KR101900259B1 - High-concentration total nitrogen removal process from high-purity NO2 purified wastewater - Google Patents

Abstract

The present invention relates to a method for removing high-concentration total nitrogen from high-purity nitrous gas purification wastewater which removes total nitrogen from nitrous gas purification wastewater existing in a high concentration of 20,000 ppm or higher by undergoing steps of coagulation, neutralization, struvite formation, and aeration, and manufactures high-purity struvite as a byproduct. The method for removing total nitrogen removes total nitrogen existing in a high concentration of 20,000 ppm or higher in wastewater by undergoing the steps of coagulation, neutralization, struvite formation, and aeration, and manufactures high-purity struvite as a byproduct. The present invention sequentially applies a struvite crystallizing process, aeration, and a bio-absorbent process to wastewater containing high-concentration total nitrogen to reduce nitrogen in steps to greatly reduce chemicals used in the struvite crystallizing process. The present invention can be repeatedly used by detaching nitrogen ions in case of a bio-absorbent onto which an ionic contaminant is adsorbed. The present invention is an eco-friendly adsorption material biodegraded when finally discarded and thus can be used as a nitrogen organic fertilizer.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-concentration total nitrogen removal process from high-purity nitrite gas purification wastewater,

The present invention relates to a method for removing high-concentration total nitrogen from highly purified nitrite gas purified wastewater, and more particularly, to a method for removing high-purity total nitrogen from purified nitrite gas purified wastewater by coagulation, neutralization, struvite formation, To a method for removing high-concentration total nitrogen from high purity nitrite gas purified wastewater which removes nitrogen and produces high purity struvite as a by-product.

In general, the nutrients contained in wastewater are inorganic elements, and they enter into rivers, coastal waters, lake (reservoirs and reservoirs), etc., thereby promoting algae growth and causing eutrophication phenomenon.

In addition, when the nutrients contained in the wastewater are introduced into the coastal sea, they cause red tide phenomenon. In severe cases, the nutrients are spoiled and odor is generated, thereby causing water pollution. It is a substance to be removed before entering the lake.

Processes for treating nutrients such as nitrogen and phosphorus include physical and chemical treatment methods and biological treatment methods.

In the biological treatment method, ammonia nitrogen and organic nitrogen which are in a dissolved state in the case of nitrogen are nitrified by nitrifying bacteria (ie, Nitrosomonas & Nitrobacter) under an aerobic condition and ammonia is nitrified (Ie, Pseudomonas, Paracoccus denitrifiers) to be used as an electron acceptor in place of oxygen in anaerobic conditions, converted to nitrogen gas and released to the atmosphere (denitrification oxidation).

However, in the method of treating wastewater containing a high concentration of total nitrogen, the method using a conventional denitrifying microorganism has a problem that the growth of the denitrifying microorganism is reduced due to the high concentration of total nitrogen, which is not treated and the treatment time is long.

Ion exchange using physicochemical methods, ammonia depletion, selective adsorption, precipitation of phosphorus using flocculant and flocculant, and precipitation of struvite formation simultaneously precipitating nitrogen and phosphorus. However, such a method is disadvantageous in that it is sensitive to temperature and is expensive, although the processing is selectively performed. In addition, since the environment required for the drug cost and operation is specific, it is difficult to operate, and the effluent is unstable, so that it is reluctant to use in the field on a global scale.

In particular, the struvite manufacturing technique is disclosed in Tsunekawa et al., Japanese Patent Application Laid-Open No. 11-267665, Trentelman US Patent No. 4,389,317, Japanese Patent Application Laid-Open No. 10-1019200, Korean Patent Application No. 2002-0005521, No. 2000-0019613 2004-0070408 and 2007-0135309 are known. However, while the concentration of nitrogen is high, excessive amounts of Mg, calcium and phosphate are required for wastewater treatment with low, or almost no (low nitrogen) concentrations of Mg, calcium and phosphate, Extra use requires additional processing to dilute the effluent. In addition, despite the neutralization and dilution treatment, a problem has arisen that a considerable amount of metal is discharged as a result.

The present invention provides a method for treating wastewater containing a high concentration of total nitrogen which is difficult to treat by conventional biological methods.

