JP3067232B2 - Monitoring method of biological activated carbon treatment system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to a biological activated carbon treatment in advanced water treatment technology, in particular ammonium nitrogen in the biological activated carbon treatment system ^- to monitor the amount of removal and chromaticity removal ratio of (NH ₄ -N) About technology.

[0002]

2. Description of the Related Art FIG. 21 shows a general structure of a water purification process. Raw water taken from rivers and lakes first reaches the landing well 1 and then is guided to the mixing pond 2. In this mixing pond 2, turbid components (raw materials such as sand, clay and algae) in the raw water
A coagulant is injected and mixed to remove the water. After this,
The water to be treated is led to the floc formation pond 3. In this floc formation pond 3, the suspended solids in the water to be treated are grown into flocs by a stirring / retaining process. The floc that has grown to the maximum is settled and separated in the settling basin 4. Further, fine flocs that cannot be removed by the sedimentation basin 4 are removed by the filtration basin 5.

This process incorporates algicidal treatment, chlorination for the purpose of decomposing and removing iron and manganese, and chromaticity. In particular, in a suburb of a large city, rivers and lakes are extremely polluted, so that the content of ammonia is high and the chromaticity component including humic substances, which are precursors of the carcinogen THM (trihalomethane), is also high. When chlorination is performed on both of the high contents, chlorine and ammonia react to generate chloramine and consume more chlorine than necessary. As a result, the chlorine injection rate increases and the THM generation ability (THMFP)
Increase.

[0004] From such a background, in recent years, a method of incorporating the advanced water purification treatment system 6 into a water purification process for the purpose of removing the above-mentioned substances has been used. As the advanced water purification treatment, there are a method of performing ozone treatment alone as an alternative to the chlorination treatment and a method of performing activated carbon treatment alone for removing trace substances harmful to health. Further, a combination process combining these two is also performed. In the case of this combination treatment, the treated water from the sedimentation basin 4 flows into the ozone contact tower 7 where the ozone treatment is performed. Thereafter, the activated carbon treatment is performed in the activated carbon packed tower 8 and flows into the filtration pond 5.

[0005] At present, biological treatment with nitrifying bacteria or the like is performed in order to efficiently remove ammonia.
In this biological treatment, air is sent to raw water that has been withdrawn, microorganisms are propagated by aeration treatment (aerobic treatment), and ammonia is removed by the metabolic ability of microorganisms. This biological treatment is a good method if the facilities of the water purification plant have room,
If there are restrictions on facilities, this method cannot be adopted. As a result, the method considered as the best means was biological activated carbon treatment.

[0006] Biological activated carbon treatment is a modification of the activated carbon treatment in the advanced treatment process in which microorganisms are propagated on the activated carbon surface and ammonia in the influent is removed, and adsorption and removal of trace organic substances is also possible. In this biological activated carbon treatment, there is a limit to the adsorption capacity of activated carbon. In the maintenance of the biological activated carbon treatment system, the ammonia removal rate of the water to be treated is measured.
There are the following methods for measuring the ammonia concentration in the current process system.

(A) Ion electrode method: Water to be treated is sampled to prepare a test water, an alkali (pH 8 or more) is added to the test water to gasify ammonia, and the gasified ammonia is converted into an electrode having selectivity. Measure through septum.

(B) High-speed ion chromatography: Water to be treated and an eluent are passed through a cation exchange resin tower to separate ammonium ions, and the separated ions are measured by conductivity measurement or the like.

(C) pH electrode method: Focusing on the fact that when microorganisms such as nitric acid bacteria perform nitrification, alkali is consumed and the pH decreases, and the pH of the water to be treated on the inflow side and the outflow side of the activated carbon layer is measured. Is used as an indicator of the ammonia removal rate (see Japanese Patent Application No. 2-203352).

[0010]

However, in the case of the ion electrode method, it takes time and effort to sample the water to be treated, the diaphragm used for the electrode deteriorates quickly, and the concentration of the test water (about 0.5 ppm). Has a problem that the detection limit is close. In the case of high-speed ion chromatography,
Problems that the limit of the number of measurements is about 1,000 to 2,000 due to the use of ion exchange resin, the equipment is expensive, and the measurement takes a long time (about 10 minutes). was there.

