JP4440323B1 - Leached water purification method and purification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat a liquid (concentrated liquid) containing impurities generated together with treated water by treating the water leached from a managed final disposal site (leached water) in a water treatment facility.
SOLUTION: A method for purifying leachate, which adjusts the pH of the leachate to an alkali side and mixes silica-containing inorganic substances to precipitate and remove metals contained in the leachate. Feature leachate purification method and apparatus. The inorganic substance containing silicic acid is fly ash.
[Selection] Figure 1

Description

  The present invention relates to a method and apparatus for treating leachate discharged from industrial waste disposal sites containing toxic substances, metal ions, etc. and wastewater containing environmental toxic substances similar thereto, and more specifically, Concerning purification methods and purification equipment for desalination and advanced treatment of leachate and sewage at managed final disposal sites, leachate by removing metals such as magnesium, calcium and iron contained in leachate and sewage The present invention relates to a useful method and apparatus that should be used for the purification of wastewater and the pretreatment for recovering valuable materials from leachate.

  In recent years, the amount of waste discharged has increased due to economic growth, improvement of people's lives, etc., and the waste treatment has been changed to a stable final disposal site, a managed final disposal site, and a cutoff final disposal site according to the waste. Disposal or ocean dumping. However, international regulations on ocean dumping have been strengthened, and what can be dumped has become very limited. In addition, waste that was considered to have few problems in the past has been accepted for treatment at a stable final disposal site with a simple structure and low construction costs. Due to the stricter regulations, more and more waste is processed into managed final disposal sites.

  A managed final disposal site is a managed final disposal site that requires a leachate collection and drainage facility for its wastewater treatment and has a leachate collection and drainage facility. Usually, the storage facility has a waste storage section surrounded by a concrete dam and a water-impervious layer made of rubber sheet or the like, and is provided with an enclosure for preventing the scattering of waste around these. At the bottom of the waste storage section, leachate collection and drainage equipment is provided for allowing the leachate that has reached the bottom to flow naturally without collecting it and to collect it into the leachate treatment facility.

  The embankment has sufficient strength against waste pressure, loading load, water pressure, etc. in order to safely store the required amount of landfill waste. The impermeable groove is to prevent the contamination of public water and groundwater by leachate and the adverse effects on the surrounding environment caused by these. The structure of the leachate collection and drainage facility is, for example, a pipe tub that is covered with a coating filler such as chestnut and the outer periphery is covered with a wire mesh or the like so that water can easily permeate.

  In this way, in the management-type waste disposal site, a rubber sheet for shielding is laid on the bottom of the disposal site, and the waste is landfilled on top of it, or concrete storage facilities are provided in the soil. In this, waste is disposed of in landfill, and leachate that leaks out from the waste is treated with leachate treatment equipment at the terminal of the disposal site by the water collecting pipe provided in the bottom of the rubber sheet diaphragm or in the concrete storage facility. It is transferred to. The leachate from managed disposal sites is high in total organic carbon (TOC) and total nitrogen (TN) and is often contaminated with various environmental hazardous substances such as harmful inorganic or organic chemicals. They are collected at the disposal facility at the end of the disposal site, detoxified, and discharged outside the disposal site. In this way, leachate containing hazardous substances, harmful substances, etc. that leach out from waste is collected from the inside shielded inside the shielding sheet or shielding concrete and detoxified, so it remains harmful. Although it does not flow into the environment, its detoxification treatment is difficult with a single means because of various pollutants, and there is a problem that it costs a lot of money.

  In general industrial waste disposal sites, the surrounding area is often contaminated with waste leachate. In such cases, leachate detoxification treatment similar to the above is required to prevent groundwater contamination. It becomes. There has been proposed a method for detoxifying leachate containing this kind of environmentally hazardous substance by combining chemical and / or physicochemical decomposition means and biological treatment means. As can be seen from these literatures, detoxification of the leachate from the final disposal site requires a complex combination process, but it still requires extremely high costs to purify to a satisfactory level. (Patent Document 1).

  In addition, a method for purifying water contained in contaminated soil around a waste disposal site by wide-area electrolytic treatment has been proposed (Patent Document 2). However, there are only a limited number of substances that can be transformed into a form that is harmless to the environment by electrolytic oxidation treatment. More basically, rather than detoxifying the contaminated soil over a wide area after the contamination has spread to the surrounding soil, it is the natural response to detoxify the waste leachate before reaching the soil contamination, and It is practical.

