JPH0724829B2 - Advanced treatment method for organic wastewater - Google Patents

Description

[Detailed Description of the Invention] [Field of industrial application] The present invention relates to an advanced treatment method for further ozone treatment of organically treated sewage, particularly secondary treated water obtained by biologically treating sewage in sewers and municipal sewers.

[Conventional technology]

In recent years, the treated water of sewage is not only discharged to rivers and sea areas, but also reused as water for tap water in buildings and hydrophilic water for recovery of clear water. In many cases, sewage secondary treated water is further sand-filtered for reuse. However, sand filtration is insufficient to remove chromaticity in sewage secondary treated water and odorous substances such as nitrogen compounds. Recently, attention has been paid to ozone treatment effective for removing these substances, and incorporation of an ozone treatment step has been studied. As for the method in which the ozone treatment is currently performed, there are many cases in which the water obtained by subjecting the secondary treated water to the sand filtration treatment is subjected to the ozone treatment.

[Problems to be Solved by the Invention]

However, this method using sand filtration has problems that the effect of ozone treatment is unstable and that a large amount of ozone is required to be injected. As a means for solving this problem, while detecting the chromaticity of filtered water, etc. It is conceivable to add a device for performing feedback control for setting an appropriate ozone injection rate, but such a method results in a complicated system and is economically very disadvantageous.

An object of the present invention is to provide a highly advanced method for treating organic wastewater which is stable in ozone treatment, is efficient with a minimum ozone injection amount, and is economically excellent.

[Means for Solving the Problems]

The present invention provides a secondary treated water obtained by biologically treating organic sewage by a biological filtration process in which a fixed bed packed with a granular medium to which microorganisms are adhered and the entire fixed bed is kept aerobic. By setting the air supply of 10 to 100% of the treated water,
The advanced treatment method for organic sewage is characterized by performing ozone treatment after treating the treated water so that the concentration of nitrite nitrogen in the treated water becomes a predetermined value or less.

Preferred embodiments of the present invention are as follows.

1) In the biological filtration process, the filtration rate is 400 m / day or less, and the amount of air fed is 10 to 100% of the amount of treated water.

2) In the biological filtration process, the nitrite nitrogen concentration was 0.6 mg /
l or less, preferably 0.3 mg / l or less.

3) In the biological filtration process, SS should be 5 mg / l or less.

In particular, an important condition here is to control the amount of air in the biological filtration process to 10 to 100% of the amount of treated water. As shown in the examples, when the amount of air is 10% or less, the amount of oxygen is insufficient, the reaction of the formula (3) described later is less likely to occur, and the concentration of nitrous acid may increase. On the other hand, when the air amount is 100% or more, the biological filtration treated water has a high SS, which is not preferable.

The granular medium to which the microorganism used in the present invention is attached is not particularly limited to inorganic materials, organic materials, combinations thereof, and the like, and specifically, known materials such as sand, anthracite, activated carbon, and plastic filter media are used. Is mentioned.

In the present invention, the packed fixed bed in the biological filtration step is not preferable because the anaerobic portion is formed unless the entire layer is aerobic and the predetermined nitrite concentration cannot be obtained. Therefore, as a means for maintaining the biological filtration step in an aerobic state, air or a gas containing at least oxygen is blown into the fixed bed, or the air or the like is blown into the secondary treated water before biological filtration. Examples of the method include a method of dissolving oxygen, a combination thereof, and the like, but the method is not particularly limited. In the blown type, oxygen can be discharged from various levels in the fixed bed, but it is particularly preferable that oxygen is blown from below the fixed bed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the flow of the present invention, and FIG. 2 shows an example of the biological filtration tank used in the biological filtration step.

Sewage secondary treated water W ₂ obtained by subjecting organic sewage sewage to known biological treatment such as biological nitrification and denitrification is biological treatment tank 1 from secondary treated water inflow pipe 2 shown in FIG. Then, the granular medium 3 to which microorganisms such as aerobic bacteria are adhered is passed through a packed and fixed layer 3'which is held and packed by a support material layer 4 to be biologically treated so as to reduce the nitrite nitrogen concentration. It is destroyed below a certain value. The obtained biological filtration treated water W ₃ is SS
And NO ₂ ^- components such as chromaticity and odorous substances by being transferred to the ozone treatment step is ozonated by effectively reduced water collecting pipe 6 sewage components such as -N is efficiently removed, highly treated water Is obtained.

