JPH0611440B2 - Sewage treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating sewage, night soil-based sewage, industrial sewage, and other sewage, in which phosphorus is removed at the same time as organic substances with high efficiency.

(Problems to be Solved by Conventional Techniques and Inventions) In recent years, the problem of eutrophication in rivers, lakes and marine areas has been widely taken up. In particular, eutrophication has been remarkably progressing in lakes such as Lake Biwa and Lake Kasumigaura. Phosphorus has been cited as one of the causes of this eutrophication. .

Conventionally, as a method for removing phosphorus, a method in which a coagulant such as Ca, Al, or Fe salt is added to sewage that has been subjected to biological treatment to coagulate and precipitate is generally adopted. However, this method produces a large amount of non-dehydrating sludge due to the injection of coagulant,
It is not an economical method because its disposal requires considerable expense. Therefore, development of a simple and efficient phosphorus processing method is desired.

Recently, studies have been conducted on a biological dephosphorization method utilizing the excessive phosphorus uptake effect of microorganisms by repeated anaerobic-aerobic treatment and a crystallization dephosphorization method using bone charcoal and phosphate rock. However, these treatment methods have drawbacks such as difficult management and difficulty in obtaining a stable treatment effect. In addition, although sewage treatment by a circulating contact aeration method using plastic, fiber or lumps as a contact filter medium is also widely used as an organic matter removal treatment, it does not have the effect of removing phosphorus, and a separate phosphorus removal method is used for removing phosphorus. Higher level treatment was required.

(Means for Solving Problems) The inventors of the present invention have completed the present invention as a result of earnest research in order to solve the drawbacks of the conventional methods in view of the above circumstances. That is, in the present invention, an iron filter medium alone or as a main material is filled as a contact filter medium, and sewage is circulated and aerated so that the phosphorus load on the surface area of the iron filter medium is 1.0 g / m ² · day or less. The present invention provides a method for treating sewage, which is characterized by removing organic matter and phosphorus in the sewage.
This has made it possible to make the removal of organic matter and phosphorus from wastewater highly efficient and stable.

Hereinafter, the method of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view of an example of a sewage treatment apparatus by a circulating contact aeration method used in the method for removing phosphorus in wastewater according to the present invention, in which a plastic filter material or a stone block filter material is used as a contact filter material. It is a well-known circulating aeration type sewage treatment device for treating biofilm sewage. That is, the sewage enters the aeration chamber 4 which is partitioned by the partition wall 3 of the contact filter medium tank 2 from the introduction pipe 1, and enters the contact filter medium tank 2 by the air lift effect of the air bubbles blown out from the diffuser pipe 5 together with the circulating sewage.
The organic matter in the wastewater is treated while passing through the contact filter medium 6 to circulate and aerate the surface of the contact filter medium, and the treated water subjected to the circulation contact aeration is discharged from the treated water discharge port 7, or It is introduced into a settling tank (figure omitted) and then discharged.

The features of the present invention are that an iron filter medium is used as the main material in the contact filter medium 6, the filling amount of the iron contact filter medium is calculated from the treated amount of phosphorus, and the removal of phosphorus by the iron contact filter medium is performed by the iron contact filter medium. The surface area of sewage and circulation aeration of sewage are the most important factors. That is, high efficiency phosphorus removal can be stably obtained by filling the iron contact filter medium so that the load of phosphorus on the surface area of the iron filter medium is 1.0 g / m ² · day or less and circulating and aeration of the sewage. . As described above, the phosphorus load on the iron contact filter medium is effective at 1.0 g / m ² · day or less, but practically 0.1 to 1.0 g / m ² ·
If it is less than 0.1 g / m ² · day, the clogging phenomenon of the filter medium due to SS in the wastewater and the generated sludge will be accelerated,
It is necessary to wash the filter medium frequently. On the other hand, if the phosphorus load on the surface area of the iron filter medium is larger than 1.0 g / m ² · day, the dephosphorization effect is small and the circulation of sewage is reduced, that is, in the case of full aeration, the treatment effect is small even with the same aeration amount. . In addition, the effect of removing phosphorus is hardly obtained when only the plastic contact filter medium is filled. Although the mechanism of phosphorus removal by iron filter media is not clear, crystalline or amorphous insoluble iron phosphate is formed by reacting Fe ion elution from the iron contact filter media with phosphorus ion components in wastewater. , It seems that the iron phosphate is included in the microbial membrane on the surface of the iron filter medium due to the cyclic aeration and becomes a mixed body. This fact and that sludge hardly flows out to the sedimentation tank, the iron contact filter medium Fe on the surface microbial film
It is considered that the excessive outflow of ions is prevented and phosphorus is efficiently removed.

Although it is related to the concentration of organic matter in the sewage, if the microbial film on the surface of the contact filter medium is excessively thickened during the treatment of sewage, the removal effect of phosphorus tends to decrease. Is desired. For cleaning the surface of the contact filter medium, it is general to use an air backwashing method in which a large amount of air is flowed through the backwashing pipe 8 for washing. The sludge separated from the filter medium by this backwash shows almost no phosphorus release even if it is stored and left for one week or more, which is significantly different from the stored sludge biologically dephosphorized by the activated sludge method.

