KR102373080B1 - Method for promoting nitrification of wastewater - Google Patents

Abstract

The present invention provides a method for accelerating the nitrification of wastewater using an accelerator for the stable treatment of wastewater, and in detail, the present invention includes the steps of: injecting wastewater into a biological wastewater treatment device to generate treated water; and measuring the concentration of ammonia nitrogen or SCN ⁱⁿ the treated water, wherein the concentration of ammonia nitrogen or SCN ⁱⁿ the treated water is 10% or more of the concentration of ammonia nitrogen or SCN ⁱⁿ the wastewater. , It provides a method for promoting nitrification of wastewater, comprising the step of injecting a nitrification promoter into the wastewater.

Description

Method for promoting nitrification of wastewater

The present invention relates to a method for promoting nitrification of wastewater.

Wastewater generated during coke manufacturing contains organic substances and substances containing nitrogen components. Therefore, in order to biologically treat the coke oven wastewater, it is operated as a treatment process that includes a nitrification-denitrification process as well as organic material removal.

Table 1 below shows the various compounds contained in the coke oven wastewater, and in particular, it shows that nitrogen compounds such as SCN ^- (thiocyanates), CN ^- (cyanides), NH ₃ /NH ₄ ⁺ (ammonia/ammonium) are present in high concentrations. show Therefore, the nitrification/denitrification process is very important in the treatment of coke oven wastewater.

division coke oven wastewater pH 7-9.5 specific conductivity (μS/cm) 5000-12500 COD(mgO ₂ /dm ³ )* 200-6500 BOD ₅ (mgO ₂ /dm ³ )** 800-3000 PAHs (mg/dm ³ )*** 5-150 Sulphides (mg/dm ³ ) 10-50 Cyanides (mg/dm ³ ) 5-20 Thiocyanates (mg/dm ³ ) 50-420 Phenols (mg/dm ³ ) 500-1500 Ammonia (mg/dm ³ ) 50-200 Chlorides (mg/dm ³ ) 2500-3500 Sulfates (mg/dm ³ ) 900-1200

*COD: Chemical oxygen demand**BOD: Biological oxygen demand

***PAH: polycyclic aromatic hydrocarbons (PAH, 6 Borneff(benzo[a]pyrene, benzo[b]fluoranthene, benzo[ghi]perylene, benzo[k]fluoranthene, fluoranthene and indeno[1,2,3-c; d]perylene))

(Main properties of coke oven wastewater. Source: The innovative system for coke oven wastewater treatment and water recovery with the use of clean technologies, Innowatreat)

In general, for the nitrification and denitrification of the coke oven wastewater treatment process, the wastewater treatment facility is designed considering the proper arrangement of the anaerobic tank and the aeration tank, and sufficient hydraulic retention time and solid retention time. Operationally, the most important part of nitrification-denitrification is the reduction of the nitrification rate by internal/external factors.

The first process in denitrification is the nitrification step, in which ammonia is oxidized to nitrites and/or nitrates. The microorganisms involved in this step are nitrifying microorganisms, which are autotrophs, and play a role in decomposing ammonia nitrogen into nitrite and nitrate nitrogen in the presence of oxygen.

However, the characteristic of nitrifying microorganisms (nitrifying bacteria) is that their growth rate is slow and their activity is inhibited by various operating factors such as the influence of oxygen concentration, making it difficult to manage effectively for nitrification. In particular, in the case of the aforementioned slow growth rate, problems such as the death of microorganisms are caused when they are inhibited by the inflow of external toxic substances, and a long time is often required to maintain the effective density of nitrifying bacteria again. Accordingly, high solids residence time is maintained to secure the number of nitrifying bacteria in various wastewater treatment processes as well as coke oven wastewater.

