JP2006055766A - Organic wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which predicts a deterioration in separability of liquid to be treated to improve the separability beforehand when the solid-liquid separation of organic wastewater is carried out by using a separation membrane. <P>SOLUTION: In the organic wastewater treatment method, when the solid-liquid separation of the organic wastewater is carried out by using the separation membrane installed in a microbiological treatment tank, a coagulant is added at the time when 10 to 40-day moving average temperature difference between water temperature in the microbiological treatment tank equipped with the separation membrane and air temperature in environment where the tank is installed is increased to 4°C or higher. In the organic wastewater treatment method, the coagulant is added when the filtration flow rate of the liquid to be treated by using filter paper reaches 10 ml/5 min or lower, or when a sugar concentration in the liquid to be treated reaches 30 mg/L or higher. In the organic wastewater treatment method, the coagulant is continuously or intermittently added into the microbiological treatment tank so that its concentration in 1-day treatment waste water reaches 1 mg/L or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic wastewater treatment method in which solid-liquid separation is performed by a separation membrane installed in a microorganism treatment tank.

  Conventionally, in organic wastewater treatment, a method of performing purification using activated microorganisms (activated sludge treatment) and further separating and purifying solid content has been widely used. For separation of the solid and liquid components, sand filtration, gravity precipitation, and the like are performed. However, solid-liquid separation by these methods has disadvantages that the SS concentration of the treated water to be obtained tends to be high and a large site is required.

  As a method for solving such inconvenience, in recent years, various methods for performing solid-liquid separation of a liquid to be treated using a separation membrane module provided with a separation membrane such as a microfiltration membrane and an ultrafiltration membrane have been studied. Yes. When the treatment liquid is filtered using the separation membrane, treated water containing almost no SS can be obtained.

  However, in the following cases, solid-liquid separation with a separation membrane may be difficult. That is, (1) When processing using microfiltration membranes and ultrafiltration membranes with a small fractional pore size, deposits on the membrane surface are accumulated little by little by long-term membrane separation treatment, and the differential pressure rises. appear. (2) When the BOD (biochemical oxygen demand) load suddenly increases or when environmental stresses are applied to microorganisms, such as during low temperatures such as in winter, the liquid to be treated is sufficiently decomposed temporarily by microorganisms. This is a case where the filtration inhibiting component of the separation membrane remains and the separation property of the liquid to be treated deteriorates.

  In the case of (1) above, it is necessary to periodically perform chemical cleaning of the separation membrane. In the case where the filtration inhibiting component is present in the liquid to be treated as in (2) above, when the filtration treatment is performed under the same conditions as in the case where the filtration inhibiting component is not present, clogging of the separation membrane proceeds, Since a rapid increase in the differential pressure is observed, it is necessary to frequently perform a cleaning operation for recovering the filtration performance of the separation membrane. If the filtration speed of the separation membrane is lowered, it is possible to alleviate the clogging of the separation membrane and suppress a sudden increase in the differential pressure, but in this case, there arises a problem that the processing capacity is reduced.

In order to improve the separability of the liquid to be treated, it is known to add an adsorbent such as activated carbon to adsorb and remove filterability-inhibiting components (see Patent Document 1), but it is not as common as organic wastewater. Even if an adsorbent such as activated carbon is added to a system containing various substances, it is difficult to remove only substances that impede filterability, so a very large amount of adsorbent is necessary to obtain a sufficient effect. There was a tendency to become necessary. Further, since the adsorption capacity of the adsorbent is saturated, this frequent renewal is necessary to maintain the effect, which is economically disadvantageous.
As a method for removing the filtration inhibiting component, it is known that the liquid to be treated is separated into a suspension component and a liquid containing the filtration inhibiting component by a flocculant (see Patent Document 2). It was difficult to decide the right time.

JP-A-10-309567 JP 2002-1333 A

  The present invention has been made in order to solve such problems. When performing solid-liquid separation treatment of organic wastewater using a separation membrane, the separation property of the liquid to be treated due to the presence of a filtration inhibiting component is improved. It provides a way to predict deterioration and improve it in advance.

