JP5059469B2 - Method for treating treated water containing iron - Google Patents

Description

  The present invention is a membrane separation treatment tank in which a separation membrane is installed, in particular, groundwater, spring water, treated water containing manganese such as underground water, or activated sludge drainage to which an iron-based flocculant is added, The present invention relates to a method for treating organic wastewater such as domestic wastewater.

  Conventionally, iron contained in groundwater, spring water, underground water, manganese, or iron contained in industrial wastewater has been a problem. Iron is an essential element for the human body, but if it exceeds a certain amount, it becomes harmful, and the water quality standard is set at 0.3 mg / L or less.

  As a method for solving such a problem, a method of solid-liquid separation by oxidizing water to be treated to form insoluble iron oxide or iron hydroxide is widely practiced. As a solid-liquid separation method, sand filtration, coagulation sedimentation, or the like is performed. However, in such a solid-liquid separation method, the SS (floating matter) concentration of the treated water to be obtained tends to be high, protozoa such as Cryptosporidium are not removed, and a vast There is also a facility problem that requires a site.

  Therefore, there are various methods for solid-liquid separation of water to be treated containing insoluble iron oxide and iron hydroxide using a separation membrane module (membrane separation device) equipped with a separation membrane such as a microfiltration membrane and an ultrafiltration membrane. It is being considered. When water to be treated is filtered using such a separation membrane, SS (floating matter) is hardly contained and safe treated water can be obtained.

However, when treating the water to be treated using the separation membrane, there are cases where solid-liquid separation by the separation membrane becomes difficult. That is, the following cases occur when the membrane separation treatment is performed using a microfiltration membrane and an ultrafiltration membrane having a small fraction pore diameter over a long period of time.
Case (1): Deposits gradually accumulate on the outer membrane surface side (treated water side), and the transmembrane pressure difference of the separation membrane increases.
Case (2): Microorganisms such as iron bacteria (iron bacteria) gradually grow on the inner surface side (treated water side), and the transmembrane pressure difference of the separation membrane increases.

  As a method for suppressing an increase in transmembrane pressure difference due to accumulation of deposits on the outer surface side (treated water side) as in the case (1), an air diffuser is provided at the lower part of the separation membrane and air bubbling is performed. The method and the method of performing physical washing regularly, such as the backwashing by the reverse water flow of a treated water, are common, and the effect is acquired.

  Further, in addition to the removal of deposits on the outer surface side (treated water side) as in the case (1), iron existing on the inner surface side (treated water side) as in the case (2). As a method for removing microorganisms such as bacteria (iron bacteria), there is a cleaning method in which a submerged membrane cartridge is taken out of a processing tank and immersed in a chemical cleaning tank for cleaning.

Alternatively, in the state where the submerged membrane cartridge is immersed in the activated sludge treatment tank, first, an oxidizing agent for decomposing an organic substance as a first cleaning chemical solution is injected into the submerged cartridge through the permeate flow path. The state in which the cleaning chemical solution permeates the filtration membrane of the submerged membrane cartridge from the permeate side to the liquid to be treated at a very low flow rate is maintained for an appropriate time, and after the first cleaning chemical solution is discharged, the second The cleaning chemical solution is characterized by injecting an acid that dissolves an inorganic substance, and maintaining the state in which the second cleaning chemical solution permeates the filtration membrane of the immersion membrane cartridge from the permeate side to the liquid to be treated at a very low flow rate for an appropriate time. A method for cleaning a submerged membrane cartridge in a tank is described (see Patent Document 1).
JP-A-8-266875

  However, in physical cleaning methods such as bubbling and backwashing, the propagation of microorganisms such as iron bacteria (iron bacteria) present on the inner surface of the membrane (treated water side) as in case (2) It was difficult to suppress.

  Further, the method described in Patent Document 1 is very effective as a method for cleaning the inner and outer surfaces of the membrane, and it is possible to return the transmembrane pressure difference to an initial state to some extent. Since the agent and the acid cleaning chemical solution permeate, it is not suitable when the treated water is used for drinking water, and it is necessary to replace the treated water in the membrane filtration treatment tank, resulting in a loss in operating time. Further, when the water to be treated is activated sludge, there is a possibility that the microorganisms in the sludge may be adversely affected.

