DE19936194C1 - Process and device for wastewater treatment using modified membrane filtration - Google Patents

Abstract

The invention relates to a cleaning process for wastewater in which the methods of membrane filtration and electrolysis are combined and thus high cleaning effects are possible with largely backwash-free operation. After cleaning, the wastewater is available in high quality. B. find use as domestic water in the household. The construction of the plant is compact and can be used as a house installation as well as in the open air as well as a retrofit kit for existing sewage treatment plants. DOLLAR A The wastewater is conducted in a container with a cathodic membrane and anode, the wastewater passing through the former and repelling negatively ionized particles, which subsequently adhere to the anodes. By cyclically reversing the polarity of the anodes, the particles were repelled from there and settled on the inclined bottom of the container. The sediment is removed via a sludge discharge. During the polarity reversal of the anodes, the cathodic membrane is backwashed.

Description

The invention relates to a cleaning process for waste water, in which the methods of Membrane filtration and electrolysis can be combined and thus high cleaning effects are possible with largely backwash-free operation.

Systems based on the activation process are known which operate in a continuous manner or in a thawing principle. The disadvantage of the solutions, however, is the large amount of space, space and / or time required for the sedimentation processes. The phosphorus elimination is largely achieved through the activated sludge discharge. Plants based on the build-up principle with more than 7 kg TS / m ³ with largely activated sludge mineralization still have a relatively high P-load between 5-15 mg / l. Drainage values of large wastewater treatment plants with P elimination of <2 mg / l cannot be achieved without flocculation / precipitation.

Microfiltration systems as plate or tube filters achieve a very good BOD / COD elimination, but also high NO ₃ ^- - and PO ₄ ^- contents in sequence. Due to the direct application of the membranes with an activated sludge / water mixture, the membranes quickly clog, calcify or salinize, so that the membranes can only be cleaned with a high backwashing capacity, which is very energy-intensive and limits the performance of the system.

Electrolysis cells for wastewater treatment have the advantage of high COD degradation rates as well good nitrogen and phosphate elimination when using sacrificial anodes that Form salts. The disadvantage, however, is the high amount of sludge caused by the high iron content (Anode material) flocculates well, but also a separate design of the container soil, because this sludge almost does not slide on the container brackets. Certain Microorganisms continue to get into the process and the bacterial count is much higher than with microfiltration.

A few published patent applications will now be discussed.

DE 40 30 912 A1 relates to a method for the deposition of metal ions from process and Waste water, an electrically conductive cathodically polarized filter aid layer from the metal ion-containing water is flowed through. Inevitably, therefore, this filter layer must be in relative short intervals can be renewed by backwashing, classifying and precoat processes.  

According to DE 42 22 031 A1, a device for the separation of dissociated Fluid flows containing substances claimed. In principle, it is about the Desalination with the help of electrolysis, the special arrangement of Electrodes and the collection and cleaning of the resulting gas should be emphasized.

DE 196 20 961 A1 describes a device for water treatment with ions exchangers described, wherein a magnet can be arranged in the inlet of the device.

Furthermore, reference should be made to DE 40 03 193 A1. It is a Method and device for softening and desalting by electrolysis, the Electrodes can be cleaned by rinsing and also by reversing the polarity.

Ultimately, DE 195 17 652 A1 still has to be discussed. It is a process to reduce the nitrate and / or nitrite content in the water by electrolytic Treatment. It is shown that the water to be treated is also inside a cathode can be fed into and through this into an anode compartment.

It is the object of the invention to clean a wastewater in such a way that high cleaning performance for biological cargo and mineral compounds as well as low bacterial counts remaining microorganisms can be reached and the waste water after cleaning in high quality is available. At this level of quality, it should be as Domestic water can be used in the household. The treatment costs should not be significant higher than in larger municipal facilities. The systems should be compact and both as a house installation as well as in the open air and as a retrofit kit for existing sewage treatment plants Find use.  

According to the invention, the object is achieved in that a method and a preliminary clearing its implementation is proposed, including entirely new features, one high biodegradation and good COD, N and P elimination with low Germ count and low operating costs is achieved.

The activated sludge process is mostly used in the further wastewater treatment Nitrification / denitrification operated. The activated sludge decreases in the denitrification phase. It will suspended by agitators or low ventilation to active activated sludge to preserve surfaces. The settling behavior in the denitrification phase is very good (Settling speeds of 1 m / 30 min are the rule, analogous to the SBR process).

The denitrification phase is used for this, the circulation for a short time approx. 15-20 min switch off and deduct the resulting clear phase. Alternatively, for example can also be carried out via an inclined clarifier. The aim is that a high proportion of activated sludge in the Animated pool / deni pool remains. Then freight fluctuations due to the high TS content <5 kg / kgd can be safely caught. The biological cleaning does not led to their maximum performance but then canceled when the Oxygen conversion / consumption decreases. This enables energy-efficient work.