In the biological filtration tank, since the air diffuser 5 is provided in the support material layer 4 to uniformly distribute oxygen to the whole fixed layer 3 ', the whole fixed layer 3'is always maintained. Can be aerobic. The position of the air diffuser is preferably lower than the fixed layer 3'as in the second illustrated example, but it may be in the fixed layer 3 '. Further, instead of the support material layer 4, a support plate such as a perforated plate may be used, and in that case, the position of the air diffuser may be above or below the support plate. Further, as the biological filtration, a type in which air or the like is blown into the secondary treated water to dissolve it may be used.

If this biological filtration is continued for a long time, clogging occurs in the fixed layer 3'and the filtration resistance increases. When a certain filtration resistance is reached, it is advisable to let air and water flow out from the air washing pipe 7 and the transfer pipe 6 to wash the fixed bed 3 '.

[Action]

First, the present inventors first 3 SS and nitrite nitrogen of sand filtration treatment water W ₃ 'in order to clarify the instability caused in the ozone treatment step of the conventional flow shown in FIG. (Hereinafter, NO ₂ ^- -N Will be written)
The effect of ozone on ozone treatment was investigated.

NO ₂ ^- -N ^{_{is, NO 2 - + O 3 →}} NO 3 - by + O expressed chemical reaction ₂ ↑ ... (1), nitrate nitrogen (hereinafter, NO ₃ ^-
-N). Remaining in the sand filtration treatment water W ₃ '▲ NO ^- ₂ ▼ was experimentally in detail the consumption of ozone on -N concentrations, the results shown in Figure 4 was obtained. In the figure, hatched portions, the NO ₂ ^- shows the variation of ozone consumption for -N concentration width (instability). Thus from the figure, the NO ₂ ^-
-It is understood that when the N concentration is 0.6 mg / l or less, preferably 0.3 mg or less, the fluctuation range of the amount of ozone consumed is reduced and the ozone amount can be reduced to 0.5 mg / l or less. .

Meanwhile, was also investigated SS remaining in the sand filtration treatment water W ₃ ', NO ₂ ^- as in the case of -N, although quantitative relationship was not determined, approximately SS1mg / l per ozone 0.1mg
About / l was needed. Therefore, it was found that the amount of ozone consumed was about 0.5 mg / l even if SS was left at about 5 mg / l, which did not significantly affect the ozone injection rate.

Meanwhile, the sewage secondary treatment water, SS is but it is common to have remained about 10mg / l, NO ₂ ^- -N is such as by the influence of the water temperature due to sewage quantity and seasonal, the magnitude of its abundance Significantly different, variations from 0 to a few mg / l can occur throughout the year and even within a day.

By sand filtration treatment, the SS is removed is a well-known fact, NO ₂ ^- removal of -N can not be expected at all. The present inventors have, NO ₂ with SS ^- as a means of removing -N, by using the above-described biological filtration device, effectively ▲ NO ^- ₂ ▼ which was achieved by removing the -N and SS is there.

That is, the biological filtration step in the present invention, in the packed fixed bed of the granular medium to which the microorganisms are attached, along with the removal of SS,
Nitrite bacteria (such as the genus Nitrosomonas) and nitric acid bacteria (Nitrobacto
It is known that the following biological reactions occur depending on the genus r).

NH ₄ ⁺ ＋ 1.5O ₂ → NO ₂ ⁻ ＋ H ₂ O ＋ 2H ⁺ … (2) NO ₂ ⁻ ＋ 0.5O ₂ → NO ₃ ^－ … (3) Sewage Secondary treated water contains 10 ammonium ions (NH ₄ ⁺ ).
It is common to be present about to 30 mg / l, which upon biological filtration process, (2), from equation (3), nitrite ion generation of (NO ₂ ^{- -)} and nitrate ion (NO ₃₎ I understand that it will be done.

Based on such a theory, the present inventors have repeated various experiments, when biologically treating the sewage secondary treated water, filtration speed of 400 m / day or less as an operating condition, 10 treated water amount as an air supply amount. % by the above, NO ₂ ^- from NO ₃ ^- in becomes higher in the production rate, NH ₄ changes from ⁺ NO ₂ ^- as well, NO ₂ present in the sewage secondary treatment water ^- even NO ₃ ^- it is possible to, constantly NO ₂ ^- can the be below 0.3 mg / l was found.

