KR101080385B1 - Method for controlling current in electrochemical wastewater treatment apparatus - Google Patents

Abstract

In the present invention, it is possible to easily remove the passivation (oxide film) and scale formed on the surface of the electrode within a very short time after the polarity reversal, even if it is not through cumbersome maintenance work such as periodic cleaning of the electrode surface. An object of the present invention is to provide a method for controlling current of an electrochemical wastewater treatment apparatus. The current control method of the electrochemical wastewater treatment apparatus of the present invention, the polarity inversion step of inverting the polarity of the electrode; And after the polarity inversion, applying an elevated voltage or an elevated current to the electrode.

Electrochemical Wastewater Treatment Equipment, Polarity Reversal

Description

Method for controlling current in electrochemical wastewater treatment apparatus

The present invention relates to electrochemical wastewater treatment, and more particularly, to a method for controlling current in an electrochemical wastewater treatment apparatus.

Electrochemical wastewater treatment devices are devices that remove or facilitate the removal of contaminants in wastewater through, for example, electrochemical treatments such as electrolysis, electrocoagulation, electroinjuries or combinations thereof.

Since electrotreatment-based water treatment was first attempted at the end of the 19th century, application research on drinking water purification systems and wastewater treatment systems using iron and aluminum as electrode materials has been conducted. In this series of studies, the electrocoagulation process has shown excellent performance in removing toxic heavy metals, improving turbidity, and improving the color of wastewater generated in the plating and semiconductor industries. Due to this situation is not widely commercialized. However, due to the recent tightened wastewater discharge regulations and the international demand for sludge reduction, electrochemical wastewater treatment is of interest.

Many conventional studies on electrochemical flocculation have proposed new techniques in the form of electrodes, flow direction of fluid, application method of electricity, additives, etc. as a means to increase the efficiency of water treatment. However, it was not possible to ultimately solve the problem that the water treatment efficiency is lowered due to the inhibition of the electrolytic reaction by the iron or aluminum passivation by the reduction phenomenon on the electrode surface and the surface adsorption of the inert colloidal material.

In the prior art using the electrocoagulation technique, generally, in order to prolong the time of electrode replacement, both the eluting electrode (elute electrode) and the negative electrode (non-ejecting electrode) are used, and the cathode and Invert the polarity of the anode. The cathode (non-ejection electrode) before polarity inversion acts as an anode (elution electrode) after polarity inversion. Thus, since all electrodes can be utilized to elute metal ions sequentially, the "electrode replacement cycle according to electrode consumption" can be extended.

In the electrocoagulation process, the anode (elution electrode) is oxidized by the electrochemical reaction to produce metal cations, convection / diffusion by electric field and concentration gradient, and electrically combined with dissolved organic matter or colloidal particles to neutralize and aggregate / Precipitates. When a current is passed through a metal as an anode in an aqueous electrolyte solution, the electrode surface is eluted as a metal, a chemical reaction between the metal ions produced by the elution and a solution component, the formation reaction of an oxide film for the anode of the metal, and a metal surface. Dissolution reaction of the produced oxide proceeds. In the electrolytic reaction of such metals, particularly aluminum metal, anodization film tends to be well formed, and the passivation film is particularly stable in the pH 4-8 region, that is, in the vicinity of neutral. If the film formation exists outside the stable oxide film, the passivation film growth shape is accelerated when the film formation rate is greater than the film dissolution rate, and the inert colloidal material adheres to the electrode surface by the electrostatic adsorption reaction to form scale. .

This passivation film and scale is more active in the cathode (non-ejection electrode) than the anode (elution electrode) in which metal ions are eluted by the electrolytic reaction, and the reaction time until the inversion time when the polarity of the electrode is reversed at regular intervals. It will increase in proportion.

Thus, the following problems occur during polarity reversal. The passivation (oxide film) and scale are formed on the surface of the cathode (non-ejection electrode) before the polarity inversion. When the cathode is polarized inverted and used as a cathode (elution electrode), due to the passivation and scale formed on the surface thereof, metal ions cannot be smoothly eluted for a considerable time. Therefore, during a considerable time after the polarity reversal, the water quality of the treated water does not satisfy the reference value or the treatment efficiency drops drastically.

Of course, polishing the surface of the electrode can solve this problem. However, in order to polish the surface of the electrode, the electrode must be detached several times before the electrode replacement cycle due to electrode consumption. In general, the electrodes of an electrochemical wastewater treatment apparatus are very large in size and weight. Therefore, in the electrochemical wastewater treatment apparatus, attachment and detachment of electrodes is the most difficult and time-consuming maintenance item. As a result, the frequent attachment and detachment and polishing of electrodes to remove the passivation and scale formed on the surface of the cathode (non-ejection electrode) before the polarity inversion not only dramatically increase the maintenance cost of the electrochemical wastewater treatment apparatus, The effective uptime of chemical wastewater treatment equipment is wasted.

