KR20050122181A - Method for wastewater treatment - Google Patents

Abstract

The present invention relates to a method for removing total nitrogen (TN) contained in the wastewater, in particular among wastewater treatment methods, and mixing sodium chloride (NaCl) in the original wastewater and caustic until the alkalinity of the wastewater reaches pH 9 or more. Soda (NaOH) is mixed, but the wastewater mixed with sodium chloride (NaCl) and caustic soda (NaOH) is heated to 40-50 ° C, and the heated wastewater is electrolytically oxidized to form ammonia nitrogen (NH₃- N) (NH₄-N) was first denitrated with nitrogen gas, and then sodium thiosulfate (Na ₂ S ₂ O ₃ ) was injected into the wastewater to remove hypochlorite ions (OCl ⁻ ) generated during the electrolytic oxidation. Next, the wastewater is permeated through a reaction tank containing a known sulfur carrier in which sulfated microorganisms are grown, and secondary nitrite nitrogen (NO₂-N) and nitrate nitrogen (NO₃-N) are removed by nitrogen gas to remove the wastewater. More completely removes total nitrogen (TN) contained in The present invention relates to a wastewater treatment method.

Description

Method for wastewater treatment

The present invention relates to a method for removing total nitrogen (TN) contained in the wastewater, in particular, wastewater treatment method, more specifically, sodium chloride (NaCl) and caustic soda (NaOH) in the wastewater to the alkalinity to pH 9 or more In addition, after heating the wastewater to 40 ~ 50 ℃, the wastewater is electrolytically oxidized to remove the first ammonia nitrogen (NH₃-N) (NH₄-N) by nitrogen gas denitrification, sodium thiosulfate (Na ₂ S ₂ O ₃ ) is injected into the wastewater to remove hypochlorite ions (OCl ⁻ ) generated during the electrolytic oxidation, and then nitrite nitrogen (NO₂-N) and nitrate nitrogen (NO₃-N) contained in the wastewater. By secondary denitrification by nitrogen gas using a known sulfur carrier desulfurization reaction by a sulfur carrier, it relates to a wastewater treatment method that can more completely remove the total nitrogen (TN) contained in the wastewater.

In general, domestic wastewater and industrial wastewater contain various harmful substances polluting rivers and oceans. Among them, ammonia nitrogen (NH₃-N) (NH₄-N), nitrite nitrogen (NO₂-N), and nitrate nitrogen Nitrogen (N), which is present in the same form as (NO₃-N), is used as an important food for microorganisms, but when too much nitrogen (N) is introduced into a stream, streams or lakes may be eutrophized and green algae may occur. In addition, when it is introduced into the ocean, it causes red tides of the near-shore seas, causing enormous disruption to fisheries such as marine farming as well as environmental pollution.

On the other hand, the conventional wastewater treatment method for purifying the wastewater, wastewater, such as electrolysis, electro-coagulation, electro-flotation as an electrolytic method using electrical energy (electrolysis) Biological wastewater treatment using microorganisms is known along with the treatment method. As a conventional wastewater treatment method for removing nitrogen contained in the wastewater, a biological denitrification method such as heterotrophic denitrification is mainly used. Denitrification by the method is shown in [Scheme 1] below.

^{_{NO 3 - + 1.08CH 3 OH +}} 3H + → 0.065C 5 H 7 O 2 N + 0.47N 2 + + 0.76CO 2 + 2.44H 2 O

However, in the case of the heterotrophic denitrification method, it is difficult to control the dosage of the methanol as well as to supply an external carbon source such as methanol, and on the other hand, there is a problem in that the operation cost is high and the operation is not easy and the economy is inferior.

In order to solve the above problems, various types of sulfur compounds (S ⁰ , S ² -S) using sulfated microorganisms such as Thiobacillus denitrificans and Thiomicrospira denitrificans are used. ^{_{, S 2 O 3 2-, S}} 4 O 6 2-, SO 3 2-) , sulfate ion (SO ₄ ^2-), while at the same time as the nitrate using a sulfated denitrification to remove nitrogen oxide gas was converted to Independent nutritional denitrification method has been proposed, the sulfated denitrification reaction by the autotrophic denitrification method is as shown in [Scheme 2].