The present invention provides a method for efficiently removing total nitrogen in a wastewater containing a high concentration of total nitrogen while reducing the amount of chemicals used even when the Struvite precipitation method is used.

One aspect of the present invention is

A method for removing a high concentration of total nitrogen from basic wastewater and acid wastewater generated after high purity nitrite gas purification,

Adding an aggregating agent to the basic wastewater containing an inorganic nitrogen compound, potassium permanganate and a suspended solid;

Neutralizing the basic wastewater supernatant from which the coagulated slurry has been removed by mixing with the acid wastewater;

Supplying magnesium ions and phosphate ions to neutralized wastewater to form struvite crystals; And

Removing the struvite crystals, and then blowing microbubbles into the wastewater to aeration, thereby effecting a high concentration of total nitrogen.

The total nitrogen removal method of the present invention can remove the total nitrogen existing at a high concentration of 20,000 ppm or more in the wastewater through coagulation, neutralization, struvite formation and aeration step, and produce high purity struvite as a byproduct.

The present invention applies struvite crystal process, aeration and bioabsorbent process sequentially to wastewater containing a high concentration of total nitrogen, and as the nitrogen is gradually reduced, the amount of chemicals used in the struvite crystal process is increased Can be reduced.

In the case of a bioabsorbent to which ionic pollutants are adsorbed, the present invention can be repeatedly used through desorption of nitrogen ions and can be utilized as a nitrogen-organic fertilizer as an environmentally friendly adsorbent material that is decomposed naturally upon final disposal.

Fig. 1 shows a process diagram of the high concentration total nitrogen removal method of the present invention.
2 shows a high concentration total nitrogen removal apparatus of the present invention.
Fig. 3 (a) is a schematic diagram of the waste water (basic wastewater) purified from the nitrite gas (NO2), Fig. 3 (b) is the precipitate sludge and the supernatant after coagulation of the basic wastewater, It is a photograph of sediment and supernatant.
Fig. 4 is a graph showing the result of performing the struvite crystallization in the first to fourth steps and photographing the supernatant and the stratified precipitate.

Hereinafter, the present invention will be described in more detail.

FIG. 1 is a process diagram of a high concentration total nitrogen removal method of the present invention, and FIG. 2 is a diagram showing a high concentration total nitrogen removal apparatus of the present invention. Referring to FIGS. 1 and 2, the high concentration total nitrogen removal method of the present invention includes an aggregation step, a neutralization step, a struvite crystal formation step, and a discard step.

The present invention relates to a method for removing a high concentration of total nitrogen from basic wastewater and acid wastewater generated after purifying high purity nitrite gas.

The results of water quality analysis of acidic wastewater and basic wastewater after high purity nitrite gas (NO2) purification are shown in Table 1 below.

Metrics unit Acid wastewater Basic wastewater pH - 1.5 9.5 T-N mg / L 23576.0 22435.2 T-P mg / L 0.661 0.624 NH ₃ -N mg / L 350.0 936.0 NO ₃ -N mg / L 12217.6 10416.2 NO ₂ -N mg / L Non-detection 86.6 Cr6 ⁺ mg / L Non-detection Non-detection Mn mg / L 0.0349 23.300 K mg / L 0.695 229.750

Table 1 shows that acidic wastewater (pH 1.5) containing inorganic nitrogen compounds such as ammonia nitrogen, nitrate nitrogen and nitrite after purifying high purity nitrite gas (NO2) and these inorganic nitrogen compounds and potassium permanganate (KMnO4 ), And basic wastewater (pH 9.5) containing suspended solids. The basic wastewater and the acid wastewater are high-concentration nitrogen-containing wastewater containing 20,000 ppm or more of inorganic nitrogen ions.

In the flocculating step, coagulant is added to the basic wastewater to precipitate potassium permanganate and suspended solids contained in the basic wastewater. The coagulation step may separate the precipitated coagulated sludge from the basic wastewater, dehydrate and dry it, and treat it as solid waste.

