JPS6244995B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing ammonia nitrogen, and in particular, to a method for treating wastewater containing ammonia nitrogen, which can efficiently adsorb ammonium ions in waste water onto activated carbon and further decompose and remove nitrogen gas. Concerning wastewater treatment methods.

In recent years, the problem of eutrophication of rivers and lakes has arisen due to the discharge of secondary treated sewage water, etc., and countermeasures are desired. Ammonia nitrogen is cited as one of the causative substances of these eutrophications. As the main removal methods, ammonia stripping method, biological nitrification method, ion exchange method, discontinuous chlorine injection method, etc. have been studied and partially implemented. Among these methods, the ammonia stripping method has been researched for a long time and is the lowest in cost, but it has the disadvantages that it may cause new air pollution as it releases ammonia into the atmosphere, and that the gas volatilization rate decreases at low temperatures. It was hot. Furthermore, while the biological nitrification and denitrification method has the advantage of being easily added to conventional secondary treatment equipment, it still has problems with stable operation, such as slowing of the metabolic rate of living organisms at low temperatures. In addition, the ion exchange method mainly uses resins such as zeolite minerals that selectively ion exchange ammonia nitrogen, but it has been pointed out that the selection of chemical solutions during regeneration and the treatment method for concentrated ammonium ions are troublesome. has been done. Furthermore, the discontinuous chlorine injection method utilizes the decomposition reaction between chlorine and ammonium ions to produce nitrogen.
This method has problems in handling toxic chlorine, increasing chlorine ions in the treated water, and decreasing PH. In this way, the conventional law has problems such as the occurrence of secondary pollution,
It has drawbacks in processing speed, economy, etc., and there remain problems in its practical application.

The present invention has been made in view of the current situation, and its purpose is to eliminate the above-mentioned drawbacks and to provide a treatment for wastewater containing ammonia nitrogen that can effectively, economically, and safely purify wastewater. The purpose is to provide a method.

The present invention has the following configuration to achieve the above object. That is, the method for treating ammonia-nitrogen-containing wastewater of the present invention involves passing ammonia-nitrogen-containing wastewater through an electrolytic cell filled with granular activated carbon between supporting electrodes constituted by one or more pairs of anodes and cathodes, and applying direct current to the electrolytic cell. The method for treating ammonia-nitrogen-containing wastewater according to the present invention is characterized in that ammonium ions are removed by adsorption on activated carbon. The method is characterized in that ammonium ions are adsorbed onto activated carbon by passing wastewater containing ammonia nitrogen through an electrolytic tank filled with the ammonia nitrogen and passing a direct current, and then regenerating the activated carbon by bringing it into contact with an electrolyte solution. The method for treating wastewater containing ammonia nitrogen according to the invention is to pass wastewater containing ammonia nitrogen through an electrolytic cell filled with granular activated carbon between supporting electrodes consisting of one or more pairs of anodes and cathodes, and to remove ammonium by passing a direct current. A method characterized by sorbing ions onto activated carbon, then regenerating the activated carbon by contacting it with a chloride solution, and then oxidizing and decomposing the ammonium ions with chlorine generated by electrolyzing the liquid from which the activated carbon was separated. It is.

Conventionally, it has been believed that activated carbon itself cannot adsorb ammonium ions, but according to the present invention, ammonium ions can be adsorbed onto activated carbon by electrically polarizing each particle of activated carbon. That is, by passing ammonia-nitrogen-containing wastewater through an electrolytic cell filled with granular activated carbon between supporting electrodes consisting of one or more pairs of anodes and cathodes, and applying a direct current, a relatively high When a voltage is applied, each particle of the granular activated carbon filled between the supporting electrodes is polarized, and ammonium ions in the wastewater are sorbed to the activated carbon due to its catalytic and electrostatic neutralizing effects, and in this case, the applied voltage is high. It is electrolytically oxidized and decomposed into nitrogen gas. Such a phenomenon occurs only in porous carbon particles such as activated carbon, and is due to the action of polarization of activated carbon. Although its mechanism of action has not been fully elucidated, it is thought to be as follows. That is, when activated carbon is immersed in a solution containing ammonium ions and an electric field is applied, the activated carbon particles themselves become polarized and at the same time become charged due to the dielectric constant. Due to this charge, ammonium ions are sorbed by electrostatic reaction with excited functional groups such as aldehyde groups, hydroxyl groups, carboxyl groups, and carbonyl groups on the surface of the activated carbon particles. Furthermore, it is considered that the electrolytic oxidation causes decomposition into nitrogen gas due to the relationship between the potential generated by the contact resistance between particles, which depends on the conductivity of the solution, and the overvoltage for the solution containing ammonium ions.