^{_{NO 3 - + 1.10S + 0.40CO 2}} + 0.76H 2 O + 0.08NH 4 + → 0.5N 2 ↑ + 1.10SO 4 2- + 1.28H + + 0.08C 5 H 7 O 2 N

However, in the case of the autotrophic denitrification method, although the external sludge generation amount does not need to be used without the need for an external carbon source such as methanol, the starting time is long, the reaction time is slow, and when the alkalinity is low, denitrification is difficult and high concentration is achieved. Denitrification is difficult, and there is an inconvenience of periodically removing the nitrogen generated during denitrification, as well as the inconvenience of having to administer limestone (limestone) as the alkalinity is lowered.

In order to solve the problems of the autotrophic denitrification method, a wastewater treatment method using a carrier in which denitrifying microorganisms are attached and grown has been proposed, wherein the carrier is filled with particulate sulfur and limestone, or In this case, the desulfurization and denitrification reaction as shown in [Scheme 2] can be obtained, but the blockage of the reaction tank caused by the limestone occurs during long-term operation. There was a problem requiring regular backwashing.

On the other hand, the sulfur carrier for wastewater treatment that solves the problems as described above is proposed in Korean Patent Laid-Open Publication No. 10-2004-0016728 (published on February 22, 2004). Calcium (CaCO₃) and magnesium oxide (MgO) are mixed at a weight ratio of 6: 3: 1, melted at 150 ° C, and the cold-dried-crushed yellow carrier is added to the reactor together with the microorganisms acclimated to the denitrifying microorganisms. After that, it is characterized in that the wastewater is introduced to treat the wastewater in a stable operation.

According to the wastewater treatment method using the conventional yellow carrier as described above, sulfur (S) acts as a substrate for denitrification of sulfated microorganisms, and calcium carbonate (CaCO₃) is supplemented with alkalinity deteriorated as the denitrification reaction proceeds. Maintain an alkalinity of pH 6-8, which can cause microbes to denitrate. Sulfation denitrification by the sulfur carrier is shown in [Scheme 2], and the reaction of calcium carbonate (CaCO₃) to neutralize hydrogen ions to supplement alkalinity is shown in [Scheme 3] below.

_{^{CaCO 3 + H + → Ca 2+}} + HCO 3 -

On the other hand, in the case of the wastewater treatment method using the yellow carrier as described above, the effect of denitrifying and removing nitrite nitrogen (NO₂-N) and nitrate nitrogen (NO₃-N) by nitrogen gas is excellent, while ammonia nitrogen ( In the case of NH₃-N) (NH₄-N), a satisfactory denitrification effect was not obtained. Magnesium oxide (MgO) contained in the yellow carrier reacted with ammonia nitrogen (NH₄-N) to form struvite, MgNH ₄ PO ₄ ) can be produced to remove ammonia nitrogen, but ammonia nitrogen (NH₃-N) (NH₄-N) compared to nitrite nitrogen (NO₂-N) and nitrate nitrogen (NO₃-N) Considering such a case as much plating wastewater), denitrification of ammonia nitrogen (NH₃-N) (NH₃-N) by magnesium oxide (MgO) contained in the yellow carrier is satisfactory in the actual wastewater treatment site. No denitrification effect could be expected. The reaction of magnesium (Mg) and ammonia nitrogen (NH₄-N) by magnesium oxide (MgO) contained in the yellow carrier is shown in [Scheme 4] below.