  The present invention has been made in view of such a situation. Specifically, in the case of treating the treated water containing iron, in particular, by the membrane filtration treatment tank in which the separation membrane is installed, the separability of the treated water is improved. It aims at providing the processing method which suppresses effectively the raise of the transmembrane differential pressure | voltage of the separation membrane by deterioration.

  As a result of intensive studies, the present inventors have conducted a method for treating water to be treated containing iron by a membrane filtration treatment tank in which a separation membrane is installed. In this method, iron bacteria (iron bacteria) on the inner surface side (treated water side) are used. The present invention has been completed by conceiving that the propagation of microorganisms such as the above can be suppressed and the effect of suppressing the transmembrane pressure difference can be obtained.

That is, the present invention relates to a method for treating water to be treated containing iron in a membrane filtration treatment tank in which a microfiltration membrane or an ultrafiltration membrane (hereinafter referred to as “separation membrane”) is installed . The concentration of soluble iron is measured, and when the concentration range exceeds 0.1 mg / L, an agent that lowers the iron concentration is added so that the concentration range of the soluble iron is 0.1 mg / L or less. It is a processing method of the to-be-processed water which comprises managing a density | concentration. The amount of the chemical added to the water to be treated is desirably 1 mmg or more and 200 mmg or less per liter of water to be treated.

  According to the present invention, when water to be treated containing iron is treated by a membrane filtration treatment tank in which a separation membrane is installed, it is propagated on the inner surface side (treated water side) by adopting the above-described configuration. Since the increase in the transmembrane pressure difference of the separation membrane caused by microorganisms such as iron bacteria (iron bacteria) can be effectively suppressed, continuous and stable membrane filtration treatment and membrane water treatment are carried out. it can.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
FIG. 1 shows an example of a treatment apparatus preferably used in the treatment method of the present invention, which is an inorganic wastewater such as groundwater, spring water, underground water, or the activity to which an iron-based flocculant is added. A membrane filtration treatment tank 1 in which organic wastewater such as sludge wastewater and domestic wastewater is supplied as treated water, and a membrane separation device 2 installed in the membrane filtration treatment layer 1 and provided with a separation membrane are provided. Configured. In this treatment apparatus, treated water is obtained by solid-liquid separation, that is, membrane treatment in the membrane separation apparatus 2.

  In addition, in the membrane filtration treatment tank 1 of this example, a chemical tank 3 in which chemicals such as additives, adsorbents, oxidants and the like are used to suppress an increase in the transmembrane pressure difference of the separation membrane, and chemicals A chemical supply device including a liquid feed pump 4 for supplying the membrane filtration treatment tank 1 and an intermittent timer 5 for controlling the operation time of the liquid feed pump 4 is connected. Further, an air diffuser 6 is installed below the membrane separation device 2 so that air can be diffused (air bubbling) toward the separation membrane.

  When the water to be treated is groundwater, spring water, underground water, or river water, the turbidity concentration is 0.1 to 2,000 degrees, and it is preferable to be in the range of approximately 100 degrees or less. When the water to be treated is organic wastewater such as activated sludge, domestic wastewater, and industrial wastewater, the MLSS concentration is preferably 3,000 to 20,000 mg / L.

  Examples of the shape of the separation membrane included in the membrane separation device 2 include a flat membrane type, a hollow fiber membrane type, a tubular membrane type, a bag-like membrane type, and the like. The hollow fiber membrane type is preferable from the viewpoint that a large membrane area per unit volume can be obtained.

  Examples of the material of the separation membrane include cellulose, polyolefin (polyethylene, polypropylene), polysulfone, polyvinyl alcohol, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, ceramic, etc. In view of the properties, chemical resistance, etc., it can be selected as needed.

  Moreover, there is no restriction | limiting also in the hole diameter of a separation membrane, Although it can set suitably, the range of 0.001-1 micrometer is preferable. By setting the pore diameter to 0.001 μm or more, a sufficient filtration flow rate tends to be obtained without increasing the pressure during filtration. More preferably, it is 0.1 μm or more. In addition, by setting the pore diameter to 1 μm or less, impurities are difficult to permeate the membrane, and there is a tendency that high quality treated water can be obtained. Furthermore, it is preferable to use a membrane generally called a microfiltration membrane.

