EP2699518A1

EP2699518A1 - Method and device for cleaning wastewater

Info

Publication number: EP2699518A1
Application number: EP12716344.2A
Authority: EP
Inventors: Karl Bleicher
Original assignee: AKW A+V Protec Industry GmbH
Current assignee: AKW A+V Protec Industry GmbH
Priority date: 2011-04-19
Filing date: 2012-04-16
Publication date: 2014-02-26
Also published as: TW201302629A; US20140054235A1; DE102011018190A1; WO2012143326A1; CA2833644A1; DE102011018190B4

Abstract

The invention relates to a method and to a device for cleaning wastewater, in particular organically polluted wastewater, by means of adding a nitrate source, the method comprising the following steps: filling the wastewater in a container until a first fill level (Niv A) of the reactor is reached, wherein the fill level (Niv A) is 80-99%, preferably 95%, mixing the waste water, measuring the pH value of the wastewater, wherein lye is added to the wastewater if the wastewater has a pH value of < 7.0 until a pH value of 7.5 is reached, adding nitrate to the wastewater, stirring the wastewater-nitrate mixture, controlling the addition of further nitrate and/or further lye by measuring at least one parameter of the wastewater-nitrate mixture, ending the stirring motion, and decanting with clarified water discharge at a second fill level (Niv B), wherein the fill level (Niv B) is 50-70%, preferably 60%.

Description

Process and apparatus for the purification of waste water

description

The invention relates to a process for the purification of wastewaters, in particular organically polluted wastewaters, with the addition of a nitrate source according to feature combination of claim 1 and an apparatus for carrying out a process for the purification of wastewater, according to feature combination of claim 13.

In conventional wastewater technology, oxygen is used as a terminal electron acceptor for the oxidation of organic material in the wastewater. To purify the waste water, the oxygen is brought into solution, finely distributed and dosed as required.

It is known to use enriched gas or pure oxygen for the purification of effluents. The aim of such efforts is to increase the dissolved content of oxygen and thus the availability of the terminal electron acceptor.

A major disadvantage of this technique is the limited amount of oxygen in the air and the limited solubility of oxygen in water (about 8 mg / l at 20 ° C). Furthermore, parameters such as salinity, pressure and especially temperature significantly affect the availability of oxygen in solution for wastewater treatment.

From the foregoing, it is therefore an object of the present invention to provide a further developed process for the purification of waste water, which dispenses with the use of oxygen or pure oxygen. In addition, a device is to be specified with which such a method can be performed.

The object of the invention is achieved by a method for the purification of waste water, especially of organically polluted wastewater, according to the teaching of claim 1, and by a device for Performing a method for the purification of waste water with the addition of nitrate, according to the teaching of claim 13, wherein the dependent claims represent at least expedient refinements and developments.

The inventive method for the purification of waste water is particularly suitable for the purification of organically polluted wastewater and is based on the addition of a nitrate source to be cleaned wastewater. Concerning. The cleaning procedure is basically carried out in the following steps:

First, each cleaning cycle begins with filling a container with waste water. A cleaning cycle may already have taken place in the container beforehand so that there is a residue of wastewater or sediment and active biomass in the container. The container is filled until reaching a first filling level. The filling level is 80-99%, preferably 95%.

First, the wastewater in the container is mixed. That is, the sediment contained in the container or the sludge is mixed with the freshly added wastewater. The mixing is preferably carried out by a stirrer. The mixing process should be carried out for at least five minutes, so that a sufficient mixing of the sludge with the wastewater can be guaranteed.

Subsequently, the pH of the wastewater is measured. If the pH is less than 7.0, lye is added to the waste water until a pH of 7.5 is reached. Preferably, lime milk is added.