In the present invention, it is possible to easily remove the passivation (oxide film) and scale formed on the surface of the electrode within a very short time after the polarity reversal, even if it is not through cumbersome maintenance work such as periodic cleaning of the electrode surface. An object of the present invention is to provide a method for controlling current of an electrochemical wastewater treatment apparatus.

The current control method of the electrochemical wastewater treatment apparatus of the present invention,

A polarity inversion step of inverting the polarity of the electrode; And

And after the polarity inversion, applying an elevated voltage or an elevated current to the electrode.

A passivation (oxide film) and scale are formed on the surface of the anode (eluting electrode) after the polarity inversion, but when an elevated voltage or an elevated current is applied to the electrode, metal ion elution reaction on the surface of the anode (eluting electrode) is forcibly enforced. Is accelerated.

Thus, in spite of the presence of the passivation (oxide film) and scale coated on the surface of the anode (elution electrode), metal ion elution proceeds actively on the surface of the anode (elution electrode) metal layer. In this process, a surprising phenomenon occurs in which the passivation (oxide film) and scale coating are peeled off from the surface of the anode (eluting electrode) metal layer.

Due to this peeling phenomenon, passivation (oxide film) and scale can be removed from the surface of the anode (eluting electrode) after polarity reversal much more easily and quickly compared to cumbersome maintenance work such as electrode surface polishing.

After the passivation (oxide film) and scale are removed from the surface of the anode (eluting electrode), the electrochemical wastewater treatment device is optimized wastewater treatment efficiency even if the voltage or current applied to the electrode is lowered to a normal voltage or a steady current. Will be used.

Hereinafter, the current control method of the electrochemical wastewater treatment apparatus of the present invention will be described in more detail.

The current control method of the electrochemical wastewater treatment apparatus of the present invention,

A polarity inversion step of inverting the polarity of the electrode; And

And after the polarity inversion, applying an elevated voltage or an elevated current to the electrode.

An electrochemical wastewater treatment apparatus includes, for example, a reaction tank having an inflow wastewater inlet and a treatment wastewater outlet; At least a pair of elutable electrodes installed in the reactor; And a DC power supply electrically connected to the at least one pair of elutable electrodes. The elutable electrode means an electrode capable of eluting metal ions when a positive voltage is applied. The elutable electrode may be, for example, iron or aluminum. Among the pair of elutable electrodes, the first electrode serves as an anode (eluting electrode), and the second electrode serves as a cathode (non-ejecting electrode).

In the polarity reversal step, the electrical connection between the DC power supply and the electrode is changed to convert the positive voltage applied to the first electrode of the pair of eluting electrodes to the negative voltage, and the negative voltage applied to the second electrode. Convert the voltage of to positive voltage. Thus, after the polarity reversal, the first electrode acts as the cathode (non-ejection electrode) and the second electrode acts as the anode (elution electrode). The change in the electrical connection for the polarity reversal can be performed, for example, by switching the polarity switching switch of the distribution circuit in the DC power supply, or by switching the polarity of the output voltage of the rectifier itself in the DC power supply.

After the polarity reversal step, an elevated voltage or an elevated current is applied to the electrode. The elevated voltage or elevated current means a voltage or current higher than the normal voltage range or the normal current range applied to the electrode in the normal operation of the electrochemical wastewater treatment apparatus. Peeling phenomenon of passivation (oxide film) and scale coating by forcibly accelerating metal ion elution reaction on the surface of anode (elution electrode) as the rise of increased voltage or elevated current on the basis of steady voltage or steady current This is getting stronger and, accordingly, the time taken to remove the passivation (oxide) and scale coating can be shortened more and more.

If the rising width of the rising voltage or rising current on the basis of the normal voltage or the normal current is made too small, only the resistance due to the passivation (oxide film) and the scale coating on the surface of the anode (eluting electrode) increases, but the passivation and scale coating are increased. Delamination can be weakly generated, and the time taken to remove the passivation and scale coating can be excessively extended. Therefore, it is desirable to initially apply a voltage or current at a level that can quickly dissolve the formed film. On the other hand, if the rising width of the rising voltage or rising current on the basis of the normal voltage or the normal current is too large, the output width of the voltage or the current of the DC power supply must be excessively large, so that the price of the DC power supply is increased. It can rise excessively and the increase of energy consumption is obvious as well. In addition, the application of current and voltage exceeding the appropriate intensity and time may be useful for the removal of passivation and scale at the beginning, but the metal electrode may be peeled into a plate by the elution of excessive metal ions, thereby narrowing the space between the electrodes. Blocking can eventually lead to poor treatment efficiency and equipment damage.