Mg ²⁺ + NH ₄ ⁺ + PO ₄ ^3- → MgNH ₄ PO ₄

An object of the present invention for solving the problems of the wastewater treatment method using the conventional yellow carrier as described above, prior to ammonia nitrogen by electrolytic oxidation of the wastewater prior to the sulphation denitrification process of nitrate nitrogen by the known yellow carrier. Primary denitrification, but the hypochlorite ion generated during electrolytic oxidation is removed by sodium thiosulfate to enable secondary denitrification by the sulfated microorganism, and caustic soda together with sodium chloride is added to the wastewater to pH After adjusting to 9 or more and heating the waste water to 40 ~ 50 ° C, electrolytic oxidation of the ammonia nitrogen contained in the waste water and the first denitrification by nitrogen gas, and injection of sodium thiosulfate into the waste water electrolytic oxidation of the waste water. After removing the hypochlorite ion generated in the waste water, the nitrite nitrogen and nitrate nitrogen contained in the waste water are known sulfur carriers. By removal of the secondary denitrification to nitrogen gas by using the sulfated denitrification, there is provided a waste water treatment method that can remove the total nitrogen than the fully contained in the waste water.

Waste water treatment method according to the present invention for achieving the above object, the first step of injecting sodium chloride (NaCl) and caustic soda (NaOH) to the first waste water and heating the waste water to 40 ~ 50 ℃ and And a second step of primary denitrification of ammonia nitrogen (NH₃-N) (NH 수 -N) contained in the wastewater by electrolytic oxidation and electroaggregation by electrolytic oxidation, and a first denitrification step by the electrolytic oxidation. in order to remove sodium thiosulfate third step, a high saturation hypochlorite ion (OCl ^-) implanting _{(Na 2 S 2 O 3)} - high saturation hypochlorite ion (OCl) generated from a known to the removed effluent sulfur carrier It is characterized in that it comprises a fourth step of causing a desulfurization denitrification reaction to secondary denitrification of nitrous nitrogen (NO₂-N) and nitrate nitrogen (NO₃-N) by nitrogen gas.

Hereinafter, a preferred embodiment of the wastewater treatment method according to the present invention will be described in detail with reference to FIGS. 1 and 2 in the following order. FIG. 1 is a process diagram showing a wastewater treatment method according to the present invention, and FIG. 2. Is a process chart according to a preferred embodiment of the present invention.

[Step 1]

First, the sodium chloride (NaCl) and caustic soda (NaOH) injection and heating process of the present invention, the waste water is introduced into the storage (storage) equipped with a conventional heater, sodium chloride (NaCl) and caustic soda (NaOH) In addition to heating the wastewater to 40 ~ 50 ℃ bar, sodium chloride (NaCl) is injected 0.5 ~ 10 [wt%] with respect to the wastewater inflow 90 ~ 99.5 [wt%] electrolytic oxidation process of the wastewater to be described later In addition to supplying chlorine (Cl) required for the first denitrification process by electrolytic oxidation, caustic soda (NaOH) is introduced in consideration of the decrease in alkalinity during the second denitrification process by the sulfated denitrification reaction described later. By injecting the alkalinity of the wastewater to pH 9 or more in proportion to the amount of wastewater used, the sulfated microorganisms can be smoothly denitrified during the secondary denitrification process.

And the heating of waste water is to improve the efficiency of the primary denitrification process by electrolytic oxidation, which will be described later by supplying heat energy to the waste water to improve the motility, wherein the expected effect is insufficient if the heating temperature is less than 40 ℃, 50 ℃ If it exceeds, it takes too much operating cost, it is preferable to perform the heating process by heating the waste water to 40 ~ 50 ℃.

[Step 2]

Referring to the primary denitrification process by electrolytic oxidation as the second process of the present invention, wastewater that has undergone sodium chloride (NaCl) and sodium hydroxide (NaOH) injection and heating is subjected to electrocoagulation by electrolytic oxidation to ammonia nitrogen (NH₃). -N) (NH₄-N) is denitrified by nitrogen gas (N₂), look at in more detail the primary denitrification process by electrolytic oxidation in the following.

First, the principle of elimination of organic substances by electrolytic oxidation is generally that organic pollutants contained in wastewater are electrochemically oxidatively decomposed by direct anodic oxidation reaction and cathodic reduction reaction and indirect oxidation reaction. Contaminants are adsorbed on the surface of the anode and oxidized by the movement of the cathode electrons. Indirect oxidation reactions occur during the electrolysis of strong oxidants such as generator oxygen (O₂), hypochlorous acid (HClO), and oxidized metal ions. Electrochemical reactions in an electrolyte cause oxidation of contaminants.

