JP2007125484A - Nitrogen-containing wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrogen-containing wastewater treatment method which enables a stable nitrogen treatment by removing problems due to calcium components remaining in wastewater containing calcium and nitrogen when treating the wastewater. <P>SOLUTION: In the nitrogen-containing wastewater treatment method, when the wastewater containing calcium and nitrogen is treated in a state of being supplied with inorganic carbon, nitrogen is treated after reducing the concentration of calcium in the wastewater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for treating waste water containing calcium and nitrogen.

  Wastewater containing calcium and nitrogen is often generated mainly by remaining calcium added to remove fluorine as calcium fluoride from wastewater such as ammonium fluoride.

In recent years, in the field of wastewater treatment, biological treatment is frequently used in which treatment is performed by changing the pollutant in wastewater to harmless substances using the physiological activity of microorganisms. In general treatment of wastewater containing ammonia nitrogen, the wastewater is contacted with autotrophic ammonia-oxidizing bacteria and nitrite-oxidizing bacteria under aerobic conditions to oxidize to nitrite ions or nitrate ions, and then oxygen-free Under conditions, it reacts with heterotrophic denitrifying bacteria to reduce it to nitrogen gas and discharge it out of the system. In recent years, the ANAMMOX (ANaerobic AMMonium OXidation) method has been proposed as a new nitrogen treatment process. In this method, half of the ammonium ions in the wastewater are oxidized to nitrite ions by ammonia-oxidizing bacteria under aerobic conditions, and the ammonium ions and nitrite ions are adjusted to a molar ratio of 1: 1, and then under anaerobic conditions. It is brought into contact with the autotrophic ANAMMOX bacteria group and converted into nitrogen gas and discharged out of the system. For example, Patent Document 1 describes an ANAMMOX method including a step of positively adding calcium. However, the method described in Patent Document 1 is premised on forming granular sludge. All of these nitrogen treatments require efficient use of autotrophic bacteria.
JP 2005-238166 A

  Since the autotrophic bacteria as described above cannot synthesize bacterial cells from organic matter, inorganic carbon such as carbonate ions is used for the synthesis of bacterial cells. Under aerobic conditions, air is supplied into the reaction tank, and carbon dioxide is supplied along with oxygen to produce an inorganic carbon source. However, in anaerobic ANAMMOX treatment, carbon dioxide gas that does not contain oxygen, or carbonate ions and hydrogen carbonate. It is necessary to supply inorganic carbon in the form of ions.

In addition, when aerobic ammonia-oxidizing bacteria oxidize ammonium ions to nitrite ions, the alkalinity of 7.17 kg CaCO ₃ is consumed for the oxidation of 1 kg of nitrogen, and an alkaline agent is added to adjust the pH. As this alkali agent, sodium hydrogen carbonate, sodium carbonate, and the like are used in addition to sodium hydroxide. Of these alkaline agents, sodium hydrogen carbonate and sodium carbonate are preferably used because they can also be a source of inorganic carbon.

  On the other hand, especially in wastewater from semiconductor factories, fluoride ions and ammonium ions are often mixed and discharged as wastewater of the same series by using ammonium fluoride or the like. Drainage standards for both nitrogen and fluorine are established, and it is necessary to remove them from the wastewater. However, since fluoride ions are an inhibitor of microbial reactions, it is necessary to remove fluoride ions before biological treatment of nitrogen. is there.

  As a treatment method of fluoride ions, generally, a method of forming and removing hardly soluble calcium fluoride by adding calcium ions is often employed. In order to achieve the fluorine drainage standard of 8 mg / L or less, it is usually necessary to add excessive calcium ions. Therefore, in addition to nitrogen in the wastewater after fluorine treatment, 100 to 1000 mg / L A certain amount of calcium ions will be present. When sodium hydrogen carbonate or sodium carbonate is added to such wastewater, not only does it produce poorly soluble calcium carbonate, it consumes inorganic carbon, but also calcium carbonate accumulates in the reaction tank, blocking pipes, etc. Causes serious problems such as a decrease in the bacterial cell ratio in sludge.

