KR100491002B1 - A method for treatment wastewater containing chrome and nitrate - Google Patents

Abstract

The present invention relates to a method for treating wastewater containing chromium and nitric acid using a microbial membrane to which denitrified microorganisms are immobilized, and adjusting the pH of the wastewater to 6.5-7.5 and denitrifying microorganisms at 6-40-100,000 mg /. A method for treating wastewater containing chromium and nitric acid by entering a bottom-filled microbial reactor fixed at l and wastewater was introduced into a first bottom-up packed microbial reactor where denitrifying microorganisms were fixed at 60,000-100,000 mg / l. After removal, the chromium-free wastewater was adjusted to 6.5-7.5 to remove denitrified microorganisms by introducing denitrified microorganisms at a fixed temperature of 60,000-100,000mg / l at 15-35 ℃ to remove nitric acid. A method of treating wastewater containing pernitric acid is provided. By this method, wastewater containing chromium and nitrogen is treated with high efficiency. In addition, the reactor is an upwardly packed reactor, in which microorganisms are immobilized at a high concentration, and there is no adverse effect on subsequent processes by removing heavy metals by biosorption. The use of anaerobic microorganisms eliminates the need for a separate air supply.

Description

Wastewater treatment method containing chromium and nitric acid {A METHOD FOR TREATMENT WASTEWATER CONTAINING CHROME AND NITRATE}

The present invention relates to a method for treating wastewater containing chromium and nitrogen, and more particularly, to a method for treating wastewater containing chromium and nitric acid using a microbial membrane to which denitrification microorganisms are immobilized.

In the pickling process, nitric acid is used to clean the surface of the metal. However, the wastewater discharged at this time contains a large amount of heavy metals and nitric acid, so the heavy metals and nitric acid treatment process must be performed before final discharge.

Conventionally, as a method of removing heavy metals, chemical precipitation (precipitation), ion exchange resin, activated carbon adsorption, ultrafiltration, reverse osmosis and electrodialysis have been used.

However, the treatment of wastewater by chemical precipitation increases dissolved solids, and the treatment of low concentrations (1-100 mg / l) of heavy metals decreases the removal efficiency and may contain toxic substances that are difficult to treat in the slurry. .

The ion exchange resin method used for heavy metal treatment and recovery is to remove the heavy metal by ion exchange using a basic anion exchange resin. Water treatment by ion exchange has little effect on the treatment efficiency even if the concentration of waste water is changed and can be concentrated and recovered, but the resin must be regenerated, which is uneconomical.

Ion exchange and activated carbon adsorption methods are generally expensive to operate and have a low specificity for selective removal of metals when other anions coexist.

In the case of reverse osmosis, the operation cost is high, and electrodialysis for reusing wastewater has a disadvantage in that the thin film is blocked by chemical precipitation of salts having low solubility at the surface of the thin film and residual colloidal organic matter in the effluent.

To treat heavy industrial wastewater containing chromium and nitric acid, the heavy metal must be removed and then nitric acid must be treated.In consideration of economic feasibility, conventionally using slaked lime to chemically aggregate and precipitate heavy metals, Has been removed. However, in this case, a large amount of residual calcium exists due to the excessive use of the chemicals introduced in the pretreatment process, and such a residual calcium cannot cover the microorganisms and kill the biological denitrification process.

In order to treat high concentration of nitrate nitrogen, denitrification microorganism should be maintained in high concentration in the reaction tank and microorganisms rapidly increasing in proportion to the incoming nitrogen wastewater concentration should be properly discharged out of the reaction tank to maintain optimal concentration of microorganisms in the reaction tank. do. To meet these conditions, floating activated sludge methods are mainly used in general sewage treatment plants and other industrial wastewater treatment facilities.

However, the floating method is low in processing efficiency, and requires an extensive site and expensive equipment costs, which is not suitable for the treatment of high concentrations of nitric acid (about 1000 mg / L) generated in the metal industry. Nitrogen removal method of high concentration organic sewage by liquid erosion method of 97-020992 and nitrogen removal method of high concentration organic sewage of Korean Patent Publication No. 94-2175 are not suitable for high concentration nitrogen treatment because they have a high concentration of microorganisms.

Accordingly, an object of the present invention is to provide a method for treating wastewater containing chromium and nitric acid by biosorption and denitrification using a microbial membrane to which denitrified microorganisms are immobilized.

Another object of the present invention is to provide a method for treating wastewater containing chromium and nitric acid using denitrification microorganisms immobilized in a bottom-up packed reactor.

According to one aspect of the invention,

In the wastewater treatment method containing chromium and nitric acid,

Wastewater containing chromium and nitric acid was adjusted to pH 6.5-7.5 and spaced at the top and bottom of the reactor at a temperature of 10-40 ° C. in a bottom up packed microbial reactor having a carrier fixed at 60,000-100,000 mg / l denitrification. A method is provided for treating influent wastewater containing chromium and nitric acid.