However, since there is a problem that the capacity of the reactor becomes too large for a high solids residence time, in reality, the instability of the nitrification process due to the loss of microorganisms is a problem that frequently occurs in the operation of wastewater treatment plants. In particular, in the case of thiocyanate (SCN ^- ) contained in coke oven wastewater, it is decomposed into ammonia and sulfate, but the decomposition rate is slow and remains after the organic carbon is removed, resulting in a problem of maintaining a long residence time for nitrification. also do it

An object of the present invention is to provide a method for accelerating nitrification of wastewater using an accelerator for stable treatment of wastewater.

In one aspect of the present invention, the present invention comprises the steps of injecting wastewater into a biological wastewater treatment device to generate treated water; and measuring the concentration of ammonia nitrogen or SCN ⁱⁿ the treated water, wherein the concentration of ammonia nitrogen or SCN ⁱⁿ the treated water is 10% or more of the concentration of ammonia nitrogen or SCN ⁱⁿ the wastewater. , It provides a method for promoting nitrification of wastewater, comprising the step of injecting a nitrification promoter into the wastewater.

In the biological treatment process of wastewater, the nitrification rate can be improved by the method of the present invention in a situation where the nitrification reaction is inhibited due to a temperature increase, such as in summer. In addition, by improving the decomposition rate and the nitrification rate of SCN ⁻ , the residence time of the biological treatment process is reduced, so that the wastewater treatment process can be compacted.

1 shows a conceptual diagram of a reactor simulating a biological treatment process, according to an embodiment of the present invention.
Figure 2 shows the results of comparing the SCN ^- decomposition rate according to the use of the nitrification accelerator of the present invention during the SCN ^- decomposition experiment.
3 shows the results of comparing the reduction rate of COD _Cr according to the use of the nitrification accelerator of the present invention during the SCN ^- decomposition experiment.
4 shows the results of comparing the reduction rate of COD _Cr according to the use of the nitrification accelerator of the present invention when nitrification is promoted.
5 shows the results of comparing the rate of ammonia nitrogen decomposition according to the use of the nitrification accelerator of the present invention when nitrification is promoted.
6 shows the results of comparing the production rate of nitrification products (nitrite) according to the use of the nitrification promoter of the present invention when nitrification is promoted.
7 schematically shows a process for treating coke oven wastewater comprising a method for promoting nitrification of wastewater of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiment of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

In the wastewater treatment process, wastewater to be treated contains a large amount of nitrogen sources, and these nitrogen sources are removed through a nitrification-denitrification reaction. However, in the case of the wastewater treatment process, the denitrification performance deteriorates depending on seasonal changes (temperature change in summer/winter season) and the operating conditions of the process. This is considered to be due to the decrease in the activity of nitrifying microorganisms used in the biological treatment process during the wastewater treatment process.

In general, when the activity of the nitrifying microorganism is reduced as described above, it takes a long time to normalize the activity of the microorganism again.

Therefore, in the biological treatment process of wastewater, the present invention promotes nitrification when the nitrification rate is reduced due to a change in the environment around the process equipment, thereby preventing the wastewater treatment time required to restore the activity of microorganisms from increasing provide a way

In detail, the present invention comprises the steps of injecting wastewater into a biological wastewater treatment device to generate treated water; and measuring the nitrification rate of the treated water, and when the nitrification rate is reduced, it provides a method for promoting nitrification of wastewater, comprising injecting a nitrification promoter into the wastewater.

The biological wastewater treatment device refers to a device that removes various contaminants such as organic matter, nitrogen, and phosphorus contained in wastewater through the metabolic process of microorganisms in a bioreactor with activated sludge.

The biological wastewater treatment device is a device including an anaerobic tank and an aerobic tank, and can be used without limitation as long as it is used as a biological wastewater treatment device, for example, an anaerobic tank, an anaerobic tank, an aerobic tank, an anoxic tank and an aerobic tank or an anaerobic tank, aerobic tank, A biological wastewater treatment device formed in the order of an anaerobic tank can be used. In the case of coke wastewater, since phosphorus (PO ₄ ^3- ) is insufficient, an anaerobic tank for removing phosphorus is not required, so a biological wastewater treatment device that does not include an anaerobic tank can be used.

