JP4800463B2 - Filtration device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a filtration apparatus for performing a filtration treatment by passing agglomeration treated water to which a flocculant has been added through a filter medium layer.
[0002]
[Prior art]
In the case of producing purified water or industrial water using river water or the like as raw water, or in wastewater treatment or the like, coagulation sedimentation treatment and filtration treatment are widely used for separation of suspended substances. That is, in the coagulation sedimentation treatment, first, an aluminum-based coagulant or the like is added to and mixed with the raw water to make the suspended substances in the raw water coarse. And this coarse floc is introduce | transduced into a sedimentation basin, and most of suspended solids are removed by carrying out a sedimentation process. Next, the supernatant water (coagulation precipitation treated water) obtained in this sedimentation basin is further treated with a filtration device to further remove the remaining fine suspension. In this way, clear treated water is obtained.
[0003]
Here, in the filtration device, when the filter medium captures a predetermined amount of suspended solids, the filtration resistance increases and the outflow of flocs increases, so backwashing is performed. This backwashing is performed by allowing backwashing water (usually treated water) to flow back through the filtration device and removing the trapped suspended matter to regenerate the filter medium.
[0004]
However, immediately after the backwashing, suspended substances (fine flocs) in the treated water increase, and sufficient filtration cannot be performed in many cases.
[0005]
This is because in normal filtration treatment, when an aluminum-based flocculant is used, aluminum hydroxide thinly adheres to the surface of the filter medium, which contributes to the removal of fine flocculent flocs. Since this deposit is removed, it is thought that the treated water immediately after backwashing deteriorates.
[0006]
Therefore, it has been proposed to perform a backwash by adding a flocculant to the backwash water. By such backwashing, a flocculant is supplied into the filter medium during backwashing, and adhesion of, for example, aluminum hydroxide on the filter medium surface is promoted. Accordingly, it is considered that fine floc can be sufficiently removed even immediately after back washing.
[0007]
[Problems to be solved by the invention]
However, even when a flocculant is added to the backwash water, it has been found that the amount of suspended solids in the treated water immediately after the end of backwash cannot be improved so much. This is because even when a flocculant is added during backwashing, it is difficult to adhere the flocculant to the entire filter medium. That is, the probability of being trapped in the lower part of the flocculant filtration layer (near the outlet) is high, and thus the above deposit is formed only on the filter medium at the lower part of the filtration layer. Moreover, since the aluminum density | concentration in washing | cleaning waste_water | drain raises, there also exists a problem that it cannot discharge as it is.
[0008]
It is also conceivable to increase the amount of flocculant added immediately after backwashing, but in this case, adhesion is formed only on the filter medium near the surface, and deposits cannot be formed on the entire filter medium. . Therefore, the deterioration of the treated water could not be prevented immediately after filtration.
[0009]
Furthermore, recently, in order to remove pathogenic protozoa such as Cryptosporidium, very precise filtration is required. Therefore, there is a demand for further reducing the outflow of suspended solids immediately after backwashing.
[0010]
This invention is made | formed in view of the said subject, and it aims at providing the backwashing method of the filtration apparatus which can perform a favorable filtration process immediately after backwashing.
[0011]
[Means for Solving the Problems]
The present invention is a filtration device for performing a filtration treatment by passing the agglomerated water added with a flocculant to the filter medium layer, and circulating the backwash water in the reverse direction to the filter medium layer to backwash the filter medium layer. Back washing means, surface washing means for supplying washing water to the surface of the filter medium layer, washing the surface of the filter medium layer, and adding polyaluminum chloride as a flocculant to the water , the pH is 5.0 ± 0.5 Coating water generating means for generating coating water for forming a coating of aluminum hydroxide on the surface of the filter medium by controlling within the range, and means for backwashing the coating water generated by the coating water generating means And supplying to the surface cleaning means, supplying coating water from both the forward and reverse directions to the filter medium layer, and forming a film of aluminum hydroxide on the filter medium surface of the filter medium layer.
