JP5604914B2 - Water treatment method and ultrapure water production method - Google Patents

Description

  The present invention relates to a raw water treatment method and an ultrapure water production method, and more particularly to a water treatment method capable of highly removing urea in raw water and an ultrapure water production method using this water treatment method.

  Conventionally, an ultrapure water production apparatus that produces ultrapure water from raw water such as city water, groundwater, and industrial water basically includes a pretreatment apparatus, a primary pure water production apparatus, and a secondary pure water production apparatus. . Among these, the pretreatment device is composed of agglomeration, levitation, and filtration devices. The primary pure water production apparatus is composed of two reverse osmosis membrane separation devices and a mixed bed type ion exchange device, or an ion exchange pure water device and a reverse osmosis membrane separation device. It consists of a low-pressure ultraviolet oxidizer, a mixed bed ion exchanger, and an ultrafiltration membrane separator.

  Patent Documents 1 to 3 describe that TOC in ultrapure water is sufficiently reduced by removing urea from the water supplied to the ultrapure water production apparatus.

In patent document 1 (Unexamined-Japanese-Patent No. 6-63592 (patent 3468784)), a biological treatment apparatus is incorporated in a pretreatment apparatus, and urea is decomposed | disassembled in this biological treatment apparatus. In Patent Document 2 (Japanese Patent Laid-Open No. Hei 6-233997 (Patent No. 3227863)), a biological treatment apparatus is incorporated into a pretreatment apparatus, and a mixed water of treated water (industrial water) and semiconductor cleaning / collecting water is passed through. The organic substance contained in the semiconductor cleaning / collecting water becomes a carbon source for the biological treatment reaction, and the decomposition rate of urea is improved. In addition, there are cases where a large amount of ammonium ions (NH ₄ ⁺ ) are contained in this semiconductor cleaning / recovered water, which becomes a nitrogen source in the same manner as urea and may inhibit the decomposition of urea. In order to solve this problem, Patent Document 3 (Japanese Patent Application Laid-Open No. 7-313994 (Patent No. 3417052)) separates the water to be treated (industrial water) and the semiconductor cleaning / recovered water after biological treatment separately, It describes that water is passed through a pure water production apparatus and a secondary pure water production apparatus.

JP-A-6-63592 JP-A-6-233997 JP-A-7-313994

  As in Patent Document 2, when a carbon source is added to the water to be treated, although the urea decomposition and removal efficiency of the biological treatment apparatus is improved, the amount of bacterial cells in the biological treatment apparatus increases, Increases the outflow of fungus bodies.

  The present invention has been made in view of the above circumstances, and a water treatment method capable of highly decomposing urea in raw water and suppressing microbial cell outflow from a biological treatment apparatus, and this water treatment method. It aims at providing the ultrapure water manufacturing method utilized.

  Further, as in Patent Document 2, when semiconductor cleaning / collecting water having a high ammonium ion content is used as a carbon source, ammonium ions inhibit the decomposition of urea.

  Another object of the present invention is to provide a water treatment method capable of sufficiently decomposing urea even in water to be treated containing ammonium ions, and a method for producing ultrapure water using this water treatment method.

The water treatment method according to the first aspect of the present invention (Claim 1) is a water treatment method for biologically treating raw water containing urea, and after adding a carbon source and a chlorine-based chemical to the raw water, it has a fixed bed of a biological support carrier. A water treatment method for conducting biological treatment by passing water through biological treatment means, wherein the raw water is groundwater, river water, city water, industrial water, recovered water from a semiconductor manufacturing process, and agglomerating and pressurizing these waters. Water that has been purified by flotation / filtration treatment or a combination of these treatments, the biological carrier is activated carbon, the chlorinated agent is a bound chlorinating agent, and the amount of carbon source added is The ratio (weight ratio) of the amount of C to the amount of N in urea is such that C / N is 100/50 to 100/2, and the amount of chlorinated chemical added is the total residual chlorine concentration in biologically treated water is Cl _{2 in} an amount of 0.02 to 0.1 mg / L It is what.

