JP3803883B2 - Purification device operation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a purification device for purifying waste water from a factory, a home, or the like.
[0002]
[Prior art]
Waste water from factories and households contains a large amount of high-molecular organic substances such as fat and protein, and if this is washed away into rivers and the sea, it causes environmental pollution. Therefore, as a purification device that gasifies and removes nitrogen components, etc. through the decomposition, nitrification, and denitrification processes by microorganisms, aerobic treatment and anaerobic treatment by microorganisms are alternately performed by intermittently aeration operation of the aeration tank It is known for the structure to do.
[0003]
The ammonium nitrogen in the waste water in the aerobic treatment (NH ₄ ⁺⁾ is nitrate nitrogen (NO ₃ ^-) and nitrite nitrogen (NO ₂ ^-) are oxidized and decomposed to and anaerobic treatment, anaerobic Denitrifying bacteria use organic carbon to reduce nitrate nitrogen (NO ₃ ⁻ ) and nitrite nitrogen (NO ₂ ⁻ ) generated by aerobic treatment and convert them into nitrogen gas (N ₂ ). In an anaerobic state, macromolecular organic substances such as fat and protein are decomposed into lower molecules such as acetic acid (CH ₃ COOH), and further decomposed into CO ₂ and CH ₄ by methanogens.
[0004]
As described above, a large amount of excess sludge is generated in an apparatus for biologically treating wastewater. Such surplus sludge is generally removed from the sedimentation tank and incinerated regularly, but since the processing cost increases, Japanese Patent Publication No. 60-3873 provides a sludge storage tank. A treatment method for digesting (decomposing gasification) surplus sludge in a storage tank has been proposed.
[0005]
Further, as prior arts in which sludge is returned from the sludge storage tank to the aeration tank to increase the nitrification efficiency, there are those disclosed in Japanese Patent Application Laid-Open Nos. 61-54295 and 2-284695.
[0006]
[Problems to be solved by the invention]
By the way, an aerobic treatment forms an oxide film on the sludge surface, and this oxide film prevents further decomposition. The present inventor does not readily destroy this oxide film in a normal reducing atmosphere. However, when the oxide film is reduced to a super anaerobic state (ORP ≦ −190 mV) where the oxidation-reduction potential is further lowered, the oxide film is reduced and softened and destroyed (disappeared). I got the knowledge that.
[0007]
In order to make the super-anaerobic state, a new super-anaerobic tank is provided or a conventional sludge storage tank is used. To lower the oxidation-reduction potential (ORP) to -190 mV or less, the sludge is allowed to stand for a predetermined period. Must.
In particular, if the sludge oxidation / reduction potential (ORP) is high when sludge is put into a super anaerobic tank or sludge storage tank, the standing time of the sludge must be lengthened accordingly. Problems arise.
On the other hand, if the sludge redox potential (ORP) is lowered by anaerobic treatment in the aeration tank and transferred to the sedimentation tank, the sludge treated in the super anaerobic tank or sludge storage tank is also redox potential (ORP) from the beginning. Therefore, the sludge standing time can be shortened. However, in this case, the anaerobic treatment time in the aeration tank must be lengthened, and the overall purification efficiency is deteriorated.
[0008]
[Means for Solving the Problems]
In the present invention, after the aeration operation in the aeration tank is stopped, the oxidation-reduction potential (ORP) of the sludge shows the highest value after a predetermined time has elapsed, and thereafter, the oxidation-reduction potential (ORP) gradually decreases. In particular, the reduction rate of the oxidation-reduction potential (ORP) is abruptly reduced when it is lowered by 200 mV or more.