[0012]
Thus, in the backwashing by the backwashing means, the coating water flowing in the reverse direction and the filter medium can be contacted by supplying the coating water to the filter medium layer. Furthermore, by supplying the coating water from the surface cleaning means, it is possible to supply the coding water in the forward direction to the filter medium layer so that the filter medium and the coating water are brought into contact with each other. In this way, by bringing the coating water flowing in both directions into contact with the filter medium, the entire filter medium of the filter medium layer can be effectively brought into contact with the coating water, and a flocculant film can be effectively formed on the surface of the filter medium. it can. Therefore, immediately after the end of backwashing, the filter medium has a sufficiently high suspension adsorbing ability, and good treated water can be obtained.
[0013]
The coating water generation means preferably adds polyaluminum chloride so as to be 40 to 80 mg / l, and controls the pH within a range of 5.0 ± 0.5 to generate coating water. It is. By contacting such coating water with the filter medium, the zeta potential on the surface of the filter medium can be reduced to about 0 to -10 mV, and subsequent filtration can be performed effectively. Polyaluminum chloride (PAC) is usually commercially available containing 10% as Al ₂ O ₃ , but 40-80 mg / l in the present invention means 1 liter of backwash water from the above-mentioned concentration of PAC. In this case, the amount of Al added is 2.12 to 4.24 mg / l.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0015]
FIG. 1 is a diagram showing the overall configuration of the coagulation / separation apparatus according to the present embodiment. Raw water such as river water and lake water is first introduced into the mixing tank 10. The mixing tank 10 is supplied with the flocculant from the flocculant storage tank 12 by the flocculant pump 14. The flocculant is preferably an inorganic aluminum flocculant, and particularly preferably PAC (polyaluminum chloride). The mixing tank 10 is provided with a stirrer 16 so that the raw water and the flocculant are rapidly stirred. In this mixing tank 10, the coagulant-mixed water in which the coagulant is mixed flows into the coagulation tank 18. A slow stirrer 20 is disposed in the coagulation tank 18, and the coagulant admixture water is slowly stirred to coalesce and coarsen the coagulation flocs.
[0016]
Next, the coagulant-mixed water after slow stirring from the coagulation tank 18 flows into the inclined plate settling tank 22. The inclined plate settling tank 22 is divided into an inlet side and an outlet side by a partition plate 22a, and a settling portion 22b having a deep tank depth is formed on the inlet side. And the lower part of this sedimentation part 22b is the sludge storage part 22c which stores sedimentation sludge. A large number of inclined plates 22d are arranged on the outlet side to form inclined plate precipitation portions 22e. The flocculant-mixed water flows into the precipitation portion 22b, where it is precipitated, and then passes under the partition plate 22a and passes upward through the inclined plate precipitation portion 22e. Then, when passing through the inclined plate 22d of the inclined plate settling portion 22e, further precipitation processing is performed, and sludge is precipitated toward the tank bottom. Since the tank bottom of the inclined plate sedimentation part 22e is inclined deeper toward the sludge storage part 22c, the sediment sludge moves to the sludge storage part 22c by gravity. Then, the supernatant that has passed through the inclined plate settling portion 22e is discharged from the inclined plate settling tank 22. In addition, the sludge settled in the sludge storage part 22c of the inclined plate sedimentation tank 22 is suitably extracted and disposed of separately.
[0017]
By such a coagulation sedimentation process, a considerable part of the suspended solids is removed from the sedimentation water from the inclined plate sedimentation tank 22. This precipitated treated water is introduced into the filter 24. The filter 24 is a gravitational rapid filter having two filtration layers of an anthracite filtration layer 24b and a sand filtration layer 24a. In some cases, additional flocculant or coagulant aid may be injected into the precipitation-treated water, stirred with a line mixer, and supplied to the filter 24. The filter is a pressure filter. Also good.