As the flocculant used in the flocculation step, known flocculants capable of flocculating potassium permanganate (KMnO4) and floating flocculent can be used without limitation. For example, in the present invention, aluminum sulfate was used to agglomerate potassium permanganate (KMnO4), and an appropriate amount of a polymer flocculant was used to agglomerate floating solids.

In the flocculation step, potassium permanganate, suspended solids and other organic matters of the basic wastewater coagulate and precipitate as sludge, and most of the inorganic nitrogen compounds remain.

The neutralization step is a step of neutralizing the basic wastewater supernatant from which the coagulated slurry is removed by mixing with the acid wastewater. Through the neutralization step, the basic wastewater and the acid wastewater are mixed to show neutrality, but the inorganic nitrogen ions in the wastewater still maintain 20,000 ppm or more.

In the struvite crystal forming step, magnesium ions and phosphate ions are supplied to neutralized wastewater to form struvite crystals.

The step of crystallizing struvite is a step of forming ammonium magnesium phosphate (MgNH ₄ PO ₄ 6H ₂ ) by reacting nitrogen, phosphoric acid, and magnesium ions at a molar ratio of 1: 1: 1 as shown in the following reaction scheme 1.

[Reaction Scheme]

Mg ^{2 +} + NH ₄ ⁺ + PO ₄ ^3- + 6H ₂ O ---> MgNH ₄ PO ₄ 6H ₂

  In the struvite crystal formation step, calcium ion may be used instead of magnesium ion, and in this case, the same analogue calcium ammonium phosphate crystallizes.

Phosphoric acid ion-providing phosphoric acid compounds include potassium phosphate, potassium pyrophosphate or potassium polyphosphate.

As the compound providing magnesium ions, magnesium chloride, magnesium hydroxide, etc. may be used.

Compounds that provide calcium ions include monocalcium phosphate (MCP), dicalcium phosphate (DCP), and triclacium phosphate (TCP).

In the struvite crystal formation step, the inorganic nitrogen ions such as ammonia nitrogen, nitrate nitrogen, and nitrite are removed by reacting with phosphoric acid and magnesium, so that the inorganic nitrogen ions in the wastewater can be reduced to 1,000 ppm or less.

The method of the present invention can be carried out by repeating the above Struvite crystal formation step several times. Referring to FIG. 2, the wastewater treatment apparatus is provided with two Sturby depositors. For example, the first-stage StruByte settler in the shear stage may reduce the total nitrogen concentration to 10,000 ppm and send the supernatant of the first settler to the second settler to perform the Struvite reaction again. The secondary settling tank can reduce the total nitrogen concentration to 1,000 ppm.

The method may further include dehydrating and drying the struvite crystals precipitated in the struvite crystal forming step to fertilize the struvite crystal. The dehydration and drying can be carried out using any known apparatus without limitation.

In the present invention, struvite crystals generated while treating wastewater containing high-concentration total nitrogen after nitrite gas purification can be recycled as high-quality compound fertilizer. In the case of phosphoric acid ions, treated water containing high concentration of phosphorus in the livestock wastewater or food wastewater treatment plant can be utilized to remove the high concentration of total phosphorus in the wastewater.

The struvite crystal forming step of the present invention reduces the nitrogen concentration in the wastewater to about 1,000 ppm, and the additional nitrogen treatment is performed in the aeration step using microbubbles or the adsorption step using the bioabsorbent material.

The aeration step may reduce the concentration of total nitrogen to 100 ppm or less by blowing microbubbles into the wastewater after removing the struvite crystals to degas the air.

The method may be combined with the biological treatment method using denitrifying microorganisms.

Unlike the conventional aeration method, microbubbles are micro-sized in water and collapsed instantaneously to generate ultrasonic waves (increase the dissolved oxygen concentration in a short time) to promote denitrification .

The method of the present invention may further comprise an adsorption step for removing ionic contaminants in the wastewater with a bioabsorbent after the aeration step.

In the adsorption step, the effluent water removed to 100 ppm or less in the aeration step may be passed through the adsorbing column of the adsorbent for adsorbing the total nitrogen concentration to 20 ppm or less.

Biosorbents can remove or recover ionic pollutants present in industrial wastewater using biomass. The adsorption mechanism combines with electrostatic attraction by the ionic contaminants and the reactors present on the surface of the biomass.

