JP4067952B2 - Oxidation ditch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxidation ditch, and in particular, in an oxidation ditch in which wastewater such as sewage containing organic matter is biologically treated with activated sludge, clear treated water that does not contain solid matter can be obtained. It is related to the oxidation ditch that makes it possible to easily perform advanced processing using existing facilities.
[0002]
[Prior art]
Conventionally, in order to treat sewage flowing into a sewage treatment plant or the like, sewage is introduced into an aeration tank (also referred to as “reaction tank” in this specification) containing activated sludge, and this is aerated and stirred. An activated sludge process for biological treatment is used. In particular, in small-scale treatment plants, oxidation ditch is adopted in various places from the standpoint of adaptability to load fluctuations and ease of maintenance.
In addition, this oxidation ditch is often provided in areas with a rich natural environment. In order to protect this natural environment, in recent years, more advanced treatment techniques are required to improve the water quality of rivers and lakes. It became so.
[0003]
[Problems to be solved by the invention]
By the way, since the conventional oxidation ditch uses an existing treatment plant facility to improve water quality, it is necessary to add a new facility such as sand filtration. There is no room for providing a new facility in a limited space, and it is not easy to further improve the current processing, and a new site is required.
[0004]
The present invention solves the problems of the conventional oxidation ditch, and in an oxidation ditch in which sewage containing organic matter is biologically treated with activated sludge, the clarification does not contain solid matter. It is an object of the present invention to provide an oxidation ditch that makes it possible to easily perform advanced treatment using existing facilities.
[0005]
[Means for Solving the Problems]
To achieve the above object, oxidation ditch of the present invention, in the oxidation ditch for biological treatment of organic wastewater by sludge microorganisms in the reaction vessel, together with so as to dip into the final sedimentation pond installing the membrane separation device The sludge mixed liquid that overflows from the aeration tank has a partition wall arranged outside the membrane separation device, the upper end being above the water surface and the lower end being spaced from the bottom of the final sedimentation basin Is configured to be introduced into a membrane filtration zone inside the partition wall .
[0006]
Since the oxidation ditch of the present invention is installed in the final settling basin of the oxidation ditch so that the membrane separation apparatus is installed, the facility that can perform advanced processing even in existing facilities with limited space, The facility can be upgraded to a facility that meets the current needs with low cost and short-term construction.After the upgrade, the treated water is taken out through the separation membrane and discharged to the outside of the treatment plant. Clearer treated water can be obtained without additional filtration equipment.
[0007]
Then , the partition wall disposed outside the membrane separation device immersed in the final sedimentation basin is arranged so that the upper end is above the water surface, the lower end is spaced from the bottom of the final sedimentation basin, and aeration is performed. Membrane cleaning is achieved by introducing the sludge mixed liquid overflowing from the tank into the membrane filtration zone inside the partition wall, and introducing the sludge mixed liquid overflowing from the aeration tank into the membrane filtration zone inside the partition wall. An upward flow is generated by the air lifting action of the membrane cleaning air diffused from the apparatus, and a downward flow is generated in the non-diffused portion, so that a circulating flow is formed in the entire zone. In the sedimentation zone outside the partition wall, there is no circulation flow, so in the sedimentation zone the influence of agitation by the membrane cleaning air It is quiescent holding without receiving, water level detection by the water level gauge can accurately and efficiently solid-liquid separation is performed.
[0008]
In this case, the operation of the membrane separation device can be stopped when the water level in the final sedimentation basin has lowered the sedimentation basin water level to a predetermined level or less.
[0009]
As a result, even if the water level in the final sedimentation basin is greatly reduced when the amount of membrane filtration is larger than the amount of the sludge mixed solution flowing from the aeration tank, this water level is detected by the water level gauge and reaches the predetermined level or lower. Since the operation of the membrane separation device is stopped at the time, the separation membrane is not exposed to the air even when the water level is lowered, and the clogging of the membrane surface can be prevented and the efficient operation can be prevented. Solid-liquid separation can be performed continuously.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the oxidation ditch of the present invention will be described with reference to the drawings .