The water treatment method of the second invention (invention 2) is a water treatment method for biologically treating raw water containing urea, and after adding a carbon source to the raw water, the water is passed through a plurality of biological treatment means in series. A water treatment method for carrying out the treatment, wherein the raw water is groundwater, river water, city water, industrial water, recovered water from the semiconductor manufacturing process, flocculation / pressure levitation / filtration treatment or these treatments. Water to be purified by a combination of the above, wherein at least the most downstream biological treatment means has a fixed bed of the biological support, the biological support is activated carbon, and the treated water flows into at least one biological treatment means On the other hand, a chlorine-based chemical is added, the chlorine- based chemical is a combined chlorine agent, and the amount of carbon source added is the ratio (weight ratio) of the amount of C in water and the amount of N of urea (weight ratio) C / N Is an amount that is 100/50 to 100/2, and is chlorine-based The addition amount of the agent is characterized in that the total concentration of residual chlorine in the biological treatment water is an amount to be 0.02~0.1mg / L as Cl _2.

The water treatment method according to claim 3 is the water treatment method according to claim 2, wherein after adding the carbon source to the raw water, the water is passed through the first biological treatment means, and the chlorine-based chemical is added to the treated water of the first biological treatment means. After the addition, water is passed through the second biological treatment means.

The ultrapure water production method of the present invention (Claim 4 ) is characterized by treating the treated water of the water treatment method according to any one of Claims 1 to 3 with a primary pure water device and a secondary pure water device. It is characterized by producing ultrapure water.

  According to the water treatment method of the first invention (invention 1), the decomposition efficiency of urea decomposition is improved by adding a carbon source to the raw water and biologically treating it. Moreover, since the biological treatment means is composed of a fixed bed of the biological support carrier, the outflow of bacterial cells from the biological treatment means is suppressed more than in the case of a fluidized bed.

According to the water treatment method of the second invention (invention 2 ), since the carbon source is added to the raw water for biological treatment, the efficiency of urea decomposition removal is improved. In particular, since the raw water is passed through a plurality of biological treatment means in series and the biological treatment is performed a plurality of times, the urea decomposition and removal efficiency is further improved. Moreover, the microbial cell which flowed out from the biological treatment means on the upstream side is captured by the biological treatment means on the downstream side. Thereby, the outflow of a microbial cell is suppressed.

Thus if you passed through in series the raw water to a plurality of biological treatment means, by a fixed bed biological treatment means at least the most downstream outflow of bacterial cells Ru is suppressed.

It was added chlorine based agents in the raw water you improved urea decomposition efficiency by biological treatment.

  The details of the mechanism for improving urea efficiency when biologically treated in the presence of an oxidant and / or fungicide are not clear, but the preferred bacterial species and the oxidant in conditions where no oxidant and / or fungicide are present It is presumed that the preferred bacterial species differ from the preferred bacterial species in the presence of the fungicide and the latter preferred bacterial species contribute to the degradation of urea and urea derivatives. That is, bacterial species that efficiently decompose urea and urea derivatives are highly resistant to oxidizing agents and / or fungicides, and even under conditions where other oxidizing species are inactivated due to the presence of oxidizing agents and / or fungicides. It is presumed that priority is given to maintaining the activity and the decomposition efficiency of urea is improved.

  In addition, when the density | concentration of the oxidizing agent and / or fungicide in raw | natural water is too high, there exists a possibility that a microbial cell may reduce by the oxidizing action of an oxidizing agent and / or a fungicide, and a urea decomposition efficiency may fall. Moreover, when the density | concentration of the oxidizing agent and / or disinfectant in raw | natural water is too low, there exists a possibility that a urea decomposition efficiency may become low. Therefore, it is preferable to perform a reduction treatment for controlling the amount of the oxidizing agent and / or the bactericidal agent added or removing the oxidizing agent as necessary.

If the raw water contains a large amount of ammonium ions (for example, 100 to 400 μg / L), the decomposition of urea in the biological treatment means is inhibited. Water to be treated containing ammonium ions, it is Ru effective der adding a chlorine-based agents as an oxidizing agent and / or disinfectant. The details of this mechanism are not clear, but when ammonium ions react with chlorine to form chloramine (bound chlorine), it becomes difficult for organisms to take up this chloramine, resulting in organisms preferentially decomposing and removing urea. It is guessed.

