KR100534040B1 - Method of high-rate denitrification using two reactors in series - Google Patents

Abstract

The present invention relates to a method for removing high-concentration nitrate nitrogen by a two-stage continuous reactor, and more specifically, divided into upper and lower portions in one reactor, which is a conventional method, by sequentially performing heterotrophic and heterotrophic denitrification, respectively. Unlike the method of removing nitrate nitrogen, two reactors are used to carry out heterotrophic denitrification in the first reactor and independent nutrient denitrification in the second reactor, but the two reactors are connected in series to be effective and economical. The present invention relates to a method for removing high concentration nitrate nitrogen by a two-stage continuous reactor for treating high concentration nitrate nitrogen.

Description

Method of removing high concentration of nitrate nitrogen by two-stage continuous reactor {Method of high-rate denitrification using two reactors in series}

The present invention relates to a method for removing high-concentration nitrate nitrogen by a two-stage continuous reactor, and more specifically, divided into upper and lower portions in one reactor, which is a conventional method, by sequentially performing heterotrophic and heterotrophic denitrification, respectively. Unlike the method of removing nitrate nitrogen, two reactors are used to carry out heterotrophic denitrification in the first reactor and independent nutrient denitrification in the second reactor, but the two reactors are connected in series to be effective and economical. The present invention relates to a method for removing high concentration nitrate nitrogen by a two-stage continuous reactor for treating high concentration nitrate nitrogen.

Nitrogen removal methods for sewage and wastewater are divided into physicochemical and biological methods. The physicochemical methods are economically expensive for biological methods and require special knowledge in operation management. Biological nitrogen removal methods have already been developed and used in various methods (AO, A2O, Bardenpho, Modified Bardenpho, UCT, Ludzack-Ettinger, etc.), but most of them use nitrogen from nutritionally constitutive (dependent) microorganisms. In order to remove the organic matter, the concentration of organic matter is lower than that of nitrogen, and in order to apply to domestic wastewater, a separate organic matter must be injected from the outside. Heterotrophic denitrification using methanol is shown in Scheme 1 below.

Scheme 1

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

As shown in Scheme 1, the amount of methanol required per 1 g of nitrate nitrogen is 2.47 g, and the total amount must be supplied from the outside for the treatment of wastewater having a low organic content. In particular, when the concentration of inlet nitrogen is high, the amount of injecting organic matter is excessively required, and thus the operating cost is very high.In the case of wastewater having a large load fluctuation of inflow nitrogen, the injected organic matter is insufficient or discharged untreated. The BOD of the treated water quality is high or the amount of sludge generated is often a problem that requires additional treatment costs.

Complementing the problem of heterotrophic denitrification is autotrophic denitrification using sulfur particles in the following Scheme 2.

Scheme 2

^{_{NO 3 - + 1.05 S + 0.74}} H 2 O + 0.28 CO 2 = 0.47 N 2 + 1.05 SO 4 2- + 1.09 H + + 0.06 C 5 H 7 O 2 N

In Korea Patent Publication No. 2000-56873, heterotrophic and autotrophic denitrification were performed together. This is effective in the case where nitrogen inflow is not large (10 to 600 mg / L) by dividing one reactor into upper and lower stages, followed by heterotrophic denitrification at the bottom, and carrying out autotrophic denitrification. Increasingly, the amount of organic matter consumed is more than necessary, and it is economically disadvantageous, and incomplete denitrification occurs and nitrite accumulation occurs. In particular, a large amount of heterotrophic microorganisms are introduced into the autotrophic denitrification tank as it is at the bottom. It has been shown to adversely affect the distribution. In conclusion, when organic matter is introduced in high concentration to high concentration of nitrogen in Hwangchungjin autotrophic denitrification tank, it leads to overgrowth of heterotrophic microorganisms, which breaks the balance of autotrophic microbial system. When denitrification is possible, up to 600 mg / L is possible, but more than that, the economic efficiency is lowered and the efficiency of denitrification becomes worse, resulting in the accumulation of nitrous acid.

In addition, the present inventor has proposed a method of simultaneously performing heterotrophic denitrification and autotrophic denitrification in one denitrification tank in Korean Patent Application No. 2000-68483, which is filed by the present inventor. Organic matter consumption can be induced by microorganisms, and organic matters are consumed more than necessary, and random autotrophic denitrification microorganisms use inorganic carbon sources when there are no organic matters, but when there is an excessive amount of organic matters, they are denitrated like general heterotrophic microorganisms. There was this.

Therefore, in the face of continued tightening of regulations on nitrogen items in domestic wastewater and wastewater emission standards, it is urgent to develop a method capable of removing nitrogen at a low cost, and in particular, a method for treating high concentrations of nitrous nitrogen discharged from large industrial complexes is needed. It is required.

