JP5763400B2 - Water purification method and water purification device - Google Patents

Description

  The present invention relates to a water purification treatment method and a water purification treatment apparatus.

In Japan's water purification technology field, membrane filtration technology is becoming more popular in place of conventional sand filtration technology. For membrane filtration, a membrane called an ultrafiltration membrane (UF membrane) or a microfiltration membrane (MF membrane) that can remove suspended substances, bacteria, and protozoa in water is about 0.01 to 0.1 μm. It is common to use. As the membrane element, a macaroni-like membrane called hollow fiber is generally used.
There are two types of membrane types: a casing storage method that bundles a large number of membrane elements into a dedicated pressure vessel and filters them at a relatively high pressure, and an immersion method in which the membrane elements are immersed directly in a water tank or the like (immersion tank). . Since the dipping method generally performs filtration at a low pressure, it has features such as low power required and stable treatment even with raw water with high turbidity load.

MF membranes and UF membranes can remove suspended substances in water, bacteria, and protozoa, but cannot remove substances smaller than the pore size of the membrane or soluble substances. On the other hand, when general surface water is used as raw water, membrane filtration alone is insufficient to treat it into water suitable for beverages, and it is often necessary to remove soluble organic substances.
As a treatment corresponding to these raw waters, for example, as in Patent Document 1, a powdered activated carbon is added as a membrane pretreatment, a soluble organic substance is adsorbed on the activated carbon, and the activated carbon itself is removed by membrane filtration. Are known. Alternatively, as in Reference Document 2, a technology that can treat with a fixed amount of powdered activated carbon injection regardless of the water quality fluctuation of raw water by increasing the recovery rate of treated water to 99% or higher and increasing the concentration of activated carbon in the immersion tank. Are known.

JP-A-5-154470 JP-A-9-28579

  However, these technologies have the following problems. When the raw water turbidity is high, or when the solid concentration of feed water is high, such as when the concentration of powdered activated carbon is high, the solids concentration in the tank increases as the treatment water recovery rate increases, and the inside of the membrane module In addition, solid matter-containing water solidifies into a cake and accumulates to reduce the effective area of the membrane, thereby reducing the amount of membrane filtration water. Therefore, when the membrane feed water solids concentration is high, the recovery rate of treated water must be lowered to prevent solids from adhering to the membrane surface. However, reducing the recovery rate increases the burden on the wastewater treatment facility, leading to a decrease in the efficiency of the entire facility, and it is desirable to maintain it as high as possible. Alternatively, in order to solve these problems, for example, air scrubbing is always performed to prevent solids from adhering to the film surface. However, there is a drawback in that the air scrubbing requires a large amount of blower power. Alternatively, it is possible to prevent the accumulation of cake-like solids (hereinafter also referred to as cakes) between the membranes by lowering the degree of membrane accumulation and arranging them sparsely, but the installation area per processing amount increases, and the equipment There was a drawback that the efficiency decreased.

  The present invention overcomes these disadvantages of the prior art, prevents the cake from adhering to the membrane surface while maintaining a high recovery rate of the treated water, and is capable of efficient operation with low power and its It is to provide an apparatus used in the method.

The present invention is as follows.
1) The solids concentration of the solids-containing water in the tank is 0.1 Ct to Ct as the limit solids concentration (Ct), or until the solids concentration reaches 3000 to 30000 mg / L. Membrane filtration step including membrane filtration and regular cleaning, drainage step of draining all or part of the solid-containing water in the tank after the membrane filtration step, supply raw water into the tank after the drainage step And a water purification method including a water-charging step of controlling the concentration of the powdered activated carbon in the solid-containing water so as to be a target value of 50 mg / L or more.
2) The above-mentioned 1), including a membrane module having a tank, a membrane element and a water collecting part, immersed in the tank, a membrane filtration device having an air diffuser installed at the bottom of the tank, and a powdered activated carbon injection device A water purification apparatus for carrying out the water purification method.

