WO2011098166A1

WO2011098166A1 - Wastewater purifying system

Info

Publication number: WO2011098166A1
Application number: PCT/EP2010/068914
Authority: WO
Inventors: Michael Weiss; Christian Naydowski; Georgios Troubonis; Thilo Ittner; Armin Bauer; Martin Staiger; Thomas Wurster; Eckhard Gutsmuths; Werner Gessler
Original assignee: Voith Patent Gmbh
Priority date: 2010-02-11
Filing date: 2010-12-06
Publication date: 2011-08-18
Also published as: DE102010001796A1

Abstract

The invention relates to a wastewater purifying system for purifying wastewater (1) of a machine for producing and/or finishing a paper, cardboard, tissue, or other fibrous material web, comprising at least one biological purification stage (3, 4). The aim of the invention is to achieve the removal of colloidally dissolved impurities in an efficient manner by feeding at least some of the wastewater (1) into an electrophysical purification stage (2) for coagulation and flocculation after a biological purification stage (4), and subsequently into a separation stage (5) with floc enlargement and floc separation.

Description

Voith Patent GmbH File: 14703 WO / PN 89522 Heidenheim 'Active Trash Catcher' '

wastewater treatment plant

The invention relates to a wastewater treatment plant for the purification of waste water of a machine for producing and / or finishing a paper, board, tissue or another fibrous web with at least one biological cleaning stage.

The increasing use of rejects and waste paper in papermaking and the increased reduction in the use of fresh water have led to an increase in harmful or disturbing substances in the water cycles. Also, chemical additives (e.g., oils, solvents, rosin size, sizing agents, adhesives, wet strength agents, retention aids, starch, biocide formulations,

Dispersants, bleaching chemicals, cleaning agents, dyes, complexing agents and solubilizers), which are specifically fed to the process, carry through

Enrichment in the circuits to an increase in the concentration of colloidally dissolved impurities directly or from the interaction with each other at. Other sources include extracts from the pulps, lignin and lignin derivatives,

Hemicelluloses and carbohydrates.

The increasing concentration of contaminants results in reduced efficiency of mostly cationic functional chemicals (e.g., fixatives, retention polymers). The saturation of the process water with colloidally dissolved, anionic impurities, which occurs at high process temperatures, increases in the cooler zones

Precipitates and deposits. Even low temperature gradients are sufficient to sticky deposits on hydrophobic or particularly adhesive surfaces

(Screen material, felt material, roll surfaces, low-flow zones) to arise. These can affect the process sensitively by forming holes in the paper, breaks and cleaning stops.

The high loads can also lead to increased microbiological activity in laid paper, as it contains easily metabolizable substances.

Paper properties such as whiteness, opacity, color and firmness are due to the

Presence of colloidal impurities also affected.

In addition, an increased tendency to odor in the paper may occur. In addition, the dewatering and drying process in papermaking can lead to a significant deterioration in runability due to the fate of these contaminants in the finest capillaries

reduce the speed.

The contaminants can further lead to increased foam by lowering the surface tension, which in turn leads to paper defects and tears or makes the increased use of antifoaming agents required.

The accumulation of contaminants in the entire water cycle system depends on the amount of raw materials supplied, the process temperature, the

Extractability, the water circulation rate, the amount discharged with the wastewater, the discharge of impurities with the paper produced and the supply of fresh water. In particular, for the narrowing of the water cycles, i. the reduced supply of fresh water and the correspondingly reduced removal of wastewater sets up an increased concentration of colloidally dissolved impurities in the circulating waters. In addition to the high concentration level, dynamic fluctuations of the contaminant loads also represent a limitation for a targeted chemical-technological management of the process. This leads to continuous incorrect dosing of functional chemicals with the effects described above.

The object of the invention is therefore to enable the removal of colloidally dissolved impurities in an efficient manner.

According to the invention the object has been achieved in that at least a portion of the wastewater after a biological purification stage in an electrophysical cleaning stage for coagulation and flocculation and then in a

Deposition stage with flake enlargement and flocculation is performed.

In the interest of a comprehensive cleaning should the

Wastewater treatment plant have several biological purification stages, from which is preferably carried out at least one anaerobic and at least one aerobic.

In anaerobic purification stages, harmful or disruptive organic carbon compounds are removed by microorganisms without oxygen.

In aerobic, biological treatment stages, microorganisms degrade the organic substances in the wastewater and partially oxidize the inorganic substances, whereby air (oxygen) is pumped into the wastewater.

