JP2004275820A - Wastewater treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment apparatus capable of efficiently performing dephosphorization or denitrification even at the time of rainy weather or the like by effectively putting an organic acid produced from sludge to practical use. <P>SOLUTION: The wastewater treatment apparatus includes a process for introducing the water flowing out of a first sedimentation basin 11 into an anaerobic tank 2 to anaerobically treat the same with microorganisms and a sludge circulating means for circulating a part of sludge first sedimented in the first sedimentation basin 11 to the water in the first sedimentation basin 11 is provided to the first sedimentation basin 11. As the sludge circulating means, a stirrer, a pressure water introducing route and a compressed air introducing route can be employed in a sludge pit other than a circulating sludge route 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wastewater treatment apparatus, and more specifically, a wastewater treatment apparatus including a step of performing anaerobic treatment with microorganisms by introducing effluent from an initial sedimentation basin into an anaerobic tank (including an oxygen-free tank) during the wastewater treatment process. About.
[0002]
[Prior art]
As wastewater treatment methods for sewage, phosphorus removal methods such as anaerobic aerobic method and nitrogen removal methods such as nitrification denitrification method are widely known to remove nutrients such as phosphorus and nitrogen. An anaerobic anaerobic aerobic method (A2O method) that combines a biological dephosphorization method and a nitrification denitrification method is also known. In such various wastewater treatment methods, in an anaerobic tank that performs anaerobic treatment and an anaerobic tank that performs anoxic treatment, if the concentration of soluble organic matter in the inflowing water decreases, the processing efficiency of phosphorus and nitrogen will decrease, and the device The overall phosphorus and nitrogen removal efficiency may be reduced.
[0003]
For this reason, when the concentration of soluble organic matter in the inflowing water during rainy weather or the like is lowered, for example, when the dephosphorization function is lowered by this, it is proposed to introduce a soluble organic acid into the anaerobic tank. (For example, refer to Patent Document 1). Moreover, it is known that an organic acid is produced in an acid fermenter in the process of methane fermentation for obtaining methane from sludge (see, for example, Patent Document 2).
[0004]
[Patent Document 1]
JP-A-2002-286894 gazette
[Patent Document 2]
JP-A-8-238499 [0006]
[Problems to be solved by the invention]
However, in the conventional apparatus, a facility for separately introducing an organic acid into an anaerobic tank or the like is required, and when the organic acid is charged from outside the system, the cost is also required. The organic acid obtained in the process of methane fermentation is used to elute phosphorus in the process of methane fermentation, and is used in a system completely different from dephosphorization and denitrification in wastewater treatment. .
[0007]
Therefore, an object of the present invention is to provide a wastewater treatment apparatus that can efficiently perform dephosphorization and denitrification even in rainy weather by effectively utilizing an organic acid generated from sludge.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus including a step of introducing an effluent from an initial sedimentation basin into an anaerobic tank and performing anaerobic treatment with microorganisms. It is characterized by providing a sludge circulation means for circulating a part of the initial sedimentation sludge precipitated in the sedimentation basin into the water in the initial sedimentation basin.
[0009]
The sludge circulation means includes a circulation sludge route for reintroducing a part of the initial settling sludge extracted from the first settling basin into the first settling basin, a mechanical stirring means provided in the sludge pit of the first settling pond, and sludge in the sludge pit. It can be formed by a route for introducing water or air for stirring. In addition, it is desirable to provide an instrument (ORP meter) for measuring the oxidation-reduction potential of the initial sludge at an appropriate position in the circulating sludge route and the initial sedimentation basin.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a system diagram of a wastewater treatment apparatus showing an embodiment of the present invention. This waste water treatment apparatus is the one in which the present invention is applied to an anaerobic anaerobic anaerobic method (A2O) method for simultaneously removing phosphorus and nitrogen in inflow water. , An anaerobic tank 13, an aerobic tank 14, and a final sedimentation tank 15, and a nitrification liquid circulation path 16 for circulating the nitrating liquid from the aerobic tank 14 to the anoxic tank 13, and the final sedimentation tank 15 for returning the activated sludge extracted from 15 to the anaerobic tank 12, the excess sludge path 18 for extracting a part of the activated sludge as excess sludge, and the first settling for removing the first settling sludge extracted from the first settling tank 11. A sludge path 19 and a circulating sludge path 20 for circulating the first settling sludge to the first settling basin 11 are provided.