  Then, the method of decomposing | disassembling hardly decomposable organic compounds, such as dioxin and PCB in a landfill leachate waste_water | drain, using the electrolyzer using a metal electrode is proposed (patent document 3). In the study by the present inventors, it can be said that the electrolysis efficiency by the metal electrode is not sufficiently high and needs to be improved. In fact, the decomposition products of these hardly-decomposable organisms remain in the electrolytically treated waste liquid. Since it cannot be discharged, secondary wastewater treatment is required.

  Further, in a water treatment method and a water treatment apparatus for desalting and highly treating leachable sewage etc. in a managed final disposal site, as a technique for treating a concentrate produced by purifying leachate by reverse osmosis, for example, concentration In order to facilitate the post-treatment of the liquid, after separating leachate containing organic substances with a membrane separation treatment device, the separated concentrated solution is evaporated to dryness with an evaporator and the exhaust gas from the evaporator is condensed. Condensate in the device, and then biologically treat the condensate condensed by the condensing device (Patent Document 4), detoxify the leachate from the waste landfill site, high purity NaCl salt and In separating and purifying KCl salt, leachate is introduced into a reverse osmosis membrane filtration device and filtered, excess water from the reverse osmosis membrane filtration device is discharged, and the concentrated solution from the reverse osmosis membrane filtration device is passed to an NF filtration device. Introducing NF After the permeated water of the apparatus is introduced into the chelate adsorption tower and chelate adsorption treatment is performed, it is heated by a heating type crystallizer to crystallize an NaCl salt, and then cooled by a cooling type crystallizer to crystallize a KCl salt. An apparatus (Patent Document 5) and the like have been proposed.

  Furthermore, with regard to salt recovery, in order to recover salt suitable for reuse efficiently with simple and compact equipment from wastewater such as leachate that flows out from the final disposal site for waste, the salt-containing treatment There has been proposed a technique for recovering a salt from treated water obtained by subjecting water to a reverse osmosis membrane device to obtain a concentrated solution and then bringing the concentrated solution into contact with activated carbon (Patent Document 6).

JP 2000-354892 A JP 2000-167559 A JP 2003-126860 A Japanese Patent Laid-Open No. 11-188389 JP 2001-321768 A JP 2007-209919 A

The present invention has been made to solve the problems of the prior art as described above. In particular, the present invention relates to a leachate treatment technology installed in a managed final disposal site, and when purifying leachate or leachate. It is an object of the present invention to provide a processing apparatus or a processing method for the produced concentrated liquid.
When leachate is treated with a conventional water treatment device, some salts such as calcium and some organic substances can be removed, but NaCl other than those salts, organic substances that are hardly biodegradable, and difficult to adsorb activated carbon Organic substances and the like cannot be completely removed. Therefore, when the treated water is discharged as it is to the river or the like, there has been a problem that the river and soil may be contaminated by these salts and undecomposed organic matter. Thus, it has been proposed to treat sewage with a membrane flow evaporator or reverse osmosis membrane device that can remove salts and persistent organic substances in raw water that cannot be removed by this type of water treatment device.

  However, in these apparatuses, when raw water containing salts and organic substances is treated, the raw water is separated into a concentrated solution obtained by concentrating the salts and organic substances and treated water from which the salts have been removed. The separated treated water is easy to treat even if it is reused or discharged as it is. However, if organic matter is contained in the raw water, the organic matter is not decomposed and mixed into the concentrated solution, It is difficult to discharge and reuse a concentrated solution containing a high concentration of as is, and how to carry out this post-treatment has become an important issue.

  The present invention solves the problem of the prior art that a satisfactory method is not obtained in terms of cost and objective satisfaction even when combining conventional detoxification means for the treatment of leachate from a managed final disposal site. In view of this, the inventors have developed by accumulating intensive research, and the purpose is to leach water from industrial waste disposal sites, particularly managed final disposal sites, and similar contaminated wastewater (hereinafter both The detoxification means that can be made highly detoxified at low cost.

