JP2006035158A5 - - Google Patents

Description

That is, the gist of the present invention is as follows.
(1) In a water treatment method of denitrifying water using hydrogen generated by electrolysis of water and denitrifying bacteria, a solid polymer as a hydrogen generating source together with a biological reaction tank charged with a denitrifying bacteria immobilized carrier Using a water electrolysis device using an electrolyte membrane electrode (hereinafter sometimes referred to as “SPE water electrolysis device”), electrolyzing the anode water on the anode side of the SPE water electrolysis device, and subjecting the water to be treated to SPE water electrolysis A water treatment method comprising passing water through a biological reaction tank through a cathode side of the apparatus.
(2) The treated water is treated by flowing the treated water from the cathode side of the SPE water electrolysis apparatus through the liquid pipe to the biological reaction tank charged with the denitrifying bacteria-immobilized carrier. Water treatment method.
(3) Electrolysis of the anode water on the anode side of the SPE water electrolysis apparatus, supply of the generated hydrogen into the water to be treated on the cathode side, and removal of the water to be treated in the biological reaction tank charged with the denitrifying bacteria-immobilized carrier. The water treatment method according to (1) or (2), wherein a nitrogen reaction is performed.
(4) depending on the quality of the water to be treated, by injecting a chemical solution for pH adjustment, and performing denitrification while supplying hydrogen ions to the water to be treated, to the (1) to ( The water treatment method according to any one of 3) .
(5) The water treatment method according to any one of (1) to (4) above, wherein the pH of the water to be treated in the biological reaction tank is 6 to 9.
(6) A biological reaction tank charged with a denitrifying carrier-immobilized carrier, a water electrolysis apparatus (SPE water electrolysis apparatus) using a solid polymer electrolyte membrane electrode as a hydrogen generation source, a bioreaction tank and an SPE water electrolysis apparatus A water treatment apparatus having a liquid pipe connecting the cathode side and a liquid flow pump to be treated as essential components, and allowing the water to be treated to flow from the cathode side of the SPE water electrolysis apparatus to the biological reaction tank. .
(7) The water treatment apparatus according to (6) , further comprising a pH adjusting device connected to the liquid pipe.

In conventional water treatment equipment using electrolysis, the cathode and anode are immersed in the water to be treated for electrolysis, so it is inevitable that dissolved oxygen generated at the anode is mixed into the water to be treated. Dissolved oxygen was an impediment to the denitrification reaction. On the other hand, in the present invention, the SPE film electrode itself is an electrode and at the same time a partition, and is structured to separate the anode chamber and the cathode chamber of the electrolysis tank. Even if the electrochemical reaction of water proceeds independently and oxygen is generated in the anode chamber, dissolved oxygen is not mixed into the water to be treated, and there is no adverse effect on the denitrification reaction. The reaction by denitrifying bacteria can be performed efficiently.

The denitrification reaction proceeds sequentially according to the following reaction formulas (1) and (2) under anaerobic conditions, and nitrate nitrogen is once reduced to nitrite nitrogen and then reduced to nitrogen gas. And detoxified.
2NO ₃ ⁻ + 2H ₂ → 2NO ₂ ⁻ + 2H ₂ O
(1)
^{_{2NO 2 - + 3H 2 + 2H}} + → N 2 + 4H 2 O
(2)
From the above reaction formulas (1) and (2), the overall denitrification reaction formula is the following reaction formula (3).
2NO ₃ ⁻ + 5H ₂ + 2H ⁺ → N ₂ + 6H ₂ O
(3)

The SPE electrolytic cell 100 shown in FIG. 2 is a monopolar cell type, and an SPE film electrode in which an anode 6 and a cathode 7 are joined to an SPE film 5 is sandwiched between an anode power supply 8, a cathode power supply 9 and a support base 10. It has a structure. The support base 10 and the power feeders 8 and 9 are provided with flow paths 11 and 12, respectively, so that the anode water and the cathode water are in contact with the SPE membrane electrode and can pass water. , 9 are in the form of slits in the flow path portion in contact with the electrodes 6, 7. The number of slits and the cross-sectional area of the cathode power supply 9 are determined so as to obtain a predetermined water flow rate from the flow rate and current density of the water to be treated. The water to be treated flows into the SPE electrolytic cell 100 from the inlet 4, receives supply of hydrogen while contacting the cathode 7 , and flows out from the outlet 3. Similarly, the anode water flows into the SPE electrolytic cell 100 from the inlet 2 and flows out from the outlet 1, but the number of slits and the cross-sectional area of the anode feeder 8 can flow out without retention of anode water and generated gas. Anything is acceptable. In a bipolar electrode type SPE electrolytic cell, a single feeder having slits on both sides is in contact with the SPE membrane electrode on both sides in the form of serving as both an anode feeder and a cathode feeder, thereby providing a plurality of SPE membrane electrodes. It becomes the structure piled up in series.

