JP5580704B2 - Purification method of contaminated water - Google Patents

Description

  The present invention relates to a method for effectively purifying water contaminated with nitrate nitrogen and / or nitrite nitrogen, and particularly to a method for quickly and easily purifying such contaminated water. .

  The following points have been pointed out as the health effects of nitrate nitrogen and nitrite nitrogen. Nitrate nitrogen is reduced to nitrite nitrogen in the human body, and nitrite nitrogen is combined with hemoglobin to form metahemoglobin, which is said to cause oxygen deficiency (methemoglobinemia). In particular, it is said that the inside of the gastrointestinal tract of infants is weak in acidity, so that nitrate nitrogen reduction by microorganisms is likely to occur and methemoglobinemia is likely to occur.

  Nitrate nitrogen and nitrite nitrogen were added to the environmental standard items in February 1999 in the “Environmental Standards for Water Pollution of Groundwater” based on Article 16 of the Environmental Basic Law. The law is constantly monitored.

  Groundwater contamination by nitrate nitrogen or nitrite nitrogen is a problematic pollutant because of various causes of contamination, such as fertilization, livestock excrement, and domestic wastewater, and the contamination can be widespread.

  Nitrate nitrogen and nitrite nitrogen are basically generated by nitrogen circulation. For example, organic nitrogen compounds including proteins are classified into insoluble organic nitrogen and water-soluble organic nitrogen. Among these, insoluble organic nitrogen is decomposed into water-soluble organic nitrogen by urea decomposing enzyme, and the water-soluble organic nitrogen is converted into ammonia.

  Ammonia easily dissolves in water and therefore exists as ammonium ions (ammonia nitrogen) in water. Ammonium ions generate nitrite ions (nitrite nitrogen) by ammonia oxidizing bacteria such as nitrosomonas in an aerobic atmosphere. Next, nitrite ions generate nitrate ions (nitric nitrogen) by nitrite oxidizing bacteria such as nitrobacter in an aerobic atmosphere. Nitrate nitrogen and nitrogen nitrite are thus present as ions in water.

  Methods for purifying water (contaminated water) containing nitrate nitrogen or nitrite nitrogen are roughly classified into physicochemical methods and biochemical methods. Among these, ion exchange methods, electrodialysis methods, reverse osmosis membrane methods, catalytic denitrification methods and the like are known as physicochemical methods. On the other hand, heterotrophic denitrification method, autotrophic denitrification method and the like are known as biochemical methods.

  The ion exchange method as a physicochemical method is a method of decomposing and removing nitrate nitrogen and nitrite nitrogen as anions using a strongly basic anion exchange resin. By using a large amount of sodium chloride for the regeneration of the ion exchange resin, there is a fundamental problem that a high concentration of sodium chloride is generated and the treatment is required.

  The electrodialysis method is a method of separating nitrate nitrogen and nitrite nitrogen by passing an anion exchange membrane. The reverse osmosis membrane method applies pressure to water containing nitrate nitrogen and nitrite nitrogen existing on one side of the semipermeable membrane to remove water from which nitrate nitrogen and nitrite nitrogen have been removed. It is a method of separating to the opposite side. Both the electrodialysis method and the reverse osmosis membrane method have a problem that the facility cost and the maintenance cost increase, and the waste water treatment in which nitrate nitrogen and nitrite nitrogen have a high concentration is required.

  Heterotrophic denitrification as a biochemical method is a method of filtering nitrate nitrogen and nitrite nitrogen-containing water through a granular filter layer on which heterotrophic denitrifiers have adhered and grown, and then removing nitrate nitrogen and nitrite nitrogen. It is reduced to nitrogen gas. In addition, the autotrophic denitrification method is the same as the heterotrophic denitrification method, with a filter layer on which sulfur denitrifying bacteria, which are autotrophic bacteria, are attached and grown. In these heterotrophic denitrification method and autotrophic denitrification method, the treatment efficiency depends on the water temperature (ie, temperature), and in particular, the autotrophic denitrification method has a slow reaction rate and easily produces sulfuric acid as a by-product. There is a problem. In addition, there is a drawback that a high level of technology is required for operation management of the apparatus.

  Various methods for purifying contaminated water have been proposed so far. For example, in Patent Document 1, a purification wall containing denitrifying bacteria and a biodegradable polymer is applied to a groundwater layer contaminated with nitric acid or phosphoric acid. A method for purifying contaminated groundwater by burying has been proposed. Patent Document 2 proposes to use a reducing agent in combination with the above-described method, and this reducing agent makes anaerobic treatment of groundwater so that denitrifying bacteria can easily perform a denitrifying activity in an anaerobic atmosphere. It is for making an atmosphere.