  As a chemical | drug | medicine thrown into the chemical | medical agent tank 3, the separation membrane by microorganisms, such as an iron bacterium (iron bacteria) which propagates in the membrane inner surface side (treated water side) by throwing into the membrane filtration processing tank 1, is carried out. Any agent that can suppress an increase in transmembrane pressure difference may be used, but an additive, an adsorbent, or an oxidant that can reduce the concentration range of soluble iron in the membrane filtration tank to 0.1 mg / L or less is suitable. is there.

  Examples of additives include commercially available phosphoric acid, phosphate compounds (sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, etc.), and aqueous solutions thereof, sodium hydroxide, potassium hydroxide. , Magnesium hydroxide, calcium hydroxide, lime, and aqueous solutions thereof. By appropriately selecting and using one or more of these, it is possible to generate iron phosphate or iron hydroxide that is insoluble in water. Furthermore, the combined use with a flocculant (inorganic flocculant, polymer flocculant) or the like is more preferable because the soluble iron concentration can be 0.05 mg / L or less.

  Examples of the adsorbent include manganese sand, a cation exchange resin, and a chelate resin that are generally commercially available and used. One or more of these can be selected and used as appropriate.

  Examples of the oxidizing agent include a commercially available sodium hypochlorite aqueous solution and ozone water. In groundwater, spring water, underground water, etc., divalent soluble iron is dissolved in water and can be oxidized to produce water-insoluble iron oxide and iron hydroxide (trivalent iron). it can.

  When treating the water to be treated with the treatment apparatus as shown in FIG. 1, the water to be treated is periodically sampled, the soluble iron concentration is measured, and the measured iron concentration is within a specific range. By performing the differential pressure suppressing step of the separation membrane, it can be effectively carried out for a long time.

  When the concentration of soluble iron in the membrane filtration treatment tank 1 is 0.1 mg / L or less, the distance between the membranes of the separation membrane by microorganisms such as iron bacteria (iron bacteria) that propagate on the membrane inner surface side (treated water side) The increase in the differential pressure becomes gradual, and there is a tendency for stable membrane treatment operation.

  When the soluble iron concentration in the membrane filtration tank exceeds 0.1 mg / L and the state continues, microorganisms such as iron bacteria (iron bacteria) are generated on the membrane surface (treated water side). There is a tendency to start breeding. The inner surface of the membrane (treated water side) is probably because there is little dissolved oxygen. Especially when the shape of the separation membrane is hollow fiber membrane type, tubular membrane type, or bag-like membrane type, iron bacteria (iron bacteria), etc. There is a tendency for such microorganisms to easily grow. When the soluble iron concentration in the membrane filtration tank exceeds 0.1 mg / L, the addition of the additive, adsorbent or oxidant is started and the difference is less than 0.1 mg / L. It is preferable for suppressing the increase in pressure, and tends to be capable of membrane treatment of water to be treated stably and continuously.

  As a method for lowering the soluble iron concentration in the membrane filtration tank to 0.1 mg / L or less, the chemical supply device is operated, and the additive, adsorbent, or oxidizing agent is intermittently or continuously added to the water to be treated. It is preferable to add them automatically. In addition, what is necessary is just to set the intermittent timer 5 suitably when adding a chemical | medical agent intermittently, and it is not necessary to use the intermittent timer 5 when adding continuously. Moreover, in carrying out such a step of increasing the differential pressure suppression, it is not necessary to stop the filtration operation by the membrane separation device 2, and it is possible to improve the separability online while treating the water to be treated. I can do it.

  While the solid-liquid separation treatment is functioning well in the membrane filtration treatment tank 1, the membrane treatment by the membrane separation device 2 also functions well and can stably treat the water to be treated. As mentioned above, when the concentration of soluble iron increases due to changes in the water to be treated, microorganisms such as iron bacteria (iron bacteria) tend to propagate on the inner surface of the membrane (treated water side). The differential pressure gradually rises and the solid-liquid separation process is hindered. The present inventors have a correlation between such a transmembrane pressure difference and the soluble iron concentration in the membrane filtration tank 1, and suppress the increase in the differential pressure using the value of the soluble iron concentration as an index. It has been found that a high effect can be obtained by suppressing the increase in the differential pressure. That is, by performing the differential pressure increase suppression process at an appropriate timing in this manner, the separability of the water to be treated can be maintained and improved, and the separation membrane is blocked, particularly the membrane inner surface (treated water side). It is possible to suppress an increase in the differential pressure due to, and prevent a decrease in the amount of treated water. In addition, by performing the differential pressure increase suppression process at an appropriate timing in this way, chemicals such as additives, adsorbents, and oxidants can effectively act, not only suppressing excessive addition, but also chemical cleaning of the membrane. Not only can the period be kept longer, but also loss of operating time and the use of cleaning chemicals can be suppressed.

