JP2020179362A - Treatment method of organic waste water - Google Patents

Abstract

To provide a method of treating organic wastewater capable of treating soluble BOD and non-soluble BOD and improving sedimentation property of sludge while suppressing the amount of sludge generated.SOLUTION: A method of treating organic wastewater includes the steps of: treating water to be treated in an aeration tank equipped with a carrier; treating the water to be treated, which has been treated in the aeration tank, in an activated sludge tank; separating the water to be treated, which has been treated in the activated sludge tank, from the activated sludge in a sedimentation tank; and returning a part of the sludge settled in the sedimentation tank to the activated sludge tank. The soluble BOD sludge in the activated sludge tank has the load of less than or equal to 0.01 kg-BOD/kg-MLSS/d and the total BOD sludge load in the range of 0.02 to 0.6 kg-BOD/kg-MLSS/d.SELECTED DRAWING: Figure 1

Description

The present invention can stably treat organic wastewater containing an insoluble BOD (Biochemical Oxygen Demand) component which is a bioprocessable SS (Suspended Solid). It relates to possible processing methods.

The activated sludge method is mainly used as a treatment method for organic wastewater, and is generally composed of an aeration tank holding active sludge and a sedimentation tank for sedimenting sludge, in order to maintain the activated sludge concentration in the aeration tank. By returning a part of the sludge from the settling tank to the aeration tank and pulling out a part as excess sludge, the BOD removal rate is 90% or more under the condition that the BOD volume load is about 0.5 to 1.0 kg / m ³ / d. Is known to be capable of operation (see, for example, Non-Patent Document 1).

On the other hand, the development of a carrier capable of retaining a high concentration of microorganisms is progressing, and a treatment method using the carrier for reducing the generation of excess sludge is known. For example, some carrier treatment methods take the following methods. This is a treatment method in which organic wastewater is flowed in the order of an aeration tank for flowing a carrier, an activated sludge tank, and a settling tank, and a part of the sludge settled in the settling tank is returned to the activated sludge tank. By a method in which the soluble BOD volume load in the tank is 1 kg / m ³ / d or more and the soluble BOD sludge load in the activated sludge tank is in the range of 0.05 to 0.6 kg-BOD / kg-MLSS / d. It is said that this makes the aeration tank compact and reduces the amount of excess sludge by self-oxidation of bacteria (see, for example, Patent Document 1).

The substances contained in the organic wastewater are divided into dissolved components and solids, and the solids are further divided into organic solids and inorganic solids. Organic solids are divided into insoluble BOD, which is an SS that can be biologically treated, and SS, which is difficult to biologically treat. Before the solid matter of organic wastewater is introduced into the biological treatment tank, impurities are removed by a screen, and the solid matter of about 0.5 mm or more is settled and separated by pre-sedimentation to suppress the generation of excess sludge. It is usual to stabilize the biological treatment (see, for example, Non-Patent Document 2).

As a method of performing biological treatment without removing SS that can be biologically treated by pretreatment, for example, air, oxygen, or a mixture thereof is introduced into a mixed solution of organic matter and microorganisms to obtain organic matter and microorganisms. While maintaining the DO (Dissolved Oxygen: dissolved oxygen) of the mixed solution at 2 mg / L or more and the BOD sludge load at 0.07 ± 0.02 kg-BOD / kg-MLVSS, the organic matter is biodecomposed and the nitrogen component is nitrified. By having an aeration step of aeration and a denitrification step of anaerobically treating the vitrified nitrogen component in the presence of organic matter, it is possible to suppress the amount of sludge generated and reduce the running cost related to the disposal of excess sludge. It is said that. (See, for example, Patent Document 2).

Japanese Patent No. 4663064 Japanese Unexamined Patent Publication No. 2006-346572

New Pollution Control Technology and Regulations 2018 (Water Quality) Technology, Published by Industrial Environment Management Association, February 10, 2018, P67 Water Environmental Engineering Basics of Water Treatment and Management, Published by Kyoritsu Shuppan, First Edition, 1st Edition, December 10, 2010, P226

In the conventional carrier treatment method as described in Non-Patent Document 2, the activated sludge tank in the subsequent stage of the aeration tank is designed with a soluble BOD sludge load, and the non-soluble BOD is not considered. Therefore, it is necessary to remove a relatively large SS by pretreatment such as precipitation treatment to remove insoluble BOD, but the initial investment cost increases because a pretreatment facility is required. In addition, there is a problem that maintenance costs such as repairs are required. Further, the method described in Patent Document 2 has a problem that costs such as a blower electric power for keeping DO high and a tank volume for keeping BOD sludge load low increase.