Specific examples of the iron filter medium used as the contact filter medium are those having a large surface area such as a reticulated iron material such as an iron plate, punching metal or expanded metal, or a spherical filler having a reticulated void or a cylindrical filler. Further, these iron filter media are preferably used alone, but they can be used in combination with a plastic filter media. At this time as well, the load of phosphorus on the surface area of the iron filter medium was 1.0 g / m ² ·
It should be less than a day.

Fig. 2 shows experimental values of phosphorus removal rate in sewage when the phosphorus load (g / m ² · day) to the iron filter medium surface area was changed by changing the amount of treated wastewater (only for plastic filter medium for comparison). in also described), phosphorus load on iron contact filter media surface area is in the range of 0.1 to 1.0 g / m ² · day were obtained 90% of the phosphorous removal rate, practically the following ^2-days 1.0 g / m It is clear that this is preferable.

(Example) An example is given below.

Examples 1-2 and Comparative Examples 1-3 In the circulating contact aeration tank (volume 67) shown in FIG. 1, expanded metal XS-42 (iron material) as a contact filter medium and plastic filter medium (small cylinder having mesh-like voids) Using and, the ratio of expanded metal and plastic filter media was changed to make the contact filter media volume 45 (filling ratio 67%), and the circulating aeration treatment was performed using artificial sewage. The amount of treated water was 40 / day and the residence time was 40 hours. The results are shown in the table below.

As a result, the treatment effect of the method of the present invention was outstanding. That is, as in Examples 1 and 2, if the phosphorus load on the surface area of the iron filter medium is 1.0 g / m ² · day or less, the effect of phosphorus removal is large, and 1.5 g / m ² · day and 1.7 g are obtained. / M ²
-The phosphorus removal rate significantly decreased on the day (Comparative Examples 1 and 2). The filling of the plastic filter medium alone as Comparative Example 3 lowered the BOD value, but the effect of removing phosphorus was hardly obtained.

Example 3, Comparative Examples 4 to 5 Circulating contact aeration tank as shown in FIG. 1 (volume 5.2)
Filled with expanded metal XS-42 (iron material) as a contact filter material, the filter material volume is about 50% (2.6, iron filter material surface area is about 0.2 m ² ) and the sewage is activated sludge treated water of industrial wastewater (phosphorus concentration). Was used to treat sewage while circulating and aeration. The treatment amount was 10 / day, and the phosphorus load on the surface area of the iron filter medium was 0.15 g / m ² · day. Further, in this case, the whole surface is aerated as a comparative example, and the other is the same as this example, but the circulation of the waste water is reduced by aeration from the lower part of the iron contact filter medium (Comparative example 4) and the contact filter medium. 1. As a plastic filter material (cylindrical material having mesh-like voids).
6 filling and circulation aeration (Comparative Example 5) were also carried out. The results are shown in the table below.

As a result, the phosphorus removing effect of Example 3 was remarkably excellent. Further, when the wastewater is not circulated as in Comparative Example 4, the removal effect is reduced even with the same aeration amount, and it is recognized that the circulation aeration as in the method of the present invention can dramatically improve the treatment efficiency. It was confirmed that the effect of removing phosphorus was remarkably low only with the plastic filter medium as in Comparative Example 5.

(Effects of the Invention) The method of using the iron contact filter medium in the circulating contact aeration method of the present invention achieves a dramatic improvement in phosphorus removal efficiency while the phosphorus removal effect is hardly obtained only by the plastic filter medium. Once the contact filter medium is installed, even if the microbial film becomes thicker on the surface of the filter medium over time, it can be washed as it is without removing it, and it is easy to circulate and aerate the contact filter medium for long-term desorption. This is an excellent sewage treatment method in which the phosphorus effect is highly efficient and sustained, and the amount of sludge generated is extremely small. Moreover, since the sludge obtained by the present invention is an organic sludge containing iron phosphate as a main component, it can be suitably used as a fertilizer for agricultural crops.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a circulating contact aeration treatment apparatus used in the method of the present invention, and FIG. 2 is phosphorus in wastewater obtained by changing phosphorus load (g / m ² · day) with respect to iron contact filter medium surface area. FIG. 3 is a correlation diagram showing the phosphorus removal rate and the phosphorus loading showing the experimental value of the removal rate. 1 ... sewage introduction pipe, 2 ... contact filter media tank, 3 ... division wall, 4
…… Aeration chamber, 5 …… Diffuser, 6 …… Contact filter, 7 …… Treated water outlet, 8 …… Backwash pipe

Claims (1)

[Claims] 1. An iron filter medium as a contact filter medium or a main filter medium filled with the filter medium, and sewage is circulated and aerated so that the phosphorus load on the surface area of the iron filter medium is 1.0 g / m ² · day or less. A method for treating sewage, which comprises removing organic matter and phosphorus in the sewage.