JPS5835111B2 - Electrification treatment method for wastewater containing sulfur-containing reducing anions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for electrification of wastewater containing sulfur-containing reducing anions, in particular, a method for electrification of wastewater containing sulfur-containing reducing anions, in particular a method for electrification of wastewater containing sulfur-containing reducing anions. This invention relates to an electrification processing method that performs purification processing while passing a weak current.

Generally, wastewater containing sulfur-containing reducing anions (hereinafter referred to as raw water) contains carbon dioxide such as sulfur and thiosulfate ions.
Since the OD component has a high COD and cannot be discharged as is, it is desired that the COD component be removed or oxidized in advance to meet wastewater standards and then be discharged.

In addition, in this electrification treatment method, carbon electrodes are placed in a treatment tank filled with activated carbon, and while a weak direct current is passed between these electrodes, an electrolytic reaction occurs from the raw water. Not only does this remove COD components, but also the oxidizing ability of the activated carbon surface and the acidic decomposition properties of the sulfur-containing reducing anions remove COD components and the like.

Therefore, in the electrolytic treatment method, raw water is purified by an electrolytic reaction caused by the application of direct current, the oxidation ability of the surface of activated carbon, and the disproportionation reaction of thiosulfate ions, which are the main components of COD, so the purification ability is extremely high. It is said to be superior to other purification methods.

However, in the electrification treatment method, suspended matter and precipitated scale contained in the raw water during treatment adhere to the surface of the activated carbon or the surface of the electrode, or are trapped between the activated carbon, reducing the effective surface area of the electrode.
The effective surface area of the activated carbon decreases and the processing capacity gradually decreases. Therefore, after the required time of processing, a cleaning medium such as air or water is periodically pumped into the processing tank for cleaning.

However, although cleaning by blowing air into the treatment tank can remove scale between the activated carbon, it cannot remove scale that has adhered to the surface of the activated carbon, or particularly scale that has adhered firmly. Normally, when the adhesion of scale etc. has progressed considerably, activated carbon is replaced with new activated carbon, but since activated carbon is expensive, replacement is expensive, time-consuming, and processing costs are high. Improvements are desired.

For this reason, a cleaning method has been proposed that can remove scale and other substances adhering to the activated carbon surface without having to replace the activated carbon with a new one.One method is to clean the activated carbon surface by pumping a solution containing hydrochloric acid into the treatment tank from the bottom. It is proposed to do so.

However, when cleaning the surface of activated carbon with a solution containing diluted hydrochloric acid in this way, even though the scale generated during the electrification reaction can be removed with diluted hydrochloric acid, during long-term operation, the scale may be removed due to acidic decomposition of reducing anions. Sulfur, etc. are present, and this sulfur, etc. adheres to activated carbon and adversely affects the electrification process.

Therefore, even if the surface of the activated carbon is cleaned with a solution containing dilute hydrochloric acid, when the amount of sulfur, etc. attached to the surface of the activated carbon reaches its limit, the activated carbon must be replaced with a new one.

However, this replacement requires time and effort to take out and pack the activated carbon, and the cost of regenerating the activated carbon is also expensive, so it is desired to be able to remove sulfur and the like from the surface of the activated carbon.

The present invention aims to solve the above-mentioned drawbacks, and in particular, in the electrification treatment method, even if sulfur etc. accumulates on the surface of activated carbon in addition to scale etc., the activated carbon cannot be taken out (the activated carbon in the treatment tank cannot be cleaned). , we propose a method for recovering removal capacity and electrification processing.

That is, the present invention provides an electrification treatment method for purifying wastewater containing sulfur-containing reducing anions while passing a weak current through an electrode in a treatment tank filled with activated carbon. When sulfur has accumulated to a predetermined amount, wastewater purification is stopped and the wastewater is removed from the treatment tank. After that, an aqueous solution containing caustic soda is pumped into the treatment tank to wash away the sulfur, and after that cleaning, the wastewater is removed again. It is characterized by starting purification of wastewater.

In addition, the method of the present invention is an electrification treatment method that purifies wastewater containing sulfur-containing reducing anions while passing a weak current through an electrode in a treatment tank filled with activated carbon. When sulfur accumulates to a certain amount on the surface,
The wastewater purification is stopped and the wastewater is removed from the treatment tank, and then an aqueous solution containing caustic soda is sent into the treatment tank to wash away the sulfur. After that cleaning, the wastewater purification is started again.
Furthermore, during this wastewater purification, if scale, etc. accumulates to a predetermined amount on the surface of the activated carbon and electrodes in the treatment tank, an aqueous solution containing hydrochloric acid is pumped into the treatment tank to wash away the scale, etc., and purify the wastewater. It is characterized by doing.

The method of the present invention will be explained in detail below.

