JPH1085513A - Treatment of suspended substance in waste water by membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate deterioration of membranes and to stabilize membrane treatment by adding a specified amount of flocculant in treating a suspended substance by means of precision filtration membranes or ultrafiltration membranes. SOLUTION: A flocculant is added in an amount 5-10 times more than usual is treating suspended matters by means of precision filtration membranes or ultrafiltration membranes in a member separation device suitable for use in the treatment of suspended matters by a waster water treatment system. When using polyamium chloride as a flocculant, for example, the concentration of 20-40mg/l of polyaluminum chloride in terms of Al2 O3 is added. Further, a pretreatment liquid prepared as described is treated with the precision filtration membrane or the ultrafiltration membrane. The flocculant is such as polyamluminum chloride, ferric chloride or aluminum sulphate. If the suspended substance is separated by the described method, the membrane treatment is stably performed without generation of a scale on the membrane face, compared with the case in which the conventional quantity of the flocculant is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating suspended solids in wastewater by a membrane method, and more particularly to a method for operating a membrane separation apparatus used for treating suspended solids in a wastewater treatment apparatus.

[0002]

2. Description of the Related Art It has been attempted to use a filtration operation using a microfiltration membrane or an ultrafiltration membrane for treating tap water, industrial waste water, industrial water, and the like. Filtration using a permeable membrane has a smaller apparatus scale than conventional sand filtration, and can completely remove suspended substances such as turbid substances or bacteria contained in raw water. In a membrane separation apparatus for treating a suspended substance, a coagulation-sedimentation treatment is performed as a pretreatment. That is, a floc containing a suspended substance is formed by adding a flocculant to wastewater, and the suspended substance is removed from the wastewater by removing the floc by membrane treatment.

[0003] For example, in the treatment of domestic wastewater and industrial wastewater (containing several to several hundred ppm of suspended solids), in the coagulation sedimentation method conventionally performed as a pretreatment, ferric chloride and aluminum sulfate are used as coagulants. And polyaluminum chloride, and depending on the type of coagulant, generally, several mg / L is added to the wastewater. For example, polyaluminum chloride (hereinafter referred to as "PAC")
When is used as a coagulant, several mg / L is added in terms of Al ₂ O ₃ . In general coagulation sedimentation, several mg / L
Since the purpose of coagulation and precipitation can be sufficiently achieved by the addition of a coagulant to such an extent, such an addition is generally applied from the viewpoint of cost.

[0004]

However, in the case of directly treating raw water having large fluctuations in water quality, there are various problems in the operation management of the apparatus, such as closing of the flow path of the membrane and clogging. For example,
As in the conventional case, when microfiltration or ultrafiltration is performed on a liquid pretreated by adding several mg / L to wastewater, scale gradually accumulates on the membrane surface, and a phenomenon in which membrane performance decreases is observed. In order to remove the scale on the membrane surface, excess membrane cleaning water is necessary, and the treatment of the wastewater is also a problem.
Furthermore, the cleaning wastewater of the membrane is discharged out of the system, and there is a problem that the ratio (recovery rate) of the treated water to the supply water to the apparatus is reduced. Therefore, the object of the present invention is to
It is an object of the present invention to provide a method for treating suspended solids in waste water, in which a scale does not accumulate on a membrane surface and a microfiltration treatment or an ultrafiltration treatment can be performed.

[0005]

Means for Solving the Problems To achieve the above object, the present inventors add a coagulant in an amount of 5 to 10 times the usual amount when a suspended substance is treated by a microfiltration membrane or an ultrafiltration membrane. A method for treating suspended solids was developed. According to the present invention, it is possible to provide a treatment method capable of stabilizing a film treatment without deterioration of the film and capable of stably treating a suspended substance for a long period of time.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for treating a suspended substance according to the present invention, a coagulant is added in an amount of 5 to 10 times the amount of a coagulant generally used for coagulation and precipitation. For example, P
When AC is used as a flocculant, PAC is converted to Al ₂ O
It is added at a concentration of 20 to 40 mg / l in terms of ₃ . The pretreatment liquid thus treated is treated with a microfiltration membrane or an ultrafiltration membrane. When the addition amount of the coagulant is less than 5 times the addition amount of the coagulant for the commonly used coagulation precipitation,
The desired effect is not obtained, and the addition of a flocculant more than 10 times is economically disadvantageous. When the suspended substance is separated by the method of the present invention, a stable treatment can be performed without a membrane surface scale as compared with the case where the conventional addition amount of the flocculant is added.