This is followed by the addition or metered addition of nitrate in the wastewater. The nitrate can be used, for example, in the form of nitric acid, preferably 25-50% nitric acid or dissolved nitrate salt z. As Ca, Na nitrate can be added. Preferably, the nitric acid after addition to the wastewater to a molar concentration (c) of 100 mg / l or a pH of 6.5. Subsequently, the wastewater-nitrate mixture is stirred. The stirring process can take place at intervals, so that the agitator, for example, for 30

Seconds, followed by a pause of 150 seconds. This sequence of operation and break may be repeated for several hours. Stirring avoids the formation of floating layers and prevents over-saturation of gases.

The cleaning method according to the invention further provides for a control of the addition of further nitrate source and / or further liquor, wherein the control takes place depending on the measurement of at least one parameter of the wastewater-nitrate mixture.

Preferably at relatively low polluted wastewater, the measurement of the pH value of the wastewater-nitrate mixture. If the pH is greater than 7.0, additional nitrate is added to the wastewater-nitrate mixture. It should be noted that this may also be a nitric acid solution. An addition of nitrate or nitric acid solution is omitted from the time when the wastewater-nitrate mixture has a pH of 7.0 or less.

If contamination and active biomass are present in the wastewater-nitrate mixture, alkalization to the original pH takes place within a short time. In principle, the wastewater-nitrate mixture is added as long as nitrate, until the alkalization is absent. The absence indicates the completion of the biological treatment of the wastewater.

Furthermore, it is conceivable that the addition of further nitrate and / or further liquor takes place on the basis of the measurement of the nitrate concentration of the wastewater-nitrate mixture. Based on the load of the waste water, it is provided, the cleaning device in a certain nitrate area such. B. operated at 50 - 200 mg / l. The nitrate concentration is determined here by means of a probe and continuously monitored over the duration of the cleaning process in order to determine fluctuations and changes in the concentration. to be able to make. The control of the addition of additional nitrate is then concentration-dependent. About the consumption of nitrates, the degree of pollution or organic pollution can be determined.

With a high concentration of organic components of the wastewater, the process of acidification can begin. This means that existing in wastewater polymers are converted into organic acids. In such a case, it is not possible to use only the pH to control the purification or to control the addition of further nitrate and / or further liquor. It must be the measurement of the redox potential of the wastewater-nitrate mixture to make the control of the cleaning associated with the addition of additional nitrate and / or further liquor.

As soon as acidification of the wastewater-nitrate mixture is detected, ie if there is a negative redox potential with a decreasing tendency, additional lye must be added, the addition having to take place until the original pH, ie 7.5, is reached.

An oxidation-reduction potential of <0 mV points to incipient anaerobic processes and acidification. Also dpH / dt <0 - ie a decreasing pH value - indicates that acidification takes place. Preferably, both the pH and the redox potential are monitored.

Once the pH returns to its original value, a metered addition of nitrate can again take place, which activates the nitrate respiration, in which preferably the organic acids are consumed and consequently the acidification is counteracted.

In highly polluted organic wastewater is preferably aeration of the wastewater-nitrate mixture with stripluft at intervals, with the ventilation within five to ten minutes for a few seconds, for example, about five seconds. The stripping of gases is for the purpose of preventing carbonation. In cases of highly polluted waste water, It can happen that soluble gases, in particular C0 ₂ accumulate as degradation end product in the reaction suspension or N ₂ and the pH is very strongly buffered by carbonate. At intervals, gases are expelled by the air jets emanating from a stripper.

As already described, the absence of alkalization of the wastewater-nitrate mixture is an indication of the end of the biological purification of the waste water, so that at this time the stirring is stopped. If dpH / dt = 0, the pH no longer changes and the redox potential> 0 mV, the stirring process, which can take up to six hours stopped.

To avoid the already described carbonation, the purification process is preferably operated in the pH range from 6.5 to 7.0.

Subsequently, the settling of the active sludge is initiated. After about 30 minutes, the part of the mechanical wastewater treatment is completed. This is followed by decanting with the withdrawal of the clear water through an opening at a second filling level of the container. This second filling level is 50-70%, preferably 60%. It can be seen that in the container mentioned by means of level switch, two working or filling levels are to be defined, which are preferably 95% and 60%.