According to another aspect of the present invention,

In the wastewater treatment method containing chromium and nitric acid,

Introducing the wastewater containing chromium and nitric acid into a first bottom-up packed microbial reactor in which denitrification microorganisms are fixed at 60,000-100,000 mg / l to remove chromium;

Adjusting the pH of the chromium-free wastewater to 6.5-7.5; And

Introducing chromium-free wastewater into a second bottom-up packed microbial reactor in which denitrification microorganisms were fixed at 60,000-100,000 mg / l at 15-35 ° C. to remove nitric acid;

A wastewater treatment method containing chromium and nitric acid is provided.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention focuses on the characteristics that the extracellular polymer (biopolymer) produced by the microorganisms adsorb heavy metals. In vitro polymer material acts as an adsorbent to remove chromium from the waste water by biological adsorption method in which metals are physically and chemically adsorbed to a biofilm formed of extracellular polymer material, and nitric acid is removed by denitrification of microorganisms.

In particular, unlike the method of extracting only the biopolymer generated by culturing the existing microorganisms and using it for biosorption, in the present invention, denitrification to generate the in vitro polymer without extracting the biopolymer produced by culturing the microorganisms separately Microbial membranes immobilized with microorganisms are used to remove chromium and nitric acid from the wastewater.

When the microorganism is immobilized on the immobilization carrier, the in vitro biopolymer produced by the microorganism forms a microbial membrane, which induces mutual adsorption between the microorganisms to form a microbial floc, which adsorbs chromium in the waste water.

In the present invention, the active part of the microorganism is maximized by using a packed reactor in which microorganisms are immobilized, and it is easy to install in a narrow space. Filled forms are more favorable for flocs than floated or fluidized forms, so microorganisms accumulate at higher concentrations of 20-30 times more than conventional floating reactors.

As such, microorganisms are concentrated at high concentrations to form an immobilized reaction tank, and when the wastewater containing chromium and nitrate nitrogen is introduced, heavy metals are first biosorbed to in vitro biopolymers produced by denitrification microorganisms, and nitrate nitrogen is nitrogen gas. Denitrification.

As shown in FIG. 3, when nitrogen and chromium coexist, wastewater containing nitrogen and chromium is first removed after chromium is removed since nitrogen treatment efficiency decreases. In addition, chromium is adsorbed and removed, and nitrate nitrogen is converted to nitrogen gas by a chemical reaction to remove the chromium.

In the method according to the present invention, as shown in FIG. 1, chromium and nitrogen are removed from one reactor having a high concentration-concentrated immobilized denitrifying microorganism located at the top and bottom of the reactor or as shown in FIG. 2. As described above, two independent reaction tanks may be used, so that the first reaction tank may be biosorbed and removed from the biopolymer membrane made of biopolymer, and the second reactor may be configured to remove nitric acid by the microorganism.

As a reaction tank, a bottom-up packed microbial membrane reactor is used. The biggest advantage of microbial immobilization of nitrate nitrogen is that it can maintain a high microbial concentration per unit volume.

On the other hand, many of the microorganisms in the reactor are in vitro polymers, which are not active parts that play a direct role in the denitrification reaction. Therefore, if these microbial parts are not properly controlled and discharged out of the reactor, the probability of microorganisms coming into contact with these materials is reduced by the reduction of treatment capacity per unit volume and the restriction of diffusion in the reactor of carbon sources or nitrate nitrogen ions. Partial blockages may cause channeling or damage to the inlet pump.

Therefore, the bottom-up reactor is used in the present invention. Bottom-up is less clogging than top-down, as wastewater enters the bottom of the reactor.

In addition, in order to control the amount of microorganisms in the conventional reactor, a method of spraying compressed air from the bottom of the reactor to desorb microorganisms of only a portion of the lower end of the total carrier capacity was used. However, this method has no effect on the microorganisms of the upper part, and in order to compensate for this, the pressure of the injected air must be kept high, so that the microorganisms of the lower part are excessively desorbed in this process. Therefore, in the present invention, one reactor may be configured in a multilayer structure such that chromium is adsorbed and removed at the bottom of the reactor and nitrate nitrogen is removed at the top.

Wastewater containing chromium and nitric acid is adjusted in the flow control tank before the flow into the reactor, the flow rate of the incoming wastewater, which may vary depending on the operating conditions, and the concentration of constituents in the wastewater, such as heavy metals and nitric nitrate.

On the other hand, in general, the external carbon source (electron donor role) required for the denitrification reaction is measured and supplied in proportion to the nitrogen concentration in the incoming wastewater.

