JP2590474B2 - Wastewater treatment method - Google Patents

Description

The present invention relates to a biological treatment method for sewage.

[Conventional technology]

The biological treatment method of sewage is roughly classified into a floating organism method and a fixed organism method according to the existence mode of organisms in a treatment reaction tank. A typical example of the floating organism method is an activated sludge method. Typical examples of the sticking organism method include a trickling filter method and a catalytic oxidation method. In addition, as a method according to the sticking organism method, microorganisms are entrapped and immobilized on natural polysaccharides (agar, K-carrageenan, etc.) or synthetic polymers (acrylamide, polyvinyl alcohol, etc.), and the microorganisms are filled in a treatment reaction tank. There is an immobilized microbial method to work, which has been receiving attention in recent years.

In the floating organism method, in order to maintain the concentration of microorganisms in the reaction tank, the sludge mixture flowing out of the reaction tank is solid-liquid separated by gravity sedimentation, and at least a part of the separated sludge is
Return to the reaction tank. In this case, the suspended solids concentration of the returned sludge obtained by gravity sedimentation is about 10,000 mg /, which is relatively low in the reaction tank. (About 200mg /) It will be diluted by raw water. For example, in the case of the standard activated sludge method in sewage treatment,
SS is usually about 1500 to 2000 mg /, and the residence time of the reaction tank needs to be about 6 to 8 hours. Therefore, there is a problem that the reaction tank becomes large.

To reduce the size of the reaction tank, increase the return ratio or the concentration of returned sludge to increase the MLSS in the reaction tank.
In the former method, the return power is large, and in the latter method, solid-liquid separation methods other than gravity sedimentation method,
For example, it is necessary to employ a pressurized flotation method or a centrifugal separation method, which also causes a problem that the operating cost becomes large. Furthermore, even if the MLSS in the reaction tank is increased by some method and the gravity sedimentation method is used for solid-liquid separation, the sedimentation velocity of high-concentration sludge is low. This requires a large area.

In the fixed organism method, since the action of microorganisms fixed on the carrier in the reaction tank is used, it is basically unnecessary to return sludge obtained by solid-liquid separation of the effluent of the reaction tank to the reaction tank.
However, the SS concentration of the reaction tank effluent is 100 to 300 mg / sewage for sewage treatment, which is less than that for the activated sludge method.
There is little co-precipitation effect between fine SS and sludge. For this reason, there is a problem that the sedimentation treated water in the fixed organism method is cloudy compared with the activated sludge treated water, and the clarity is low. In addition, the sediment sludge in the sticking organism method is not always pulled out unlike the activated sludge method, so the lower part of the sedimentation basin becomes anaerobic in some cases, generating odor due to decay of sludge and floating and rising of sludge due to gas generation. The deterioration of the treated water is caused by the incorporation of sludge into the treated water. Such a problem,
The case where the reaction tank and the sedimentation tank are separated and the case where they are integrated are common. In order to remove the turbidity in the treated water to a high degree, it is necessary to perform special treatment such as coagulation sedimentation treatment and sand filtration.
This has resulted in new problems such as an increase in operating costs. Furthermore, the bond between the carrier and the microorganism in the fixed organism method is due to a viscous substance or hyphae produced by the microorganism, and is weak against shearing force. Therefore, the sticking biofilm is peeled off in the process of water treatment or washing of sewage,
There is also a problem that sewage treatment performance is reduced.

The immobilized biological method solves some of the above problems in the fixed biological method. In this method, microorganisms are sealed in a three-dimensional cage-shaped carrier made of a polymer, and the concentration of microorganisms in the reaction tank is improved and resistance to shearing force is increased. It is a measure.

[Problems to be Solved by the Invention] However, even the immobilized biological method could not solve the problems of white turbidity of the sedimentation treatment water, decay of the settled sludge, and floating and outflow of SS.

The present invention has been made to solve the above problems, and has as its object to obtain a wastewater treatment method described below.