Therefore, an object of the present invention is that when the organic wastewater contains SS, it is possible to treat soluble BOD and insoluble BOD even when the pre-sedimentation facility is not provided, and sludge while suppressing the amount of sludge generated. It is possible to improve the sedimentation property of the organic wastewater and provide a method for treating organic wastewater.

The above objectives are a step of treating the water to be treated in an aeration tank equipped with a carrier, a step of treating the water to be treated in the aeration tank in an activated sludge tank, and the treated water treated in the activated sludge tank. A step of separating the activated sludge from the settling tank and a step of returning a part of the sludge settled in the settling tank to the activated sludge tank are provided, and the soluble BOD sludge load of the activated sludge tank is 0.01 kg-BOD / kg-. It can be achieved by a method for treating organic wastewater, which is MLSS / d or less and the total BOD sludge load is in the range of 0.02 to 0.6 kg-BOD / kg-MLSS / d.

It is preferable to remove 70% or more of the soluble BOD of the water to be treated in the step of treating in the aeration tank provided with the carrier.

It is preferable not to have a precipitation step before the step of treating in the aeration tank provided with the carrier.

The carrier is preferably one or more types of carriers selected from the group consisting of gel-like carriers, plastic carriers and fibrous carriers.

It is preferable that the carrier is a gel-like carrier, and the gel-like carrier is a polyvinyl alcohol cross-linked gel carrier.

According to the present invention, when SS is contained in organic wastewater, it is possible to treat soluble BOD and insoluble BOD even when a pre-sedimentation facility is not provided, and sludge sedimentation while suppressing the amount of sludge generated. It can be made to have good properties and can provide a method for treating organic wastewater.

It is a figure which represented typically the flow of an example for carrying out this invention. It is a graph which shows the transition of the cumulative surplus sludge amount of Example 1 and Comparative Example 2.

The present invention includes a step of treating the water to be treated in an aeration tank equipped with a carrier, a step of treating the water to be treated in the aeration tank in an activated sludge tank, and the treated water treated in the activated sludge tank. A step of separating the activated sludge from the settling tank and a step of returning a part of the sludge settled in the settling tank to the activated sludge tank are provided, and the soluble BOD sludge load of the activated sludge tank is 0.01 kg-BOD / kg-. This is a method for treating organic wastewater, which is MLSS / d or less and the total BOD sludge load is in the range of 0.02 to 0.6 kg-BOD / kg-MLSS / d. According to this method, when SS is contained in the organic wastewater, the soluble BOD is mainly removed in the aeration tank equipped with the carrier, and the insoluble BOD remaining without being decomposed becomes the load of the activated sludge tank in the subsequent stage. It is presumed that the treatment makes it possible to operate the sludge with good sedimentation while suppressing the amount of sludge generated. Therefore, the organic wastewater to be treated must contain insoluble BOD, and the BOD component of the organic wastewater to be treated must have an insoluble BOD / total BOD of 0.17 or more. Is preferable, and 0.33 or more is more preferable. The total BOD concentration is preferably 5000 mg / L or less, and more preferably 2000 mg / L or less. Moreover, the total BOD concentration is preferably 100 mg / L or more. The SS concentration is preferably 2000 mg / L or less, and more preferably 1000 mg / L or less. The SS concentration is preferably 100 mg / L or more.

If the organic wastewater contains impurities, it may interfere with the operation of the wastewater treatment facility. Therefore, it is preferable to remove the impurities with a screen or the like before introducing the organic wastewater into the aeration tank.

When organic wastewater (water to be treated) containing SS capable of biological treatment is introduced into an aeration tank in which a carrier flows, it is preferable that 70% or more of the soluble BOD in the water to be treated is oxidatively decomposed by bacteria. , 80% or more, more preferably 90% or more, and particularly preferably 95% or more. Even in the aeration tank, the insoluble BOD can be partially decomposed.

