JP2004188281A - Method and apparatus for wastewater treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain discharge water which sufficiently satisfies a water quality standard even if a large amount of wastewater containing an organic substance in high concentration in wastewater treatment accompanying microaerophilic aeration treatment. <P>SOLUTION: Microbial electron acceptor-adjusted water returned from a supernatant water re-aeration tank 4 is mixed with waste raw water flowing in an inflow tank 1 to aerate the waste raw water under such a condition that the amount of dissolved oxygen is substantially 1 mg/L or less. This aerated water is sent to a reaction tank 2 to be aerated under such a condition that the amount of dissolved oxygen is substantially 1 mg/L or less. Next, the treated water is separated into supernatant water and sludge in a sedimentation tank 4 and all amount of sedimented sludge is returned to the reaction tank 2. The supernatant water is re-aerated in the supernatant water re-aeration tank 4 under such a condition that the amount of dissolved oxygen is substantially 1 mg/L or less and a part of this treated water is returned to the inflow tank 1 and the remainder thereof is stationarily stored in a storage tank 6. The supernatant water re-aeration tank 4 and the storage tank 6 are integrated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wastewater treatment method and a wastewater treatment apparatus for purifying wastewater containing organic matter by treating the wastewater with microorganisms.
[0002]
[Prior art]
The process of a general activated sludge treatment method is as follows. First, inflow wastewater that has been subjected to pretreatment such as filtration and precipitation is sent to an aeration tank, and activated sludge is stirred and aerated to mineralize water-soluble organic compounds, colloidal organic compounds, and the like in the wastewater.
[0003]
Next, the wastewater is sent to a sedimentation tank to separate and sediment the sludge, and the supernatant water is sterilized so as to be equal to or lower than a legal standard value, and then discharged to a river or the like. Sludge settled in the lower layer of the sedimentation tank is sent to a storage tank, and when a predetermined amount is accumulated, the sludge is appropriately disposed of. If necessary, a part of the sludge in the settling tank may be returned to the aeration tank and used for adjusting the concentration of microorganisms in the sludge in the aeration tank.
[0004]
The above-mentioned conventional activated sludge treatment method generally uses an aerobic microorganism, keeps the dissolved oxygen amount (DO) in an aeration tank at a high level, promotes the active growth of the aerobic microorganism, and uses the aerobic respiration as a substrate. Oxidatively decomposes organic waste. For this reason, the dirt in the wastewater coagulates together with the dead bodies of microorganisms, and a large amount of sludge is generated.
[0005]
Although a part of the sludge is returned to the aeration tank as described above, a large amount of excess sludge has been subjected to landfill treatment, incineration treatment, and the like. However, surplus sludge contains harmful substances, which itself causes various environmental pollutions. Therefore, it is desired that surplus sludge is not generated as much as possible.
[0006]
In addition, in the activated sludge treatment method, since odor is generated in each treatment step, a deodorizing device must be installed, and equipment costs, running costs, and the like are burdensome.
[0007]
Further, a wastewater treatment method using anaerobic or facultative anaerobic microorganisms in combination with the above-described activated sludge treatment method is also known.However, since a new anaerobic treatment device is required, the cost of installing new equipment and There is a problem that the burden of the running cost increases.
[0008]
On the other hand, it is a sludge treatment method using anaerobic and facultative anaerobic microorganisms, comprising a wastewater raw water storage mechanism, a stirring anaerobic treatment mechanism, an aeration treatment mechanism, and a separation treatment mechanism. A system has been proposed in which a return to the aeration treatment mechanism and a predetermined ratio of supernatant water and settled sludge are returned to the stirring anaerobic treatment mechanism, and the agitated anaerobic treatment mechanism and the aeration treatment mechanism are used to perform a passivated anaerobic treatment with a reduced amount of air. (Ref. 1).