As a result of intensive studies, the present inventors have found that the relationship between the water temperature in the microorganism treatment tank and the temperature of the installation environment of the tank is closely related to the appropriate addition timing of the flocculant, and completed the present invention. .
That is, in the present invention, when performing solid-liquid separation using a separation membrane installed in a microorganism treatment tank, a moving average of the water temperature in the microorganism treatment tank in which the separation membrane is installed and the temperature of the environment in which the tank is installed is 10 to 40 days. The present invention relates to a method for treating organic wastewater in which a flocculant is added when a temperature difference is increased to 4 ° C. or more.

According to the present invention, when performing solid-liquid separation treatment of organic wastewater using a separation membrane, it is possible to predict deterioration of separability due to the presence of a filtration inhibiting component and improve it in advance. It is possible to prevent an increase in the differential pressure of the membrane and a reduction in the amount of wastewater treated due to the blockage of the membrane, and it is possible to avoid adding a flocculant more than necessary.
In the case of having a plurality of biological reaction tanks, in the case of having an anaerobic tank or an anaerobic tank, etc., the present invention is particularly effective in wastewater treatment having a process in which the properties of the liquid to be treated are likely to deteriorate.

  Hereinafter, the present invention will be described with reference to the drawings according to an embodiment.

FIG. 1 is a schematic view showing a method for treating organic waste water according to the present embodiment.
In the microorganism treatment tank 1, the liquid to be treated is subjected to purification treatment with activated sludge. A plurality of microbial treatment tanks 1 can be installed according to the purpose.

  Next, a solid-liquid separation process is performed by the membrane separation device 2 installed inside the microorganism treatment tank 1. The activated sludge concentration (MLSS) in the microorganism treatment tank 1 is preferably in the range of 3,000 to 15,000 mg / L. This is because by setting it as 3,000 mg / L or more, it exists in the tendency which can prevent the early obstruction | occlusion of the separation membrane by an undecomposed component. More preferably, it is 5,000 mg / L or more, and still more preferably 7,000 mg / L or more. Moreover, it is because it exists in the tendency which can avoid the nonuniformity of the air bubbling to a separation membrane and the early obstruction | occlusion of a separation membrane resulting from the viscosity increase of activated sludge by setting it as 15,000 mg / L or less. More preferably, it is 12,000 mg / L or less, More preferably, it is 10,000 mg / L or less.

  Examples of the shape of the separation membrane used in the present invention include a flat membrane type, a hollow fiber membrane type, a tubular membrane type, and a bag-like membrane type. These shapes can be appropriately selected according to need, but the hollow fiber membrane type is preferable from the viewpoint that a large membrane area per unit volume can be obtained when unitized.

  Examples of the material of the separation membrane used in the present invention include cellulose, polyolefin, polysulfone, polyvinyl alcohol, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, and ceramic. . These materials can be appropriately selected as necessary from the viewpoint of processability, chemical resistance, and the like.

The pore diameter of the separation membrane used in the present invention can be appropriately selected and is not particularly limited, but is preferably in the range of 0.001 to 1 μm. This is because 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. Further, by setting the pore diameter to 1 μm or less, impurities are difficult to permeate the membrane, and a high water quality filtrate tends to be obtained.
In the present invention, it is preferable to use a membrane generally called a microfiltration membrane.

  While the microbial treatment is functioning well in the microbial treatment tank 1, the membrane separation process also works well and the water treatment can be carried out stably. However, due to the above-mentioned causes, the microbial treatment tank 1 When the property of the liquid to be treated deteriorates, the membrane differential pressure rises rapidly with rapid clogging of the separation membrane, causing trouble in the solid-liquid separation treatment.

  However, the separability of the liquid to be treated can be maintained and improved by grasping the appropriate timing for adding the flocculant at an early stage. As a result, the clogging of the separation membrane can be suppressed, and a reduction in the amount of wastewater treated due to the clogging of the separation membrane can be prevented. Further, since the flocculant can be added at a time when the flocculant acts effectively, excessive use of the flocculant can be suppressed.