  However, the technique disclosed in Patent Document 1 has a basic problem that the purification process takes too long. In addition, in the technique of Patent Document 2, in addition to the above problems, microbial degradation may occur such that degradation of the biodegradable polymer is inhibited by the presence of iron powder, and the amount of iron powder added is small However, depending on the type of biodegradable polymer, the effect of iron powder varies (effectively and ineffectively) depending on the type of biodegradable polymer. is there.

  Moreover, in the method using the denitrifying bacteria and the purification wall containing the biodegradable polymer, there are various kinds and amounts of denitrifying bacteria present in the actual treated soil and the purification wall, and in some cases, the denitrification is sufficiently performed. In some cases, the amount of total organic carbon in the treated water increases due to decomposition of the biodegradable polymer, and secondary treatment such as activated carbon treatment or ozone treatment may be required.

  On the other hand, a method has also been proposed in which nitrate nitrogen or nitrite nitrogen is once reduced to ammonia nitrogen by various reducing agents, and then ammonia nitrogen is purified. Such a technique facilitates the subsequent purification process by once reducing nitrate nitrogen or nitrite nitrogen to ammonia nitrogen.

As such a technique, for example, Patent Document 3 uses ferrous sulfate (FeSO ₄ ), ferrous chloride (FeCl ₂ ) and other ferrous compounds as a reducing agent, and nitrate nitrogen or nitrite in contaminated water. A method for reducing nitrogen has been proposed. Patent Document 4 discloses that various forms (powder, granules, plates, etc.) of iron are used as a reducing agent and brought into contact with nitrate nitrogen or nitrite nitrogen, thereby causing nitrate nitrogen or nitrite. A method for reducing reactive nitrogen has also been proposed.

  However, the reducing agents proposed in these techniques cannot be said to have sufficient reducing ability of nitrate nitrogen or nitrite nitrogen, and the actual situation is that further improvement is desired. Moreover, in the technique of the said patent document 3, it is necessary to perform a sludge process and there also exists a problem that a process becomes complicated.

JP 2000-254687 A JP 2001-300509 A JP 2006-263705 A Japanese Patent Laid-Open No. 10-277567

  The present invention has been made under the circumstances as described above, and an object thereof is a useful method for purifying contaminated water by quickly and reliably removing nitrate nitrogen and nitrite nitrogen. Is to provide.

  In the method of the present invention that has been able to solve the above-mentioned problems, in purifying water contaminated with nitrate nitrogen and / or nitrite nitrogen, the contaminated water is treated with 0.3 to 2.0 sulfur. Purify the water by bringing it into contact with the iron powder containing mass%, reducing the nitrate nitrogen and / or nitrite nitrogen to ammonia nitrogen, and removing the ammonia nitrogen from the water containing the ammonia nitrogen. It has a gist in terms.

  In the method of the present invention, it is useful to bring the contaminated water into contact with an adsorbent having a cation exchange capacity together with the iron powder, whereby ammonia nitrogenous from nitrate nitrogen and / or nitrite nitrogen. Simultaneously with the reduction to nitrogen, ammoniacal nitrogen can be removed.

  According to the present invention, it is possible to quickly and reliably remove nitrate nitrogen and nitrite nitrogen by contacting contaminated water with iron powder containing 0.3 to 2.0 mass% of sulfur. A useful method for purifying contaminated water has been realized.

It is a schematic explanatory drawing which shows an example of the process of reduce | restoring nitrate nitrogen and nitrite nitrogen to ammonia nitrogen. It is a schematic explanatory drawing which shows another example of the process of reduce | restoring nitrate nitrogen and nitrite nitrogen to ammonia nitrogen. It is a graph which shows the influence of pH which acts on the passive potential of Fe.

  There are two possible routes for ammonia, which is the source of nitrate nitrogen and nitrite nitrogen, as shown below. First, there is a path through which ammonia changes to nitrate nitrogen or nitrite nitrogen, and two more paths are possible. As one of the routes in which ammonia changes to nitrate nitrogen or nitrite nitrogen, ammonia dissolves in rainwater to become ammonia nitrogen, and rainwater in which ammonia nitrogen is dissolved is oxidized to nitrate nitrogen and enters the soil. This is the penetration path. This is because rainwater is in the range of about pH 5-6, oxidation-reduction potential [standard hydrogen electrode (SHE) standard: the same applies hereinafter) +0.8 to +1.0 V. In this range, ammonia nitrogen is reduced to nitrate nitrogen. Is done.