[0009]
[Patent Document 1]
JP-A-11-47787 [0010]
However, this wastewater purification system has a problem that a sufficient amount of microorganisms cannot be maintained depending on the inflow conditions, aeration conditions, and the like of raw wastewater, and stable purification treatment cannot be performed. Further, since the supernatant water and the sediment sludge are returned to the stirring anaerobic treatment mechanism at a predetermined ratio, the control system is also complicated.
[0011]
From such a fact, the present inventors mixed the electron acceptor conditioning water first, and aerated with microaeration to suppress the generation of surplus sludge, and it was odorless, and even wastewater with a low BOD concentration was used. An epoch-making wastewater treatment system capable of stably and efficiently purifying wastewater has been proposed (Japanese Patent Application No. 2001-175094). This wastewater treatment system mixes microbial electron acceptor adjusted water into wastewater raw water, aeration is performed in a microaerobic state having a dissolved oxygen content of substantially 1 mg / L, and then the treated liquid is subjected to precipitation separation treatment. The precipitated sludge is aerated again under the condition that the dissolved oxygen content is substantially 1 mg / L or less, and the supernatant water is returned to the raw wastewater as electron acceptor adjusted water.
[0012]
[Problems to be solved by the invention]
However, after further study, the wastewater treatment system with aerial treatment in microaerobic conditions, including the wastewater treatment system developed by the present inventors, has the following problems in actual operation. I knew it would be done.
[0013]
First, when a large amount of high-concentration (for example, 5000 ppm) sludge flows into an aeration tank that is operated with microaerobic (1 mg / L or less), the treated water is not sufficiently digested in the aeration tank and the treated water is removed. After flowing into the sedimentation tank, a large amount of sludge is deposited in a short time. Since denitrification by microorganisms is performed in this settling tank, there is a concern that the deposited sludge is pushed up by the generated nitrogen gas and the like, and is scummed and floats on the surface of the tank (deterioration of discharged water quality).
[0014]
Second, when a large amount of high-concentration organic matter sludge flows in as described above, the height of the sludge in the sedimentation tank increases, resulting in an insufficient sedimentation state, and the sludge may flow out in the discharge water stream. .
[0015]
Third, in the case of a large amount of inflowing organic matter in a short time during microaerobic operation, the SS (suspended matter) of the supernatant water in the sedimentation tank becomes high, and may become cloudy. Even if this SS is within the effluent quality standards, it may be a source of off-flavors.
[0016]
The present invention has been proposed to solve the above problems. That is, the present invention sufficiently satisfies the water quality standards even in a case where a large amount of wastewater containing high-concentration organic substances flows in wastewater treatment with microaerobic aeration treatment as disclosed in Japanese Patent Application No. 2001-175094. It is an object of the present invention to provide a wastewater treatment method and a wastewater treatment method capable of obtaining discharged water.
[0017]
Another object of the present invention is to provide a wastewater treatment apparatus that can achieve compactness and low cost of the wastewater treatment apparatus, particularly by integrating the re-aeration tank and the storage tank in the final treatment step.
[0018]
[Means for Solving the Problems]
The present invention has been proposed as a result of repeated studies to solve the above problems, and a wastewater aeration treatment step of aerating wastewater containing organic sludge in a microaerobic state, and treating the treated liquid into settled sludge and supernatant water. In a wastewater treatment method having a sedimentation separation treatment step of separating,
The method is characterized in that the whole amount of the settled sludge in the sedimentation separation process is returned to the wastewater aeration process, and the supernatant water is transferred to the re-aeration process to be re-aerated in a microaerobic state.
[0019]
In the waste water aeration treatment step and the supernatant water re-aeration treatment step, aeration is performed under the condition that the dissolved oxygen amount is practically 1 mg / L or less. Further, the treated water in the supernatant water re-aeration step is mixed with the waste water sent to the waste water aeration step as the microorganism electron acceptor adjusted water. Further, the treated water in the supernatant water re-aeration step is transferred to a stationary storage step, and the supernatant water in the stationary storage step is discharged to a sewer, a river, or the like.