It is thought that such a function is exerted by the polarization of the granular activated carbon particles, but it was confirmed that this polarization is likely to occur in activated carbon particles with a particle size of about 5 mm or more. Therefore, in the present invention, it is desirable to use granular activated carbon of this size. Further, the shape of the granular activated carbon is not particularly limited, but a relatively spherical shape is generally effective.

The amount of ammonium ions removed by the present invention is
The amount increases in proportion to the amount of electricity applied, but in this case, oxidative decomposition into nitrogen gas is involved, and 0.01 to 0.02 g of ammonium ions are removed per unit weight (g) of activated carbon, and furthermore, the ammonium ion concentration in the wastewater is reduced.
It has been confirmed that it is particularly effective for low concentration solutions of 2000 ppm or less.

According to the present invention, it is possible to operate at any processing level and processing speed by simply adjusting the amount of electricity, so the same effect can be obtained by both distribution and batch operations, and efficient ammonium ion production is possible. Removal is possible.

Ammonium ions adsorbed on granular activated carbon are naturally eluted when the electric field is removed, but in the present invention, in order to promote this elution, granular activated carbon that has sorbed ammonium ions is brought into contact with an electrolyte solution. That is, according to the present invention, by immersing granular activated carbon in which the amount of ammonium ions adsorbed is saturated in an electrolyte solution such as a sodium chloride solution, the sorbed ammonium ions are eluted, and the granular activated carbon is can be played. As the electrolyte, in addition to sodium chloride, calcium chloride, calcium sulfate, etc. can be used.
In the case of a sodium chloride solution, it is appropriate that the electrolyte solution has a relatively high concentration of about 1 to 10%. The amount of elution in this case depends on the stirring speed and solution temperature, but the stirring should be done at a level that does not wear the granular activated carbon, and the higher the liquid temperature, the better the results.
~90% by weight of ammonium ions can be eluted.

In the present invention, ammonium ions are eluted using the above sodium chloride solution (preferably at a concentration of 1 to 10%) as an electrolyte solution, and the ammonium chloride solution obtained by removing activated carbon is subjected to another activated carbon-free electrolysis process. By introducing the ammonium ion into a tank and electrolyzing it, the ammonium ion is oxidized and decomposed into nitrogen gas. The reaction between chlorine and ammonium ions by electrolysis is shown by the following formula: 2NH ₄ ⁺ +3Cl ₂ →N ₂ +6HCl + 2H ⁺ The reaction molar ratio of [NH ₄ ]/[Cl ₂ ] is 1.5. As shown in the experiments in Examples below, the decomposition of ammonium ions by electrolytic chlorine in this case requires a current flow (constant current of 1A) such that the amount of chlorine generated is approximately 1.5 times the amount of chlorine required for the above reaction. The electrolysis time is approx.
It has been confirmed that this can be achieved in just 40 minutes).

In the present invention, ammonium ions can be further removed by oxidative decomposition to nitrogen gas as described above, and the resulting electrolyte can be recycled.
In other words, the chlorine ion concentration of the electrolytic solution after electrolysis is almost the same as the initial value, and the pH decreases due to the production of hydrochloric acid, so by neutralizing it with alkali,
It can be used cyclically as an ammonium ion eluent and an electrolyte. Further, the chlorine ion-containing solution used to elute ammonium ions can be used without being consumed unless it is diffused by chlorine gas.

As described above, according to the present invention, ammonium ions in wastewater can be efficiently removed, and the treatment equipment is also very compact and easy to operate. will be explained in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a specific example of the apparatus used in the present invention, in which 1 is a treatment tank, 2 is an electrolysis zone, 4 is a support electrode, 7 is a DC power supply, 9 is a wastewater inflow pipe, 10 11 indicates a treated water outflow pipe, and 12 indicates an exhaust pipe. The treatment tank 1 has a cylindrical shape, and supporting electrodes 4 are provided concentrically therein, and granular activated carbon 10 is filled between them. The waste water is introduced through the inlet pipe 9 and enters the electrolytic zone 2 between the layers of granular activated carbon 10 .
Particles of the granular activated carbon 10 are polarized by electricity supplied from the DC power source (rectifier) 7, and ammonium ions in the waste water are adsorbed inside the granular activated carbon 10. In this case, when the applied voltage is high and the contact potential between particles of the granular activated carbon 10 becomes large, ammonium ions are oxidized and decomposed into nitrogen gas by the catalytic action of the activated carbon. Electrolytic gas consisting of hydrogen and oxygen generated in the electrolysis zone 2 is discharged from an exhaust pipe (vent) 12 provided at the upper part of the treatment tank 1, and treated water is discharged from an outflow pipe 11.