1 is a process schematic diagram of treating chromium and nitric acid-containing wastewater using a single reactor. When treating the wastewater containing chromium and nitric acid using a single reactor as shown in Figure 1, after adjusting the pH of the wastewater in the pH adjustment tank to 6.5-7.5, the wastewater is introduced into the reactor at a temperature of 10-40 ℃.

In the case of using two reactors to remove chromium in the first reactor and nitric acid in the second reactor as shown in FIG. 2, after adjusting the flow rate of the wastewater, the chromium is adsorbed and removed from the first reactor, and then chromium is removed. The pH of the removed wastewater is adjusted to 6.5-7.5 and then introduced into the second reactor at a temperature of 15-35 ° C. to remove nitrate nitrogen with nitrogen gas.

When treating wastewater containing nitrogen at a high concentration of 500 mg / L or more, it is recommended to treat the wastewater using two separate reactors.

In a packed reactor in which denitrification microorganisms are immobilized, chromium is biosorbed to a biopolymer formed by denitrification microorganisms and removed from the wastewater. The ion exchange mechanism of heavy metal biosorption is as follows.

Metal cations are adsorbed by attacking negatively charged sites on the surface of the adsorbent, which usually occurs when the strength of the bond with the metal cations in the solution is greater than the cations already bound to these sites. That is, heavy metal ions remove weak metal cations (Na ⁺ , Mg ²⁺ , Ca ²⁺ ) or hydrogen ions (H ⁺ ) attached to the biomass, and the biomass strong / weak acidic functional groups ) The anionic ligand that binds to the metal ion is a hydroxyl group of phosphoryl, carboxyl and membrane protein.

In general, the ion exchange mechanism of binding to a metal cation is as follows.

[Formula 1]

Me ²⁺ + 2A · B ↔ Me · B ₂ + 2A ⁺

Where Me is a heavy metal cation, B is biomass, and A is a cation attached to B (light metal or hydrogen ion). As in this scheme, Me ²⁺ is exchanged with A ⁺ . Since the reaction is reversible, it can be regenerated in a strong salt solution such as NaCl after the biomass has been saturated with Me ²⁺ .

By the mechanism described above, chromium in the wastewater is biosorbed and removed from the biopolymer formed by the denitrification microorganism in the reaction tank.

When chromium is adsorbed and removed by a biopolymer, chromium is adsorbed and separated on a biopolymer already formed by denitrification microorganisms, so it is not necessary to adjust the temperature of the reactor and the pH of the wastewater in particular. Good to do.

However, nitric acid is removed by the microorganisms and the conditions of the reactor and the wastewater must be adjusted to maintain the activity of the microorganisms. That is, the reactor is adjusted to 15-35 ° C. and the wastewater to pH 6.5-7.5.

Therefore, when chromium and nitric acid are removed in one reactor, wastewater is introduced into the reactor by operating the pH of the wastewater at 6.5-7.5 and the reactor at 10-40 ° C before introducing the wastewater into the reactor.

In addition, in the case of wastewater treatment in one reaction tank, a diaphragm in the form of a membrane that can be divided into upper and lower sides may be installed in the reactor so that chromium adsorption is performed at the bottom and nitrogen is denitrated at the top.

On the other hand, in the case of using two reactors to remove chromium from the first reactor using two reactors and nitric acid from the second reactor, after adjusting the flow rate of wastewater, the chromium is adsorbed and removed from the first reactor. After the chromium is removed, the wastewater is adjusted to 6.5-7.5 through a pH adjusting tank and then flows into a second reactor at 15-35 ° C. to remove nitric acid.

Before entering the denitrification reactor, the pH of the wastewater is adjusted to 6.5-7.5 in a pH adjuster.

In general, the waste water of the metallurgical industry is adjusted to pH 6.5-7.5 using a neutralizing agent such as caustic soda, because the pH is 2-3 levels.

Denitrification microorganisms are immobilized at the level of 60,000-100,000 mg / l and the extracellular polysaccharides produced by them, that is, biopolymers, adsorb heavy metals. When denitrification microorganisms are immobilized in the above-mentioned amounts, optimum results are obtained in consideration of the replacement cycle of the reaction tank.

As the microorganism, any denitrifying microorganism may be used, but is not limited thereto, and examples thereof include Pseudomonas denitrificans , Paracoccus , Escherichia , and the like.

On the other hand, if the chromium is adsorbed to the biofilm as a 1000mg-chromium / g-biopolymer after treatment to regenerate the biofilm. In the method of regenerating the biofilm, most of the heavy metals are desorbed and reused by slowly stirring the hydrochloric acid or sulfuric acid while maintaining the pH at 2 or less for 10 hours or more (100 rpm or less). In the case of regenerating the biofilm from the beginning, a new biofilm is formed within 30 days by introducing sewage sludge into a new reactor and then continuously introducing a low concentration of nitrogen nitrate (200 mg / L) at room temperature. In the treatment of high concentration of nitrate nitrogen, backwashing is performed by supplying compressed air from the bottom of each stage and periodically discharges the desorbed microorganisms through the outlet of each stage.