The decantation may take about 14 minutes, after the withdrawal of the clear water, a new cleaning cycle can be carried out with the method steps according to the invention. After every fifth to tenth cleaning cycle, the excess sludge must be removed.

The present method is particularly suitable for the purification of waste waters with easily degradable substances, since the oxidation force of the terminal electron acceptor is reduced compared to conventional oxygen. Nitrate respiration can be assigned a standard Nernst + 400 mV potential, whereas respiration with oxygen is a standard Nernst potential of + 800 mV is assigned. However, the oxidation power of the reaction is limited enough for a variety of organic substances having similar properties such as alcohols, aldehydes, organic acids and already activated hydrocarbons without substitution by heteroatoms such as nitrogen, sulfur and halogens.

Preferred fields of application therefore form effluents whose chemical oxygen demand (COD) corresponds approximately to the biological oxygen demand (BOD). This applies, for example, to waste and starch-containing wastewater, acids and alcohols.

The process of the invention can be used in a very wide range of applications. The COD of the wastewater can be from 200 mg / l to 20,000 mg / l.

Wastewater from the solar industry, which are contaminated with PEG as polymer, can also be purified by the method according to the invention. Hot waste water can be cleaned very well with the help of the method, since the activity of the microorganisms rises with the temperature.

Sewage temperatures of up to 45 ° C do not represent disabilities, as is the case with conventional cleaning processes. It eliminates the standardized cooling of wastewater. In the case of purification with oxygen, the negative solubility dependence forms a significant limiting factor with increasing temperature.

The denitrification resp. Nitrate respiration can be simplified:

3 HN0 ₃ + 15 [H] <-> 1.5 N ₂ + 9 H ₂ 0

2 HNO ₃ + CH ₃ OH <-> N ₂ + C0 ₂ + 3 H ₂ 0 The following characteristic values speak for the application of the method according to the invention:

Possible room loads: up to 2 - 4 kg / m ³ * day COD

degradation performance

Consumption of nitric acid: approx. 0.8 - 1.2 kg / kg COD degraded

Sludge accumulation: approx. 0.25 kg / kg COD degraded

The present invention additionally comprises a device which is designed to carry out the method according to the invention.

The device comprises a container with a settling trough in the bottom of the container as well as an agitator and a pH meter and a dossier device for adding a nitrate source. The sizing of

Container is to be made according to the expected amount of waste water and composition. In this case, exceeding a volume load of 4 kg COD / m ³ * day is to be avoided. The container may have any geometry. In order to make the mixing and stirring by means of an agitator simple, a container with a cylindrical geometry is preferably provided.

The device preferably has a nitrate concentration measuring device and / or a redox potential measuring device.

A ventilation or stripping device may also be provided. Especially with organically polluted wastewater such a ventilation device is beneficial.

The container of the device has two working or filling levels, which are preferably 95% and 60%. Level switches should be used to define the above-mentioned levels, with an outlet for clear water withdrawal at the filling level of 60%. Other fittings such as one or more membrane aerators in the form of plates or hoses, Abwasserzu- and drain and a sludge removal device are also provided. Depending on the wastewater composition, a device for the addition of liquid may be necessary.

Likewise, the device for the purification of wastewater on a temperature detection device, as soon as extreme temperature fluctuations in

Wastewater is expected. At high wastewater loads, measurable heat can be generated during the dismantling, which must also be taken into account in the control system. In this case, a temperature fluctuation in the sewage inflow of +/- 5 ° C is allowed around the previously defined operating point. The operating point can be at long time intervals z. B. 5 ° C per week vary in a range between 15 ° C and 45 ° C, but longer time periods for the adjustment of the biomass are needed.

The inventive method for the purification of waste water with the addition of nitrate and the inventive device for carrying out a process for the purification of waste water with the addition of nitrate will be explained below with reference to embodiments and with the aid of a figure.

Application Example 1

In the following illustrated example for the application of the method according to the invention, wastewater from the solar industry is purified. When cutting silicon ingots, wastewater contaminated with polyethylene glycol (PEG) accumulates.