The pH of the aeration tank through which the carrier flows is preferably 5 to 9 and more preferably 6 to 8 from the viewpoint of the reactivity of the biological reaction. The temperature in the aeration tank is preferably 10 to 35 ° C., more preferably 20 to 30 ° C. from the viewpoint of the reactivity of the biological reaction. The DO in the aeration tank is preferably 1 mg / L or more, more preferably 2 mg / L or more, and further preferably 3 mg / L or more. Moreover, the DO is preferably 9 mg / L or less.

An example of the wastewater treatment flow of the present invention is shown in FIG. In this system, the total BOD volume load in the aeration tank in which the carrier flows is preferably 1 kg / m ³ / d or more. The total BOD volume load is preferably 10 kg / m ³ / d or less, and more preferably 5 kg / m ³ / d or less. The higher the total BOD volume load, the smaller the size of the aeration tank through which the carrier flows. The total BOD volume load is obtained by adding the flow rate per day to the total BOD concentration of the inflowing organic wastewater and dividing by the volume of the aeration tank in which the carrier flows.

The carrier used in this aeration tank is a solid to which microorganisms adhere, and various known microbial-immobilized carriers can be used, but the carrier is selected from the group consisting of gel-like carriers, plastic carriers and fibrous carriers. It is preferable to use at least one microbial immobilization carrier. The materials include vinyl alcohol resins such as polyvinyl alcohol; ether resins such as polyethylene glycol; acrylic resins such as polymethacrylic acid; acrylamide resins such as polyacrylamide; olefin resins such as polyethylene and polypropylene, and styrene resins such as polystyrene; polyethylene. Ester resins such as terephthalate and polybutylene terephthalate; Acrylonitrile resins such as polyacrylonitrile; Urethane resins such as polyurethane sponge; Polysaccharides such as calcium alginate, κ (kappa) carrageenan, agar, and cellulose derivatives; polyester acrylate, epoxy acrylate, urethane acrylate Photocurable resin such as; Porous inorganic compound such as activated carbon can be exemplified. Among them, a gel-like carrier is preferable from the viewpoint of excellent immobilization of microorganisms, and polyvinyl has a porous and network-like structure up to the inside and a large amount of water can be taken into the gel. A polyvinyl alcohol-based hydrogel carrier made of an alcohol-based resin is preferable, and a polyvinyl alcohol cross-linked gel carrier such as a formalized polyvinyl alcohol-based hydrogel or an acetalized polyvinyl alcohol-based hydrogel is more preferable. The microbial immobilization carrier can be used alone or in combination. From the viewpoint of wastewater treatment efficiency and carrier fluidity, the filling rate is preferably 5% or more and 50% or less, and more preferably 10% or more and 30% or less of the tank volume.

The equivalent sphere diameter of the carrier is preferably 1 to 10 mm. When the equivalent diameter of the sphere is small, when a screen for preventing the outflow of the carrier is installed in the aeration tank, it is necessary to reduce the mesh size of the screen, which may cause clogging. Therefore, the equivalent diameter of the sphere is more preferably 2 mm or more. On the other hand, if the equivalent diameter of the sphere exceeds 10 mm, the fluidity of the carrier may decrease. Therefore, the equivalent diameter of the sphere is more preferably 6 mm or less. Here, the sphere equivalent diameter is the diameter of a sphere having a volume equal to the volume of the particles.

The specific gravity of the carrier is slightly larger than that of water, and it is preferable that the carrier has a specific gravity that can be swung in the aeration tank so as not to be washed away from the aeration tank. In the treatment method of the present invention, by using a carrier having a specific gravity slightly higher than that of water, wastewater can be treated more stably without causing the carrier to run off, so that the specific gravity of the carrier is 1.001 or more. It is preferably 1.005 or more, and more preferably 1.005 or more. On the other hand, the specific gravity is preferably 1.2 or less, more preferably 1.1 or less, and even more preferably 1.05 or less.

