JP3264691B2 - Water treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment method for preventing the deterioration of biological contact filtration performance when the turbidity of raw water is significantly increased in biological contact filtration used for biological treatment of tap water. .

[0002]

2. Description of the Related Art In recent years, a large number of water supply companies have been studying the introduction of advanced water purification treatment accompanying the deterioration of water quality of raw water. In particular, river water in metropolitan areas where population is extremely concentrated,
Water pollution due to domestic wastewater is severe, and it is necessary for waterworks to cope with various pollutants.

In tap water having severe water pollution, there is a problem that diosmin and 2-MIB produced by plankton are present, and the tap water becomes musty. In addition, humic substances, which are abundant in domestic wastewater, are stable organic substances that are hardly decomposed even by microorganisms, and react with chlorine used in the water purification process to generate carcinogenic organic chlorine compounds. Both of these substances are dissolved organics and cannot be removed by current standard water purification systems (rapid filtration systems).

Attention has been paid to advanced water purification treatments such as biological treatment, ozone treatment, and granular activated carbon treatment as being effective for removing such dissolved organic substances. Of these, ozone treatment and granular activated carbon treatment are not only used as main processes when the purpose is to remove organochlorine compound precursors in tap water, but also when ammonia nitrogen, which consumes chlorine during disinfection, is high. It is necessary to reduce the amount of chlorine injection by combining biological treatment. In particular, since rivers in Japan have short flow distances, nitrification of ammonia nitrogen by the self-cleaning action of rivers cannot be expected, and biological treatment must be performed at the stage of raw water intake.

[0005] Among the biological treatments used in waterworks, the biological contact filtration method is a treatment in which raw water is directly flowed down to various carriers for retaining living organisms, and the raw water quality improvement effect is excellent in a short time. Is obtained. In particular, it has the characteristic of extremely high turbidity removal as well as nitrification of ammonia nitrogen.

[0006] Usually, this method is usually carried out at a raw water intake stage, and as shown in Fig. 3, raw water is subjected to biological contact filtration directly or after a sand basin, and then treated by coagulation sedimentation and rapid sand filtration. The method has been adopted.

[0007] However, in this conventional method, a stable treated water turbidity can be obtained when the raw water turbidity is around 10 degrees. However, if the raw water turbidity rises significantly due to the effect of heavy rain, etc., the removal rate does not decrease. Although not possible, the turbidity of the treated water increases as the turbidity of the raw water increases. For example, if the raw water turbidity is 100
When the temperature rises to about 20 degrees, the turbidity of the biological contact filtration water rises to about 20 degrees. At this time, since both the raw water turbidity and the biological contact filtration water turbidity rapidly increase in a short time, the subsequent coagulation sedimentation and the rapid sand filtration are carried out by increasing or decreasing the coagulant injection amount accordingly. And it was difficult to control the amount accurately. Furthermore, when performing the coagulation sedimentation treatment, the higher the raw water turbidity, the greater the number of turbidity particles in the water, which increases the chance of contact between the turbidity particles and facilitates floc formation. If the biological contact filtration was performed before, it was necessary to increase the injection amount of the flocculant.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and reduces the turbidity load on biological filtered water when the raw water turbidity is significantly increased, thereby reducing the amount of coagulant injected. It is an object of the present invention to provide a water treatment method for preventing deterioration of biological filtered water quality.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the turbidity of the biologically filtered water has been increased by performing the coagulation sedimentation treatment before the biological contact filtration. It has been found that it is possible to solve the problem in the operation management of the subsequent process, and arrived at the present invention.

That is, in the present invention, in the biological contact filtration for the purpose of improving the water quality of tap water, if the turbidity of the raw water rises to 50 ° C. or more due to the effect of heavy rain, etc., the coagulation and sedimentation will be carried out in the preceding step of the biological contact filtration. The gist of the present invention is a water treatment method for performing a treatment to prevent deterioration of water quality of biologically-contact filtered water. The flocculation and sedimentation is performed to prevent the turbidity of the biologically-contacted filtered water from deteriorating due to the increase in the turbidity of the raw water. It is processed.

[0011]

According to this configuration, it is possible to prevent the turbidity of the biologically-contacted filtered water from deteriorating, and it is possible to always obtain treated water having a stable water quality. In addition, the coagulation / sedimentation equipment for this purpose does not require a scale used in a conventional rapid filtration system, and the object can be achieved with a smaller equipment.