[0009]
That is, the operation method of the purification apparatus according to the present invention is to perform aerobic treatment and anaerobic treatment with microorganisms by intermittently operating the aeration tank, and transfer the waste water after the treatment with microorganisms to the sedimentation tank. Separation of solid and liquid, a part of the settled sludge is super anaerobically treated to destroy the oxide film on the surface of the sludge, and the sludge whose oxide film has been destroyed is returned to the aerobic tank. In the operation method, the start point of the transfer of waste water from the aeration tank to the settling tank was set to a time point when the oxidation-reduction potential (ORP) in the aeration tank decreased from the maximum value by 200 mV or more.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a purification apparatus used for carrying out the method of the present invention. The purification apparatus is a raw solution tank 1, a flow rate adjustment tank 2, an aeration tank 3, a precipitation tank 4, a sand filtration tank 5, and an activated carbon in order from the upstream side. A tank 6 and a disinfection tank 7 are provided, and a super anaerobic tank 8 is provided on the downstream side of the precipitation tank 4 separately from the filtration tank 5.
[0011]
The stock solution tank 1 is provided with a filter 9 that removes large foreign matters such as wood chips, and waste water that has passed through the filter 9 is sent to the flow rate adjusting tank 2 by the pump 10, and the measuring rod 12 is sent from the flow rate adjusting tank 2 to the pump 11. Waste water is sent to the aeration tank 3 and a certain amount of waste water is supplied to the aeration tank 3 through the measuring tank 12 to perform aerobic treatment and anaerobic treatment.
[0012]
An aeration device 13 and an agitation device 14 are disposed at the bottom of the aeration tank 3, aerobic treatment is performed in the aeration tank 3 by supplying air from the aeration device 13, and aeration is performed by stopping the operation of the aeration device 13. Anaerobic treatment is performed in the tank 3. The stirrer 14 is for quickly switching the inside of the aeration tank to an aerobic atmosphere or an anaerobic atmosphere, and can be operated in any of an aerobic treatment and an anaerobic treatment.
[0013]
In addition, the switching between the aerobic treatment and the anaerobic treatment in the aeration tank 3 can be performed by using the DO value, pH value, ORP value, etc. of the waste water in the aeration tank 3 as a switching factor in addition to the switching by the timer.
[0014]
Then, the waste water that has undergone the aerobic treatment and the anaerobic treatment in the aeration tank 3 is sent to the precipitation tank 4 by the pump 15, and is left to stand for solid-liquid separation into the supernatant liquid and the sludge 16. The sludge 16 inside settles at the bottom of the settling tank 4.
[0015]
The supernatant liquid in the settling tank 4 is discharged into the sewage or the like through the sand filtration tank 5, the activated carbon tank 6 and the disinfection tank 7 through the quantitative transfer device 17, and one of the sludge 16 that has settled at the bottom of the settling tank 4. The part is returned to the aeration tank 3 by a pump 18 as a nutrient source for microorganisms, and the other part is sent to the super anaerobic tank 8 by a pump 19.
[0016]
In the super anaerobic tank 8, the sludge oxidation-reduction potential (ORP) is maintained in an anaerobic state until it becomes −190 mV or less. When the oxidation-reduction potential (ORP) is −190 mV or less, as shown in FIG. 2, the surface oxide film 16 a of the sludge 16 is softened and destroyed.
[0017]
Then, the sludge 16 whose surface oxide film 16a has been destroyed is returned to the flow rate adjusting tank 2 via the pump 20 and the sludge return pipe 21. The flow rate adjusting tank 2 is in an aerobic state because the waste water flows in, and the sludge 16 in which the surface oxide film 16a is destroyed is subjected to aerobic treatment to some extent in the flow rate adjusting tank 2 and a part thereof is nitrate nitrogen ( It is supplied to the aeration tank 3 in a state converted to NO ₃ —N) or nitrite nitrogen (NO ₂ —N).
Further, the supernatant liquid of the super anaerobic tank 8 is returned to the flow rate adjusting tank 2 via the quantitative transfer device 22 and the return pipe 23.
