JP7618153B1 - Ammonia-containing water treatment device - Google Patents

Abstract

The present invention provides an apparatus for treating ammonia-containing water, which can efficiently and reliably remove ammonia from ammonia-containing water and allows easy maintenance of the diaphragm and the apparatus.
[Solution] The electrolytic cell 12 is provided with ammonia-containing water for electrolysis, and has a diaphragm 14 inside the electrolytic cell 12. The electrolytic cell 12 has an anode chamber 18 connected to the positive side of a DC power supply, and a cathode chamber 22 adjacent to the anode chamber 18 via the diaphragm 14. The anode chamber 18 has an anode 16, and the cathode chamber 22 has a cathode 20. The diaphragm 14 has a large number of slits which are minute water-passing holes. The slits are of a size that allows water to pass through in a laminar flow state and does not cause diffusion due to turbulence, and are of a size that allows treated water Wb from ammonia-containing water from which ammonia has been removed to pass through.
[Selected Figure] Figure 1

Description

This invention relates to a treatment device that removes ammonia from saltwater, such as seawater, that contains ammonia.

Conventionally, microorganisms have been used as a method for decomposing ammonia in seawater. Treatment using microorganisms involves oxidation to nitrate ions followed by denitrification. Both nitrification and denitrification utilize biological reactions, and therefore have the disadvantages of being slow and requiring large equipment. In addition, because biological denitrification reactions require organic matter, it is often necessary to add acetic acid or alcohol. Therefore, although methods using microorganisms are effective for treating human waste and sewage, when treating ammonia in seawater or saltwater using microorganisms, the ability of microorganisms in saltwater to decompose ammonia and other substances is low, and therefore a high purification ability for ammonia cannot be achieved. Therefore, an electrolytic treatment device has been proposed as a treatment device that efficiently removes ammonia from seawater, which electrolyzes ammonia-containing water to remove ammonia.

For example, the method disclosed in Patent Document 1 involves electrolyzing seawater to generate active chlorine, which is then used to decompose and remove _NH3 . This method has the problem that unreacted active chlorine that is not used to decompose _NH3 remains in the water, which has a detrimental effect on fish in the water. Therefore, in Patent Document 1, seawater containing active chlorine after electrolysis is supplied to an activated carbon packed bed, and the active chlorine is removed by the catalytic action of the activated carbon.

The seawater circulation device for aquaculture disclosed in Patent Document 2 is a seawater circulation device for aquaculture that circulates seawater in aquaculture tanks where fish and shellfish are cultivated, and is equipped with an electrolysis means in the circulation path for circulating the seawater, which performs processes such as decomposing ammonia in the seawater. This seawater circulation device for aquaculture also does not use microorganisms for processes such as decomposing ammonia, but instead uses electrolysis to decompose ammonia.

As disclosed in Patent Document 3, a closed circulation aquaculture system has been proposed in which seawater in a breeding tank is purified while being circulated to breed fish and shellfish in the breeding tank, and which includes an anode chamber and a cathode chamber separated by a diaphragm. This closed circulation aquaculture system includes an electrolytic cell that electrolyzes seawater supplied from the breeding tank, an aeration tank to which seawater is supplied from the anode chamber, a chlorine dissolution tank in which water is stored or passed and whose space above the water surface is connected to the space above the water surface of the aeration tank, an aeration device that sprays air from the space in the chlorine dissolution tank into the seawater in the aeration tank and into the water in the chlorine dissolution tank to aerate, a neutralization tank that neutralizes active chlorine remaining in the seawater supplied from the aeration tank with a carbonizing agent, and a mixing tank that mixes seawater supplied from the cathode chamber and seawater supplied from the neutralization tank and returns the mixture to the breeding tank.