  More specifically, water that is leached from a managed final disposal site (leached water) is treated at a water treatment facility, and the purpose is to treat liquids (concentrates) that contain impurities that are generated along with the treated water. is there. It is known that the components of this concentrated liquid are inorganic salts mainly composed of sodium chloride, and involve considerable risks in processing. Therefore, the present inventors provide a technique for removing metals such as magnesium, calcium, and iron contained in the concentrated liquid and aim to purify the concentrated liquid. Furthermore, the present invention produces an alkali solution (main component caustic soda) and an acid solution (main component hydrochloric acid) using sodium chloride, which is the main component of the concentrate, by removing impurities in the concentrate. The purpose is to encourage the development of new technologies related to the technology to be reused.

The present invention relating to a method for purifying leachate concentrate for solving the above-described problems comprises the following technical means.
(1) A method for purifying leachate concentrate, wherein the fly ash collected from pulverized coal combustion is adjusted to the alkali side by removing ammonia contained in the concentrate and adding sodium hydroxide. A method for purifying leachate, which comprises precipitating and removing magnesium, calcium and iron contained in the concentrate by mixing 1.0 to 4.0% by weight .
( 2 ) The method for purifying leachate according to (1 ) above, wherein the pH value of the concentrated liquid whose pH is adjusted is 10 or more.
( 3 ) The pH is adjusted to the alkali side by removing ammonia and adding sodium hydroxide, and fly ash collected from pulverized coal combustion is mixed in 1.0 to 4.0% by weight in the concentrated liquid. The method for purifying leachate according to (1) or (2) above, wherein a step of adding carbon dioxide gas or carbonate to the concentrated solution after removing the magnesium, calcium and iron contained in the precipitate is provided.
( 4 ) The method for purifying leachate according to any one of (1) to ( 3 ), wherein a step of recovering ammonia to be removed is provided.
(5) The method for purifying leachate according to ( 4 ) above, wherein the nitrogen-containing material is recovered while blowing air and heating.

The leachate purification method of the present invention can be implemented as the following purification device.
That is, a pH adjuster that adjusts the leachate concentrate to alkalinity, a blender that feeds fly ash collected from pulverized coal combustion into the concentrated solution after pH adjustment, and separates the generated precipitate and silicic acid-containing inorganic substances from the concentrate An apparatus for purifying leachate, wherein the metal contained in the concentrated liquid comprising a filtering device is removed by precipitation.
Further preferably, (1) the pH is adjusted to the alkali side, and carbon dioxide or carbonate is added to the concentrated solution after precipitation and removal of metals contained in the concentrated solution by mixing the fly ash. This is a leachate purification device provided with an apparatus for charging, or (2) a leachate purification device provided with a nitrogen-containing material recovery device that volatilizes when the pH of the concentrate is adjusted to the alkali side.

The present invention has the following effects.
(1) It is possible to provide a method and apparatus for treating leachate discharged from an industrial waste disposal site containing hazardous substances and the like, and wastewater containing environmentally hazardous substances similar thereto.
(2) To provide a useful method and apparatus that can be used as a pretreatment for purifying leachate and recovering valuable materials from leachate by precipitating and removing metals such as magnesium, calcium, and iron contained in leachate. be able to.
(3) A simple leachate purification method and apparatus for removing metals in the leachate by a simple process comprising a neutralization operation and a precipitation filtration operation can be provided.
(4) The leachate treated in the present invention can easily and efficiently recover valuable materials contained therein.
(5) The present invention provides a technique useful as a novel application of fly ash, in which the treatment of fly ash, which is expected to reach about 10 million tons, is considered a problem.

At present, the entire amount of waste or landfill disposal at a final disposal site is generally performed after intermediate treatment such as incineration. The leachate generated at this final disposal site, for example, shows the results of water quality analysis shown in Table 1, and requires advanced water treatment because it contains contaminants such as salts and organic matter that are leached from the waste. . In such a final disposal site, leachate containing various salts leached from landfilled waste is desalted and variously treated by electrodialysis, reverse osmosis membrane, thin film flow-down evaporator, etc. In particular, according to desalting using a reverse osmosis membrane or a thin film falling evaporator, leachate can be treated efficiently and treated water with very good water quality can be obtained.
In the present invention, the leachate refers to “waste water that has permeated rainwater or the like in a landfill disposal site and exuded by touching the waste”. In the present invention, the leachate is subjected to some treatment. The produced liquid substance, for example, a concentrated liquid is also included. Hereinafter, the present invention will be described using a concentrated liquid produced by treating leachate as a specific example. An example of the leachate analysis is shown in Table 1.