Next, FIG. 2 is a schematic cross-sectional view showing one specific example of the apparatus used in the present invention, which has an electrolytic zone for an electrolyte (in the case of using chloride) solution containing eluted ammonium ions. is a treatment tank, 2 is an electrolytic zone, 3 is an ammonium ion (NH ₄ ⁺ ) electrolytic zone, 4 is a supporting electrode, 5 is an anode, 6 is a cathode, 7 is a DC power supply, 8 is a storage tank for chloride solution, 9 is waste water 10 is a granular activated carbon, 11 is a treated water outlet pipe, 12 is an exhaust pipe, 13 is an inlet pipe, 14 is a nitrogen gas exhaust pipe, and 15 is a pump. The treatment tank 1 is cylindrical and has an electrolysis zone 2 with an activated carbon packed bed at the top.
and a lower NH ₄ ⁺ electrolysis zone 3.
In the electrolytic zone 2, granular activated carbon 1 is placed between supporting electrodes 4.
The zeros are filled so that they touch each other. On the other hand, the NH ₄ ⁺ electrolytic zone 3 is a zone without any filling, in which a large number of anodes 5 and cathodes 6 are arranged.
In addition to the processing tank 1, this apparatus is equipped with a DC power source 7 for energizing and a storage tank 8 for a chloride solution serving as an eluent. The wastewater enters the electrolysis zone 2 through the wastewater inflow pipe 9 and flows through a layer of polarized granular activated carbon 10, and ammonium ions in the wastewater are sorbed to the granular activated carbon 10 by the electrostatic neutralization effect of each particle of the granular activated carbon 10. Ru. The waste water from which ammonium ions have been removed may be discharged from the outflow pipe 11. Hydrogen gas and oxygen gas generated during the electrolysis operation are released from an exhaust pipe 12 at the upper part of the processing tank 1. When these sorption operations reach saturation, a chloride solution is introduced from the storage tank 8 into the electrolytic zone 2, the granular activated carbon 10 is immersed in this solution, and the sorbed ammonium ions are eluted in the form of ammonium chloride. . The eluate is introduced into the electrolytic zone 3 via the inlet pipe 13. Electrolytic zone 3
In this case, ammonium ions are oxidized to nitrogen by chlorine generated by electrolytic oxidation of ammonium chloride and excess chloride. In addition, the chloride solution treated in the electrolysis zone 3 is sent to the pump 15 for reuse.
It is returned to the storage tank 8 via.

Next, the present invention and its effects will be explained with reference to Examples, but the present invention is not limited to these in any way.

Example 1 In this example, an experiment was conducted using the apparatus shown in FIG. FIG. 3 is a schematic cross-sectional view of this device, in which 1 is a treatment tank, 4 is a supporting electrode, 7 is a DC power supply, 9 is an inflow pipe for the sample solution, 10 is granular activated carbon, 11 is an outflow pipe, and 12 is a Showing the exhaust pipe. The treatment tank 1 has a rectangular shape with a length of 250 mm, a width of 150 mm, and a width of 50 mm. A ferrite support electrode 4 with a thickness of 5 mm is inserted into the side surface, and 150 mm of spherical granular activated carbon 10 with an average particle size of 8 mm is inserted between the electrode plates. (approximately 300g). Electricity is supplied through a support power source 7 provided outside the processing tank 1.
This was done by adjusting the current using a constant current rectifier. An ammonium sulfate aqueous solution containing 500 ppm of ammonium ions was used as the test solution. 500 ml of this solution was placed in treatment tank 1, and a current of 1 A was applied to perform electrolysis. Changes in ammonium ion concentration with respect to the amount of current applied were determined, and changes in PH and specific conductivity were also measured. The results are shown in FIG. That is, FIG. 4 is a graph showing changes in residual ammonium ion concentration, pH, and specific conductivity with respect to electrolysis time. It can be seen from this graph that as the amount of current applied increases, the residual ammonium ion concentration decreases, and the pH and specific conductivity of the solution also tend to decrease gradually. It was confirmed that such a reduction effect was observed when the ammonium ion concentration in the test solution was within 2000 ppm, and that the amount of reduction was approximately proportional to the amount of current applied.