In the biological wastewater treatment device, ammonia nitrogen or SCN ^- is decomposed by microorganisms to form nitrification materials such as NO ₂ ^- and/or NO ₃ ^- , for example, SCN ^- is converted to NH ₃ , Then, NO ₂ ^- and NO ₃ ^- is subjected to the formation process. Therefore, if the decomposition of nitrogen sources such as SCN ^- in the biological wastewater treatment device is not smooth, it may cause a problem in the water treatment facility.

Furthermore, the wastewater may be coke oven wastewater, and the coke oven wastewater may be discharged from a coke manufacturing process used as a reducing agent for iron ore.

On the other hand, the step of measuring the nitrification rate of the treated water is to measure the nitrification and denitrification of the wastewater, and can be performed by analyzing the concentration of ammonia nitrogen or SCN ⁻ in the treated water as well as nitrite or nitrate.

At this time, when the nitrification rate is reduced in the present invention, the concentration of ammonia nitrogen in the treated water does not decrease compared to the initial wastewater and maintains a certain level of concentration, or SCN ^- is decomposed and maintained without being reduced, nitrite and It may mean a case where the concentration of nitrate does not increase. However, when CN ^- /SCN ^- and organic nitrogen components are decomposed, the concentration of ammonia nitrogen may temporarily increase. This means that the nitrifying microorganisms of the wastewater treatment device do not sufficiently function.

Therefore, in the present invention, when the concentration of ammonia nitrogen or SCN ⁱⁿ the treated water does not decrease significantly compared to the initial wastewater, or when the concentrations of nitrite and nitrate in the treated water do not significantly increase compared to the initial wastewater, the nitrification rate is reduced. , At this time, a nitrification promoter may be injected into the wastewater.

Specifically, in the present invention, in the treated water (for example, the treated water discharged from the rear end of the aerobic tank), the concentration of ammonia nitrogen or the concentration of SCN ^- is 10% or more of the concentration in the initial wastewater (wastewater before injection of the biological treatment device) , Preferably, when it remains at a level of 30% or more, more preferably, when it remains at a level of 50% or more of the concentration in the initial wastewater, the nitrification accelerator may be injected into the wastewater. For example, when the concentration of ammonia nitrogen in the wastewater was 80 mg/L and the concentration of ammonia nitrogen in the treated water was 40 mg/L, the concentration of ammonia nitrogen in the treated water was at least 50% of the initial wastewater, At this time, the nitrification accelerator may be injected.

Furthermore, when the concentration of ammonia nitrogen or SCN in the treated water is reduced ^to less than 10% of the ammonia nitrogen or SCN concentration ⁱⁿ the initial wastewater, it can be determined that nitrification is normally occurring by the nitrifying microorganism in the biological wastewater treatment device, However, if the level of 50% or more remains, it can be judged that the activity of nitrifying microorganisms is severely inhibited, so a nitrification accelerator must be injected.

On the other hand, the nitrification rate of the present invention can be performed by analyzing nitrite or nitrate as well as the concentration of ammonia nitrogen or SCN-. If the concentration of nitrite or nitrate in the treated water does not increase, the nitrification accelerator of the present invention is injected can do.

In fact, normally treated wastewater may have an ammonia nitrogen concentration of 0 to 5 ppm, preferably 0 to 1.0 ppm, in the treated water (eg, treated water discharged from the rear end of the aerobic tank), and also SCN ⁻ The concentration may be 0 to 1 ppm, preferably 0 to 0.5 ppm. Furthermore, 95% to 100%, preferably 98% to 100%, based on Total Kjeldahl Nitrogen may be converted to nitrite.

Therefore, according to the present invention, when the nitrification rate measured in the treated water decreases as described above, the wastewater treatment apparatus can be normalized by injecting the nitrification accelerator.

The nitrification accelerator used at this time may include at least one selected from the group consisting of activated carbon, clay, bun coke, zeolite and illite, and preferably activated carbon.