[0012]

Embodiments of the present invention will be specifically described below. When raw water turbidity rises significantly compared to normal due to the effects of heavy rain during a typhoon, etc., raw water is subjected to biological contact filtration as it is, and coagulation and sedimentation is performed before biological contact filtration, and then biological contact filtration is performed. A comparative study was conducted on the case of performing.

Hereinafter, a brief description of the experimental facilities and experimental conditions will be given. Biological contact filtration is 300mm inside diameter and 4000 height
Spherical fiber carriers were packed in transparent vinyl chloride columns of mm and 5000 mm, and water was passed down in a two-stage process. The spherical fiber carrier was made of polyester and had a diameter of about 5 to 7 mm. The filling height of the carrier was 2.0 m for both the first and second stages, the filtration speed was 480 m / day, and the continuous operation was performed with a treated water amount of 33.6 m ³ / day.

The coagulation and sedimentation equipment comprises a rapid mixing pond, a floc forming pond and a sedimentation pond, each having a residence time of 1 minute.
15 minutes and 30 minutes. The coagulant used was polyaluminum chloride, the volume injection rate was 5 ppm, and the raw water turbidity was
When the temperature exceeded 50 ° C., the coagulant injection was started, and when the temperature dropped to 40 ° C., the automatic operation was performed so as to stop the coagulant injection, coagulating and sedimenting the raw water, and flowing down to the biological contact filtration step.

The raw water turbidity was continuously measured by an integrating sphere turbidity meter, and the treated water turbidity of each step was measured by a tabletop integrating sphere turbidity meter. First, FIG. 4 shows the results of treatment by a conventional method in which raw water is allowed to flow as it is into biological contact filtration, followed by flocculation and rapid sand filtration. In this case, the raw water turbidity is about 80
Turbidity, while the turbidity of the biological contact filtrate decreased to about 10 degrees. Therefore, by injecting the flocculant at a volume injection rate of 15 ppm, the turbidity of the coagulated sediment water was reduced to about 1 degree, and the turbidity of the rapid sand filtration water could be maintained at 0.1 degree.

Next, FIG. 2 shows the results of the treatment according to the embodiment of the present invention in which raw water is subjected to coagulation and sedimentation treatment based on the treatment flow shown in FIG. 1, then allowed to flow down to biological contact filtration, and then subjected to direct filtration treatment. In this case, the turbidity of the raw water increased to about 90 °, the turbidity of the coagulated sedimentation treated water became about 30 °, the turbidity of the biologically contacted filtered water changed at about 1 °, and Maintained a turbidity of about 0.1 degree. At this time, the coagulant injection rate was 5 ppm, and according to the example of the present invention in which the coagulation operation was performed on the higher turbidity side, a treatment result equivalent to the conventional method was obtained with a small amount of the coagulant. In addition, since the flocculation is performed when the raw water turbidity is high, turbid particles are easily aggregated even in a rapid mixing pond and a floc forming pond with a residence time shorter than usual, and the flocculant having a low injection rate is used. Was obtained.

[0017]

As described above, according to the present invention, biological contact filtration can be performed not only when the raw water turbidity is low and stable, but also when the raw water turbidity is significantly increased. Is obtained, and the water quality improving function is more effectively exhibited with a small amount of coagulant injection. As a result, the coagulation and sedimentation equipment needs to be very compact and the operation management is very easy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a processing flow in an embodiment of the present invention.

FIG. 2 is a graph showing a processing result according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a processing flow in a conventional example.

FIG. 4 is a graph showing a processing result according to a conventional example.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Hideo Tateiri 2-115 Obamachi, Moriguchi-shi, Osaka Pref. Nishikubo Water Purification Plant, Osaka Water Works Department (72) Inventor Nobuyuki Aoyama 2-115 Obamachi, Moriguchi-shi, Osaka (56) References JP-A-4-277085 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 3/06 C02F 1/52 C02F 9/00 501 C02F 9/00 502

Claims (2)

(57) [Claims] 1. A water treatment method in which a coagulation sedimentation treatment is performed in a treatment process of raw tap water before a biological contact filtration.
In addition, the coagulation sedimentation treatment is performed with a rapid mixing pond with a residence time of 1 minute.
A floc formation pond with a residence time of 15 minutes and a sedimentation time of 30 minutes
Water treatment wherein the treatment with the gluteal pond. 2. Raw water turbidity is continuously measured using an industrial turbidity meter.
And when the raw water turbidity becomes 50 degrees or more, inject coagulant
Start and when the raw water turbidity drops below 40 degrees, the flocculant
The water treatment method according to claim 1, wherein an automatic operation for stopping the injection is performed .