As the flocculant used in the method for treating a suspended substance of the present invention, ferric chloride, aluminum sulfate and the like can be used in addition to PAC.

[0008] In the case of membrane treatment, the generation of giant flocs by coagulation rather than fine flocs enables stable treatment without blocking of the pores of the membrane. Generally, a membrane having a pore size of about 0.1 to 1 μm is used.

In the microfiltration test, quantitative filtration can be performed with a flux of 70 L / (m ² · h) as schematically shown in FIG. In this case, the performance is P _E = (P
₁ + P ₂₎ / can be evaluated by the effective pressure P _E represented by 2-P _3. Here, P ₁ represents the inlet pressure of the primary side of the membrane, P ₂ represents the primary side outlet pressure of the membrane, and P ₃ represents the secondary side pressure of the membrane. According to this equation, indicating that the higher the P _E increases, the membrane performance is lowered according to the filtration progresses.

[0010] When the addition amount of the aggregating agent used for ordinary flocculation as in the conventional method is added, increases the P _E gradually film but performance is reduced, typically using aggregation as in the present invention 5 to 10 with respect to the amount of coagulant added for precipitation
When adding volumes of coagulant, increase in P _E is no performance degradation of the membrane is not observed.

[0011]

The present invention will be described in more detail with reference to the following examples.
However, these are intended to limit the present invention.
It is not intended. PAC is changed to Al_TwoO_Three
The case of adding at a concentration of 4 mg / L in terms of
PAC is converted to Al according to the method of the present invention._TwoO_ThreeConverted to
20 mg / L or 40 mg / L
As an example, the membrane area is 0.05m^TwoThrough the microfiltration membrane
Was. Flux = 70 L / (m^Two
H), water flow time is 15 minutes, backwashing is 65 seconds and air pressure 6
kg / cm^TwoG. Comparative example and PAC were 20
back pressure P in the example where mg / L was added_ThreeAnd effective pressure P
_E2 is shown in FIG. 2, and 40 mg / L of PAC was added.
Back pressure P in the embodiment_ThreeAnd effective pressure P_EFigure 3 shows the change
Show.

PAC is converted to Al ₂ O ₃ and is 4 mg / L.
(Comparative Example), the back pressure P
₃ decreases, although P _E is increased with it, Al ₂ O
₃ in terms of the case of adding a PAC 20 mg / L or 40 mg / L (Example) is, P ₃ also without reducing, did not increase almost no P _E. Therefore, PA
It was found that when the coagulant was added in an amount of 5 to 10 times the amount of the coagulant for coagulation and precipitation generally using C, the membrane performance did not decrease even if the filtration was continued.

[0013]

As is apparent from the above description, according to the present invention, when a pretreated liquid is treated with a microfiltration membrane or an ultrafiltration membrane, the membrane is not deteriorated and the membrane treatment is stabilized. The suspension can be stably treated for a long period of time while maintaining a high recovery rate.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a microfiltration test.

FIG. 2 is a graph showing the results of a continuous water flow test of a comparative example and an example in which PAC was added at 20 mg / L.

FIG. 3 is a graph showing the results of a continuous water flow test of an example in which PAC was added at 40 mg / L.

Claims (2)

[Claims] 1. A method for treating a suspended substance by a membrane method, wherein a coagulant is added in an amount of 5 to 10 times the usual amount during a treatment operation of the suspended substance by a microfiltration membrane or an ultrafiltration membrane. 2. The method according to claim 1, wherein the coagulant is polyaluminum chloride.