[0011]
An embodiment of the present invention is shown in FIGS.
FIG. 1 is a flow diagram of an existing oxidation ditch to which the present invention is applied, FIG. 2 is an explanatory diagram of a final sedimentation basin in which the oxidation ditch is updated, and FIG. 3 is a plan view of the final sedimentation basin.
To do.
[0012]
In FIG. 1, sewage A that has flowed into an oxidation ditch such as a sewage treatment plant that treats sewage firstly removes sand and residue from the sewage in the pretreatment facility 1 and then aeration tank or reaction tank. The water is fed to 2 and agitated and aerated by driving the aerator 6 in the aeration tank 2, so that it is biologically treated with activated sludge.
The sewage treated in the aeration tank 2 is sent as a sludge mixed solution to the final sedimentation basin 3, specifically to the center well 7 provided in the final sedimentation basin 3. Furthermore, the supernatant water separated in the final sedimentation basin 3 overflows from the final sedimentation basin 3 and is guided to the disinfection tank 4 where it is sterilized in a predetermined manner and then discharged into a river or the like as treated water B. Is done.
[0013]
The sludge precipitated in the final sedimentation basin 3 is collected by the sludge scraper 8 disposed in the final sedimentation basin 3 to the bottom center of the final sedimentation basin 3, and returned to the sludge pump 5 via the pipe 22. And is returned to the aeration tank 2 as return sludge C.
Although not particularly limited, the aeration tank 2 is provided with an aeration machine 6 such as a screw type for aeration agitation, so that sewage is aerated and agitated, so that microorganisms in the sludge are oxygenated. Will be supplied.
Further, the sludge that has settled in the final sedimentation basin 3 and increased to a predetermined amount is periodically withdrawn as excess sludge D, and processing such as concentration and dehydration is performed in a separate sludge treatment facility.
[0014]
In updating the existing oxidation ditch configured in this way so that it can be advanced, in the present invention, the center well 7 and the sludge scraper 8 provided inside the final sedimentation basin 3 are removed, and FIGS. As shown in FIG. 2, a submerged membrane separation device 10, a partition wall 11, a membrane cleaning device 12, and a water level meter 15 are installed.
The membrane separation device 10 is disposed so as to be immersed in the final sedimentation basin 3, specifically, in a substantially central position in the final sedimentation basin 3 so as to be completely immersed in the flowing sludge mixed solution. The membrane separation device 10 may be an immersion type membrane, and the material of the membrane and the element type are not limited.
Further, a partition wall 11 is disposed so as to surround the outer peripheral portion of the membrane separation apparatus 10. In this case, the partition wall 11 is installed so that the upper end thereof is positioned above the water surface and the lower end thereof is provided with a necessary gap between the bottom of the final sedimentation basin 3 and the partition wall 11 and the aeration tank. 2 is connected by a pipe 20, whereby the sludge mixed liquid overflowed from the aeration tank 2 is caused to flow into the partition wall 11.
The membrane cleaning device 12 is disposed inside a partition wall 11 at a lower position of the membrane separation device 10, and the membrane cleaning device 12 and a blower 13 provided outside are connected by a pipe. As a result, the air (cleaning air) sent from the blower 13 provided outside is diffused from the membrane cleaning device 12 disposed at the lower part of the membrane of the membrane separation device 10, and the rise of the bubbles causes the membrane separation device 10 to It is configured to clean impurities and the like adhering to the film surface.
Thereby, an efficient separation process is performed without reducing the solid-liquid separation ability of the membrane separation apparatus 10.
The water level meter 15 is installed in the final sedimentation basin 3 so that the water level in the final sedimentation basin 3 can be detected, and the detection signal is input to the control device 16 to provide a suction pump for the membrane separation device 10. 14 is controlled, and the installation position is not particularly limited. As a result, when the water level in the final sedimentation basin falls below a predetermined level, the operation of the membrane separator is stopped.