The bioabsorbent can be produced using biomass such as seaweed, microorganism, biological sludge, fermentation anhydrous (fermentation cell).

The bioabsorbent may be one having an anionic adsorption function so as to adsorb NH ₄ ⁺ in the wastewater.

The bioabsorbent can be repeatedly used by regenerating through desorption of nitrogen ions even when the breakthrough point of the adsorbed cationic contaminants including NH ₄ ⁺ is adsorbed. In addition, the bioabsorbent can be utilized as an organic fertilizer containing an inorganic nitrogen compound as an environmentally friendly adsorbent material which is decomposed spontaneously upon disposal.

Referring to FIG. 2, the present invention can provide a high-concentration total nitrogen removal apparatus.

The high concentration total nitrogen removal apparatus of the present invention may include an aggregation tank, a Struvite sedimentation tank, an aeration tank, and an adsorption apparatus.

The apparatus may include a plurality of Struvite sedimentation tanks to reduce the nitrogen concentration stepwise.

The apparatus of the present invention may include a neutralization tank between the flocculation tank and the Struvite sedimentation tank. Further, the apparatus of the present invention can be coagulated and neutralized simultaneously in a flocculation tank without a separate neutralization tank.

The flocculation tank, the Struvite sedimentation tank, the aeration tank, the adsorption apparatus, and the like can be referred to above.

 Hereinafter, the present invention will be described in more detail with reference to the following examples, but they should be construed as merely illustrative of preferred embodiments of the present invention, and the examples do not limit the scope of the present invention.

Example  One

Wastewater (acidic wastewater and basic wastewater) purified with high purity nitrite gas (NO2) was stored in the collection tank. The results of water quality analysis of wastewater are shown in Table 1 above.

     Basic wastewater (3,000 mL) was supplied to the flocculation tank, and aluminum sulfate (40% aluminum sulfate solution, 10 mL) and polymer flocculant (0.1% polyacrylamide solution, 40 mL) were injected into the flocculation tank. The reaction time of the flocculation tank was stirred at 250 rpm within 5 minutes.

      The supernatant (2,000 mL) of the coagulation tank was sent to the first settling tank, and acidic wastewater (1,000 mL) was supplied to the first settling tank to neutralize the pH of the supernatant to 7.5. The total concentration of nitrogen in the wastewater of the first settling tank containing neutralized wastewater (3,000 mL) was 23,200 ppm. 200 mL of 1 M potassium phosphate solution and 200 mL of 2M magnesium chloride solution were injected into the first settling tank and stirred at 250 rpm for 5 minutes. Truvite crystals were generated. The pH was adjusted to 8 by adding 380 mL of 2M NaOH solution to smoothly produce struvite crystals. The struvite crystals formed in the first settling tank were precipitated for 30 minutes, and then the supernatant and struvite were separated. At this time, the total nitrogen of the supernatant was reduced to 10,900 ppm, and the produced struvite crystal was 62 g.

       Secondary Struvite crystallization was carried out to reduce the concentration of total nitrogen removed through the first Struvite crystallization. The supernatant (2,000 mL) from which primary struvite crystals had been removed was sent to the second settler, 150 mL of 1M potassium phosphate solution and 150 mL of 2M magnesium chloride solution were added, and stirred at 250 rpm for 5 minutes to produce struvite crystals. The pH was adjusted to 8 by adding 170 mL of 2M NaOH solution to smoothly produce struvite crystals. The second-produced struvite crystals were precipitated for 30 minutes and then the supernatant and struvite were separated. At this time, the total nitrogen of the supernatant was reduced to 5,921 ppm, and the produced struvite crystals were 50 g.

       Third-order struvite crystallization was performed to reduce the concentration of total nitrogen removed through the secondary Struvite crystallization. The supernatant (1000 mL) from which the secondary struvite crystals had been removed was sent, and 100 mL of 1M potassium phosphate solution and 100 mL of 2M magnesium chloride solution were added and stirred at 250 rpm for 5 minutes to produce struvite crystals. The pH was adjusted to 8 by adding 110 mL of 2M NaOH solution to smoothly produce struvite crystals. After the struvite crystals were precipitated for 30 minutes, the supernatant and struvite were separated. At this time, the total nitrogen in the supernatant was reduced to 2,521 ppm, and the produced struvite crystals were 38 g.