[0020]
According to a preferred embodiment of the present invention, in the method for treating wastewater containing organic sludge, an electron acceptor adjusted water is mixed into raw wastewater, and aeration is performed under the condition that the dissolved oxygen capacity is substantially 1 mg / L or less. The first step,
A second step of aerating the treated water of the first step under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less;
A third step of subjecting the treated water of the second step to precipitation separation treatment, and returning the entire amount of the settled sludge to the second step;
The supernatant separated in the third step is re-aerated under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less, and a part of the treated water is used as an electron acceptor adjusting water in the first step. A fourth step of returning and resting and storing the remaining treated water.
[0021]
In the fourth step, the remaining treated water returned to the first step can be discharged as it is.However, once it is stored and settled once and subjected to sedimentation separation processing, the supernatant water is discharged to ensure the water quality standard. It will be clean and clear water.
[0022]
The wastewater treated by the wastewater treatment method of the present invention includes all domestic wastewater or industrial wastewater such as human wastewater, livestock manure wastewater, and industrial wastewater. In the aeration treatment in the present invention, a normal method such as a diffused aeration method or a mechanical aeration method is sufficient as long as the contents are stirred and aerated by supplying air into the aeration tank. The dissolved oxygen amount (DO) in the aeration tank is adjusted to the above-mentioned range by adjusting the air supply amount.
[0023]
The electron acceptor adjusted water used in the present invention is a liquid containing a large amount of a chemical substance having an oxidizing ability as an energy source by microorganisms, and specifically, nitrate, sulfur produced by microbiology, An inorganic solution containing a large amount of compounds, phosphates and the like.
[0024]
In the present invention, the reason that the dissolved oxygen amount is substantially 1 mg / L or less in all the steps of performing the aeration treatment is to supply the minimum necessary oxygen to the microorganisms and promote the consumption of electron acceptors other than oxygen. This is to promote active growth of microorganisms. Also, when the concentration is 1 mg / L or more, the aerobic microorganisms actively grow and the activated sludge treatment method is driven by oxygen. A dissolved oxygen meter is provided in each aeration tank, and the amount of supplied oxygen is controlled so that the amount of dissolved oxygen is substantially 1 mg / L or less.
[0025]
Here, the term “substantially” is intended to include a fine difference range in which an effect equivalent to that of the present invention can be obtained even at 1 mg / L or more. Note that the dissolved oxygen amount may be zero. This means that the microorganism includes a state of consuming more oxygen than the supplied oxygen amount.
[0026]
An apparatus for realizing the above-described wastewater treatment method of the present invention is a wastewater treatment system having a wastewater aeration tank for aerating wastewater containing organic sludge in a microaerobic state, and a sedimentation tank for separating the treated liquid into settled sludge and supernatant water. In the apparatus, after the sedimentation tank, a supernatant water re-aeration tank for re-aeration of the supernatant water transferred from the sedimentation tank in a slightly aerobic state is provided, and the entire amount of the settled sludge in the sedimentation tank is supplied to the wastewater aeration tank. It is characterized by providing means for transferring. The means for transferring the entire amount of the sedimentation sludge in the sedimentation tank to the wastewater aeration tank is a device that pumps up the entire amount of the sedimentation sludge continuously or at predetermined time intervals and transfers it to the wastewater aeration tank by a transfer pipe or the like. The specific configuration does not matter.
[0027]
The waste water aeration tank and the supernatant water re-aeration tank are aeration tanks for performing aeration by setting the dissolved oxygen amount to substantially 1 mg / L or less. In addition, a means is provided for mixing the treated water in the supernatant water re-aeration tank with the waste water supplied to the waste water aeration tank as the electron acceptor adjusted water for microorganisms. Specifically, the supernatant re-aeration tank and the waste water aeration tank or the tank in the previous process of the waste water aeration tank are connected by a feed pipe, and the microbiological of the waste water supplied to the waste water aeration tank is continuously, periodically, or supplied to the waste water aeration tank. What is necessary is just to return the treated water according to conditions, and the specific structure does not matter.