  However, when the leachate is treated, treated water with extremely good water quality can be obtained, but organic matter, various metals, etc. are concentrated in the concentrate, so that advanced water treatment technology is required for the treatment. In addition, a large amount of processing equipment, adsorbents for processing, and chemicals were required. The present invention solves such problems of the prior art, and particularly relates to a technique for purifying and purifying the concentrated liquid by removing metals contained in the concentrated liquid produced by treating the leachate. In addition, it further contributes to the development of technology that allows further processing of the concentrated liquid to enable the recovery process of useful substances and release to the natural world.

  The leachate is, for example, an evaporation method (multi-effect method, multistage flash evaporation method, vapor pressure concentration method) freezing method, dialysis vaporization method, reverse osmosis method, etc. Specifically, a thin film flow down evaporation device, a reverse osmosis membrane device The thin film flow-down evaporator has, for example, a large number of circular tubes inside, and waste water flows down the inner wall of the circular tubes. It consists of an evaporator heated with steam from the outside of the tube. The waste water is once stored in the raw water tank, and then reaches the thin film flow-down evaporator by the raw water pump. While the waste water flows down along the inner wall of the circular tube in the thin film flow evaporator, it is heated by the steam outside the tube to evaporate the moisture, and the generated steam enters the gas-liquid separator. In the gas-liquid separator, the concentrated liquid brought together with the flowing-down steam is separated. The concentrated liquid remaining in the lower part of the evaporator and the concentrated liquid separated by the gas-liquid separator are discharged. The steam emitted from the gas-liquid separator is heat-exchanged with the cooling water in the condenser to become a condensate.

  The reverse osmosis membrane device includes, for example, a device using a reverse osmosis membrane module in which a plurality of spacers are arranged, and a flat membrane-like reverse osmosis membrane is interposed between the spacers. And a reverse osmosis membrane module in which a reverse osmosis membrane (flat membrane) is interposed between the spacers. The reverse osmosis membrane module has a structure in which disk-type flat membranes and spacers with dimples are alternately stacked. A reverse osmosis membrane module has a cylindrical reverse osmosis membrane module body in which a plurality of sets of reverse osmosis membrane portions each having a disk-like flat membrane (reverse osmosis membrane) provided between disc-like spacers are laminated. Configured. A treated water channel for introducing treated water is provided on the inner peripheral surface of the module body of the reverse osmosis membrane module, and the treated water is introduced from the treated water channel to the surface of the reverse osmosis membrane. The treated water separated by the reverse osmosis membrane is discharged by the permeate pipe. Moreover, the concentrated liquid concentrated by each reverse osmosis membrane is discharged out of the module body by the concentrated liquid pipe.

  The following Table 2 and Table 3 show an example of the water quality analysis result of the purified water treated by the thin film falling evaporator and the concentrated liquid produced by the treatment.

  As shown in Table 3, the concentrated solution contains various compounds. Among them, chloride ions, sodium ions, potassium ions, ammonium ions, nitrate ions, sulfate ions, etc. are present at high concentrations. is doing. The metal content in the concentrate varies depending on the type of waste and the operation method of the disposal facility, but the upper limit of the metal content is about 1800 ppm for calcium, about 7500 ppm for magnesium, and about 20 ppm for iron. Is often in the range of about 800 ppm calcium, about 1000 ppm magnesium, and about 10 ppm iron. A special treatment is required to recover these metal ions for effective use or detoxification. For example, to treat a solution having various impurities such as a concentrated solution by electrodialysis and to separate chloride ions and alkali metal ions into acid and alkali, magnesium, calcium and iron present in the concentrated solution When inorganic substances such as components are present, they adhere to the electrodialysis machine as a scaling component, give a large load to the membrane itself, and even if it can be separated, the quality of the product itself deteriorates. It is not economical because it takes many times. The present invention develops and proposes a technique for efficiently removing metal ion components such as magnesium, calcium and iron components in a concentrated liquid.

  In general, most of the metal components present in the solution can be precipitated and removed as a hydroxide by adjusting the pH of the solution to the alkali side, but an alkali such as sodium hydroxide (NaOH) is added to the concentrate. Thus, the metals cannot be completely removed from the concentrate by simply adjusting the solution to the alkali side. That is, metals such as calcium, magnesium, and iron that are present in a dissolved or suspended state in the concentrate change into a hydroxide form by the addition of alkali. It is considered difficult to remove efficiently from the solution. Therefore, in order to efficiently perform precipitation and filtration operations of metal hydroxides, it is preferable to add a silicic acid-containing inorganic substance. For example, fly ash which is a silicic acid-containing substance is used. In particular, it was found that the precipitation filtration operation can be performed quickly by the presence of fly ash. Fly ash is a kind of waste generated in large quantities in a thermal power plant or the like, and the present invention provides this effective utilization technique.