[0011]
The removal of phosphorus by this A2O method means that phosphorus accumulating bacteria in activated sludge exhale phosphorus in an anaerobic state in the anaerobic tank 12, and absorb more phosphorus than the amount exhaled in the aerobic state in the aerobic tank 14. When the concentration of the soluble organic substance in the inflow water decreases, the discharge of phosphorus in the anaerobic tank becomes insufficient and the dephosphorization efficiency decreases.
[0012]
The removal of nitrogen is performed in a nitrification reaction in which ammonia nitrogen is oxidized to nitrite or nitrate nitrogen in an aerobic state in an aerobic tank 14 and in activated sludge in an oxygen-free state in an anaerobic tank 13. Nitrite respiration or nitrate respiration by a denitrifying bacterium using a denitrification reaction in which nitrite nitrogen or nitrate nitrogen is reduced to nitrogen gas. When the concentration of the organic substance decreases, the denitrification reaction does not proceed sufficiently and the denitrification efficiency decreases.
[0013]
On the other hand, the anaerobic digestion of sludge, that is, the biodegradation of organic matter performed in the absence of oxygen, is the acidic fermentation period (first stage), acidic decline period (second stage) and alkaline due to the action of anaerobic bacteria. It goes through the fermentation period (third period). In the first and second phases, carbohydrates, proteins, fats, and other high-molecular organic substances containing cellulose in sludge, mainly acetic acid, propionic acid, butyric acid, etc. Hydrolyzes to volatile organics and lower alcohols.
[0014]
Research has been conducted to produce organic acid from the initial sedimentation sludge extracted from the first sedimentation basin 11 using this, and as a result, only conditions such as pH and sludge residence time are controlled for the primary sedimentation sludge. It has been found that organic acids are readily formed. Conditions regarding the production of this organic acid include pH and raw sludge concentration. When the pH is about 5.5, the organic acid production rate becomes high. At pH 6 or more, methane fermentation proceeds. The organic acid is generated even at the residence time, the organic acid generation rate is low at low water temperature, and the raw sludge concentration is about 20000 mg / L, the pH can be adjusted without using a pH adjuster depending on the generated organic acid. Knowledge such as being maintained at about 5.5 has been obtained. From these facts, in the first settling basin 11, the above-mentioned organic acids such as acetic acid, propionic acid and butyric acid are generated in the first settling basin 11 by setting the residence time of at least a part of the initial settling sludge to a certain time or more. It becomes possible to do.
[0015]
Therefore, by providing a circulating sludge path 20 as a sludge circulation means for circulating a part of the initial settling sludge extracted from the first settling basin 11 to the first settling basin 11, the initial settling sludge is retained in the first settling basin 11 for a certain period of time. Therefore, it can be expected that organic acids are produced in the first and second stages of the anaerobic digestion of the sludge.
[0016]
Since the produced organic acid is soluble, it is separated from the solid and dissolved in the inflowing water, and flows into the anaerobic tank 12 together with the supernatant of the settling tank 11 first. Thereby, since the soluble organic substance density | concentration in the anaerobic tank 12 can be made into a sufficient state, the fall of dephosphorization efficiency can be suppressed. Furthermore, since the liquid containing the organic acid flows from the anaerobic tank 12 to the oxygen-free tank 13, the concentration of soluble organic matter in the oxygen-free tank 13 can be made sufficient, and the decrease in denitrification efficiency can be suppressed. Can do. That is, the efficiency of the anaerobic treatment in the anaerobic tank 12 and the anaerobic tank 13 can be increased.
[0017]
Therefore, since the organic acid can be sent to the anaerobic tank 12 by first circulating it to the settling basin 11 before the organic acid is generated and methane fermentation occurs, the organic acid is also prevented from being consumed by the methane fermentation. be able to. Thereby, the utilization efficiency of the produced | generated organic acid can be improved, and it can also suppress that methane fermentation advances in the first sedimentation tank 11. FIG.
