JPS60166097A - Dephosphorizing method by biological treatment - Google Patents

Abstract

PURPOSE:To remove 90% each of BOD, nitrogen, and phosphorus by repeating sewage agitation and aeration in a treating vessel, spending more time for the agitation than for the aeration, and limiting a set of time for both processes within several hours. CONSTITUTION:The sewage is continuously introduced into treating vessel 1, and agitation and aeration are carried out in cycle. Both processes are alternately repeated. Accordingly, anaerobic conditions by the agitation and aerobic conditions by aeration are alternately and repeatedly applied to the sewage. In this case, at least more time must be spent for the agitation than for the aeration to remove the phosphorus. The time spent for one cycle is necessarily limited within several hours, preferably within 2hr. In addition, the dephosphorizing effect can be increased by changing the time for aeration and agitation at any time in correspondence with the water temp. of the vessel, the BOD concn. in the inflowing water, and the nitrogen concn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dephosphorization method using biological treatment that effectively dephosphorsizes by combining a stirring step and an aeration step.

When sludge is kept under anaerobic conditions for a certain period of time, microorganisms in the sludge elute phosphorus to preserve life.

Afterwards, when the sludge from which phosphorus has been eluted is kept under aerobic conditions, the microorganisms in the sludge ingest an excessive amount of phosphorus, and the phosphorus content in this sludge is 2 to 4 times higher than that of sludge that has not passed through anaerobic conditions. It will be about twice as expensive.

The first biological dephosphorization process utilizing this phenomenon is
What is proposed is shown in the figure. However, this process requires a separate anaerobic treatment tank, and in order to perform effective dephosphorization, the residence time of each type must be within a predetermined range. There is a drawback that the dephosphorization effect decreases not only when the anaerobic time is short, but also when the anaerobic time is longer than necessary, and even when the aerobic process time is long or long.

Furthermore, in the above process, since the various capacities are fixed, when the inflow amount of wastewater changes, the various residence times change, making it impossible to perform stable dephosphorization. In addition,
If the tank capacity is designed with a margin in mind, the residence time in the tank will be too long and the phosphorus removal rate will decrease. Therefore,
In order to prevent this, a large-capacity flow regulating tank is required, which is uneconomical.

In order to eliminate the above-mentioned drawbacks, the present invention aims to provide a dephosphorization method using biological treatment that performs effective dephosphorization by alternately repeating a stirring step and an aeration step at predetermined intervals.

An embodiment of the present invention will be described below with reference to the drawings.

For example, as shown in FIG. 2, an apparatus to which the present invention is applied includes a processing tank 1 and a settling tank 2.

Sewage is continuously introduced into a treatment tank 1, where it is subjected to a predetermined treatment, and then guided to a settling tank 2 as a mixed liquid. After the sedimentation treatment in the sedimentation tank 2, the sedimentation supernatant liquid is discharged as treated water, while the sedimentation sludge is returned to the treatment tank 1.

In the treatment tank 1, as shown in FIG. 3, one stirring step and one aeration step constitute one cycle, and both steps are repeated alternately. Therefore, the wastewater is alternately put into anaerobic conditions due to the stirring process and aerobic conditions due to the aeration process.

Here, in order to remove phosphorus, it is necessary to make the stirring process time longer than the aeration process time, and in the example shown in Fig. 3, the aeration process is repeated for 15 minutes and the stirring process for 45 minutes alternately. ing.

Figure 4 shows the experimental results showing the relationship between the time ratio of stirring process: aeration process (stirring process/aeration process) and the phosphorus removal rate. I understand what I can get. As is clear from this figure 4,
In order to effectively remove phosphorus, the stirring step time needs to be 1 to 5 times (preferably 2 to 3 times) longer than the aeration step time. This is because phosphorus must be eluted from the sludge under anaerobic conditions during the stirring process. At this time, if the stirring step is too long, the BOD removal rate of the treated water will decrease.

Furthermore, if the length of one set of the above-mentioned steps and one cycle of the pick is too long, the phosphorus removal rate will decrease.