  The pH of the concentrate is usually around 4, but an alkali, for example, sodium hydroxide is added to the concentrate to adjust the pH of the concentrate to the alkali side to convert dissolved metals into hydroxides. Can do. The pH of the concentrated solution is preferably adjusted to the alkali side, for example, pH 10 or higher, but by further adjusting the pH to a range of 12 or higher, conversion to a metal hydroxide is promoted. The amount of alkali added varies depending on the pH of the concentrate, the type of coexisting compound, the content, and the like, but it is preferable to add alkali using the pH of the concentrate as an index. The temperature of the concentrated solution at the time of adding the alkali is preferably high, for example, 80 ° C. or more from the viewpoint of precipitation, but is not particularly limited. It has been found that the concentrated solution after the alkali is added and the precipitate is removed contains, for example, calcium ions, magnesium ions, and iron ions, and further contains ammonium ions and nitrate ions.

  However, precipitation filtration of the alkali-treated concentrate is difficult. For example, it takes several hours to filter about 5 L of the concentrate containing the precipitate, and in some cases it cannot be filtered. I couldn't. Thus, it has been clarified that the filtration time is significantly shortened by adding fly ash to the concentrate together with the pH adjustment of the concentrate. The fly ash may be added to the concentrate before or after adjusting the pH of the concentrate, and at any point in time between alkali and fly ash. No special operation is required for the addition and mixing of the fly ash concentrate, and a normal mixing and stirring device is applied. Although there is no restriction | limiting in particular also about the liquid temperature at the time of addition of fly ash, Operation in 70 degreeC or more is suitable when the formation state of precipitation particle | grains, the case where the collection process of ammonia is provided, etc. are considered.

In fly ash used in the present invention, the dust collected from the combustion gas of the partial pulverized coal combustion boiler (fly ash in a narrow sense) or the combustion gas of the pulverized coal combustion boiler is used as an air preheater, Contains dust collected when passing through a charcoal container (sink), or dropped on the bottom of a pulverized coal combustion boiler (clinker), etc. Examples include finely collected powder or coarse powder obtained by classifying raw powder or raw powder, and fine powder or coarse powder obtained by classifying raw powder, or pulverized powder subjected to pulverization classification. The fly ash used in the present invention can be appropriately selected from these, mixed and used, or commercially available fly ash can be appropriately selected and used. Examples of commercially available fly ash include fly ash sold in various places such as final ash (JIS type 1), four-electric fly ash (JIS type 2 and eco-ash (JIS type 4)).
The main components of typical fly ash are silica (SiO ₂ ) and alumina (Al ₂ O ₃ ). These two inorganic substances account for 70 to 80% of the total, and other small amounts of ferric oxide (Fe ₂ O ₃ ), magnesium oxide (Mg0), calcium oxide (CaO), and a collection of fine spherical particles in which the particle size distribution is 0.1 mm or less and the particle size accounts for 80% or more.

  In order to adjust the concentrated solution to the alkali side and precipitate various metals such as alkaline earth metals and iron, it is preferable to adjust the pH of the concentrated solution to about 10 or more. The nitrate nitrogen component in the liquid is difficult to vaporize. Therefore, when providing the process of recovering the ammonia or nitrate nitrogen component from the concentrate, it is preferable that the pH of the concentrate is 12 or more.

  In treating the concentrate with fly ash, in order to determine the range of the optimum addition amount, 1.0 to 4.0 wt% fly ash was added to the concentrate adjusted to pH 12 with alkali. When the metal content of the concentrate was measured, the metal concentration of the concentrate after treatment was reduced to a range of 0.48 to 1.6 mg / L for magnesium ions, and a range of 265 to 411 mg / L for calcium ions. It was found that the amount of iron ions decreased to a range of 0.18 to 0.22 mg / L. By performing the test while changing the amount of fly ash added, the amount of fly ash added to the concentrate is preferably 0.5 to 6% by weight, more preferably 2 to 4% by weight. % Range was found. If the amount of fly ash added is less than the lower limit, the precipitation accelerating effect decreases and becomes impractical, and if the amount exceeds the upper limit, uniform addition and mixing of fly ash becomes difficult, and the processing cost increases due to the price of fly ash. In addition, a phenomenon such as an increase in impurities in the treated concentrated liquid occurs, which is not desirable.

