JPS6295500A - Method of treating decanting water - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a treatment method suitable for improving the settling properties of microparticle-sized cruds with poor settling properties and hydroxide compound cruds.

[Background of the invention]

Conventionally, a filter using an auxiliary agent was used as a filter, and when a differential pressure of more than a predetermined value occurred, the auxiliary agent was backwashed and discharged to a storage tank, and the supernatant water in the storage tank was drained. , the solids were settled, decanted, and treated.

On the other hand, from the viewpoint of reducing the amount of secondary waste generated, non-auxiliary filters that do not use any additives have come to be widely used.

The backwash water of non-auxiliary filters contains solids such as crud trapped by the filter, but those with fine particle size or hydroxide compounds have poor settling properties and must be decanted. It is not possible to measure the effective use of the tank. When an auxiliary agent was used, fine particles or hydroxide compounds with poor sedimentation properties were attached to the auxiliary agent, so that the problem of poor sedimentation did not occur.

[Purpose of the invention]

An object of the present invention is to provide a method for treating backwash water from a non-auxiliary filter, in which gold is recycled into backwash water.

It is an object of the present invention to provide a treatment method and treatment equipment for converting a hydroxide compound into an oxide and flocculating it to improve sedimentation properties.

(Summary of the invention) A non-auxiliary type filter that does not use an auxiliary agent is provided to replace the auxiliary agent type (KC block, powdered resin, etc.) that has been conventionally used in the treatment of waste liquid generated from nuclear power plants, etc. This is becoming widely used.

This is because in an auxiliary agent type filter, the auxiliary agent becomes secondary waste and the amount of waste increases. As a non-auxiliary filter,
As hollow cell filters and membrane filters,
Hollow cell filter membrane filters and the like are used.

The captured solids include colloidal substances that have poor sedimentation properties, such as iron hydroxide.

For this reason, the backwash water received into the backwash water receiving tank of the non-auxiliary filter has poor sedimentation properties, making it difficult to decant the supernatant water, making it difficult to make effective use of the tank. are doing. In conventional auxiliary type filters, colloidal substances adhere to the auxiliary agent, so they do not interfere with sedimentation and do not pose a major problem.

Effective countermeasures against this problem include a method of converting the hydroxide into an oxide using an oxidizing agent, and a method of thermally transforming the hydroxide into an oxide or anhydride.

This is because iron hydroxide is easily oxidized by an oxidizing agent and becomes stable iron hydroxide.

Various oxidizing agents can be used as the oxidizing agent, but hydrogen peroxide (HzOz) is suitable from the viewpoint of protecting the tank material.

Moreover, as a thermal treatment method, a method of heating to a temperature of 60' to 100° C. to convert it into an oxide is effective.

[Embodiments of the invention]

<Example 2> All of the backwash water from the non-auxiliary filter is put into the backwash water receiving tank 4 and left standing. Solids settle at the bottom of the tank, but colloidal substances such as iron hydroxide do not settle and float at the top of the tank.

When the decant valve located below the water level of the backwash water receiving tank is opened and the supernatant water containing iron hydroxide is passed through the regeneration heat exchanger 2 and heated to 60°C to 100°C in the heat exchanger 3, iron hydroxide is extracted. becomes anhydride or iron oxide.

The supernatant water heated by the heat exchanger is cooled by the regenerative heat exchanger 2 and returned to the backwash water receiving tank. Thermal efficiency can be improved by using the heat exchanger 3 and the regenerative heat exchanger.

After the above operation is continued for a predetermined period of time and the radioactivity concentration of the supernatant water reaches a predetermined value or more, the supernatant water is decanted from the decant line.

Figure 2 shows the sedimentation rates of iron hydroxide and iron oxide particles, and it can be seen that iron hydroxide has an extremely slow sedimentation rate because it is colloidal.

<Example 2> An example will be explained with reference to FIG.

The backwash water in the backwash water receiving tank is heated with a heat exchanger 3 or a heater (not shown) to a temperature of 60°C to 100°C, converting iron hydroxide to iron oxide and causing sedimentation. improve.

After maintaining the above-mentioned temperature for a predetermined time, when the solid content concentration of the supernatant water reaches a certain value or more, the supernatant water is decanted from the decant line.

〔Effect of the invention〕

The effects of the present invention are shown below.

■ Sedimentation separation performance of backwash water of non-auxiliary filter mixed with iron hydroxide has been reduced from 1/10 to 1/1000 of the conventional one.
It can be improved by 0 times.

■By using a regenerative heat exchanger and a heat exchanger as a heating source, thermal efficiency can be significantly improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a decant treatment system, FIG. 2 is a diagram of sedimentation characteristics of iron hydroxide and iron oxide, and FIG. 3 is a schematic diagram of a decant treatment system. 1... Decant valve, 2... Regeneration heat exchanger, 3...
... Heat exchanger, 4... Backwash water receiving tank.

Claims (1)

[Claims] 1. In a method for treating backwash water of a non-auxiliary filter generated from a nuclear power plant, etc., means for heating supernatant water in a backwash water receiving tank to 60°C to 100°C. A decant water treatment method comprising: 2. In claim 1, the supernatant water is heated to 60°C or more.
A decant water treatment method comprising a regenerative heat exchanger and a heating heat exchanger as means for heating to 100°C.