[0015]
In addition, by providing a suction pump 14 outside and connecting the header pipe 17 and the pipe 21 of the membrane separation device 10, the filtered water F filtered by the membrane separation device 10 by driving the suction pump 14 is Via the valve 18 or 19 connected to the suction pump 14, the sterilization tank 4 is supplied or discharged to the outside of the treatment site.
In this case, when it is obliged to disinfect the treated water, the valve 19 and its piping are not used, and the entire amount needs to be sent to the disinfecting tank.
Further, depending on the location conditions, the membrane separation apparatus 10 may be a gravity filtration system without using the suction pump 14.
[0016]
Next, the operation of the present invention will be described.
The treated water that has flowed into the treatment plant and biologically treated with microorganisms in the activated sludge in the aeration tank 2 overflows from the aeration tank 2 as a sludge mixed solution and passes through the pipe 20 to the inside of the partition wall surrounded by the partition wall 11. It flows into the membrane filtration zone.
In this membrane filtration zone, the air diffused from the membrane cleaning device 12 provided at the lower part of the membrane separation device 10 comes into contact with the membrane surface while adhering to the membrane surface while rising as coarse bubbles. Remove and wash the sludge. Since an upward flow is generated by this air lift action, a downward flow is generated in a portion where air is not diffused, and a circulating flow is formed in the entire zone. On the other hand, the sedimentation zone outside the partition wall 11 is connected to the membrane filtration zone at the lower part of the partition wall 11 but can be allowed to stand without causing a circulation flow as in the membrane filtration zone.
[0017]
Next, in this state, when the suction pump 14 connected to the membrane separation device 10 installed inside the partition wall 11 is operated through the pipe 21, the suction water is passed through the separation membrane by the suction pressure of the suction pump, and clear treated water is obtained. Only the treated water is collected in the header pipe 17 as filtered water, and then drained or discharged.
This filtered water F is sent to the disinfection tank 4 when the valve 18 is opened, and is directly discharged when the valve 19 is opened.
In addition, since the filtered water F that has passed through the membrane of the membrane separation device 10 is sanitized to a level equivalent to or higher than the sterilized treated water, it is not usually necessary to send the water to the sterilization tank 4 for sterilization. The valve 19 can be opened and discharged as it is. However, when a small amount of E. coli or the like is mixed into the treated water due to partial damage of the membrane, the valve 18 is opened and the disinfection tank 4 is used for disinfection. Release.
At this time, along with the membrane filtration, the sludge concentration in the membrane filtration zone gradually increases, and if the sludge concentration is left in a state where the sludge concentration has risen to a certain value or more, the filtration capacity may be lowered. In order not to reduce the filtration capacity, the return sludge pump 5 is operated to return part or all of the sludge to the aeration tank 2 through the pipe 22 connected to the bottom of the final sedimentation tank 3.
[0018]
The water level in the final sedimentation basin 3 changes with membrane filtration. That is, the water level in the final sedimentation basin 3 rises and falls according to the amount of the sludge mixed solution flowing in from the aeration tank 2 and the amount filtered by the membrane of the membrane separation device 10. In this case, when the amount of membrane filtration is larger than the inflow rate, the water level gradually decreases, so this is detected by the water level meter 15, and when it reaches a predetermined water level or lower, suction is performed via the control device 16. The pump 14 is stopped to stop (pause) the membrane filtration. Thereby, it is possible to prevent the separation membrane from being exposed to the air and clogging the membrane surface.
[0019]
On the other hand, when the membrane filtration amount is smaller than the inflow amount, the water level gradually rises and reaches the overflow weir in the final sedimentation basin 3. At this time, a part of the sludge mixed solution that has flowed into the membrane filtration zone flows out from the lower part to the precipitation zone outside the partition wall, but in the precipitation zone, there is no influence of stirring by the air for membrane cleaning, and it is left to stand and solidify. Since the liquid is separated, the supernatant water overflows into the disinfection tank 4. The supernatant water that has flowed into the disinfection tank 4 can be disinfected and discharged as long as the water quality is acceptable. However, for reprocessing, the pump well, the aeration tank 2 and the final sedimentation of the pretreatment facility 1 are used. It is also possible to return to the pond 3.