Publication No. 2002-10724 Publication No. 2002-335811 Publication No. 2006-204235

In the case of the above-mentioned background art patent documents 1 and 2, the treatment equipment is large-scale, and ammonia is decomposed by hypochlorous acid generated on the anode side, so the efficiency of decomposition and removal of ammonia is not high relative to the total capacity of the treatment tank. In contrast, in the case of patent document 3, an anode chamber and a cathode chamber separated by a diaphragm are provided, so the efficiency of decomposition of ammonia in the anode chamber is high, but since an ion exchange membrane is used as the diaphragm, performance deteriorates due to contamination of the diaphragm over long-term use, and maintenance of the diaphragm is troublesome and costly. In addition, in the device disclosed in patent document 3, seawater is introduced into the cathode chamber and the anode chamber, and the treated water flowing out from both chambers is mixed again and circulated, so the efficiency of ammonia treatment is not high.

This invention was made in consideration of the problems in the background art described above, and aims to provide an ammonia-containing water treatment device that can efficiently and reliably remove ammonia from ammonia-containing water and that also allows easy maintenance of the diaphragm and device.

The present invention provides an ammonia-containing water treatment device comprising an electrolytic cell for electrolyzing ammonia-containing water, a diaphragm provided in the electrolytic cell, the electrolytic cell being partitioned into an anode chamber having an anode connected to the positive side of a DC power supply and a cathode chamber adjacent to the anode chamber via the diaphragm and having a cathode connected to the negative side of the DC power supply, the diaphragm having a large number of minute water-passing holes, the water-passing holes being of a size that allows water to pass through in a laminar flow state and does not cause diffusion due to turbulence with respect to the flow rate of the ammonia-containing water passing through the water-passing holes, and being of a size that allows treated water from the ammonia-containing water from which ammonia has been removed to pass through.

The water passage holes are multiple slits, and the width of the water passage holes is such that water passes through in a laminar flow state and does not cause diffusion due to turbulence.

The diaphragm is an insulating plate, and the width of the slit is 0.3 to 0.7 mm. Furthermore, the diaphragm is a synthetic resin plate, and the slits are formed parallel to each other from one side edge of the synthetic resin plate toward the other side edge, and are provided at a predetermined distance from the other side edge, and the width of the slits is preferably 0.4 to 0.6 mm.

The synthetic resin plate has a thickness of 5 to 6 mm, and the slits are formed parallel to each other from one side edge of the synthetic resin plate to the other side edge, and are of a width that allows water to pass through in a laminar flow state and does not cause diffusion due to turbulence.

The ammonia-containing water treatment device of the present invention can efficiently and reliably remove ammonia from ammonia-containing water, and the cleaning of the diaphragm and other maintenance of the device are easy, enabling efficient removal of ammonia at low cost.

1 is a conceptual diagram of an ammonia-containing water treatment device according to an embodiment of the present invention. 3A is a plan view, FIG. 3B is a front view, and FIG. 3C is a bottom view of a diaphragm of the treatment device for ammonia-containing water of this embodiment.

Below, an embodiment of the present invention will be described with reference to the drawings. Figs. 1 and 2 show one embodiment of the present invention, in which an ammonia-containing water treatment device 10 of this embodiment is provided with an electrolytic cell 12 that electrolyzes the water to be treated Wa, which is ammonia-containing water. The water to be treated Wa, which is ammonia-containing water, is salt water such as seawater used for land-based aquaculture of saltwater fish. In particular, it is seawater discharged or circulating water for land-based aquaculture that circulates seawater.

First, the treatment of ammonia will be described using wastewater treatment related to land-based aquaculture of saltwater fish as an example. In fish farming, if ammonia discharged from farmed fish accumulates in the farm tank, it will have a negative effect on the habitat of the fish, so the treatment of ammonia is important in land-based aquaculture that uses recycled seawater. The mechanism of ammonia removal in the present invention utilizes the reaction between hypochlorite ions and ammonium ions generated by electrolysis of seawater using an electrolytic cell. The reaction at the anode in the electrolytic cell of the present invention is as shown in the following formula (1).
Cl ^- +H ₂ O → ClO ^- + 2H ⁺ + 2e ^- (1)
The ammonia removal reaction is shown in the following formula (2).
2NH ₄ ⁺ +3ClO ^- → N ₂ ↑+3Cl ^- +3H ₂ O+2H ⁺ (2)
These reactions have the advantages of being fast, requiring small equipment, and allowing the amount of ammonia removed to be easily controlled by the amount of electricity.