It is a systematic diagram showing the biological treatment method according to the embodiment. It is a systematic diagram which shows the ultrapure water manufacturing method using the biological treatment method which concerns on embodiment.

  Hereinafter, the present invention will be described in more detail.

<First Embodiment>
The water treatment method according to the first embodiment is a water treatment method in which raw water containing urea is biologically treated, and after adding a carbon source to the raw water, water is passed through a biological treatment means having a fixed bed of a biological support carrier. Thus, biological treatment is performed.

  As water to be treated by this water treatment method, ground water, river water, city water, other industrial water, recovered water from semiconductor manufacturing processes, and the like are used. Moreover, what purified these water may be used. As this purification treatment, a pretreatment system in the production process of ultrapure water or a treatment similar thereto is suitable. Specifically, treatments such as flocculation, pressurized levitation, filtration, and combinations of these treatments are suitable.

  The urea concentration in the raw water (treatment target water) is preferably about 5 to 200 μg / L, particularly about 5 to 100 μg / L.

  As the carbon source to be added, an easily decomposable organic substance is suitable. Examples thereof include acetates such as acetic acid and sodium acetate, methanol, ethanol, acetone and the like. This carbon source is taken up by living organisms (bacteria) during biological treatment (assimilation), so it rarely flows out to the downstream side, but from the viewpoint of removing it by post-treatment when it flows out, such as acetate Thus, those that can be ionized in an aqueous solution and removed with an ion exchange resin or the like are preferable. The amount of carbon source added to the raw water is such that the ratio (weight ratio) of the amount of C in the water after addition and the amount of urea N (weight ratio) C / N is 100/50 to 100/2, particularly 100/10 to 100/5. Is preferred. Moreover, it is preferable to add suitably the nutrient source which activates biological activities, such as phosphorus, trace metals, such as iron, nickel, and cobalt, as needed.

  It is preferable to add an oxidizing agent and / or a bactericidal agent before introducing the raw water (treatment target water) into the biological treatment means. Thereby, urea decomposition efficiency improves. Moreover, urea decomposition efficiency improves more by processing so that the density | concentration of the oxidizing agent and / or disinfectant which remain | survive in biological treatment water may become a predetermined range.

  There is no restriction | limiting in particular in the kind of oxidizing agent and / or disinfectant to add, What can give priority to the bacterial species which decomposes | disassembles urea efficiently is used suitably. Specifically, chlorine-based oxidizing agents such as sodium hypochlorite and chlorine dioxide, and bonded chlorine agents (stabilized chlorine agents) such as monochloramine and dichloroamine are preferably used.

  As will be described later, when activated carbon is used as a carrier, free chlorine and bonded chlorine are decomposed by catalytic reaction of activated carbon, etc., but bonded chlorine is less likely to be decomposed even when it comes into contact with activated carbon. Therefore, when activated carbon is used as the carrier, it is preferable to use a combined chlorine agent as the oxidizing agent and / or bactericidal agent. In particular, as the oxidizing agent and / or the bactericidal agent, a linking chlorinating agent having a slow reaction with activated carbon, for example, a chlorinated oxidizing agent composed of a chlorinated oxidizing agent and a sulfamic acid compound is suitable.

The amount of the oxidizing agent and / or the bactericidal agent added is preferably such that the concentration of the oxidizing agent and / or the bactericidal agent remaining in the biologically treated water is not more than a predetermined concentration. This predetermined concentration varies depending on the type of oxidizing agent and / or bactericidal agent, but in the case of a chlorinated chemical, the total residual chlorine concentration in biologically treated water is 0.1 mg or less as Cl ₂ , for example, 0.02 to 0.1 mg / L. In particular, it is preferably 0.02 to 0.06 mg / L. Here, the total residual chlorine is a sum of free residual chlorine and combined residual chlorine, and the total residual chlorine concentration means the sum of the free residual chlorine concentration and the combined residual chlorine concentration. Oxidizing / sterilizing ability of free residual chlorine is higher than that of combined residual chlorine. Therefore, it is preferable that this free residual chlorine concentration is 0.02 mg / L as Cl ₂ or less. According to this chlorinated chemical, inhibition of urea decomposition by ammonium ions in the raw water is suppressed as described above.