Therefore, the present inventors have studied to solve the above problems, in the two-stage continuous reactor that is clearly distinguished between the heterotrophic denitrification tank and the autotrophic denitrification tank, the maximum amount of organic matter injected in the heterotrophic denitrification tank of shear The present invention was completed by treating the high concentration of nitrate nitrogen wastewater with a low C / N ratio and more than 500 mgN / L by efficiently performing autotrophic denitrification using the generated alkalinity.

Therefore, the present invention is particularly effective in removing nitrogen for wastewater containing high concentrations (more than 500 mg / L) nitrate nitrogen, which is economically expensive for organic carbon sources and which cannot be highly treated by conventional methods. Phosphorus operation is possible, and it is easy to operate by reducing the factors to be considered during operation, and the purpose is to provide a method for removing high concentration nitrate nitrogen by a simple two-stage continuous reactor.

The present invention provides a method for removing nitrate nitrogen in wastewater by heterotrophic denitrification and autotrophic denitrification, wherein heterotrophic denitrification is carried out by introducing an external carbon source of 1/8 to 1/2 of the heterotrophic denitrification requirement into the heterotrophic denitrification tank. High concentration quality by two-stage continuous reactor, characterized in that to efficiently process the high concentration of nitrate nitrogen contained in the waste water by performing autotrophic denitrification in an autotrophic denitrification tank filled with sulfur particles and limestone continuously. It is characterized by a method of removing acidic nitrogen.

Referring to the present invention in more detail as follows.

The present invention separates the heterotrophic / independent nutrient denitrification into two tanks and performs denitrification using a two-stage continuous reactor in which a storage tank is placed therebetween. Each reactor can be operated differently as necessary and dependent on the independent nutrient denitrification tank. The aim is to ensure the prevention of nutrient denitrification microorganisms to reduce the amount of organic matter more than necessary.

For the treatment of wastewater containing high concentrations of nitrate nitrogen, in order to carry out heterotrophic denitrification first, the concentration of organic matter and the biologically degradable COD concentration in the wastewater should be determined, which corresponds to about 50% of the incoming nitrogen. Inject additional methanol to remove 500 mgN / L. Since the efficiency of heterotrophic denitrification is entirely controlled by the amount of methanol injected, it is possible to further reduce the cost of methanol by increasing the fraction of autotrophic denitrification when the concentration of inflow nitrate is relatively low. After the heterotrophic denitrification, the wastewater contains enough alkalinity required for autotrophic denitrification, so it is introduced into the sulfur particle column as it is, or in the case of suspended solids, through the settling tank. The nitrate nitrogen in the waste water is reduced and removed by the electrons of the sulfur particles as the sulfur particles pass through the column filled with the upstream, and the generated hydrogen ions consume alkalinity and are discharged into the treated water near the neutral. Autotrophic denitrification can be processed more than 90% by efficiently utilizing the contact area with biofilms formed on sulfur particles to perform denitrification efficiently even for short hydraulic residence time.

The present invention shows a two-stage continuous denitrification process for treating a high concentration of nitrate nitrogen wastewater, consisting of a heterotrophic denitrification tank, a storage (sedimentation) tank, and an independent nutrition denitrification tank, each of which is described in detail below.

Heterotrophic denitrification tank is a rectangular reaction tank, which puts a sponge carrier to allow heterotrophic denitrification microorganisms to grow in a fixed state rather than suspended and to prevent the loss of carriers and microorganisms by installing a net at the top of the reactor. At this time, as a carrier, various commercially available products can be used. Porous polyurethane sponge type which can reduce the hydraulic retention time and effectively use denitrification microorganisms by preventing microbial loss and widening the microbial contact surface. Carriers are preferred. Heterotrophic microorganisms that perform denitrification using organic carbon present or added in the influent can adhere to the surface of the suspended carrier to form a wide contact surface to actively remove the nitrate nitrogen components in the influent. The concentration of organic matter is added so that about 50 to 60% of the high concentration (500 mgN / L or more) nitrogen nitrate introduced can be removed. Preferably, an external carbon source (organic substance) of about 1/8 to 1/2 of the heterotrophic denitrification requirement is added, and as the addition of organic matter is more economical, the concentration of inflow nitrogen nitrate is low (500 mgN / L or less). 100% autotrophic denitrification or 1/8 organic matter is added to increase the utilization of autotrophic denitrification, and the alkalinity required at this time can be sufficiently supplemented with limestone of autotrophic denitrification tank. In addition, as the concentration of inflow nitrate nitrogen increases (more than 500 mgN / L), the alkalinity necessary for autotrophic denitrification may be insufficient, or the denitrification rate of autotrophic denitrification itself may be limited. Using denitrification at the same time is more effective. Heterotrophic denitrification: When autotrophic denitrification is used at about 1: 1, there is no need to introduce more than half of the organics since the balance between production and consumption of alkalinity is theoretically balanced. In addition, preferred external carbon sources include methanol, ethanol, acetate, glucose and the like, but methanol is widely used as the most economical and effective carbon source.