[0028]
Further, the supernatant water re-aeration tank is provided with a storage tank for statically storing the treated water in the supernatant water re-aeration tank. This storage tank may be provided separately from the supernatant water re-aeration tank, but is preferably provided integrally with the supernatant water re-aeration tank.
[0029]
A preferred embodiment of the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus containing organic sludge,
An inflow tank for storing wastewater raw water and aerating the wastewater raw water under the condition that the dissolved oxygen capacity is substantially 1 mg / L or less;
A reaction tank in which the treated water in the inflow tank is aerated under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less;
A sedimentation separation treatment of the treated water of the reaction tank, and a precipitation tank for returning the entire amount of the settled sludge to the reaction tank,
The supernatant separated in the sedimentation tank is re-aerated under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less, and a part of the treated water is returned to the inflow tank, and the remaining treated water is removed. It consists of a supernatant water re-aeration tank with a storage tank for stationary storage.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIG. In the figure, 1 is a wastewater raw water inflow tank, 2 is a reaction tank, 3 is a sedimentation tank, 4 is a supernatant re-aeration tank, and 5 is a storage tank.
[0031]
Raw water wastewater to be treated flows into the raw water wastewater inflow tank 1, and is subjected to pretreatment such as screening processing, and by temporarily storing the wastewater raw water, the flow rate of the constantly changing wastewater raw water is adjusted.
[0032]
As described later, the treated water in the supernatant water re-aeration tank 4 is mixed into the inflow tank 1 as electron acceptor adjustment water. The electron acceptor conditioning water is an inorganic solution containing a large amount of nitrate, sulfur compound, and phosphate, and is used by diluting to an appropriate concentration if necessary. At the time of starting up the wastewater treatment apparatus, the electron acceptor conditioned water generated by another wastewater treatment apparatus is supplied.
[0033]
In the inflow tank 1, after the electron acceptor conditioning water is mixed into the raw wastewater, aeration treatment is performed under the condition that the dissolved oxygen amount is 1 mg / L or less. In this inflow tank 1, deodorant microorganisms are mainly propagated. The electron acceptor of deodorant microorganisms is driven by oxygen, and under the low dissolved oxygen amount described above, deodorant microorganisms start using nitrate contained in the electron acceptor conditioned water, and also use oxygen entering the area at the same time Is done.
[0034]
The deodorant microorganism is, for example, a chemically synthesized bacterium, a methofile bacterium, or the like, and decomposes and deodorizes odor components such as ammonia and methyl sulfide as electron donors. The deodorant microorganisms grown in the inflow tank 1 are used in all steps, and the generation of odor in all steps can be microbiologically suppressed. It should be noted that chemically synthesized bacteria produce nitric acid, and Methofile bacteria synthesize sulfide. These will be used in the next step.
[0035]
The treated water in the inflow tank 1 is transferred to the reaction tank 2 and aerated for a predetermined time (days) under the condition that the amount of dissolved oxygen is 1 mg / L or less, as in the inflow tank 1. The purpose of the reaction tank 2 is to completely mineralize organic substances in the treated water. In the reaction tank 2, fermentative microorganisms and facultative anaerobic microorganisms digest and decompose most of organic substances in the treated water, and generate and release nitrogen (denitrification), mainly using nitrate contained in the electron acceptor conditioned water as an electron acceptor. . Electron donors are microorganisms that are broken down into smaller organic matter. The fermentative microorganisms and facultative anaerobic microorganisms include, for example, yeast, Bacillus, Alcaligenes, Clostridium, Pseudomonas, lactic acid bacteria and the like.
[0036]
The products of fermenting microorganisms and facultative anaerobic microorganisms, especially H ₂ is methemoglobin file bacteria, archaea, is consumed by the sulfur-reducing bacteria or the like, and the growth of fermenting microorganisms, organic matter digestion is accelerated due to this You. The odor components generated by the fermentative microorganisms and the facultative anaerobic microorganisms are propagated in the inflow tank 1 and consumed by the transferred deodorant microorganisms.
