JP7391366B2 - Contaminated water purification method and device for removing phosphate ions and nitrate ions - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies Date: June 25, 2019 Name of meeting: 21st Japan Water Award 2019 Japan Stockholm Youth Water Award Award Ceremony/Award Activities Presentation Venue: Miraikan (Miraikan) (Koto-ku, Tokyo) [Publications] Date of publication: June 25, 2019 Name of publication: 21st Japan Water Award Award-Winning Activities Collection Location: Pages 86 to 91

The present invention removes and recovers phosphate ions in water by precipitating them with iron ions eluted from the iron negative electrode of an iron-carbon battery, and generates hydrogen by electrolysis of water using the electric power obtained from the iron-carbon battery. The present invention relates to a method for purifying polluted water such as eutrophic lakes and marshes, and an apparatus for purifying contaminated water such as eutrophic lakes, which simultaneously reduces and removes nitrate ions in the water using hydrogen.

Severe eutrophication of water is occurring in many lakes around the world. Blue-green algae phenomena are often seen throughout the lake, and in developing countries in particular, the destruction of ecosystems and the impact on human life and health are serious, and it can sometimes be difficult to secure safe water. Substances that cause eutrophication are nutrient salts such as nitrogen and phosphorus, which are emitted from all aspects of human life, including factories, domestic wastewater, and agriculture. On the other hand, although there is concern that phosphorus is a depletable resource, no system has been established to recover and reuse it.

In order to deal with eutrophication, which has become a serious problem in closed water bodies such as lakes, there is an increasing need to remove phosphorus and nitrogen from various types of wastewater. Treatment methods have been proposed. Generally, the pH of these wastewaters is about 3 to 10. When focusing on phosphorus and nitrogen oxides represented by nitric acid and nitrous acid among nitrogen compounds, conventional methods for removing these can be classified as follows.

(1) Conventional method for removing phosphorus from water
(1-A) Biological phosphorus removal treatment method As a biological phosphorus removal treatment method, the phosphorus over-uptake function of microorganisms is used to incorporate phosphorus into the bacterial cells, and the bacterial cells are separated from the treated water. There is a method to do so (Non-Patent Document 1). This method has the problem that stable treatment is difficult because the reaction of excessive phosphorus uptake by microorganisms is greatly affected by the BOD value in the water to be treated and the anaerobic degree in the reaction tank. Furthermore, since there is a limit to the amount of phosphorus that can be taken into the microbial cells, there is a limit to the amount of phosphorus that can be removed with a given amount of microorganisms. Furthermore, since these microorganisms re-release the phosphorus they have taken in due to changes in conditions such as the surrounding oxygen concentration, it is necessary to handle the sludge in a way that prevents the microorganisms (sludge) from re-releasing the phosphorus. Depending on conditions such as the processing capacity of sludge treatment equipment, phosphorus re-released from sludge may return to the treated water system (Non-Patent Document 2).

(1-B) Physicochemical phosphorus removal method As a physicochemical phosphorus removal method, (a) Treatment is performed by adding an aluminum-based or iron-based flocculant such as polyaluminum chloride or ferric chloride to the treated water. (b) a phosphate method in which phosphorus in the treated water is reacted with calcium ions or ammonium-magnesium ions to produce sparingly soluble calcium phosphate or ammonium magnesium phosphate; and (c) a phosphate method in which phosphorus in the treated water is reacted with calcium ions or ammonium-magnesium ions. There is an iron phosphate method in which iron phosphate, which is a sparsely soluble salt, is formed by the action of iron ions eluted from iron, and this is separated by precipitation.

Problem (a) is that the coagulant used is expensive as a chemical and is therefore not economical.The coagulated precipitate becomes a mixture with other coexisting inorganic and organic solids, and the phosphorus There is a problem that recovery and reuse is difficult (Non-Patent Document 3). Furthermore, there is a problem in that ions and components other than iron ions and aluminum ions are also added to the water. In other words, as iron salts and aluminum salts are added to the water to be treated, counter ions such as chloride ions and sulfate ions that combine with iron or aluminum ions to form iron or aluminum salts are also added to the water to be treated. There is a problem that the chloride ion concentration and sulfate ion concentration in the water to be treated increase, causing an adverse effect on the ecosystem (Non-Patent Document 4). Therefore, there is a need for an efficient phosphorus removal method that does not require adding unnecessary ions or components to water and can quickly remove phosphorus from water.

(b) is that in order to precipitate poorly soluble salts such as calcium phosphate or ammonium magnesium phosphate, the pH must be raised to make it alkaline; calcium salts, ammonium salts, magnesium salts, etc. There is a problem that it is not economical because it requires the addition of several drugs (Non-patent Documents 5 to 10).

(c) utilizes a mechanism in which iron and dissolved oxygen are combined to form a local concentration cell and iron ions are eluted, so aeration is required to advance the reaction. However, there is a problem in that power equipment and operating costs are required for this aeration. When the dissolved oxygen concentration in water increases due to aeration, a problem arises in that nitrogen oxides such as nitrate ions are difficult to remove. Furthermore, since the rate of dissolution is very low at the level of the electromotive force generated by the local concentration cell of iron and dissolved oxygen near neutrality, there is also the problem that sufficient phosphorus removal efficiency cannot be obtained.

(2) Conventional methods for removing nitrogen oxides such as nitric acid and nitrite
Although there are various methods for removing nitrogen oxides from water, it is ultimately preferable to treat the water as nitrogen gas through denitrification.

(2-A) Biological denitrification treatment method A biological denitrification treatment method is generally used to treat nitrogen oxides in water as nitrogen gas. The main methods are (a) biological nitrification and denitrification method (Non-Patent Document 11), in which denitrifying bacteria reduce nitrate ions using organic matter and electron donors such as hydrogen under anaerobic conditions; ) There is an ANAMMOX method (anaerobic ammonium oxidation, Non-Patent Document 12) in which ammonia is partially nitrified to become nitrite, and the mixed state of ammonia and nitrite is reduced to nitrogen by ANAMMOX bacteria.

In order to achieve a high nitrogen removal rate in (a), it is necessary to limit the chemical environment conditions for bacteria growth, such as pH and dissolved oxygen, to conditions suitable for bacterial growth, and to also remove the chemical substances from outside the reaction system, such as methanol. It is necessary to add organic substances and electron donors such as hydrogen, making it difficult to control reaction conditions and increasing drug costs. Furthermore, since the reaction rate of the biological denitrification reaction is low, in order to perform a satisfactory treatment, it is necessary to increase the volume of the reaction tank to ensure sufficient reaction time.

The problem with (b) is that ANAMMOX bacteria are not easily available, and the growth rate and reaction rate of these bacteria are low. Furthermore, during treatment, it is necessary to partially nitrify ammonia to produce nitrous acid, creating a mixture of ammonia and nitrite in a ratio of approximately 6:4. Moreover, it is quite difficult to implement with strict control. Furthermore, if the concentration of organic matter in the water to be treated is high, there is a problem that the reduction of the mixture of ammonia and nitrite to nitrogen does not proceed sufficiently.

(2-B) Physicochemical nitrogen removal methods Physicochemical nitrogen removal methods are particularly suitable for water purification treatment, and methods that have been put into practical use include the ion exchange method, electrodialysis method, and reverse osmosis membrane method. There are ``catalytic methods'' and ``electrolysis methods'' that are in the research stage. Each of the physicochemical methods that have been put into practical use has the advantage of being fast and relatively easy to maintain and manage, but in principle they are separation techniques for dissolved salts and selective treatment of nitrate ions. It is difficult to do so, and there is also the problem of discharging high salt concentration waste liquid. In reality, many treatment facilities often discharge or discharge waste liquid directly or diluted into the ocean, sewers, or fields (Non-Patent Document 13). Therefore, it can be seen as an excellent treatment method from the perspective of water use, but as mentioned above, it is not positioned as a fundamental treatment technology from the perspective of preserving the natural environment and realizing a sustainable society. do not have. The outline of each physicochemical method is as follows.