  As another route, ammoniacal nitrogen is converted into nitrate nitrogen or nitrite nitrogen by bacteria. Nitrite nitrogen is generated in the middle of the reaction from ammonia nitrogen to nitrate nitrogen. Since nitrite nitrogen has a higher oxidation reaction rate than ammonia nitrogen, nitrite nitrogen usually does not accumulate in soil. However, when the activity of nitrate bacteria is suppressed due to the influence of pH or the like, nitrite nitrogen may accumulate in the soil.

  The second route of ammonia, which is the source of nitrate nitrogen and nitrite nitrogen, may be adsorbed by clay minerals and humus in the soil and remain ammonia nitrogen. This is because ammonia nitrogen is positively charged, and clay minerals and humus soil in the soil are negatively charged.

  The present inventors examined from various angles how quickly and surely the nitrate nitrogen and nitrite nitrogen that have penetrated into the soil can be rendered harmless in consideration of the above situation. By reducing nitrate nitrogen and nitrite nitrogen to ammonia nitrogen that is easy to purify, and purifying ammonia nitrogen from the contaminated water containing ammonia nitrogen obtained (nitrogen gasification of ammonia nitrogen), It is known to purify contaminated water (Patent Documents 3 and 4). However, the reducing agents that have been proposed so far have limitations on their reducing ability.

  The present inventors have further examined a reducing agent that reduces nitrate nitrogen or nitrite nitrogen to ammonia nitrogen, and it is extremely preferable to use iron powder containing 0.3 to 2.0 mass% of sulfur. It was found useful and the present invention was completed.

  In the method of the present invention, it is important to use iron powder containing 0.3 to 2.0% by mass of sulfur as a reducing agent for reducing nitrate nitrogen or nitrite nitrogen to ammonia nitrogen. In order to effectively exhibit the effect as the reducing agent, the sulfur content in the iron powder needs to be 0.3% by mass or more. Moreover, reduction efficiency can be improved after suppressing the cost increase of a reducing agent by making sulfur content into 2.0 mass% or less. The sulfur content is preferably 0.6% by mass or more and 1.5% by mass or less.

  In order to reduce nitrate nitrogen or nitrite nitrogen to ammonia nitrogen, the idea that the oxidation-reduction potential should be controlled to be +0.4 V or less in the range of pH 5 to 6 has been obtained. . That is, it was considered that the reducing agent used in the present invention can effectively reduce nitrate nitrogen and nitrite nitrogen by using a standard hydrogen electrode standard redox potential of +0.4 V or less.

  As a metal whose oxidation-reduction potential is +0.4 V or less, in addition to iron, copper, bismuth, lead, tin, nickel, cobalt, titanium, indium, cadmium, gallium, chromium, zinc, manganese, aluminum, beryllium, magnesium, Various things such as sodium, calcium, strontium, barium, cesium, rubidium, potassium, lithium and the like can be considered. Also. Examples of alloys whose oxidation-reduction potential is +0.4 V or less include iron-based alloys such as cast iron, carbon steel, nickel chrome steel, nickel chrome molybdenum steel, chrome steel, chrome molybdenum steel, manganese steel, bronze, red brass, brass, etc. Copper-base alloys, lead-tin alloys such as solder, etc. are also conceivable.

  However, even if only the requirement that the oxidation-reduction potential is +0.4 V or less is satisfied, the ability as a reducing agent has been found to be limited. In addition, these reducing agents have the following problems in terms of safety and cost.

  Copper and zinc have little effect on the human body, but may have an effect on animals and plants. Bismuth is expensive and has the potential to be harmful. Lead, cadmium, and chromium may cause secondary contamination due to their elution. Tin can cause tin pneumonia by aspirating the dust. Nickel and cobalt are expensive. Indium and beryllium are carcinogenic. Gallium has a high melting point and has a problem in handling.

  Titanium, Aluminum, Magnesium, Sodium, Calcium, Strontium, Barium, Cesium, Rubium, Potassium, Lithium ignites by contact with air, ignites by contact with water, or generates flammable gas It is dangerous and requires advanced techniques for handling. When manganese is a relatively highly reactive powder, it reacts with water and oxygen in the air to form oxides, so the amount of manganese ions eluted into water is reduced, and there is a problem with the sustainability of the reduction reaction. .

