KR20010002276A - Method and equipment for the treatment of wastewater containing nitrate-nitrogen - Google Patents

Abstract

PURPOSE: A method for treating wastewater containing high concentration of nitrate-nitrogen and system thereof is provided, which uses microorganism media, i.e. biofilter tank to increase treatment efficiency per area. CONSTITUTION: The method comprises the follow parts: (i) an equalization tank (10) for controlling volume of wastewater; (ii) a buffer solution container (40) for adjusting pH of wastewater to be proper for the growth of denitrification microorganism; (iii) an apparatus (50) for both measuring NOx and feeding external carbon sources; (iv) the first denitrification tank (20a) packed with denitrification microorganism, wherein wastewater (2) upflow into the tank; (v) two apparatuses (60, 70) for both measuring pH and feeding acidic solution, thereby neutralizing wastewater; (vi) the second denitrification tank (20b) packed with denitrification microorganism, wherein wastewater (2) upflows into the tank; (vii) a return pipe (5) for recycling a portion of wastewater. In the method, volume of wastewater return is controlled to 50-200 vol.%, based on the volume of raw wastewater inflow so that stable operation is warranted even if shocking-loads of nitrogen.

Description

METHODS AND EQUIPMENT FOR THE TREATMENT OF WASTE WATER CONTAINING NITATE-NITROGEN

The present invention relates to a method and apparatus for treating wastewater containing nitrate nitrogen, and more particularly, to a method for treating nitrate nitrogen wastewater in high concentrations discharged from an industry, etc. simply and efficiently by using a biofilm method. Relates to a device.

Nitrogen components in the waste water exist in the form of organic nitrogen and inorganic nitrogen, which are collectively called total nitrogen (TN). Inorganic nitrogen is again classified into ammonia nitrogen and nitrate nitrogen (NO _x ), and ammonia nitrogen and organic nitrogen are called TKN (Total Kjeldahl Nitrogen).

Nitrate nitrogen present in the waste water is basically oxidized by denitrifying bacteria using nitrate nitrogen as an electron acceptor instead of oxygen which is insufficient in anoxic conditions, and nitrate nitrogen is reduced to nitrogen gas (N ₂ ) and released into the atmosphere. By processing.

Nitrate nitrogen removal in waste water using the denitrification microorganism is widely used because it is the most competitive in terms of economics compared to other physicochemical methods using reverse osmosis membranes or ion exchange resins.

In general, the method of treating wastewater using microorganisms can be broadly classified into a floating activated sludge method widely used in existing sewage treatment processes and a biofilm method using microorganisms attached to a carrier. Known in the art (Wastewater Engineering, Ecalf and Eddy, 1992; Biological Wastewater Treatment, Grady, Daigger and Lim, 1999).

The advantage of the biofilm method over the floating activated sludge method is that the microorganisms can be concentrated at a high concentration, so that the treatment efficiency per unit volume is high. Therefore, interest in the wastewater treatment method using the same is increasing day by day.

However, many existing methods for treating wastewater containing high concentrations of nitrate (eg, Korean Patent Publication No. 97-20992, Korean Patent Publication No. 94-2175, Manual-Nitrogen Control, EPA, 1993 Although these methods have already been proposed, these methods are not easily applied to the existing wastewater treatment process due to the problem of requiring a large installation space and inferior treatment efficiency and convenience of operation.

Therefore, the technical problem to be achieved by the present invention is to overcome the constraints of the installation space, stable processing operation even in the nitrogen load fluctuations can be maintained, the maximum nitrogen removal treatment efficiency can be maintained, and the operation is easy to minimize the operator's workload It is possible to provide a wastewater treatment method containing a high concentration of nitrate nitrogen.

Another technical problem to be achieved by the present invention is to provide a wastewater treatment apparatus used to implement the wastewater treatment method.

1 is a flow chart schematically showing a nitrate nitrogen wastewater treatment process according to an embodiment of the present invention.

2 is a graph showing the results of nitrate nitrogen wastewater treatment according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: adjustment tank

20a, 20b: biofilm reactor

30: Chinese tank

40: pH measurement and buffer supply

50: nitrogen concentration measurement and carbon source supply

60, 70: pH measurement and acid supply

The present invention to achieve the above technical problem,

Introducing a nitrate nitrogen wastewater to be treated into the adjustment tank, measuring the pH, and adjusting the pH to a pH range suitable for growth of denitrifying microorganisms by adding a buffer;

Allowing the pH-controlled wastewater to flow into the first reactor in an upflow manner to proceed with denitrification by denitrification microorganisms attached to the carrier;

Measuring the pH of the treated water discharged from the first reaction tank, and supplying an acid aqueous solution to readjust the pH to a pH range suitable for growth of denitrifying microorganisms;

Allowing the treated water discharged from the first reactor to adjust the pH to the second reactor in an upflow manner to proceed with denitrification by denitrification microorganisms attached to the carrier;

Circulating a portion of the treated water discharged from the second reaction tank into the adjustment tank and introducing the remaining water into the neutralization tank; And

It provides a method for treating nitrate nitrogen wastewater comprising measuring the pH of the treated water introduced into the neutralization tank, supplying an acid aqueous solution to neutralize and then discharging it as the final treated water.