  In addition, when the oxidant is originally contained in the water to be treated (for example, when all residual chlorine such as tap water is present) or when the oxidant is used in the pretreatment of the biological treatment, it remains as it is. By accepting the biological treatment, the biological treatment can be carried out in the presence of an oxidizing agent. However, when the oxidant concentration of the biological treatment feed water is low, the oxidant is consumed at an early stage in the biological treatment and cannot be in the presence of the oxidant. Moreover, when the concentration of the oxidizing agent and / or the bactericidal agent in the water to be treated is excessively high, the cells of the biological treatment means may be deactivated or killed by the bactericidal action of the oxidizing agent and / or the bactericidal agent. . Therefore, it is preferable to measure the concentration of the oxidizing agent and / or the bactericidal agent in the water to be treated, and to control the addition amount of the oxidizing agent and / or the bactericidal agent so that the concentration falls within a predetermined range, or in some cases, the reduction treatment. .

  There are no particular restrictions on the method for measuring the concentration of the oxidizing agent and / or bactericide, but for example, the method of measuring the chlorine concentration by the DPD (N, N-diethylphenylenediamine) method, polarography, absorptiometry, And a method of measuring the oxidation-reduction potential (ORP) of the inside and estimating the concentration of the oxidizing agent and / or the bactericidal agent based on this oxidation-reduction potential. Based on the measurement results, the reducing agent is added when the oxidizing agent and / or the bactericidal agent is excessive, and the oxidizing agent and / or the bactericidal agent is added when the oxidizing agent and / or the bactericidal agent is insufficient.

  In the present embodiment, the biological treatment system for biologically treating the water to be treated is preferably a fixed bed made of a biological carrier, particularly a downward flow type fixed bed with less bacterial cell outflow.

  When the biological treatment means is a fixed bed, it is preferable to wash the fixed bed as necessary. As a result, it is possible to prevent the occurrence of blockage of the fixed bed, mudballing, reduction in the decomposition and removal efficiency of urea, and the like due to the growth of organisms (fungal bodies). There is no particular limitation on this cleaning method. For example, backwashing, that is, flowing the cleaning water in the direction opposite to the direction of passing raw water to fluidize the carrier, discharging sediment out of the system, It is preferable to perform pulverization, exfoliation of a part of the organism, and the like.

  There are no particular restrictions on the type of carrier for the fixed bed, and activated carbon, anthracite, sand, zeolite, ion exchange resin, plastic molded products, etc. are used, but biological treatment is carried out in the presence of oxidizing agents and / or bactericides. In order to achieve this, it is preferable to use a carrier that consumes less oxidizing agent and / or fungicide. However, in the case where there is a possibility that a high concentration of oxidizing agent and / or bactericidal agent flows into the biological treatment means, a carrier such as activated carbon that can decompose the oxidizing agent and / or the bactericidal agent may be used. Thus, when activated carbon etc. are used, even if it is a case where the density | concentration of the oxidizing agent and / or disinfectant in to-be-processed water is high, it is prevented that a microbial cell is inactivated and killed.

The water flow rate to the biological treatment means is preferably about SV5 to 50 hr- ¹ . It is preferable that the temperature of water supplied to the biological treatment means is normal temperature, for example, 10 to 35 ° C., and the pH is almost neutral, for example, 4 to 8. Therefore, if necessary, a heat exchanger or pH adjustment is provided before the biological treatment means. It is preferable to provide an agent addition means.

  FIG. 1 (a) shows an example of the flow of the first embodiment (embodiment of claim 2). In FIG. 1 (a), raw water is treated water of a pretreatment system of an ultrapure water production apparatus. In FIG. 1 (a), this pretreatment system treated water is biologically treated after adding a combined chlorine agent together with a carbon source, and this biologically treated water is supplied to the primary pure water system.