As a control experiment, the granular activated carbon 10 was simply mixed with ammonium sulfate solutions with ammonium ion concentrations of 100 ppm and 500 ppm without applying an electric field to the granular activated carbon 10.
When immersed in 500 ml for 1 hour, changes in residual ammonium ion concentration and specific conductivity with respect to immersion time were measured. As a result, as is clear from the graph of FIG. 5, no change was observed in the ammonium ion concentration or specific conductivity, and no adsorption or sorption phenomenon was observed. This shows that in order to treat a solution containing ammonium ions with activated carbon to adsorb ammonium ions, it is necessary to apply a DC electric field to the activated carbon particles. Furthermore, regarding the amount of ammonium ions sorbed, although oxidative decomposition into nitrogen gas is involved, results have been obtained in which the weight of ammonium ions per unit weight (g) of activated carbon is 0.01 to 0.02 g.

Example 2 An experiment was conducted using the same apparatus shown in FIG. 3 as in Example 1, except that the rectangular processing tank 1 had a volume of 300 ml. Between the supporting electrodes 4, 100 g of spherical granular activated carbon 10 having an average particle size of 8 mm was filled. The current was supplied to a constant current using a constant current rectifier from an external DC power source 7, so that the voltage at that time could be measured. First, 150 g of ammonium sulfate aqueous solution having an ammonium ion concentration of 1000 ppm was added to 100 g of the activated carbon 10.
ml, electrolytic treatment was carried out in the same manner as in Example 1, and sorption was carried out until the ammonium ion concentration was reduced to 100 ppm.

Next, the granular activated carbon 10 that had absorbed ammonium ions was placed in 300 ml of 3% saline, and the ammonium ions were eluted with stirring at room temperature, and the amount of ammonium ions eluted with respect to the elution time was measured. The results are shown in the graph of FIG. As is clear from this graph, the amount of ammonium ions initially sorbed to the granular activated carbon is
Since the amount was 135 mg, the elution amount reached almost equilibrium at 120 mg in 5 hours, and the elution rate was 89%.

Next, an electrolysis experiment was conducted on a saline solution containing eluted ammonium ions (without activated carbon filling). As mentioned above, the reaction molar ratio of [NH ₄ ]/[Cl ₂ ] is 1.5.
Therefore, the following conditions were used as the electrolytic conditions, and the operation was performed at a constant current of 1 A based on the amount of chlorine generated previously determined by electrolyzing only saline solution.

Treatment tank for electrolysis: square, 300ml Electrode, ferrite plate (100 x 100mm, thickness 5mm) Electrode spacing 30mm Electrolyte (NH ₄ ) ₂ SO ₄ 0.15% (NH ₄ ⁺ 400ppm) NaCl 2.0% Liquid volume 200ml Electrolysis conditions Current: 1 A (current density: 1.25 A/dm ² ) Constant voltage: 6 to 6.5 V Temperature: 19 to 23° C. Time: 70 minutes The obtained results are shown in the graph of FIG. This graph shows the relationship between changes in residual ammonium ion concentration and residual chlorine ion concentration due to changes in electrolysis time. From now on, as electrolysis progresses, the residual ammonium ion concentration will gradually decrease until 30 minutes pass. However, while
The residual chlorine ion concentration decreased slightly after 45 minutes, and then tended to recover to the initial concentration. Such characteristics indicate that the reaction rapidly progresses around 40 minutes of electrolysis time when the amount of generated chlorine reaches a reaction molar ratio of 1.5 with ammonium ions. Further, as a result of analyzing the gas generated during electrolysis, its components were only oxygen, hydrogen, and nitrogen, and no nitrogen oxides were observed. From the above results, the amount of chlorine required for the decomposition of ammonium ions by electrolytic chlorine is approximately
It was found that the amount of electricity that generated 1.5 times as much chlorine was sufficient to achieve the purpose. Also, from the above results,
Although the chlorine ion concentration of the electrolyte is almost the same as the initial value, the pH decreases due to the production of hydrochloric acid, so it is clear that it can be recycled as an eluent and electrolyte by neutralizing it with an alkali.

Note that we also conducted experiments in which the current was set to 0.5 A and the solution concentration was varied, and two of these will be shown as experimental examples.

Experimental Example 1 Using the same apparatus as in Example 2, an electrolysis experiment of saline solution containing ammonium ions was conducted under the following conditions.

Electrolyte solution (NH ₄ ) ₂ SO ₄ 0.15% (NH ₄ ⁺ 400ppm) NaCl 1.0% Liquid volume 200ml Electrolysis conditions Current 0.5A Constant voltage 9V Temperature 16-19°C Time 70 minutes The results obtained are shown in Figure 8. FIG. 8 is a graph showing changes in residual ammonium ion concentration and pH with respect to electrolysis time. As is clear from this graph, the decomposition of ammonium ions is not as good as in Example 2, but this is thought to be because the salt concentration is lower than the ammonium ion concentration in the electrolyte.