  The addition time of the flocculant in the present invention is when the moving average temperature difference between the water temperature in the microorganism treatment tank provided with the separation membrane and the temperature of the installation environment of the tank is expanded to 4 ° C. or more.

  The moving average temperature difference for 10 to 40 days in the present invention is the difference between the moving average water temperature for 10 to 40 days in the microorganism treatment tank provided with the separation membrane and the moving average temperature for 10 to 40 days in the setting environment of the tank. Each moving average has the same reference period, and is calculated based on daily average data of water temperature or air temperature. When data is missing on a specific day, the moving average can be obtained by ignoring the missing part. However, if there is a large omission, it is difficult to determine the temperature difference and there is a possibility that confirmation of an appropriate timing for adding the flocculant may be delayed.

  The moving average in the present invention needs to be 10 to 40 days. This is because, if it is less than 10 days, it is difficult to obtain the above-mentioned average temperature difference because the temperature variation from day to day cannot be absorbed. Preferably, it is 20 days or longer. Further, if it exceeds 40 days, the temperature change is excessively averaged, and therefore, confirmation of an appropriate timing for adding the flocculant tends to be delayed. Preferably it is 30 days or less.

  The moving average temperature in the present invention is preferably based on data obtained when the water temperature in the microorganism treatment tank is 20 ° C. or lower. This is because when the water temperature in the microorganism treatment tank is 20 ° C. or lower, the clogging of the separation membrane due to deterioration of the properties of the liquid to be treated tends to proceed, so that the addition of the flocculant tends to be more effective. .

In the present invention, it is necessary to add a flocculant when the above average temperature difference is expanded to 4 ° C. or more.
This is because when the temperature difference is less than 4 ° C., the properties of the liquid to be treated do not deteriorate so much and the clogging of the separation membrane does not progress, so the addition of the flocculant is not efficient. This is because the membrane clogging may occur due to the unreacted flocculant, which may increase the membrane differential pressure. Preferably, it is when it expands to 4-7 degreeC. This is because by setting the above-mentioned average temperature difference to 7 ° C. or less, the coagulant tends to be added before the deterioration of the properties of the liquid to be treated becomes significant.

The addition time of the flocculant in the present invention is preferably a period in which the moving average water temperature in the microorganism treatment tank and the moving average temperature in the installation environment of the tank are decreasing.
In addition, the next flocculant addition time after the implementation of the present invention passes through a period in which the water temperature in the microbial treatment tank exceeds 20 ° C., and again the moving average water temperature in the water microbial treatment tank and the moving average temperature in the installation environment of the tank. Is preferable, and the above-mentioned average temperature difference is preferably expanded to 4 ° C. or more.
For example, when an unused separation membrane is installed in a microorganism treatment tank and solid-liquid separation is newly started, the water temperature in the microorganism treatment tank is 20 ° C. or lower, and the above-mentioned moving average water temperature and moving average air temperature When the difference is already 4 ° C. or higher, a flocculant may be added when the difference is confirmed.

  The filtration flow rate of the liquid to be processed by the filter paper and the sugar concentration in the liquid to be processed can be used as a standard for deterioration of the separation performance of the liquid to be processed. In the present invention, it is preferable to add a flocculant when the flow rate of the liquid to be treated is 10 ml / 5 min or less, or the sugar concentration in the liquid to be treated is 30 mg / L or more.

  The filtration flow rate is a measured value of the filtration amount after 5 minutes when a sample of 50 ml is poured into a folded 5C185 mm filter paper ("Study on sludge filterability in submerged separation activated sludge method" (32nd Water According to the method described in Environmental Society: 2-A-11-1).

The ease of filtration by the separation membrane can be judged by the filtration flow rate by the filter paper, and when it becomes less than the above numerical value, the filtration differential pressure tends to increase.
Moreover, a decrease in the filtration flow rate or an increase in the viscosity of the activated sludge can be determined depending on the sugar concentration. If the above numerical value is exceeded, the differential pressure of the separation membrane tends to increase rapidly.

