JPH0634996B2 - Biological treatment method of water containing trace organic matter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biological treatment method for trace organic matter-containing water,
In particular, trace amount organic substance-containing water, which is considered to be difficult to treat biologically when the concentration of organic substance is 5 mg / or less, can be efficiently decomposed by oligotrophic bacteria and is suitable for application to pure water production process. It relates to a biological treatment method for water.

[Prior Art] In the manufacture of LSIs and VLSIs, a large amount of pure water or ultrapure water is used as cleaning water. Ultrapure water is the theoretical resistance of pure water (water consisting of H ₂ O only) 18.24 MΩ · c
Pure water having a resistivity of 17 to 18 MΩ · cm, which is extremely close to m. Even in such nutrient water as ultrapure water or pure water, microorganisms are present in a very small amount, but when organic substances are present in pure water even in the ppb order, the microorganisms grow and the RO device This may cause troubles in the pure water producing device.

Also, when collecting and reusing the cleaning wastewater, it is necessary to remove a trace amount of organic matter in the recovered water.

The present applicant has previously proposed that, as a method of suppressing the growth of microorganisms in water containing an extremely small amount of organic matter, such as ultrapure water used in the electronics industry, etc. A method for removing phosphorus components in water to make phosphorus-deficient water by biological treatment was applied, and a patent application was filed (Japanese Patent Application No. 59-231737, hereinafter, “Prior Application I”).
Say. ).

Further, the present applicant has also proposed that in an ultrapure water production apparatus having a membrane treatment device and an ion exchange tower, as an ultrapure water production apparatus that also solves the problem caused by the growth of microorganisms in water containing trace organic matter, A biological treatment means comprising a biological reaction tank for biological treatment in the presence of an energy source and / or a nutrient source and a bacterial cell separator for separating and removing bacterial cells grown in the biological reaction tank is added. We applied for a patent for an ultrapure water production system (Japanese Patent Application No. 59-23173).
8. Hereinafter referred to as "first application II". ).

The method of treating water containing a trace amount of organic matter disclosed in the above-mentioned prior applications I and II with oligotrophic bacteria has high treatment efficiency and has a running cost higher than that of the ultraviolet oxidation method which has been generally performed conventionally. It is a low and extremely effective treatment method.

Thus, conventionally, when performing biological treatment of raw water, the activated sludge method and the biofilm method have been generally applied. In this case, the microorganisms in the reaction tank are developing in a floc shape or a film shape, and the BOD of the obtained treated water is several ppm or more. This value depends on the substrate affinity of microorganisms used for biological treatment, and for example, the substrate affinity constant (Ks) of activated sludge is several + ppm.

Therefore, in biological treatment of trace organic matter-containing water, treated water of good quality cannot be obtained by such general microorganisms.

On the other hand, oligotrophic bacteria such as oligotrophic bacteria that live in clear water such as tap water have a substrate affinity constant (Ks) of several tens of ppb or less, and can decompose trace organic substances efficiently. .

[Problems to be Solved by the Invention] Therefore, when treating trace organic matter-containing water, it is required to make oligotrophic bacteria inhabit the reaction tank and develop it in a good form. Little is known about the retention of oligotrophic bacteria. Even when the oligotrophic bacteria are attached to a carrier and treated in a fluidized bed system or a fixed bed system, the oligotrophic bacteria do not grow well, and the carrier There have been problems that the surface is occupied by activated sludge microorganisms, and even if oligotrophic bacteria grow, the excellent treatment effect cannot be obtained due to the poor development form.

[Means for Solving Problems] In order to solve the above problems, the present invention has an organic substance concentration of 5 m.
In a method of biologically treating water to be treated containing a trace amount of organic matter of less than g / in a reaction vessel having a biological carrier with oligotrophic bacteria, the carrier surface area load of the biological carrier is 0.5 g-C /
m ² · day or less, preferably 0.1 g-C / m ² · day or less.