<Second Embodiment>
The water treatment method according to the second embodiment is a water treatment method in which raw water containing urea is biologically treated, and after adding a carbon source to the raw water, the water is passed through a plurality of biological treatment means in series. It is characterized by performing. According to this embodiment, since raw water is passed through a plurality of biological treatment means in series and biological treatment is performed a plurality of times, urea decomposition and removal efficiency is further improved as compared with the case where the biological treatment is performed once.

  The carbon source is added to raw water upstream from the most upstream biological treatment means. However, a carbon source may be added to the inflow water to the biological treatment means in the second and subsequent stages. Thereby, the urea removal efficiency in the biological treatment means in the second and subsequent stages is improved.

  In the present embodiment, the biological treatment means for biologically treating the water to be treated is not particularly limited in the biological treatment means other than the final stage. Biological treatment means other than the final stage (for example, in the case of two-stage treatment, the first-stage biological treatment means) may use a biological treatment system such as a fluidized bed or a suspended activated sludge method. For the last stage, a biological treatment means of a fixed bed carrier type is preferable.

  When the fixed bed carrier method is employed, bacterial cells are prevented from flowing out and decreasing, and degradation efficiency is prevented. Further, it is possible to prevent the bacterial cells from flowing out and becoming a turbid load in the primary pure water system or the like on the rear stage side or causing a slime failure. As the biological treatment means used for biological treatment by this fixed bed carrier method, the downward flow type with less biological outflow is preferred. By using at least the most downstream biological treatment means as a fixed bed type, it is possible to suppress the outflow of organisms (fungal bodies) to the downstream side. When all the biological treatment means are fixed bed type, the outflow of the organism or the carrier is remarkably reduced, and the post-treatment load in the subsequent stage is remarkably reduced. Further, if the biological treatment means on the most downstream side is a fixed bed type and at least one of the other biological treatment means is a fluidized bed type, the fluidized bed biological treatment means improves the decomposition and removal efficiency of urea, and this Since the organism flowing out from the fluidized bed biological treatment means is sufficiently captured by the fixed bed biological treatment means on the downstream side thereof, the load on the downstream side of the biological treatment means is reduced.

  Even in the present embodiment, it is preferable to perform biological treatment in the presence of an oxidizing agent and / or a bactericidal agent in at least one biological treatment means, thereby improving urea decomposition efficiency. For example, when raw water is passed through two biological treatment means in series, the oxidizing agent and / or the bactericidal agent may be added to the first stage of the first stage biological treatment means. It may be added during the biological treatment means in the second stage, or may be added to both.

  In addition, you may vary the microflora of the microbial cell hold | maintained at each biological treatment means by adjusting the density | concentration of a carbon source, the density | concentration of an oxidizing agent, and / or a disinfectant to a different value for every biological treatment means. Thereby, the decomposition and removal of urea can be improved by biological treatment in various forms.

  FIG. 1 (b) shows an example of the second embodiment. In FIG. 1 (b), the raw water is treated water of the pretreatment system of the ultrapure water production apparatus. A carbon source is added to the pretreatment system treated water, water is passed through the first biological treatment means 1, and treated water from the first biological treatment means 1 is passed through the second biological treatment means 2. The biologically treated water of the second biological treatment means 2 is supplied to the primary pure water system.

  As described above, the first biological treatment means 1 is not limited to a fixed bed but may be a fluidized bed or the like. The second biological treatment means 2 is a fixed bed, and is preferably a downward flow fixed bed type.

  FIG. 1 (c) shows another example of the second embodiment. FIG. 1 (c) shows a case in which a combined chlorine agent is added as a bactericidal agent to the treated water from the first biological treatment means 1 in FIG. 1 (b). Other configurations are the same as those in FIG. 1 (b).

  FIG. 1 (d) shows still another example of the second embodiment. In FIG. 1 (d), a carbon source and an oxidizing agent (chlorine agent in this embodiment) are added to the treated water from the pretreatment system in FIG. 1 (c). Other configurations are the same as those in FIG. 1 (c).

  In addition, the other suitable structure in 2nd Embodiment is the same as that of 1st Embodiment.