[0018]
A filter medium other than anthracite may be used as the filter medium for the filter layer 24b, or the filter layer 24b itself may be omitted. Moreover, it is also suitable for the filtration layer 24a to use garnet or the like instead of sand, or to make the sand and garnet multilayer.
[0019]
Then, the filtered water of the filter 24 is distributed in the treated water tank 26 and then distributed.
[0020]
The treated water in the treated water tank 26 can be supplied to the bottom of the filter 24 by the backwash pump 28. Therefore, the treated water is supplied to the filter 24 in an upward flow so that the filtration layer in the filter 24 can be backwashed.
[0021]
That is, as the water flow continues, the suspended substance trapped in the filtration layer gradually increases, the filter medium is saturated, and the filter 24 cannot capture the suspended substance any more. This can be detected by an increase in filtration resistance, an increase in treated water turbidity, or the like. Therefore, the filter medium is regenerated by washing before the filter medium is completely saturated.
[0022]
The timing of this cleaning is performed by setting a timer based on empirically obtained time or setting a filtration resistance by a differential pressure gauge. Further, the backwashing is performed by combining backwashing using filtered water or backwashing with surface washing or air washing.
[0023]
Here, in this embodiment, the flocculant from the flocculant storage tank 30 is added by the flocculant pump 32 to the backwash water line from the backwash pump 28 to the filter 24. As this flocculant, PAC is usually used similarly to the flocculant storage tank 12 described above, and the flocculant from the flocculant storage tank 12 may be added. Further, an acid (acid solution such as sulfuric acid) from the acid storage tank 34 is added by the acid pump 36.
[0024]
Thus, in this embodiment, in addition to normal backwashing, backwashing with backwashing water (coating water) containing a flocculant is performed, and thereby a flocculant film is formed on the surface of the filter medium. That is, a predetermined amount of backwash water adjusted to a predetermined pH and added with a predetermined amount of flocculant is passed through the filter 24, whereby a flocculant film is formed on the surface of the filter medium.
[0025]
A branch line is connected to a line for supplying backwash water to the bottom of the filter 24, and this branch line is connected to the surface cleaning nozzle 38 of the filter 24. This surface cleaning nozzle 38 is for ejecting water from here in the initial stage of the backwashing process, hitting the surface of the filter medium layer, and destroying the surface of the filter medium layer capturing the solid matter.
[0026]
In this embodiment, the surface cleaning nozzle 38 can be supplied with coating water to which a flocculant and an acid have been added. Further, a valve 40 is provided in the line for supplying backwash water to the bottom of the filter 24, and a valve 42 is provided in the branch line. By switching these valves, the coating water is supplied to the bottom of the filter 24, or the surface. The supply to the cleaning nozzle 38 or to both of them can be switched.
[0027]
The backwash pump 28, the flocculant pump 32, the acid pump 36, and the valves 40 and 42 are controlled by the controller 44. In particular, it is preferable to provide a pH meter and a flow meter in the backwash line and supply the detection result to the controller 44, so that the controller 44 can control the flocculant pump 32 and the acid pump 36 based on the detection result. By controlling the driving, the pH of the backwash water and the amount of the flocculant added can be controlled to be a predetermined amount. In addition, it is possible to control how much coating water flows through which route.
[0028]
An appropriate flocculant film is formed on the surface of the filter medium by passing a predetermined amount of backwash water and surface washing water adjusted to a predetermined pH and added with a predetermined amount of flocculant through the filter 24. The zeta potential of the filter medium of the filtration layer 24a in the filter 24 is controlled to be 0 to -10 mV. That is, in the case of PAC, the zeta potential of the filter medium increases due to the aluminum hydroxide adhering to the filter medium surface. Further, since the zeta potential is changed by the addition of acid, the amount of acid added is also adjusted. Thereby, the zeta potential on the surface of the filter medium is controlled to 0 to -10 mV.