[0037]
By such an ecological cycle of microorganisms, a large amount of organic matter in the treated water is decomposed and consumed, and the amount of microorganisms in the reaction tank 2 can be kept stable. In the experiment, the MLSS (mixture suspension material) of the reaction tank 2 could be maintained at about 10,000 mg / L.
[0038]
The treated water in the reaction tank 2 is then transferred to the sedimentation tank 3, where the treated water is allowed to stand for a predetermined time (the number of days) to precipitate sludge contained in the treated water and separate from the supernatant water. In the sedimentation tank 3, if the above-mentioned reaction tank 2 is functioning sufficiently, organic matter is almost completely consumed by the fermentative microorganisms and the facultative anaerobic microorganisms and is mineralized. In addition, sludge is digested by microorganisms such as sulfur-reducing microorganisms, and dephosphorization is performed by phosphoric acid-absorbing microorganisms, and the phosphorus component in the supernatant water is reduced.
[0039]
All the settled sludge deposited in the settling tank 3 is returned to the reaction tank 2 continuously or at a predetermined time interval, and the aeration treatment is repeated in the reaction tank 2.
[0040]
The supernatant water of the settling tank 3 is transferred to the supernatant water re-aeration tank 4. The supernatant water re-aeration tank 4 is one in which a single treatment tank is partitioned by a partition wall 6 and a storage tank 5 is also provided. As described above, the supernatant water of the sedimentation tank 3 may be out of the discharge water quality standard depending on the organic matter concentration, flow rate, and other operating environment of the wastewater, and may not be discharged as it is. Therefore, the supernatant water is transferred to the re-aeration tank 4, and the supernatant water is re-aerated for a predetermined time (number of days) under the condition that the amount of dissolved oxygen is 1 mg / L or less as described above. Thereby, the organic matter contained in the supernatant water is consumed by the remaining fermenting microorganisms, facultative anaerobic microorganisms, and the like, and is sufficiently mineralized.
[0041]
A part of the processing liquid in the supernatant water re-aeration tank 4 is returned to the inflow tank 1 as the electron acceptor adjusting water, and the remaining processing water is transferred to the storage tank 5 provided therewith. The purpose of the storage tank 5 is to store the re-aeration treated water, but sludge such as microbial dead bodies slightly contained in the treated water precipitates in a lower layer, and the supernatant water is subjected to sterilization treatment or the like as necessary. , Discharged into sewers, rivers, etc. The precipitated sludge is digested by the remaining microorganisms or is periodically withdrawn. The supernatant water of the storage tank 5 may be returned to the inflow tank 1 as the electron acceptor adjusted water.
[0042]
In the present invention, even when wastewater raw water having a BOD of about 2000 ppm flows into the inflow tank 1, the discharge water from the storage tank 5 can clear the reference values of BOD 300 ppm or less, SS 200 ppm or less, and n-Hex 10 ppm or less. .
[0043]
【The invention's effect】
According to the present invention described above, by adjusting the electron acceptor of the microorganisms and promoting the active proliferation of the microorganisms required in each treatment step, the wastewater is purified to an environmental standard value or less, and no generation of excess sludge is generated. Alternatively, it can be suppressed as much as possible. In addition, all the processing steps can be performed in an odorless state. For this reason, the sludge treatment cost and the equipment cost of a deodorizing device and the like can be reduced.
[0044]
Further, according to the present invention, since the amount of microorganisms in the treatment step, particularly in the reaction tank, can be kept in a stable state, even wastewater having a low BOD concentration can be stably and efficiently purified.