  Next, a method for producing ultrapure water using the water treatment method of the present invention will be described with reference to FIG. In the ultrapure water production method shown in FIG. 2, raw water is treated by the pretreatment system 10, the biological treatment system 11, the ultrafiltration membrane separation (UF) device 12, the primary pure water treatment system 20, and the subsystem 30.

  The pretreatment system 10 includes agglomeration, pressure levitation (precipitation), a filtration (membrane filtration) device, and the like. In the pretreatment system 10, suspended substances and colloidal substances in the raw water are removed. The pretreatment system 10 can also remove high molecular organic substances, hydrophobic organic substances, and the like.

  A carbon source and, if necessary, an oxidizing agent and / or a bactericidal agent are added to the effluent from the pretreatment system 10, and the biological treatment system 11 performs the above biological treatment. The biological treatment system 11 may be any of FIGS. 1 (a) to (d). The ultrafiltration membrane separation device 12 installed on the downstream side of the biological treatment system 11 separates and removes microorganisms, carrier fine particles, and the like flowing out from the biological treatment system 11. However, the ultrafiltration membrane separation device 12 may be omitted.

  The primary pure water treatment system 20 includes a first reverse osmosis (RO) membrane separator 21, a second reverse osmosis (RO) membrane separator 22, and a mixed bed ion exchanger 23 in this order. . However, the apparatus constituting the primary pure water treatment system 20 is not limited to this. For example, a reverse osmosis apparatus, an ion exchange treatment apparatus, an electrodeionization exchange treatment apparatus, a UV oxidation treatment apparatus, etc. may be combined. Good.

  The sub system 30 includes a sub tank 31, a heat exchanger 32, a low-pressure ultraviolet oxidizer 33, a mixed bed ion exchanger 34, and a UF membrane separator 35 in this order. The treated water of the primary pure water treatment system 20 is introduced into the low-pressure ultraviolet oxidizer 33 through the sub-tank 31 and the heat exchanger 32 in the sub-system 30, and the contained TOC is ionized or decomposed. The organic matter is removed by the mixed bed ion exchanger 34 in the subsequent stage. The treated water of the mixed bed type ion exchange device 34 is further subjected to membrane separation treatment by the UF membrane separation device 35 to obtain ultrapure water. However, the apparatus constituting the subsystem 30 is not limited to this. For example, a degassing apparatus, a UV oxidation apparatus, an ion exchange apparatus (non-regenerative type), an ultrafiltration membrane apparatus (fine particles) (Removal) and the like may be combined.

  According to this method for producing ultrapure water, urea is sufficiently decomposed and removed in the biological treatment system 11, and therefore high purity ultrapure water can be produced efficiently. Further, when the biological treatment means at the final stage of the biological treatment system 11 is a fixed bed, it is possible to prevent the living organisms (fungal bodies), carrier fine particles, and the like from flowing out from the biological treatment system 11. Thereby, it is prevented that a microbial cell etc. becomes a turbid load by a back | latter stage primary pure water system etc., or causes a slime failure.

  According to this ultrapure water production method, the raw water is introduced into the pretreatment system 10 before the raw water is introduced into the biological treatment system 11 to remove turbidity in the raw water. For this reason, the decomposition and removal efficiency of urea in the biological treatment system 11 is prevented from being reduced due to turbidity, and an increase in pressure loss of the biological treatment system 11 due to the turbidity is suppressed. Moreover, according to this ultrapure water production method, the ultrafiltration membrane separation device 12, the primary pure water system 20, and the subsystem 30 are provided on the downstream side of the biological treatment system 11. Living organisms or carriers are favorably removed by the ultrafiltration membrane separation device 12, the primary pure water system 20, and the subsystem 30.

  In FIG. 2, the urea removal process is performed after the pretreatment, but the urea removal process may be performed before the pretreatment.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Example 1]
As shown in the flow of FIG. 1 (a), a carbon source, a combined chlorine agent, and a phosphorus source were added to raw water, and then water was passed through one stage of biological treatment means for biological treatment.