Also, it was confirmed that SS could always achieve 5 mg / l or less under such conditions. However, if the amount of air fed is 100% or more of the amount of treated water, the packed fixed bed of the granular medium may be stirred and SS may leak into the treated water, which is not preferable.

〔Example〕

Examples of the present invention will be described below, but the present invention is not limited thereto.

In the flow chart of the present invention shown in FIG. 1, an example of the present invention using the biological filtration tank shown in FIG. 2 and a comparative example (1) of the conventional method flow shown in FIG. Both Comparative Example (2) and Comparative Example (3) in which the air supply amount was changed were carried out under the treatment conditions shown in Table 1 using the same secondary treated sewage water, and the results are shown in Table 2.

From Table-1 and Table-2, in the present invention, the ozone injection rate is 2-3 mg /
Even in the case of l, a chromaticity removal rate of about 80% was stably obtained. On the other hand, in Comparative Example (1) of the conventional method, the chromaticity removal rate is only 40% even if the ozone injection rate is about twice that of the present invention. This value is an average value, NO ₂ as previously described ^- by increasing or decreasing the -N, actually varied in 10% to 80%.

Further, regarding the total organic carbon (TOC), the effect of removing ozone in the ozone treatment step is not significantly different between the present invention and the conventional method. However, since the biological filtration step has a higher removal effect than the sand filtration step, the present invention as a whole has a higher removal rate than the conventional method.

In Comparative Example (2), since the amount of air fed was 10 Nm ³ / (m ² · day), which was less than 10% of the treated water amount, NO ₂ -N
The concentration is high, and the TOC and chromaticity removal rates are lower than those of the examples even if the ozone injection amount is increased about twice as much as the examples.
In Comparative Example (3), the amount of air supplied is 25 ONm ³ / (m ² ·
Day) and the treated water amount exceeds 100%, the SS removal rate of the biological filtered water deteriorates, and the SS, chromaticity, and TOC removal rates are lower than those of the examples even if the ozone injection amount is slightly increased. To do.

〔The invention's effect〕

From the above, when the secondary treated water such as sewage is treated with ozone,
By performing the biological filtration treatment before the ozone treatment step, the ozone injection rate can be reduced and a high chromaticity removal effect can be stably obtained. Further, since the present invention can obtain at least the result of the conventional method in terms of the removal rate of other sewage components, it is found that the present invention is extremely excellent in water purification as a whole as compared with the conventional method. .

[Brief description of drawings]

FIG. 1 shows a flow sheet of the present invention, and FIG. 2 shows
Diagram for explaining an example of a biological filtration tank used for biological filtration process of the present invention, FIG. 3 is a view showing a flow sheet of the prior art, Fig. 4, NO ₂ remaining in the sand filtration treatment water ^- -N It is a graph which shows the amount of ozone consumption with respect to concentration. Explanation of symbols 1: Biological filtration tank, 2: Secondary treated water inflow pipe 3: Granular medium with microorganisms attached 3 ': Packed fixed bed, 4: Support material layer 5: Air diffuser, 6: Biological filtered water collection Water pipe 7: Air washing pipe, 8: Discharge pipe W ₂ : Secondary sewage treated water, W ₃ : Biological filtered treated water W ₃ ′: Sand filtered treated water

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI technical display location C02F 9/00 504 D 7446-4D (72) Inventor Yuichi Fuchu 1-6 Konan, Minato-ku, Tokyo No. 27 Ebara Infilco Co., Ltd. (72) Inventor Eiji Tochikubo 1-6-27 Konan, Minato-ku, Tokyo Ebara Infilco Co., Ltd. (56) Reference JP-A-57-53289 (JP, A) JP Sho 55-27072 (JP, A) Japanese Patent Sho 61-46198 (JP, B2)

Claims (1)

[Claims] 1. A secondary treated water obtained by biologically treating organic wastewater,
In a fixed bed packed with a granular medium to which microorganisms are attached, and by setting the air supply amount of air to 10 to 100% of the amount of treated water in the biological filtration step in which the entire fixed bed is maintained in an aerobic state, A method for advanced treatment of organic sewage, which comprises performing ozone treatment after treating the treated water so that the concentration of nitrite nitrogen in the treated water becomes a predetermined value or less.