  Therefore, the problem of the present invention is that when treating wastewater containing calcium and nitrogen as described above, it is possible to remove defects caused by calcium components remaining in the wastewater and perform stable nitrogen treatment. An object of the present invention is to provide a method for treating nitrogen-containing wastewater.

  In order to solve the above-mentioned problems, the nitrogen-containing wastewater treatment method according to the present invention reduces nitrogen concentration after reducing the calcium concentration in wastewater when treating wastewater containing nitrogen and calcium with inorganic carbon supplied. It consists of the method characterized by performing the process.

  That is, in the present invention, before performing biochemical nitrogen treatment of waste water containing calcium and nitrogen, calcium ions are reduced to a predetermined concentration or less, thereby causing no problems such as generation of scale due to calcium salts. The present inventors have found that processing can be performed stably.

  In the nitrogen-containing wastewater treatment method according to the present invention, biological treatment can be adopted as the nitrogen treatment method.

  Nitrogen treatment includes an ammonia oxidation process in which at least a part of ammonium ions in waste water is oxidized to nitrite ions by contacting with autotrophic bacteria under aerobic conditions and waste water containing ammonium ions and nitrite ions. It can be set as the process including the denitrification process which contacts with autotrophic bacteria under anaerobic conditions, and denitrifies.

  When this ammonium ion is nitrified to nitrous acid or nitrate ion by autotrophic bacteria under aerobic conditions, carbonate ion or bicarbonate ion can be supplied for pH adjustment.

  The calcium concentration in the waste water can be reduced by, for example, a method selected from ion exchange, electrodeionization, aggregation precipitation, crystallization, electrophoresis, and aggregation-membrane separation.

  It is preferable that the calcium concentration in the waste water is reduced to, for example, 100 mg / L or less.

  Thus, it is desirable to stably carry out desirable denitrification treatment for wastewater containing calcium, which has been difficult to apply by using the present invention, particularly denitrification treatment using autotrophic bacteria. Is possible.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the flow illustrated in FIG. 1, particularly in the case where wastewater containing calcium and ammonium ions is treated using the ANAMMOX process.

<Removal of calcium>
The wastewater containing calcium and nitrogen is previously reduced in calcium concentration in the calcium (Ca) removing device 1. In the present invention, the calcium removal apparatus 1 is brought into contact with, for example, a method of contacting with an ion exchange resin, a method of electrical desalting (more specifically, desalting using an electric regenerative continuous ion exchange device (EDI)), or carbonate ions. To form and precipitate calcium carbonate, to add crystallization by adding carbonate ions, electrophoresis, to form calcium carbonate by adding carbonate ions, and then to separate the solid and liquid using a membrane separator It can be selected according to the method to be performed. It is desirable that the calcium concentration in the waste water is reduced to about 100 mg / L or less by the calcium removing device 1.

Here, the effectiveness of setting the calcium concentration to 100 mg / L or less is recognized, for example, through the Langeria index as follows. That is, assume that the Langeria index is calculated under the following conditions, for example.
(A) Ca concentration: 500mg / L
pH: 7.5
Water temperature: 30 ° C (normally the temperature at which ANAMMOX treatment is performed)
M alkalinity: 80mgCaCO ₃ / L (equivalent to bringing in from nitritation tank)
In this case, the Langeria index = 0.8.
(B) Ca concentration: 100mg / L
pH: 7.5
Water temperature: 30 ° C (normally the temperature at which ANAMMOX treatment is performed)
M alkalinity: 80mgCaCO ₃ / L (equivalent to bringing in from nitritation tank)
In this case, the Langeria index = 0.1.

  When the Langeria index is a positive value, the larger the positive value, the faster the precipitation of solids including calcium carbonate. When the Langeria index is negative, calcium carbonate does not precipitate. Therefore, by setting the Ca concentration to 100 mg / L or less, the Langeria index can be brought to a value close to 0, and precipitation of calcium carbonate can be prevented.