(a) Ion exchange method The ion exchange method is a method of separating and removing nitrate ions by exchanging chloride ions and nitrate ions with a strongly basic anion exchange resin, and there are many reported examples (Non-patent Document 14) , 15). The nitrate ion selectivity of anion exchange resins varies depending on the presence or absence of other anion species and their concentrations, and sulfate ions are more selective than nitrate ions and pose a problem in environmental water. Since sulfate ions normally exist in groundwater at a concentration equal to or higher than that of nitrate ions, sulfate ions in groundwater greatly affect the treatment performance of the ion exchange method. Moreover, the regeneration process of the ion exchange resin becomes a factor that greatly increases the processing cost. Electrodialysis is a method in which cation exchange membranes and anion exchange membranes are alternately arranged between an anode and a cathode and a direct current is applied to concentrate and desalt a solution (Non-Patent Document 16) . In this method, scaling on the cathode and increased electrical resistance due to desalination are factors that reduce processing efficiency, and countermeasures such as sulfuric acid injection and polarity conversion complicate processing operations.

(b) Reverse osmosis method Reverse osmosis membrane method is a technology often used for desalination of seawater, which removes dissolved salts by mechanically applying pressure higher than osmotic pressure to the solution through a semipermeable membrane. This is a method to extract water that is not present. Therefore, when focusing on the treatment of nitrate nitrogen, the problem is that the selectivity is low and the cost of the secondary treatment becomes extremely high.

(c) Catalytic method The catalytic method is a method of reducing nitrate ions to nitrogen gas by reacting them with dissolved hydrogen via a metal catalyst such as palladium or copper, and the treatment can be carried out at room temperature and pressure. This treatment technology is the only physicochemical method that converts nitrate nitrogen into nitrogen gas, and it is thought that it can be an extremely superior technology without problems with waste liquid or sludge. However, at present, there are still many issues that need to be considered, such as accumulation of ammonia nitrogen and deterioration of the catalyst (Non-Patent Document 17).

(d) Electrolysis method Electrolysis method converts nitrate nitrogen into nitrogen gas using hypochlorous acid produced by electrolyzing chloride ions using electrode materials and electrode structures with excellent catalytic activity for nitrate ion reduction. Since it is converted and released into the atmosphere, it has little impact on the environment, and denitrification can be performed without adding organic carbon sources. Since this method applies electrolysis, it can be miniaturized, does not require management or replenishment of organic sources, and can handle fluctuations in processing capacity due to load fluctuations or temperature changes, making the system easy to maintain and manage. It has advantages. Furthermore, it is particularly effective for raw water with a BOD/N ratio of 1 or less. However, since the cost of electricity used for electrolysis and the catalyst used are expensive, the cost is enormous, and since chloride ions are required, there is a problem that the effect is low in freshwater areas.

(3) Attempt to simultaneously remove phosphoric acid and nitrate ions Simultaneous removal of nitrogen and phosphorus is essential for maintaining the normal aquatic ecosystem, but simultaneous removal is also necessary from the perspective of wastewater treatment technology. Required. At present, environmental standards and wastewater standards for nitrogen and phosphorus have been established for lake basins, and studies are also underway for marine areas, so even if limiting factors for nutrients differ depending on the target water area, advanced treatment Measures should be taken to reduce both carbon and phosphorus.

(3-A) Biological nitrogen and phosphorus simultaneous removal Biological methods are common as methods for simultaneously removing nitrogen and phosphorus, and representative methods include activated sludge method, oxidation ditch method, There are biofilm methods, self-granulation methods, comprehensive immobilization methods, aquatic plant remediation methods, and soil remediation methods, but removal using microorganisms has a large effect on the BOD value of the water to be treated and the anaerobic degree in the reaction tank. There is a problem that stable processing is difficult because of the Another problem is the treatment of organic matter such as sludge and plants produced from nitrogen and phosphorus.

(3-B) Physicochemical simultaneous removal of nitrogen and phosphorus There are almost no methods for simultaneously removing nitrogen and phosphorus that can be achieved using only physicochemical methods, and (1-A) or (2-A) and (1 -B) or a combination with (2-B), that is, a biological method is incorporated somewhere in the system. Therefore, similar to (3-A), stable treatment is difficult and treatment of organic matter such as sludge and plants produced from nitrogen and phosphorus becomes a problem.

Under such circumstances, cases have been reported in which nitrogen and phosphorus were simultaneously removed using electrolytic reactions. The removal of phosphorus is based on the precipitation reaction of Formula 1, which uses an aluminum or iron-based electrode as the cathode material and a reaction between Al ³⁺ or Fe ³⁺ eluted from the cathode material and phosphate ions (Non-Patent Document 18).

Nitrogen removal is based on a reduction reaction represented by Formula 2 shown below (Non-Patent Document 19).

By performing electrolysis using an iron electrode, the iron phosphate method of (1-B) (c) is carried out by the iron ions eluted from the iron electrode, and the electrolysis method of (2-B) (d) is simultaneously carried out. Although it is a wonderful method that combines the advantages of each method, the problems of each method remain.

Tetsuro Fukase et al., "Basic study on the mechanism of biological phosphorus removal," Water Pollution Research, 5(6), 309-317 (1982). Marais G.V.R., Loewenthal R.E. and Siebritz L.: "Observation supporting phosphate removal by biological excess uptake.", JAWRP post conference seminar on phosphate removal in biological treatment process(1982). E.P.A.: "Process Design Manual for Phosphorus Removal", Water Pollution Control Research Series. Edited by the Environmental Equipment Utilization Encyclopedia Editorial Committee: "Techniques and Equipment for Water Pollution Prevention", published by the Industrial Research Group (1988). "Advanced Treatment Design Manual (Draft)", Sewage Works Association, (1994). Nobuhiro Shimizu et al.: "Removal of phosphorus from wastewater from food manufacturing industry - Example of wastewater treatment in red bean paste manufacturing industry" Fukuoka Prefecture Health and Environment Research Institute Annual Report No. 28, 101-104, (2001) Isao Joko: "Phosphorus and nitrogen fixation and dephosphorization process using MAP crystallization method" Hirozo Ota: "Recovery of phosphorus resources by MAP granulation dephosphorization method" Water Desalination Technology, 22(1), 64-67 (1996). Tsuno et al.: "Study on recovery of stobalite from digester desorbed fluid" Sewerage Association Transactions, 28(324), 68-77 Shizuo Abe, Mio Murosum: "Development of advanced treatment and MAP method in Fukuoka City" Journal of Japan Sewage Works Association, 32(389), 89(1995) Taro Yoshikura, Takayuki Nishio, Isao Fukunaga, Advanced treatment of wastewater by biological nitrification-denitrification method, Life hygiene (Seikatsu Eisei) Vol. 43 No. 2 49-64 (1999) 49 Yamagiwa, Y. et al.: Proceeding of 1st International Anammox Symposium 2011, p.217 (2011). Japan Water Works Association (2000) Guide to measures against nitrate nitrogen and nitrite nitrogen in water supplies, 68. Lauch, P. and Guter, A. (1986) Ion exchange for the removal of nitrate from well water, JAWWA, May,83-88. Clifford, D and Liu, X. (1993) Ion exchange for nitrate removal, JAWWA, April, 135-143. Kazuo Tomie, Fumio Hanada, Noboru Takemura, Kenji Fujita (1999) Removal of nitrate nitrogen from groundwater by electrodialysis, Journal of Japan Water Works Association, 68(7), 25-33. Horold, S., Tacke, T. and Vorlop, K. D. (1993) Catalytic removal of nitrate and nitrite from drinking water: 1. Screening for hydrogen catalysts and influence of reaction conditions on activity and selectivity, Environ. Tech., 14, 931 -939. Masataka Morizumi et al.: "Study of optimal electrolytic conditions for iron electrolysis method in phosphorus removal technology" Journal of Japan Society for Water Environment, 23(5), 279-284 (2000). Katsuaki Shimazu: "Electrochemical reduction of nitrate nitrogen" Catalysis, 44(3), 162-166 (2002). Kenichi Nakajima et al., Examination of the amount of processed scrap generated for estimating the amount of iron scrap, Journal of the Japan Institute of Metals, Vol. 66, No. 9, pp. 917-920, (2002). Hokkaido Branch of the Japanese Society for Analytical Chemistry, Water Analysis. 4th edition, Kagaku Doujin (1994).