According to one embodiment of the present invention, prior to the step of introducing into the first reaction tank, measuring the nitrate nitrogen ion concentration of the pH-controlled wastewater in the control tank, in proportion to the input of a carbon source for subsequent denitrification reaction It is preferable to further include.

The amount of carbon source proportional to the nitrate nitrogen ion concentration is preferably 2.5 to 3 g methanol / g nitrate when the carbon source is methanol.

The buffer solution may include sodium hydrogen carbonate and hydrochloric acid, and the acid aqueous solution may include hydrochloric acid.

The suitable pH range for the denitrification microorganism to grow is preferably pH 7.0 to 7.5.

In addition, according to one embodiment of the present invention, by supplying compressed nitrogen gas from the bottom of the first and second reaction tank to remove the overgrown microorganisms from the carrier further discharge the excess growth microorganisms accumulated in the reactor bottom It is preferable to include.

In addition, the present invention to achieve the above technical problem,

An adjustment tank for introducing and storing nitrate nitrogen wastewater to be treated and discharging the wastewater at an appropriate flow rate;

An apparatus for measuring pH and supplying a buffer solution to maintain the pH of the wastewater in the adjusting tank in a range suitable for growth of denitrification microorganisms;

Nitrate nitrogen ion concentration measurement and carbon source supply device for measuring the nitrate nitrogen ion concentration of the waste water discharged from the adjustment tank, and proportionally input the carbon source required for the subsequent denitrification reaction;

The pH-controlled wastewater is introduced into the upflow. A first reactor through which denitrification proceeds by denitrification microorganisms attached to the carrier;

PH measurement and acid supply device for measuring the pH of the treated water discharged from the first reaction tank, supplying an acid aqueous solution to readjust the pH range suitable for the growth of denitrifying microorganisms; And

A second reaction tank discharged from the first reaction tank into which treated water whose pH is adjusted is introduced, and a denitrification reaction by denitrifying microorganisms attached to the carrier is performed;

Internal circulation means for returning a part of the treated water discharged from the second reaction tank to the adjustment tank; And

It provides a nitrate nitrogen wastewater treatment apparatus including a neutralization tank to flow in the remainder of the treated water discharged from the second reaction tank, to measure the pH, to supply an acid aqueous solution to neutralize the treated water and then discharged as the final treated water. do.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a process flow chart for explaining the wastewater treatment method according to an embodiment of the present invention. High concentration nitrogen wastewater discharged from industry can vary considerably in the concentration and flow rate of nitrogen depending on the process conditions of the shear and the type of product produced. Therefore, the adjustment tank 10 adjusts these variables by diluting the inflow water 1 with the return water 5 partially returned from the treated water 4 discharged from the second biofilm reaction tank 20b. That is, the adjustment tank 10 allows the wastewater to be treated to the subsequent biofilm reactor 20a to be supplied at a uniform flow rate, and reduces the impact load due to the high concentration of nitrate nitrogen, which may sometimes occur, by mixing it with a portion of the treated water. .

In addition, the adjustment tank 10, so that the pH of the waste water, which may not be constant depending on the operating conditions of the shearing process can be adjusted to a range (pH7.0-7.5) suitable for the habitat of the microorganisms performing the denitrification reaction in the subsequent biofilm reaction tank, An apparatus 40 for supplying a buffer by measuring pH may be installed. It is preferable to use sodium hydrogencarbonate and hydrochloric acid aqueous solution as pH buffer.

Bicarbonate ion (HCO ₃ ^-) will also serve to prevent the pH of the treated water due to the hydroxyl ions, and that the strongest buffering action in the vicinity of pH 8.3, produced a subsequent denitrification results abruptly increases. For a detailed description thereof, reference may be made to the description of the biofilm reactor described below.

After the adjustment tank 10, the nitrate nitrogen concentration is measured by the nitrogen concentration measuring apparatus 50 for the wastewater 2 flowing into the first biofilm reactor 20a for the denitrification reaction. The denitrification reaction is different in the reaction rate when there is no organic matter, and the case where there is no organic matter is called endogeneous denitrification and the denitrification rate is slow and requires a long residence time. The denitrification rate is so fast that the residence time can be shortened.