In the present invention, the limit solids concentration (Ct), or the solids concentration range is determined in advance from preliminary tests, empirical rules, etc., and the solids concentration of the solid-containing water in the tank is 0.1 Ct to Ct, or Filter the solid-containing water until it becomes 3000 to 30000 mg / L, and then drain the solid-containing water to discharge the solid to clean the inside of the tank, and solid matter around the membrane surface and the membrane After that, the raw water is supplied into the tank and the activated carbon concentration in the solid-containing water is charged so as to reach a certain target value, thereby maintaining the performance of the treated water. While maintaining a high recovery rate, the cake is prevented from adhering to the membrane surface, and efficient operation with low power is possible.
In the present invention, the limit solids concentration (Ct) means that when the solids concentration C in the tank reaches a certain level, the cake adhered to the film surface can be peeled even if air scrubbing cleaning is performed on the film. The solid concentration when the cake starts to grow and is defined as Ct. Here, the solid material includes powdered activated carbon (hereinafter also referred to as activated carbon), SS component of raw water (for example, fine particles derived from clay minerals), agglomeration flocs of the SS component by a flocculant, and a mixture thereof. included.
Further, the initial membrane feed water solid concentration C ₀ is practically calculated by the following equation.
C ₀ = D · E1 + C1 · E2 + C2
D: Raw water turbidity E1: Conversion rate between turbidity and SS (floating matter) C1: Coagulant injection rate (converted to aluminum oxide)
E2: Ratio of aluminum hydroxide to aluminum oxide 1.53
C2: Powdered activated carbon injection rate Since the present invention can perform regular washing, powdered activated carbon injection, etc. in the membrane filtration step, the C becomes the above-mentioned predetermined solid concentration during the membrane filtration step. Will increase to. And when it becomes this predetermined density | concentration, the drainage process of this invention is implemented.

From the above definition, Ct is not practically a constant threshold value but a transition region having a width. The specific value of Ct depends on the composition of the components derived from solids such as the quality of raw water, flocculant, and added amount of activated carbon, but it can be concluded from the experience that the inventor repeated many experiments that it is around 3000 to 30000 mg / L. .
Therefore, in order to prevent the cake from adhering to the film surface, the maximum solid concentration in the tank (maximum solid concentration in the tank) Cmax must be Ct or less, or 3000 to 30000 mg / L. Ct and thus Cmax are theoretical values that can be appropriately set by the operation manager.

  According to the present invention, it is possible to prevent the cake from adhering to the membrane surface while maintaining a high recovery rate of treated water by periodically draining the entire volume or partially draining under certain conditions, and also by activated carbon. The adsorption effect can be kept high.

It is a figure explaining an example of the water purification apparatus applied to implementation of the method of this invention. It is a figure explaining the membrane filtration apparatus of FIG. It is a graph which shows notionally the time-dependent change of the solid substance density | concentration in a tank in this invention method and the method outside this invention. The vertical axis C represents the solid matter concentration in the tank, and the horizontal axis represents time. It is a graph which shows notionally the change with time of activated carbon concentration in a tank in the method of the present invention and the method outside the present invention. The vertical axis a indicates the activated carbon concentration in the tank, and the horizontal axis indicates time. It is a graph which shows the activated carbon injection | pouring rate into the tank over time in this invention method and the method outside this invention. The vertical axis A represents the rate of activated carbon injection into the tank, and the horizontal axis represents time.

The membrane filtration step of the present invention is a step of obtaining purified water by subjecting solid-containing water to membrane filtration. In the membrane filtration step, the membrane is periodically washed by the washing means during the membrane filtration step. Here, “periodic” means that continuous washing is not performed during the membrane filtration process, and the operation manager can arbitrarily set the time in consideration of various conditions such as water quality and equipment configuration. This refers to performing cleaning for an arbitrarily set time with an interval. Here, the cleaning means is also arbitrarily selected. In the present invention, cleaning is performed intermittently as described above, and there is an advantage that it is labor-saving. For example, when air scrubbing cleaning is applied as the cleaning, it is sufficient to perform air scrubbing cleaning at intervals of 30 to 60 minutes for about 1 to 2 minutes. Moreover, the filtration time in a membrane filtration process and the space | interval of a drainage process and a drainage process are about 1 to 10 days.
The membrane filtration device used in the membrane filtration step is not particularly limited, but has a membrane module having a tank, a membrane element and a water collecting part and immersed in the tank, and a diffuser installed at the bottom of the tank. Is mentioned.

The drainage step of the present invention is a step of draining all or part of the solid-containing water in the tank after the membrane filtration step. In this drainage process, drainage is started when the solid concentration C in the tank can be regarded as Cmax, that is, when Cmax is reached.
In the case of partial drainage in this drainage process, activated carbon is also contained in the solid matter, so that it can be selectively drained so that part or all of the activated carbon remains.
That is, in the present invention, it is preferable to drain the solid-containing water so that the solid concentration after filling in the filling step is 0.1 Ct or less, or 3000 mg / L or less.
Moreover, it is preferable to control a water filling process so that the activated carbon density | concentration in solid substance containing water may be set to the target value of 50 mg / L or more. The activated carbon may be freshly used or may be replaced with a part or all of the activated carbon left in the draining process.