In view of such problems, the present inventors have provided a pH electrode method in Japanese Patent Application No. 2-203352. In this method, although the sensor is excellent in reliability and maintainability as a sensor, It was not suitable for calculating the ammonia concentration.

[0012] As described above, in the continuous measurement of ammonia in the biological activated carbon treatment, the conventional ammonia concentration measurement technique has many problems, and the systematization of the maintenance and management of the biological activated carbon treatment has been hindered.

The present invention has been made in view of the above circumstances and provides a technique for maintaining and managing a biological activated carbon treatment excellent in reliability and maintainability, specifically, a method for monitoring an ammonia removal rate and a chromaticity removal ratio. Aim.

[0014]

The inventors of the present invention have conducted intensive experiments and found that the main wavelength component is 220 nm or 2 nm.
The absorbance at 60 nm is determined by nitrate nitrogen (NO ₃ ^-- N)
It was confirmed that there was a correlation with the density or chromaticity.

In the present invention, attention is paid to this point, and the main wavelength component 220 nm
And detecting the absorbance at 260nm, NO ₃ from these detected amount ^- determined -N density and the chromaticity respectively, further NH ₄ from these values ^- is set to ask the removal amount and chromaticity rejection -N. Based on these values, the load state of the biota and the adsorption capacity of the activated carbon can be grasped.

[0016]

EXAMPLES In maintenance of biological activated carbon treatment in advanced water treatment, NH ₄ ^- it becomes the main point to ensure a high rate of removal of -N and chromaticity, it is important to understand these components. The present inventors, NH ₄ ^- for establishing a method to grasp the concentration of -N and chroma components, the continuous experiments using various biological activated carbon treatment system to measure a change in the water quality.

[0017]

[Continuous experiment of biological activated carbon treatment] In this continuous experiment, the following three biological activated carbon treatment systems were used. The first treatment system (hereinafter referred to as AC1) is a system comprising a coagulation / precipitation treatment, an ozone treatment, and a coconut shell-based granular activated carbon treatment. The second treatment system (hereinafter, referred to as AC2) is a system comprising a coagulation / precipitation treatment, an ozone treatment, and a coal-based granular activated carbon treatment. Third
(Hereinafter referred to as AC3) is a system comprising a coagulation / precipitation treatment and a coal-based granular activated carbon treatment.

As the co-test raw water for each treatment system, treated water simulating sedimentation effluent was used. This treated water is obtained by the following steps. First, a stock solution was diluted humus extracted water obtained by boiling for 1 hour mulch to 10 times, and further diluting this stock solution five times, NH ₄ ^- ammonium chloride is added 0.5 mg / l as -N At the same time, iron and manganese are added as chromaticity components. This treated water was subjected to a coagulation / precipitation treatment at a coagulant injection rate of 1,000 ppm, and the supernatant was used as co-test raw water. When this co-test raw water is subjected to the next treatment (ozone treatment or coal-based granular activated carbon treatment), the chlorine is dechlorinated about 2,500 times based on the stock solution so as to have the same water quality as the actual coagulation / precipitation treatment water. Diluted with water.

In the activated carbon treatment (granular coconut shell activated carbon or granular activated carbon coal), water was passed through the treatment tower under the following water flow conditions. That is, the processing tower sectional area A is 10.7 c
m ² , activated carbon filling height BH is 100.0 cm, linear velocity LV
Is Q / A (cm / min) and the cylinder speed SV is LV / BH
(/ Min) and the residence time T is BH / LV (min). Q is the flow rate (ml / min), and FIG. 2 shows the change over time. This figure shows the flow rate Q from the end of January to the end of September by the number of elapsed weeks. (A) is AC1,
(B) shows AC2 and (C) shows AC3. As shown in this figure, water flow starts at an average water flow rate of 40 ml / min,
Thereafter, the average water flow rate was increased to 60 ml / min, and further increased to the average water flow rate of 70 ml / min. The sudden change in the water flow in the thirteenth week is due to artificially lowering the water flow to 20 ml / min because maintenance and inspection cannot be ensured during this period due to consecutive holidays.