In view of this point, for example, the rising width of the increased voltage or the increased current based on the steady voltage or the steady current may be about 20% to about 35% of the steady voltage or the steady current. More specifically for example, in electrochemical wastewater treatment apparatus, a steady current of about 2 mA / electrode surface area-cm ² to about 5 mA / electrode surface area-cm ² is typically used. In this case, the elevated current may be about 2.4 mA / electrode surface area-cm ² to about 6.75 mA / electrode surface area-cm ² . The current and voltage applied to the electrode plate vary greatly depending on the physical properties such as the electrical properties of the raw water supplied and the content of insoluble solids, the surface area of the electrodes in contact with the raw water, the spacing between the electrodes, and the flow velocity of the fluid. As such, the scope of the present invention is not limited to the above examples.

The form of applying the elevated voltage or the elevated current to the electrode may be, for example, stepped, quadratic, toothed, or a mixture thereof. The stepped form may be, for example, a single stepped step or a multistage stepped step. In terms of maximizing the effect of promoting the passivation of the passivation and scale coating, as the amount of metal ions eluted increases (or as the elution of metal ions proceeds after polarity inversion) Conversely, it is preferable to apply to the electrode to decrease in the form of the second function. In terms of ease of application, one-step staircase or multi-step staircase is preferable.

This type of application can be easily provided by, for example, an output current or output voltage adjusting means built in the DC power supply and a timer capable of controlling the output time.

<Examples>

Example  One

A 50-ppm test wastewater obtained by mixing a 1000-ppm copper standard solution with pure water after installing a pair of iron electrodes (250 mm wide, 300 mm long, 10 mm thick) in a 4-liter reactor with a 10 mm gap. Was fed continuously to the reactor. In addition, the supply flow rate of the test wastewater was adjusted so that the residence time of the test wastewater in the reactor was 40 seconds. Using a direct current rectifier, a current of 3 mA / cm ² was applied to the electrode. After operating for 10 minutes under these conditions, the polarity of the electrode was reversed. Polarity reversal was done instantaneously using the DC rectifier switch. After polarity reversal, a current of 4 mA / cm ² is applied to the electrode for 30 seconds, followed by a current of 3.5 mA / cm ² for 30 seconds, followed by a current of 3 mA / cm ² again. To the electrode (this application is in the form of two-stage stepped current control). In order to evaluate the removal efficiency of copper ions in the test wastewater, the treated wastewater was taken at intervals of 30 seconds from 60 seconds before the polarity inversion, and the copper content in the treated wastewater was analyzed using an atomic absorption spectrometer. The results are shown in FIG.

Comparative example  One

A 50-ppm test wastewater obtained by mixing a 1000-ppm copper standard solution with pure water after installing a pair of iron electrodes (250 mm wide, 300 mm long, 10 mm thick) in a 4-liter reactor with a 10 mm gap. Was fed continuously to the reactor. In addition, the supply flow rate of the test wastewater was adjusted so that the residence time of the test wastewater in the reactor was 40 seconds. Using a direct current rectifier, a current of 3 mA / cm ² was applied to the electrode. After operating for 10 minutes under these conditions, the polarity of the electrode was reversed. Polarity reversal was done instantaneously using the DC rectifier switch. Even after polarity inversion, the same current of 3 mA / cm ² was applied to the electrode. In order to evaluate the removal efficiency of copper ions in the test wastewater, the treated wastewater was taken at intervals of 30 seconds from 60 seconds before the polarity inversion, and the copper content in the treated wastewater was analyzed using an atomic absorption spectrometer. The results are shown in FIG.

Evaluation result comparison

1 and 2, the copper ion removal efficiency of the y-axis was calculated as follows.

As shown in FIG. 1, in the case of Example 1 in which the increased current after the polarity inversion was applied to the electrode in the form of a two-stage step wave, the copper ion removal efficiency was maintained not less than 75% after the polarity inversion, as well as the polarity inversion. After the recovery time of copper ion removal efficiency was only 120 seconds.

On the other hand, as shown in FIG. 2, in Comparative Example 1, in which the increased voltage or current was not applied even after the polarity inversion, the lowest value of the copper ion removal efficiency after the polarity inversion was drastically lowered to 30%, as well as the polarity inversion. After that, it took about 200 seconds to recover the copper ion removal efficiency.

In Example 1, the copper ion removal efficiency after the polarity inversion does not significantly decrease, and the recovery time of the copper ion removal efficiency after the polarity inversion is short is that the passivation formed on the surface of the cathode (non-ejection electrode) before the polarity inversion. (Oxide film) and scale have been removed effectively and quickly. In addition, the performance difference between Example 1 and Comparative Example 1 obtained using the test wastewater is further amplified in the long term operation using the actual wastewater.

1 is a graph showing the change of copper ion removal efficiency in test wastewater obtained in the example according to the present invention.

2 is a graph showing a change in copper ion removal efficiency in test wastewater obtained in a comparative example according to the prior art.

Claims (1)

A polarity inversion step of inverting the polarity of the electrode; And Immediately after the polarity inversion step, applying an elevated voltage or an elevated current to the electrode; Current Control Method of Electrochemical Wastewater Treatment System.

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