Conventionally, biological methods have generally been used to remove phosphate ions and nitrate ions at the same time, but this method greatly affects the water quality and temperature of the water to be treated, the anaerobic degree in the reaction tank, etc. This makes stable treatment difficult, and the treatment of organic matter such as sludge and plants produced from nitrogen and phosphorus has become a problem. Furthermore, since the reaction rate of the biological phosphorus accumulation reaction and denitrification reaction is low, in order to perform a satisfactory treatment, it is necessary to increase the volume of the reaction tank to ensure sufficient reaction time. On the other hand, there are few reports on methods for simultaneously removing nitrogen and phosphorus using only physicochemical methods. Among them, a case has been reported in which nitrogen and phosphorus were successfully removed simultaneously using an electrolytic reaction using an iron electrode. Since this method applies electrolysis, it can be miniaturized, does not require management or replenishment of organic sources, and can handle fluctuations in processing capacity due to load fluctuations or temperature changes, making the system easy to maintain and manage. It has advantages. Furthermore, it is particularly effective for raw water with a BOD/N ratio of 1 or less. However, the cost is enormous due to the high cost of electricity used for electrolysis and the high cost of the catalyst used, and chloride ions are required to reduce nitrate ions, resulting in low effectiveness in freshwater areas.

purpose of invention

The present invention was made to solve these problems, and its purpose is to remove nitrogen oxides and phosphorus, such as nitric acid and nitrite, which are factors that cause eutrophication of rivers and lakes, by using electricity. To provide a contaminated water purification method and a purification device that can achieve a high recovery rate of phosphorus and a high decomposition rate of nitrate ions regardless of freshwater or seawater without requiring the cost of expensive catalysts or the like.

(1) In a battery tank containing a battery with iron as a negative electrode and carbon as a positive electrode, contaminated water is used as electrolyzed water to generate electricity, iron ions are eluted to remove phosphate ions, and phosphorus is removed in a precipitation tank. A phosphate ion removal and recovery step in which acid ions are precipitated as iron phosphate, and a step in which iron ions are eluted to remove the phosphate ions are performed in a battery tank, and the power obtained is used to clean contaminated water. In a contaminated water purification method comprising a hydrogen generation step of generating hydrogen through electrolysis, and a nitrate ion removal step of reducing and removing nitrate ions using the generated hydrogen, Using the process of oxidizing iron ions and the process of reducing iron ions by using tea lees, which is an organic substance that reduces the oxidized iron ions, and light, the treated water obtained by electrolyzing contaminated water is transferred to a battery. It is characterized by adjusting the hydrogen ion concentration and dissolved oxygen concentration in the battery tank and electrolytic tank to a predetermined range so that phosphate ions and nitrate ions can be removed simultaneously by circulating and supplying them to the tank. Contaminated water purification method.

According to the present invention, a high recovery rate of phosphorus and a high rate of decomposition of nitrate ions can be achieved regardless of freshwater or seawater, without requiring the cost of electricity or expensive catalysts.

(2) First perform a phosphate ion removal process in the battery tank, then perform a hydrogen generation process in which contaminated water is electrolyzed to generate hydrogen, and finally perform a nitrate ion removal process in which nitrate ions are reduced and removed. The contaminated water purification method according to (1), characterized in that:

According to the present invention, a high recovery rate of phosphorus and a high rate of decomposition of nitrate ions can be achieved regardless of freshwater or seawater, without requiring the cost of electricity or expensive catalysts.

(3) The contaminated water purification method according to (1), characterized in that batteries having iron as a negative electrode and carbon as a positive electrode and battery tanks containing the batteries are connected in multiple stages.

According to the present invention, a high recovery rate of phosphorus and a high rate of decomposition of nitrate ions can be achieved regardless of freshwater or seawater, without requiring the cost of electricity or expensive catalysts.

(4) A battery tank containing a battery with iron as the negative electrode and carbon as the positive electrode, in which contaminated water is used as electrolyzed water to generate electricity and iron ions are eluted to remove phosphate ions, and as iron phosphate. Contaminated water is electrolyzed using electric power obtained by performing a precipitation tank to remove and recover phosphate ions, and a battery tank to elute iron ions to remove the phosphate ions. In a contaminated water purification apparatus comprising an electrolytic cell for generating hydrogen and reducing and removing nitrate ions using the generated hydrogen, a reduction tank for reducing iron ions used for electrolysis of contaminated water is provided. , A supply part that can continuously supply tea lees, which is a reducing organic substance, is connected to a separation part for tea lees, which is a reducing organic substance, which continuously discharges used tea lees, which is a reducing organic substance. A contaminated water purification device featuring:

According to the present invention, there is a production device for producing nitrogen oxides and phosphorus that can achieve a high recovery rate of phosphorus and a high decomposition rate of nitrate ions regardless of freshwater or seawater without requiring the cost of electricity or expensive catalysts. can get.

(5) The contaminated water purification device according to (4) , further comprising a sedimentation tank for precipitating phosphate ions in the contaminated water and separating solid and liquid between the battery tank and the electrolytic tank.

According to the present invention, there is a production device for producing nitrogen oxides and phosphorus that can achieve a high recovery rate of phosphorus and a high decomposition rate of nitrate ions regardless of freshwater or seawater without requiring the cost of electricity or expensive catalysts. can get.

(6) The contaminated water purification device according to (4), wherein the positive electrode of the battery tank is connected to the anode of the electrolytic tank, and the negative electrode of the battery tank is connected to the cathode of the electrolytic tank.

According to the present invention, there is a production device for producing nitrogen oxides and phosphorus that can achieve a high recovery rate of phosphorus and a high decomposition rate of nitrate ions regardless of freshwater or seawater without requiring the cost of electricity or expensive catalysts. can get.

(7) The reduction tank and the electrolytic tank are connected so that the reduced iron ions are supplied from the reduction tank to the cathode tank of the electrolytic tank, and the iron ions oxidized in the electrolytic tank are returned to the reduction tank. (4) Contaminated water purification equipment.

According to the present invention, there is a production device for producing nitrogen oxides and phosphorus that can achieve a high recovery rate of phosphorus and a high decomposition rate of nitrate ions regardless of freshwater or seawater without requiring the cost of electricity or expensive catalysts. can get.

According to the present invention, it is possible to efficiently remove phosphate ions and nitrate ions, which are the cause of eutrophication in lakes, from contaminated water at low cost. It is possible to provide a contaminated water purification method and device that can reuse phosphorus from materials.

The contaminated water purification device of the present invention has a compact and simple structure and does not require a power source, so it can be installed on an appropriate scale and in a pinpoint manner according to the situation of the pollution source in the water body. Acid ions can be removed in a timely manner.

The contaminated water purification method of the present invention does not require strict control of treatment conditions to maintain high and stable microbial activity as in (1-A) and (2-A), and is easy to operate. and can be implemented in a compact size. In addition, there are also chemicals for regeneration treatment like (a) in (1-B), expensive catalysts like (b), and expensive flocculation like (a) and (b) in (2-B). Since no chemicals are required, the process as a whole is low cost. In addition, since chloride ions are not required as in (b), nitrate ions can be removed in fresh water, and neutralization can be achieved without detonation as in (c) of (2-B). It is possible to remove phosphoric acid nearby, and as shown in (d), there is no need for an external power supply, expensive catalysts, or chloride ions, so it can be removed from rivers, lakes, etc., regardless of whether it is freshwater or seawater. Eutrophication can be prevented sustainably.

The contaminated water purification method of the present invention enables new recycling methods for iron scrap materials, new ways to utilize raw garbage such as tea and coffee grounds, and new industries and agriculture using recovered phosphorus and hydrogen. It can also contribute to revitalizing the economies of developing countries and regions.

The method for purifying contaminated water according to the present invention can be used in developing countries to remove and recover phosphoric acid by using iron and carbon batteries. can be implemented. Furthermore, if electrode materials that do not easily deteriorate, such as titanium or stainless steel, and permeable membranes or semipermeable membranes that can be substituted for cation exchange membranes are available, nitrate ion electrolysis can be carried out by low-voltage electrolysis.

In developed countries, the contaminated water purification method of the present invention can be incorporated into conventional water purification facilities and septic tanks to add nitrogen and phosphorus removal functions in a safe and inexpensive manner.