That is, the present inventors have conducted extensive studies on the habitation or growth conditions of oligotrophic bacteria, and as a result, even under conditions in which oligotrophic bacteria grow, when the organic matter load per carrier surface area is large, the bacteria will be formed on the carrier surface. It was found that the bacterial affinity deteriorates and the treatment effect decreases because the bacterium develops. The present invention has been completed by finding suitable operating conditions for water containing a small amount of organic matter based on this finding.

The present invention will be described in detail below.

When biologically treating raw water containing a trace amount of organic matter, the amount of sludge produced by the biological treatment is small, and thus the floating method cannot maintain the cells. Therefore, in the present invention, the treatment is carried out by a fixed bed system or a fluidized bed system using a biological reaction tank containing a biological carrier. As the biological carrier, glass beads, ceramics, activated carbon and the like are preferably used.

Therefore, in treating the raw water, the carrier surface area load of such a biological carrier is adjusted to 0.5 g-C / m ² · day or less, preferably 0.1 g-C / m ² · day or less. . When the carrier surface area load exceeds 0.5 g-C / m ² · day, oligotrophic bacteria develop into a film on the carrier surface, the substrate affinity deteriorates due to the permeation rate of raw water, and the treated water quality deteriorates.

Note that the carrier surface area load of 0.5 g-C / m ² · day or less does not overlap with the surface area load of the biofilm wastewater treatment equipment. By the way, even in the standard sprinkling filter method and catalytic oxidation method, which are said to have a relatively low load, the surface area load is 0.5 to 1.0 g-
It is about C / m ² · day, and is 7.8-in the tower type sprinkling filter method.
20 g-C / m ² · day, 6 to 15 g-C by the rotating disk method
/ M ² · day is a high value.

[Function] The oligotrophic bacteria are wastewater with a BOD of about several ppm, biologically treated water,
It is a microorganism that inhabits and grows in clear water such as natural water and tap water (chlorine removal).

Such an oligotrophic bacterium has a substrate affinity constant (Ks) of several p.
As shown in FIG. 1, the maximum specific growth rate (μmax) is about the same as that of the activated sludge microorganism, although it is extremely low at about pb. Therefore, the oligotrophic bacterium can quickly decompose a trace amount of organic matter to obtain treated water with extremely good water quality. The oligotrophic bacterium does not need to be specially cultivated and cultivated, and a trace amount of organic matter-containing water is spontaneously propagated on the surface of the carrier by continuously passing the water through a biological reaction tank containing a biological carrier.

Fig. 1 shows Ks of oligotrophic bacteria isolated from tap water.
3 is a graph showing μmax and μmax.

According to the method of the present invention, such oligotrophic bacteria grow on the surface of the carrier in the reaction vessel in an extremely good form, and therefore it becomes possible to efficiently treat the trace amount organic matter-containing water.

[Examples] The present invention will be described more specifically with reference to the following examples.

Example 1 As shown in FIG. 2, a biological treatment of synthetic water in which acetic acid was added to pure water was performed using a fluidized bed type bioreactor 1 containing glass beads as a filler 2. Incidentally, in FIG. 2, 3
Is a raw water supply pipe, 4 is a treated water discharge pipe, and 5 is a circulation line.

The biological treatment conditions were adjusted such that the pH was 6.0 ± 0.5, the temperature was 20 ° C., and the residence time was 10 minutes (based on the empty volume of the carrier-filled portion). Then, Ks is obtained by changing the acetic acid concentration, and the average particle size of the glass beads to be filled is set to 0.
The surface loading of the biocarrier was varied by varying from 1 to 10 mm. For the measurement of the value of Ks, the specific growth rate μ is measured as shown in FIG. 1 and the substrate concentration giving half the maximum specific growth rate μmax is Ks. There is a method in which γs is measured and Ks is defined as the substrate concentration which gives a half of the maximum substrate removal rate γmax.
In this Example and the following Example 2, Ks was measured by the latter method. That is, the raw water is continuously passed through the biological reaction tank 1, the treatment is carried out by changing the raw water substrate concentration by several points, and the treated water substrate concentration and the substrate removal rate at that time are plotted in the X-axis direction and the Y-axis direction, respectively. The substrate concentration giving half the maximum substrate removal rate was defined as Ks.