In this SPE water electrolysis, unlike a normal electrolysis tank using an electrode plate, the SPE film electrode itself is an electrode and at the same time a partition, and has a structure in which the anode chamber and the cathode chamber of the electrolysis tank are separated . For this reason, during the electrolysis, the electrochemical reaction of water proceeds independently in each electrode chamber. In the denitrification reaction using denitrifying bacteria, dissolved oxygen in water becomes an inhibiting factor, but when hydrogen is supplied by the SPE water electrolyzer, even if oxygen is generated in the anode chamber, it does not have any effect. .

The SPE water electrolyzer 100 includes an SPE membrane electrode that is a joined body of the electrode and the membrane, power feeders 8 and 9 for feeding power to the electrode, and a support base 10. When a voltage is applied to the SPE film electrode through the feeders 8 and 9, an electrochemical reaction proceeds at the interface between the electrodes 6 and 7 and the SPE film 5, and water is decomposed at the anode 6 according to the following reaction formula (4). Oxygen is generated and released into water through a minute gap in the anode 6.
H ₂ O → _1/2 O ₂ + 2H ⁺ + 2e ⁻
(4)
(4) produced hydrogen ions (H + ^· xH 2 _O) by equation moves to the cathode through the ion-exchange groups in the membrane, recombine with electrons, follow the following reaction formula (5), hydrogen It is generated as a gas (molecular hydrogen) and is similarly released into water through a minute gap in the cathode.
2H ⁺ + 2e ⁻ → H ₂
(5)

According to the above reaction formulas (4) and (5) , the SPE film electrode becomes strongly acidic by electrolysis. Therefore, acid resistance is required as a material to be used as an electrode, and from the point of catalytic activity, platinum group metals and These alloys and oxides are used. For the cathode 7, for example, Pt, Pt—Pd, Ir—Pt or the like is used, and for the anode 6, for example, insoluble Ir, Ir—Ru, Ir—Pt or the like is used. In addition to supplying power to the electrodes, the feeders 8 and 9 have a role of water and gas flow paths, and in the case of a bipolar tank, the partition between adjacent bipolar chambers and the role of electron conduction. As a material used for the power feeding bodies 8 and 9, good electrical conductivity and corrosion resistance against an electrolytic atmosphere are required. For example, Pt-plated Ti, Ti, Nb, Ti—Pd, C, or the like is used.

Further, as can be seen from the above reaction formula (5) , on the cathode surface 7, only a reaction in which hydrogen ions carried from the anode 6 through the SPE film 5 receive electrons to become hydrogen occurs, and a by-product is generated. The hydroxide ions are not generated, and the metal salt does not adhere to the cathode as a scale even when energized for a long period of time. Therefore, it is not necessary to switch the polarity in order to clean the electrode, and the electrode life is prolonged, so that the operation management is simplified and the operation management cost can be reduced.

According to the above reaction formula (5) , a small hydrogen bubble (molecular hydrogen) having a diameter of several tens of μm is generated by energization . If the consumption or dissipation of hydrogen does not occur, the existence probability of each increases, so that the minute hydrogen bubbles repeatedly collide with other generated hydrogen bubbles and grow into bubbles having a larger diameter. As the diameter of hydrogen bubbles increases, the hydrogen dissolution efficiency decreases, and hydrogen bubbles are released from the water to be treated, leading to a decrease in hydrogen utilization efficiency. It is desirable to diffuse hydrogen into water in as short a time as possible.

In order to achieve this object, the SPE water electrolysis apparatus 200 used in the present invention sufficiently treats minute hydrogen bubbles generated by energization of the water to be treated on the cathode surface 7 of the SPE electrode tank 100. The amount is preferably such that it can be dissolved in the solution. Such a water flow amount is determined as an appropriate value according to the current density at the required energization amount .

In addition, since the reaction of the above reaction formula (4) proceeds at the anode of the SPE electrode tank, if a large amount of cations such as calcium ions are present in the anode water, this will hinder the movement of hydrogen ions, resulting in a long-term operation. In addition, the hydrogen generation efficiency may be reduced. Therefore, it is preferable to use pure water or water close to it as the anode water, and ion exchange water, purified water, distilled water, and the like are suitable. Further, when using tap water, it is better that the hardness is low, and periodic acid cleaning of the anode with sulfuric acid or the like is required.

In the water treatment apparatus of the present invention, the hydrogen utilization efficiency in the above reaction formula (3) is excellent, so the dissolved hydrogen concentration in the liquid of the biological reaction tank 25 is about 0.01 mg / L, and hydrogen into the gas phase There is very little outgassing. For this reason, the hydrogen concentration in the gas phase is about 1%, and does not reach the explosion lower limit of 4%. Therefore, as with normal electrolyzed water generators, there is no danger of explosion due to hydrogen gas. There is no need for an explosion-proof structure.