According to the present invention, phosphate ions in water are precipitated and removed by iron ions eluted from the iron negative electrode of an iron-carbon battery, and phosphoric acid can be recovered from the recovered precipitate. Furthermore, when the solution treated with the iron-carbon battery is injected into the cathode tank of a two-tank electrolyzer and hydrogen is produced by low-voltage electrolysis using the power supplied from the iron-carbon battery, the produced hydrogen The nitrate ions in the water are reduced and removed from the water as nitrogen gas. In addition, according to the present invention, the removal and recovery of phosphate ions using an iron-carbon battery and the removal of nitrate ions in water using hydrogen gas generated by low-voltage electrolysis using the power of the battery can be carried out in a timely manner using a small-scale device. This makes it possible to take low-cost and sustainable measures against eutrophication.

Currently, 35 million tons of scrap iron is generated annually in Japan. In the future, the amount of scrap metal generated is expected to increase and exceed the domestic demand for steel, and it is said that even if all steel is supplied with recycled products, scrap metal will definitely remain (Non-Patent Document 20). There is.

Below, the best mode of a contaminated water purification method and apparatus for removing phosphate ions and nitrate ions will be explained using drawings and formulas.

FIG. 1 is a diagram illustrating a contaminated water purification method and apparatus for removing phosphate ions and nitrate ions according to the present invention, in which 11 is a nitrate ion, 12 is a phosphate ion, 13 is an iron-carbon battery, and 14 is an iron carbon battery. A negative electrode, 15 is a carbon positive electrode, 16 is a conducting wire, 17 is a precipitate formed by iron ions and phosphate ions 12, 18 is a solution after treatment with the iron-carbon battery 13, 19 is the power supplied from the iron-carbon battery 13 , 111 is an anode tank, 112 is a cathode tank, 113 is a hydrogen ion exchange membrane, 114 is an anode, 115 is a cathode, 116 is a power source, 117 is a reducing organic substance such as tea lees, 118 is sunlight, 119 is a reduction tank, 120 each represents an electrolytic cell.

An iron-made negative electrode 14 and a carbon-made positive electrode 15 are directly connected by a conductive wire 16, and the iron-made negative electrode 14 and the carbon-made positive electrode 15 are placed in close positions facing each other, thereby producing an iron-carbon battery 13. The iron-carbon battery 13 is placed in an aqueous solution containing nitrate ions 11 and phosphate ions 12. The dissolution rate of iron is very low near neutrality, but by using iron as the negative electrode and a carbon material with a lower ionization tendency than iron as the positive electrode, the dissolution rate of iron can be increased and the dissolution rate of iron can be increased. The phosphate ions 12 in the water are precipitated by the iron ions eluted from the negative electrode 14, and the precipitates 17 are separated from the water, thereby removing the phosphate ions 12 in the water. When the solution 18 treated with the iron-carbon battery 13 is injected into the cathode tank 112 of a two-tank electrolyzer and hydrogen is produced by low-voltage electrolysis using the electric power 19 supplied from the iron-carbon battery 13, hydrogen is produced. Nitrate ions 11 in the water are reduced by the hydrogen produced and removed as nitrogen gas 110 out of the water.

An anode tank 111 and a cathode tank 112 are blocked by a hydrogen ion exchange membrane 113. The anode tank is impregnated with an anode 114, and the cathode tank is impregnated with a cathode 115. A voltage is applied to the anode 114 and the cathode 115 by a power source 116.

The reduction tank 119 is filled with an aqueous solution of iron nitrate (trivalent), and trivalent iron ions are supplied, and the tea lees, which is a reducing organic substance, acts as a photocatalyst, promoting the reaction of formula 3 with the energy of sunlight. However, trivalent iron ions are reduced to divalent iron ions and hydrogen ions are generated.

Hydrogen ions generated in the reduction tank 119 pass through the hydrogen ion exchange membrane 113 and move into the cathode tank 112, where they are attracted to the cathode and become hydrogen. On the other hand, in the anode tank 111, the reduced divalent iron ions are attracted to the anode 114, the reaction of formula 4 occurs, electrons are taken away, the iron ions are oxidized to trivalent iron ions, and oxygen is generated.

In the conventional hydrogen production method using water electrolysis, water is oxidized according to Equation 5, so it was necessary to apply a voltage of 3 volts or more. Trivalent iron ions are continuously reduced by the organic matter 117 and sunlight 18, and water electrolysis proceeds continuously at a voltage of 1 volt or less due to the continuous presence of the reduced divalent iron ions.

Next, the detailed structure of the iron-carbon battery in the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions of the present invention will be explained using FIG. 2. In the figure, 21 is a bolt, 22 is a plastic positive electrode fixing plate, 15 is a carbon positive electrode, 23 is a positive electrode current collector plate, 24 is a mesh plastic separator, 14 is an iron negative electrode, and 25 is a negative electrode collector. An electric plate, 26 a negative electrode fixing plate made of plastic, and 27 a nut.

How to assemble an iron-carbon battery will be explained using FIG. 2. An iron plate (length 15 cm x width 4.5 cm) is used as the negative electrode 14, a carbon plate (length 10 cm x width 4 cm) is used as the positive electrode 15, and a plastic net (length 10 cm x width 4 cm) is placed between the negative electrode 14 and the positive electrode 15. was sandwiched between them, used as a separator 24, and sandwiched from the outside between a plastic positive electrode fixing plate 22 and a plastic negative electrode fixing plate 26. Bolts 21 were passed through and nuts 27 were tightened to assemble an iron-carbon battery.

As the iron material used for the negative electrode 14, so-called ordinary steel, soft iron, etc. can be used.

Further, the shape of this iron material is not particularly limited. For example, any material such as a flat plate, a net, a perforated flat plate (punched metal), a rod, a net, a particle, a thread, etc. can be used. In order to increase the contact area with iron, it is preferable to use a net shape, a perforated flat plate shape, or a particle shape.

As the material used for the negative electrode 14, a material with a nobler potential than iron is used. Carbon materials, stainless steel, copper, etc. can be used as materials with a higher potential than iron. The carbon material can be in the form of, for example, a flat plate, a rod, a fiber, a woven fabric, or a nonwoven fabric.

In an iron-carbon battery, it is preferable to arrange the negative electrode 14 and the positive electrode 15 so that they face each other.

The smaller the distance between the negative electrode 14 and the positive electrode 15, the larger the current, so it is preferable, but in consideration of ease of liquid flow, etc., the distance is preferably 1 mm to 50 mm, and more preferably 2 mm to 10 mm. If there is no agitation of the liquid in the bath of the water to be treated, the gap between the two should be reduced, if there is agitation of the liquid in the bath, the gap between the two should be increased, and as the agitation speed increases, the gap between the two should be reduced. Can be made larger.

When the iron-carbon battery is immersed in the water to be treated, the temperature may be room temperature, and no particular heating or cooling is required. Furthermore, the water to be treated may be in a neutral range, but may also be weakly acidic or weakly alkaline. However, if the pH exceeds 8, iron becomes passive and does not dissolve in water, which is not preferable. Further, since the treatment of water using an iron-carbon battery involves mass transfer, it is preferable to stir the bath of the water to be treated. Similarly, it is preferable that the contact area between the negative electrode 14, the positive electrode 15, and the water to be treated be large. Therefore, it is preferable that the negative electrode 14 and the positive electrode 15 be porous.

Next, the detailed structure of the battery tank in the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions of the present invention will be explained using FIG. 3. In the figure, 31 is the inlet of the battery tank, 32 is the battery tank, 33 is sample water, 34 is the positive electrode connected to the anode of the electrolyzer, 35 is the negative electrode connected to the cathode of the electrolyzer, 36 is the outlet of the battery tank, 37 is the first water tank, 38 is the second water tank, 39 is the third water tank, 310 is the fourth water tank, 311 is the fifth water tank, 312 is the sixth water tank, 13 is the iron carbon battery, 14 is the iron negative electrode, 15 is carbon 16 represents a conductive wire, and 24 represents a separator.