On the other hand, most of the colloids contained in the wastewater have a negative charge, so they are suspended in repulsive state due to the repulsive force between similar charges, and the contaminants in the colloidal state in the wastewater are eluted from the plate by electric energy. It is removed by the oxidation / reduction reaction together with the aggregation reaction which is neutralized with the metal cation electrically, and the precipitation and removal of contaminants by the formation of metal hydroxide by the hydrolysis of the metal eluted at the anode as described above. In more detail, when electricity is applied to the waste water, the metal ions, which are cationic at the anode, are oxidized to +2 or + trivalent ions, and the hydroxyl ions (OH ⁻ ) generated at the cathode are oxidized. Oxygen is generated, and this oxygen is involved in the oxidation of organic matter and at the same time at the cathode This reaction won up of neutral conditions hydroxyl groups (OH ^-), carboxyl (HCOO ^-), and generate a negative charge in water it has a phosphate group (PO ₄ ^3-), dew Roppongi (SO ₄ ^2-), etc., such The functional groups react with metal ions between polyatoms to form hydrolysis and various complexes. The positively charged metal hydroxide complex formed under acidic or neutral conditions according to the pH of the water electrically neutralizes the surface charge of the colloid, which is a negatively charged organic pollutant, by agglomeration by double layer compression. Organics are aggregated / precipitated.

When the electroaggregation treatment by electrolytic oxidation as described above is used, the nitrogen contained in the waste water is removed by reacting with nitrogen gas and water by electrooxidation. Nitrogen (NH₃-N) (NH₄-N) is removed with nitrogen gas (N₂) as shown in Scheme 5 below. [Scheme 5]-(1) is the denitrification by cathodic reduction at the cathode, [Scheme 5]-(2) is the denitrification by direct anodic oxidation at the anode, [Scheme 5]-(3) and [Scheme 5]-(4) shows the denitrification reaction by indirect anodic oxidation at the positive electrode.

2NH ₄ + 2e → N ₂ ↑ + 4H ₂ ---------- (1)

^{_{NH 3 + 3OH - → 0.5N 2}} ↑ + 3H 2 O + 3e - ---------- (2)

^{_{2NH 3 + 6Cl - → N 2}} ↑ + 6HCl + 6e - ---------- (3)

_{^{2NH 4 + + 3HOCl - → N}} 2 ↑ + 3H 2 O + 5H - + 3Cl - ---------- (4)

In addition to the above reaction, chlorine (Cl) contained in the waste water reacts to generate hypochlorous acid (HOCl), and the pH is lowered as the ammonia nitrogen (NH₃-N) (NH₄-N) contained in the wastewater is removed. Increasing the fraction of chloric acid (HOCl) promotes the indirect oxidation reaction by hypochlorous acid, the indirect oxidation reaction by hypochlorous acid (HOCl) is as shown in [Scheme 6]. [Scheme 6]-(1), (2), (3), (4a) or (4b) shows that ammonia nitrogen (NH₄-N) is a nitrogen gas (N₂) due to indirect oxidation by hypochlorous acid (HOCl). The deoxidation reaction denitrified by) is sequentially shown according to the migration route of nitrogen (N).

HOCl + NH ₄ ⁺ → NH ₂ Cl + H ₂ O + H ⁺ ---------- (1)

HOCl + NH ₂ Cl → NHCl ₂ + H ₂ O ---------- (2)

_{NHCl 2 + H 2 O → NOH} + 2H + + 2Cl - ---------- (3)

_{NOH + NH 2 Cl → N 2} ↑ + H 2 O + H + + Cl - ---------- (4a)

_{NOH + NHCl 2 → N 2 ↑} + HOCl + H + + Cl - ---------- (4b)

On the other hand, some of the ammonia contained in the waste water which is generated at the cathode hydroxy group (OH ^-) is nitrated to nitrite nitrogen (NO₂-N) or nitrate nitrogen (NO₃-N) by the sulfation denitrification will be described later Is removed with nitrogen gas in the secondary denitrification process. The nitrification reaction of the ammonia nitrogen (NH₃-N) is as shown in [Scheme 7]. [Scheme 7]-(1) is a reaction to denitrify with nitrite nitrogen (NO₂-N), and [Scheme 7]-(2) is a reaction to denitrify with nitrate nitrogen (NO₃-N).