Therefore, the nitric acid concentration measuring device 50 measures the concentration of nitrate nitrogen ions in the wastewater 2 which has passed through the adjustment tank 10 and supplies the organic material, that is, the carbon source 7, necessary for the denitrification reaction. When the carbon source is methanol, the carbon source supply ratio according to the nitrate nitrogen ion concentration is preferably 2.5 to 3.0 g methanol / g nitrate nitrogen.

However, if the organic matter content is high from the beginning according to the type of waste water, the step may be omitted.

Wastewater with adjusted pH and organic matter concentration is supplied to two sets of biofilm reactors 20a and 20b arranged in series. The biofilm reactor has a structure filled with a plastic ring carrier in a cylindrical body. Preferably, the carrier is filled to about 70% of the volume of the reactor and the wastewater 2 is introduced in an upflow manner. Denitrifying microorganisms grow by attaching to a floating carrier, and microorganisms overgrown by an appropriate amount of inflow nitrogen and supply carbon are discharged to the outlet of the bottom of the reactor through a backwashing process.

In order to control overgrown microorganisms, compressed nitrogen gas may be supplied to the bottom of the reaction tanks 20a and 20b. When compressed nitrogen gas is supplied, the carriers packed in the reaction tank are mixed, and the overgrown microorganisms are separated from the carrier and accumulated at the bottom of the reaction tank so that they can be discharged.

In the wastewater treatment method and apparatus of the present invention, two biological membrane reactors are arranged in series as follows.

The denitrification reaction increases the pH in the reaction tank because the hydroxyl ion is increased in proportion to the inflow concentration of nitrate nitrogen, as shown in Scheme 1 below.

^{_{6NO 3 - + 5CH 3 OH →}} 5CO 2 + 3N 2 + 7H 2 O + 6OH -

This increase in pH inhibits the activity of the denitrifying microorganisms and drastically lowers the denitrification efficiency. Therefore, the present invention adopts the following two methods to control such rapid pH rise.

First, pH buffer (bicarbonate ion + acid) is supplied from the initial adjustment tank 10. A portion of the pH buffer (bicarbonate ion) to be supplied introduces an internal circulation line so that it is self-supplyed from the return water (5).

Second, the pH of the treated water 3 flowing into the second reactor 20b is readjusted to 7.0 to 7.5 by measuring the pH between the two tanks 20a and 20b and supplying the aqueous acid solution 8.

The present invention uses a biofilm reactor capable of high concentration of microorganisms to treat high concentrations of nitrate nitrogen wastewater. Such biofilm reactors, unlike floating activated sludge reactors, which are mixed by an agitator, are completely mixed with the fluid flowing into the reactor in an instant. Since the acid solution for pH adjustment is added directly to the reactor, the microorganism may be locally damaged.

Therefore, in the present invention, the pH was adjusted in the above-described manner, and since the two reactors were arranged in series, even if nitrate nitrogen was not removed in the first reactor, it could be completely removed from the second reactor. Is improved.

The carbon dioxide and hydroxide ions generated as a result of the denitrification reaction of Scheme 1 generate bicarbonate ions as shown in Scheme 2 below, and the bicarbonate ions having the strongest buffering effect near pH 8.3 play a natural pH control role to prevent a sharp increase in pH. do.

^{_{CO 2 (aq) + OH -}} → HCO 3 -

Therefore, when the internal circulation of a portion (5) of the treated water discharged to the second biofilm reactor to the adjusting tank 10 can reduce the process cost by reducing the external supply of sodium hydrogen carbonate of the buffer to be input from the adjusting tank 10, The buffer capacity of the adjustment tank 10 can be increased, and the nitrogen concentration of the influent 1 can be diluted, thereby increasing the treatment efficiency. The remainder of the treated water 4 which has passed through the second biofilm reactor is discharged as the final treated water 6 after the pH is adjusted in the pH neutralization tank 30.

Hereinafter, the present invention will be described in more detail through examples of the present invention, but many modifications of the following examples are possible, but are not necessarily limited thereto.

<Example>

A laboratory scale apparatus was installed to implement the method of the present invention to treat high concentrations of nitrate nitrogen influent.

First, a 20 L volumetric adjustment tank was installed, and two biofilm reactors were connected in series at the rear stage. The total volume of each reactor used was 6.5 L, of which 4.6 L, which corresponds to 70%, was filled with a carrier. It was a volume.

The biofilm reactor was a cylindrical reactor with a diameter-to-height ratio of about 3.6, and the hydraulic retention time (HRT) was 4 hours. The carrier was a polypropylene 5/8 inch polling, with a porosity of 0.9 kg / m ³ and filled with 70% of the reactor volume. The nitrate nitrogen wastewater was supplied from the adjustment tank at a flow rate of 38 ml / min, and the daily wastewater treatment capacity was 54.7 liters.

