JP3587685B2 - Advanced sewage treatment method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an advanced sewage treatment method.
[0002]
[Prior art]
In the usual sewage treatment process, sewage is subjected to primary treatment (removal of fine suspended matter) and secondary treatment (removal of colloidal solid matter and organic matter by microorganisms) after removing coarse solid matter in a sand basin or the like. After that, it is sterilized and released.
[0003]
Therefore, most of the organic matter remaining in the secondary treated water that has undergone appropriate treatment is hardly decomposable organic matter that is hardly decomposed by living organisms, and advanced treatment is required as a technique for further removing such organic matter. is there.
[0004]
Highly treated water is used for various purposes, such as industrial water, hydrophilic water, landscape water, and river water during the drought period.The required water quality varies depending on the purpose of use, but higher quality treated water quality is required. Is required, ozone treatment and activated carbon treatment are performed.
[0005]
Ozone treatment is a technique for removing hard-to-decompose organic substances, chromaticity, odor, and the like in water using the strong oxidizing power of ozone. In the water purification field, activated carbon treatment is performed after ozone treatment.
[0006]
In the activated carbon treatment, treatment is carried out with activated carbon called biological activated carbon to which organisms have spontaneously attached, and easily decomposable organic substances remaining in the ozonized water are biodegraded by the attached organisms, and the hardly decomposable organic substances are adsorbed on the surface. Like that.
[0007]
Therefore, when the sewage secondary treatment water is treated with ozone and biological activated carbon, the quality of the treated water is very good.
[0008]
[Problems to be solved by the invention]
However, the quality of the ozone + biological activated carbon treated water is strongly affected by the quality of the secondary treated water. To explain using CODMn as an index indicating the quality of treated water, if CODMn of secondary treated water rises, CODMn of ozone + biological activated carbon treated water also rises under certain conditions, making it difficult to secure stable treated water quality. is there.
[0009]
For this reason, the current situation is to ensure stable treated water quality by increasing the ozone injection rate, but the effect of this is also limited, and simply increasing the ozone injection rate requires a larger ozone generator. is necessary.
[0010]
In addition, since both ozone and activated carbon are very expensive, reduction of initial cost and running cost has been an issue. Since SS (suspended matter) contained in the secondary treatment water wastes ozone, it is necessary to provide some sort of filtration step before ozone treatment to remove SS from the viewpoint of cost reduction. As for activated carbon, it is known that attached organisms decompose and remove some of the adsorbed organic matter, resulting in a longer life of the activated carbon.The longer the life, the lower the cost and the lower the cost of the activated carbon. Proliferation is indispensable, but on the other hand, organisms generated on the biological activated carbon may leak, so it is necessary to install a disinfection facility after the biological activated carbon treatment.
[0011]
In other words, ozone + biological activated carbon treatment requires four processes of filtration + ozone + activated carbon + disinfection, and equipment is required for each process. There is a demand for a simple equipment configuration.
[0012]
An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide an advanced sewage treatment method capable of securing stable treated water quality with a compact facility configuration.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the advanced sewage treatment method of the present invention introduces secondary treatment water of sewage into an activated carbon tank having a biological activated carbon layer, and thereafter introduces the treated water into an ozone reaction tank and flows out of the ozone reaction tank. A part of the ozone-treated water is circulated to the inflow section of the activated carbon tank to remove the SS component , adsorb organic matter and biodegrade with the biological activated carbon layer in the activated carbon tank, and remove the SS component to the ozone reaction tank. Introduce activated carbon treated water, oxidize and decompose organic matter with ozone in an ozone reaction tank, sterilize biological activated carbon treated water , and derive the remaining ozonated water flowing out of the ozone reaction tank as highly treated water. Features.
[0014]
The control of the amount of water circulating from the ozone reaction tank to the activated carbon tank is performed based on the absorbance at 260 nm of ultraviolet light of the biological activated carbon treated water flowing out of the activated carbon tank or the ozone treated water flowing out of the ozone reaction tank.
[0015]
In general, most of the soluble organic substances contained in the secondary treatment water are hardly decomposable organic substances, and also contain a relatively large amount of SS components.
According to the above-described configuration, the secondary treatment water is circulated in the order of the activated carbon tank and the ozone reaction tank, thereby removing the SS component and biodegrading the easily decomposable organic matter in the biological activated carbon layer, and further increasing the strength of ozone. By the oxidizing power, the process of decomposing and removing hardly decomposable organic matter or converting it to easily decomposable organic matter will be repeatedly performed, so that the ozonized water has a very high treated water quality equivalent to highly treated water. Become.
[0016]
At this time, since the biologically activated carbon-treated water from which the SS component has been removed is introduced into the ozone reaction tank, waste of ozone can be suppressed, and ozone treatment can be performed effectively even if the ozone injection rate is reduced.
[0017]
In addition, since microorganisms and bacteria leaked into the biological activated carbon treated water can be sterilized by ozone treatment, a separate disinfection step is not required.