For this purpose, various methods, such as the activated sludge method, the

Trickling filter method, the Tauchkörperverfahren, the fixed bed reactor method u.a. developed.

In this case remains after this biological, aerobic purification stage, a biologically inert COD (chemical oxygen demand), which can be advantageously reduced by the fact that between the biological and / or between the biological and the electrophysical cleaning stage, a cleaning stage with wet oxygenation is present. Wet oxidation is understood to mean the chemical oxidation of organic compounds in a liquid phase.

In this case, the wet oxidation by the introduction of ozone or oxygen (at high pressure and high temperature) can be brought about. However, it is considerably more efficient and less costly if the wet-oxidation purification stage is designed electrochemically and / or UV-supported.

In electrochemical wet oxidation, radicals or strong

Oxidizing agents (ozone, OH, O +) by decomposing water

produced electrolytic ways.

By applying a DC voltage, the water is decomposed, producing at the anode OH radicals and above a certain current ozone and at the cathode hydrogen. For this purpose, inert electrodes, preferably so-called diamond electrodes should be used.

In UV-based wet oxidation, the radicals or oxidants are generated by the irradiation of the waste water with UV radiation.

To intensify the COD reduction, it may be advantageous to use the electrochemical and the UV-supported wet oxidation in combination.

As a result, in particular, colloidally dissolved impurities in the wastewater are oxidized by this wet oxydation and their long-chain molecules are broken up. The broken-up molecules can then be broken down in the subsequent purification stage.

In the purification step with electrophysical precipitation for coagulation and flocculation of colloidally dissolved impurities, the water to be treated is passed through a reactor equipped with sacrificial electrodes in which various electrochemical reactions take place by applying an electric current. This produces metal hydroxide flakes and various highly reactive radicals. The metal hydroxide flakes have a high adsorption capacity and can thus bind finely divided particles to themselves. It also leads to Mitfällungs- and

Inclusion precipitation reactions in which the colloidally dissolved substances are precipitated. In addition to the precipitation reactions, there are also oxidative effects, mainly by highly reactive oxygen radicals, which leads to further degradation of organic compounds.

In this case, the electrophysical cleaning stage should advantageously with after the last biological purification stage, preferably after the purification stage with

Wet oxidation can be arranged. In the subsequent to the electrophysical purification stage

Abscheidungsstufe it comes to flake enlargement and flocculation, in particular by means of flotation, sedimentation, filtration or the like. Accordingly Here, the particle agglomerates, which were generated by means of the electro-physical precipitation / flocculation in the previous step, here separated from the purified filtrate. In particular, the electrophysical cleaning stage allows in the invention, a demand-oriented, targeted transfer and the discharge of the most

anionic contaminant as a solid.

As a result, the treated wastewater may be used as a partial or complete fresh water replacement in the manufacturing process, i. be returned to the production machine of the fibrous web.

With regard to the control of the wastewater treatment plant, it is advantageous if the pollution level of the wastewater is measured and the intensity of the wastewater treatment plant

electrophysical cleaning is at least partially controlled in a load level temporally uniform way.

On the one hand, this involves reducing the overall load level of the waters with colloidally dissolved impurities, so that certain water qualities are achieved, which reduce the use of fresh water.

Another often much more important object of the invention is the timely

Elimination or reduction of peak loads with the aim of setting a constant level of disturbance.

The measurement of the load level of the effluent, i. The concentration of impurities should be determined by measuring the chemical oxygen demand (COD), the dissolved carbon (DOC), the turbidity, the anionic charge character (SCD), the evaporation residue, the titrated cationic demand or similar. respectively.

In this case, the intensity of the electrophysical cleaning via the electrical power consumption, i. over the height of the voltage applied to the electrodes

Voltage and / or the amperage can be controlled. The invention should advantageously be used in particular in partially or completely closed processes with high levels of contaminant load and / or large fluctuations and / or small amounts of sewage or fresh water, since in these cases the effects of the concentration of colloidally dissolved impurities on the process stability are particularly disturbing are.

The invention will be explained in more detail with reference to an exemplary embodiment. In the attached drawing shows:

Figure 1: an investment scheme of a wastewater treatment plant and

Figure 2: a schematic cross section through an electrophysical

Cleaning stage.

In the wastewater treatment plant according to Figure 1, the wastewater 1 a

Paper mill for COD reduction led by an anaerobic 3 and a subsequent aerobic 4 purification stage.