FIG. 5 shows the experimental results of 1 cycle time and phosphorus removal rate.

As is clear from FIG. 5, the length of one cycle must be within several hours (preferably within 2 hours).

This is because if the length of one cycle is too long, the phosphorus eluted during the stirring process will be discharged as is. If the time of one cycle is shortened, phosphorus elution will occur at the beginning of treatment tank 1, but as the elution and over-intake is repeated several times or more in treatment tank 1, the amount of elution decreases, and elution will no longer occur even with excessive intake. Phosphorus removal rate is improved. Regarding nitrogen removal, if one cycle takes a long time, nitric acid is discharged during the aeration process and ammonia is discharged during the stirring process, so the denitrification rate also decreases.

Note that an adjustment period (idle step) in which neither aeration nor stirring is performed may be provided between or during the aeration step and the stirring step. Also, what is the water temperature of the tank and the BOD concentration of the inflow water? The dephosphorization effect can be improved by changing the aeration and stirring times according to the element concentration.

Furthermore, the following means can be considered in order to carry out more effective dephosphorization and also to achieve other purposes at the same time.

(2) Measure the Do in the treatment tank 1 during the aeration process, and control the DO value to be, for example, 2 q/L. This means that if the Do is high during the aeration process, the time it takes for the DO to reach zero will be longer and the time in aerobic conditions will be substantially longer, and if the DO is low, the time in anaerobic conditions will be longer. . By controlling DO, the substantial aerobic time and anaerobic time can be appropriately adjusted.

This control may be performed by known means such as P4A rotation speed control.

■If denitrification is also performed, NH4-N, NCh of the treated water
By measuring -N and N03-N and controlling the N removal rate so that it approaches 100, the phosphorus removal rate can often be kept high.

■ Even in cases where NH4-H is discharged without the purpose of nitrification or denitrification, the method of this invention involves repeating stirring and aeration alternately over a period of several hours, and making the stirring process longer than the aeration process. can be applied effectively, and more than 90 phosphorus can be removed. Note that an aeration zone may be provided between the treatment tank 1 and the settling tank 2 at all times.

As described above, according to the present invention, by repeating the stirring step and the aeration step alternately under specific conditions, biological dephosphorization can be performed and BOD.

It has the effect of removing over 90% of both nitrogen and phosphorus.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional biological dephosphorization process, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is an explanatory diagram of process time, and Fig. 4 is a diagram showing phosphorus removal rate and stirring/aeration. FIG. 5 is a diagram showing the relationship between the phosphorus removal rate and the one cycle time of both steps. 1... Processing tank, 2... Sedimentation tank. Patent Applicant Nishihara Environmental Health Research Institute Co., Ltd. Agent Patent Attorney 1) Hiroshi Sawa, Agent Patent Attorney Nobuo Ishibashi Agent Patent Attorney Kimiyoshi Kato Drawing 3 (No change in content) Figure 1, Figure 2 Figure 4: Aeration: Darkness 1v Iku J Shino B Kishishi Continued from page 1 [Phase] Inventor Makoto Tabata - 3-6-18 Shibaura, Minato-ku, Tokyo Nishihara Environmental Health Research Co., Ltd. Internal procedure amendment (method) % formula % 1. Indication of the case Japanese Patent Application No. 59-21814 2. Name of the invention Dephosphorization method based on biological theory 3. Relationship with the case of the person making the amendment Patent applicant address name Nishihara Yokyo Health Research Institute Co., Ltd. Date of amendment order April 24, 1980 7 Contents of amendment (1) Engraving of application (no change in content) C) Engraving of specification (no change in content) ( 3) Engraving of drawings (no changes to the contents)

Claims (2)

[Claims] (1) A method of treating the wastewater by causing the wastewater to flow into a treatment tank and repeating a stirring process and an aeration process alternately in the treatment tank, wherein the stirring process time is longer than the aeration process time. , and a method for dephosphorization by biological treatment, characterized in that the time for one set of both steps is within several hours. (2) The dephosphorization method by biological treatment according to claim 1, characterized in that the stirring step time is at least twice as long as the aeration step time.