In addition, if the membrane filtration step of the present invention satisfies the above conditions, the activated water, the flocculant, the pH adjuster, and the like are basically various from raw water until reaching Cmax as described above. It is possible to add other additives.
In this invention, it is preferable to have the process of inject | pouring activated carbon according to raw | natural water quality after a water filling process in a membrane filtration process. The step of injecting the activated carbon may be continuous or intermittent, constant or indefinite, or a combination thereof. As for the activated carbon density | concentration of the solid content water in a membrane filtration process, 50-500 mg / L is mentioned at the time of Cmax, for example.

  In the present invention, the operation manager determines the Cmax according to the raw water state, and considers the tank capacity (solid matter-containing water acceptance amount) of the membrane filtration device, etc., and the membrane filtration step, the drainage step, the water filling step. The time schedule such as filtration time, drainage time, water filling time, activated carbon injection time, etc., and the washing conditions in the membrane filtration step, the flocculant injection rate, the powdered activated carbon injection rate, etc. are determined. The water purification apparatus of this invention can have the control part which memorize | stored the operation management conditions determined in this way, and communicated with the activated carbon injection | pouring apparatus, the membrane filtration apparatus, etc. in order to enforce this management conditions. The specific configuration of the management conditions can be changed as appropriate according to the raw water condition.

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings.
An example of the device of the present invention is shown in FIGS.
As shown in detail in FIG. 2, the membrane filtration device F includes a membrane module 5 having a tank 4, a membrane element 5a, a water collecting portion 5b, and a lower support 5c, an air diffuser 6, a blower 7, and a drainage valve. 8 is provided.
The raw water 1 is added with a pH adjusting agent 11 as necessary, and then added with a flocculant 12 and flows into the mixing tank 2. After being agglomerated by the stirrer 3, after passing through the inflow valve 14, the activated carbon 13 is added, and the solid-containing water (film supply water) 15 flows into the normal water level L ₀ of the tank 4. The solid-containing water 15 passes through the membrane module 5 to become filtered water 17 and is guided to the treated water tank 10 by the suction pump 9. On the other hand, suspended solids in the solid-containing water cannot pass through the membrane module 5 and therefore stay in the tank 4.
When the solid-containing water concentration in the tank reaches Cmax, a part or all of the solid-containing water is drained 16 from the mud valve 8. By scrubbing with the cleaning air 18 from the diffuser 6 at the time of drainage, it is possible to further promote the peeling of the cake adhering to the film surface due to the water flow when the bubbles burst near the liquid surface. Although it is desirable to drain the entire amount, some drainage may be used if there is a limit on the amount of drainage due to the conditions of the drainage destination. In that case, as shown in FIG. 2, and drained until the water level L ₁ of the tank 4 after drainage has reached a position lower than the lowermost portion of the membrane element 5a, the entire membrane element is to be exposed to the air.
After draining the entire amount, the membrane supply water 15 is filled into the tank 4 from the inflow valve 14. When the entire amount is drained, the solid content concentration C in the tank once decreases to the solid concentration Co of the membrane feed water.
The maximum concentration Cmax of the solid concentration in the tank is approximated by Cmax = Co / (1-R) where R is the recovery rate of Co and treated water.
In addition, the filtration time T (h) until the total drainage is defined as V (m ³ ) for the tank volume and α as the ratio of the drainage capacity to the tank volume (α = 1 for total drainage). Assuming that (film supply water amount) is Q (m ³ / h), the relationship of R = Q · T / (Q · T + αV) is established. From this, T = αR · V / (Q · (1-R)), and by draining the entire amount of water in the tank every filtration time T, a high recovery rate is maintained within a range where the cake does not adhere to the membrane surface. be able to.
In order to show the merit of this method, the conceptual time-dependent change of the solid substance concentration C in the tank which became the steady state is shown in FIG. In the following, a case where all the water is drained during drainage (the above-described α = 1) will be described.
A dotted line 1 indicates a device according to this operation method (assuming drainage of the entire amount). As a comparative control, an example of an apparatus that continuously drains water is shown by a solid line 2, and an example of an apparatus that drains a very small amount for every cleaning is shown by a dotted line 3. In either case, the recovery rate R as an apparatus can be set to the same value by controlling the amount of drainage. The Cmax in the tank is the same, but it can be seen that the dotted line 1 has the lowest average concentration during the membrane filtration process. This is self-evident because this average concentration is proportional to the area between the line and the time axis.
If Cmax is well below Ct, there is little risk of cake growth for either method. However, in practice, it is preferable that the recovery rate R is high, and therefore Cmax is often set in the vicinity of Ct. In this case, the operation method indicated by the dotted line 1 indicates that the time during which the solid concentration in the tank is in the vicinity of Ct, that is, the time Tctt1 in which Ct transition region Ctt is present or present in Ctt is the shortest, and therefore the risk of cake growth. It turns out that the nature is the lowest. In the conventional methods 2 and 3, the times Tctt 2 and 3 existing in Ctt are always in Ctt in the steady state.
On the other hand, FIG. 4 conceptually shows the concentration of the activated carbon in the solid-containing water and FIG. 5 shows the injection rate of the activated carbon. The activated carbon injection method according to this method is indicated by a dotted line 1, and the conventional constant injection method is indicated by a solid line 2.
The activated carbon added to the raw water 1 accumulates in the tank as filtration and washing are repeated. Immediately before the drainage step, the concentration of activated carbon in the tank reaches the maximum value a _max .
Next, in the drainage process, the activated carbon flows out of the tank together with the drainage. When the entire amount is drained, the amount of activated carbon in the tank becomes zero after draining. Or even when it drains partially, the amount of activated carbon in a tank falls to the quantity of 1-alpha times before drainage. (Α is the ratio of the amount of drainage to the tank capacity described above). Therefore, immediately after the start of filtration, the amount of activated carbon in the tank is not sufficient, and with the constant injection as in the prior art, the organic substance removal effect cannot be expected sufficiently. In order to correct these, in this method, the activated carbon injection rate A is activated carbon with a temporarily high injection rate (A ₁ ) during the charging process after drainage of the entire amount (time is t ₀ and is sufficiently shorter than T). It was added, the concentration in the bath with a _0. Thereafter, during the filtration time T, operation is performed at an injection rate (A ₂ ) smaller than A _{1 in} order to compensate for the activated carbon adsorption capacity in the tank that decreases with time. The activated carbon concentration in the tank gradually increases as the operation progresses. This is expressed as follows.
a (t) = a ₀ + A ₂ Q (t−t ₀ ) / V
a _max = a ₀ + A ₂ QT / V
a (t): Activated carbon concentration in the tank after operation t time a ₀ : Activated carbon concentration in the tank after the filling time t ₀ Q: Inflow amount to the tank per hour (membrane supply water amount)
V: tank capacity t: elapsed time t ₀ : initial water filling time T: filtration time