Furthermore, the nitrification accelerator may be used in an amount of 5.0 g or less (excluding 0), preferably 2.0 g or less (excluding 0), and more preferably 0.5 g to 1.0 g per 1 L of the injected wastewater. If the nitrification accelerator is not injected, the effect of promoting SCN ^- decomposition and nitrification in wastewater cannot be seen ^. Problems can arise with the use of expensive nitrification accelerators.

On the other hand, in the present invention, when the nitrification promoter is injected in an excessive amount, the increase in its effect is insignificant. Therefore, it is necessary to stop the injection of the nitrification promoter after SCN ^- decomposition and nitrification promotion are normalized. For example, after injecting the nitrification accelerator into the wastewater, when the nitrification rate of the treated water starts to increase again, or when the wastewater is normally treated, the injection of the nitrification accelerator is stopped or the injection amount is reduced. , it can enable economical use of nitrification accelerators.

Specifically, in the present invention, after the injection of the nitrification accelerator, the concentration of ammonia nitrogen or SCN in the treated water decreases to less than 50% ^of the concentration of ammonia nitrogen or SCN ⁱⁿ the wastewater. Since it can be determined that the activity of microorganisms is restored to normal, the injection of the nitrification promoter can be controlled at this time, that is, the injection of the nitrification promoter can be reduced.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are only examples to help the understanding of the present invention, and the scope of the present invention is not limited thereto.

Example

In order to confirm whether the nitrification accelerator of the present invention promotes the decomposition and nitrification of SCN ^- , after injecting activated carbon into the actual wastewater generated in the coke oven, during aeration, the concentration of SCN ^- and NH ₄ ⁺ , NO ₂ ^- , NO ₃ ^{-Concentrations} were confirmed.

(1) SCN ^- resolution measurement

The SCN ^- decomposition rate was confirmed using the influent and return activated sludge from a biological treatment process that actually treats coke oven wastewater. For the experimental conditions, 400 mL of returned activated sludge, 1,000 mL of incoming raw water, and 600 mL of tap water were mixed to make a total volume of 2,000 mL, and four reactors were prepared. The temperature of the reaction was maintained at 35°C, which is the actual operating temperature of the wastewater treatment plant, and mixing was performed well through a mixer.

Furthermore, air was supplied using a sparger at the bottom of the reactor to form aerobic conditions. A 0.1N caustic soda solution was supplied so that the pH during the biological reaction was 7.2 or higher. It was classified into a reactor without activated carbon (Comparative Example 1), a reactor containing 1 g of activated carbon (Example 1), a reactor containing 2 g of activated carbon (Example 2), and a reactor containing 4 g of activated carbon (Example 3). .

As shown in FIG. 2 , when activated carbon is used as an accelerator for promoting decomposition, the time taken ^for SCN ^at the initial 220 ppm level to be lowered to 0 ppm is faster by about 9 times compared to the case where no accelerator is used. you can see This can be seen as the improvement in the activity of microorganisms by the decomposition accelerator of the present invention.

Since the adsorption amount of the decomposition promoter for SCN ^- is about 2 mg/g per gram weight of activated carbon based on TN, there is almost no adsorption of SCN ^- present as ions, so the reduction in SCN ^- concentration is due to decomposition by microorganisms. It can be judged to be due only to the influence. At this time, the result of analyzing the organic matter content in the water by the dichromate method chemical oxygen demand (COD _Cr ) is shown in FIG. 3 , and as shown in FIG. It can be seen that the microbial activity is well maintained.

Although the activity of microorganisms is maintained ^, the decomposition of SCN- is remarkably low in Comparative Example 1, indicating that the decomposition of ^SCN- was promoted by the nitrification promoter of the present invention.

(2) Measurement of nitrification promotion

The nitrification rate was confirmed using the influent from the biological treatment process that actually treats the coke oven wastewater and the return activated sludge. For the experimental conditions, 1000 mL of returned activated sludge, 500 mL of incoming raw water, and 500 mL of tap water were mixed to make a total volume of 2,000 mL, and four reactors were prepared. Unlike (1) above, the ratio of the influent raw water was lowered so that nitrification and decomposition of organic materials were performed quickly. The temperature of the reaction was maintained at 35°C, which is the actual operating temperature of the wastewater treatment plant, and mixing was performed well through a mixer.

