 18 into the semicircular duct 14 through which they reach the bottom of the denitrification space 5. Thus the separated sludge is returned to the denitrification space 5. the purified water flows from the separation space 7 through the inlet 9 of purified water to the outlet 10.

When the wastewater inlet 16 is stopped, the purified water is also discharged through the outlet 10. The fluidized layer in the separation space 7 then drops down and its flakes are sucked through the orifice 17 together with the activating mixture sucked through the opening 13 of the activation space 8. any activated sludge separated from water from the activation mixture pushed into the separation space 7 is also sucked off by the mixture. Only the purified water remains in the separation space 7 above the opening 13, which is then pushed through the inlet 9 of the purified water. to outlet 10 as described above. The purified water remaining in the separation space 7 is thus water from the activation mixture in part of the activation space 8.

Adjacent to the aperture 13 which has previously passed through the denitrification space 5 and the activation space 8, thereby removing biodegradable substances and nitrogen compounds therefrom.

Thus, the described operation of the present embodiment of the device is the waste water entering the device through the inlet 16 purified from biodegradable substances and nitrogen compounds and flows out of it as purified water through the outlet 10.

As a result of the activated sludge accumulating in the fluidized bed of the flocculent cloud in the denitrification space 5, which is continuously fed there by the mammoth pump 18 and only the flotated sludge and excess sludge passes into the activation space. In the case of a smaller amount of activated sludge in the whole plant, for example at the start of operation, virtually all sludge could accumulate in the denitrification space 5, so that the activation sludge 8 is permanently deficient in the activated sludge. This would then lead to disruption of nitrification in the activation space 8 and hence to impair the function of the device. Also, in the event of a long-term power failure, thereby stopping the operation of the mammoth pump 18 and stopping the flow in the denitrification space 5, the function of the apparatus could be impaired by sedimenting the fluidized layer in the denitrification space 5 to form a sediment over time. he was no longer hovering after the restoration. To avoid such cases, an auxiliary aeration element 21m is provided which is installed in the denitrification area 5 at part 2 'of the bottom 2. When this auxiliary aeration element 21 is switched on, the air coming out of it breaks and floats any possible sediments from part 2' of the bottom 2. mixes the fluidized bed in the denitrification chamber 5 such that the activated sludge passes therefrom together with the flowing water into the activation chamber 8. Therefore, the intermittent occasional switching on of the auxiliary aeration element 21 may serve to prevent said disturbances.

In order to document the operation of the device, the following table shows the results of the trial operation, which were obtained from a series of withdrawals from the operation of ten test units deployed in family houses, where the population ranged from 2 to 7 persons. The functional spaces of said test unit had the following volumes: denitrification space 5 0.25 m ³ , separation space j 0.4 m ³ , activation space 8 1.1 m ³ .

The date COD BSKj NL N-NH4 ⁺ N-NO ₃ 28/8/96 15.4 2.7 1.4 0.00 5.6 04/09/96 23.2 3.9 2.8 0.50 5.2 11/9/96 13.8 4.0 4.3 0.55 4.9 18/9/96 12.1 1.8 3.7 0.30 6.1

10/2/96 30.0 5.0 6.0 0.78 5.2 10/16/96 40.1 8.5 7.2 0.81 8.9 10/23/96 24.2 4.8 8.7 0.60 5.6 11/6/96 10.0 7.0 7.0 0.92 7.6 11/13/96 15.0 8.0 n, o 0.85 3.6 11/21/96 30.0 15.0 14.0 1.22 8.7 11/27/96 20.0 n, o 7.2 0.72 6.2 11/12/96 18.3 4.3 5.3 0.50 5.9 12/17/96 15.1 5.4 3.9 0.45 5.1 10/1/97 21.2 7.5 6.3 0.62 6.7 14/1/97 23.0 8.2 7.9 0.73 8.3 22/1/97 16.7 5.1 4.9 0.49 5.7 29/1/97 13.9 3.2 2.6 0.30 4.8 10/2/97 19.2 5.7 3.3 0.52 5.3 12/2/97 15.0 4.2 2.8 0.41 4.9 16/2/97 22.3 7.6 7.9 0.49 7.9 23/2/97 18.0 6.3 6.3 0.31 6.1 03/04/97 15.3 5.4 5.4 0.39 5.7 14/3/97 21.2 8.1 7.3 0.85 8.4 21/3/97 18.4 6.5 6.2 0.60 6.7 28/3/97 15.7 4.1 5.1 0.35 5.1 average 19.5 6.1 5.9 0.57 6.2

In the table, COD means BOD ₅ NL

N-NH?

n-no ₃

All values reported are chemical oxygen demand biological oxygen demand insoluble nitrogen in the form of ammonium nitrogen in the form of nitrates.

mg / l.