In this invention, it is preferable to add the coagulant | flocculant of the quantity from which the density | concentration in the processing waste water of 1 day becomes 1 mg / L or more continuously or intermittently in a microorganism treatment tank.
This is because by setting the concentration of the flocculant to 1 mg / L or more, the separability of the liquid to be treated tends to be maintained and improved. More preferably, it is 5 mg / L or more. The concentration of the flocculant is preferably 30 mg / L or less. This is because even if the concentration is excessively increased, the effect of adding the flocculant tends not to change, and the cost tends to be disadvantageous.

  In addition, by adding the flocculant continuously or intermittently, the flocculant acts more effectively, and the amount of the flocculant used tends to be reduced. It is more preferable to add the flocculant in an amount such that the concentration in the daily treatment wastewater is 1 mg / L or more continuously or intermittently over 1 day. If necessary, the flocculant can be initially added in a large amount to a certain extent, and then a continuous addition or an intermittent addition in a small amount can be performed.

  The addition of the flocculant is preferably carried out until the separation of the liquid to be treated is improved, such as the recovery of the filter paper filtration flow rate, the reduction of the sugar concentration and the stabilization of the differential pressure of the separation membrane. More preferably, the amount of the flocculant in the daily treatment wastewater is 1 mg / L or more to be added per day. There is no particular limitation on the period of addition of the flocculant, and it can be selected as appropriate depending on the use environment and the type of wastewater. In consideration of the influence on the differential pressure of the membrane, etc., it is preferable to add 1 to 4 weeks as a guide.

  For example, by using a flocculant tank 5 to which a tube connecting the intermittent timer 3 and the liquid feeding pump 4 is connected, the flocculant is intermittently added to the microorganism treatment tank 1 in which the membrane separation device 2 is installed. Can do. In this case, the filtration operation at the separation membrane is continued as it is, and the separability can be improved online without stopping the filtration operation. When continuous addition is performed, the intermittent timer 3 can be omitted.

  Examples of flocculants that can be used in the present invention include inorganic flocculants such as commercially available ferric chloride solution (iron chloride), polyiron sulfate solution (polyiron), and polyaluminum chloride solution (PAC). Examples thereof include cationic, anionic and amphoteric polymer flocculants. One or more of these can be appropriately selected and used, but it is preferable to use an inorganic flocculant that has high versatility and can be used easily.

Hereinafter, the present invention will be described specifically by way of examples.
Example 1
Using the apparatus shown in FIG. 1, the treatment of domestic wastewater was performed at Mitsubishi Rayon Co., Ltd. Drainage Experiment Station under the following conditions.
1. A membrane separation device (membrane area 43.5 m ² ) 2 was prepared in which a plurality of elements in which hollow fiber membranes made of polyvinylidene fluoride for microfiltration having an average pore size of 0.4 μm were developed and fixed in a screen shape were laminated.
2. Microbial treatment tank 1 (length 1000 mm x width 1100 mm x height 4600 mm)
The secondary side of the membrane separation device 2 installed inside is sucked, and the membrane filtration flux LV = 0.8
The wastewater of the domestic wastewater system was treated at m ³ / m ² / Day.
At this time, air diffused from the air diffuser 6 installed below the filtration device was always carried out. The amount of air diffused was 150 Nm ³ / m ² · hr per projected area of the hollow fiber membrane part.
3. Filtration was performed with the intermittent interval of the filtration operation set to 7 minutes suction to 1 minute stop.
4). The MLSS of the liquid to be treated at the start of the test was 10,000 mg / L, the filter paper filtration amount was 25 ml / 5 min, and the sugar concentration was 20 mg / L.
The test is started under the above conditions, the water temperature in the microorganism treatment tank 1 and the temperature of the installation environment of the microorganism treatment tank 1 are measured, the moving average water temperature in the microorganism treatment tank 1 and the installation of the microorganism treatment tank 1 are measured. The 40-day moving average temperature of the environment was determined. The result is shown in FIG.
Although the water temperature and air temperature both decreased from the beginning of the test and the difference between the moving average temperatures tended to increase, there was no increase in the differential pressure between the membranes, and the wastewater treatment was able to continue smoothly. .
When the moving average temperature difference expanded to 4 ° C. (indicated by the arrow in FIG. 2), the sample liquid was sampled. As a result, the filtration flow rate through the filter paper was 18 ml / 5 min, and the sugar concentration was 35 mg / L. It was confirmed that the properties of the liquid began to deteriorate.
Therefore, a tube in which the intermittent timer 3 and the liquid feed pump 4 are connected under the condition that the concentration of PAC in the daily treatment wastewater is 5 mg / L per day and used once every 10 minutes for 30 seconds. The operation of intermittent addition using the flocculant tank 5 connected to was continued for 4 weeks. As a result, the filter paper filtration amount of the liquid to be treated was 30 ml / 5 min, the sugar concentration was 20 mg / L, and the recovery of the properties of the liquid to be treated was confirmed. Meanwhile, the pressure difference did not increase under the filtration conditions at the start of the test, and the wastewater treatment could be continued.