The battery tank 32 is an aquarium partitioned into a first aquarium 37 , a second aquarium 38 , a third aquarium 39 , a fourth aquarium 310 , a fifth aquarium 311 , and a sixth aquarium 312 . The size of these six water tanks is 5 cm width x 1.5 cm depth x 8 cm height, and the total volume of the six water tanks, that is, the volume of the battery tank 32 is approximately 800 mL. One iron-carbon battery 13 was placed in each of six tanks, from the first tank to the sixth tank, and the iron negative electrode 14 and carbon positive electrode 15 of the adjacent iron-carbon batteries were connected in series with a copper wire 16. . Sample water 33 is supplied from the inlet 31, enters the first water tank 37 from the top, touches the iron-carbon battery 13 in the first water tank 37, enters the second water tank 38 from the bottom, and enters the second water tank 38 from the bottom. After touching the iron-carbon battery 13, enter the third water tank 39 from above, and after touching the iron-carbon battery 13 in the third water tank 39, enter from the bottom of the fourth water tank 310, and enter the iron-carbon in the fourth water tank 310. After touching the battery 13, enter the fifth water tank 311 from above, and after touching the iron-carbon battery 13 in the fifth water tank 311, enter from the bottom of the sixth water tank 312, and enter the iron-carbon battery 13 in the sixth water tank 312. , the treated sample water 33 is discharged from the outlet 36.

[Example 1 (Power supply by iron-carbon battery and phosphoric acid removal and recovery method)]
An iron plate (length 15 cm x width 4.5 cm) was used as the negative electrode 14, a carbon plate (length 10 cm x 4 cm) was used as the positive electrode 15, and a plastic net was used as the separator 24. Sample water 33 was obtained by filtering water from Maki Pond and then adding disodium hydrogen phosphate dodecahydrate (Na₂HPO₄・12H₂O) and sodium dihydrogen phosphate dihydrate (NaH₂P.O.₄・2H₂Phosphate (PO) was prepared using equal amounts of₄-P) concentration was adjusted to 0.05 mmol/L (annual maximum value of phosphate ion concentration in the inflow ditch of Asaki Pond, about 10 times the average value) and pH was adjusted to 7.0. In the experiment, 1.6L of sample water 33 was sent through the inlet 31 at a rate of 26 mL per minute, allowed to flow out from the outlet 36, and the sample water 33 after treatment was again poured into the inlet 31. circulated. Since the total volume of the sample water that entered the battery tank was 0.8 L, the sample water in the battery tank was replaced in about 30 minutes. The phosphate phosphorus concentration was measured by molybdenum blue absorption spectrophotometry (Non-patent Document 21), and the phosphate ion concentration was measured by molybdenum blue absorption spectrophotometry (Non-Patent Document 21). 'removal rate' was defined by Equation 6.

When one iron-carbon battery 13 was placed in sample water 33, the open voltage was approximately 0.5V. When six iron-carbon batteries 13 were connected in series, a voltage of about 3V was generated. It was found that if the voltage is 1 V or higher, hydrogen production using oxidation of divalent iron ions is possible, and therefore hydrogen production is possible by supplying electric power from an iron-carbon battery.

The removal rate of phosphate ions was 54.4% when the number of circulations was 1, 71.4% when 2 times, 88.5% when 3 times, and 94.6% when 4 times. there were.

Table 1 shows the pH and oxidation-reduction potential (ORP) of the battery water tank. It can be seen that iron ions were eluted from the iron-carbon battery because the pH of the sample water that flowed into the battery tank increased and the redox potential decreased to a negative value. Therefore, Fe ²⁺ and Fe ³⁺ are present in the battery cell. Since the solubility product of Fe ²⁺ and anions is much larger than that of Fe ³⁺ , it is thought that almost no Fe ²⁺ precipitate exists, indicating that the precipitate was generated by the reaction between Fe ³⁺ and anions. I decided that. The precipitates generated by reacting with Fe ³⁺ include Fe(OH) ₃ (s), FePO ₄ (s), Fe ₂ (CO ₃ ) ₃ (s), and Fe ₃ (SO ₄ ) ₂ (s). Listed. Among these four types of precipitates, Fe ₂ (CO ₃ ) ₃ (s) and Fe ₃ (SO ₄ ) ₂ (s) had a very large solubility product, so it was thought that no precipitates were formed. From the chemical equilibrium and equilibrium constants for Fe(OH) ₃ (s) and FePO ₄ (s), it was not considered stoichiometrically that a FePO ₄ (s) precipitate was formed, so the formed precipitate was FePO 4 (s). (OH) ₃ (s), and it is thought that along with the formation of this precipitate, phosphoric acid (H ₃ PO ₄ ^- H ₃ PO ₄ ^- and H ₃ PO ₄ ^2- ) was removed by co-precipitation. Ta.

As a result of continuing this experiment for 15 hours, the removal rate of phosphate ions from water became 100%. The precipitate was collected and completely dried to obtain 0.31 g of collected material. 0.031 g, which is 0.1 times the mass of the recovered material, was placed in 160 mL of sulfuric acid solution (1 mol/L), which was 0.1 times the volume of the sample water used in the experiment, and after stirring at 300 rpm for 30 minutes, The concentration of phosphate ions eluted into the solution was measured. The phosphoric acid recovery rate according to Equation 7 confirmed that almost 100% of phosphate ions in water could be recovered as precipitates.

[Example 2] (Simultaneous implementation of nitrate ion reduction and removal method using hydrogen generated by low-voltage electrolysis using electricity supplied from an iron-carbon battery and phosphoric acid coagulation precipitation method using iron salts)
Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 4 is a diagram illustrating an embodiment of the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions of the present invention, 13 is an iron carbon battery, 17 is a precipitate generated from iron ions and phosphate ions, 111 is an anode tank, 112 is a cathode tank, 113 is a hydrogen ion exchange membrane, 114 is an anode, 115 is a cathode, 118 is sunlight, 119 is a reduction tank, 120 is an electrolytic tank, 31 is an inlet of the battery tank 32, 32 is a battery tank, 33 is sample water, 34 is a positive electrode connected to the anode of the electrolyzer, 35 is a negative electrode connected to the cathode of the electrolyzer, 36 is an outlet of the battery tank 32, 37 is a first water tank, 38 is a second water tank, 39 is a third tank, 310 is a fourth tank, 311 is a fifth tank, 312 is a sixth tank, 41 is a valve for supplying tea lees and water, and 42 is a solution containing a mixture of iron ions and reducing organic matter. , 43 is a space, 44 is a stirring motor, 45 is a pipe that returns waste liquid from the anode tank to the reduction tank, 46 is a stirring propeller, 47 is a valve for disposing of used reducing organic matter, 48 is a filter, and 49 is a reduction tank. A pipe from the tank 119 to the pump 410, 410 an infusion pump from the reduction tank 119 to the anode tank 111, 411 a pipe from the pump 410 to the anode tank 111, 412 a conductor, 413 an outlet for the cathode tank, 414 a cathode The inlet of the tank, 415 is a pipe that connects the pump 416 and the inlet 414, 416 is an infusion pump that sends the supernatant of the solution 419 in the precipitation tank 420 to the cathode tank 112, 417 is a pipe that connects the precipitation tank 420 and the pump 416, 418 419 is a space, 419 is the sample water 33 treated in the battery water tank 32, 420 is a sedimentation tank, 421 is a valve for disposing of the sediment 17, 422 is a pipe connecting the outlet 36 of the battery water tank 32 and the sedimentation tank 420, respectively.

The main parts of the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions of the present invention are as shown in FIG. The iron-carbon battery 13 generates electricity, and the aqueous solution in the cathode tank 112 is electrolyzed by oxidation of iron ions in the aqueous solution containing divalent iron ions in the anode tank 111 to generate hydrogen from hydrogen ions, and the nitric acid in the cathode tank is It is comprised of an electrolytic cell 120 that reduces and removes ions with hydrogen, and a reduction tank 119 that reduces trivalent iron ions generated in the anode cell 111 and regenerates them into divalent iron ions.

The reduction tank 119 will be explained using FIG. 5. FIG. 5 is a diagram illustrating the detailed structure of the reduction tank 119 according to the second embodiment of the present invention. In the figure, 119 is a reduction tank, 42 is a solution containing a mixture of iron ions and reducing organic matter, 44 is a stirring motor, 46 is a stirring propeller, 47 is a valve for disposing of used reducing organic matter, and 51 to 55 are Each represents a window that brings in light from the outside.