However, in the activated carbon tank, since the secondary treatment water is directly introduced, the time required for the activated carbon to reach the adsorption saturation is short. Therefore, the removal of organic substances by biodegradation is mainly performed rather than the removal of organic substances by adsorption.
[0018]
On the other hand, fluctuations in the quality of the secondary treated water throughout the day and throughout the year can be dealt with by changing the circulating water amount while keeping the ozone injection rate constant. Although the chemical oxygen demand (CODMn) is often used as an index indicating the quality of the treated water, as shown in FIG. 4, the absorbance (E260) of the secondary treated water at an ultraviolet ray of 260 nm is equal to the chemical oxygen demand (CO260). CODMn). Therefore, by monitoring E260, it is possible to estimate an approximate organic matter concentration in the secondary treated water, and to set a circulating water amount corresponding to the target treated water quality.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an advanced treatment facility for performing advanced treatment of sewage. The advanced treatment facility has an activated carbon tank 1, an ozone reaction tank 2, and a water storage tank 3.
[0020]
In the activated carbon tank 1, a biological activated carbon layer 4 made of activated carbon to which organisms are spontaneously attached is formed at the lower part of the tank, and a secondary treated water supply pipe 5 for leading secondary treated water from the previous step is provided. A biologically activated carbon treated water outlet pipe 6 is provided at the upper part of the tank and communicates below the biologically activated carbon layer 4 to extract the biologically activated carbon treated water that has passed through the biologically activated carbon layer 4.
[0021]
The ozone reaction tank 2 is provided with an ozone diffuser 8 for ejecting ozone supplied from an ozone generator 7 outside the tank at a lower portion of the tank. And an ozone-treated water outlet pipe 9 that communicates with the lower part of the tank and that leads the ozonated water that has been ozone-treated in the tank to the water storage tank 3.
[0022]
In the water storage tank 3, a circulation pump 10 is interposed, and a base end of a circulation pipe 11 that circulates and returns a part of the ozonized water stored in the tank to the middle of the secondary treatment water supply pipe 5. And a discharge path 12 for discharging the remaining ozonated water out of the system is provided.
[0023]
An ultraviolet absorbance meter 13 is provided in the middle of the biological activated carbon treated water discharge pipe 9. The ultraviolet absorbance meter 13 is electrically connected to the ultraviolet absorbance meter 13 and the circulation pump 10, and is transmitted from the ultraviolet absorbance meter 13. A control device 14 that controls the circulating pump 10 by an inverter based on an electric signal is provided. Reference numeral 15 denotes a constant flow valve.
[0024]
The operation of the above configuration will be described.
During normal treatment, the secondary treatment water is supplied through the secondary treatment water supply pipe 5 and a part of the ozone treatment water is circulated and returned through the circulation pipe 11. And flows downward through the biological activated carbon layer 4. As a result, the SS component contained in the water to be treated W0 is captured in the biological activated carbon layer 4, the biodegradable organic matter is biodegraded by microorganisms attached to the activated carbon particles, and some of the biodegradable organic matter and other The pollutants are adsorbed on the activated carbon particles, and the biological activated carbon treated water W1 from which these are removed is sent to the ozone reaction tank 2 through the biological activated carbon treated water outlet pipe 6.
[0025]
The biologically activated carbon treated water W1 sent from the activated carbon tank 1 flows into the upper part of the ozone reaction tank 2 and descends, and the ozone O spouted from the ozone diffuser 8 may be removed due to the removal of SS. With the efficient oxidizing power of ozone O, some of the hard-to-decompose organic substances are decomposed and removed, and the remaining hard-to-decompose organic substances are converted to easily-decomposable organic substances, including the easily-decomposable organic substances. The ozone-treated water W2 is sent to the water storage tank 3 through the ozone-treated water outlet pipe 9.
[0026]
The ozonized water W2 sent from the ozone reaction tank 2 flows into the water storage tank 3, and a part thereof is circulated and returned to the middle of the secondary treatment water supply pipe 5 through the circulation pipe 11, as described above. The remainder is discharged to the outside of the system through the discharge path 12 as highly treated water.
[0027]
At this time, the ultraviolet absorbance (E260) of the ultraviolet ray 260 nm of the biological activated carbon treated water W1 sent from the activated carbon tank 1 to the ozone reaction tank 2 is monitored by the ultraviolet absorbance meter 13, and the absorbance data is transmitted to the controller 14 as an electric signal. You. Then, in the control device 14, based on the transmitted absorbance data, the organic matter concentration in the biologically activated carbon-treated water W1 is estimated from the relationship between the absorbance and the organic matter concentration stored in advance, and based on the estimated organic matter concentration. A predetermined amount of circulating water that can bring the biological activated carbon treated water W1 closer to the target organic matter concentration is selected, and the circulation pump 10 is inverter-controlled at a rotation speed corresponding to the selected amount of circulating water, and ozone treatment of the selected amount of circulating water is performed. The water W2 is circulated and returned in the middle of the secondary treatment water supply pipe 5.