[0029]
Here, the zeta potential of the filter medium indicates the adhesion state of the flocculant (for example, aluminum hydroxide) to the filter medium surface. Therefore, by setting the zeta potential of the filter medium to a predetermined value (0 to -10 mV), the surface state of the filter medium can be adjusted to a state in which fine flocs can be easily captured. And by attaching the aluminum hydroxide to the surface of the filter medium with the backwash water adjusted as described above, in the filtration after the backwash, the fine floc is prevented from flowing out from the beginning, and the water quality is good. Treated water can be obtained.
[0030]
Moreover, in this embodiment, backwashing is performed in the following procedure. (I) The treated water in the filter 24 is discharged and the water level is at least lower than the surface of the filter medium layer. Then, the backwash pump 28 is driven to discharge the treated water from the surface cleaning nozzle 38 and strike the surface of the filter medium. LV = 6 m / h × 4 minutes. In this case, the valve 40 is closed and the valve 42 is opened. (Ii) Next, the valve 42 is closed, the valve 40 is opened, and backwashing is performed to reversely flow the filtered water. For example, LV (empty linear velocity) = 40 m / h × 8 minutes. Air backwashing may be combined. After finishing such surface washing and backwashing and adjusting the filter medium layer, (iii) Next, backwashing with backwashing water to which a flocculant (PAC) and an acid (sulfuric acid) are added is performed. LV = 40 m / h × 0.6 minutes. The time is set to be in the range of 1.5 to 2.5 times the void volume of the filter medium layer. (Iv) Next, water to which a flocculant (for example, PAC) and an acid are added is supplied to the surface cleaning nozzle 38, and the coating water is passed through the filter medium layer in the forward direction at 6 m / h × 1.4 minutes. In this case, the water flow rate may be about 0.5 times the void volume of the filter medium layer.
[0031]
In this way, intermittent backwashing is performed in which backwashing with a backwashing water to which a flocculant and an acid as a zeta potential adjusting agent are added is performed for a short time, and then a rest period is set. As a result, the flocculant and the filter medium are sufficiently mixed, a time for contact is obtained, and the aluminum hydroxide is sufficiently adhered to the surface of the filter medium.
[0032]
In particular, the coating water to which the flocculant and the acid are added according to the present embodiment uses PAC (a liquid containing 10% of the active ingredient Al ₂ O ₃ ) as the flocculant, and the addition amount is 40 to 80 mg / L. And the pH of the coating water is 5.0 ± 0.5, and this is the total amount of water from the backwash and the surface nozzle, and the amount of the pore volume of the filter medium in the filter 24 is 1.5 to 2.5 times the amount. To do. By such distribution of the coating water to the filter medium, it is possible to perform a process for adjusting the zeta potential of the filter medium as described above to 0 to -10 mV. Note that even if the amount of coating water passed is increased, there is no adverse effect on the zeta potential control of the filter medium. However, meaningless backwashing is performed, and energy and coagulant are wasted. Therefore, it is preferable to control within the above range.
[0033]
As described above, in this embodiment, the amount of flocculant added to the backwash water is adjusted so that the zeta potential of the filter medium is 0 to −10 mV. This zeta potential indicates the electrical potential that exists across the solid-liquid interface and indicates the surface charge for suspended matter in water. Normally, suspended substances (viscosity components, algae, etc.) contained in river water are negatively charged, and each suspended substance is negatively charged. It has become. The aggregating agent first neutralizes this potential to weaken the repulsive force, and then agglomerates or aggregates. Therefore, it is desirable that the zeta potential of the aggregate floc is closer to the neutral point, that is, zero. Usually, the zeta potential of suspended substances in raw water is −20 mV or less, and the zeta potential of aggregated floc is −10 mV or more.
[0034]
Here, in the coagulation sedimentation / rapid filtration method generally used in water purification treatment, it is known that minute floc flows out from the rapid filter, particularly immediately after the start of filtration. It is known that the zeta potential of this minute floc is as low as −15 mV or less and aggregation is not sufficiently performed.
