JPS6233598A - Treatment of sludge - Google Patents

Abstract

PURPOSE:To control the elution of phosphorus from sludge by stopping the aeration of excess sludge having taken in an excess amt. of phosphorus for a specified time, resuming the aeration and repeating the process. CONSTITUTION:The aeration of excess sludge contg. a large amt. of phosphorus generated in the biological dephosphorization of sewage is stopped for a specified time, then the aeration is carried out for 12hr and the process is repeated. The sludge is stored and then brought out or dehydrated after aeration is carried out the specified number of times. Consequently, the elution of phosphorus from sludge can be prevented, the excess sludge can be stored in a storage tank, etc., for a long time (e.g., one week) without eluting phosphorus to the outside of the system even when the sludge is used in a small-scale sewage treating apparatus with comparatively less frequency of inspection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a sludge treatment method for preventing re-elution of excessive phosphorus taken into excess sludge.

[Conventional technology]

Recently, as a method to remove phosphorus from wastewater! IJ Ki-
Biological dephosphorization methods using aerobic methods are attracting attention.

However, with these methods, if sludge that has taken in too much phosphorus is placed under anaerobic conditions such as in a sludge reduction tank or storage tank, the phosphorus that has been taken in will re-elute from the sludge. There was a problem in that the tank supernatant water and dehydrated separated liquid returned to the water treatment system, resulting in a decrease in the phosphorus removal rate in the water treatment system.

Therefore, in order to re-uptake the phosphorus eluted from the sludge into the sludge using the same principle as the biological dephosphorization method described above, it is necessary to re-uptake the phosphorus eluted from the sludge within a certain period of time (for example, within 24 hours from the elution).
Sludge is being re-aerated.

However, the reaeration time is longer than a certain time (for example, 12
If the condition continues for more than an hour, the aerobic conditions will continue for too long and the sludge's ability to absorb excess phosphorus will decline.

There was a problem in that the phosphorus concentration in the molten enemy increased. For example, FIG. 4 is a diagram showing the correlation between the re-aeration time and the phosphorus concentration in the solution when sludge from which phosphorus has been eluted is re-aerated for 24 hours under anaerobic conditions. From this, it can be seen that when the above-mentioned re-aeration time is 12 hours or more, the concentration of phosphorus in the solution increases, and the function of excessive phosphorus intake is reduced as described above.

This invention was made in order to solve the above-mentioned problems, and is a sludge treatment method that suppresses the elution of phosphorus by stopping aeration for a predetermined time and repeating aeration for surplus sludge that has taken in too much phosphorus. The purpose is to provide

[Means for solving problems]

The sludge treatment method according to the present invention repeats an aeration stop step for a predetermined time to place surplus sludge under anaerobic conditions, and a subsequent aeration step for a predetermined time to place the surplus sludge under aerobic conditions.
This prevents the elution of phosphorus from sludge for a relatively long period of time.

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

This invention is directed to excess sludge that has been overingested with phosphorus generated during biological dephosphorization treatment. Therefore, an example of the treatment flow sheet including the water treatment system is 2jf
, shown in Figure 1.

In FIG. 1, 1 is an anaerobic tank, 2 is an aeration tank, 3 is a sedimentation tank, 4 is a storage tank, and 5 is a dehydrator.

In this treatment flow sheet, first, sewage 6 and return sludge 7 are mixed in an anaerobic tank 1, kept under anaerobic conditions, and phosphorus in the sludge is released.

The plate ft treated anaerobically in this way is led to the aeration tank 2,
The aeration treatment here causes the released phosphorus and inflow phosphorus to be excessively ingested into the sludge.

The aerated liquid is subjected to solid alpha separation in the settling tank 3, and the supernatant water is discharged as treated water 8. A part of the separated activated sludge 9 is returned to t1 as return sludge 7, and the remainder is surplus sludge 10. It is introduced into the storage tank 4 as a liquid. The sludge introduced into storage tank 4 is
After being stored in the condition 11 for less than 4 hours, aeration is performed for less than 12 hours using an aeration device (not shown) provided in the storage tank 4.

Repeat these steps fc multiple times to dewater the sludge after aeration! 5 and dehydrated.

FIG. 2 is intended to show the change in phosphorus concentration in the solution over time when this invention is practiced. Phosphorus eluted during the aeration stop process is absorbed into the sludge during the aeration process.

In this way, by repeating the aeration stop for 18 hours and the aeration for 6 hours, even during storage for 5 days.

The phosphorus concentration in the solution after aeration is approximately Olq/l.

Here, if the aeration stop step is set to within 24 hours, for example, and aeration is carried out after maintaining anaerobic conditions for 24 hours or more as shown in Figure 3, the sludge will be reduced to 98% in 48 hours and 96% in 72 hours. This is because the reuptake rate of phosphorus decreases in inverse proportion to the time it is kept under anaerobic conditions.

Then, after the aeration stop step and the subsequent aeration step are alternately repeated as described above, the excess sludge is taken in phosphorus by the aeration step, and then taken to a dewatering step by a dehydrator or directly carried out to the outside of the system.

〔Effect of the invention〕

As described above, according to the present invention, phosphorus is eluted from the sludge by alternately repeating the process of keeping surplus sludge containing excessive phosphorus in a state where aeration is stopped for a predetermined period of time, and then aerating for a predetermined period of time. Even when used in small-scale sewage treatment equipment that requires relatively infrequent inspection and management, excess sludge can be stored in a storage tank or the like for a long period of time (for example, one week) without leaching phosphorus out of the system. This has the advantage that it is possible to

[Brief explanation of drawings]

Figure 1 is a treatment process diagram including the sewage treatment system, Figure 2 is an explanatory diagram showing changes in the phosphorus concentration in the solution at each step when the surplus sludge treatment method according to the present invention is carried out, and Figure @3 is the surplus sludge treatment method. for the time the sludge was under anaerobic conditions. Figure 419 shows the relationship between the re-aeration time and the phosphorus concentration in the solution. In the figure, 4 is a storage tank, 5 is a dehydrator, 7 is return sludge,
10 is surplus sludge

Claims (3)

[Claims] (1) Excess sludge with high phosphorus content generated in biological dephosphorization treatment of wastewater is stored while repeating an aeration stop step in which aeration is stopped for a predetermined time and an aeration step in which aeration is performed for a predetermined time. A sludge treatment method characterized by carrying out or dewatering sludge. (2) The sludge treatment method according to claim 1, characterized in that the predetermined time of the aeration stop step is within 24 hours. (3) The sludge treatment method according to claim 1, characterized in that the predetermined time of the aeration step is within 12 hours.