^{_{NH 3 + 7OH - → NO 2}} + 5H 2 O + 6e - ---------- (1)

^{_{NH 3 + 9OH - → NO 3}} + 6H 2 O + 8e - ---------- (2)

The first step of denitrification by electrolytic oxidation, which is the second step of the present invention, can be carried out using a conventional electrolytic cell (or electrolytic tube), and many kinds of the electrolytic cell (or electrolytic tube) are already known at present. In the present invention, as shown in FIG. 2, one or more other known electrolytic cells (or electrolytic tubes) may be used in combination.

On the other hand, the wastewater undergoing the first denitrification step by the electrolytic oxidation is preferably discharged nitrogen gas (N ₂ ) in the container as shown in Figure 2 prior to the third step to be described later.

[Step 3]

A third step of the present invention Referring to sodium thiosulfate (Na ₂ S ₂ O ₃₎ implantation process, the electrolytic high saturation hypochlorite ion in the waste water during the oxidation of waste water according to the second step (OCl ^-) are generated bar, the high saturation Chloric acid ions (OCl ⁻ ) have a strong sterilizing ability to sterilize the sulfated microorganisms causing the sulfated denitrification reaction described later, so that the primary denitrification by the electrolytic oxidation to facilitate the sulfated denitrification reaction by the sulfated microorganisms. sodium thiosulfate by flowing the waste water subjected to the process in a water bath (Na ₂ S ₂ O ₃₎ for injection by a high saturated hypochlorite ion (OCl ^-) a, wherein the first waste water flowing into the tank through the primary denitration step 90 to 99.9, but eliminate [ It is preferable to inject sodium thiosulfate (Na ₂ S ₂ O ₃ ) in an amount of 0.1 to 10 [% by weight] with respect to the weight%, and then pass about 24 hours in the water bath. The reaction in which sodium sulfate (Na ₂ S ₂ O ₄ ) is produced by the reaction of sodium thiosulfate (Na ₂ S ₂ O ₃ ) with hypochlorite ion (OCl ⁻ ) is shown in Scheme 8 below.

_{Na 2 S 2 O 3 + OCl} - → Na 2 SO 4 + Cl

[Step 4]

As described above, ammonia nitrogen (NH₃-N) (NH₄-N) is removed by nitrogen gas (N₂) by performing a primary denitrification process by electrolytic oxidation, or nitrite nitrogen (NO₂-N) or nitric acid. nitrogen electrolytic high saturated acid generated during oxidation after nitrification in ^{(NO₃-N) (OCl -} ) after removing the ions, the fourth step by using a well-known sulfur carrier the nitrite nitrogen (NO₂-N) and nitrate as The secondary denitrification process of denitrification of nitrogen (NO₃-N) with nitrogen gas (N₂) is carried out. The secondary denitrification process by the sulfated denitrification using the sulfur carrier will be described in more detail below.

The secondary denitrification process according to the present invention uses a known yellow carrier, and the yellow carrier is mixed with sulfur (S), calcium carbonate (CaCO₃) and magnesium oxide (MgO) in a weight ratio of 6: 3: 1. It is already known as previously mentioned to melt at 150 ° C. and then cool-dry-crushed, and the known yellow carrier is added to the reactor together with the microorganisms acclimated to the denitrifying microorganisms, and then the operation is made stable. By introducing the wastewater that passed through the first denitrification process and the sodium thiosulfate (Na ₂ S ₂ O ₃ ) injection process to undergo a second denitrification process, total nitrogen (TN) contained in the waste water can be more completely removed.