Experimental example 2 An experiment similar to Experimental Example 1 was conducted under the following conditions.

Electrolyte (NH ₄ ) ₂ SO ₄ 0.08% (NH ₄ ⁺
250ppm) NaCl 2.0% Liquid volume 200ml Electrolysis conditions Current 0.5A Constant voltage 4.5V Temperature 19-24°C Time 100 minutes The results obtained are shown in Figure 9. FIG. 9 is a graph having the same meaning as Experimental Example 1. As is clear from this graph, ammonium ions rapidly decreased, while pH gradually decreased, but rose again after 40 minutes. This indicates that hydrochloric acid is generated as ammonium ions are decomposed. This experimental result is thought to be due to the higher salt concentration than the ammonium ion concentration in the electrolyte.

As described above, according to the present invention, ammonium ions can be efficiently sorbed and removed from ammonia nitrogen-containing wastewater onto granular activated carbon, and furthermore, granular activated carbon can be easily regenerated by elution of ammonium ions. Furthermore, ammonium ions in the eluate can be oxidized and decomposed into nitrogen gas by electrolyzing the eluate.
The device used to implement the present invention is very simple and the above functions can be performed within the same device, making it easy and economical to operate. It is something.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic cross-sectional views showing specific examples of the apparatus used in the present invention, FIG. 3 is a schematic cross-sectional view of the experimental apparatus used in the examples of the present invention, and FIG. Electrolysis time and residue in the experiment of Example 1
A graph showing the relationship between NH ₄ ⁺ concentration, PH, and specific conductivity. Figure 5 is a graph showing the relationship between immersion time, residual NH ₄ ⁺ concentration, and specific conductivity in the control experiment of Example 1 of the present invention. , FIG. 6 is a graph showing the relationship between elution time and ammonium ion elution amount in the experiment of Example 2 of the present invention, and FIG. 7 is a graph showing the relationship between electrolysis time and residual ammonium ion concentration and FIG. 8 is a graph showing the relationship between electrolysis time, residual ammonium ion concentration, and PH in Experimental Example 1 of the present invention, and FIG. 9 is Experimental Example 2 of the present invention. 2 is a graph showing the relationship between electrolysis time, residual ammonium ion concentration, and PH. 1... treatment tank, 2... electrolytic zone, 3... NH ₄ ⁺
Electrolytic zone, 4... Support electrode, 5... Anode, 6...
Cathode, 7... DC power supply, 8... Storage tank, 9... Waste water inflow pipe, 10... Granular activated carbon, 11... Treated water outflow pipe, 12... Exhaust pipe, 13... Inlet pipe, 14...
...Nitrogen gas exhaust pipe, 15...pump.

Claims (1)

[Claims] 1. Ammonia nitrogen-containing wastewater is passed through an electrolytic cell filled with granular activated carbon between supporting electrodes consisting of one or more pairs of anodes and cathodes, and a direct current is applied to collect ammonium ions in the activated carbon. A method for treating wastewater containing ammonia nitrogen, characterized by removing the ammonia nitrogen. 2. The method for treating ammonia nitrogen-containing wastewater according to claim 1, wherein the granular activated carbon has a particle size of about 5 mm or more and is spherical. 3. Ammonia nitrogen-containing wastewater is passed through an electrolytic cell filled with granular activated carbon between supporting electrodes consisting of one or more pairs of anodes and cathodes, and direct current is applied to adsorb ammonium ions onto the activated carbon. A method for treating ammonia nitrogen-containing wastewater, which comprises regenerating it by contacting it with an electrolyte solution. 4. The method for treating ammonia nitrogen-containing wastewater according to claim 3, wherein the granular activated carbon has a particle size of about 5 mm or more and is spherical. 5 Ammonia nitrogen-containing wastewater is passed through an electrolytic cell filled with granular activated carbon between supporting electrodes consisting of one or more pairs of anodes and cathodes, and ammonium ions are adsorbed onto the activated carbon by passing a direct current, and then the activated carbon is sorbed into chloride. A method for treating ammonia-nitrogen-containing wastewater, which comprises regenerating it by contacting it with a solution, and oxidizing and decomposing ammonium ions with chlorine generated by electrolyzing a liquid obtained by separating the activated carbon. 6. The method for treating ammonia nitrogen-containing wastewater according to claim 5, wherein the granular activated carbon has a particle size of about 5 mm or more and is spherical.