By performing such an operation, stable activated carbon treatment can be performed from the beginning of filtration through the filtration time T.
In addition, about the injection | pouring rate of activated carbon, according to water supply facility design guideline 2000 (published by Japan Water Works Association, p291), it is set as 10-30 mg / L in the case of removing off-flavor, and 30-100 mg / L in the case of removing trihalomethane precursor. However, in practice, it is often operated in the range of about 5 to 25 mg / L from the viewpoint of economy. On the other hand, when the average time during which the effect of the adsorption performance of the activated carbon is maintained is 5 to 10 hours, when the general residence time in the immersion tank is 30 minutes, the actual injection rate in the immersion tank is 10 to 20 times. It becomes calculation that activated carbon accumulates. From this, the A ₁ value is 10 to 20 times the A ₂ value, that is, a high concentration of 50 to 500 mg / L, whereby the organic substance removing ability at the initial stage of filtration can be expressed. The filtration time (interval between drainage and drainage) depends on the membrane filtration flux and the recovery rate, but is usually between about 1 day and 10 days. On the other hand, is filled with water time _{t 0} is about 10 minutes to 60 minutes.

  Examples of the present invention will be described below. In addition, this invention is not restrict | limited at all by this Example.

An example showing the results of the present invention is shown in Table 1. In accordance with the apparatus configuration and method of FIGS. 1 to 5, Experiments 1 and 2 (Comparative Example) are experimental examples in which a small amount of waste water (1.2 to 1.5 L) is drained by the conventional method every 20 minutes of cleaning. In 3 (Example), the entire amount was drained once every about 8 days without draining after every 20 minutes of washing. In any case, the recovery rate R is 99.7%, but the average turbidity in the tank is lower when the whole amount is drained. Moreover, while the adhesion of the cake was observed in the experiments 1 and 2 during the experiment, in the experiment 3, the adhesion of the cake to the film surface was not observed in any step during the experiment.
Further, the quality of the treated water with the ultraviolet absorbance as an index was treated well without any significant difference in any of 1-3.