(1) The treatment apparatus can be made compact, and gravity sedimentation separation is used for solid-liquid separation of the sludge mixture flowing out of the reaction tank.

(2) Obtain treated water with high clarity.

(3) Stable treatment is performed with little influence on the treatment due to separation of sludge from the carrier in the process of passing water or cleaning.

[Means for solving the problem]

The present invention has been made in order to achieve the above object, and in biologically treating sewage, first performs treatment in an immobilized microorganism reaction tank, and then performs treatment in a floating organism reaction tank, or fixed. After performing biological treatment in a reaction tank where coexisting microorganisms and floating organisms coexist, aeration treatment is performed in an aeration tank, and then solid-liquid separation is performed in a sedimentation tank to obtain settled sludge and treated water. At least a part of the settled sludge is returned to the floating organism reaction tank or the immobilized microorganism reaction tank or both, and the sludge mixed liquid in the aeration tank or a part of the sludge mixed liquid flowing out from the aeration tank is suspended or fixed. The present invention provides a method for treating sewage returned to the activated microorganism reaction tank or both.

[Action] After the treatment in the immobilized microorganism reaction tank, the treatment in the floating organism reaction tank is performed, or the biological treatment is performed in the reaction tank in which the immobilized microorganisms and the suspended organism coexist, and then the aeration treatment is performed in the aeration tank. Performing, and then performing solid-liquid separation in the sedimentation tank to obtain the settled sludge and treated water, and returning at least a part of the settled sludge from the sedimentation tank to the floating organism reaction tank or the immobilized microorganism reaction tank or both, A part of the sludge mixture in the aeration tank or a part of the sludge mixture flowing out of the aeration tank is returned to the floating organism reaction tank or the immobilized microorganism reaction tank or both.

Embodiment FIG. 1 is a schematic diagram for explaining an embodiment of the present invention. This equipment is provided with an activated sludge treatment apparatus including a reaction tank 2 having a carrier 1 holding immobilized microorganisms therein, an aeration tank 3 and a sedimentation tank 4 in order. For biological treatment under aerobic or anaerobic conditions. In this case, the carrier 1 may be of various shapes such as granular, string-like, plate-like, and tubular, and the packed bed may be a fluidized bed or a fixed bed. It is also possible to adopt a rotating disk shape. The flow of the sewage in the reaction tank 2 may be an upward flow, a downward flow, or a completely mixed flow. By rationally selecting the three-dimensional shape, particle size, or both of the immobilized carrier in the reaction tank 2, the concentration and properties of the microorganisms held in the reaction tank 2 can be increased to perform high-speed processing.

The effluent 6 from the reaction tank 2 has low soluble BOD and low soluble COD, but the effluent 6 contains microorganisms released from the carrier 1 and SS components such as SS brought from the raw wastewater 5. Therefore, the turbidity becomes high. The effluent 6 is introduced into the aeration tank 3 together with the return sludge 8 which is a part of the settling sludge 7 extracted from the sedimentation tank 4, and is subjected to aeration treatment. The sludge mixed liquid 9 flowing out of the aeration tank 3 is introduced into the sedimentation tank 4 and subjected to solid-liquid separation processing to obtain treated water 10 as supernatant water and precipitated sludge 7. Due to the microbial action in the aeration tank 3 and the co-precipitation effect of the high-concentration sludge mixture, the treated water 10 becomes good with little SS.

Most of the sewage treatment is a reaction tank 2 that holds a high concentration of microorganisms
The process is completed while passing through the process, and in the subsequent activated sludge treatment, a short-time aeration treatment as a so-called “finishing” and a sedimentation separation treatment are performed. Therefore, the volume of the microbial reaction processing section including the reaction tank 2 and the aeration tank 3 can be reduced in size. Further, it is possible to obtain treated water having sufficiently high clarity by using a gravity sedimentation tank in the solid-liquid separation part, and there is no possibility that sludge stays in the sedimentation tank or sludge floats due to decay. Further, even when sludge is peeled off due to water passing or backwashing in the reaction tank 2 and the treatment capacity is reduced, the sludge is complemented in the subsequent activated sludge treatment step, and the removal treatment of untreated pollutant components and Stabilized treatment can be performed by capturing and flocking the separated sludge.