FIGS. 3 and 4 show the temperatures of the inflow water and the outflow water of each treatment tower. 3A shows the effluent of AC1, FIG. 3B shows the effluent of AC2, FIG. 3C shows the ozone-treated water (the inflow of AC1 and AC2), and FIG. 4A shows the effluent of AC3. , (B) show the AC3 influent. As shown in these figures, the water temperature of each treatment tower rises with the seasonal change, but the fluctuation range is 18 to 23 ° C., which is smaller than that of the actual water purification plant. This is because the temperature of the inflow water was controlled in consideration of the influence of the temperature on the substance adsorption characteristics of the activated carbon, and the apparatus was provided with heat insulation measures and the like.

In the above continuous experiments, NH ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ in each part of each treatment system were measured, and the nitrification process of ammonia was observed. This measurement was performed by an ion chromatography method. The measured NH ₄ ⁻ −N concentrations are shown in FIGS. 5 and 6, the measured nitrite (NO ₂ ⁻ −N) concentration is shown in FIGS. 7 and 8, and the measured NO ₃ ⁻ −N concentration is shown in FIG. 9,
It is shown in FIG. 5, 7, and 9, (A) shows the effluent of AC1, (B) shows the effluent of AC2, (C) shows the ozonated water (the inflow of AC1, AC2), and FIGS. (A) shows the outflow of AC3, and (B) shows the inflow of AC3.

As shown in FIG. 5 and FIG.
H ₄ ^- -N concentrations, although unstable in the initial, was about 0.5 mg / l on average. Moreover, NH ₄ remaining in the effluent ^- -N concentrations, passing water in early 20-4
Despite the relatively low load of 0 ml / min,
A high value of about 0.1 to 0.2 mg / l was confirmed up to the seventh week from the start of the experiment. Also, as shown in FIGS.
O ₂ ^- -N concentration tended to increase until a period of up to seven weeks after the start of the experiment, but gradually will decrease. Thereafter, NO ₂ to 23 weeks in AC2 ^- -N was left.

The unstable state at the beginning of these experiments is as follows:
It is thought to occur for the following reasons. That is, nitrifying bacteria are roughly classified into nitrite bacteria and nitrate bacteria. If both bacteria maintain their activities together and coexist, the biological oxidation reaction will continue to accumulate and nitrate will accumulate.If the nitrate bacteria are in the growth phase or if the growth conditions of the nitrate bacteria are inappropriate, In the nitrification process, an unstable state occurs due to accumulation of nitrous acid. This is because NO ₂ ⁻ − shown in FIGS.
The behavior of N and the behavior of NO ₃ ⁻ −N shown in FIGS. When comparing the behavior of both, NO ₂ ^- period -N are accumulated NO ₃ ^- it can be seen that an increase in -N is hardly observed. In water quality standards of tap water based on the Water Supply Law, 10 mg / l as NO ₃ ^-- N and NO ₂ ^-- N
Considering that it is specified that the standard value is used as the reference value,
It is appropriate to recognize that nitrification has occurred at the stage where NO ₂ ⁻ −N was generated.

FIG. 11 is NH ₄ ^- shows the removal rate of -N. In this figure, (A) is AC1, (B) is AC2, (C)
Indicates AC3. In this figure, the ammonia removal ratio of AC3 is low, this measurement is NO ₃ ^- is a value based -N concentration, NO ₂ ^- ammonia when (see FIG. 8) that -N is accumulated Considering that the removal rate is low, the ammonia removal rate of AC3 is actually not very low. If the ammonia removal rate including NO ₂ ⁻ −N is determined, the removal rate in each activated carbon treatment is 85 to 95%.
Is high.

[0025]

[Relationship between water quality and absorbance] Next, the relationship between water quality and absorbance will be described. In this continuous experiment, E220 (wavelength 220 nm (ultraviolet region)) and E220 for each part of each processing system were used.
The absorbance at 260 (wavelength 260 nm (ultraviolet region)) was measured. 12 and 13 show changes in the absorbance of E220.
As can be seen from these figures, the absorbance of the outflow water tended to be higher than that of the inflow water. FIGS. 14 and 15 show E
The change in absorbance at 260 is shown. As can be seen from these figures, a tendency opposite to that of E220 was observed in E260. That is, according to the absorbance of E220, it can be recognized that some substance was produced by the biological activated carbon treatment,
According to the absorbance of 60, it can be recognized that some substance has been removed.

