JP5170971B2 - Water treatment method using powdered activated carbon - Google Patents

Description

  The present invention relates to a method for removing odor components and chromaticity components by adding powdered activated carbon to raw water among water purification treatments using membrane treatment.

  Conventionally, raw water has been mainly filtered by sand filtration at water purification plants, but it requires a large site area and requires a long time for the filtration process. There are an increasing number of water purification plants that employ membrane filtration. In particular, if a filter membrane having a membrane pore size that does not allow bacteria and protozoa in raw water to pass through is employed, it is possible to cope with deterioration of the raw water quality.

  However, the separation membrane can separate SS and bacteria in raw water, but cannot remove odor components and chromaticity components dissolved in raw water. Therefore, as shown in Patent Document 1, activated carbon treatment in which powdered activated carbon is added to raw water to remove odor components and chromaticity components may be used in combination. In this case, the added activated carbon is sent to the separation membrane in the subsequent stage by the circulation pump together with the raw water and separated and recovered.

As described above, when the activated carbon treatment and the membrane treatment are used in combination, the powdered activated carbon is added in an amount proportional to the raw water flow rate. At this time, the activated carbon addition rate is based on the assumption that the contact between the added powdered activated carbon and the raw water is performed only in the section from the addition position to the separation membrane. Was set to an amount that exerts an adsorption effect. For this reason, in the past, a slightly excessive amount of powdered activated carbon has been added, and the running cost for this has not been negligible.
JP-A-10-309567

  The present invention solves the above-mentioned conventional problems and uses powdered activated carbon that can reduce the amount of powdered activated carbon and reduce running cost without reducing the ability to remove odor components and chromaticity components. It was made to provide a water treatment method.

The present invention was made to solve the above problems by adding powdered activated carbon to raw water and mixing it to adsorb odor components and chromaticity components, and then using powdered activated carbon together with SS in raw water in a membrane module in the latter stage In the water treatment method using powdered activated carbon for membrane separation, during the filtration continuation time, the contact between the powdered activated carbon and the raw water in the section from the addition position of the powdered activated carbon to the separation membrane is always continued , In order to keep the sum of the removal amount by contact of powdered activated carbon and raw water in this section and the removal amount by powdered activated carbon deposited inside the membrane module in relation to the removal amount of the chromaticity component, it is deposited inside the membrane module. The amount of powdered activated carbon added to the raw water flow rate is gradually reduced by the increase in the amount removed by the powdered activated carbon, and the powder in the section from the powdered activated carbon addition position to the separation membrane is reduced. It is characterized in reducing the amount removed by the contact of the raw water Metropolitan activated carbon.

  In addition, the method of decreasing the addition amount of the powdered activated carbon with respect to a raw | natural water flow rate stepwise within the filtration continuation time, or the method of reducing continuously within the filtration continuation time is employable.

  According to the present invention, at the initial stage of filtration, the required amount of powdered activated carbon is added to the raw water flow rate as in the past to adsorb odor components and chromaticity components contained in the raw water. Is captured on the membrane surface of the subsequent separation membrane, and is retained on the membrane surface as it is during the filtration duration. Moreover, this powdered activated carbon has not lost its adsorption effect. Therefore, even if the addition amount of the powdered activated carbon with respect to the raw water flow rate is gradually reduced within the filtration duration by the adsorption effect by the powdered activated carbon held in the membrane module, the necessary adsorption effect can be maintained. Therefore, the amount of powdered activated carbon added can be greatly reduced as compared with the prior art, and the running cost can be reduced.

Preferred embodiments of the present invention are shown below.
In FIG. 1, 1 is a raw water tank, 2 is a filtration pump, and 3 is a membrane module. Raw water such as river water and groundwater is stored in the raw water tank 1, driven into the membrane module 3 by the filtration pump 2, membrane filtered, and taken out as treated water. The separation membrane used in the membrane module 3 may be an organic membrane or a ceramic membrane, and the membrane shape may be any of a flat membrane, a tubular membrane, a monolith membrane, etc. A monolithic ceramic membrane manufactured by the company is used, and dead-end filtration is performed.

  A powdered activated carbon supply means 5 is provided in a pipe line 4 connecting the raw water tank 1 and the membrane module 3. The powdered activated carbon supply means 5 has a function of cutting out the powdered activated carbon from the hopper 6 and supplying it to the raw water flowing in the pipe 4. In order to ensure the contact time between the raw water and the powdered activated carbon, the installation position of the powdered activated carbon supply means 5 is preferably near the outlet of the raw water tank 1. Further, a mixing tank provided with a stirring blade may be provided between the raw water tank 1 and the membrane module 3, and mixing may be performed while stirring.