[0045]
Furthermore, according to the present invention, even when a large amount of wastewater containing high-concentration organic matter flows in, effluent that sufficiently satisfies the water quality standard can be obtained. In addition, the re-aeration tank and the storage tank are integrated in the final treatment step, so that the wastewater treatment apparatus can be made compact and low-cost.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a wastewater treatment apparatus for carrying out the present invention.
[Explanation of symbols]
1 is an inflow tank 2 is a reaction tank 3 is a sedimentation tank 4 is a re-aeration tank 5 is a storage tank 6 is a partition

Claims (10)

In a wastewater treatment method having a wastewater aeration treatment step of aerating wastewater containing organic sludge in a microaerobic state, and a sedimentation separation treatment step of separating the treated liquid into settled sludge and supernatant water,
A wastewater treatment method comprising returning all of the settled sludge from the precipitation separation treatment step to the wastewater aeration treatment step, transferring the supernatant water to the re-aeration treatment step, and re-aeration in a slightly aerobic state. The wastewater treatment method according to claim 1, wherein in the wastewater aeration treatment step and the supernatant water re-aeration treatment step, the dissolved oxygen amount is practically aerated under a condition of 1 mg / L or less. 3. The wastewater treatment according to claim 1, wherein the treated water in the supernatant water re-aeration step is mixed with the wastewater sent to the wastewater aeration treatment step as microbial electron acceptor adjusted water. 4. Method. 4. The method according to claim 1, wherein the treated water in the supernatant water re-aeration step is transferred to a stationary storage step, and the supernatant water in the stationary storage step is discharged. 5. Wastewater treatment method. In a method for treating wastewater containing organic sludge,
A first step of mixing an electron acceptor adjusted water with wastewater raw water and aeration under a condition that the dissolved oxygen capacity is substantially 1 mg / L or less;
A second step of aerating the treated water of the first step under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less;
A third step of subjecting the treated water of the second step to precipitation separation treatment, and returning the entire amount of the settled sludge to the second step;
The supernatant separated in the third step is re-aerated under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less, and a part of the treated water is used as an electron acceptor adjusting water in the first step. The fourth step of returning and resting and storing the remaining treated water,
A method for treating wastewater, comprising: In a wastewater treatment apparatus having a wastewater aeration tank for aerating wastewater containing organic sludge in a microaerobic state and a settling tank for separating the treated liquid into settled sludge and supernatant water,
A means for providing a supernatant water re-aeration tank for re-aeration of the supernatant water transferred from the settling tank in a slightly aerobic state after the settling tank, and a means for transferring the entire amount of settled sludge in the settling tank to the waste water aeration tank. A wastewater treatment device characterized by comprising: The wastewater treatment apparatus according to claim 6, wherein the wastewater aeration tank and the supernatant water re-aeration tank are aeration tanks for performing aeration by setting the amount of dissolved oxygen to substantially 1 mg / L or less. The wastewater according to claim 6 or 7, further comprising means for mixing the treated water in the supernatant water re-aeration tank with the wastewater supplied to the wastewater aeration tank as a microbial electron acceptor adjusted water. Processing equipment. 7. The supernatant water re-aeration tank is provided with a storage tank for statically storing the treated water of the supernatant water re-aeration tank, the storage tank being integrated with the supernatant water re-aeration tank. A wastewater treatment apparatus according to any one of claims 8 to 13. In the treatment equipment for wastewater containing organic sludge,
An inflow tank for storing wastewater raw water and aerating the wastewater raw water under the condition that the dissolved oxygen capacity is substantially 1 mg / L or less;
A reaction tank in which the treated water in the inflow tank is aerated under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less;
A sedimentation separation treatment of the treated water of the reaction tank, and a precipitation tank for returning the entire amount of the settled sludge to the reaction tank,
The supernatant separated in the sedimentation tank is re-aerated under the condition that the amount of dissolved oxygen is substantially 1 mg / L or less, and a part of the treated water is returned to the inflow tank, and the remaining treated water is removed. A supernatant re-aeration tank with a storage tank for stationary storage,
A wastewater treatment device comprising:

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