FIG. 1 is a layout diagram of an example of an apparatus for carrying out the method of the present invention, and in the drawing, reference numeral 1 indicates a raw water inlet, 2 indicates a treatment tank, 3 indicates a carbon electrode, 4 indicates activated carbon, and 5 indicates a tooth bar. , 6 is a water supply bulk, 7 is an air supply valve, 8 is a caustic soda supply bulk, 9 is a caustic soda circulation pump, 10 is a caustic soda dilution tank, 11 is a caustic soda outlet valve, 12 is a caustic soda transfer pump, 13 is a caustic soda circulation valve, 14
15 shows a caustic soda receiving tank, 15 shows a blower pipe, 16 shows a treated water outlet, and 17 shows a drain valve.

First, in FIG. 1, raw water is introduced into the treatment tank 2 from the raw water inlet 1, a weak current is passed between the carbon electrodes 3 in the treatment tank 2, and the raw water flows through the activated carbon 4 between the carbon electrodes 30. While the water passes through the water, the raw water is treated by a weak electric current and the oxidizing ability of the activated carbon surface, and after the treatment is taken out from the treated water outlet 16.

That is, in the treatment tank 2, dissolved sulfur and thiosulfate ions contained in the raw water generate sulfur through the following reaction in the anode area where the electrode 3 and activated carbon 4 are integrated by the action of a weak current.

S2−→S0+2e−・・・・・・・・・・・・・−
(1) 8203'=10H10→S0+H8O, -...(
2) The generated sulfur remains in the activated carbon, and during long-term operation, this sulfur accumulates and covers the surface of the activated carbon, gradually reducing its ability to purify raw water.

When sulfur adheres to the activated carbon surface and the amount of the adhesion exceeds a predetermined value, the inflow of raw water is stopped and the raw water in the treatment tank 2 is drained using the drain valve 17.

In this case, when there is a trapped substance between the activated carbons 40, the air supply valve 7 is opened to introduce cleaning air for cleaning, and the water supply valve 6 is further opened to introduce cleaning water upward.

Next, after removing the trapped substances between the activated carbons 40 as described above, a caustic soda solution diluted to a predetermined concentration is introduced into the treatment tank 2, and this caustic soda solution is circulated to adhere to the surface of the activated carbon 40. Removes accumulated sulfur.

In this case, the caustic soda solution can be introduced in any manner, but is preferably introduced as shown in FIG.

In other words, a caustic soda solution with a concentration of about 45% is placed in dilution tank 1.
The caustic soda solution is fed to the electrification treatment tank 2 via the blower pipe 15 using the caustic soda supply valve 8 and the caustic soda circulation pump 9, and is then diluted to 4-20% in the dilution tank 10. contact with.

This contact dissolves the sulfur that has accumulated on the surface of the activated carbon and transfers it to the cleaning solution.

When the caustic soda solution is successively fed into the electrification treatment tank 2 in this manner, the cleaning waste liquid overflows from the upper part of the electrification treatment tank and is sent into the caustic soda receiving tank 14 through the trough.

When the washing waste liquid flows into the caustic soda receiving tank 14, the caustic soda transfer pump 12 is operated to return it to the dilution tank 10, so that the caustic soda can be recycled.

In this case, the concentration of the caustic soda solution is appropriately determined within the range of 4 to 20% depending on the degree of adhesion of sulfur content.

If it is less than 4%, the cleaning ability will not be sufficient, and if it exceeds 20%, it will not only be disadvantageous in terms of cost, but also the electrification treatment after cleaning will not be advantageous, so it should be used in the range of 4 to 20%. be.

According to experiments conducted by the present inventors, a sufficient cleaning effect was obtained at around 8%.

In addition, after washing and removing sulfur on the surface of the activated carbon 40 as described above, raw water is introduced again from the raw water inlet 1, and the raw water is treated while flowing a weak current between the electrodes 3 as described above. At this time, if scale or the like accumulates on the surface of the activated carbon 40, it is sufficient to clean it with a dilute hydrochloric acid solution.

Further, when raw water is electrified while removing scale in this way, the amount of sulfur accumulated on the surface of the activated carbon 40 increases after a predetermined period of time, but in this case it is natural to clean it as described above.

That is, in the treatment tank 2, in the anode area, as described above (
Sulfur is precipitated and separated according to the formulas 1) and (2), but poorly water-soluble magnesium hydroxide and calcium hydroxide are generated on the surface of the electrode 30, which acts as a cathode, and these precipitate as scales. Scale adheres to the electrode surface and activated carbon surface, reducing cleaning performance.

Further, scale cannot be removed by cleaning air introduced from the air supply valve 7 or the like.

For this purpose, a solution containing hydrochloric acid is introduced into the processing tank 2 as a cleaning agent to remove scales and the like adhering to the surfaces of activated carbon, electrodes, and the like.

It is usually sufficient to dilute the hydrochloric acid with water and introduce the solution containing hydrochloric acid, similarly to the solution containing caustic soda.