  On the other hand, in the case of alloys, those that form a passive state, such as stainless steel containing chromium in the iron-based alloy, inhibit the elution of metal into water, so there is a problem in the persistence of the reduction reaction, forming a passive state. Preferred is an alloy that does not. Therefore, in the present invention, iron powder containing a predetermined amount of sulfur is used as a reducing agent.

  The iron powder used as a reducing agent in the present invention has a large reaction area (that is, a large specific surface area). For example, granules may be used, but the size is preferably about 1 μm or more and 10 mm or less in terms of average particle size from the viewpoint of handleability. More preferably, it is 10 μm or more and 5 mm or less.

  The purification method of the present invention includes (1) a step of reducing nitrate nitrogen or nitrite nitrogen to ammonia nitrogen, and (2) a step of removing ammonia nitrogen.

  As the step (1), for example, as shown in FIG. 1, contaminated water (nitric acid, nitrite-containing nitrogen-containing water) is passed from the introduction part to the layer filled with the reducing agent (reducing agent packed layer), This is achieved by adopting a structure for taking out (discharge part) as ammoniacal nitrogen-reduced water. Alternatively, as shown in FIG. 2, contaminated water (nitric acid, nitrite-containing nitrogen-containing water) is introduced into the stirring tank in which the reducing agent is dispersed, and taken out as ammoniacal nitrogen-reduced water (discharge part). It is also achieved by adopting a configuration. In any case, it is desirable to shut off the air from the outside by performing a nitrogen purge or the like in order to cut off the oxygen supply from the outside and secure a reducing atmosphere.

  In the reducing agent packed layer shown in FIG. 1, powder particles (for example, natural minerals) for increasing the porosity of the packed layer may be used in combination with the reducing agent in order to ensure water permeability. . In addition, both upward flow and downward flow can be used for passing contaminated water.

  Further, when the stirring tank as shown in FIG. 2 is employed, a stirrer may be installed as shown in order to increase the reactivity. This stirrer can employ either a wing-like one or a conveyor-like one. Further, the settling tank shown in FIG. 2 is for preventing the floating reducing agent from being discharged to the outside, and is provided side by side as necessary.

  Next, in the step (2), at least a conventionally known method such as a microbial denitrification method, an ammonia stripping method, a discontinuous point chlorine addition method, an ion exchange method, a zeolite adsorption method, a membrane separation method, or a catalytic denitrification method is used. Ammonia nitrogen is gasified and removed by one or more methods.

  It is also effective to employ a configuration in which an adsorbent having a cation exchange capacity is simultaneously brought into contact with contaminated water together with the reducing agent (iron powder) used in the present invention. Ammonia nitrogen can be removed simultaneously with reduction from nitrate nitrogen to ammonia nitrogen. Examples of the adsorbent having cation exchange ability include natural minerals such as zeolite, silica gel, activated alumina, cation exchange resin and the like.

When the reducing agent used in the present invention contains at least an iron component, the reduction reaction proceeds according to the following formula (1), and hydroxide ions are concentrated with the passage of time, and the pH rises to 9 or more. . The influence of pH on the passive potential of Fe is shown in FIG. 3 (in the figure, region A shows a stable region of Fe, region B shows a corrosion region, and region C shows a passive region).
2Fe + O ₂ + 2H ₂ O → 2Fe ²⁺ + 4OH ⁻ (1)

  As the pH increases, it is considered that the passive region is expanded (passivity is formed) and the reduction reaction is difficult to proceed. However, by adding chlorine to the treated water (that is, by adopting the discontinuous point chlorine addition method), hydrogen ions are generated, so that the increase in pH can be suppressed and ammonia nitrogenous from nitrate nitrogen or nitrite nitrogen. This is preferable because ammonia nitrogen can be removed simultaneously with the reduction to nitrogen.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and is suitable as long as it can meet the purpose described above and below. It is also possible to carry out by changing to the above, and they are all included in the technical scope of the present invention.

[Example 1]
(Reduction test from nitrate nitrogen to ammonia nitrogen)
Ion exchange water: To 2,000 mL, 243 mg of sodium nitrate reagent (special grade: manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred using a stirrer to obtain an aqueous solution (hereinafter referred to as “raw water”). 250 mL of this raw water is put into a 500 mL polyethylene container, and 50 g of iron powder with different sulfur content is added as a reducing agent, and nitrogen gas is purged at a flow rate of 500 L / min for 3 minutes, and then at 25 ° C. The shaker was shaken at 140 rpm for up to 96 hours.