Next, the ammonia-containing water treatment device 10 will be described with reference to Figures 1 and 2. The treatment device 10 includes an electrolytic cell 12 in which water to be treated Wa, which is ammonia-containing water, is charged and electrolyzed, and a diaphragm 14 is provided in the electrolytic cell 12. The electrolytic cell 12 is partitioned into an anode chamber 18 in which an anode 16 connected to the positive side of a DC power supply (not shown) is provided, and a cathode chamber 22 in which a cathode 20 is provided adjacent to the anode chamber 18 via the diaphragm 14 and connected to the negative side of a DC power supply (not shown). Above the cathode chamber 22, a drain outlet 26 is formed for the treated water Wb from which ammonia has been removed.

The diaphragm 14 has a large number of tiny slits 24 formed therein. The slits 24 are of a width that allows water to pass through in a laminar flow state and does not cause diffusion due to turbulence, and are of a size that allows treated water Wb, from which ammonia has been removed, to pass through in a laminar flow state.

Specifically, the capacity of the anode chamber 18 and the cathode chamber 22 is, for example, 300 mL each. The electrodes used are a platinum-plated titanium plate for the anode 16 and a stainless steel wire for the cathode 20. As shown in FIG. 2, a synthetic resin plate such as an acrylic plate with slits 24 formed therein is used for the diaphragm 14. The synthetic resin plate has a thickness of 5 to 6 mm, for example 5 mm, and the width of the slits 24 is 0.3 to 0.7 mm, preferably 0.4 to 0.6 mm, for example 0.5 mm. The spacing between the slits 24 is 4 to 6 mm, for example 5 mm.

Next, the function of the ammonia-containing water treatment device 10 of this embodiment will be described below. Water to be treated Wa, which is ammonia-containing water from aquaculture ponds or the like, flows into the anode chamber 18 of the electrolytic cell 12. The water to be treated Wa passes through the slit 24 of the diaphragm 14 and moves to the cathode chamber 22. Here, since the electrolytic cell 12 is divided into the anode chamber 18 and the cathode chamber 22 by the diaphragm 14, ClO 2 ⁻ generated at the anode 16 can be efficiently contacted with ammonium ions in the water to be treated Wa, which is raw water. Furthermore, when the flow rate passing through the slit 24 is, for example, 75 mL/min in the example described below, the water to be treated Wa passing through the slit 24 can pass only in a laminar flow state, and the water in the anode chamber 18 and the water in the cathode chamber 22 do not mix due to turbulent diffusion. As a result, the treated water Wa from which ammonia has been effectively removed by the above reaction in the anode chamber 18 passes through the slits 24 in the diaphragm 14 as treated water Wb and is discharged from the discharge port 26 of the cathode chamber 22.

The reason for using a plate with slits 24 as the diaphragm 14 is that, unlike porous diaphragms such as ceramic plates, the slits have a width of 0.5 mm, so the diaphragm 14 does not block the space between the anode chamber 18 and the cathode chamber 22, the diaphragm 14 is easy to clean, and further electrolysis is possible while the treated water Wb passes through the slits 14. In addition, even if the diaphragm 14 is not a porous plate or other plate with fine holes, the plate with the slits 24 formed has a thickness, so turbulent diffusion is suppressed and the liquids in the anode chamber 18 and the cathode chamber 22 do not mix, and it can function as a diaphragm.

According to the ammonia-containing water treatment device 10 of this embodiment, ammonia can be efficiently and reliably removed from the ammonia-containing water to be treated Wa, cleaning of the diaphragm 14 and other maintenance of the device are easy, the durability of the diaphragm can be made high, and efficient ammonia removal is possible at low cost. As a result, ammonia can be efficiently and continuously removed from seawater or salt water in a circulating aquaculture tank, and the device can be effectively used for fish and shellfish farming, etc. In addition, the diaphragm 14 having the slits 24 can be easily and efficiently manufactured by, for example, laser processing of a synthetic resin plate.

The ammonia-containing water treatment device of this invention is not limited to the above embodiment, and the size of the water tank and diaphragm of the electrolytic cell, the size and material of the electrodes, etc. can be changed as appropriate. The water passage holes of the diaphragm may be through-holes other than slits, and the diameter and width can be set as appropriate, as long as the size and thickness of the diaphragm do not allow the water to be treated to pass through or diffuse in a turbulent state.