  The powdered activated carbon supply means 5 supplies powdered activated carbon in an amount corresponding to the flow rate of raw water flowing through the pipe line 4 detected by the flow meter 7, but supplies an amount proportional to the flow rate of raw water as in the prior art. Instead, the control device 8 gradually decreases the amount of powdered activated carbon added to the raw water flow rate within the filtration duration. That is, a sufficient amount is supplied with respect to the raw water flow rate at the start of filtration, but thereafter, the amount of powdered activated carbon added to the raw water flow rate is continuously or stepwise reduced.

  The reduction ratio is determined in consideration of the adsorption effect due to the powdered activated carbon held in the membrane module. That is, the added powdered activated carbon adsorbs odor components and chromaticity components in the raw water while flowing in the pipeline 4, but is still captured by the membrane surface of the membrane module 3 while retaining a part of the adsorption capability. The Therefore, the total removal amount of odor components and chromaticity components in the raw water = removal amount by contact with powdered activated carbon while flowing in the pipeline 4 + removal amount by the powdered activated carbon deposited inside the membrane module 3, Since the amount of powdered activated carbon deposited in the membrane module 3 gradually increases, even if the amount of powdered activated carbon added to the raw water flow rate is decreased by that amount, the total removal amount of odor components and chromaticity components can be kept constant. it can.

  FIG. 2 is a graph showing a change in the removal amount of odor components and chromaticity components when the addition amount of powdered activated carbon is continuously reduced. As shown in this graph, according to the present invention, the running cost can be reduced by reducing the amount of powdered activated carbon used without reducing the effect of removing the odor component and chromaticity component. On the other hand, in the conventional constant addition rate method shown in FIG. 3, excessive removal is performed.

  The membrane module 3 is back-washed every time a filtration operation is performed for 180 minutes, for example, and the activated carbon powder is removed together with SS deposited on the membrane surface. Therefore, the increase / decrease in the amount of powdered activated carbon is repeated with this filtration duration as one cycle.

  An example in which the present invention is applied to lake water containing 20 ng / L of the odorous substance 2-MIB is shown. In the conventional method, as shown in FIG. 4, a 5 mg / L activated carbon is added in proportion to the flow rate to obtain a removal rate of 100%. For comparison, the removal rate of 2 mg / L shown in FIG. 5 does not provide a sufficient removal rate at the beginning of the treatment, but the removal rate increases with the continuation of the treatment, and a removal rate of 100% is obtained when it exceeds 150 minutes. The odor removal effect of the activated carbon held in the membrane module was confirmed. In the treatment method to which the present invention is applied, as shown in FIG. 6, the initial addition rate is 5 mg / L, and the addition rate after 90 minutes of filtration is 2 mg / L, thereby ensuring a removal rate of 100% throughout. Compared with the conventional method in which 5 mg / L is constantly added, the required amount of activated carbon can be reduced by about 40%.

  As shown in the data of the above examples, according to the present invention, the amount of activated carbon powder can be reduced and the running cost can be reduced without reducing the odor component and chromaticity component removal ability. There are advantages you can do.

It is explanatory drawing which shows embodiment of this invention. It is a graph which shows the change of the addition rate and removal amount of the powdered activated carbon of this invention. It is a graph which shows the change of the addition rate and removal amount of the conventional powdered activated carbon. It is a graph which shows the change of the addition rate and odor removal rate of the powdered activated carbon of the conventional method in an Example. It is a graph which shows the change of the addition rate and odor removal rate of the powdered activated carbon of the comparative method in an Example. It is a graph which shows the change of the addition rate and odor removal rate of the powdered activated carbon of this invention method in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Filtration pump 3 Membrane module 4 Pipe line 5 Powdered activated carbon supply means 6 Hopper 7 Flow meter 8 Control device

Claims (3)

In the water treatment method using powdered activated carbon that adds powdered activated carbon to raw water and adsorbs it to adsorb odor components and chromaticity components, and membrane-separates the powdered activated carbon together with SS in the raw water with the membrane module in the latter stage,
While continuously filtering, the contact between the powdered activated carbon and the raw water in the section from the addition position of the powdered activated carbon to the separation membrane,
Regarding the removal amount of odor components and chromaticity components in raw water,
In order to keep the sum of the removal amount by contact between powdered activated carbon and raw water in the section and the removal amount by powdered activated carbon deposited inside the membrane module, the removal amount by powdered activated carbon deposited inside the membrane module increased. The amount of powdered activated carbon added to the raw water flow rate was gradually reduced by the amount, and the amount of removal by contact between the powdered activated carbon and the raw water in the section from the addition position of the powdered activated carbon to the separation membrane was used. Water treatment method.   The water treatment method using powdered activated carbon according to claim 1, wherein the amount of powdered activated carbon added to the raw water flow rate is decreased stepwise within the filtration duration.   The water treatment method using powdered activated carbon according to claim 1, wherein the amount of powdered activated carbon added to the raw water flow rate is continuously reduced within the filtration duration time.

Images