In this example, tea lees were used as the reducing organic substance, and sunlight was used as the irradiation light. The reduction tank 119 takes in sunlight through windows 51 to 55 that take in light from the outside. The trivalent iron ions react with the tea lees 117 stirred by the stirring propeller 46 while absorbing sunlight, and are reduced to divalent iron ions. The solution 42 in which divalent iron ions and tea lees are mixed is separated from the used tea lees and the supernatant of the reduction tank by a filter 48, and is led to the anode tank 111 by a pump 416. Used tea lees are continuously separated and removed. The bottom of the reduction tank 19 is sloped so that the used tea lees can efficiently flow toward the used tea lees disposal valve 47.

Next, the electrolytic section of the example will be explained. The main parts of the electrolysis section include an anode tank 111, a cathode tank 112, and a hydrogen ion exchange membrane 113, which will be explained in order.

Details of the anode tank 111 in FIG. 4 will be explained using FIG. 6. In FIG. 6, 45 is a pipe that returns waste liquid from the anode tank to the reduction tank, 411 is a pipe for supplying the solution containing divalent iron ions from the reduction tank, 61 is the first chamber (lower part) of the anode tank, and 62 63 is the second chamber (center) of the anode tank, 63 is the third chamber (upper part) of the anode tank, and 64 is a hole for bolts (for fixing the cation exchange membrane between the anode tank and the cathode tank). holes) are shown respectively.

A solution containing divalent iron ions formed in the reduction tank 119 described above is supplied from the supply pipe 411 to the first chamber 61 located at the lower part of the anode tank. When the first chamber 61 is filled with the solution, the solution flows into the second chamber 62 located in the center of the anode cell. Inside the second chamber 62, ten narrow channels are formed in parallel in the vertical direction, and these channels are arranged at positions where the flow passes over the surface of the anode 14 in FIG. Therefore, the solution flowing from the first chamber 61 completely touches the surface of the anode 14 shown in FIG. 4 inside the second chamber 62, and then flows out to the third chamber 63 located at the upper part of the anode tank. In the third chamber 63, the flow from the flow path that was branched inside the second chamber 62 is collected, and a solution containing trivalent iron ions generated by oxidizing divalent iron ions in the anode tank is collected. It passes through the pipe 45 and is returned to the reduction tank 119 in FIG. 4, where it is regenerated into divalent iron ions.

Next, the cathode tank 112 will be explained using FIG. In the figure, 413 is the outlet of the cathode tank, 414 is the inlet of the cathode tank, 71 is the first chamber (lower part) of the cathode tank, 72 is the second chamber (center part) of the cathode tank, and 73 is the inlet of the anode tank. In the third chamber (upper part), 74 represents holes for passing bolts.

The supernatant of the settling tank 420, that is, sample water from which phosphate ions have been removed and nitrate ions remain, is supplied from the inlet 414 of the cathode tank by a pump 416. The supplied sample water is supplied to the first chamber 71 located at the bottom of the cathode tank. Once the first chamber 71 is filled with solution, water flows into the second chamber 72 located in the center of the anode cell. A narrow meandering flow path is formed inside the second chamber 72, and this flow path is arranged at a position where the liquid flows over the surface of the cathode 115 in FIG. Therefore, the solution flowing from the first chamber 71 completely touches the surface of the cathode 115 shown in FIG. 4 inside the second chamber 72. Hydrogen generated on the surface of the cathode 15 reduces nitrate ions contained in the sample water in the cathode tank 112 and converts them into nitrogen gas, which is discharged from the outlet 413 of the cathode tank 112 together with the water.

Next, using FIG. 8, the detailed structure of the entire electrolytic section consisting of an anode section, a cathode section, a cation exchange membrane, etc. of a hydrogen production apparatus according to an embodiment of the present invention will be explained. In the figure, 112 represents a cathode tank, 113 represents a hydrogen ion exchange membrane, 114 represents an anode, 115 represents a cathode, 81 represents a bolt, and 82 represents a nut.

A method of assembling an electrolytic device consisting of an anode 114, a cathode 115, and a hydrogen ion exchange membrane 113 will be described using FIG. 8. As the anode 114 and the cathode 115, a reticular platinum-plated titanium electrode (width 10 cm x length 30 cm) was used. The anode 114 and the cathode 115 were formed by bonding a titanium plate around a titanium net and plating it with platinum. After the cation exchange membrane 113 (width 10 cm x length 30 cm) is sandwiched between the anode 114 and the cathode 115, it is sandwiched from the outside between the cathode tank 114 and the anode tank 115, the bolt 81 is passed through, and the nut 82 is tightened to assemble the electrolytic part. Ta.

Next, the conditions of each part in this example will be explained. In the reduction tank 119, the following conditions were used.

An aqueous iron nitrate solution was used as the electrolyte for soaking the tea leaves. The redox potential of Fe(III)/Fe(II) is affected by the total iron ion concentration, the ratio of Fe(III)/Fe(II), pH, anion species, etc. The reaction of formula (1) progresses more easily when the Fe(III) ion concentration is higher and the pH is also higher. On the other hand, in the reaction of formula (2), it is better to have a high Fe(II) ion concentration and a low pH. Both reactions are in equilibrium with the reverse reaction, so highly active catalysts and efficient light irradiation methods are important to increase the reaction rate and shift the equilibrium over a wide range.

In this example, 606 g of iron (III) nitrate (Fe(NO ₃ ) _{3.9H 2} O) and 10 L of water at room temperature were used as the electrolyte, and the trivalent iron ion concentration was 0.15 mol/L ( 150mM) sample water was prepared. 10 L of sample water and 1 kg of broken tea lees with a maximum length of 3 mm were placed in the reaction container shown in FIG. 5. The volume of the reduction tank 119 is 12.5L.

The light irradiation method must irradiate the catalyst and solution with light as efficiently as possible. In this example, sunlight was used. Use mirrors, aluminum foil, etc. to prevent sunlight from escaping, and use an optical system with high capture efficiency. Pyrex, which has high transmittance and is relatively inexpensive, was used as the window material for the sunlight intake windows 51 to 55. Plastics with high transmittance can also be used instead of Pyrex.

In this example, in order to further disperse the solution 42 in which iron ions and tea lees were mixed, a stirring propeller 46 was rotated and stirred by a stirring motor 44 . The bottom surface of the reduction tank 119 has an inclination, so that the precipitated tea lees gather near the bottom of the propeller 46, and the precipitated tea lees are suspended inside the reduction tank 119 by stirring by the propeller 46. When the stirring of the propeller 46 is stopped, the precipitated tea lees collect near the used tea lees disposal valve 47 due to the slope of the bottom of the reduction tank 119, and the used tea lees are taken out from the reduction tank 119. be able to. Then, the electrolytic solution containing divalent iron ions generated by reducing the trivalent iron ions is separated from the tea lees and then sent to the anode tank 111 by the pump 410.

The electrolytic solution sent to the anode tank undergoes the reaction of formula 2 in a two-tank electrolytic cell in which an anode tank and a cathode tank are partitioned by a hydrogen ion exchange membrane 113. Semipermeable membranes, dialysis membranes, ion exchange membranes, salt bridges, ceramic membranes, etc. can be used as membranes to partition a two-tank electrolytic cell, but the mobility of hydrogen ions is sufficiently larger than that of iron ions. Therefore, a hydrogen ion exchange membrane is desirable, and in this example, a hydrogen ion exchange membrane (Nafion, manufactured by DuPont) was used.

As the cathode 115 on the hydrogen generation side, a material with a small hydrogen overvoltage is desirable, and platinum, nickel, a carbon electrode carrying a small amount of platinum, a titanium electrode plated with platinum, etc. can be used. In this example, titanium electrodes plated with platinum were used in consideration of cost.

On the other hand, as the anode 114 for oxidizing divalent iron ions, in addition to the above electrodes, a carbon electrode that does not support platinum can also be used. In this example, titanium electrodes plated with platinum were used in consideration of cost.

In order to lower the electrolysis voltage, it is important to take measures such as shortening the distance between the electrodes, increasing the reaction temperature, lowering the electrode current density, and using current collectors. In this example, the distance between the electrodes was the thickness of the hydrogen ion exchange membrane. The reaction temperature was room temperature. The electrode current density was 3 amps/cm2. Furthermore, in order to enhance the current collection effect, a plate-shaped frame was provided around the mesh-shaped electrode, as shown in the electrode structure shown in FIG.