  FIG. 1 shows the relationship between the added amount of fly ash and the precipitation action of the precipitate. From FIG. 1, it was found that as the amount of fly ash added was increased, the sedimentation of the precipitate was accelerated, but it was optimal to add 3% by weight of fly ash. If it was not added with fly ash, sedimentation of the precipitate stopped, and thereafter the precipitate did not settle.

  It is well known that fly ash contains arsenic and selenium as impurities. For example, 1 kg of dried product contains 17.2 mg of arsenic and 2.2 mg of selenium, but is concentrated after treatment with fly ash. It was found that the residual concentration in the liquid was very small as shown in Table 4, for example.

  The concentrated solution subjected to the step of precipitation removal of metals such as alkali metal compounds and iron by adjusting to alkalinity and adding fly ash contains a large amount of nitrogen-containing substances. Ammonia nitrogen and nitrate nitrogen can be volatilized and recovered by addition of strong alkali. The concentrated liquid contains, for example, 6960 mg / L of ammonia nitrogen and 1390 mg / L of nitrate nitrogen. After the pH of this concentrate is adjusted to 12, the nitrogen component contained in the air is discharged into the atmosphere by heating from 86 to 96 ° C. in the container and blowing air to recover the nitrogen component. it can. It was found that about 99% of the ammonium nitrogen contained in the concentrate was released after 4 hours and about 98% of the nitrate nitrogen was released. This indicates that 98% of the nitrogen component contained in the concentrate can be recovered by the conventional method.

  It is clear from the above description that metals such as magnesium, calcium, and iron can be removed by treating the concentrate to be alkaline, and the concentrate can be purified, but at the same time, a considerable amount of calcium ions cannot be removed. Was found to remain. The cause of the difference in behavior of such calcium ions is not clear, but it is also possible that calcium hydroxide becomes a fine precipitate and is difficult to filter. When the alkali-treated concentrated liquid is processed in some steps and then effectively used, it may be necessary to remove the calcium ions when it is necessary to make the calcium ions have the same concentration as the magnesium ions.

  Therefore, changes in the calcium ion concentration due to the carbon dioxide gas blowing process or the sodium hydrogen carbonate charging process are applied to the filtrate (pH 13: containing 201 ppm of calcium ions) after removing the magnesium ions and iron ions by alkali treatment of the concentrate. investigated. As a result, it was found that the calcium ion concentration was reduced to 1.2 to 1.8 ppm by blowing carbon dioxide. On the other hand, when 20% sodium bicarbonate was added in excess, the calcium ion concentration decreased to 1.0 ppm, but the concentration of carbonate ion after the treatment showed a large value. It was found that the standing time of the liquid after carbon dioxide was charged was 30 minutes, the calcium concentration in the supernatant liquid was 1.0 to 2.0 ppm, and the hydroxide was precipitated rapidly.

  Next, details of the present invention will be described with reference to examples. The present invention is not limited to these examples.

  In this example, alkali was added to the concentrated solution to remove precipitates of metal ions in the concentrated solution. The concentrate used has the components shown in Table 2. 500 mL of this concentrate is placed in a container, sodium hydroxide solution (6N) is added to adjust the pH to 12, and then a predetermined amount of fly ash (four electric vehicles) is used. Made by Business Co., Ltd .: Product name Ekoash (JIS 4 types) was added and stirred so that it was evenly dispersed. The distance to the upper surface of the precipitate was measured, and the concentration of metal ions contained in the supernatant was collected for each measurement.The sedimentation rate of the precipitate is shown in Table 5, and the concentration of metal ions in the supernatant The measured values are shown in Table 6. For the analysis of the metal ions, the supernatant was filtered through a filter paper Whatman No. 41 and used as a sample.