Under such conditions, the relationship between Ks and the carrier surface area load was determined, and it was as shown in FIG.

That is, when the surface area load of the biological carrier exceeds 0.5 g-C / m ² · day, Ks becomes almost constant at about 1000 μg-C /, and sharply decreases below 0.1 g-C / m ² · day. I understand.

In this experiment, the expansion rate differs depending on the average particle diameter of the glass beads, and the expansion rates of the average particle diameters of 0.1 mm, 0.2 mm and 0.4 mm are 100% and 35%, respectively.
% And 5%, but average particle size 1.0 mm and 10 m
The m's did not unfold and had a fixed bed. Therefore, it is considered that the treatment performance depends on the surface area load rather than the filter bed type (fluidized bed, fixed bed, etc.).

The treated water quality is the surface area load of the biological carrier of 0.5 g-
Reactor 1 at any load of C / m ² or less
The organic matter concentration of the treated water in Example 2 was 10 μg-C / or less after separating the cells with a 0.45 μm filter paper, and good treated water was obtained.

Example 2 Using a fluidized bed type bioreactor containing spherical activated carbon (10 mesh pass, 32 mesh on: average diameter 1.5 mm) as a filler, biological treatment of water obtained by adding isopropyl alcohol to pure water was performed. . Biological treatment conditions are pH 6
-7, temperature 20-25 ° C, residence time 15 minutes. Ks was determined while changing the carrier surface area load by changing the concentration of isopropyl alcohol. The relationship between Ks and the carrier surface area load was as shown in FIG.

That is, when the carrier surface area load exceeds 0.5 g-C / m ² · day, Ks becomes approximately constant at about 100 μg-C /, which means that glass beads are used as the carrier and the organic substance is acetic acid. The results were similar.

[Effects of the Invention] As described in detail above, in the method of the present invention, the water to be treated containing a trace amount of organic matter is applied at a surface area load of a biological carrier of 0.5 g-C / m ^2.
The treatment is carried out for less than or equal to one day, preferably 0.1 g-C / m ² · day or less, and under such conditions, an oligotrophic bacterium with a high decomposition efficiency of trace organic substances inhabits in the reaction tank,
Moreover, it grows without forming a film on the surface of the carrier. Therefore, according to the method of the present invention, effective biological treatment of trace organic matter-containing water is possible.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the concentration of acetic acid and the specific growth rate of oligotrophic bacteria separated from tap water, FIG. 2 is a diagram showing the constitution of the biological reaction tank used in Example 1, and FIG. 3 is a graph showing the relationship between the substrate affinity constant and the surface area load of the biological carrier obtained in Example 1. FIG. 4 is a graph showing the relationship between the substrate affinity constant obtained in Example 2 and the surface area load of the biological carrier. 1 ... Biological reaction tank, 2 ... Filling material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References “Chemical pollution control technology and equipment 5, advanced treatment and reuse of wastewater” edited by Japan Society of Chemical Engineering, Baifukan (Sho 54-10-25) p. 132-140 Shimizu, Ushio, “Microbial Ecology ▲ II ▼ -Microorganisms in the Ecosystem” Kyoritsu Publishing (SHO 60-11-20) P. 77 ~ 81

Claims (2)

[Claims] 1. A method for biologically treating water to be treated containing a trace amount of organic matter having an organic matter concentration of 5 mg / or less with a oligotrophic bacterium in a reaction vessel having a biological carrier, in which the carrier surface area load of the biological carrier is set to 0. A biological treatment method of trace organic matter-containing water, which comprises treating at 5 g-C / m ² · day or less. 2. The method according to claim 1, wherein the carrier surface area load is treated at 0.1 g-C / ² · day or less.