The Langeria index is an index related to water erosion. When the pH value is low, facilities such as iron pipes such as metals and concrete are often corroded and dissolved. An index is determined, and if the value is negative, the water is erodible. As a method for obtaining the Langeria index, for example, it can be obtained from the pH value of water, the amount of calcium ions, the total alkalinity, and the amount of soluble substance by the following equation.
Langeria index = pH value of water-pHs
pHs = 8.313-log (Ca ²⁺ ) -log (A) + S
Ca ²⁺ : meq / L ・ ・ ・ Ca ²⁺ mg / L ÷ (40.1 ÷ 2)
A: Total alkalinity meq / L ... Total alkalinity mg / L ÷ (100 ÷ 2)
S: 2√μ / (1 + √μ), μ: 2.5 × 10-5sd, sd: soluble substance (mg / L)
(However, the above formula is a value of 25 ° C., and the Langeria index increases by 1.5 × 10 −2 for a temperature increase of 1 ° C.)

<Nitrogen treatment>
As a method for treating nitrogen, a general biochemical treatment method can be used, but the present invention is particularly suitable for a denitrification apparatus using an autotrophic denitrifying bacterium and utilizing the ANAMMOX reaction represented by the following reaction. Can be used for
_{^{1.0NH 4 + + 1.32NO 2 - +}} 0.066HCO 3 - + 0.13H +
→ 1.02N ₂ + 0.26NO _3- + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O

  As described above, the ANAMMOX reaction is a reaction that produces nitrogen gas from ammonia nitrogen and nitrite nitrogen under anoxic conditions by an autotrophic fungus group, and usually a part of ammonia nitrogen in raw water Is converted to nitrite ion by contacting with ammonia-oxidizing bacteria, which are autotrophic bacteria under aerobic conditions, and then subjected to ANAMMOX reaction.

  Ammonia nitrogen-containing wastewater with reduced calcium concentration is supplied to an aerobic reaction tank (for example, nitritation reaction tank 2 shown in FIG. 1) equipped with oxygen supply means, and is an autotrophic bacterium under aerobic conditions. In contact with an ammonia-oxidizing bacterium, some of the ammonium ions are oxidized to nitrite ions. The rate of oxidation is preferably about half that of ammoniacal nitrogen. In addition to the method of flowing the entire amount of wastewater into the aerobic reaction tank 2 and oxidizing a part of ammonia nitrogen to nitrite nitrogen, a method of physicochemical oxidation using a catalyst or the like, a branch line Divide a part of the wastewater as shown in 7 and pass a part through the aerobic reaction tank to oxidize most of the ammonia nitrogen to nitrite nitrogen and mix it with the branched waste water. A method for obtaining waste water containing ammonia nitrogen and nitrite nitrogen can be suitably used. Since alkalinity is consumed with the oxidation of ammonium ions, an aerobic reaction tank 2 is provided with an inorganic carbon source supply means and a pH regulator supply means 8. As the pH adjusting agent, a general alkaline substance can be used, and sodium carbonate, sodium hydrogen carbonate and the like, which are carbonates, can be suitably used in addition to sodium hydroxide and potassium hydroxide.

  The waste water containing ammonia nitrogen and nitrite nitrogen is sent to the ANAMMOX reactor 3 after being oxidized in the aerobic reactor 2. In the present reaction tank 3, contact with the microorganism group responsible for the ANAMMOX reaction is performed under anoxic conditions. The ANAMMOX reaction consumes hydrogen ions, which increases the pH of the solution. Therefore, a pH adjusting agent supply means 9 is added to the reaction tank 3. A general acidic substance can be used as the pH adjuster, and sulfuric acid, hydrochloric acid, and the like can be used. Carbon dioxide or the like can also be suitably used as the pH adjusting gas. Since the microorganism responsible for the main reaction of the ANAMMOX reaction is an autotrophic bacterium, an inorganic carbon source is required for cell growth. If a sufficient amount of inorganic carbon cannot be secured in the inflow water of the ANAMMOX reactor, inorganic carbon is supplied by the inorganic carbon supply means 10. As the inorganic carbon source, sodium hydrogen carbonate, sodium carbonate, carbon dioxide and the like can be suitably used.