From Table 5, it became clear that sedimentation of the generated precipitate was promoted by adding fly ash. As the added amount of fly ash, the precipitation accelerating effect was recognized by adding 1% by weight or more. However, when the fly ash was left for 3 hours, the difference in effect due to the added amount of fly ash disappeared. The effect of promoting precipitation by fly ash was effective from the addition of about 0.5% by weight. From the metal ion analysis results in Table 6, the effect of removing iron ions and magnesium ions in the concentrated solution was remarkable. A removal effect was also observed for calcium ions. In addition, almost no elution of arsenic and selenium components contained in fly ash into the concentrate was observed.
From the above results, it has been found that by adjusting the pH of the concentrate to the alkali side and adding fly ash, precipitation of metal ions contained in the concentrate and precipitation settling are promoted.

  Component analysis of the concentrate revealed that the concentrate contained a large amount of ammonium nitrogen and nitrate nitrogen, so in this example, an attempt was made to remove or recover the nitrogen component. 3 L of the concentrated solution was placed in a 5 L beaker equipped with a stirrer and an aeration device, and a sodium hydroxide solution (6 N) was added to adjust the pH to 12. The test apparatus is shown in FIG. The concentrated liquid whose pH was adjusted was heated to 80 ° C. or higher to promote the volatilization of the nitrogen compound, and the change in the content of the nitrogen compound every hour was measured over 4 hours. The test results are shown in Table 7. The ammonium nitrogen contained in the concentrate at about 7000 mg / L decreased to about 100 mg / L after 4 hours, and the nitrate nitrogen contained at about 1400 mg / L decreased to about 34 mg / L after 4 hours. It was. This test result shows that 99% of ammonium nitrogen and nitrate nitrogen can be recovered, and the concentrate can be purified.

  As is clear from the results of Example 1, the pH of the concentrated solution was adjusted to the alkali side, and calcium ions were removed by the treatment with fly ash. It has been found that L to about 400 mg / L may remain. Although magnesium ions are almost completely removed, the different behavior of calcium ions is not clear for any reason, but the presence of calcium ions in the concentrate further increases the concentration of the treated concentrate. Since it is considered that the treatment is an obstacle to the effective use of the concentrated solution, the treatment for reducing the calcium ion concentration was tested. For example, when the concentrated solution is electrodialyzed, magnesium ions and iron ions in the concentrated solution are particularly hindered, but it is preferable to reduce the calcium ion concentration in the solution.

Therefore, a test for confirming that calcium ions are replaced by calcium carbonate and removed using carbon dioxide was performed. In the same manner as in Example 1, a solution was prepared by removing the precipitate formed by adjusting the alkaline pH and adding fly ash to the concentrated solution. The calcium ion concentration and carbonate ion concentration after the following treatment was performed on 400 mL of the sample were measured.
1: Untreated 2: Carbon dioxide was introduced at 1 liter / min, and the introduction of carbon dioxide gas was stopped at intervals of 1 minute, and the batch system was passed until there was no pH fluctuation.
3: Carbon dioxide gas was introduced at 1 liter / min, and carbon dioxide gas was continuously passed until there was no fluctuation in pH.
4: Carbon dioxide gas was charged at 1 liter / min and continuously charged for 8 minutes.
5: 40 g of sodium bicarbonate was added and stirred for 30 minutes.
Table 8 shows the results of analyzing the back solution obtained by filtering the treated sample with filter paper (using Whatman No. 41).

As a result, it was found that the calcium ions in the concentrated liquid became calcium carbonate using carbon dioxide gas and could be removed from the solution.
It was also found that the concentration of carbonate ions remaining in the solution after removing calcium ions varied from about 2 times to about 5 times depending on the carbon dioxide gas input conditions. It was also found that there was a relationship between the amount of carbon dioxide and pH at the end of the process.

  Experiments were conducted to confirm the relationship between the amount of carbon dioxide input and the calcium ion removal rate, and the residual amount of carbonate ions in the solution. A sample solution from which magnesium ions and the like were removed was prepared in the same manner as in Example 1, and when this was treated with carbon dioxide gas, the test was performed while changing the carbon dioxide gas charging time, the stirring time, and the standing time. . The solution was filtered through filter paper (using Whatman 5B) and then subjected to analysis. The results are shown in Table 9.

  As a result of the test, it was found that by introducing carbon dioxide into a concentrated solution adjusted with alkali, calcium ions are definitely changed to calcium carbonate and can be removed as a solid. Carbonate ions exist up to a certain pH, but carbonate ions are unlikely to remain until about pH 7.2 to pH 6.7. By stirring, calcium ions are likely to become calcium carbonate. I understood.