  The raw water used was city water (Nogi-cho water; average urea concentration 10 μg / L, average TOC concentration 500 μg / L) with reagent urea (manufactured by Kishida Chemical Co., Ltd.) added as necessary.

  Sodium acetate (manufactured by Kishida Chemical Co., Ltd.) was used as the carbon source, and slime control agent (bonded chlorine-based “Kuriverta IK110”) manufactured by Kurita Kogyo Co., Ltd. was used as the bound chlorine agent. As the phosphorus source, sodium dihydrogen phosphate (manufactured by Kishida Chemical) was used.

  As a biological treatment means, a granular activated carbon (“Crycol WG160, 10/32 mesh”, manufactured by Kurita Kogyo Co., Ltd.) as a biological carrier was filled into a cylindrical container and used as a fixed bed. In addition, as a biological treatment means, the one that has been habituated with the reagent urea and urea resolution has already been developed was used.

First, after adding sodium acetate, slime control agent, and sodium dihydrogen phosphate to city water (no reagent urea added) to the city water to the following concentrations, I passed water. The water flow rate SV was 20 / hr (water flow rate per hour ÷ filled activated carbon amount). The urea concentration was analyzed about the biological treatment water after water flow. The results are shown in Table 1.
Sodium acetate: 500 μg / L
Slime control agent: 0.2 mg / LasCl ₂
Sodium dihydrogen phosphate: 5 μg / L

  After 48 hours had passed, the reagent urea was added to the city water at a rate of 100 μg / L together with the above chemicals as simulated raw water, which was passed through the biological treatment means. This water flow was continued, and the urea concentration of the biologically treated water was analyzed at 6 hours, 12 hours and 24 hours, respectively. The results are shown in Table 1.

  The procedure for urea analysis is as follows. That is, first, the total residual chlorine concentration in the test water is measured by the DPD method, and is reduced with a considerable amount of sodium bisulfite. (Subsequently, the total residual chlorine is measured by the DPD method and it is confirmed that it is less than 0.02 mg / L.) Next, this reduced test water is used as an ion exchange resin (“KR-UM1”, Kurita). Kogyo Kogyo Co., Ltd.) was passed through SV50 / hr, deionized, concentrated 10 to 100 times with a rotary evaporator, and then the urea concentration was quantified by the diacetyl monooxime method.

In addition, pH adjustment was not implemented during the test period. The pH during the test period was 6.8-7.5. Since the water temperature of the city water during the test period was 24 to 26 ° C. (15 ° C. or higher), it was determined that the water temperature was not inhibited by the biological reaction, and the water temperature was not adjusted. Since the dissolved oxygen (DO) concentration of the biologically treated water during the test period was 3.8 to 4.5 mg / L, it was judged that there was no shortage of dissolved oxygen, and the dissolved oxygen concentration was not adjusted. During the test period, the total residual chlorine concentration in the biologically treated water was 0.05 to 0.1 mg / LasCl ₂ (the free residual chlorine concentration was 0.02 mg / LasCl ₂ or less).

Table 2 shows the FI (SDI) value of the biologically treated water after the lapse of 24 hours. Here, FI (Fouling Index) and SDI (Silt Density Index) are values used as a water supply index of a reverse osmosis membrane, and are mainly used as index values for measuring the degree of occurrence of turbid load and slime damage. . This FI (SDI) value is obtained by the following procedure. That is, using a membrane filter having a diameter of 47 mm and a nominal pore diameter of 0.45 μm, the entire amount is filtered at an operating pressure of 0.2 MPa (30 PDI). Then, from the time T ₁ (second) required for the initial 500 mL filtration and the time T ₂ (second) required for the 500 mL filtration after 15 minutes of filtration, the FI (SDI) value is calculated using the following equation. In addition, the RO water supply standard of this FI (SDI) value is less than 3-4.
FI (SDI) = (1−T ₁ / T ₂ ) / 15

[Comparative Example 1]
The simulated raw water was treated in the same manner as in Example 1 except that no carbon source was added. The results are shown in Tables 1 and 2.

