EP1763491A1

EP1763491A1 - Method and apparatus for continuously controlling denitrification in variable nitrogen loads in wastewater

Info

Publication number: EP1763491A1
Application number: EP05769794A
Authority: EP
Inventors: Jürgen KAHLERT; Frank Niemeyer; Matthäus SCHMIDT
Original assignee: Bayer Healthcare AG
Current assignee: KAHLERT, JUERGEN; NIEMEYER, FRANK; SCHMIDT, MATTHAEUS
Priority date: 2004-06-18
Filing date: 2005-06-16
Publication date: 2007-03-21
Also published as: NO20070215L; WO2005123611A1; US7476319B2; DE102004029539A1; US20080017583A1

Abstract

The invention relates to a method and an apparatus for continuously controlling denitrification in variable nitrogen loads during wastewater purification in a sewage plant comprising at least one denitrification stage (14). Said method comprises the following steps: a) excess sludge is provided; b) the excess sludge is treated according to predefined operational parameters; c) the treated excess sludge is divided into an organic portion and an inorganic portion; d) real values for diluted organic carbon (DOC) are measured in the organic portion; e) the organic portion is redirected into one of the denitrification stages; f) real values are compared to given setpoint values for DOC concentrations, and modified operational parameters for treating the excess sludge in step b) are determined if there is a difference between the real values and the setpoint values; g) steps a) to f) are repeated.

Description

Method and device for the continuous control of the denitrification in the case of fluctuating nitrogen loads in the waste water

The invention relates to denitrification in the case of fluctuating nitrogen loads in the waste water. Denitrification is the conversion of nitrate compounds to pure nitrogen. This process is carried out with the exclusion of air (anaerobic) from bacteria, provided that sufficient carbon compounds are present so that the nitrogen can be substituted by carbon and C0 ₂ can be produced. The conversion takes place in two stages, first from nitrate to nitrite and then from nitrite to N ₂ .

Wastewater treatment plants are designed in such a way that denitrification takes place in a first or a later biological treatment stage, depending on the expected wastewater composition, which is referred to here as the denitrification stage. If the wastewater itself has high nitrate loads and few other nitrogen compounds, then the denitrification can usually take place in the first stage of the clarification process. The wastewater often contains the nitrogen load in the form of nitrogen compounds such as ammonium, urea or organic nitrogen compounds. In this case, nitrification takes place in a first biological clarification stage, that is, these nitrogen compounds are converted into nitrate compounds. This is done in air (aerobic) with the help of appropriate bacteria in two stages via nitrite to nitrate. In this case, denitrification takes place in a second biological clarification stage.

Usual denitrification stages are constructed in such a way that the liquid phase from the denitrification stage - if necessary after passing through a secondary clarifier / settling basin - is discharged as clarified waste water and part of the sludge, ie the solid phase, is returned to the denitrification stage. The remaining sludge forms the so-called excess sludge. This excess sludge is either completely disposed of or subjected to a further treatment and then wholly or partly returned to the denitrification stage.

The bacteria in the denitrification stage require certain amounts of carbon, but also nitrogen and phosphorus, for optimal denitrification performance. The required amounts of these elements vary with the wastewater composition, especially with the nitrogen load. Often the amount of C, N and P necessary for optimal denitrification is added directly from storage containers. The necessary amounts of C, N and P are adjusted for optimal denitrification of the respective nitrogen load. However, it is also known to recover C, N and P from the organic portion of the excess sludge.

From EP 1 254 865 AI it is known to mechanically disintegrate excess sludge and then to treat it with ozone and the liquid phase of the treated excess sludge attributed to the denitrification stage. In the ozone treatment stage, ozone is added in an amount of 100 to 150 g / kg dry matter.

No. 6,337,020 B1 discloses the treatment of excess sludge from a biological treatment stage by mechanical disintegration and addition of ozone. The treated excess sludge is completely returned to the biological treatment stage. In the ozone treatment stage, ozone is added in an amount of 1 to 20 g / kg dry matter and the pH is 6 to 9.

EP 0 645 347 B1 discloses the treatment of excess sludge from an aerobic biological treatment stage by mechanical disintegration and addition of ozone and the return of the treated excess sludge to the biological treatment stage. In the ozone treatment stage, ozone is added in an amount of 2 to 50 g / kg dry matter and the pH is at most 5.

From US 4,370,235 it is known to mechanically disintegrate excess sludge from a biological treatment stage and then to treat it with ozone and to return the liquid phase of the treated excess sludge to the biological treatment stage. In the ozone treatment stage, 4.4 g of ozone is added and the pH is 7.2.