  The iron bacterium (iron bacterium) referred to in the present invention refers to a group of bacteria that acquire energy by oxidizing bivalent iron to trivalent iron and proliferate. Gallionella ferruginea, Leptothrix ochracea, Crenothrix polyspora, Clonothrix Examples include fusca, Toxothrix trichogenes, and the genus Siderocapsa and Siderocystis ("Waterworks in Japan-Photos and Explanations", Japan Waterworks Association, 1995, P169-176). As a method for confirming iron bacteria (iron bacteria), it can be easily observed in a cotton-like or filamentous form by SEM observation or the like.

  These iron bacteria (iron bacteria) generally inhabit groundwater with high iron concentration, spring water, underground water, etc. In some cases, ferrous chloride, polyiron sulfate, When water treatment is performed by adding polysilica iron or the like, there are cases where it adheres to and propagates on the wall of a coagulation sedimentation tank, or a membrane filtration tank, piping, or the like. Examples of damage caused by iron bacteria (iron bacteria) include red water, odor (golden odor), iron pipe blockage, and equipment failure due to slime formation.

  As a method for measuring the concentration of soluble iron in the membrane filtration tank, it is first necessary to remove solids such as turbidity and SS (floating matter) as pretreatment. The iron concentration in the treated water after membrane filtration or the treated water is dissolved by measuring the iron concentration in the filtrate filtered using a membrane filter having a size of 0.45 μm (nominal pore size) or less. The ionic iron concentration can be measured. As a method for quantitative determination of iron, phenanthroline spectrophotometry, flame atomic absorption, flameless atomic absorption, or ICP emission spectrometry can be used. JIS K 0101 Industrial Water Test Method (published by the Japanese Standards Association) ) Can be used. Among these, it is preferable to use a flameless atomic absorption method in which the lower limit of quantification of iron is 5 μg / L or an ICP emission analysis method in which the lower limit of quantification is 20 μg / L.

  As a method for managing the concentration of soluble iron in the membrane filtration tank, if the quality of the water to be treated is stable, the soluble iron concentration can be measured once a week or once a month. Although it is good, when there is a change in the iron concentration in the water to be treated, such as when an iron-based flocculant is added, frequently measure the soluble iron concentration, for example about 2 to 3 times a week, and It is preferable to perform the differential pressure increase suppression process at a proper timing.

  As a method for lowering the soluble iron concentration in the membrane filtration tank to 0.1 mg / L or less, as described above, the drug supply device is operated and the drug (additive, adsorbent, oxidant, etc.) is applied. A method of intermittently or continuously adding to the treated water is preferable. Although there is no restriction | limiting in particular in the quantity of the chemical | medical agent added here, It is preferable to add so that the density | concentration per to-be-processed water may be 1 mg / L or more. Thus, by making the density | concentration of the chemical | medical agent per to-be-processed water be 1 mg / L or more, it exists in the tendency for the separability of to-be-processed water to be maintained and improved favorably. More preferably, it is 5 mg / L or more. Moreover, it is preferable that the density | concentration of the chemical | medical agent per to-be-processed water shall be 200 mg / L or less. This is because even if the drug concentration is excessively increased, the effect of addition tends not to change, and there is a possibility that the separation membrane may be clogged or deteriorated.

  Addition of such chemicals suppresses the growth of microorganisms such as iron bacteria (iron bacteria) on the inner surface of the membrane (treated water side), stabilizes the transmembrane pressure difference of the separation membrane over the long term, It is suitable to carry out until the time when the soluble iron concentration in the water to be treated is improved, and can be set as appropriate according to the water treatment conditions, the type of water to be treated, and the like.