  The concentration of nitrate nitrogen and nitrite nitrogen in the raw water and after shaking for 48 hours, after shaking for 48 hours, and after shaking for 96 hours was measured for each iron powder used.

  The concentration of nitrate nitrogen and nitrite nitrogen in the raw water and the solution after shaking for each time was determined using a portable absorptiometer (trade name “ODYSSEY” manufactured by HACH). Nitrate nitrogen was analyzed using a TNT reagent by a diazotization method.

  These results are shown in Table 1 below (Experiment Nos. 1 to 6). As the sulfur content increases, the concentration of nitrate nitrogen is reduced, and in particular, iron with a sulfur content of 0.3% by mass or more. It can be seen that the nitrate nitrogen concentration was effectively reduced when powder was used as the reducing agent (Experiment Nos. 2 to 6).

[Example 2]
(Reduction test from nitrate nitrogen to ammonia nitrogen)
Ion exchange water: To 1000 mL, 121 mg of sodium nitrate reagent (special grade: manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred using a stirrer to obtain an aqueous solution (hereinafter referred to as “raw water”). 250 mL of this raw water was placed in a 500 mL polyethylene container, and experiment No. 1 was used as a reducing agent. 125 g of iron powder having a sulfur content of 1.20% by mass and an average particle size of 54 μm used in No. 5 was added and purged with nitrogen gas at a flow rate of 500 L / min for 3 minutes, and then 140 rpm on a horizontal shaker at 25 ° C. And shaken for 48 hours.

[Example 3]
(Ammonia nitrogen adsorption test with reducing agent and cation adsorbent from nitrate nitrogen to ammonia nitrogen)
250 mL of the raw water is put into a 500 mL polyethylene container, and 62.5 g of the same iron powder as used in Example 2 is used as a reducing agent, and zeolite (trade name “ZO # 2070”: Nitto) as a cation adsorbent. After adding 62.5 g of powdered product and purging nitrogen gas at a flow rate of 500 L / min for 3 minutes in the same manner as in Examples 1 and 2, the mixture was shaken for 48 hours at 140 ° C. with a horizontal shaker at 25 ° C. I did it.

  The concentrations of nitrate water and nitrite nitrogen in the raw water and the solutions after shaking in Examples 2 and 3 were measured in the same manner as in Example 1. The concentration of ammonia nitrogen was also measured by the following method. The results are shown in Table 2 below together with the total amount of nitrate nitrogen, nitrite nitrogen and ammonia nitrogen (total nitrogen).

[Ammonia nitrogen concentration measurement]
The concentration of ammoniacal nitrogen was analyzed by a distillation-titration method (JIS K 0102 42.1, 42.3). In addition, each nitrogen concentration was analyzed for the solution after shaking by the filtrate which filtered with the suction filter [Omnipore membrane (model number: JMWP04700)].

  From this result, it can be considered as follows. In Example 2, nitrate nitrogen was reduced from 20.3 mg / L to 1.2 mg / L, ammonia nitrogen was 18.0 mg / L, and nitrate nitrogen was reduced to ammonia nitrogen. I understand that

  On the other hand, in Example 3, nitrate nitrogen remained at 7.2 mg / L, but total nitrogen was reduced from 20.3 mg / L to 7.2 mg / L. This difference in the total nitrogen concentration is considered to be adsorbed on zeolite which is a cation adsorbent. It can be seen that this method can reduce the total nitrogen concentration.

  Thus, it turns out that total nitrogen can be reduced efficiently and simply by using together the iron powder containing sulfur, and the adsorbent which has cation exchange ability.

Claims (2)

In purifying water contaminated with nitrate nitrogen and / or nitrite nitrogen, the contaminated water is passed through a reducing agent packed bed in which powder particles and a reducing agent are used in combination, and sulfur is reduced to 0.1 . Using iron powder containing 3 to 2.0% by mass as the reducing agent, nitrogen purge is performed to block air from the outside, and the contaminated water and the reducing agent are brought into contact with each other. Alternatively, a method for purifying contaminated water, comprising purifying water by reducing nitrite nitrogen to ammonia nitrogen and removing ammonia nitrogen from water containing ammonia nitrogen.   The contaminated water is brought into contact with an adsorbent having a cation exchange capacity together with the iron powder, and simultaneously with the reduction of nitrate nitrogen and / or nitrite nitrogen to ammonia nitrogen, removal of ammonia nitrogen is performed. The method for purifying contaminated water according to claim 1 to be performed.

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