The clear phase with a small proportion of activated sludge reaches an inventive one Device consisting of a combination of an electrolytic cell and membrane filtration. there is an electrical for the formation of the membrane or as a support material for the membrane conductive material used, which is connected as a cathode. Particularly suitable precious metals, metal grids, metal gauzes or coated membranes based on Carbon fibers, stainless steel and carbon fiber structures with and without coating or others, Electron emitting materials are also suitable.

The procedure is dependent on the water quality and water hardness. The voltage applied to the electrodes should be selected so that there is a slight OH ^- ion overpressure on or in the cathode, which builds up a negative field in front of the membrane, converts metal ions into hydroxides as far as possible in front of the membrane and, if possible, no metal ions into the Penetrate membrane cell. There is a relationship between voltage / current flow, pore size and flow rate or vacuum in the membrane.

Sacrificial materials such as iron materials, aluminum etc. are used as the anode or a combination of these.

Graphite electrodes are also possible. A suitable arrangement of the cathode and anode forms a gap through which the waste water flows and the ionized waste water components form on the anode SO ₄ ^- , NO ₃ ^- , NO ₂ ^- , Cl ^- , PO ₄ , bacteria and viruses etc. get to the anode and carry out the electron exchange, outgas as gas or sink as sludge without binding forces from the anode.

The removal of Fe ⁺⁺⁺ from the anode accelerates the settling behavior. However, it is also possible to use graphite or stainless steel as the anode if no higher anodic effect is desired.

The invention will be explained in an expedient embodiment.

Show:

Fig. 1 - The device in the front view for further purification of the waste water after the biological treatment.

Fig. 2 - device of FIG. 1 in side view.

Fig. 3 - device according to FIG. 1 in plan view.

Waste water runs from a preceding clarification stage into tank 1 via a lockable inlet 3 that can be controlled. The inlet is arranged so that a high flow rate at the anodes 5 and the cathode or membrane ( 6 ) is created in the inlet. The container 1 is provided with a gastight cover 2 . A degassing line 4 is provided. The anodes 5 and the cathodic membrane 6 are arranged on a spacer frame 7 . The inclined floor 8 is inclined in two dimensions, so that the sludge discharge 10 is located at the lowest point.

The direct current required for the electrolysis is provided using the mains connection 13 , variable transformer 12 and rectifier 11 . The spacer frame 7 is designed so that the gap width between the anode 5 and cathodic membrane 6 can be changed so that it can be adapted to the electrolytic behavior of the waste water, as well as current, voltage and time. The regulation can take place via a known control unit.

For municipal wastewater, for example, a voltage of 2-4 volts, a pore size of 1-2 µm and an excess pressure of 20 cm water column is sufficient to achieve discharge values of <100 mg / l COD, <5 mg / l NH ₄ ^- N, < 2 mg / l P and bacterial counts <10.

By increasing the pore size to 1-2 µm in diameter, the passage area increases from 0.03-0.2 µm ² with known microfiltration to 0.78-1.5 µm ² .

The consequences are lower negative pressures on the membrane. A 20 cm water column is sufficient for free discharge, as well as lower counter-flushing pressures of 0.1-0.2 bar. Very high throughputs of 100 to 200 l / m ² can be achieved.

The device configured to carry out the method is shown below elements that are linked by their functionality:

The power supply for the electrolysis takes place via the electrode connections 14 to the anodes 5 and catholic membrane 6 with a clean membrane, ie the waste water to be cleaned passes unhindered through the pores of the cathodic membrane 6 . The clear water runs without pressure or with a low vacuum generated via the clear water outlet 9 . The water level is at a level as indicated by the position symbol 16 [min]. When the wastewater to be cleaned rises, for example, to the level as is illustrated by the position symbol 15 [max] (because the passage area of the cathodic membrane 6 is somewhat reduced), the cathodic membrane 6 is backwashed using a backwash pump, not shown, via the Drain 9 and blocking the inlet 3 . Dilute acid can be added to the backwashing water so that blocking of the cathodic membrane 6 with hydroxides is avoided. An opposite-pole switchover of the power supply and the particles at the anodes 5 and the cathodic membrane 6 are promptly switched off, the waste water rinsing stream swirling the particles. The power supply via the electrode connections 14 is switched off. The sludge settles on the inclined floor 8 and, as already described, is removed via the sludge discharge 10 .

The area throughput is around 175-200 l / m ² h in unpressurized operation (free spout, 20 cm water level difference).

For example, an area of 0.6 m ^{2 is} sufficient for an 8-person household with 1200 l / d with a nitrification / denitrification time of 16 h / 8 h and taking into account the impact load Q _d10 × 120 l / h.

Mainly hydrogen and ammonium ions reach the cathode, those on the cathode outgas.

The particular advantage of the process and device combination is that the anodic effect means that the residual activated sludge does not reach the cathode = membrane and the cathode in turn does not absorb any salt formers SO ₄ ^- , PO ₄ ^- due to its repellent effect. Overall, the entire surface of the membrane is negatively charged by the OH ^- ions forming in the cathode membrane 6 . Metal ions attracted to the cathode are already converted to metal hydroxide in a thin layer in front of the membrane and precipitated and thus do not get into the interior of the membrane. By regulating the current flow, it is avoided that too much OH ^- ions are formed, or too few, since otherwise metal hydroxide will fail in the membrane.