The known methods for treating excess sludge serve only to reduce the excess sludge. They are not optimized with regard to the efficiency and effort of denitrification. The provision of an excess sludge, which is optimized in its composition, in particular in the contents of C, N and P for the denitrification stage, is not discussed. In the event of fluctuating nitrogen loads, the driving parameters have to be adapted for optimal, ie complete, denitrification of the nitrogen load in the wastewater, because certain driving parameters are suitable for high nitrogen loads, others for low nitrogen loads. Adding too much ozone, which can easily occur without adjustment at low nitrogen loads, can, for example, result in the cells in the excess sludge not only being broken open, but also in the cell contents being oxidized, so that the excess sludge returned contains too little C, N and P. to ensure optimal further processing in the denitrification stage. The known methods also do not take into account that mechanical disintegration, like the production of ozone, is very energy-intensive and that this effort should be adapted to the effect achieved, the effect achieved in turn being dependent on the particular wastewater composition. The object of the invention is therefore to optimize the known methods for treating excess sludge so that the best possible result in the denitrification stage is achieved with the least possible use of resources and the excess sludge is minimized as much as possible.

The solution to the problem according to the invention consists in a method for the continuous control of the denitrification in wastewater treatment in a sewage treatment plant with at least one denitrification stage with fluctuating nitrogen loads, comprising the steps a) provision of excess sludge, b) treatment of the excess sludge according to previously determined driving parameters, c) separation of the treated excess sludge into an organic fraction and an inorganic fraction, d) measurement of actual values for dissolved organic carbon (DOC) in the organic fraction, e) return of the organic fraction to one of the denitrification stages, f) comparison of Actual values with predefined target values for DOC components and if there is a difference between the actual and target values, determination of changed driving parameters for the treatment of the excess sludge in step b. g) repetition of steps a. to f.

The excess sludge can come from one of the denitrification stages, but also from another part of the sewage treatment plant.

DOC (Diluted Organic Carbon) in the organic portion of the treated surplus sludge, which is returned to one of the denitrification stages, serves as a control variable for the driving parameters in the treatment of the surplus sludge. With an optimal (target) DOC value, the organic portion of the excess sludge which is returned to the denitrification stage contains the optimal amounts of carbon compounds, N and P for the denitrification, these optimal amounts depending on the nitrogen load. A certain optimal DOC value can be assigned to each nitrogen load.

The driving parameters that can be varied in the treatment of the excess sludge with an actual-target difference in the DOC value are the pH value of the excess sludge, the connection or disconnection of the mechanical disintegration and the connection or disconnection of the ozone addition and the amount of ozone added. The pH is preferably set in a range between 7 and 13. The amount of ozone added is preferably not greater than 100 g / kg dry matter.

At least one optimal combination of the three driving parameters mentioned can be assigned to each DOC value. If there are several optimal combinations, the one that means the least amount of resources is preferably selected. As a rule, this means that preference should be given to those combinations of driving parameters in which mechanical disintegration takes place as far as possible and no or only small amounts of ozone are added.

The object according to the invention is further achieved in a device for continuously controlling the denitrification in wastewater treatment in a sewage treatment plant with at least one denitrification stage in the case of fluctuating nitrogen loads containing at least one denitrification stage, means for providing excess sludge, a treatment stage for treating the excess sludge according to previously determined driving parameters, - means for separating the treated excess sludge into an organic portion and an inorganic portion, means for recycling the organic portion of the treated excess sludge into one of the denitrification stages, means for measuring dissolved organic carbon (DOC) in organic fraction of the treated excess sludge, means for comparing measured actual values for DOC with specified target values for DOC, means for determining changed driving parameters f r the treatment of excess sludge at detected difference between actual values and target values for DOC.

The means for providing the excess sludge from the denitrification stage or from another part of the sewage treatment plant usually comprises a secondary clarifier, in which the sludge sinks following gravity after the sedimentation process. The excess sludge is drawn off at the bottom of the secondary clarifier.

The treatment stage for the excess sludge can comprise a container with an addition device for pH-influencing agents, a mechanical disintegrator and / or an ozonizer with injectors for introducing the ozone into the excess sludge to be treated. Ozone is usually added at overpressure. Can be used as mechanical disintegrators For example, a shear gap homogenizer, a high-pressure homogenizer, an ultrasonic homogenizer or an agitator ball mill are used as described in J. Kopp et al with disperse solids, Chapter 3: Sewage sludge digestion.

The means for separating the treated excess sludge into an organic fraction and an inorganic fraction can be a secondary clarifier or a filter system for filtering off the inorganic fraction.