  In this way, the concentration of nitrogen in the wastewater is reduced, but some nitrate ions remain due to the ANAMMOX reaction principle. In addition, ammonium ions and nitrous acid may remain depending on processing conditions, and these nitrogen components are processed using a normal nitrification denitrification system or the like as necessary. For example, as shown in FIG. 1, a nitrification reaction tank 4 to which a pH adjuster supply means 9 is added, a denitrification tank 5 to which a pH adjuster supply means 9 and a hydrogen donor supply means 11 are added, and a reoxidation tank 6 are provided. Processing can be performed using a nitrification denitrification system.

  Below, the test done in order to confirm the effect of this invention is shown. This test does not limit the scope of the present invention.

Test 1
Put a 5mm square polyethylene sponge carrier with a fungus group with ANAMMOX activity into a 2L sealable complete mixing tank and stir it with a stirrer, and it will become 0.5kgN / m ³ / day as a nitrogen load Thus, raw water having the composition shown in Table 1 below was continuously passed. A pH sensor was installed in the tank, and carbon dioxide gas was added so that the pH was 7.5.

Comparative test 1
Under the same conditions as in Test 1, raw water to which CaCl ₂ was added was added to the raw water so that calcium chloride was 500 mg / L as calcium ions. In addition, in order to prevent calcium carbonate formation before water flow, sodium hydrogen carbonate of raw water was added to the tank as a separate system.

As a result, during the test period of Comparative Test 1, about 70% of the calcium contained in the raw water was found to be in the treated water, and the remaining 30% was considered to have accumulated in the tank. After about 30 days, the fixed matter considered to be calcium carbonate adhered and accumulated on the inner wall surface and the lower part of the tank, and the treatment could not be performed stably. In Test 1 in which CaCl ₂ was not added, such a situation did not occur, and as a result, the effectiveness of reducing the calcium concentration before ANAMMOX treatment could be confirmed.

It is a process flow figure which illustrates the processing method of the nitrogen content drainage concerning one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ca removal apparatus 2 Nitrite reaction tank 3 ANAMMOX reaction tank 4 Nitrification reaction tank 5 Denitrification tank 6 Reoxidation tank 7 Branch line 8 Inorganic carbon source and pH adjuster supply means 9 pH adjuster supply means 10 Inorganic carbon supply means 11 Hydrogen donor supply means

Claims (6)

  A method for treating nitrogen-containing wastewater, characterized in that when treating wastewater containing nitrogen and calcium in a state where inorganic carbon is supplied, nitrogen treatment is performed after reducing the calcium concentration in the wastewater.   The method for treating nitrogen-containing wastewater according to claim 1, wherein the method for treating nitrogen is biological treatment.   Nitrogen treatment is anaerobic with an ammonia oxidation process in which at least some ammonium ions in the wastewater are oxidized to nitrite ions by contacting with autotrophic bacteria under aerobic conditions and wastewater containing ammonium ions and nitrite ions The method for treating nitrogen-containing wastewater according to claim 1 or 2, further comprising a denitrification step in which denitrification is performed by contact with autotrophic bacteria under conditions.   The carbonate ion or the bicarbonate ion is supplied for adjusting pH when the ammonium ion is nitrified to nitrite or nitrate ion by autotrophic bacteria under aerobic condition. Nitrogen-containing wastewater treatment method.   The calcium concentration in the waste water is reduced by a method selected from ion exchange, electrodeionization, aggregation precipitation, crystallization, electrophoresis, and aggregation-membrane separation. Of treating wastewater containing nitrogen.   The method for treating nitrogen-containing wastewater according to any one of claims 1 to 5, wherein the calcium concentration in the wastewater is reduced to 100 mg / L or less.

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