Next, an experimental example using the treatment method of the treatment apparatus 10 for ammonia-containing water will be described.
[Experimental Result 1]
Ammonia nitrogen (ammonium ion) concentration in seawater: 1.0 mg-N/L
Flow rate 75mL/min (residence time: 4 minutes for each tank)
Current 20mA (constant current operation)
When an experiment was carried out using the same electrolytic cell under the above conditions, the following results were obtained.
[When the diaphragm of the present invention is present in the electrolytic cell]
Treated water ammonium ion concentration: 0.50 mg-N/L
Voltage 2.8V (power consumption 56mW)
[If the electrolytic cell does not have a diaphragm]
Treated water ammonium ion concentration: 0.80 mg-N/L
Voltage 2.6V (power consumption 52mW)

From the above experimental result 1, it was confirmed that in the case of the treatment device equipped with the diaphragm of the present invention, the ammonium ion concentration in the seawater to be treated was 1.0 mg/L, while the ammonium ion concentration in the treated water was 0.50 mg/L, which was a significant reduction in ammonium ions compared to the ammonium ion concentration of 0.80 mg/L in the treated water without the diaphragm.

[Experimental Result 2]
Ammonium ion concentration in seawater: 1.0 mg/-NL
Flow rate 75 mL/min (residence time: 4 minutes for each tank)
Current 30mA (constant current operation)
[When the diaphragm of the present invention is present in the electrolytic cell]
Treated water ammonium ion concentration: 0.02 mg-N/L
Voltage 3.3 V (power consumption 99 mW)

Since it was confirmed from the above Experimental Result 1 that the ammonium ion concentration of the treated water can be significantly reduced when a diaphragm is present, a similar experiment was performed with the current value increased from 20 mA in Experiment 1 to 30 mA, and it was confirmed that the ammonium ion concentration can be significantly reduced further. However, if the current value is increased and electrolysis proceeds too far, excess ClO ^- remains, which has an adverse effect on the farmed fish, so it can be said that it is preferable to reduce the ammonium ion concentration to the level of the above Experimental Result 2.

Reference Signs List 10: Apparatus for treating ammonia-containing water 12: Electrolytic cell 14: Diaphragm 16: Anode 18: Anode chamber 20: Cathode 22: Cathode chamber 24: Slit 26: Drain Wa: Water to be treated Wb: Treated water

Claims (5)

The electrolytic cell is provided with an electrolytic cell in which ammonia-containing water is charged and subjected to electrolysis, a diaphragm is provided in the electrolytic cell, and the electrolytic cell is partitioned into an anode chamber in which an anode connected to a positive side of a DC power supply is provided, and a cathode chamber adjacent to the anode chamber via the diaphragm and in which a cathode connected to the negative side of the DC power supply is provided,
The diaphragm is formed with a large number of minute water passage holes, and the water passage holes are of a size that allows water to pass through in a laminar flow state and does not cause diffusion due to turbulence with respect to the flow rate of the ammonia-containing water passing through the water passage holes, and is of a size that allows treated water from the ammonia-containing water from which ammonia has been removed to pass through. The apparatus for treating ammonia-containing water according to claim 1, wherein the water passage holes are a plurality of slits, and the width of the water passage holes is such that water passes through in a laminar flow state and does not diffuse due to turbulence. The ammonia-containing water treatment device according to claim 2, wherein the diaphragm is an insulating plate and the width of the slit is 0.3 to 0.7 mm. The ammonia-containing water treatment device according to claim 3, wherein the diaphragm is a synthetic resin plate, the slits are formed parallel to each other from one side edge of the synthetic resin plate toward the other side edge, and are provided at a predetermined distance from the other side edge, and the width of the slits is 0.4 to 0.6 mm. The ammonia-containing water treatment device according to claim 3, wherein the synthetic resin plate has a thickness of 5 to 6 mm, the slits are formed parallel to each other from one side edge of the synthetic resin plate toward the other side edge, and have a width that allows water to pass in a laminar flow state and does not cause diffusion due to turbulence.

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