Depending on the sludge concentration, the solid-liquid separation effect in the precipitation zone is insufficient, and the sludge may overflow. In that case, a water level gauge can be added to detect the water level immediately before overflowing, and control such as stopping the operation of the sewage pump that supplies water to the aeration tank can be performed using the signal. .
[0020]
As mentioned above, although the oxidation ditch of the present invention has been described based on the embodiments thereof, the present invention is not limited to the configurations described in the above embodiments, and the configuration is appropriately changed without departing from the spirit thereof. Is something that can be done.
[0021]
【The invention's effect】
According to the oxidation ditch of the present invention, since the membrane separation device is installed so as to be immersed in the final sedimentation basin of the oxidation ditch, the facility capable of advanced processing even in existing facilities with limited space In addition, the facility can be upgraded to a facility that meets the current needs with low cost and short-term construction. It is possible to obtain clearer treated water without adding sand filtration equipment.
[0022]
And since the upper end of the partition wall arranged outside the membrane separator is on the water surface and the lower end is installed with a gap between the bottom of the final sedimentation basin, it overflows from the aeration tank. Flow into the membrane filtration zone inside the partition wall, causing an upward flow due to the air-lifting action of the membrane cleaning air diffused from the membrane cleaning device, and downward in the parts where it is not diffused As a result, a circulation flow is formed in the entire zone, so that adhesion of impurities to the membrane surface in the membrane filtration zone is suppressed, and no circulation flow is generated in the precipitation zone outside the partition wall. Therefore, the stationary state is maintained in the precipitation zone without being affected by the agitation by the membrane cleaning air, the water level can be detected with high accuracy, and the solid-liquid separation is performed efficiently.
[0023]
Also, even if the water level in the final sedimentation basin is greatly reduced when the amount of membrane filtration is larger than the amount of sludge mixed solution flowing from the aeration tank, the water level is detected by the water level gauge and when the water level falls below the specified level. Therefore, the operation of the membrane separation device is stopped, so that the separation membrane is not exposed to the air even if the water level is lowered, and the clogging of the membrane surface can be prevented from proceeding efficiently. Liquid separation can be performed continuously.
[Brief description of the drawings]
FIG. 1 is an embodiment showing a flow of an oxidation ditch to which the present invention is applied.
FIG. 2 is an explanatory diagram of a final sedimentation basin in which the oxidation ditch renewal method of the present invention is implemented.
FIG. 3 is a plan view of a final sedimentation basin.
[Explanation of symbols]
1 Pretreatment equipment 2 Aeration tank (reaction tank)
DESCRIPTION OF SYMBOLS 3 Final sedimentation tank 4 Disinfection tank 5 Return sludge pump 6 Aeration machine 7 Center well 8 Sludge scraping machine 9 Precipitation separation tank 10 Membrane separation device 11 Partition wall 12 Membrane cleaning device 13 Blower 14 Suction pump 15 Water level meter 16 Control device 17 Header Pipe 18 Valve 19 Valve A Sewage B Treatment water C Return sludge D Surplus sludge E Washing air F Filtration water

Claims (2)

In the oxidation ditch for biological treatment of organic sewage by sludge microorganisms in the reaction tank, a membrane separation device is installed so as to be immersed in the final sedimentation basin, and a partition wall disposed outside the membrane separation device, The upper end is on the water surface, the lower end is spaced from the bottom of the final sedimentation basin, and the sludge mixture overflowed from the aeration tank is introduced into the membrane filtration zone inside the partition wall. An oxidation ditch characterized by 2. The oxidation ditch according to claim 1, wherein the operation of the membrane separator is stopped when the water level in the final sedimentation basin is lowered to a predetermined level or less by a water level gauge provided in the final sedimentation basin.

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