In FIG. 1, the reaction tank 2 can be formed into an aerobic treatment tank by aeration or rotary aeration, and can be formed into an anaerobic treatment tank by restricting the supply of oxygen. The aeration tank 3 can be made anaerobic as limited aeration or non-aeration, and can be made anaerobic activated sludge together with the subsequent settling tank 4. Anaerobic activated sludge is preferable from the viewpoint of reduction in operation power, but aerobic activated sludge is preferable from the viewpoint of downsizing of the apparatus and upgrading of treated water. In small-scale treatment plants and industrial wastewater treatment plants where the amount of influent water fluctuates greatly over time, the control tank and the reaction tank 2 should be combined to equalize the amount and quality of sewage introduced into the treatment equipment. Is also possible. An embodiment in this case is shown in FIG.

In the present embodiment, the flowing water contamination 11 is introduced through the introduction groove 12 into the adjustment reaction tank 14 in which the immobilized microorganism holding carrier 13 is present in at least a part of the container.
The adjustment is performed between the upper water level 15 and the lower water level 16 of the adjustment reaction tank 14 by turning on and off the liquid supply pump 17. Conditioning reaction tank 14
Sewage is always present in the area below the sewage level of 16 and the residence time determined by the ratio with the inflow is secured. Thus, the effluent 18 from the regulating reaction tank 14 is
The water has been adjusted and treated with microorganisms on the carrier 13. This adjustment reaction tank 14 can also be in an aerobic state or an anaerobic state. By introducing and treating the effluent 18 into a receiving biological treatment process such as an activated sludge process, it is possible to bring about effects such as downsizing of a treatment apparatus, upgrading of treatment water quality, and stabilization of treatment results in the method of the present invention. It becomes possible.

FIG. 3 is a schematic view showing another embodiment of the present invention. In this embodiment, the return destination of the return sludge 8 in the embodiment shown in FIG. In this case, as compared with the embodiment of FIG. 1, when the reaction tank 2 is operated under aerobic conditions, the required amount of oxygen in the reaction tank 2 is large, but the sludge concentration is large, so the treatment system The effect is that the overall reactor volume is smaller. In this case, the shearing force acting on the microbial membrane increases due to the increase in the amount of aeration air for oxygen supply, but all the sludge held on the carrier is released due to the use of immobilized microorganisms, affecting the treatment. There is no danger of doing so. Further, in the embodiment of FIG. 3, when the volume of the reaction tank 2 and the amount of microorganisms in the reaction tank 2 are sufficiently large compared to the pollution load, the aeration tank 3 can be omitted from the processing flow. It is. In this case, it is preferable to operate the reaction tank 2 under aerobic conditions from the viewpoint of ensuring high-grade treated water quality and making the reaction tank 2 compact.

FIG. 4 is a schematic view showing still another embodiment of the present invention. In the present embodiment, a reaction tank 2 containing a microorganism-immobilized carrier 1 under anaerobic conditions, an aeration tank 3 and a sedimentation tank 4 are sequentially arranged, and sewage 5 to be treated is introduced into the reaction tank 2. The effluent 6 is introduced into the aeration tank 3 for aeration. At least a part of the sludge mixture 9 flowing out of the aeration tank 3 is introduced into the sedimentation tank 4, and the sludge is settled and separated to obtain the treated water 10. At least a part of the settled sludge 7 obtained by the settling tank 4 is returned to the reaction tank 2 as returned sludge 8, and the remaining part of the settled sludge 7 is separately treated as excess sludge. Further, a part of the sludge mixture liquid in the aeration tank 3 or the sludge mixture liquid 9 flowing out from the aeration tank 3 is returned to the reaction tank 2.