[Reference Example 1]
The simulated raw water was treated in the same manner as in Example 1 except that the slime control agent (bonded chlorine agent) was not added and the slime control agent was not added during habituation. The results are shown in Tables 1 and 2.

[Example 2]
As the biological treatment means, the same biological treatment means as in Example 1 was used in two stages in series, and the same as in Example 1 except that no slime control agent was added to city water. Simulated raw water was treated. This flow corresponds to the flow in which not only the C source but also the phosphorus source is added to the water to be treated in FIG. 1 (b). The results are shown in Tables 1 and 2.

  As shown in Table 1, in Example 1, the change in the biologically treated water concentration before and after the change in the urea concentration (load fluctuation) in the raw water was very small. On the other hand, in Comparative Example 1 in which no carbon source was added, the urea concentration after 24 hours was still high due to load fluctuations (that is, after the raw water to be passed was switched from the non-urea added water to the simulated raw water), the load The followability to fluctuation was insufficient.

  In Reference Example 1 in which no combined chlorine agent was added, the quality of biologically treated water was slightly deteriorated compared to Example 1, but it was recognized that there was some degree of followability to load fluctuations. In Example 2 in which the two-stage biological treatment was performed, no change in the biological treatment water was observed before and after the load change, and the followability to the load change was extremely good.

  As shown in Table 2, in Examples 1 and 2 and Comparative Example 1 to which the slime control agent was added, the FI (SDI) value was 3 to 4, whereas in Reference Example 1 in which the slime control agent was not added, FI (SDI) ) Value was greater than 6. This result can be determined to be a result due to a decrease in the outflow amount of bacterial cells or inactivation of the bacterial cells, and it is determined that the burden on post-treatment can be reduced by performing biological treatment in the presence of a slime control agent.

DESCRIPTION OF SYMBOLS 1, 2 Biological treatment means 10 Pretreatment system 11 Biological treatment system 12 Ultrafiltration membrane separator 20 Primary pure water treatment system 30 Subsystem

Claims (4)

In a water treatment method for biologically treating raw water containing urea,
A water treatment method for performing biological treatment by adding water to a biological treatment means having a fixed bed of a biological carrier after adding a carbon source and a chlorine-based chemical to raw water,
The raw water is ground water, river water, city water, industrial water, recovered water from the semiconductor manufacturing process, water obtained by purifying these waters by coagulation / pressure levitation / filtration treatment or a combination of these treatments,
The biological carrier is activated carbon;
The chlorinated drug is a combined chlorinating agent;
The amount of carbon source added is such that the ratio (weight ratio) C / N of the amount of C in the water after addition and the amount of N in urea is 100/50 to 100/2,
Amount of chlorine agents, water treatment method characterized by total residual chlorine concentration in the biological treatment water is an amount to be 0.02~0.1mg / L as Cl _2. In a water treatment method for biologically treating raw water containing urea,
A water treatment method of performing biological treatment by adding water in series to a plurality of biological treatment means after adding a carbon source to raw water,
The raw water is ground water, river water, city water, industrial water, recovered water from the semiconductor manufacturing process, water obtained by purifying these waters by coagulation / pressure levitation / filtration treatment or a combination of these treatments,
At least the most downstream biological treatment means has a fixed bed of biological support,
The biological carrier is activated carbon;
Add chlorinated chemicals to the treated water flowing into at least one biological treatment means,
The chlorinated drug is a combined chlorinating agent;
The amount of carbon source added is such that the ratio (weight ratio) C / N of the amount of C in the water after addition and the amount of N in urea is 100/50 to 100/2,
Amount of chlorine agents, water treatment method characterized by total residual chlorine concentration in the biological treatment water is an amount to be 0.02~0.1mg / L as Cl _2. In Claim 2 , after adding a carbon source to raw | natural water, it lets water flow to the 1st biological treatment means, and after adding a chlorinated chemical | medical agent with respect to the treated water of this 1st biological treatment means, the 2nd biological treatment means A water treatment method characterized by passing water through. Ultrapure water production characterized in that ultrapure water is produced by treating the treated water of the water treatment method according to any one of claims 1 to 3 with a primary pure water device and a secondary pure water device. Method.

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