[0018]
Furthermore, considering that the temperature of the sewage flowing into the first settling basin 11 is relatively high, the generation of the organic acid is hardly hindered. In addition, if the initial sedimentation sludge is retained in the first sedimentation basin 11 for a long time, the oxidation-reduction potential becomes too low and a toxic gas such as hydrogen sulfide may be generated. An ORP meter 21 is provided as an instrument for measuring the oxidation-reduction potential of the first settling sludge at an appropriate position, and the oxidation-reduction potential is measured. When the oxidation-reduction potential falls below a certain value, the first precipitation basin is formed by aeration, for example. It is preferable to supply oxygen into 11 and maintain the oxidation-reduction potential in the sedimentation tank 11 in an appropriate range first.
[0019]
In addition, since the circulation amount of the initial sedimentation sludge in the first sedimentation basin 11 varies depending on conditions such as the quality of the influent water, the amount of water, and the amount of rain, an appropriate circulation amount should be selected by performing experiments on site. Moreover, when sufficient dissolved organic matter is contained in the inflowing water, the circulation of the initial settling sludge may be stopped, and the circulation amount of the initial settling sludge may be changed according to the concentration of the soluble organic matter. Furthermore, when the ORP meter 21 is installed, the circulation rate can be changed according to the measured value.
[0020]
FIG. 2 shows an example in which the present invention is applied to a wastewater treatment apparatus for removing phosphorus by an anaerobic aerobic method. In the following description, components that are the same as or similar to the components shown in the above-described embodiment are given the same reference numerals, and detailed descriptions thereof are omitted. The waste water treatment apparatus using the anaerobic aerobic method shown in FIG. 2 arranges the treatment tanks in the order of the first sedimentation tank 11, the anaerobic tank 12, the aerobic tank 14, and the final sedimentation tank 15 from the upstream side. The return sludge path 17 for returning the activated sludge extracted from the anaerobic tank 12, the excess sludge path 18 for extracting a part of the activated sludge as excess sludge, and the first settling sludge for extracting the first settling sludge extracted from the first settling tank 11 A path 19 and a circulating sludge path 20 for circulating the primary sedimentation sludge to the primary sedimentation basin 11 are provided.
[0021]
Also in this waste water treatment device, the initial settling sludge is circulated through the circulating sludge route 20 and the sludge is retained in the first settling basin 11 for a certain period of time, so that organic acid can be generated from the sludge and sent to the anaerobic tank 12. Even when the concentration of the soluble organic substance in the inflow water is lowered, the phosphorus can be sufficiently discharged from the phosphorus accumulating bacteria in the anaerobic tank 12. Thereby, the fall of dephosphorization efficiency can be suppressed.
[0022]
FIG. 3 shows an example in which the present invention is applied to a wastewater treatment apparatus that removes nitrogen by a nitrification denitrification method. This waste water treatment apparatus arranges each treatment tank in the order of the first sedimentation tank 11, the anaerobic tank 13, the aerobic tank 14, and the final sedimentation tank 15 from the upstream side, and nitrifies from the aerobic tank 14 to the anaerobic tank 13. A nitrification liquid circulation path 16 for circulating the liquid, a return sludge path 17 for returning the activated sludge extracted from the final sedimentation basin 15 to the anaerobic tank 12, an excess sludge path 18 for taking a part of the activated sludge as excess sludge, An initial sedimentation sludge path 19 for taking out the initial sedimentation sludge extracted from the first sedimentation tank 11 and a circulating sludge path 20 for circulating the primary sedimentation sludge to the first sedimentation tank 11 are provided.
[0023]
Also in this waste water treatment apparatus, since the organic acid can be first generated in the settling basin 11 and sent to the anoxic tank 13 in the same manner as described above, even if the concentration of soluble organic matter in the inflowing water is reduced, the anoxic tank 13 The denitrification reaction in can be sufficiently advanced, and a decrease in denitrification efficiency can be suppressed.
[0024]
4 to 9 show an example in which the sludge circulation means is not provided in the first settling basin, and the sludge circulation means is installed in the first settling basin. FIGS. 4 to 6 show that the first settling basin is a rectangular pond. 7 to 9 show the case where the initial settling basin is a circular pond.
