JPH04310299A - Advanced treatment methods and equipment for tap water raw water - Google Patents

Abstract

PURPOSE:To sufficiently remove the contaminant contained in raw clean water. CONSTITUTION:Raw clean water is biologically treated in a nitration tank 1, a denitrification tank 2 and a sedimentation filter tank 6 in succession. Oxygen enriched air is supplied to the nitration tank 1 from an oxygen enriched air preparing device 3 to perform nitration treatment under the control of ORP. By controlling ORP by supplying oxygen enriched air to the denitrification tank 12 from the oxygen enriched air preparing device 3, denitrification treatment is performed. The flocculation, sedimentation and filtering of bacteria are performed in the sedimentation filter tank 6. Thereafter, ozone treatment is performed. Oxygen enriched air is supplied to an ozone generator 10 from the oxygen enriched air preparing device 3 and an ozone contact tank 9 is packed with an Fe type amorphous material.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to advanced treatment of raw water.

0002

BACKGROUND OF THE INVENTION Clean water is normally taken from rivers, etc., and is supplied after being subjected to treatments such as filtration. As raw water becomes increasingly contaminated, simple filtration and chlorine disinfection are no longer sufficient for water treatment, and advanced treatments such as biological treatment, ozone treatment, and activated carbon treatment are now required.

[0003] Biological treatment is a method in which a honeycomb tube or the like is immersed as a filler in the water of a treatment tank, microorganisms are attached to it, and the biofilm of the microorganisms is brought into contact with raw water for purification. That is, when raw water is supplied while blowing air into the treatment tank to maintain an aerobic atmosphere, the biofilm of microorganisms attached to the surface of the filler decomposes and aggregates various substances contained in the raw water. Furthermore, since ozone is the second most powerful oxidizing agent after fluorine, ozone treatment utilizes this oxidizing power to blow ozone into raw water. Furthermore, activated carbon treatment is a process that uses the adsorption power of activated carbon to remove dissolved organic matter.

0004

[Problems to be Solved by the Invention] Recently, however, the water quality of rivers, which are Japan's main water sources, has been rapidly deteriorating due to the inflow of treated sewage water, etc., and conventional techniques have been unable to produce odor or contain carcinogenic substances such as trihalomethane. It has become impossible to deal with the increase in ammonia nitrogen and ammonia nitrogen. The conventional advanced processing described above also has the following problems.

First, in biological treatment, plastic products such as honeycomb tubes are often used as carriers for immobilizing microorganisms, but honeycomb tubes have the following drawbacks. First, microorganisms are difficult to immobilize on the surface of honeycomb tubes due to their material and surface properties. Therefore, a long acclimatization period is required for the process to proceed smoothly. In addition, honeycomb tubes are prone to blockage between the tubes, and once blockage occurs, uneven flow occurs within the reaction tank, reducing the quality of the treated water. It is quite difficult to correct the blockage by backwashing with water or the like.

Regarding the removal of nitrogen, it has been possible to remove ammonia nitrogen by advancing the nitrification reaction to some extent with conventional biological treatment, but the treatment is unstable because there is no clear indicator to control the nitrification reaction. Met. Furthermore, little consideration is given to converting nitrate nitrogen into nitrogen gas through a denitrification reaction and completely removing nitrogen.

[0007] Regarding odor removal, biological treatments are unstable and highly variable. Further, removal of trihalomethane precursors and the like cannot be expected to be very effective.

When ozone treatment and activated carbon treatment are used together, the effect of removing trihalomethanes and the like becomes more apparent when the amount of ozone consumed is increased. In addition, the odor level is 80-90 with ozone treatment.
%, almost 100% can be removed by using activated carbon together, but nitrogen removal cannot be expected.

Furthermore, by combining biological treatment, ozone treatment, and activated carbon treatment, trihalomethane, etc. and odor can be almost completely removed. Nitrogen removal is also effective to some extent until nitrification, but it is unstable. Furthermore, there is a problem that denitrification is not performed and the efficiency is low, resulting in an increase in processing cost.

[0010] The present invention provides an advanced treatment technology for raw water that can comprehensively and sufficiently remove contaminants contained in raw water.

[0011]

[Means for Solving the Problems] The method of the present invention involves using saddle-shaped ceramics to immobilize microorganisms in the nitrification tank and the denitrification tank when biologically treating raw water in a nitrification tank, a denitrification tank, and a sedimentation filter tank in sequence. Provided as a carrier, nitrification is performed by supplying oxygen-enriched air from the oxygen-enriched air production device to the nitrification tank and controlling ORP, and supplies nitrogen-enriched air from the oxygen-enriched air production device to the denitrification tank. This is an advanced treatment method for raw water, which is characterized by denitrification treatment by controlling ORP, followed by coagulation and sedimentation of microorganisms in a sedimentation filtration tank, filtration treatment, and then ozone treatment. The device of the invention consists of a nitrification tank, a denitrification tank, a sedimentation filter tank, and an ozone treatment device, and the nitrification tank and denitrification tank are provided with saddle-shaped ceramics as microorganism immobilization carriers, and the nitrification tank and denitrification tank are equipped with an ORP control device. , configured to supply oxygen-enriched air from the oxygen-enriched air production device to the nitrification tank and the ozone generator of the ozone treatment device, and supply nitrogen-enriched air from the oxygen-enriched air production device to the denitrification tank, This is an advanced treatment device for raw water, characterized in that an ozone contact tank of the ozone treatment device is filled with an Fe-based amorphous material.