Further, from the above reaction formula (3) , as the denitrification reaction proceeds, the denitrifying bacteria consume hydrogen ions in the water, so that the pH in the biological reaction tank 25 increases. The activity of denitrifying bacteria is affected by pH, and the activity is highest near pH 7.5, and the activity decreases under high pH conditions of 8 or more. Further, when the pH is high, metal ions such as calcium ions and magnesium ions are deposited on the surface and inside of the denitrifying bacteria-immobilized carrier, reducing the contact efficiency between the denitrifying bacteria and the water to be treated, and inhibiting the denitrification reaction. Therefore, when the nitrate nitrogen concentration of the water to be treated is high or the pH is high, hydrogen ions are supplied from the outside to adjust the pH as necessary to promote the denitrification reaction. There is a need.

Due to the characteristics of the denitrification reaction, in the water treatment method of the present invention in which water is denitrified using denitrifying bacteria, an appropriate amount of a pH adjusting chemical solution is injected by a pH adjusting device according to the quality of the water to be treated. Thus, denitrification is performed while supplying hydrogen ions to the water to be treated. PH is preferably from 6 to 9 of the water to be treated in the bioreactor, PH6.8～8.0 is optimal. A strong acid such as sulfuric acid or hydrochloric acid is suitable as the chemical solution used for pH adjustment, and it is appropriately diluted according to the quality of the water to be treated, and the injection rate is determined.

When pH adjustment of to-be-processed water is performed, as shown in FIG. 1, a pH adjustment apparatus is installed in the middle of liquid piping. The pH adjusting device includes a pH measuring electrode 28, a pH meter 29, a chemical injection pump 30, and a chemical liquid tank 31. The pH of the water to be treated is adjusted such that the chemical injection pump 30 is ON / OFF controlled by the pH measuring electrode 28 and the pH meter 29 so that the pH in the biological reaction tank 25 becomes a predetermined value, dilute sulfuric acid or the like. The pH adjusting chemical solution is intermittently injected into the water to be treated from the inlet 32. The pH in the biological reaction tank 25 is preferably 6-9, in which hydrogen ions can sufficiently contribute to the denitrification reaction, and the activity of denitrifying bacteria is relatively high, and pH 6.8-8.0 is optimal. .

A preliminary test was performed using the SPE electrolytic cell 100 shown in FIG. 2, and an overall hydrogen transfer capacity coefficient was determined in order to see how hydrogen generated by electrolysis of water moves to the water phase on the cathode side.
The dissolution rate of hydrogen in the liquid is expressed by the following equation (10) when it is assumed that the hydrogen gas is dissolved only from hydrogen gas bubbles in the liquid.

dC / dt = KLa × (Cs−C)
(6)
Here, C is the dissolved hydrogen concentration, Cs is the saturated dissolved hydrogen concentration, t is the time, and KLa is the overall hydrogen transfer capacity coefficient. If the saturated dissolved hydrogen concentration Cs is constant, the hydrogen dissolution rate is determined by the dissolved hydrogen concentration C and the overall hydrogen transfer capacity coefficient KLa. That is, using the SPE electrolyzer 100 of FIG. 2, the water concentration in the liquid in each case is varied by varying the water flow rate on the cathode side under the condition of a constant energization amount, that is, a constant hydrogen generation amount. By measuring, the overall hydrogen transfer capacity coefficient KLa in each case can be obtained from Equation (6) .

Claims (7)

  In a water treatment method for denitrifying water using hydrogen and denitrifying bacteria generated by electrolysis of water, a solid polymer electrolyte membrane electrode as a hydrogen generation source together with a biological reaction tank charged with a denitrifying bacteria immobilization support A water electrolysis apparatus using water is used, and water to be treated is passed through a biological reaction tank through the cathode side of the water electrolysis apparatus while electrolyzing anode water on the anode side of the water electrolysis apparatus. Water treatment method.   The water to be treated is treated by flowing it through a liquid piping from a cathode side of a water electrolysis apparatus using a solid polymer electrolyte membrane electrode to a biological reaction tank charged with a denitrifying bacteria-immobilized support. Item 2. The water treatment method according to Item 1.   In a biological reaction tank that electrolyzes anode water on the anode side of a water electrolyzer using a solid polymer electrolyte membrane electrode, supplies the generated hydrogen to the water to be treated on the cathode side, and is loaded with a denitrifying bacteria immobilization support The water treatment method according to claim 1 or 2, wherein a denitrification reaction of water to be treated is performed. Depending on the quality of the water to be treated, by injecting a chemical solution for pH adjustment, and performing denitrification while supplying hydrogen ions to the water to be treated, in any one of claims 1 to 3 The water treatment method as described. The water treatment method according to any one of claims 1 to 4 , wherein the pH of the water to be treated in the biological reaction tank is 6 to 9.   A biological reaction tank charged with a denitrifying carrier-immobilized carrier, a water electrolysis apparatus using a solid polymer electrolyte membrane electrode as a hydrogen generation source, a liquid pipe connecting the biological reaction tank and the cathode side of the water electrolysis apparatus, A water treatment apparatus comprising a treatment liquid water pump as an essential component, and flowing treated water from a cathode side of an SPE water electrolysis apparatus to a biological reaction tank. The water treatment apparatus according to claim 6 , further comprising a pH adjusting device connected to the liquid pipe.