After the heterotrophic denitrification in the heterotrophic denitrification tank, a storage (sedimentation) tank may be installed so that the microorganisms and suspended solids discharged with the treated water in the suspended state can be precipitated and returned to the heterotrophic denitrification tank for removal. . The supernatant from the reservoir is introduced into an autotrophic denitrification tank. In other words, the high concentration of nitrate nitrogen is introduced into the heterotrophic microorganisms as necessary (1/2 to 1/4), and the remaining nitrogen is introduced into the autotrophic denitrification tank with almost all organic matters exhausted. It can be processed economically.

The wastewater treated with heterotrophic denitrification is then passed upstream to an autotrophic denitrification tank using a pump.

In addition to completely independent nutrient denitrification microorganisms, independent autotrophic denitrification microorganisms also exist in autotrophic denitrification tanks.In organic-rich conditions, they act as heterotrophic denitrification microorganisms. It is necessary to operate the sulfur particle denitrification tank in full autotrophic conditions.

The sulfur particles needed for autotrophic denitrification are electrons in the role of organics in heterotrophic denitrification, which allows the reduction of nitrate nitrogen and the energy source of autotrophic denitrification microorganisms. It is used as a filter in the physical sense. The diameter of the particles can be used as it is 4 to 6.5 mm and at least one year as a single filling. In this case, when the diameter of the sulfur particles is large, the contact surface area between the microorganisms adhering to the surface of the sulfur particles and the waste water decreases, so the denitrification efficiency decreases, and when the particles are too small, the surface area is large, but the waste water flow may be obstructed or blockage Can be. Once a year or more, depending on the load of inflow nitrogen, supplement the amount of sulfur particles consumed through the upper part of the denitrification tank.

On the other hand, limestone is filled with sulfur particles, which use the alkalinity consumed during autotrophic denitrification as produced in heterotrophic denitrification and is used as an auxiliary alkali source to supplement the shortfall. It depends on the degree of inflow nitrogen loading and heterotrophic denitrification, but depending on the conditions, evenly mixing the volume ratio of limestone and sulfur particles in a ratio of 1: 1 to 1: 3 may serve as an alkalinity supplement. This mixing ratio is based on the reaction formula of autotrophic denitrification, which requires a ratio of about 1: 1. However, autotrophic denitrification microorganisms grow by sticking more to sulfur particles than limestone, and exist in raw wastewater as well as limestone or heterotrophic denitrification. Considering the alkalinity supplemented with, it is determined from the fact that a slightly higher ratio of sulfur particles is advantageous. Limestone starts to elute only when the alkalinity is insufficient, especially pH 7.1 or lower, so it is much easier and simpler to operate than when using sodium hydrogen carbonate in solution. Although studies using shells and steel slugs are underway, the solubility of shells is not stable compared to limestone, and steel slugs are less effective as alkaline sources than limestones. The size of the limestone particles is suitably about 1 to 2 cm in diameter and is also used as a support for growth of denitrified microorganisms.

Autotrophic denitrification microorganisms include Thiobacillus denitrificans , Thiomiceospira denitrificans , Thiobacillus versutus , and Thiocillus taiassi . Thiobacillus thyasiris , Thiosphaera pantotrophs and Paracoccus denitrificans are also known to denitrify using sulfur. These microorganisms can be identified in the return sludge of a general sewage treatment plant and cultured at high concentration under appropriate conditions. Autotrophic denitrification can be actively carried out at a temperature of pH 6 to 8.5 and 15 to 35 ° C. Active denitrification takes place in the biofilm of autotrophic denitrification microorganisms formed in the sulfur particles filled in the denitrification tank, and high concentrations of nitrate nitrogen are rapidly reduced and removed.

Therefore, the method for removing nitrogen nitrate by the two-stage continuous reactor according to the present invention is an economical nitrogen treatment method with the lowest installation and operating costs. The production of nitrogen and phosphate fertilizers with low C / N ratio, plywood production, pesticide production It can be effectively used for nitrogen treatment of industrial wastewater, leachate, groundwater, etc.