0012

[Operation] Fig. 1 shows an example of the advanced treatment device for tap water raw water according to the present invention.

In the present invention, a nitrification tank 1 and a denitrification tank 2 are provided to completely remove ammonia nitrogen. In the nitrification tank 1, for example, +100 to +150 mV using ORP (oxidation-reduction potential) as an index (gold-silver/silver chloride standard).
By maintaining an aerobic atmosphere like this, microorganisms are allowed to oxidize and decompose various substances. For example, nitrifying bacteria oxidize ammonia nitrogen. In the next denitrification tank 2, nitric acid is converted into nitrogen gas and removed into the air by maintaining an anaerobic atmosphere at, for example, -50 to -150 mV using ORP as an index.

[0014] As an ORP measuring device, a composite electrode consisting of gold or an alloy of gold and antimony and silver-silver chloride as an electrode is suitable for use in the present invention because the indicated value is stable. is desirable.

The reason why saddle-shaped ceramics are provided in the nitrification tank 1 and the denitrification tank 2 as microorganism immobilization carriers is to increase the amount of attached microorganisms and improve treatment efficiency. With conventional honeycomb tubes, the amount of microorganisms that adhere to them is small, but when ceramics are immersed in a treatment tank, the microorganisms actively enter the interior of the ceramics, so the amount of microorganisms that adhere to them increases. In addition, in order to improve contact with raw water, the shape of the ceramic is preferably saddle-shaped. The saddle type has a shape as shown in FIG. 2, and by immersing it in a treatment tank, it is possible to increase the amount of attached microorganisms and improve contact with raw water.

[0016] As saddle type ceramics, those whose main raw material is granulated blast furnace slag are particularly desirable. Granulated blast furnace slag contains Fe and Mg, which are micronutrient sources for microorganisms, which improves the adhesion of microorganisms, and also contains Ca as a main component, which can lower the firing temperature of ceramics. This is because mold ceramics can be manufactured at low cost.

In order to control the ORP of the nitrification tank 1 and the denitrification tank 2, an oxygen enriched air production device 3 is used.

Oxygen-enriched air obtained from an oxygen-enriched air production device 3 is supplied to the nitrification tank 1 in order to maintain an aerobic atmosphere using ORP as an index. The nitrification tank 1 can be maintained in an aerobic atmosphere more efficiently than simply supplying air.

Further, the denitrification tank 2 is supplied with nitrogen-enriched air from an oxygen-enriched air production device 3 in order to maintain an anaerobic atmosphere using ORP as an index. In order to create an anaerobic atmosphere, the supply of air may be stopped, but even if nitrogen-enriched air is supplied as in the present invention, an anaerobic atmosphere is created. Moreover, the supply of nitrogen-enriched air agitates the inside of the treatment tank, promoting the reaction. Since nitrogen-enriched air is also produced as a by-product when oxygen-enriched air is supplied, the present invention makes effective use of this.

[0020] The water flowing out from the denitrification tank 2 is led to a sedimentation filter tank 6, where microorganisms are coagulated and precipitated, filtered, and discharged. Since ozone treatment is performed after discharge, microorganisms must be completely removed here. This is to avoid ozone being wasted if microorganisms remain. Here, it is also possible to utilize the saddle type ceramics mentioned above for filtration.

[0021] The water that has undergone the above biological treatment is then subjected to ozone treatment. Biological treatment is performed before expensive ozone treatment, so
The treatment efficiency is higher than that of ozone treatment alone. As mentioned above, ozone is the second most powerful oxidizing agent after fluorine, and this oxidizing power is used to treat raw water by blowing it into it. Through this treatment, trihalomethane precursors such as humic acid and residual substances such as odors can be completely removed.

However, although ozone generators have been improved, there is a problem in that ozone production requires a large amount of electricity. For this reason, ozone is quite expensive, and since its solubility in water is relatively low, an increase in treatment costs is unavoidable, and it is currently not widely used in Japan. It was important to develop effective treatment methods to take advantage of ozone's superior treatment capabilities without increasing treatment costs. In order to solve this problem, the present invention not only performs biological treatment and then ozone treatment, but also supplies the oxygen-enriched air from the oxygen-enriched air production device 3 together with the nitrification tank 1 to the ozone generator 10 of the ozone treatment device. We also supply
Further, the ozone contact tank 9 of the ozone treatment device is filled with Fe-based amorphous material.

First, the efficiency of the ozone generator 10 is increased by supplying the oxygen-enriched air from the oxygen-enriched air production device 3 to the ozone generator 10 as well. In other words, it is more efficient to produce ozone from oxygen-enriched air than from air.