Taking the known table values for daily water consumption and pollution production per equivalent population (150 l, 60 g BOD, 12 g N) taken as input values, the average values achieved correspond to the removal of 91,5% nitrogen and 98,5% BOD. .

The method and apparatus of the invention have many advantages. The concentration of activated sludge in the fluidized layer of the flocculent cloud in the denitrification space 5 is higher than the concentration of activated sludge in the activation space 8, resulting in a rate of denitrification per unit volume higher than that of the mechanically stirred denitrification space. The substrate that enters the denitrification space 5 and serves for denitrification is retained there in the fluidized layer of the flocculent cloud, so that its use for denitrification is higher than that of the mechanically stirred denitrification space. No mechanical device is required to keep the sludge slurry suspended within the denitrification chamber 5. All of this reduces equipment investment costs and increases the efficiency of cleaning processes.

Industrial use

The method and apparatus of the invention is not limited to the purification of waste water and to the exemplary apparatus described. It can also be used for other purposes, for example to remove nitrates from drinking water, where a hygienically suitable organic substance such as alcohol, sugar and the like will be added as a substrate. Likewise, the apparatus for carrying out the process according to the invention may have different internal arrangements, in which only the basic principle of the invention is essential, namely that the apparatus comprises an upwardly extending denitrification space in which a nitrate-containing water feed, activated sludge and a denitrification substrate . It is irrelevant whether the water supply containing nitrates, activated sludge and the substrate for denitrification is carried out jointly, as in the example apparatus described, or as separate inlets of the individual components to the bottom of the denitrification space 5. All kinds of utilization of the basic principle devices utilizing the above-described ideas of the invention do not thereby depart from the spirit of the invention.

Claims (9)

PATENT CLAIMS Process for removing nitrogen and its compounds from a biological process in an activated sludge slurry, characterized in that nitrogen in the form of nitrates or nitrites is removed by denitrification, which is carried out in a fluidized layer of a flocculent cloud formed by a sludge of biological sludge and maintained in a fluidized state. The method of claim 1, wherein the activated biological sludge suspension is fed to the denitrification region by a bottom-up flow, wherein the flow rate in the bottom-up flow is slowed down at least at the bottom of the denitrification region. Method according to claim 2, characterized in that excess activated sludge is discharged from the upper part of the denitrification area in the form of a suspension, which is subsequently subjected to aeration, separated from water and returned to the lower part of the denitrification area. Method according to claim 2 or 3, characterized in that at least in the lower part of the fluidized bed the flow rate decreases upwards, and in the lower part of the fluidized bed, water containing nitrates, activated sludge and a substrate which is biologically oxidized during denitrification . Method according to claim 1, 2, 3 or 4, characterized in that, after denitrification, the water and excess activated sludge are removed from the top of the fluidized bed and the removed activated sludge is aerated to remove adhered excreted nitrogen, separated from the purified water and returned back to the bottom. Method according to claim 3, 4 or 5, characterized in that during aeration nitrogen in the form of ammonia and organic nitrogen is biologically oxidized to nitrates and the water with these nitrates together with the activated sludge is returned to the denitrification process. -117. Apparatus for carrying out the method according to any one of claims 1 to 6, characterized in that it comprises an upwardly extending denitrification space (5), into which a nitrate-containing water inlet, an activated sludge inlet and a biologically oxidized substrate in denitrification enter. Apparatus according to claim 7, characterized in that the denitrification space (5) is in its upper part connected to the activation space (8), which comprises aeration elements (20) and is connected to the separation space (7), in wherein a denitrified water circuit (10) is arranged at the top, the separation slurry (7) being associated with a withdrawal of the separated sludge, equipped with a source of forced movement and opening to the bottom of the denitrification compartment. Apparatus according to claim 7 or 8, characterized in that the removal of the separated sludge is located in the lower part of the separation space (7) near its interconnection with the activation space (8), wherein the discharge of water with nitrates from the activation space (8). ) for its return to the denitrification area (5) is provided by identical structural elements. Apparatus according to claim 7, characterized in that the supply of nitrate-containing water, the activated sludge supply and the biologically oxidized substrate supply during denitrification are provided as a common supply.