In consideration of the measurement results, E220, E26
The correlation between the absorbance of 0 and the water quality factor was examined. As a result, E
220 Most water factors that correlated nitrate ions (NO ₃ ^-
-N). FIG. 16 shows the relationship between the two. The vertical axis indicates the NO ₃ ⁻ -N concentration (by the ion chromatography method), the horizontal axis indicates the absorbance.
The mark indicates effluent of AC2, the mark x indicates effluent of AC3, the mark □ indicates raw water, and the mark ▽ indicates ozone-treated water. As can be seen from this figure, there is some variation on the high concentration / high absorbance side, but regardless of the type of treated water, both have a high single correlation (correlation coefficient:
0.8789, residual square sum: 8.2163, and linear regression equation: Y = 3.1799 · X + 0.0972). Although the influence of other water quality factors is considered to be small, the relationship was examined especially for nitrite ion. FIG. 17 shows the relationship between the two. As can be seen from this figure, nitrite ions are correlated on the high absorbance side (correlation coefficient: 0. 1).
7768, residual square sum: 0.6829, linear regression equation: Y
= 1.0868.X-0.5793), which is considered to slightly interfere with the correlation between nitrate ion and E220 absorbance. However, as described above, NO ₂ ⁻ −N
It suffices if the NO ₃ ⁻ −N concentration including the concentration can be grasped, and there is no problem as long as the nitrite ion shows a positive correlation. On the other hand, it was found that the water quality factor most correlated with E260 was chromaticity. FIG. 18 shows the relationship between the two. The vertical axis indicates chromaticity (converted from the absorbance of E370 (visible region)), and the horizontal axis indicates the absorbance of E260. In general, E370 is said to have a high correlation with chromaticity, but also at E260, although the absorbance sensitivity is low, a high correlation (correlation coefficient: 0.8)
526, residual square sum: 20.022, linear regression equation: Y =
89.8760.X + 0.3836).

[0027]

[Maintenance of Biological Activated Carbon Treatment] Based on the correlation confirmed in this way, in this embodiment, the NO ₃ ⁻ -N concentration is estimated from the absorbance of E220 using the equation (1).

[0028] Y = 3.1799 · X + 0.0972 ... (1) In addition, (1) NO ₃ of influent water as determined by formula ^- -N concentration Y _in (mg / l) and the effluent NO ₃ ^- -N Density Y _out (m
from g / l), NH ₄ using (2) ^- -N removal amount NH
_DIFF (mg / l) can be estimated.

[0029] _{NH DIFF = Y out -Y in ...} (2) The thus obtained NH ₄ ^- To confirm the validity of -N removal amount NH _DIFF, and measured values this estimate NH _DIFF (ion chromatography Method). The result is shown in FIG. The vertical axis indicates the actually measured value, and the horizontal axis indicates the estimated value. As shown in the figure, both have a high correlation (correlation coefficient: 0.8004, residual square sum: 0.4287, linear regression equation: Y = 1.122)
3.X + 0.0277) was confirmed.

In maintaining and managing the biological activated carbon treatment,
Continuous sampling is performed at two points, the inflow side and the outflow side, and E
The absorbance at 220 is detected, and NH _DIFF is estimated from the measured value and used. At the initial start-up of the biological activated carbon treatment tower, the growth period of the microorganisms is reached. Therefore, the inflow load is grasped and controlled from the estimated value NH _DIFF to maintain good growth conditions. Also, at the time of steady operation, the load state of the biota is grasped by monitoring the ammonia removal amount. In the biological activated carbon treatment, the load (ammonia concentration) in the drought season (summer season) fluctuates remarkably. Therefore, in maintenance in a steady state, it is important to grasp the load state of the biological activated carbon treatment system. FIG. 19 shows a schematic trend graph of the estimated value NH _DIFF .

Similarly, for the chromaticity, E260 for inflow water and outflow water is calculated using the linear regression equation of FIG.
The respective chromaticities C _in and C _out are obtained from the absorbance of
The chromaticity elimination ratio C _rr can be obtained by equation (3).