As electrolysis progresses, the concentration of divalent iron ions around the anode 114 decreases, so the aqueous solution around the electrode is stirred or directly connected to the reduction tank 119 to constantly circulate a solution with a high concentration of divalent iron ions. system is preferred.

In order to optimize the conditions for the simultaneous removal of nitrate ions and phosphate ions, the following experiment was conducted.
(Experiment 1)
As sample water 33, after filtering the water from Maki Pond, using potassium nitrate (KNO ₃ ), the nitrate nitrogen (NO ₃ -N) concentration was adjusted to 2 mmol/L, and disodium hydrogen phosphate dodecahydrate ( Using equal amounts of Na ₂ HPO _{4.12H 2} O) and sodium dihydrogen phosphate dihydrate (NaH ₂ PO _{4.2H 2} O), the concentration of phosphate phosphorus (PO ₄ -P) was adjusted to 2 mmol/ L, pH was adjusted to 7.0.
A sample with a trivalent iron ion concentration of 0.15 mol/L (150 mM) was prepared using 606 g of iron (III) nitrate (Fe(NO ₃ ) _{3.9H 2} O) and 10 L of water at room temperature as the electrolyte 42. Prepared water supply.
10 L of electrolytic solution 42 and 1 kg of broken tea lees with a maximum length of 3 mm were placed in the reduction tank 119 shown in Fig. 5, and eight 1,000 lm LED bulbs (excluding ultraviolet light) were placed near windows 53 and 54. The inside of the reduction tank 119 was stirred at 300 rpm while irradiating light using an illuminance of approximately 20,000 lux (one-tenth the intensity of sunlight on a clear day) to reduce the concentration of divalent iron ions. While preventing this, the electrolytic solution was sent at a rate of 50 mL per minute using the pump 410 to circulate between the reduction tank 119 and the anode tank 111.
At the same time, the sample water is sent to the battery tank 32 at a rate of 26 mL per minute, the sample water 33 treated in the battery tank 32 is sent to the cathode tank 112 of the electrolyzer 412, and the sample water treated in the cathode tank 112 is sent to the battery tank 32 again. The sample water was circulated by feeding the sample water, and changes in the concentrations of nitrate nitrogen, nitrite nitrogen (NO ₂ -N), ammonia nitrogen (NH ₄ -N), and phosphate phosphorus were measured. Nitric acid was measured by zinc reduction-naphthylethylenediamine spectrophotometry (Non-Patent Document 21), nitrite was measured by naphthylethylenediamine spectrophotometry (Non-Patent Document 21), and ammonia was measured by indophenol blue spectrophotometry (Non-Patent Document 21). did.

The phosphate phosphorus concentration in Experiment 1 became approximately 0 mmol/L in 20 hours, and all phosphate ions in the water were removed.

Normally, the lower the pH of the sample water in the battery tank 32 (the higher the hydrogen ion concentration), that is, the more acidic it is, the faster the dissolution rate of the iron negative electrode 14 will be, and the faster the reaction rate with phosphate ions will be. Be expected. In the present invention, when the sample water that has been treated in the cathode tank 112 is sent to the battery tank 32 while saving hydrogen generation at the cathode 115 and the sample water is circulated, hydrogen ions are supplied from the cathode tank 112 and the battery The pH of the sample water supplied to the battery tank 32 can be lowered, and the elution rate of iron ions for reaction with the phosphate ions contained in the sample water in the battery tank 32 can be increased without imposing a burden on the environment. It became possible to do so.

Normally, if the pH of the sample water in the battery tank 32 is less than 5.0, the solubility of the phosphorus compound that has been precipitated and removed increases, making it impossible to efficiently remove phosphorus. In the present invention, when the sample water that has been treated in the cathode tank 112 is sent to the battery tank 32 and circulated while hydrogen is sufficiently generated in the cathode 115, hydrogen ions are consumed in the cathode tank 112, and the battery The pH of the sample water supplied to the tank 32 can be increased (the hydrogen ion concentration can be lowered), and the phosphate ions contained in the sample water in the battery tank 32 are more likely to precipitate.

Normally, when the pH of the sample water in the battery tank 32 exceeds 8.0, dissolved metal ions react with hydroxide ions to form hydroxide, which inhibits the formation of phosphoric acid compounds. It ends up. In the present invention, when the sample water that has been treated in the cathode tank 112 is sent to the battery tank 32 while saving hydrogen generation at the cathode 115 and the sample water is circulated, hydrogen ions are supplied from the cathode tank 112 and the battery The pH of the sample water supplied to the battery tank 32 can be lowered, and this is a particularly preferable pH value of 7, which allows the metal ions and phosphate ions contained in the sample water in the battery tank 32 to react without imposing a burden on the environment. It is now possible to adjust to .0.

The nitrate nitrogen concentration in Experiment 1 reached 1 mmol/L in 60 hours, and 50% of the nitrate ions in the water were removed. The nitrite nitrogen concentration was always 0 mmol/L during the experiment period, but the ammonia nitrogen concentration was always 0.2 mmol/L, suggesting that nitrate ions were reduced and removed. The iron ion concentration in the treated water was 0 mmol/L, and during the experiment period, a current of about 1 mA x 1 V and generation of gas from the cathode could be visually confirmed, so it is thought that hydrogen generation was occurring due to low-voltage electrolysis.

When the pH is 7, nitrite ions (NO₂ ^-) and ammonium ion (NH₄ ⁺), the nitrite ion is converted into nitrogen gas (N₂) and the half-reaction equation (Equation 8) and ammonium ion when reduced to The half-reaction equation (Equation 9) is established when is oxidized to nitrogen gas, and the Gibbs free energy in the total equation (Equation 10) is negative, so a small amount of hydrogen gas from the cathode and the hydrogen gas supplied from the battery tank are Nitrite ions and ammonium ions present in water are reduced due to the reducing potential of the water. It was suggested that the reaction to produce nitrogen gas proceeded and the nitrate ions were removed.

Normally, when the dissolved oxygen concentration (DO) in water is high, nitrate ions present in water are not reduced. In the present invention, since dissolved oxygen in water is consumed by the iron-carbon battery 13 in the battery tank 32, by sending waste water from the battery tank 32 to the cathode tank 112, the surface of the cathode 115 in the cathode tank 112 is It became possible to reduce nitrate ions to nitrogen gas.

Normally, when the oxidation-reduction potential (ORP) in water is a positive value (oxidative), nitrate ions present in water are difficult to reduce. In the present invention, the oxidation-reduction potential in the water becomes a negative value and continues to decrease as the battery tank 32 progresses through the partitioned first water tank 37, second water tank 38, ..., sixth water tank 312. By sending the wastewater from the cathode tank 112 to the cathode tank 112, it became possible to reduce nitrate ions to nitrogen gas with high efficiency on the surface of the cathode 115 in the cathode tank 112.

Normally, when the concentration of hydrogen ions (H ⁺ ) in water is low, nitrate ions present in water are difficult to reduce. In the present invention, when trivalent iron ions are reduced to divalent iron ions in the reduction tank 119, hydrogen ions are generated from water, and are passed from the anode tank 111 through the hydrogen ion exchange membrane 113. Since the sample water is supplied to the cathode tank 112, even if sample water near neutrality (pH 7) is supplied to the battery tank 32, the hydrogen ion concentration of the sample water sent from the battery tank 32 to the cathode tank 112 is high. As a result, it became possible to reduce nitrate ions to nitrogen gas on the surface of the cathode 115 in the cathode tank 112.

(Experiment 2)
The removal equipment was used at Asaki Pond during clear skies. Water collected near the inflow groove of Asami Pond is poured into the inlet 31 of the battery tank 32 at a rate of 26 mL per minute, and the treated water flowing out from the outlet 413 of the cathode tank 112 of the electrolyzer 412 is poured into the battery tank 32 again. , and was circulated at the same flow rate as in Experiment 1.

The phosphorus concentration before treatment was 0.5 mg/L. More than 60% of the phosphate ions were removed in the first cycle, and more than 90% was removed after 4 cycles. The nitrate nitrogen concentration before treatment was 1.5 mg/L. The removal rate of nitrate ions was low until the second circulation, but gradually increased after the third circulation, and about 20% was removed after four circulations.