In addition, it is sufficient to determine the concentration of the solution containing hydrochloric acid in relation to the degree of scale adhesion, but in normal cases, if the concentration of hydrochloric acid is 0.1% or more, the removal effect of scale etc. is large and short. If it exceeds 5%, there is a risk of corroding processing equipment, etc., and generally around 1 to 3% is sufficient.

Next, an example will be described.

Example 1 First, in the apparatus shown in FIG. 1, leachate from blast furnace slag was electrified, and as a decrease in treatment capacity was observed, the treatment was stopped and the Each activated carbon in tank C was washed with water.

The amount of attached sulfur (rn9/S') after this water washing was calculated as shown in the following table, and since the amount of attached sulfur in the first tank A was the largest, the amount of attached sulfur in the first tank A was subsequently When only the activated carbon was washed, the results were as shown in the table below.

As a result, it was found that most of the attached sulfur could be removed using a 20% caustic soda solution, so when the activated carbon in the second tank B and the third tank C were also washed with the 20% caustic soda solution, the attached sulfur was removed as shown in the table above. I was able to remove most of it.

Example 2 When the same leachate as in Example 1 was treated using the apparatus shown in FIG. 1, the relationship between the COD concentration of the leachate and the water flow rate was as shown by the dotted line in FIG.

Therefore, when the water flow rate was around 1000 m', cleaning was performed with a 10% caustic soda solution, and then the leachate was further treated, as shown by the solid line in FIG.

The treatment capacity of activated carbon in the electrification treatment equipment gradually deteriorates as the amount of leachate processed increases, but it is regenerated by cleaning, and after cleaning it hardly deteriorates until the water flow rate reaches 800 m3. It was found that deterioration begins when the temperature exceeds this point.

At this time, when cleaning with a 2% hydrochloric acid solution, the processing capacity could approach the solid line in Figure 2, and as the washing operation with this hydrochloric acid solution was repeated, the processing capacity approached the dotted line in Figure 2. When this state was reached, cleaning was performed with a caustic soda solution, and the state could be returned to the dotted line in FIG.

As explained in detail above, the method of the present invention is to regenerate wastewater containing sulfur-containing cyclic anions by removing sulfur adhering to the surface of the activated carbon with a caustic soda solution when electrifying it with activated carbon. Most of the sulfur deposited and accumulated on the surface of the activated carbon is dissolved and removed, and the treatment capacity of the activated carbon can be almost completely restored.

Also, from this reason, expensive activated carbon can be used as a new 1. (There is no need to replace the product, and there is no need to replace it.) Wastewater containing sulfur-containing reducing anions can be treated very economically.

In addition, after removing sulfur and other substances with a solution containing caustic soda and restoring the activated carbon's ability, if the surface of the activated carbon is repeatedly washed with a solution containing hydrochloric acid, the activated carbon, electrodes, etc. will always remain in good condition. Raw water can be treated in a very economical manner without the need to replace expensive activated carbon.

[Brief explanation of the drawing]

Figure 1 is a layout diagram of an example of a device for carrying out the method of the present invention;
The figure is a graph of changes in wastewater treatment capacity before and after washing with caustic soda. Code, 1... Raw water inlet, 2... Treatment tank, 3... Carbon electrode, 4... Activated carbon,
5... Booth bar, 6... Water supply valve, 7... Air supply valve, 8... Caustic soda supply valve, 9... Caustic soda Circulation pump, 10... Caustic soda dilution tank, 11.
... Caustic soda outlet valve, 12 ... Caustic soda transfer pump, 13 ... Caustic soda circulation valve, 14 ... Caustic soda receiving tank, 15 ...
... Blower pipe, 16 ... Treated water outlet, 17.
·····drain valve.

Claims (1)

[Scope of Claims] 1. In an electrification treatment method for purifying wastewater containing sulfur-containing reducing anions while passing a weak current through an electrode in a treatment tank filled with activated carbon, When sulfur accumulates to a certain amount on the surface of activated carbon, the purification of the wastewater is stopped and the wastewater is removed from the treatment tank. After that, an aqueous solution containing caustic soda is sent into the treatment tank to wash away the sulfur, and after this cleaning, the wastewater is drained again. An electrification treatment method for wastewater containing sulfur-containing reducing anions that starts the purification of sulfur-containing reducing anions. 2 In an electrification treatment method that purifies wastewater containing sulfur-containing reducing anions while passing a weak current through an electrode in a treatment tank filled with activated carbon, sulfur is located on the surface of the activated carbon in this treatment tank. When a certain amount has been accumulated, wastewater purification is stopped and the wastewater is removed from the treatment tank, and then an aqueous solution containing caustic soda is sent into the treatment tank to wash away the sulfur.
After cleaning, the purification of the wastewater is started again, and during this wastewater purification, if scale, etc. accumulates to a certain amount on the surface of the activated carbon and electrodes in the treatment tank, an aqueous solution containing hydrochloric acid is pumped into the treatment tank. An electrification method for treating wastewater containing sulfur-containing reducing anions, which purifies the wastewater by washing away scale, etc.