Hereinafter, the present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Example 1: Confirmation of Nitrate Nitrogen Removal Using Two Stage Continuous Reactor

Table 1 summarizes the denitrification method by a two-stage continuous reactor, and shows the carriers used in the heterotrophic denitrification tank and the autotrophic denitrification tank, the denitrification capacity, and the operating conditions.

The denitrification experiments were performed on laboratory scale two-stage reactors with influent loads of 500, 750 and 1,000 mgNO ₃ ^-- N / L. The test period was 125 days in total and operated at 41, 34 and 50 days at each inlet concentration. Influent wastewater was controlled only by the concentration of nitrate nitrogen using artificial wastewater containing minerals. The concentration of organics (methanol) was infused with 625, 937.5 and 1,250 mgMeOH / L, respectively 1/2 of theoretical requirements.

Heterotrophic denitrification tank prevented the loss of microorganisms by adding a fibrous biofilm carrier and polyurethane sponge carrier using 1L flask, and seeding of heterotrophic denitrification tank was injected by returning 1/3 of the liquid volume of municipal sludge treatment plant for 24 hours. It was left as it was and operated. The effluent treated in the heterotrophic denitrification tank was collected in a reservoir prior to being introduced into the autotrophic denitrification tank, to precipitate lost microorganisms, and then injected into three columnar autotrophic denitrification tanks connected in parallel and operated upstream. Independent nutritional denitrification columns (1, 2, 3) were filled with sulfur particles and limestone in a volume ratio of 1: 1, and the diameters of the charged sulfur particles were independent (independent 1: <2 mm, independent 2: 2-4.75 mm, independent 3). : 4.75-6 mm)

Hydraulic retention time was 5 hours for heterotrophic denitrification tank and 4 hours for independent nutrient denitrification tank.

As a result, Figure 6 shows the nitrate nitrogen concentration change during the experimental period. When the inlet concentration was 500, 750, and 1,000 mg / L, about 250, 375, and 500 mg / L, respectively, were removed by heterotrophic denitrification, and the remaining nitrogen was subsequently treated with an autotrophic denitrification column. The desulfurization capacity of each of the columns with different charged sulfur particles was similar and contained about 5 mg / L nitrate nitrogen in the effluent.

Figure 7 shows the relative fraction of heterotrophic / independent nutrient denitrification to total denitrification. The total denitrification efficiencies at three influent concentrations were 96, 97 and 94%, respectively, with the relative contributions of heterotrophic and autotrophic denitrification. An average of 55/45, it can be seen that the denitrification as intended as the amount of organic matter injection.

Table 2 summarizes the results of the denitrification test of the two-stage reactor. High denitrification rate of more than 95% was obtained for each inflow load, and alkalinity produced by heterotrophic denitrification could satisfy the degree required for autotrophic denitrification. It is a very good result that the denitrification efficiency of wastewater with inflow load of 1,000 mgN / L is more than 95%, and the organic matter injected here is economically advantageous because it is about 1/2 of the amount required for existing heterotrophic denitrification.

division Hydraulic stay time (HRT) Type of carrier Electron donor Treatable Nitrate Concentration (mgN / L) Nitrogen Removal Efficiency Heterotrophic denitrification tank 2 to 6 Fibrous biofilm, polyurethane sponge carrier Methanol, Organic Components in Wastewater 10 to 1,000 More than 95% Autotrophic denitrification tank 4 to 8 Sulfur particles, limestone Sulfur particles 10 to 600 More than 95%

Date range Nitric acid concentration (mgN / L) Average N Removal Rate (%) Alkalinity change (mg / L as CaCO ₃ ) SO ₄ ^2- / N ratio during autotrophic denitrification Heterotrophic denitrification Autotrophic denitrification TOTAL Heterotrophic denitrification Autotrophic denitrification 0 to 41 500 49.88 (± 12.75) 46.29 (± 12.97) 96.17 (± 4.91) +621 (± 13) -532 (± 22) 6.21 (± 1.30) 42 to 75 750 63.72 (± 4.23) 33.51 (± 4.05) 97.23 (± 2.29) +1326 (± 48) -890 (± 27) 7.23 (± 0.56) 76-125 1,000 43.94 (± 13.07) 50.54 (± 13.31) 94.48 (± 4.57) +1275 (± 57) -1397 (± 1.2) 6.58 (± 1.20)

Comparative Example 1

Nitrogen removal process of Patent Publication No. 2000-56873 is referred to as anoxic tank-aeration tank-sulfur denitrification tank or aeration tank-sulfur denitrification tank, in which case alkalinity (sodium bicarbonate) is added or sulfur in heterotrophic denitrification if alkalinity is not sufficient. It is contents to use with use denitrification.