C _rr = C _out / C _in (3) In maintaining and managing the biologically activated carbon, monitoring of chromaticity is also important. The chromaticity components in the raw water include iron, manganese, humic substances and the like. In particular, humic substances are known to be substances which produce THM (trihalomethane) which is a carcinogenic substance. Therefore, it is necessary to monitor the chromaticity. In this embodiment, continuous sampling of the absorbance at E260 is performed in the same manner as at E220, and the chromaticity removal ratio C _rr is determined from the measured value to monitor the adsorptivity of activated carbon with respect to the chromaticity. This monitoring also makes it possible to predict the breakthrough of activated carbon. FIG. 20 is a schematic trend graph of the chromaticity removal ratio C _rr of activated carbon.

Here, since both E220 and E260 are in the ultraviolet region, simultaneous measurement with a single measuring instrument (for example, a UV meter or the like) becomes possible by improving the apparatus. Further, by adopting a configuration in which the output signal of the measuring instrument is recorded in a recorder or a computer, it is possible to easily cope with systemization. Further, the biological activated carbon treatment system includes a downflow fixed bed system and an upflow variable bed system, and this embodiment can be applied to any of them.

[0034]

As explained above, according to the present invention,
Detecting a main wavelength components 220nm and 260nm absorbance for effluent and influent biological activated carbon treatment system, NH ₄ from these detected amount ^- Request -N removal amount and chromaticity rejection. As the absorbance measuring device, an existing device having excellent reliability can be used, so that an accurate measurement value can be obtained and the maintainability is excellent. Moreover NH ₄ ^- so specifically obtain a -N removal amount and chromaticity rejection as numbers and maintenance becomes easier, there is an advantage that easy to systems of maintenance can be addressed.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an estimated value of an NH ₄ ⁻ −N removal amount and an actually measured value.

FIG. 2 is a graph showing water flow rates of AC1 to AC3.

FIG. 3 is a graph showing water temperatures of AC1 and AC2.

FIG. 4 is a graph showing a water temperature of AC3.

[5] AC1, AC2 NH ₄ of ^- graph showing -N concentration.

[6] AC3 NH ₄ of ^- graph showing -N concentration.

FIG. 7 is a graph showing the concentration of NO ₂ ⁻ −N in AC1 and AC2.

FIG. 8 is a graph showing the concentration of NO ₂ ⁻ −N in AC3.

FIG. 9 is a graph showing NO ₃ ⁻ −N concentrations of AC1 and AC2.

FIG. 10 is a graph showing the concentration of NO ₃ ⁻ −N in AC3.

[11] NH ₄ ^- a graph showing the removal ratio of -N.

FIG. 12 is a graph showing a change in absorbance of E220 of AC1 and AC2.

FIG. 13 is a graph showing a change in absorbance of E220 of AC3.

FIG. 14 is a graph showing a change in absorbance of E260 of AC1 and AC2.

FIG. 15 is a graph showing a change in absorbance of E260 of AC3.

FIG. 16 is a graph showing a relationship between E220 and NO ₃ ⁻ −N concentration.

FIG. 17 is a graph showing the relationship between E220 and NO ₂ ⁻ −N concentration.

FIG. 18 is a graph showing a relationship between E260 and chromaticity.

FIG. 19 is a graph showing a schematic trend graph of NH ₄ ⁻ −N removal amount (NH _DIFF ).

FIG. 20 is a schematic trend graph of a chromaticity removal ratio C _rr of activated carbon.

FIG. 21 is an explanatory diagram showing a general configuration of a water purification process.

Claims (1)

(57) [Claims] 1. A monitoring method for a biological activated carbon treatment system provided with a biological activated carbon layer made of activated carbon that has formed a biota, the method including a step of obtaining an ammonia removal amount and a chromaticity removal ratio of the biological activated carbon treatment system. As a step of obtaining the ammonia removal amount, a step of detecting the absorbance of the main wavelength component 220 nm for inflow water and outflow water of the biological activated carbon treatment system, and the nitrate nitrogen concentration from each absorbance using a linear regression equation Calculating the difference between the concentrations of nitrate nitrogen and taking this value as the removal amount of ammonia nitrogen.The step of obtaining the chromaticity removal ratio includes the step of obtaining the inflow water and the outflow water of the biological activated carbon treatment system. Detecting the absorbance for the main wavelength component 260 nm as a target,
Calculating chromaticity from each absorbance using a linear regression equation, taking a ratio of each chromaticity, and setting this value as a chromaticity removal ratio.