(Experiment 3)
Similar results were obtained in the Tomoe River and Sunpu Castle moats, so we decided to develop a system that can remove nitrate ions and phosphoric acid at the same time by simply pouring water from common rivers and lakes. I can confirm that it was successful.

(Experiment 4)
When using water that has been treated in a septic tank or sewage treatment plant, the concentration of phosphorus in the form of phosphate reached approximately 0 mmol/L in 6 hours, and all phosphate ions in the water were removed. The nitrate nitrogen concentration became 1 mmol/L in 20 hours and 0.2 mmol/L in 60 hours, and 90% of the nitrate ions in the water were removed. The nitrite nitrogen concentration was always 0 mmol/L during the experiment period, but the ammonia nitrogen concentration was always 0.2 mmol/L, suggesting that nitrate ions were reduced and removed. As in Experiment 1, the iron ion concentration in the treated water was 0 mmol/L, and during the experiment period a current of approximately 1 mA x 1 V and gas generation from the cathode could be visually confirmed. It is thought that hydrogen production was occurring.

In the example, phosphate ions in water were precipitated and removed by iron ions eluted from an iron-carbon battery using an iron plate as a negative electrode and a carbon plate as a positive electrode, and phosphoric acid was recovered from the collected precipitate. At the same time, nitrate ions in the solution were reduced and removed using hydrogen produced by water electrolysis using electricity supplied by an iron-carbon battery. In addition, hydrogen for reducing nitrate ions is obtained by reducing trivalent iron ions to divalent iron ions using sunlight and tea lees, and by oxidizing divalent iron ions using low voltage water of 1V or less. The hydrogen was supplied using a hydrogen production method that combines electrolysis and is safe, inexpensive, and reduces energy consumption by half.

FIG. 1 is a diagram illustrating a contaminated water purification method and apparatus for removing phosphate ions and nitrate ions according to the present invention. FIG. 2 is a diagram illustrating the detailed structure of the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions according to the present invention. FIG. 3 is a diagram illustrating the detailed structure of the battery tank in the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions according to the present invention. FIG. 4 is a diagram illustrating an embodiment of the contaminated water purification method and apparatus for removing phosphate ions and nitrate ions according to the present invention. FIG. 5 is a diagram illustrating the detailed structure of the reduction tank according to the second embodiment of the present invention. FIG. 6 is a diagram illustrating the detailed structure of the anode portion of the hydrogen production apparatus according to the second embodiment of the present invention. FIG. 7 is a diagram illustrating the detailed structure of the cathode section of the hydrogen production apparatus according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating the detailed structure of an electrolytic device comprising an anode section, a cathode section, a cation exchange membrane, etc. of a hydrogen production apparatus according to a second embodiment of the present invention.

11 Nitrate ion 12 Phosphate ion 13 Iron carbon battery 14 Iron negative electrode 15 Carbon positive electrode 16 Conductor 17 Precipitate generated from iron ions and phosphate ions 12 Solution 19 after treatment with iron carbon battery 13 Iron carbon battery Electric power supplied from 13 111 Anode tank 112 Cathode tank 113 Hydrogen ion exchange membrane 114 Anode 115 Cathode 116 Power supply 117 Reducing organic matter such as tea lees 118 Sunlight 119 Reduction tank 120 Electrolytic tank 21 Bolt 22 Plastic positive electrode fixing plate 23 Positive electrode current collector plate 24 Net-like plastic separator 25 Negative electrode current collector plate 26 Plastic negative electrode fixing plate 27 Nut 31 Battery tank inlet 32 Battery tank 33 Sample water 34 Positive electrode 35 connected to the anode of the electrolyzer Negative electrode 36 connected to the cathode Battery tank outlet 37 First water tank 38 Second water tank 39 Third water tank 310 Fourth water tank 311 Fifth water tank 312 Sixth water tank 41 Valve 42 for supplying tea lees and water ions) and reducing organic matter 43 Space 44 Stirring motor 45 Pipe 46 for returning waste liquid from the anode tank to the reduction tank 46 Stirring propeller 47 Disposal valve for used reducing organic matter 48 Filter 49 From the reduction tank 119 Pipe 410 to pump 410 Infusion pump 411 from reduction tank 119 to anode tank 111 Pipe 412 from pump 410 to anode tank 111 Conductor 413 Cathode tank outlet 414 Cathode tank inlet 415 Pump 416 and inlet 414 are connected Pipe 416 Infusion pump 417 that sends the supernatant of solution 419 in sedimentation tank 420 to cathode tank 112 Pipe 418 connecting sedimentation tank 420 and pump 416 Space 419 Sample water 33 after being treated in battery tank 32
420 Sedimentation tank 421 Valve for disposing of sediment 17 422 Pipe 51 connecting outlet 36 of battery water tank 32 and sedimentation tank 420 Window 52 that takes in light from outside Window 53 that takes in light from outside Window that takes in light from outside 54 Window that takes in light from the outside 55 Window that takes in light from the outside 61 First chamber of the anode tank (lower part)
62 Second chamber of anode tank (center)
63 Third chamber of anode tank (upper part)
64 Hole for passing bolt 71 First chamber of cathode tank (lower part)
72 Second chamber of cathode tank (center)
73 Third chamber of anode tank (upper part)
74 Hole for passing bolt 81 Bolt 82 Nut

Claims (7)

Contaminated water is used as electrolyzed water to generate electricity in a battery tank containing a battery with iron as a negative electrode and carbon as a positive electrode, and iron ions are eluted to remove phosphate ions, and phosphate ions are generated in a precipitation tank. The process of removing and recovering phosphate ions to precipitate them as iron phosphate, and the process of eluting iron ions to remove the phosphate ions, are carried out in a battery tank, and the electricity obtained is used to electrolyze contaminated water. In a contaminated water purification method comprising a hydrogen generation step in which hydrogen is generated by hydrogen, and a nitrate ion removal step in which nitrate ions are reduced and removed by the generated hydrogen, iron ions from the electrolysis of the contaminated water are added to the electrolysis of the contaminated water. Using a process of oxidation and a process of reducing iron ions using tea lees, which is an organic substance that reduces the oxidized iron ions, and light, the treated water that has been electrolyzed from contaminated water is circulated to the battery tank. Contaminated water purification characterized by adjusting the hydrogen ion concentration and dissolved oxygen concentration in a battery tank and an electrolytic tank to a predetermined range so that phosphate ions and nitrate ions can be simultaneously removed by supplying Method. The phosphate ion removal and recovery process is first carried out in the battery tank and precipitation tank, then the hydrogen generation process in which contaminated water is electrolyzed to generate hydrogen, and finally the nitrate ion removal process is carried out to reduce and remove nitrate ions. The contaminated water purification method according to claim 1, characterized in that the method is carried out in an electrolytic cell. 2. The contaminated water purification method according to claim 1, wherein batteries having iron as a negative electrode and carbon as a positive electrode and battery tanks containing the batteries are connected in multiple stages. A battery tank containing a battery with iron as the negative electrode and carbon as the positive electrode, which generates electricity using contaminated water as electrolyzed water, and elutes iron ions to remove phosphate ions, and precipitates them as iron phosphate. A precipitation tank is used to remove and recover phosphate ions, and a battery tank is used to elute iron ions to remove the phosphate ions.Using the electricity obtained, contaminated water is electrolyzed to generate hydrogen. In the contaminated water purification apparatus, the reduction tank for reducing iron ions used in the electrolysis of contaminated water has a reducing property. A supply section that can continuously supply tea lees, which is an organic substance, is connected to a separation section for tea lees, which is a reducing organic substance, and which continuously discharges used tea lees, which is a reducing organic substance. Contaminated water purification equipment. 5. The contaminated water purification device according to claim 4, further comprising a precipitation tank provided between the battery tank and the electrolytic tank to precipitate phosphate ions in the contaminated water and separate solid and liquid. 5. The contaminated water purification device according to claim 4, wherein the positive electrode of the battery tank is connected to the anode of the electrolytic tank, and the negative electrode of the battery tank is connected to the cathode of the electrolytic tank. Claim 4 characterized in that the reduction tank and the electrolytic cell are connected so that the reduced iron ions are supplied from the reduction tank to the cathode cell of the electrolytic cell and the iron ions oxidized in the electrolytic cell are returned to the reduction tank. The contaminated water purification device described.