       Fourth-order struvite crystallization was performed to reduce the concentration of total nitrogen removed through the third-order struvite crystallization. The supernatant (500 mL) from which the tertiary struvite crystal was removed was sent, and 50 mL of 1M potassium phosphate solution and 50 mL of 2M magnesium chloride solution were added and stirred at 250 rpm for 5 minutes to produce struvite crystals. The pH was adjusted to 8 by adding 50 mL of 2M NaOH solution to smoothly produce struvite crystals. The struvite crystals formed in the fourth step were precipitated for 30 minutes, and then the supernatant and struvite were separated. At this time, the total nitrogen of the supernatant decreased to 1,034 ppm, and the produced struvite crystal was 29 g.

       The supernatant after the fourth generation struvite crystals were transferred to the aeration tank and aerated with microbubbles for 10 minutes to reduce the total nitrogen concentration to 95 ppm and the total nitrogen concentration to 15 ppm by passing through the final bioadsorbent column.

       Table 2 shows the results of analysis of chemical inputs and total nitrogen concentrations in each process for total nitrogen removal from wastewater.

division Amount of input TN
(ppm) The amount of struvite crystallization (g) Wastewater Magnesium chloride Potassium phosphate NaOH Raw water source 3L - - - 23,204 - Primary crystallization 3L 200 mL 200 mL 380 mL 10,902 62 Secondary crystallization 2L 150 mL 150 mL 170 mL 5,921 50 Tertiary crystallization 1L 100 mL 100 mL 110 mL 2,521 38 Quaternary crystallization 500ml 50 mL 500 mL 50 mL 1,034 29 Aeration tank - - - - 95 - Bioabsorbent
Adsorption column - - - - 15 -

Fig. 3 (a) is a schematic diagram of the waste water (basic wastewater) purified from the nitrite gas (NO2), Fig. 3 (b) is the precipitate sludge and the supernatant after coagulation of the basic wastewater, It is a photograph of sediment and supernatant.

Fig. 4 is a graph showing the result of performing the struvite crystallization in the first to fourth steps and photographing the supernatant and the stratified precipitate.

Table 2 shows the amounts of wastewater, magnesium chloride, potassium phosphate, NaOH, total nitrogen, and struvite crystallization in Table 1.

  Referring to Table 2, the total nitrogen concentration of 23,204 ppm contained in the waste water was sequentially decreased to 1,034 ppm, 95 ppm, and 15 ppm through the struvite crystal formation step, the aeration tank, and the biosorption step, It can be discharged below the allowable limit value.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Those skilled in the art will readily appreciate that various changes, modifications, and variations may be made without departing from the spirit and scope of the present invention, as defined by the following claims and accompanying drawings.

Claims (4)

A method for removing a high concentration of total nitrogen from basic wastewater and acid wastewater generated after high purity nitrite gas purification,
Adding an aggregating agent to the basic wastewater containing an inorganic nitrogen compound, potassium permanganate and a suspended solid;
Neutralizing the basic wastewater supernatant from which the coagulated slurry has been removed by mixing with the acid wastewater;
Supplying magnesium ions and phosphate ions to neutralized wastewater to form struvite crystals; And
Removing the struvite crystals, and then blowing microbubbles into the wastewater to aeration.
The method of claim 1, wherein the high concentration total nitrogen removal step further comprises an adsorption step of removing ionic contaminants in the wastewater with a bioabsorbent after the aeration step. The method according to claim 1, wherein the basic wastewater and acid wastewater generated after purifying the high purity nitric acid gas contain 20,000 ppm or more of inorganic nitrogen ions,
Wherein the struvite crystal forming step comprises treating the inorganic nitrogen ions in the wastewater with 1,000 ppm or less,
Wherein the aeration step treats the inorganic nitrogen ions in the wastewater to 100 ppm or less. The method of claim 1, further comprising dehydrating and drying the struvite crystals precipitated in the struvite crystal formation step to fertilize the struvite crystal.

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