[0028]
In order to evaluate the effect of circulation in the advanced treatment method described above, each of secondary treatment water, influent water (secondary treatment water + circulated ozonated water), biological activated carbon treated water, and ozone treated water The change in CODMn concentration when the amount of circulating water was changed while the amount of injected ozone was kept constant was examined. The results are as shown in FIG. In the figure, no circulation means a one-pass type in which no circulation is performed, 0.5Q circulation means 0.5 times the amount of inflow water, 1Q circulation means 1 time, and 2Q circulation means 2 times the amount of inflow water. It can be seen that the quality of the treated water improves as the amount of circulating water increases.
[0029]
In addition, the daily change of the CODMn concentration when the secondary treatment water is subjected to sand filtration + ozone + biological activated carbon treatment as in the past, and the CODMn when the secondary treatment water is subjected to biological activation carbon + ozone circulation treatment as described above. The change over time in the concentration was examined. The results are as shown in FIGS. 3A and 3B, respectively. In each figure, a black circle indicates the CODMn concentration of the secondary treatment water, and a black square indicates the CODMn concentration of the treatment water led out of the system. As can be seen from FIGS. 3A and 3B, in the conventional method, the quality of the treated water is strongly influenced by the quality of the secondary treated water, which is the raw water, and tends to follow the quality of the secondary treated water. In this method, the quality of the treated water was hardly affected by the quality of the secondary treated water, was almost constant, and a stable treated water quality could be secured.
[0030]
From these results, not only good treated water with low CODMn can be obtained by the biological activated carbon + ozone circulation, but also stable treated water quality by controlling the amount of circulating water based on the quality of the biologically activated carbon treated water (E260). It can be seen that can be maintained.
[0031]
Even if the amount of circulating water is controlled on the basis of the ozone-treated water E260, a similarly stable treated water quality can be maintained. However, since the E260 of the ozonized water is very small, it is easier to control the amount of circulating water based on the E260 of the biologically activated carbon treated water.
[0032]
A small amount of living organisms may be contained in the ozone-treated water W2 discharged from the water storage tank 3 as highly treated water through the discharge path 12, but since the ozone-treated water W2 has been sterilized by the ozone treatment, a separate disinfection process is required. Is unnecessary.
[0033]
【The invention's effect】
As described above, according to the present invention, the secondary treatment water of sewage is subjected to the biological activated carbon layer + ozone circulation treatment, so that the quality of the treated water is equal to or higher than that of the conventional filtration + ozone + biological activated carbon one-time treatment water. While the above treated water quality can be ensured, organisms leaked from the biological activated carbon can be killed by ozone, and a compact apparatus configuration can be realized because the conventionally required filtration step and sterilization step are unnecessary.
[0034]
In addition, by controlling the amount of circulating water based on the absorbance E260 of the biological activated carbon treated water, a stable treated water quality can be secured even if the quality of the secondary treated water as raw water fluctuates.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a schematic entire configuration of an advanced treatment facility in which an advanced sewage treatment method according to an embodiment of the present invention is performed.
FIG. 2 is a graph showing the effect of circulation in the advanced sewage treatment method of the present invention in relation to the amount of circulating water and the CODMn concentration.
FIG. 3 compares the daily change of the CODMn concentration of the secondary treated water as the raw water and the highly treated treated water in the advanced sewage treatment method of the present invention with the daily change in the conventional advanced sewage treatment method. FIG.
FIG. 4 is a graph showing a relationship between a conventionally known CODMn concentration and an absorbance (E260) at an ultraviolet ray of 260 nm.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Activated carbon tank 2 Ozone reaction tank 4 Biological activated carbon layer 5 Secondary treated water supply pipe 6 Biological activated carbon treated water discharge pipe 9 Ozone treated water discharge pipe 11 Circulation pipe 13 Ultraviolet absorbance meter 14 Controller

Claims (2)

The secondary treatment water of sewage is guided to an activated carbon tank having a biological activated carbon layer, and then introduced into the ozone reaction tank, and a part of the ozonized water flowing out of the ozone reaction tank is circulated to the inlet of the activated carbon tank. In the activated carbon tank, removal of SS and adsorption and biodegradation of organic matter are performed by the biological activated carbon layer, and biologically activated carbon-treated water from which SS components have been removed is introduced into the ozone reaction tank. , And sterilizing biologically activated carbon-treated water , and deriving remaining ozone-treated water flowing out of the ozone reaction tank as highly-treated water. The control of the amount of water circulating from the ozone reaction tank to the activated carbon tank is performed based on the absorbance of ultraviolet light at 260 nm of biologically activated carbon treated water flowing out of the activated carbon tank or ozone treated water flowing out of the ozone reaction tank. 1. The advanced treatment method for sewage according to 1.

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