In this example, wastewater (initial pH 7.4) containing high concentrations of nitrogen ions of 1000 mg-N / L was treated using an apparatus configured as shown in FIG.

For the convenience of experiments, the initial pH was adjusted by supplying a pH buffer solution containing 500 g of sodium bicarbonate 500 g / hydrochloric acid (37%) with respect to 100 L of wastewater without artificially adopting the circulation rate of the internal circulation line. Adjusted. However, the internal circulation rate (50-200%) and pH measurement in actual wastewater treatment can be easily adjusted by the operator according to the operating conditions and the wastewater properties and can be adjusted according to the site conditions.

The measurement of the concentration of incoming nitrate nitrogen and the supply of carbon source in proportion to it can be easily achieved by the on-line device that can measure the nitrate nitrogen and the simple pump operation operated in proportion.

The pH of the treated water discharged from the first reactor was 9.12, and the pH before entering the second reactor was adjusted to 7.2 using 3N hydrochloric acid solution. The pH of the treated water discharged from the second reactor was 9.1, and the pH of the final discharged water was adjusted to 7.0 using 3N hydrochloric acid in the neutralization tank.

From the second day of operation, the nitrate nitrogen concentration of the effluent treated and discharged finally was measured and shown in a graph of FIG. 2. According to the graph of FIG. 2, the removal efficiency of 80% or more is shown on the second day, the removal efficiency of 90% or more from the seventh day of operation, and the removal rate of 95% or more is maintained stably from the eleventh day.

According to the wastewater treatment method according to the present invention, wastewater containing a high concentration of nitrate nitrogen can be efficiently treated using a biofilm reactor with a high concentration of microorganisms, and the apparatus according to the present invention can be installed in a small area. It is easy to apply to existing processes and has the advantage of easy maintenance. Therefore, with increasing concern about environmental issues, it is easy to meet the increasingly stringent effluent standards and contribute to the reduction of environmental burdens that must be considered when producing products.

Claims (5)

Introducing a nitrate nitrogen wastewater to be treated into the adjustment tank, measuring the pH, and adjusting the pH to a pH range suitable for growth of denitrifying microorganisms by adding a buffer; Allowing the pH-controlled wastewater to flow into the first reactor in an upflow manner to proceed with denitrification by denitrification microorganisms attached to the carrier; Measuring a pH of the treated water discharged from the first reaction tank, and supplying an acidic aqueous solution to adjust a pH range suitable for growth of denitrifying microorganisms; Allowing the treated water discharged from the first reactor to adjust the pH to the second reactor in an upflow manner to proceed with denitrification by denitrification microorganisms attached to the carrier; Circulating a portion of the treated water discharged from the second reaction tank into the adjustment tank and introducing the remaining water into the neutralization tank; And Measuring the pH of the treated water introduced into the neutralization tank, and neutralizing by supplying an aqueous acid solution and then discharged as the final treated water. The method of claim 1, wherein the pH buffer solution comprises sodium bicarbonate and hydrochloric acid, and the acid aqueous solution comprises hydrochloric acid. The method of claim 1, wherein a portion of the pH buffer to be supplied to the control tank is internally circulated so that it is self-supply from the return water, the internal circulation rate is adjusted to 50-200% of the influent to reduce the impact nitrogen load due to dilution at the same time How to. The method according to claim 1, wherein an acid aqueous solution is supplied between the first and second reactors to maximize the denitrification efficiency in the second reactor by maintaining the initial pH environment of the second reactor in an optimal state. . An adjusting tank for introducing nitric acid wastewater to be treated and discharging the wastewater at an appropriate flow rate; An apparatus for measuring pH and supplying a buffer solution to maintain the pH of the wastewater in the adjusting tank in a range suitable for growth of denitrification microorganisms; Nitrate nitrogen ion concentration measurement and carbon source supply device for measuring the nitrate nitrogen ion concentration of the waste water discharged from the adjustment tank, and proportionally input the carbon source required for the subsequent denitrification reaction; The pH-controlled wastewater is introduced into the upflow. A first reactor through which denitrification proceeds by denitrification microorganisms attached to the carrier; PH measuring and acid supply apparatus for measuring the pH of the treated water discharged from the first reaction tank, supplying an aqueous acid solution to adjust the pH range suitable for the growth of denitrifying microorganisms; And A second reaction tank discharged from the first reaction tank into which treated water whose pH is adjusted is introduced, and a denitrification reaction by denitrifying microorganisms attached to the carrier is performed; Internal circulation means for returning a part of the treated water discharged from the second reaction tank to the adjustment tank; And The rest of the treated water discharged from the second reaction tank is introduced, the nitrate nitrogen wastewater treatment apparatus including a neutralization tank for measuring the pH, supplying an acid aqueous solution to neutralize the treated water and discharged as the final treated water.