The operating conditions of the experiment are as follows.
Raw water: River surface water Membrane filtration flow rate: 0.8-1.0 m / d
Membrane supply water amount Q: 0.02 to 0.025 m ³ / L
Membrane immersion tank volume V: 0.7 m ³
Activated carbon addition amount A: 0 to 25 mg / L
Recovery rate R: 99.7%
Raw water ultraviolet absorbance: average 0.362
Cmax is a numerical value converted from the membrane feed water solids concentration Co and the recovery rate R. Both test periods are 30 days or more. The ultraviolet absorbance of raw water and treated water is 260 nm according to the water test method (2001, Japan Water Works Association). Was measured with a 50 mm cell.

  As mentioned above, it turned out that the operation | movement using this patent method shown in Experiment 3 is effective in obtaining favorable treated water quality, suppressing the cake adhesion to a film | membrane.

1: Raw water, 2: Mixing tank, 3: Stirrer, F: Membrane filtration device, 4: Tank, 5: Membrane module, 5a: Membrane element, 5b: Water collecting part, 5c: Lower support, 6: Air diffuser , 7: blower, 8: drainage valve, 9: suction pump, 10: treated water tank, 11: pH adjuster, 12: flocculant, 13: powdered activated carbon, 14: inflow valve, 15: solid-containing water (membrane) Supply water), 16: drainage, 17: filtered water, 18: washing air, L ₀ : normal water level, L ₁ : water level after drainage

Claims (7)

Solids concentration of solids-containing water in the tank is, until the cake adhering to the membrane surface is 3000~30000mg / L was determined in advance as a solid concentration at which begin to grow and have membrane filtration The solids-containing water Membrane filtration process ,
During the membrane filtration step, a cleaning step that performs cleaning intermittently with an arbitrarily settable time interval, and
A drain step of draining the solids-containing water in the cistern after the membrane filtration step,
Characterized in that it comprises a <br/> and filled with water steps powdered activated carbon concentration of solids content in water is controlled to a target value of more than 50 mg / L supplies raw water into the cistern after the drainage step Water purification method.
{However, the said solid substance concentration means the density | concentration of the total amount of the aggregation floc by the powdered activated carbon, the floating substance component in raw | natural water, and the flocculant of this floating substance component. } The drainage process, water purification treatment method according to claim 1, wherein the draining solids containing water so that the solid matter concentration after filling of water in the filling of water step is below 3 000mg / L. The said membrane filtration process includes the injection | pouring process which inject | pours powdered activated carbon according to the raw | natural water quality after the said water filling process, The water purification method of Claim 1 or 2 characterized by the above-mentioned . When draining by the draining process, water purification treatment method according to any one of claims 1 to 3, characterized in that it comprises an air diffuser supplying air to the membrane. A mixing tank in which a flocculant is added to raw water and agglomerates by stirring;
An activated carbon injection device for injecting powdered activated carbon after the agglomeration to obtain solid-containing water;
A tank into which the solid-containing water is introduced, a membrane element and a membrane module having a water collecting part, and a membrane element that is installed in the lower part of the tank and is used to discharge cleaning air when draining the solid-containing water It consists diffuser you supplied to the solids concentration of the solids-containing water in the tank is a 3000~30000mg / L was determined in advance as a solid concentration when the cake adhering to the film surface starts to grow A membrane filtration device for draining the solid-containing water ,
The water purification apparatus characterized by having .
{However, the said solid substance concentration means the density | concentration of the total amount of the aggregation floc by the powdered activated carbon, the floating substance component in raw | natural water, and the flocculant of this floating substance component. } The activated carbon injection rate A by activated carbon injection of the activated carbon injection device when the entire amount of the waste water is drained is a temporarily high injection rate (A ₁ ) And then the high injection rate (A ₁ ) Less injection rate (A ₂ ) And the following formula a (t) and formula a _max The water purification apparatus according to claim 5, wherein:
Activated carbon concentration in the tank after operation t: a (t) = a ₀ + A ₂ Q (t-t ₀ ) / V
Maximum activated carbon concentration in the tank before draining: a _max = A ₀ + A ₂ QT / V
{However, a ₀ : Recharge time t ₀ The concentration of activated carbon in the tank (concentration in the tank), Q: inflow amount to the tank per hour (film supply water amount), V: tank capacity, t: elapsed time, t ₀ : Initial charging time, T: Filtration time. } The solid concentration (maximum concentration Cmax) of 3000 to 30000 mg / L determined in the tank is Cmax = Co / (1-R), and the filtration time T (h) to the total amount drainage is T = αR · V / (Q · (1-R))
{ However, Co: solid concentration of membrane feed water, R: recovery rate of treated water, V: volume of tank (m ³ ), α: ratio of drainage capacity to tank volume, Q: inflow per hour (m ³ / h)}
The water purification apparatus according to claim 6 .

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