This process is easy to control, since the conductivity decreases after a certain dwell time hence the flow of electricity. Conditions can be easily regulated via the flow of electricity and waste water adjust.

A redox measurement in the anode-cathode space or in the drain water of the membrane can provide exact evidence of this. Furthermore, the cathodic membrane 6 receives new active properties for the chemical-physical treatment of the waste water while at the same time protecting the membrane against blockage or deposits of salts and bacterial cultures.

The membrane is therefore not only a mechanical sludge separating element, but an active one Element for physico-chemical treatment of waste water.

The low power consumption of around 1 kWh per m ^{3 of} wastewater enables high energy savings because the O ₂ input from biology can be reduced. To solve the problem of calcification of the membrane, a dilute acid can be added to the backwash water. This removes the attached hydroxides and at the same time regulates the pH value, which shifts to the basic range if the voltage is too high (formation of OH ^- ions). If the proportion of lime in the wastewater is too high, a known electrolysis cell or other suitable aids or devices can be connected upstream.

List of the reference symbols used

1

- Container

2nd

- gastight cover

3rd

- lockable inlet

4th

- degassing line

5

- anodes

6

- cathodic filter membrane

7

- spacer frame

8th

- sloping floor

9

- Clear water drain

10th

- mud vent

11

- rectifier

12th

- variable transformer

13

- mains connection

14

- Electrode connections

15

- Position sign [max.]

16

- Position sign [min.]

Claims (12)

1. A method for wastewater purification using a modified membrane filtration, the wastewater taken from the separated phase of a biological purification system, passed into a container ( 1 ) with anodes ( 5 ), an electrically conductive catholic filter membrane ( 6 ) and electrode connections ( 14 ) and is guided into the space between the anodes ( 5 ) and an electrically conductive cathodic filter membrane ( 6 ), then passed out of the space between the anodes ( 5 ) and the cathodic filter membrane ( 6 ) through the cathodic filter membrane ( 6 ) and via a clear water outlet ( 9 ) is removed, a voltage being applied to the electrodes in order to set a slightly increased pH value via the electrolytic decomposition of the water in the space between the cathodic filter membrane ( 6 ) and the anode ( 5 ) in front of the cathodic filter membrane ( 6 ), the regulation of the current flow between the electrodes ( 5 , 6 ) and the flow of the Abw assers done. 2. A process for wastewater purification according to claim 1, characterized in that when cleaning the cathodic filter membrane ( 6 ) and the anodes ( 5 ), a polarity reversal takes place via the electrode connections ( 14 ) and thus repel attached particles, and at the same time backwashing the cathodic filter membrane ( 6 ) is carried out and, using the backwashing water, the wastewater particles are swirled between the cathodic filter membrane ( 6 ) and the anodes ( 5 ). 3. Process for waste water purification according to claim 2, characterized in that the Backwash water is added dilute acid. 4. A method for wastewater treatment according to claim 1, characterized in that the sedimented and retained wastewater constituents are removed from the container ( 1 ) via a sludge discharge ( 10 ). 5. A process for wastewater treatment according to claim 1, characterized in that the wastewater after the treatment leaves the container ( 1 ) via the clear water outlet ( 9 ) without pressure or with a slight negative pressure. 6. A method of wastewater treatment according to claim 1, characterized in that the resulting gases, especially hydrogen, are collected in an orderly manner and one be used for further use. 7. A device for wastewater treatment using a modified membrane filtration according to claim 1, with an inlet ( 3 ), a container ( 1 ) with anodes ( 5 ), an electrically conductive cathodic filter membrane ( 6 ) and electrode connections ( 14 ), the electrically conductive cathodic filter membrane ( 6 ) in the space between the anodes ( 5 ) is attached and the interior of the cathodic filter membrane ( 6 ) is connected to a clear water outlet ( 9 ). 8. A device for wastewater treatment according to claim 7, characterized in that the container ( 1 ) is provided with a gas-tight lid ( 2 ). 9. A device for wastewater treatment according to claim 7, characterized in that the cathodic filter membrane ( 6 ) is tubular or plate-shaped and a separate cathode is mounted at a spatial distance from the cathodic filter membrane ( 6 ) within a membrane space. 10. A device for wastewater treatment according to claim 7, characterized in that the cathodic filter membrane ( 6 ) has a conductive coating which is applied to a textile carrier. 11. A device for wastewater treatment according to claim 7, characterized in that the even non-conductive cathodic filter membranes with conductive layers form a spatial unit, the conductive layers before or after or before and are arranged after the cathodic filter membranes. 12. A device for wastewater treatment according to claim 7, characterized in that in the reaction spaces between cathodic filter membrane ( 6 ) and anode ( 5 ) or / and in the process redox, pH or conductivity electrodes are used.