  According to the above treatment method, it is possible to grasp the increase in the transmembrane pressure difference of the separation membrane due to the propagation of microorganisms such as iron bacteria (iron bacteria) on the inner surface side (treated water side), and to suppress the increase in the differential pressure. The process can be carried out effectively at an appropriate timing. Therefore, this method has characteristics of the water to be treated, such as a treatment apparatus that treats the water to be treated using a plurality of membrane filtration treatment tanks 1 and a treatment apparatus that has an anaerobic tank or an anaerobic tank as the membrane filtration treatment tank 1. This is particularly effective when water treatment is performed using an apparatus that is easily deteriorated.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Test Example 1)
Using the treatment apparatus shown in FIG. 1, the treatment of domestic wastewater was performed at Mitsubishi Rayon Co., Ltd. Drainage Experiment Station under the following conditions.

The flux and hydraulic residence time of the membrane filtration tank 1 are 0.8 m ³ / m ² / Day and 5 hours, respectively. As the separation membrane of the membrane separation device 2, an element in which a hollow fiber membrane made of polyvinylidene fluoride for microfiltration having a nominal pore diameter of 0.4 μm was developed and fixed in a screen shape was used.

  The seed sludge at the start-up of the treatment apparatus was collected from another membrane-separated activated sludge treatment apparatus installed in the drainage test station, and was provided so that the activated sludge concentration was approximately 10,000 mg / L. During operation, the sludge was drawn out so as to be 10,000 to 12,000 mg / L.

The filtration operation of the membrane separation device 2 was an intermittent operation in which suction was performed for 7 minutes and stopped for 1 minute. At this time, air diffused from the air diffuser 6 installed below the membrane separation device 2 was always performed. The amount of air diffused was 100 Nm ³ / m ² · hr per projected area of the hollow fiber membrane part.

  In the measurement of the soluble iron concentration in the membrane filtration treatment tank, the iron concentration in the treated water after membrane filtration was quantified by ICP emission spectrometry once a week.

  At the start of the test, the soluble iron concentration in the treated water was 0.02 mg / L or less, and the transmembrane pressure difference was 5 kPa or less.

(Test Example 2)
In Test Example 1, when 6 months passed from the start of the test, chemical cleaning of the membrane was performed, and the transmembrane pressure difference was returned to the initial state (5 kPa or less). Thereafter, ferric chloride was continuously added to the membrane filtration treatment tank 1 so as to be 1 mg-Fe / L per water to be treated, and the operation was resumed. One week after the start of ferric chloride addition, the iron concentration in the treated water was 0.2 mg / L. Thereafter, the concentration was not controlled so that the iron concentration in the treated water was 0.1 mg / L or less, and the operation was continued.

(Example)
As a result of measuring the iron concentration in the treated water once a week for 6 months from the start of the test, it was always 0.1 mg / L or less. During this time, the transmembrane pressure difference was 5 kPa. When the membrane was sampled and the surface inside the membrane (treated water side) was observed by SEM, almost no deposits were observed, and filamentous bodies such as iron bacteria (iron bacteria) were not observed.

(Comparative example)
Subsequent to Test Example 1, Test Example 2 was conducted for 6 months. As a result of measuring the iron concentration in the treated water once a week, it sometimes exceeded 0.1 mg / L. The transmembrane pressure difference was 12 kPa. When the membrane was sampled and the inner surface (treated water side) was observed with an SEM, it was confirmed that fine filamentous microorganisms were attached and that iron bacteria (iron bacteria) were growing. .

It is a schematic block diagram which shows an example of the processing apparatus used with the processing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane filtration processing tank 2 Membrane separation device 3 Drug tank 4 Liquid feed pump 5 Intermittent timer 6 Air diffuser

Claims (2)

In a method of treating water to be treated containing iron with a membrane filtration tank equipped with a microfiltration membrane or an ultrafiltration membrane , the concentration of soluble iron in the membrane filtration tank is measured, and the concentration range is 0.1 mg / A treatment method of water to be treated comprising, when L is exceeded, introducing an agent that lowers the iron concentration and managing the iron concentration so that the concentration range of the soluble iron is 0.1 mg / L or less.   The processing method of the to-be-processed water of Claim 1 including making the addition amount of the said chemical | medical agent added to to-be-processed water be 1 mmg or more and 200 mmg or less per liter of to-be-processed water.

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