Wastewater quantity: 150 m ³ / day

COD (Chemical Oxygen Demand) 2,500 mg / liter

Organic Ingredients: PEG 200 The requirements for purified wastewater are as follows:

COD: <500 mg / liter

Suspended matter: <400 mg / liter

For the application of the method according to the invention, the following characteristic values are decisive or typical:

COD reduction per day: 315 kg

Reactor volume: 150 m ³ (distributed over 3 stirred tank with 50 m ³ volume)

Operating temperature: 28 - 32 ° C

Room load: 2.5 kg COD / m ³ * day

Consumption of nitrous oxide 504 kg (50% solution)

3.4 cycles a day with 20 hours

reaction time

Application Example 2

The following example shows that the method according to the invention is also suitable for the purification of waste water in the food industry. In a cereal wash fall to waste water with moderate organic stress, which does not allow a direct discharge into a receiving water.

Wastewater volume:

CSB in the inflow:

Organic ingredients

The requirements for the purified water are as follows:

COD: <100 mg / liter For the application of the method according to the invention, the following characteristic values are decisive or typical:

COD removal per day: 15 kg

Reactor volume: 50 m ³

Operating temperature: 15 - 20 ° C

Room load: 0.5 kg COD / m ³ * day

Consumption of Salpetersä 57.6 kg (25% solution)

5 cycles a day with 15 hours

reaction time

In the figure, an apparatus for carrying out the method according to the invention for the purification of waste water is shown.

First, in the container 1 of the device via a feed 2 wastewater, which is preferably organically polluted wastewater, given. The container 1 is filled up to a first filling level (level A). It may well be the case that residual sludge from a previous cleaning cycle is still present in the container. The first fill level (Niv A) is preferably 95%. That is, the container 1 is 95% full.

This is followed by mixing the wastewater. The mixing is carried out with a stirrer 3, so that the remaining components of a previous cleaning cycle and the fresh wastewater are mixed. The mixing process takes about five minutes, after which a measurement of the pH value is made. For this purpose, the device has measuring devices 4, which in this case is a pH sensor.

If a pH of less than 7.0 is determined, lye is preferably added to the wastewater in the form of lime milk. This addition takes place via a liquid metering device 6 until a pH of 7.5 is reached. In order to start the biological cleaning process, nitrate is added to the waste water in the container 1 via a nitrate dosing device 5. The nitrate causes nitrate respiration in the container 1, so that the organic components of the wastewater are bound and filtered out. Preferably, nitrate is added in the form of nitric acid having a molar concentration c = 100 mg / l or a pH of 6.5.

The nitrate and waste water are mixed by means of a stirring process at intervals to a wastewater-nitrate mixture. The device according to the invention preferably has an aeration device 7. The ventilation with stripluft also takes place at intervals. Ventilation is especially beneficial for highly polluted wastewater. The ventilation takes place for example in five minutes cleaning phase for about five seconds. Due to the ventilation z. B. C0 ₂ or N ₂ expelled through the vent 8.

By means of existing measuring devices, in turn, a measurement of the pH of the wastewater-nitrate mixture is carried out, wherein at a pH greater than 7.0 nitric acid is added.

Furthermore, a measurement of the redox potential of the wastewater-nitrate mixture is provided, wherein in an arrangement of measuring devices 4 in this case a redox potential measuring device is provided. With a decreasing pH value and a redox potential of less than 0 mV, an incipient anaerobic process and acidification are detected. This is prevented by adding more milk of lime to the wastewater-nitrate mixture via the liquid-feeding device 6 until a pH of 7.5 is reached.

Once this initial pH is reached, the biological purification can be resumed by adding nitrate in the form of nitric acid solution via the nitrate dosing device 5. In this case, the same parameters as for the initial nitrate addition are selected with regard to the molar concentration and the pH. This example shows that with the method according to the invention at low-loaded wastewater Already by a single nitrate dosage of 100 mg / l, the cleaning goal can be achieved.