At the bottom of the sulfur-using denitrification tank, heterotrophic denitrification is carried out to separate the reaction tank and inject organic matter.At this time, suspended heterotrophic denitrification microorganisms and organic matter are introduced into the autotrophic denitrification tank, so the sulfur particle autotrophic denitrification tank Autotrophic denitrification of is virtually inhibited. When the alkalinity (sodium bicarbonate injection) and organic matter (methanol) were sufficient, total nitrogen removal efficiencies through anoxic-aerated-sulfur-desulfurization tanks were 100% and 81% at an inlet concentration of 600 mgN / L. At this time, the HRT of each reactor was 12, 48, 14 hours, and the temperature was adjusted to 35 ° C., and thus the sulfur particles could not be clearly compared with the results of experiments conducted at 5, 4 hours, and room temperature (20 ° C.) of the present invention. It was not known how autotrophic microorganisms contributed to total denitrification in packed denitrification tanks. In addition, there is no data to determine how much the nitrification rate and the denitrification rate are, respectively. Even though it is mentioned that a considerable amount of N ₂ O gas has been recovered by incomplete denitrification, it is difficult to trust the exact result because 100% nitrogen is removed.

Comparative Example 2

Patent application No. 2000-68483 is a denitrification by injecting methanol and ethanol 1/2 to 1/4 of the theoretical amount of organic matter in one reaction column filled with sulfur particles, the difference from the present invention is one reactor Dependent / independent nutrient denitrification is carried out simultaneously. The removal efficiency of inflow nitrogen nitrate 600 mgN / L is 50.8% when methanol and ethanol are injected from 1/4 to 1/2, respectively, under low alkalinity conditions. Up to 93.1%. This method inhibits sulfated denitrification microorganisms by increasing the amount of organic matter injected (especially in the case of ethanol). On the contrary, when the amount of organic matter is injected, the total denitrification efficiency decreases, which is more effective in treating low concentrations of nitric acid. It is not suitable for denitrification.

As described above, the method for removing nitrogen nitrate by the two-stage continuous reactor according to the present invention is a method capable of economical nitrogen treatment at the lowest installation and operating cost, and the production of nitrogen and phosphate fertilizers with low C / N ratio and plywood It can be effectively used for nitrogen treatment of industrial wastewater, leachate and groundwater in manufacturing, pesticide manufacturing and leather manufacturing.

Figure 1 shows a sequential dependent / independent nutrition denitrification method (Domestic Patent Publication No. 2000-56873) using a single reactor.

Figure 2 shows a simultaneous dependent / independent nutrition denitrification method (Domestic Patent Application No. 2000-68483) using a single reactor.

Figure 3 shows a two-stage continuous hetero / independent nutrition denitrification method according to the present invention.

4 shows only the heterotrophic denitrification tank in a two stage continuous reactor.

Figure 5 shows only the autotrophic denitrification tank in a two stage continuous reactor.

6 is a graph showing the removal effect of nitrate nitrogen over time in a two-stage continuous denitrification reaction [inflow: influent concentration; Dependent: nutrient denitrification effluent; Independent 1: Independent nutrition denitrification tank 1; Independent 2: Independent nutrition denitrification tank 2; Independence 3: Independent Nutrition Denitrification Tank 3; 1,2 and 3 refer to denitrification tanks each having a sulfur particle size of <2 mm, 2 to 4.75 mm, and 4.75 to 6 mm].

Figure 7 shows the relative fraction of heterotrophic / independent nutrient denitrification relative to total denitrification [% of independent denitrification: results of autotrophic denitrification tank 2].

Claims (4)

delete In the method for removing nitrate nitrogen in wastewater by heterotrophic denitrification and autotrophic denitrification, Heterotrophic and independent nutrient denitrification tanks are installed separately, In the heterotrophic denitrification tank, an external carbon source of 1/8 to 1/2 of the required amount of heterotrophic denitrification is introduced, and a porous polyurethane sponge carrier for de noxifying microorganisms is fixed and grown, and for preventing loss of the carrier and microorganisms. A mesh is installed, The autotrophic denitrification tank is filled with sulfur particles and limestone to efficiently remove high concentrations of nitrate nitrogen contained in the wastewater. 3. The high concentration nitrate by a two-stage continuous reactor according to claim 2, wherein the heterotrophic denitrification microorganisms which are lost are separated and returned between the heterotrophic denitrification tank and the autotrophic denitrification tank. Nitrogen removal method. 3. The method of claim 2, wherein the autotrophic denitrification tank is filled with sulfur particles and limestone in a volume ratio of 1: 1 to 3: 1.