The method of treating the contaminants by attaching the denitrifying microorganism of the present invention to a carrier included in the reaction tank is more efficient than general floating type in the case of high concentration wastewater.

Hereinafter, the present invention will be described in detail through examples.

Example

The reactor was operated from the bottom up using a cylindrical reactor having a ratio of diameter 1: 2-1: 5. The carrier was filled with 75% by volume of polyethylene using less specific gravity than water so that it could be operated upward. As microorganisms, the sludge of the sewage treatment plant was immobilized on a carrier.

After inoculating the microorganism with 30% of the volume of the carrier, 500 mg / l of nitric acid and 1500 mg / l of methanol (denitrification only) were supplied at room temperature of 15-30 ° C. for 20 days or more. The sludge of the treatment plant was grown to form a biofilm.

In this way, the reactor in which the microbial membrane was formed was prepared, and then arranged in a single reactor and two separate reactors as shown in FIGS. 1 and 2, respectively, to prepare a wastewater treatment apparatus, and 500 mg / l of chromium and 1000 mg / of nitric acid. L containing wastewater was treated.

(1) Wastewater treatment using single reactor

A diaphragm was installed inside the single reactor to remove chromium from the bottom and nitrate nitrogen from the top. After adjusting the flow rate of the wastewater, the wastewater was treated for 20 days by adjusting the pH to 6.5-7.5 and the temperature of the wastewater to 10-40 ^° C.

Methanol, a carbon source, was fed to the top only as it was needed for denitrification.

(2) Wastewater treatment using two reactors

Waste water was flowed into the first reactor at a temperature of 10-40 ^o C by adjusting the flow rate so that the residence time is 4 hours to adsorb and remove chromium. Thereafter, the pH was adjusted to 6.5-7.5 and the wastewater was treated for 20 days by introducing chromium-free wastewater into the second reactor at 15-35 ^° C.

In the wastewater treatment using one reactor and two reactors, the denitrification is more limited than the adsorption removal reaction, so the inflow rate of wastewater is 30 mg of chromium in the adsorption reactor for chromium treatment. Adsorption is possible even in childbirth, you can operate based on this. However, the nitrogen removal rate of the denitrification microorganism was operated in consideration of both conditions because the residence time in the reactor was treated over 1000 hours / 1000mg / L nitric acid.

3 and 4 show the results of treatment of chromium and nitrogen-containing wastewater using the single reactor and two reactors. In the case of using a single reactor and two reactors, as shown in Figure 3 and 4 showed excellent chromium and nitrogen removal effect.

Wastewater containing chromium and nitrogen is treated with high efficiency by biosorption and denitrification using a packing reactor having a microbial membrane to which denitrified microorganisms are immobilized.

In addition, the reactor is an upwardly packed reactor, in which microorganisms are immobilized at a high concentration, and there is no adverse effect on subsequent processes by removing heavy metals by biosorption. Furthermore, the use of anaerobic microorganisms does not require a separate device for supplying air as compared with the case of biosorption using aerobic microorganisms.

1 is a view showing an example of the present invention for treating chromium and nitric acid-containing wastewater using a single reactor,

2 is a view showing an example of the present invention for treating chromium and nitric acid-containing wastewater using two reactors,

3 is a graph showing the effect of chromium on nitric acid treatment,

4 is a graph showing the efficiency of chromium and nitric acid treatment in wastewater by the method of the present invention.

Claims (3)

In the wastewater treatment method containing chromium and nitric acid, Wastewater containing chromium and nitric acid was adjusted to pH 6.5-7.5 and spaced at the top and bottom of the reactor at a temperature of 10-40 ° C. in a bottom up packed microbial reactor having a carrier fixed at 60,000-100,000 mg / l denitrification. Wastewater treatment method containing influent chromium and nitric acid. In the wastewater treatment method containing chromium and nitric acid, Introducing the wastewater containing chromium and nitric acid into a first bottom-up packed microbial reactor in which denitrification microorganisms are fixed at 60,000-100,000 mg / l to remove chromium; Adjusting the pH of the chromium-free wastewater to 6.5-7.5; And Introducing chromium-free wastewater into a second bottom-up packed microbial reactor in which denitrification microorganisms were fixed at 60,000-100,000 mg / l at 15-35 ° C. to remove nitric acid; Waste water treatment method containing chromium and nitric acid. The method of claim 1 or 2, wherein the microorganism is selected from the group consisting of Pseudomonas denitrificans , Paracoccus , Escherichia .