Regarding the catalytic action of amorphous materials in ozone treatment, in the catalytic action of metals,
It is known that amorphous materials exhibit higher activity than crystalline materials ("Amorphous Materials", University of Tokyo Press).
However, there is no example of its use as a catalyst for water treatment using ozone. The present inventor has confirmed that the efficiency of ozone treatment can be improved by 2 to 3 times when an Fe-based amorphous material is used as a catalyst. That is, in terms of processing time, it can be shortened to 1/2 to 1/3 compared to the case of ozone treatment alone.

Regarding the mechanism by which the Fe-based amorphous material improves the efficiency of ozone treatment, in addition to the fact that the amorphous material has many active points per surface area, the surface of the Fe-based amorphous material is easily oxidized, and the oxidation effect of ozone causes the surface to deteriorate. It is thought that this is because iron peroxide (FeOOH) is produced and this oxidizes and decomposes the target component. Without an amorphous material, the nascent oxygen will turn into O2 in a short time and will not contribute to the decomposition of the target component, but iron peroxide (FeOOH) remains in this form for a long time, improving processing efficiency. It is.

After the ozone treatment, it is also possible to install an activated carbon treatment device to further improve the quality of the treated water.

[0027]

[Example] Simultaneous removal of organic matter, nitrogen, musty odor substances, and humic acid in raw water from tap water

The present method was applied to remove organic matter, nitrogen, musty-smelling substances, and humic acid contained in raw tap water. This method first decomposes most of the above substances through biological treatment.
Since the remaining substances are removed and then decomposed by highly efficient ozone treatment, it is possible to significantly improve treatment efficiency and treated water quality compared to the case of ozone treatment alone.

The experiment was conducted according to the following procedure. First, as raw water for tap water, 2 MIB (2
500 ng/l of methyl isoborneol), 3 mg/l of NH4-N as nitrogen, and 1 mg/l of humic acid.
1 was used. This is based on the assumption that the water quality would be the worst in the summer when the water quality of raw water is the worst. Subsequently, the biological treatment device and the ozone treatment device were operated under the conditions shown in Table 1.

[0030]

[Table 1]

The results are shown in Table 2.

[0032]

[Table 2] Treatment experiment results

As is clear from Table 2, trihalomethane precursors such as odorants (2MIB), NH4-N, and humic acid can be almost completely removed by this method. Furthermore, compared to the ozone treatment method alone, the ozone injection rate can be reduced to 1
It can be reduced to /3 to 1/4.

In this embodiment, a ribbon-shaped ferrite-based amorphous material was used, but the same effect can be obtained using a linear or chip-shaped amorphous material (1 to 10 cm) in the present invention.

[0035]

According to the present invention, ammonia nitrogen in raw water can be completely removed in 1/2 to 1/3 of the biological treatment time compared to conventional biological treatment. In addition, since water after biological treatment is treated with ozone with higher efficiency, ozone treatment can be reduced to 1/3 to 1/4 compared to ozone treatment alone, and the final treated water is almost completely free of trihalomethane precursors and odors. removed, resulting in extremely high cleanliness.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an advanced treatment device for raw water of tap water according to the present invention.

FIG. 2 is a diagram showing an example of saddle-shaped ceramics used in the present invention.

[Explanation of symbols]

1 Nitrification tank 2 Denitrification tank 3 Oxygen-enriched air production equipment 4 ORP control device 5 ORP measurement device 6 Sedimentation filtration tank 7. Air diffuser pipe 8 Water pump 9 Ozone contact tank 10 Ozone generator 11 Exhaust ozone treatment equipment 12 Saddle type ceramics

Claims (4)

[Claims] Claim 1: When raw water is subjected to biological treatment in a nitrification tank, a denitrification tank, and a sedimentation filtration tank in sequence, saddle-shaped ceramics are provided in the nitrification tank and denitrification tank as microorganism immobilization carriers, and the nitrification tank is enriched with oxygen. Nitrification treatment is carried out by supplying oxygen-enriched air from an air production device and controlling ORP,
Denitrification treatment is performed by supplying nitrogen-enriched air from an oxygen-enriched air production device to a denitrification tank and controlling ORP, followed by coagulation and sedimentation of microorganisms and filtration treatment in a sedimentation filtration tank.
An advanced treatment method for raw water, which is characterized in that it is then subjected to ozone treatment. 2. The method for advanced treatment of raw water according to claim 1, characterized in that the saddle-shaped ceramic is made of granulated blast furnace slag as a main raw material. 3. Consisting of a nitrification tank, a denitrification tank, a sedimentation filtration tank, and an ozone treatment device, the nitrification tank and the denitrification tank are provided with saddle-shaped ceramics as a carrier for immobilizing microorganisms, and the nitrification tank and the denitrification tank are provided with an ORP control device. Equipped with
The ozone treatment device is configured to supply oxygen enriched air from the oxygen enriched air production device to the nitrification tank and the ozone generator of the ozone treatment device, and supply nitrogen enriched air from the oxygen enriched air production device to the denitrification tank. An advanced treatment device for raw water, characterized in that an ozone contact tank is filled with an Fe-based amorphous material. 4. The advanced treatment system for raw water according to claim 3, wherein the saddle-shaped ceramic is made of granulated blast furnace slag as a main raw material.