JPH06170388A - Treatment of sewage - Google Patents

Abstract

PURPOSE:To provide a sewage treatment method shortening a treatment time to a large extent to reduce the scale of an apparatus and capable of enhancing the removal ratio of a nitrogen compd. to a large extent. CONSTITUTION:Inflow sewage hot passed through a final sedimentation basin is supplied to a contact stable tank 1 along with the return sludge from a sludge aeration tank 2 and the org. matter and suspended substance in sewage are adsorbed on the sludge to denitrify nitrate nitrogen. The mixed liquid is separated into supernatant water and separated sedimented sludge in a sedimentation tank 3 and the supernatant water is discharged as treated water while a part of the separated sedimented sludge is discharged as excessive sludge. The separated sedimented sludge withdrawn from the sludge pits 4 on and after the second pit among the separated sedimented sludges is aerated in the sludge aeration tank 2 to perform the decomposition of the org. matter and the nitration of ammoniacal nitrogen and the aerated sludge is suplied to the contact stable tank 1 as return sludge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating sewage.

[0002]

2. Description of the Related Art As a conventional general sewage treatment method, a standard activated sludge method is known as shown in FIG. In this method, the inflowing sewage is first guided to the sedimentation tank 21 and suspended solids (SS)
Is precipitated and then aerated together with the returned sludge in the aeration tank 22 to decompose organic matter, and further separated into supernatant water and sedimentation sludge in the final settling tank 23. However, in this method, the standard treatment time is 2.5 hours in the first settling tank 21, 6 hours in the aeration tank 22, and 3.5 hours in the final settling tank 23.
There is a drawback that the processing time is long and the equipment scale is increased accordingly.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in order to provide a method for treating sewage which solves the above-mentioned problems of the prior art. It is to reduce the scale. The second purpose is to significantly improve the removal rate of nitrogen compounds, which could be removed only by about 20 to 30% by the conventional method.

[0004]

The present invention, which has been made to solve the above-mentioned problems, is to supply inflowing sewage and return sludge from a sludge aeration tank to a contact stabilization tank, and to sludge the organic matter in the sewage and floating. After adsorbing pollutants such as substances and denitrifying nitrate nitrogen, the mixed solution is separated into supernatant water and sedimentation separation sludge in a sedimentation tank, and the supernatant water is discharged as treated water. Part discharges as excess sludge,
The remainder of the settling sludge is characterized by aeration in a sludge aeration tank to decompose organic matter, nitrifying ammonia nitrogen, and then supplying it to the contact stabilization tank as return sludge.

The flow of the present invention will be described below in more detail with reference to FIG. First, unlike the conventional case, the inflow sewage is first supplied to the contact stabilization tank 1 without passing through the settling tank, and is agitated together with the returned sludge from the sludge aeration tank 2. The returned sludge is activated by aeration, and here pollutants such as organic substances and suspended substances in the sewage are adsorbed by the sludge. In addition, since the returned sludge has changed its organic nitrogen and ammonia nitrogen to NO _x -N of nitric acid or nitrous acid by aeration in the sludge aeration tank 2, it desorbs organic substances in sewage, especially soluble organic substances as hydrogen donors. Be suffocated. The treatment time in the contact stabilizing tank 1 may be about 0.5 to 1.5 hours, but it is preferably about 1.5 hours to complete denitrification.

The mixed liquid flowing out of the contact stabilizing tank 1 then enters the settling tank 3. A plurality of sludge pits 4 are provided at the bottom of the settling tank 3.
Are formed, and the supernatant water is discharged as a treatment liquid after a sedimentation time of about 3.5 hours. A part of the settling separation sludge is discharged as excess sludge, and the rest is sent to the return sludge. preferable. The reason is that, as shown in FIG. 2, when the proportion of the sludge extracted from the first sludge pit 4 from the mixed liquid inflow side increases, it takes time to activate the sludge in the subsequent sludge aeration tank 2. Is. In other words, since the settling separation sludge in the second and subsequent sludge pits contains a large amount of activated sludge, the settling separation sludge in the first sludge pit 4 contains a large amount of specific gravity and large organic particles in the inflowing sewage. , After the organisms in the activated sludge assimilate it,
This is because it takes time to activate.

Next, the settling separation sludge enters the sludge aeration tank 2,
Activated by aeration. The sludge aeration tank 2 is a fluidized bed type aeration tank to which a carrier slightly heavier than water (that is, a specific gravity of about 1.01 to 1.05) is added, and aeration is performed while the carrier 5 is prevented from flowing out by the screen 5. The aeration time is 6 to 8 hours when the carrier is absent, and 3 to 4 hours when the carrier is 20%, but it is about 1/3 on the basis of inflow sewage, so It is 2.0 to 2.7 hours without the carrier and 1.0 to 1.3 hours with the carrier. In this sludge aeration tank 2, organic nitrogen and ammonia nitrogen are nitrified. As described above, in the present invention, when the sludge aeration tank 2 is filled with 20% of the carrier, the sewage can be treated for 5.0 to 6.5 hours and 6.0 to 8.0 hours without filling.

Next, examples of the present invention are shown in Table 1 together with the conventional method. As is clear from Table 1, according to the present invention, it is possible to process up to a water quality that is not much different from the conventional method in about half the processing time of the conventional method, and TN (total nitrogen) is the same as the conventional method. It can be seen that the removal rate is significantly improved compared to the above.

[0009]

[Table 1]

[0010]

As described above, according to the sewage treatment method of the present invention, the conventional first settling basin can be omitted without deteriorating the quality of the treated water. It can be reduced to /2.5 to 2/3, and the scale of sewage treatment equipment can be reduced accordingly. In addition, according to the sewage treatment method of the present invention, it is 20 to 30 in the conventional method.
The nitrogen removal rate, which was%, can be increased to 60 to 70% by normal nitrification / denitrification and improvement of organic nitrogen and ammonia nitrogen adsorption in the contact stabilizing tank. The present invention can be used not only for ordinary sewage treatment, but also for treatment of industrial wastewater containing organic matter, waste water leaching, and the like.

[Brief description of drawings]

FIG. 1 is a flow sheet illustrating a process of the present invention.

FIG. 2 is a graph showing the relationship between the mixing ratio of the first pit sedimentation separation sludge in the sludge aeration tank and the aeration time required to activate the returned sludge.

FIG. 3 is a flow sheet illustrating steps of a conventional standard activated sludge method.

[Explanation of symbols]

 1 Contact stabilization tank 2 Sludge aeration tank 3 Settling tank 4 Sludge pit 5 Screen

Claims (3)

[Claims] 1. Influent sewage and return sludge from a sludge aeration tank are supplied to a contact stabilization tank to adsorb contaminants such as organic substances and suspended solids in sewage to the sludge and denitrify nitrate nitrogen, The mixed solution is separated into supernatant water and sedimentation separation sludge in a sedimentation tank, and the supernatant water is discharged as treated water, part of the sedimentation separation sludge is discharged as excess sludge, and the rest of the sedimentation separation sludge is a sludge aeration tank. A method of treating sewage, which comprises aerating with a gas to decompose organic matter, nitrifying ammonia nitrogen, and then supplying it as return sludge to a contact stabilization tank. 2. The sewage according to claim 1, wherein the settling tank has a plurality of sludge pits, and the settling separation sludge drawn from the second and subsequent sludge pits from the mixed liquid inflow side is used as return sludge. Processing method. 3. A sludge aeration tank is a fluidized bed aeration tank,
The sewage treatment method according to claim 1, wherein the aeration is performed while preventing the carrier from flowing out by a screen.