  In addition, in this experiment, when comparing carbon dioxide and carbonate, it was clearly found that the calcium ion precipitation separation operation using carbon dioxide has greater merit. However, when treated with carbon dioxide, a significant amount of carbonate ions remain in the solution compared to before treatment. In the electrolytic treatment of the concentrate, it is said that the upper limit of the concentration of carbonate ions present in the solution is 10,000 ppm. Since the carbonate ions dissolved after the treatment with carbon dioxide gas are 10000 ppm or less, it is expected that the electrolytic treatment can be carried out without causing any problems thereafter.

  Comparing the running cost of calcium ion removal between carbon dioxide and sodium carbonate, the amount of carbonate required to process a 500 ml sample solution was about 100 g, and the amount of carbon dioxide was about 60 liters. Assuming that the carbonate is 110 yen / kg and the carbon dioxide gas is 50 yen / kg, the carbonate is 11 yen for 11 yen and 6 yen for the carbon dioxide gas.

  In this example, the relationship between the sedimentation state of precipitates and the metal content after treatment due to the difference in the time of addition of fly ash was tested. The test method was the same as in Example 1, and fly ash was added to the concentrate at a ratio of 3%. The tests were (1) when fly ash was added directly to the concentrate (no pH adjustment), (2) when fly ash was added after adjusting the concentrate to pH 12, and (3) ammonia removal treatment of the concentrate Thereafter, fly ash was added and the pH was adjusted separately. The result is shown in FIG. In (2) and (3), sedimentation of the precipitate started, and a stable sedimentation state was obtained after about 20 minutes. The filtration operation could be easily performed. However, in the case of (1), the initial sedimentation speed was the fastest among the three. However, the produced sediment caused the filter paper (Whatman 41) to clog and filtered the whole liquid. Could not finish. Therefore, it was found that the addition of fly ash and pH adjustment were essential.

  Table 10 shows the analysis results of calcium, magnesium and iron in the filtered liquid. As a result, these metals in the sample obtained the removal rate as expected in (2) and (3). In the case of (3), the removal of calcium and magnesium was particularly excellent. With the addition of fly ash only (1), no metal removal effect was obtained.

  The present invention relates to a method and apparatus for treating leachate discharged from industrial waste disposal sites containing hazardous substances, etc. and wastewater containing environmental hazardous substances similar thereto, and in particular, managed final disposal. The present invention relates to a purification method and a purification treatment apparatus for advanced treatment of leached sewage and the like at a site. The present invention provides useful technology that contributes to the sound operation of a treatment plant, prevention of environmental pollution, and promotion of industrial waste treatment by purifying leachate sewage discharged from an industrial waste treatment plant. is there. Furthermore, the present invention is useful as a basic treatment for purifying leachate by precipitating and removing metals such as magnesium, calcium and iron contained in leachate and recovering valuable materials from leachate. The present invention provides a treatment method and apparatus for leachate, and develops and provides a technology useful for smooth production activities throughout the industry.

The change over time of the amount of fly ash added and the amount of precipitate formed is shown. The experimental apparatus which disperses the nitrogen compound in a concentrate is shown. The change of the amount of precipitation formed by the difference in the addition time of fly ash is shown.

Explanation of symbols

1: Stirring blade 2: Air inlet 3: Gas containing ammonia 4: Motor 5: Container

Claims (5)

A method for purifying leachate concentrate, wherein ammonia is contained in the concentrate and pH is adjusted to the alkali side by adding sodium hydroxide, and fly ash collected from pulverized coal combustion is used . A method for purifying leachate characterized by precipitating and removing magnesium, calcium and iron contained in the concentrate by mixing 0 to 4.0% by weight . The method for purifying leachate according to claim 1, wherein the pH value of the concentrated liquid whose pH is adjusted is 10 or more. It is contained in the concentrate by adjusting the pH to the alkali side by removing ammonia and adding sodium hydroxide and mixing 1.0 to 4.0% by weight of fly ash collected from pulverized coal combustion. The method for purifying leachate according to any one of claims 1 and 2 , further comprising a step of adding carbon dioxide or carbonate to the concentrated solution after removing magnesium, calcium and iron by precipitation. The method for purifying leachate according to any one of claims 1 to 3 , further comprising a step of recovering ammonia to be removed . The method for purifying leachate according to claim 4, wherein the recovery of the nitrogen-containing material is performed while blowing air and heating.