The means for returning the organic portion of the treated excess sludge to one of the denitrification stages are usually the corresponding lines, which are optionally equipped with pumps.

The means for measuring dissolved organic carbon (DOC) in the organic portion of the treated excess sludge can be a continuous process analyzer for online measurement. However, individual samples can also be taken and analyzed in the laboratory using customary methods.

The means for comparing measured actual values for DOC with predetermined target values for DOC is normally an electronic data processing device. The means for determining changed driving parameters can be an electronic data processing device in combination with a database.

The advantage of the method and the device according to the invention is that even with fluctuating nitrogen loads, the denitrification process runs continuously at the optimum or close to the optimum, so that as complete a denitrification as possible takes place while conserving resources. If the denitrification process runs at its optimum, the excess sludge is minimized at the same time.

Figures and examples

The figures show

Fig. 1 Schematic structure of the wastewater treatment plant in Wuppertal

Fig. 2 Influence of driving parameters on DOC and excess sludge

3a, 3b influence of the driving parameters on DOC and excess sludge in comparison

Fig. 4 Dependence of the DOC in the clear phase on the pH value with different nitrogen loads

Fig. 5 Dependence of the DOC in the clear phase on the mechanical dispersion with different nitrogen loads FFiigg .. 66 Dependence of the DOC in the clear phase on the amount of ozone with different nitrogen loads

Fig. 7 dependence of the DOC in the clear phase of pH and dispersion

Fig. 8 Dependence of the DOC in the clear phase on pH and amount of ozone

Fig. 9 Dependence of the DOC in the clear phase on the dispersion and amount of ozone FFiigg .. 1100 Dependency of the rate of degradation of the excess sludge on the pH value with different nitrogen loads

11 dependence of the rate of degradation of the excess sludge on the mechanical dispersion with different nitrogen loads

Fig. 12 Dependence of the rate of degradation of the excess sludge on the amount of ozone with different nitrogen loads

Fig. 13 dependence of the rate of degradation of the excess sludge on pH and dispersion

Fig. 14 Dependence of the degradation rate of the excess sludge on pH and amount of ozone FFiigg .. 1155 Dependence of the degradation rate of the excess sludge on dispersion and amount of ozone

Fig. 1 shows the schematic structure of the wastewater treatment plant in Wuppertal 10, in which the inventive method is used. The wastewater 1 1 from the Bayer plant in Wuppertal is fed to a first biological clarification stage 12, in which nitrification of the nitrogen compounds such as ammonium, urea or organic nitrogen compounds takes place. The wastewater then reaches the second biological clarification stage, the denitrification stage 14, via an intermediate clarifier 13. The clear phase 16 and the sludge 21 are separated in a post-clarifier 15 downstream of the denitrification stage 14. The clear phase 16 is discharged as purified wastewater. About 90% of the sludge 21 from the clarifier 15 is discharged into the denitrification tion level 14 returned. About 10% of the sludge 21 is subjected to a further treatment as excess sludge 17. In treatment stage 18 there is a pH adjustment and / or mechanical disintegration and / or ozone addition. The treated excess sludge 22 is fed to a second clarifier 19, in which the clear phase 23 containing the organic components of the treated excess sludge 22 and the inorganic components 24 of the treated excess sludge 22 are separated. The inorganic portions 24 of the treated excess sludge 22 are removed for further disposal. The clear phase 23 is returned to the denitrification stage 14 via the intermediate clarifier 13. The measurement 25 of the actual value for the DOC takes place in the clear phase 23. The measurement 25 of the actual value for the DOC is carried out online using a continuous process analyzer. The target DOC is determined via the nitrogen load in the wastewater. The nitrogen load in the wastewater is measured online using a continuous process analyzer.

The assignment of the measured nitrogen load to the target DOC is done empirically and according to the stoichiometric conditions. If the measured actual value deviates from the target value for the DOC, a changed set of driving parameters (pH, mD, ozone) is determined. The driving parameters are pH (pH), mechanical disintegration yes / no (mD) and added ozone (ozone [g / kg dry matter]).

In a series of tests on a semi-industrial scale, the DOC value or the rate of decomposition of the excess sludge was measured for different nitrogen loads for different combinations of driving parameters (pH, mD, ozone). The influence of the driving parameters on the DOC value and the degradation rate for excess sludge was analyzed for different nitrogen loads via linear or multiple regression of the measured values depending on individual driving parameters or combinations of driving parameters. The experiments have shown that the pH value has the greatest influence on the DOC value and the rate of degradation of the excess sludge, followed by dispersion and the amount of ozone (Fig. 2, Fig. 3a, -3b).