[0025]
First, the first sedimentation basin 31 composed of a rectangular pond shown in FIGS. 4 to 6 is provided with an outflow path 33 at the upper part of the opposite surface of the inflow path 32 and a sludge pit 34 on the inflow path side at the bottom of the pond. The sludge scraper 35 for scraping the sludge deposited on the pond bottom toward the pond 34 is provided. At the bottom of the sludge pit 34, the first settling sludge path 19 for extracting the first settling sludge from the pond is provided. It is connected.
[0026]
In such a first sedimentation basin 31, in the embodiment shown in FIG. 4, a sludge agitator 36 is provided in the sludge pit 34, and the agitator blade 38 is rotated by a motor 37, whereby the initial sedimentation in the sludge pit 34 is performed. The sludge can be stirred. That is, by reducing the sludge extraction frequency from the first settling sludge passage 19 less than usual, the first settling sludge is retained in the sludge pit 34 to generate organic acid, and then the agitator 36 is operated to remove the first settling sludge. By stirring and circulating in water, the generated organic acid can be dissolved in water, and a water flow can be generated in the sludge pit 34 to prevent the inside of the sludge pit 34 from becoming an anaerobic state. Therefore, by appropriately setting the residence time of the first settling sludge in the sludge pit 34 and operating the stirrer 36 at an appropriate time, the organic acid generated from the first settling sludge can be dissolved in water, Generation of toxic gases such as hydrogen sulfide can also be prevented.
[0027]
In the embodiment shown in FIG. 5, a pressure water introduction path 39 for sludge stirring is provided in the sludge pit 34. Also in this embodiment, the residence time of the first settling sludge in the sludge pit 34 is set appropriately, and water having an appropriate pressure from the pressure water introduction path 39 at an appropriate time, for example, secondary treated water or sedimentation basin outflow Water such as water is supplied by a pump and ejected into the sludge pit 34 from the nozzle 40 at the tip to stir the first settling sludge, thereby dissolving the organic acid generated from the first settling sludge in water, hydrogen sulfide, etc. The generation of toxic gases can be prevented.
[0028]
In the embodiment shown in FIG. 6, the sludge pit 34 is provided with a compressed air introduction path 41 for stirring sludge. Also in this embodiment, the residence time of the first settling sludge in the sludge pit 34 is set appropriately, compressed air is supplied from the compressed air introduction path 41 at an appropriate time, and the nozzle 42 at the tip enters the sludge pit 34. By ejecting and stirring the primary sedimentation sludge, the organic acid generated from the primary sedimentation sludge can be dissolved in water and the generation of toxic gases such as hydrogen sulfide can be prevented.
[0029]
The first sedimentation basin 51 composed of a circular pond shown in FIGS. 7 to 9 is provided with a sludge pit 53 at the center of the bottom of the circular pond having an outflow trough 52 on the outer periphery, and settles on the pond bottom toward the sludge pit 53 on the outer periphery. The sludge scraping machine 54 for scraping the sludge is provided, and the first settling sludge path 19 is connected to the bottom of the sludge pit 53.
[0030]
In the first sedimentation basin 51 composed of such a circular pond, in order to stir the initial sedimentation sludge in the sludge pit 53, a mechanical stirrer 55 as shown in FIG. By providing the pressure water introduction path 56 or by providing the compressed air introduction path 57 as shown in FIG. 9, the organic acid generated from the first settling sludge is dissolved in water, and hydrogen sulfide or the like is provided. Generation of toxic gas can be prevented.
[0031]
Moreover, as shown in FIGS. 4 to 9, even when the sludge circulation means is first installed in the settling basin, an ORP meter is installed at an appropriate position to measure the oxidation-reduction potential so as not to be in an extreme anaerobic state. It is desirable to monitor. Furthermore, by providing the sludge circulation means as shown above and stirring the sludge, water is not formed in the sludge pit, and the removal of the first settling sludge is not hindered. The sludge circulation means can be used in appropriate combination.
[0032]
【The invention's effect】
As described above, according to the wastewater treatment apparatus of the present invention, even when the concentration of soluble organic matter in the inflowing water is low, the dephosphorization efficiency and the denitrification efficiency are not reduced, so that the removal of phosphorus and nitrogen is ensured. Can be done. In addition, compared to conventional wastewater treatment equipment, it is only necessary to add simple equipment such as a sludge circulation path, a stirrer, a pressure water introduction path, and a compressed air introduction path, so it can be used with existing equipment. There is no need for new chemicals or treatment tanks, and the cost required for facilities and the cost required for operation are extremely small.