(Example 2)
In Example 1, the result of calculating | requiring 30 day moving average water temperature and 30 day moving average air temperature is shown in FIG. The average temperature difference was 4 ° C. at substantially the same time as that of Example 1 (at the time indicated by the arrow), and it was confirmed that the flocculant could be added at an appropriate time even under this condition.

(Example 3)
In Example 1, the result of having calculated | required 20 day moving average water temperature and 20 day moving average air temperature is shown in FIG. The average temperature difference was 4 ° C. at substantially the same time as that of Example 1 (at the time indicated by the arrow), and it was confirmed that the flocculant could be added at an appropriate time even under this condition.

Example 4
FIG. 5 shows the results of obtaining the 10-day moving average water temperature and the 10-day moving average air temperature in Example 1. The average temperature difference was 4 ° C. at substantially the same time as that of Example 1 (at the time indicated by the arrow), and it was confirmed that the flocculant could be added at an appropriate time even under this condition.

(Comparative Example 1)
In Example 1, the result of calculating | requiring 50 day moving average water temperature and 50 day moving average air temperature is shown in FIG. The average temperature difference becomes 4 ° C. later than the time point in Examples 1 to 4 (at the time of the arrow), and at this time point, the deterioration of the properties of the untreated liquid is already remarkable (filter paper filtration amount is 10 ml / 5 min, The membrane filtration flux (LV = 0.8 m ³ / m ² / Day) at the start of the test could not be maintained due to the increase in the differential pressure with a sugar concentration of 40 mg / L.

(Comparative Example 2)
FIG. 7 shows the results of obtaining the 5-day moving average water temperature and the 5-day moving average air temperature in Example 1. Due to the large variation in data, the point in time when the temperature difference reached 4 ° C. could not be determined.

It is a general | schematic flowchart which shows an example of the processing method of this invention. 3 is a graph showing the transition of the moving average temperature in Example 1. It is a graph which shows transition of the moving average temperature in Example 2. It is a graph which shows transition of the moving average temperature in Example 3. It is a graph which shows transition of the moving average temperature in Example 4. It is a graph which shows transition of the moving average temperature in the comparative example 1. It is a graph which shows transition of the moving average temperature in the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microbial processing layer 2 Membrane separator 3 Intermittent timer 4 Liquid feed pump 5 Coagulant pump 6 Air diffuser

Claims (3)

In the case of performing solid-liquid separation using a separation membrane installed in the microorganism treatment tank, the moving average temperature difference between the water temperature in the microorganism treatment tank in which the separation membrane is installed and the temperature of the installation environment of the tank is 4 ° C. A method for treating organic wastewater, in which a flocculant is added when expanded above. The method for treating organic waste water according to claim 1, wherein the flocculant is added when the flow rate of the liquid to be treated is 10 ml / 5 min or less or the sugar concentration in the liquid to be treated is 30 mg / L or more. The processing method of the organic waste water of Claim 1 or 2 which adds the coagulant | flocculant of the quantity which the density | concentration in 1 day of treatment wastewater becomes 1 mg / L or more continuously or intermittently in a microorganism treatment tank.

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