To clean the wastewater 1 by settling is before the biological treatment stages 3.4, a pre-clarifier 7 and after this a post-clarifier 8. Possibly in conjunction with mechanical purification stages so the waste water 1 can be sufficiently freed from suspended solids.

In the subsequent purification stages 6.2, the inert, i. for the

biological treatment methods inaccessible residual COD can be reduced.

In the interest of maximum reduction of the COD, the wastewater 1 from the post-clarification tank 8 can be conducted to a purification stage 6 with wet oxidation for this purpose. Easily oxidizable substances are to be converted into anionically charged impurities, which are more accessible to the precipitation and flocculation treatment in an electrophysical purification stage 2.

With the help of inert electrodes and an applied electrical potential difference, ozone and highly reactive OH radicals are generated in the purification stage 6 with wet oxydation, which radicals act as oxidizing agents. In the course of this

Process are colloidally dissolved impurities oxidized in the water. Contaminants consisting of long-chain molecules are broken up in this oxidation process and thus made accessible to the downstream electro-physical precipitation / flocculation 2. After the optional wet oxidation 6, the wastewater 1 passes through a

Purification level 2 for coagulation and flocculation.

In this case, the colloidally dissolved impurities (anionically charged interfering substances, such as hemicelluloses, resins, polysaccharides, etc., which occur in particular in waste water from papermaking) are to be converted into larger agglomerates.

For this purpose, the waste water 1 is guided in a container 13 shown in Figure 2, which has a sacrificial anode 1 1, for example made of aluminum and a particular inert cathode 12, which are connected via a control unit 9 with a DC voltage source 14. However, the cathode 12 may also be made of sacrificial anode material, which provides the opportunity for pole reversal.

As already described, the electrical current flow leads to a

Electrophysical precipitation for the purpose of coagulation and flocculation of colloidally dissolved impurities. Depending on the measured COD value of the wastewater 1, the current intensity can be changed via the control unit 9 so that it is not just one

Reduction, but temporally also comes to a homogenization of the residual CODs. In the subsequent to the electrophysical cleaning stage 2

Separation stage 5 it comes to flake enlargement and flocculation, in particular by means of flotation, sedimentation, filtration or the like.

In this case, the particle agglomerates 10, which were produced with the aid of the electro-physical purification stage 2, separated from the effluent 1 and discharged.

The combination of biological 3,4 and electrophysical 2

Purification stage allows the partial or complete return of the cleaned effluent 1 after the deposition stage 5 to the paper machine, without affecting the paper machine operation, the effectiveness of the process chemicals, etc. by the concentration of colloidally dissolved, anionic or non-ionic impurities.

Thus, the proportion of continuously added fresh water as well as the discharged amount of wastewater 1 can be reduced.

Claims

Claims 1. Wastewater treatment plant for the purification of waste water (1) of a machine for producing and / or finishing a paper, board, tissue or another fibrous web with at least one biological purification stage (3, 4), characterized in that at least a part of the waste water ( 1) after a biological treatment stage (4) into an electrophysical cleaning stage (2) for coagulation and flocculation and then into a separation stage (5) with flake enlargement and flake separation.

2. Wastewater treatment plant according to claim 1, characterized in that it comprises a plurality of biological purification stages (3,4), of which preferably at least one anaerobic (3) and at least one aerobic (4) is executed.

3. Wastewater treatment plant according to one of the preceding claims, characterized in that between the biological (3,4) and / or between the biological (4) and the electrophysical (2) purification stage a

Cleaning stage (6) with wet oxygenation is present.

4. wastewater treatment plant according to claim 2 or 3, characterized in that the electrophysical cleaning stage (2) after the last biological treatment stage (4), preferably after the cleaning stage (6) with Nassoxydation follows.

5. Wastewater treatment plant according to one of the preceding claims, characterized in that the purified wastewater (1) is returned to the machine.

6. A method for controlling the wastewater treatment plant according to one of

preceding claims, characterized in that the Level of pollution of the waste water (1) is measured and the intensity of the electro-physical cleaning is controlled at least partially in a time level equalizing the load level.

7. A method for controlling the wastewater treatment plant according to claim 6,

characterized in that the load level of the waste water (1) is determined by measuring the chemical oxygen demand (COD), the dissolved carbon (DOC), the turbidity, the anionic charge character (SCD), the

Evaporation residue, the titrated cationic demand or similar is determined.

8. A method for controlling the wastewater treatment plant according to claim 6 or 8, characterized in that the intensity of the electro-physical cleaning is controlled by the electrical power consumption.