By performing such a driving operation, the process of discharging and denitrifying phosphorus from sludge by the anaerobic reaction in the reaction tank 2, the process of incorporating phosphorus into sludge by the aerobic reaction in the aeration tank 3, and the nitrification process are performed. It is possible to remove BOD and COD by anaerobic reaction and aerobic reaction, and to remove nitrogen and phosphorus, while it is possible to stably obtain high-grade treated water with low SS concentration using a compact treatment device. Become.

FIG. 5 is a schematic view showing another embodiment of the method of the present invention. In this embodiment, a reaction tank 2 and a reaction tank 18a containing an immobilized carrier 1 operated under anaerobic conditions, an aeration tank 3 and a sedimentation tank 4 are arranged in this order, and sewage water 5 to be treated is supplied to the reaction tank. 2
And the effluent 6 from the reaction tank 2 is introduced into the reaction tank 18a and subjected to anaerobic treatment.
Is introduced into the aeration tank 3 to perform aeration treatment. At least a part of the sludge mixture 9 flowing out of the aeration tank 3 is introduced into the sedimentation tank 4, and the sludge is settled and separated to obtain the treated water 10. At least a part of the settling sludge 7 obtained from the settling tank 4 is returned to the reaction tank 2 as returned sludge 8. In addition, the sludge mixture in the aeration tank 3 or a part of the sludge mixture 9 flowing out of the aeration tank 3 is returned to the reaction tank 18a.

By performing such an operation, the process of discharging phosphorus from sludge by the anaerobic reaction in the reaction tank 2 and the reaction tank 18
The denitrification treatment by the anaerobic treatment in a and the treatment of phosphorus incorporation into the sludge by the aerobic reaction in the aeration tank 3 are performed.
While removal of nitrogen and phosphorus can be performed together with removal of D and COD, high-grade treated water with a low SS concentration can be stably obtained with a compact device. Unlike the embodiment shown in FIG. 4, in this embodiment, the anaerobic treatment step is divided into a reaction tank 2 for discharging phosphorus and a reaction tank 18a for denitrification treatment. If oxides are present, the reaction of discharging phosphorus from sludge is suppressed, so that NO ₂ and NO ₃ generated by the aeration tank 3 are prevented from being introduced into the reaction tank 2 for discharging phosphorus. It is.

Next, an experimental example in which sewage treatment is performed using a treatment apparatus according to the present invention and a treatment apparatus according to a conventional method will be described. As the raw water for the experiment, the overflow of the first sedimentation basin of a certain sewage treatment plant was used. An example of the component analysis is as shown in Table 1.

The immobilized carrier used in the experiment was based on PVA, and the preparation method was as follows.

1 volume of 20% PVA aqueous solution, sodium alginate 3.0
0.5 volume% aqueous solution and centrifugal concentrate of activated sludge (MLSS 90
000 mg /), and dropped into a 0.2 M CaCl ₂ aqueous solution from a syringe to form a primary gel of calcium alginate. The gelled carrier was transferred to a saturated boric acid solution, allowed to stand for 24 hours, and then washed with water. Thus, a microorganism-immobilized carrier based on PVA was obtained.

Experimental apparatus A in the conventional method is a reaction tank having a content of 10,
On the other hand, the immobilized carrier was added to 3.2 (apparent volume), and raw water was introduced at an hourly rate (residence time: 5 hours) while aeration was performed so that the DO became 2 mg / or more.

The experimental apparatus B in the conventional method was an activated sludge apparatus having an effective volume of 10 in the aeration tank, and the raw water was similarly supplied such that the residence time in the aeration tank was 5 hours. DO was aerated in the aeration tank so as to be 2 mg / min or more, and the MLSS in the aeration tank was operated at a target of 2000 mg /.