[0018]
The sludge 16 may be returned to the aeration tank 3 in an aerobic state without returning to the flow rate adjustment tank 2. However, returning to an anaerobic aeration tank is not preferable in terms of purification efficiency. That is, even if it returns to an anaerobic aeration tank, the sludge whose oxide film was destroyed is not converted into nitrate nitrogen (NO ₃ -N) or nitrite nitrogen (NO ₂ -N), and the next aerobic state It is because it will wait until.
[0019]
FIG. 3A is a graph showing a change in DO value in an aeration tank, and FIG. 3B is a graph showing a change in ORP value in an aeration tank, a precipitation tank, and a super anaerobic tank. 3 (a) and 3 (b), after stopping the aeration operation in the aeration tank 3, the oxidation-reduction potential (ORP) of the sludge shows the highest value after a predetermined time has elapsed, and thereafter the oxidation-reduction potential (ORP) gradually increases. However, it is understood that the reduction rate of the oxidation-reduction potential (ORP) is abruptly reduced when it is reduced by 200 mV or more from the maximum value.
Therefore, it can be said that it is advantageous in terms of purification efficiency to shift to the precipitation tank 4 when the oxidation-reduction potential (ORP) decreases by 200 mV or more from the maximum value.
[0020]
Further, from FIG. 3 (b), at the intermediate point of the anaerobic treatment of the aeration tank, the curve indicating the redox potential (ORP) has an inflection point H, and the redox potential (ORP) showed the highest value. It has also been found that when a time “b” that is substantially the same as the time “a” from the time point to the time point indicating the inflection point H passes the inflection point H, the rate of reduction of the oxidation-reduction potential (ORP) rapidly decreases. Therefore, the time from when the redox potential (ORP) shows the maximum value to the time when the inflection point H is measured is measured, and after anaerobic treatment in the aeration tank for this time, the process proceeds to the precipitation tank 4. Is also considered advantageous in terms of purification efficiency.
[0021]
As shown in FIG. 3 (b), the sludge transferred from the aeration tank 3 to the settling tank 4 has a further reduced ORP value, and the sludge transferred from the settling tank 4 to the super anaerobic tank has a redox potential. Let stand until (ORP) is -190 mV.
[0022]
【The invention's effect】
As described above, according to the present invention, in operating a purification apparatus that performs aerobic treatment and anaerobic treatment by microorganisms by operating the aeration tank intermittently, the aeration tank is moved from the aeration tank to the sedimentation tank. Since the redox potential (ORP) in the aeration tank decreased to 200 mV or more from the maximum value, the start point of the transition of the waste water was set at the anaerobic treatment time in the aeration tank and the super anaerobic tank or sludge storage tank. A balance with the super-anaerobic treatment time can be achieved, and the purification apparatus as a whole can be operated efficiently.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a purification apparatus used in carrying out the method of the present invention. FIG. 2 is a diagram illustrating a state of destruction of a surface oxide film of sludge. FIG. 3 (a) is a change in DO value in an aeration tank. (B) is a graph showing the change in the ORP value from the aeration tank to the super-aeration tank.
DESCRIPTION OF SYMBOLS 1 ... Stock solution tank, 2 ... Flow control tank, 3 ... Aeration tank, 4 ... Precipitation tank, 5 ... Filtration tank, 8 ... Super anaerobic tank, 13 ... Aeration apparatus, 14 ... Stirrer, 16 ... Sludge, 16a ... Sludge Surface oxide film, 21 ... sludge return pipe.

Claims (1)

By performing intermittent operation of the aeration tank, aerobic treatment and anaerobic treatment by microorganisms are performed on wastewater, and the wastewater that has been treated by microorganisms is transferred to a precipitation tank for solid-liquid separation. An operation method of a purification apparatus in which an anaerobic treatment is performed to destroy the oxide film on the surface of the sludge, and the sludge in which the oxide film is destroyed is returned to the tank in an aerobic state, from the aeration tank to the settling tank A method for operating a purification apparatus, characterized in that the start point of the transfer of wastewater is set to a point in time when the oxidation-reduction potential (ORP) in the aeration tank has decreased by 200 mV or more from the maximum value.

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