On the other hand, in the secondary denitrification process using the yellow carrier, sulfur (S) acts as a substrate for denitrification of sulfated microorganisms, and calcium carbonate (CaCO₃) supplements alkalinity that is degraded as the denitrification reaction proceeds. Maintains an alkalinity of pH 6-8, which can cause sulfate denitrification, and magnesium oxide (MgO) denitrates traces of ammonia nitrogen (NH₄-N) remaining after the first denitrification process. The sulfated denitrification reaction of the yellow carrier is the same as in the above-mentioned [Scheme 2], the reaction by the calcium carbonate (CaCO₃) is the replenishment of alkalinity is the same as the [Scheme 3], and the ammonia by magnesium oxide (MgO) Denitrification of nitrogen (NH₄-N) is shown in [Scheme 4].

Looking at the action of the wastewater treatment method according to the present invention as described above, injecting 0.5-10 [wt%] of sodium chloride (NaCl) to the inflow of 90 ~ 99.5 [wt%] of the wastewater to be treated first; In addition, caustic soda (NaOH) is injected until the alkalinity of the wastewater reaches pH 9, and the wastewater is heated to 40 to 50 ° C. to carry out a pretreatment process prior to denitrification and sulfate denitrification by electrolytic oxidation. Then, the wastewater was electrocoagulated by electrolytic oxidation to remove firstly denitrified ammonia nitrogen (NH₃-N) (NH₄-N) contained in the wastewater with nitrogen gas (N₂), followed by sodium thiosulfate (Na _2). S ₂ O ₃ ) is injected to remove hypochlorite ions (OCl ⁻ ) generated during electrolytic oxidation of the wastewater, and then permeate the primary denitrified wastewater into a reaction vessel containing a known yellow carrier, in which sulfated microorganisms are grown. Nitrite nitrogen (NO₂-N) and Residual ammonia nitrogen (NH₃-N) (NH₄-N) together with acidic nitrogen (NO₃-N) is removed by secondary denitrification with nitrogen gas (N₂) to more completely remove total nitrogen (TN) contained in the wastewater. Can be removed.

According to the present invention as described above, the denitrification by electrolytic oxidation of the ammonia nitrogen contained in the wastewater and the removal of hypochlorite ions generated during the electrolytic oxidation of the wastewater with sodium thiosulfate is known using a denitrifying microorganism Denitrification of nitrite nitrogen and nitrate nitrogen is possible as the yellow carrier, and as a result, there is an effect of more completely denitrifying the total nitrogen contained in the waste water.

1 is a process chart showing a wastewater treatment method according to the present invention

2 is a process diagram according to a preferred embodiment of the present invention

Claims (3)

Inject 0.5 ~ 10 [wt%] of sodium chloride (NaCl) to 90 ~ 99.5 [wt%] of wastewater and add caustic soda (NaOH) until the concentration of wastewater reaches pH 9. A first step of heating to 50 ° C .; A second step of electrolytic oxidation of the wastewater to first denitrify and remove ammonia nitrogen (NH₃-N) (NH 수 -N) contained in the wastewater with nitrogen gas; A third step of injecting sodium thiosulfate ion (Na ₂ S ₂ O ₃ ) into the waste water to remove hypochlorite ions (OCl ⁻ ) generated during electrolytic oxidation of the waste water according to the second step; Secondary nitrite nitrogen (NO₂-N) and nitrate nitrogen (NO₃-N) are secondary to nitrogen gas by using a sulfidation denitrification reaction using a known sulfur carrier in the wastewater from which the hypochlorite ion (OCl ⁻ ) is removed. A wastewater treatment method comprising a fourth step of denitrification. The method of claim 1; In the fourth step, sulfur (S), calcium carbonate (CaCO₃) and magnesium oxide (MgO) are mixed at a weight ratio of 6: 3: 1, melted at 150 ° C, and then cooled, dried, and crushed sulfur carriers. Waste water treatment method characterized in that the desulfurization and denitrification by injecting the waste water into the reaction tank with the microorganisms adapted to the denitrification microorganisms. The method of claim 1 or 2; In step ₃ , 0.1 to 10 [% by weight] of sodium thiosulfate (Na ₂ S ₂ O ₃ ) was injected into the wastewater 90 to 99.9 [% by weight] which passed through the first and second steps, followed by 24 hours in a water tank. Wastewater treatment method characterized in that.