[0033]
Furthermore, since the initial settling sludge flows sufficiently, it does not partially become extremely anaerobic, does not require special deodorizing equipment, and can suppress generation of toxic gases such as hydrogen sulfide. In addition, since the initial sedimentation sludge concentration in the sludge pit can be stably increased, it becomes easy to dispose of the extracted primary sedimentation sludge.
[Brief description of the drawings]
FIG. 1 is a system diagram of a wastewater treatment apparatus showing an embodiment in which the present invention is applied to an anaerobic anaerobic and aerobic (A2O) method.
FIG. 2 is a system diagram of a waste water treatment apparatus showing an embodiment in which the present invention is applied to an anaerobic aerobic method.
FIG. 3 is a system diagram of a wastewater treatment apparatus showing an embodiment in which the present invention is applied to a nitrification denitrification method.
FIG. 4 is a schematic diagram showing an example in which a stirrer for stirring sludge is installed in a first sedimentation basin composed of rectangular ponds.
FIG. 5 is a schematic view showing an example in which a pressure water introduction path for agitation of sludge is installed in a first settling basin composed of rectangular ponds.
FIG. 6 is a schematic view showing an example in which a compressed air introduction path for sludge agitation is installed in a first settling basin composed of rectangular ponds.
FIG. 7 is a schematic view showing an example in which an agitator for agitation of sludge is installed in an initial sedimentation basin composed of a circular pond.
FIG. 8 is a schematic view showing an example in which a pressure water introduction path for agitation of sludge is installed in a first sedimentation basin composed of a circular pond.
FIG. 9 is a schematic view showing an example in which a compressed air introduction path for agitation of sludge is installed in a first sedimentation basin composed of a circular pond.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... First sedimentation tank, 12 ... Anaerobic tank, 13 ... Anaerobic tank, 14 ... Aerobic tank, 15 ... Final sedimentation tank, 16 ... Nitrification liquid circulation path, 17 ... Return sludge path, 18 ... Excess sludge path, 19 ... Initial sedimentation sludge route, 20 ... circulating sludge route, 21 ... ORP meter, 31 ... first sedimentation basin, 32 ... inflow route, 33 ... outflow route, 34 ... sludge pit, 35 ... sludge scraper, 36 ... agitator, 37 ... motor, 38 ... stirring blade, 39 ... pressure water introduction path, 40 ... nozzle, 41 ... compressed air introduction path, 42 ... nozzle, 51 ... first sedimentation basin, 52 ... outflow trough, 53 ... sludge pit, 54 ... sludge scraping Machine: 55 ... Agitator, 56 ... Pressure water introduction path, 57 ... Compressed air introduction path

Claims (7)

In the wastewater treatment apparatus including the step of introducing anaerobic water from the first sedimentation basin into the anaerobic tank and performing anaerobic treatment with microorganisms, a part of the initial sedimentation sludge precipitated in the first sedimentation basin is placed in the first sedimentation basin. A wastewater treatment apparatus provided with a sludge circulation means for circulating in water. The wastewater treatment apparatus according to claim 1, wherein a meter for measuring an oxidation-reduction potential is provided in the first settling basin. 2. The wastewater treatment apparatus according to claim 1, wherein the sludge circulation means is a circulation sludge route for reintroducing a part of the initial sedimentation sludge extracted from the initial sedimentation basin into the initial sedimentation basin. The waste water treatment apparatus according to claim 3, wherein an instrument for measuring the oxidation-reduction potential of the circulating primary sludge is provided in the circulating sludge path. The wastewater treatment apparatus according to claim 1, wherein the sludge circulation means is a mechanical stirring means provided in a sludge pit of an initial settling basin. The wastewater treatment apparatus according to claim 1, wherein the sludge circulation means is a path for introducing water for agitation of sludge into a sludge pit of an initial sedimentation basin. The wastewater treatment apparatus according to claim 1, wherein the sludge circulation means is a path for introducing air for agitation of sludge into a sludge pit of an initial settling basin.

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