As soon as the pH value no longer changes and the redox potential is greater than 0 mV, it can be assumed that the biological treatment of the wastewater has been completed. In this case, the agitator 3 is stopped and followed by a settling phase, which is part of the mechanical purification of the wastewater.

Within about 30 minutes sludge settles in a settling trough in the bottom of the container.

This is followed by the decanting process with the withdrawal of the clear water. For this purpose is at the level of a second filling level (Niv B), which is preferably 60%, a clear water outlet 9, through which the clarified by the settling clear water can be deducted. So there is an exchange ratio of about 30% of the reactor volume. In container 1, a mud bed 10 remains after a 14-minute clear-water removal phase.

The cleaning cycle is completed after the clear water discharge, so that a new cleaning cycle can be started by filling the container 1 with "fresh" wastewater After about every fifth to tenth cleaning cycle, the sludge excess has to be pumped out via a sludge discharge 11.

LIST OF REFERENCE NUMBERS

1 container

2 inlet

3 agitator

4 measuring devices

5 nitrate dosing device

6 Lye dosing device

7 ventilation device

8 ventilation

9 clear water outlet

10 mud bed

11 sludge discharge

Niv A first filling level

Niv B second filling level

Claims

claims

1. A process for the purification of waste water, in particular of organically contaminated wastewater, with the addition of a nitrate source,

characterized by the following steps:

a) filling the waste water into a container until reaching a first

Filling levels (Niv A) of the reactor, wherein the filling level (Niv A) is 80-99%, preferably 95%,

b) mixing the wastewater,

c) measuring the pH of the effluent, wherein at a pH of the effluent of <7.0 leach is added to the effluent until a pH of 7.5 is reached,

d) adding nitrate to the wastewater,

e) stirring the wastewater-nitrate mixture,

f) controlling the addition of further nitrate and / or further liquor by measuring at least one parameter of the wastewater-nitrate mixture, g) stopping the stirring,

h) Decanting with clear water removal at a second filling level (Niv B), wherein the filling level (Niv B) is 50-70%, preferably 60%

2. The method according to claim 1,

characterized in that

the nitrate is added in the form of nitric acid or dissolved nitrate salt.

3. The method according to claim 1 or 2,

characterized in that

the stirring of the wastewater-nitrate mixture is carried out at intervals.

4. The method according to claim 1, 2 or 3,

characterized in that

Lye in the form of lime milk is added.

5. The method according to any one of the preceding claims, characterized in that

the addition of further nitrate and / or further liquor based on the measurement of the pH of the wastewater-nitrate mixture is carried out.

6. The method according to claim 5,

characterized in that

at a pH> 7.0 of the wastewater-nitrate mixture further nitrate is added.

7. The method according to any one of the preceding claims,

characterized in that

the addition of further nitrate and / or further liquor on the basis of the measurement of the nitrate concentration of the wastewater-nitrate mixture is carried out.

8. The method according to any one of the preceding claims,

characterized in that

the addition of further nitrate and / or further liquor on the basis of the measurement of the redox potential of the wastewater-nitrate mixture takes place.

9. The method according to claim 8,

characterized in that

is fed with a negative and decreasing redox potential of the wastewater-nitrate mixture more liquor until a pH of 7.5 is reached.

10. The method according to any one of the preceding claims,

characterized in that

at a constant pH value and a redox potential> 0 mV, the stirring is stopped.

11. The method according to claim 10,

characterized in that

the pH is between 6.5 and 7.0.

12. Method according to one of the preceding claims,

characterized in that

the wastewater-nitrate mixture is aerated with stripluft air.

13. Apparatus for carrying out a method according to one of

Claims 1 to 12,

characterized in that

the device comprises a container (1) with a settling recess in the bottom of the container and an agitator (3) and further comprising a pH meter and a dossier for adding nitrate (5).

14. Device according to claim 13,

characterized in that

the device is a nitrate concentration meter and / or a

Redox potential measuring device (4) includes.

15. Device according to claim 13 or 14,

characterized in that

the device comprises a ventilation device (7).