[0035]
The filter medium is negatively charged as it is in the suspended substance in water. By setting the zeta potential of the filter medium to −10 mV or more, the adhesion of the flocculant hydroxide to the filter medium surface can be made sufficient. And by forming this deposit | attachment, the capture | acquisition ability of a floc can be improved and the raise of the suspended solid concentration in a treated water can be prevented. It is not preferable to set the zeta potential to 0 mV or more because it is not economical and the aluminum concentration in the cleaning wastewater becomes high.
[0036]
In this embodiment, PAC (a liquid containing 10% of the active ingredient Al ₂ O ₃ ) is used as the flocculant, and the amount added is 40 to 80 mg / L. The pH of the backwash water is 5.0 ± 0.5, and this is the total amount of water, which is 1.5 to 2.5 times the void volume of the filter medium in the filter 24. By such circulation of the backwash water to the filter medium, the zeta potential of the filter medium is adjusted to 0 to -10 mV.
[0037]
In the above-described embodiment, normal surface washing with treated water to which no flocculant is added and backwashing are completed, and then the liquid is settled, and then backwashing and surface washing are performed with coating water in which flocculant is added to the treated water. However, in some cases, normal surface washing and backwashing are performed at the same time, and while the main surface washing and backwashing are continued, a flocculant is added to the treated water to form coating water in the latter half. The zeta potential of the filter medium may be adjusted by washing and backwashing.
[0038]
In the embodiment described above, the backwash pump 28 is used for surface washing and backwashing with treated water. However, the treated water tank may be installed at a high position, and may be washed and backwashed depending on the water head difference. In this case, a flocculant is added to the pipe to be surface-washed and back-washed with a water head difference so that it can be generated as coating water.
[0039]
【Example】
Experiments were performed using the apparatus of FIG.
[0040]
"Experimental conditions"
・ Raw water flow rate: 3000m ³ / D
Mixing tank: residence time 4 minutes, G value 250 to 400 s ⁻¹
・ Sedimentation basin: Sedimentation basin with upward flow type inclined plate, residence time 40 minutes, rising speed 5 cm / min
・ Filter specifications: φ5000mm × 5000mm × H4000mm (filtration area 25m ² )
-Filtration rate (LV): 5 m / h (120 m / d)
Filter medium: Silica sand Specific gravity 2.5, porosity 45%, effective diameter 0.6mm, uniformity coefficient 1.4, filter layer height 600mm
・ Water flow time: 48 hours (Washing starts with a timer)
-Raw water turbidity: 8-30 degrees-Raw water pH: 7.2-7.5
・ Filtered water pH: 6.9 to 7.3
-Flocculant: PAC 10-30 mg / l
・ Target treatment water turbidity: less than 0.1 degree ・ Cleaning conditions:
(I) Surface cleaning: LV = 6 m / h × 4 minutes, water amount = 25 m ² × 6 m / h × (4 ÷ 60) = 10 m ³ / times (ii) Water backwashing: LV = 40 m / h × 8 minutes = 25 m ² × 40 m / h × (8 ÷ 60) = 133.3 m ³ / times (iii) Coating water backwashing: LV = 40 m / h × 0.6 minutes, amount of water = 25 m ² × 40 m / h × (0 .6 minutes ÷ 60 minutes) = 10 m ³ / time, filter medium void volume = 25 m ² × 0.6 m × 0.45 = 6.75 m ³ , and 1.5 times the water flow, 6.75 m ³ × 1.5 = 10.1 m ³ / times backwash water: filtered water is used. Adjust the pH to 5.0 ± 0.5.
PAC: Adjusted to be 40-80 mg / L.
