JPS5855839B2 - Wastewater treatment method using electrolysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wastewater treatment method in which phosphorus contained in wastewater is removed by electrolyzing wastewater.

As a method for removing phosphorus contained in wastewater, a method of electrolyzing wastewater using iron as an anode and a cathode is known.

However, this method has the disadvantage that excess iron ions are eluted during electrolysis, turning the wastewater red.

Furthermore, in order to remove phosphorus and iron ions, a method of electrolysis using aluminum as an anode and a cathode is known.

This method has the disadvantage of high running costs because it uses expensive aluminum.

Furthermore, when aluminum is used for the anode, scale adheres to the anode surface and the scale becomes passivated, making it difficult to operate continuously for a long period of time.

The present invention solves the above-mentioned drawbacks, and aims to provide a wastewater treatment method that has low running costs and does not turn wastewater red.

The wastewater treatment method of the present invention is characterized in that in a method of electrolyzing wastewater using iron as an anode and aluminum as a cathode, polarity conversion is performed to use aluminum as an anode to actively elute aluminum. It is something to do.

In this way, the present invention uses a combination of iron and aluminum in the electrode, and uses iron, which has a large amount of elution, to remove phosphorus, and aluminum, which has a small amount of elution, to remove excess iron ions. There is no risk of deterioration, and running costs are reduced.

The present invention will be explained in detail below.

In the present invention, iron is used for the anode of the electrolytic cell, and aluminum is used for the cathode.

Therefore, at the anode, iron becomes divalent iron ions Fe2+ and is eluted.

Some of these iron ions are oxidized in the wastewater and become trivalent iron ions, Fe3+.

These divalent and trivalent iron ions then ionically bond with phosphoric acid ionoPO4 in the wastewater.

Since Fe5(PO4)2 and FePO4 generated by this ionic bond are poorly soluble,
It is deposited during this electrolysis.

☆ ☆ Generally, the cathode does not dissolve, but when the cathode is made of aluminum, the presence of OH- near the cathode causes it to react with and chemically dissolve to form aluminate ions.

Note that since hydrogen gas is generated from the cathode surface, passivation due to an oxide film does not occur.

To remove iron ions, use a molar ratio of Fe:A11:0.
2 to 1 aluminum is required, but the amount of aluminum dissolved at the cathode is 20 to 60% of the theoretical electrochemical equivalent (when aluminum is used as the anode), so there is enough aluminum to remove iron ions. Acid ions are obtained.

When these aluminate ions are present in wastewater, iron ions and aluminate ions react to generate hydroxide flocs containing both ions.

Therefore, not only the iron ions previously contained in the wastewater but also the iron ions generated by electrolysis are removed, and the problem of red coloring does not occur.

When the content of iron ions is high, the amount of aluminum electrode is required.

For this purpose, aluminum is used as an anode and actively eluted.

However, when aluminum is used for the anode, continuous operation is not possible because scale adheres and passivation occurs.

To prevent this, the polarity is changed by using iron for one electrode and aluminum for the other electrode.

That is, iron is first used as the anode, and after a certain period of time, the polarity is changed and aluminum is used as the anode.

When iron is used as the anode, eluted iron ions perform dephosphorization.

Next, when aluminum is used as an anode, the aluminum is eluted and removes excess iron ions eluted during electrolysis.

The aluminum electrode is usually a flat plate, but if the electrode is shaped like a net or a slit with a width of 5 to 250 mm, the amount of scale deposited can be reduced due to the edge effect.

Next, an example will be given and explained.

Example 1 Secondary treated water from urban sewage (activated sludge treated water) was used as raw water,
After adjusting the pH to 6 with sulfuric acid, an electrolytic tank with iron as an anode and aluminum as a cathode (flow rate 2.22 m/hr
) was electrolyzed.

During this electrolysis, the current density was set to 0.3 to IA/dm
As a result of experiments, the results shown in Table 1 were obtained.

This corresponds to a two-tank method for removing iron ions and phosphorus disclosed in Japanese Patent Publication No. 56-12476, which is further simplified in structure by changing it to a one-tank method.

Example 2 Electrolysis was carried out using iron and aluminum as electrodes and the polarity was changed at 10 minute intervals. The results shown in Table 2 were obtained.

In this example, the aluminum elution efficiency was higher than the theoretical efficiency, and contaminant removal was good.

According to the present invention having the above configuration, since iron is used for the anode and aluminum is used for the cathode, the wastewater does not turn red due to the excess iron ions eluted.

In addition, the running cost is significantly lower than the method of electrolyzing using only aluminum, and there is no risk of scale adhesion and passivation.

In addition, since it is an electrolytic treatment, there is little variation in pH, and S
S, BOD, COD, etc. can also be removed.

Claims (1)

[Claims] 1. Iron is used for one electrode and aluminum is used for the other. First, wastewater is electrolyzed using iron as an anode, and then the polarity is changed and aluminum is used as an anode to elute aluminum, and the aluminum is eluted into wastewater. A wastewater treatment method characterized by removing phosphorus contained therein. 2. The wastewater treatment method according to claim 1, wherein the electrode has a mesh shape. 3. The wastewater treatment method according to claim 1, wherein the electrode has a slit shape with a width of 5 to 250 mrn. 4. The wastewater treatment method according to any one of claims 1 to 3, wherein the aluminum includes an aluminum alloy.