The tested areas for the driving parameters are standardized in the figures. The pH value of -1 corresponds to 7.6 and +1 corresponds to 12.7. A dispersion of -1 means that mechanical disintegration was not used and a dispersion of +1 means that mechanical disintegration was used. An ozone amount of -1 corresponds to an ozone amount of 16 g / kg dry matter and an ozone amount of -1 corresponds to an ozone amount of 84 g / kg dry matter. In addition, the nitrogen load was varied in the range of 6 kg / h (= -1) and 12 gh (= +1). The breakdown rate for the excess sludge is given as a percentage of the dry matter and the DOC value in the clear phase in milligrams per liter.

4 to 6 show the dependence of the DOC in the clear phase on the pH value, the mechanical dispersion and the amount of ozone with different nitrogen loads.

7 to 9 show the dependence of the DOC in the clear phase on two of the three driving parameters (pH, mD, ozone).

10 to 12 show the dependence of the rate of degradation of the excess sludge on the pH value, the mechanical dispersion and the amount of ozone with different nitrogen loads.

13 to 15 show the dependence of the rate of degradation of the excess sludge on two of the three driving parameters (pH, mD, ozone).

For the changed set of driving parameters, the basic rule is that the pH value is varied first, since it has the greatest influence on the DOC value and a small amount of energy is required to change the setting. The fine adjustment is then made by switching the mechanical disintegration on or off and varying the amount of ozone added, which is kept as low as possible.

The set of driving parameters assigned to each target value for the DOC is reproducibly determined on a technical scale by series of tests, taking into account the above-mentioned criteria and stored in a database.

In the plant according to the invention, the denitrification performance can be maximized and the excess sludge can be reduced by up to 90%.

Claims

claims

1. A process for the continuous control of the denitrification in the wastewater treatment in a sewage treatment plant with at least one denitrification stage with fluctuating nitrogen loads, comprising the steps a) provision of excess sludge, b) treatment of the excess sludge according to previously determined driving parameters, c) separation of the treated excess sludge into an organic one Part and an inorganic part, d) measurement of actual values for dissolved organic carbon (DOC) in the organic part, e) return of the organic part to one of the denitrification levels, f) comparison of actual values with the specified target - Values for DOC shares and in the event of a difference between the actual and target values, determination of changed driving parameters for the treatment of the excess sludge in step b. g) repetition of steps a. to f.

2. The method according to claim 1, characterized in that the treatment consists in adjusting the pH of the excess sludge, preferably to a driving parameter range between 7 and 13.

3. The method according to claim 1, characterized in that the treatment consists in adding ozone in a driving parameter range of 1 to 100 g ozone / kg dry matter.

4. The method according to claim 1, characterized in that the treatment consists in a mechanical dispersion of the excess sludge.

5. The method according to claim 1, characterized in that the treatment consists in a combination of pH adjustment, preferably to a driving parameter range between 7 and 13, a mechanical dispersion and a subsequent addition of ozone in a driving parameter range There is 1 to 100 g of ozone / kg of dry matter.

6. The method according to claim 3 or 5, characterized in that the ozone is introduced into the excess sludge by injectors and the ozone is added at excess pressure.

7. The method according to any one of claims 1 to 6, characterized in that the excess sludge to be treated comes from one of the denitrification stages.

8. Device for the continuous control of the denitrification in the wastewater treatment in a sewage treatment plant with at least one denitrification stage in the case of fluctuating nitrogen loads containing at least one denitrification stage, means for providing excess sludge, a treatment stage for the treatment of the excess sludge according to previously determined driving parameters, - means for Separation of the treated excess sludge into an organic portion and an inorganic portion, means for recycling the organic portion of the treated excess sludge into one of the denitrification stages, means for measuring dissolved organic carbon (DOC) in the organic portion of the treated excess sludge, means for comparison of measured actual values for DOC with specified target values for DOC, means for determining changed driving parameters for the treatment of excess sludge when a difference is found between actual values and target values for DOC.

9. The device according to claim 1, characterized in that the treatment stage for the treatment of the excess sludge according to previously determined driving parameters contains a means for adjusting the pH of the excess sludge, preferably to a driving parameter range between 7 and 13.

10. The device according to claim 1, characterized in that the treatment stage for the treatment of the excess sludge according to previously determined driving parameters contains a means for adding ozone in a driving parameter range of 1 to 100 g ozone / kg dry matter.

1 1. Device according to claim 1, characterized in that the treatment stage for the treatment of the excess sludge according to previously determined driving parameters contains a means for mechanical dispersion of the excess sludge.

2. Device according to claim 10, characterized in that the means for adding ozone has injectors and the addition of ozone takes place at excess pressure.