(Iv) Surface wash coating: LV = 6 m / h × 1.4 minutes, water amount = 25 m ² × 6 m / h × (1.4 minutes ÷ 60 minutes) = 3.5 m ³ / time, filter medium void volume = 25 m ² × 0.6 m × 0.45 = 6.75 m ³ , 0.5 times the water flow, 6.75 m ³ × 0.5 = 3.4 m ³ / time,
Use filtered water. Adjust the pH to 5.0 ± 0.5.
PAC: Adjusted to be 40-80 mg / L.
[0041]
"Experimental result"
Add 10 mg / L of PAC as a flocculant to raw water with a turbidity of 8 degrees, add sulfuric acid as an acid in order to adjust the pH to 7.0, and mix using the stirrer 16 in the mixing tank 10. The mixture was gently stirred at 18 and subjected to precipitation treatment in an inclined plate settling tank (may be without an inclined plate) 22 and then supplied to a filter 24 to obtain treated water.
[0042]
If the filter 24 performs water flow to some extent, the gap between the filter media is saturated due to the turbidity, and the water flow cannot be continued. The time until the filtration cannot be continued depends on the turbidity concentration in the inflow water of the filter, the water flow rate, and the like, and is usually about 24 to 72 hours. In this experiment, backwashing was performed every 48 hours. .
[0043]
In the back washing step, PAC 60 mg / L and sulfuric acid as described above were injected to perform back washing and surface washing with pH 5 ± 0.5 coating water. By such treatment, it was confirmed that the treated water was not deteriorated immediately after backwashing and the target turbidity could be maintained continuously.
[0044]
【The invention's effect】
As described above, according to the present invention, in the backwashing by the backwashing means, the coating water flowing in the reverse direction and the filter medium can be contacted by supplying the coating water to the filter medium layer. Furthermore, by supplying the coating water from the surface cleaning means, it is possible to supply the coding water in the forward direction to the filter medium layer so that the filter medium and the coating water are brought into contact with each other. In this way, by bringing the coating water flowing in both directions into contact with the filter medium, the entire filter medium of the filter medium layer can be effectively brought into contact with the coating water, and a flocculant film can be effectively formed on the surface of the filter medium. it can. Therefore, immediately after the end of backwashing, the filter medium has a sufficiently high suspension adsorbing ability, and good treated water can be obtained.
[0045]
Further, by adding polyaluminum chloride so as to be 40 to 80 mg / l, and controlling the pH within a range of 5.0 ± 0.5 and using coating water, the zeta potential on the surface of the filter medium is set to 0 to 0. It can be about -10 mV, and subsequent filtration can be performed effectively.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an apparatus according to an embodiment.
[Explanation of symbols]
10 Mixing tank, 18 Coagulation tank, 22 Inclined plate sedimentation tank, 24 Filter, 30 Coagulant storage tank, 32 Coagulant pump, 38 Surface cleaning nozzle, 40, 42 Valve.

Claims (2)

In the filtration device that passes the flocculated water subjected to the flocculation treatment with the addition of the flocculating agent to the filter medium layer and performs the filtration treatment,
A backwashing means for circulating backwashing water in the reverse direction to the filter medium layer, and backwashing the filter medium layer;
Surface cleaning means for supplying cleaning water to the surface of the filter medium layer and cleaning the surface of the filter medium layer;
Coating water generation that adds polyaluminum chloride as a flocculant to water and controls the pH within a range of 5.0 ± 0.5 to generate coating water for forming a coating of aluminum hydroxide on the filter medium surface Means,
Have
The coating water generated by the coating water generating means is supplied to the backwashing means and the surface cleaning means, the coating water is supplied from both the forward direction and the reverse direction to the filter medium layer, and aluminum hydroxide is applied to the filter medium surface of the filter medium layer. The filtration apparatus characterized by forming the film of this. The apparatus of claim 1.
The said coating water production | generation means adds the polyaluminum chloride so that it may become 40-80 mg / l, and produces | generates the said coating water, The filtration apparatus characterized by the above-mentioned.

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