The experimental apparatus C in the method of the present invention is an apparatus in which the experimental apparatus A in the conventional method and the activated sludge apparatus in the aeration tank 2 are disposed as in the embodiment in FIG. (Dwell time in the entire reaction tank is 3 hours), DO in the reaction tank and the aeration tank is diffused so as to be 2 mg / or more.
MLSS was operated at 2000 mg /.

The experimental device D in the method of the present invention is a device in which two sets of the experimental device A in the conventional method and the activated sludge experimental device of the effective volume 10 of the aeration tank are arranged in order as shown in FIG.
/ Hour, in the aeration tank with the target of MLSS 2000mg /
The operation was performed so that the DO became 2 mg / or more, and the sludge mixture was returned from the aeration tank to the reaction tank 18a in FIG. 5 at a flow rate of 10 / hour.

The results of the above experiments are as shown in Table 1. The treated water in the flow according to the embodiment of FIG. 1 using the experimental device C is better than the treated water according to the conventional method using the experimental device A, and is equal to the conventional treated water using the experimental device B. Met. Although the total reaction tank residence time in the experimental apparatus C was shorter than the reaction tank residence time in the experimental apparatus B, both treated water qualities were substantially the same. Indicates that it is useful. Further, the analysis result of the treated water by the method of the present invention using the experimental apparatus D shows that the method of the present invention can be applied to not only the removal of BOD and COD but also the removal of nitrogen and phosphorus.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the following remarkable effects can be obtained.

(1) The processing apparatus can be made compact, and gravity sedimentation separation can be used for solid-liquid separation of the sludge mixture flowing out of the reaction tank.

(2) It is possible to obtain treated water having high clarity.

(3) There is little effect on the treatment due to the separation of sludge from the carrier in the process of passing water or cleaning, and the treatment can be performed stably even with load fluctuations.

(4) Depending on the selection of the process, not only the removal of organic substances but also the removal of nitrogen and phosphorus can be performed.

(5) The present invention can be applied not only to the aerobic reaction treatment of living organisms but also to the anaerobic reaction treatment.

[Brief description of the drawings]

FIG. 1, FIG. 2, FIG. 3, FIG. 4, and FIG. 5 are schematic views for explaining an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Immobilized microbial holding carrier, 2 ... Reaction tank, 3 ... Aeration tank, 4 ... Settling tank, 5 ... Sewage to be treated, 6 ... Effluent, 7 ... Settled sludge, 8 ... Returned sludge, 9 sludge mixture, 10 treated water, 11 sludge inflow, 12 ditches,
13 ... Immobilized microorganism holding carrier, 14 ... Adjustment reaction tank, 15 ...
… High water level, 16 …… Low water level, 17 …… Send pump, 18 …… Outflow water, 18a …… Reaction tank

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location C02F 9/00 503 C02F 9/00 503C 503G 504 504A (72) Inventor's Bureau Toshiaki Marunouchi, Chiyoda-ku, Tokyo 1-1-2 Nippon Kokan Co., Ltd. (72) Inventor Yasunori Tanji 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-55-22324 (JP, A)

Claims (1)

(57) [Claims] In the biological treatment of sewage, first, treatment is performed in an immobilized microorganism reaction tank and then in a floating organism reaction tank, or in a reaction vessel in which immobilized microorganisms and suspended organisms coexist. After performing the biological treatment, aeration treatment is performed by an aeration tank, and then solid-liquid separation is performed by a sedimentation tank to obtain settled sludge and treated water, and at least a part of the settled sludge from the settling tank is suspended in the floating organism. The sludge mixed liquid in the aeration tank or a part of the sludge mixed liquid flowing out from the aeration tank is returned to the reaction tank or the immobilized microorganism reaction tank or both, and the floating organism reaction tank or the immobilized microorganism reaction tank or a mixture thereof. A method for treating sewage, which is returned to both.