Furthermore, air was supplied using a sparger at the bottom of the reactor to form aerobic conditions. A 0.1N caustic soda solution was supplied so that the pH during the biological reaction was 7.2 or higher. Classified into a reactor without activated carbon (Comparative Example 2), a reactor containing 0.5 g of activated carbon (Example 4), a reactor containing 1 g of activated carbon (Example 5), and a reactor containing 2 g of activated carbon (Example 6) did

Figure 4 shows the reduction rate of COD _Cr during the reaction in an aerobic condition. In the case of COD _Cr , only the difference in the amount corresponding to the maximum adsorption amount of the nitrification accelerator occurred, but the effect of the input of the nitrification accelerator could not be confirmed. That is, it can be seen that the nitrification promoter has little effect on the reduction of COD _Cr , and through this, it can be seen that the nitrification promoter has little effect on heterotrophs.

However, as shown in FIGS. 5 and 6, when looking at the concentration of ammonia nitrogen and the concentration of nitrite, which can determine the nitrification rate according to the use of the nitrification accelerator, in the case of ammonia nitrogen, when the nitrification accelerator is not added (Comparative Example 2) ), it can be seen that the concentration of ammonia gradually increases. This is considered to be because organic nitrogen and thiocyanate (SCN- ⁾ present in the reactor are decomposed in the form of ammonia.

On the other hand, when the nitrification accelerator was added (Examples 4, 5, and 6), the concentration of ammonia nitrogen was rapidly reduced, and the concentration of ammonia was increased because the nitrification rate was faster than the ammonia nitrogen generated by the decomposition of organic nitrogen and thiocyanate. It can be seen that the concentration of nitrite sharply increases accordingly.

As an effect of the injection of the accelerator, similar results can be confirmed in Examples 5 and 6, and in Example 4, it can be seen that the production rate of ammonia nitrogen and the production rate of nitrite are somewhat slower than in Examples 5 and 6. there was.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible within the scope without departing from the technical spirit of the present invention described in the claims. It will be apparent to those of ordinary skill in the art.

Claims (8)

injecting wastewater into a biological wastewater treatment device to generate treated water; and
A nitrification rate measurement step of measuring the concentration of ammonia nitrogen or SCN ^- in the treated water,
When the concentration of ammonia nitrogen or SCN in the treated water is 10% or more ^of the concentration of ammonia nitrogen or SCN ⁱⁿ the wastewater, injecting a nitrification promoter into the wastewater,
The nitrification accelerator will include at least one selected from the group consisting of activated carbon, clay, bun coke, zeolite and illite,
A method of promoting nitrification of wastewater.
The method of claim 1,
The method for promoting nitrification of wastewater, wherein the biological wastewater treatment device includes an anaerobic tank and an aerobic tank.
The method of claim 1,
The method for promoting nitrification of wastewater, wherein the wastewater is coke oven wastewater.
3. The method of claim 2,
The method for promoting nitrification of wastewater, wherein the treated water is discharged from the rear end of the aerobic tank.
delete The method of claim 1,
The method for promoting nitrification of wastewater, wherein the nitrification promoter is injected in an amount of 5.0 g or less (excluding 0) per 1L of the injected wastewater.
The method of claim 1,
The step of injecting the nitrification accelerator into the wastewater is carried out when the concentration of ammonia nitrogen or SCN- of the treated water is 50% or more of the concentration of ammonia nitrogen or ^{SCN- of} the wastewater. How to promote.
8. The method of claim 7,
After injecting the nitrification accelerator, when the concentration of ammonia nitrogen or SCN in the treated water decreases to less than 50% ^of the concentration of ammonia nitrogen or SCN ⁱⁿ the wastewater, controlling the injection of the nitrification accelerator A method for promoting nitrification of wastewater, further comprising a step.

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