The carrier preferably has a communication hole, and the pore size of the communication hole is preferably a hole diameter at which only bacteria can live inside the carrier. The pore size near the surface of the carrier is preferably 0.1 to 100 μm. If the pore size is less than 0.1 μm, bacteria may not be able to invade the inside of the carrier. The pore diameter near the surface is more preferably 0.5 μm or more. On the other hand, if the pore size near the surface exceeds 100 μm, large organisms other than bacteria may invade. The pore diameter is more preferably 50 μm or less. The hole diameter of the communication hole can be measured by a method such as observation using an electron microscope.

The treated water in the aeration tank in which the carrier flows is introduced into the activated sludge tank in the subsequent stage. When the organic wastewater contains insoluble BOD, the total BOD source in the activated sludge tank has a high proportion of insoluble BOD. In the activated sludge tank, the remaining soluble BOD and insoluble BOD are oxidatively decomposed to entrain the fine sludge generated in the aeration tank in the sludge, and the sedimentation property is enhanced. In addition, the fine sludge generated in the aeration tank is self-oxidized to reduce the sludge. In order to efficiently entrain and settle fine sludge, the soluble BOD sludge load in the activated sludge tank is 0.01 kg-BOD / kg-MLSS / d or less. The total BOD sludge load is 0.02-0.6 kg-BOD / kg-MLSS / d. From the viewpoint of more stable sedimentation of activated sludge, the total BOD sludge load in the above activated sludge tank is preferably 0.1 kg-BOD / kg-MLSS / d or less.

The value of the total BOD sludge load in the activated sludge tank is adjusted according to the total amount of BOD remaining after removal of all BOD in the aeration tank and the amount of MLSS in the activated sludge tank. When the total BOD removal rate in the aeration tank is high and the total BOD required for the activated sludge tank is insufficient, there is a method of distributing a part of raw water or the like to the activated sludge tank to secure the required total BOD.

The pH of the activated sludge tank is preferably 5 to 9 and more preferably 6 to 8 from the viewpoint of reactivity of biological reaction. The temperature of the activated sludge tank is more preferably 10 to 35 ° C., more preferably 20 to 30 ° C. from the viewpoint of the reactivity of the biological reaction. The DO of the activated sludge tank is preferably 1 mg / L or more. Further, the DO is preferably 9 mg / L or less.

The MLSS concentration in the activated sludge tank is not particularly limited, but is preferably 3000 to 10000 mg / L.

The operating conditions of the water area load in the settling tank may be the same as those of the conventional activated sludge method. Specifically, the water area load is preferably 15 m ³ / m ² / d or less.

If the sludge sedimentation property is poor in the settling tank, a coagulant reaction tank may be provided between the activated sludge tank and the settling tank, and a coagulant may be added. The amount of the flocculant added is preferably until the SVI of the sludge in the activated sludge tank becomes 200 mL / g or less.

The coagulant to be added is not particularly limited, and a coagulant that can be used for ordinary water treatment can be used. For example, as inorganic flocculants, aluminum sulfate (aluminum sulfate), polyaluminum chloride (PAC), ferrous sulfate, ferric sulfate, ferric chloride, copper chloride, sodium aluminate, ammonium alum, potash alum, slaked lime. , Fresh lime, soda ash, sodium carbonate, magnesium oxide, iron-silica polymer and the like. Organic (polymer) flocculants include polyacrylamide, sodium alginate, sodium carboxymethyl cellulose salt, sodium polyacrylate, maleic acid copolymer, water-soluble aniline, polythiourea, polyethyleneimine, quaternary ammonium salt, and polyvinylpyridine. Kind, polyoxyethylene, caustic starch and the like. It is also possible to use two or more kinds of coagulants together.

If the amount of these coagulants added is too small, the coagulation effect cannot be obtained, and if it is too large, the solid content becomes excess sludge and the amount of sludge drawn out increases. As a method of addition, there are an intermittent addition method in which sludge is added until the sedimentation property is improved and then not added until the sedimentation property is deteriorated, and a continuous addition method in which a small amount of coagulant is always added. is there.

Some coagulants specify a pH and temperature range suitable for coagulation, and some coagulants cause a change in pH when added, so they are suitable for coagulation such as pH adjustment as necessary. It is preferable to manage the water quality.

All or part of the sludge settled in the settling tank is returned to the activated sludge tank. A wastewater treatment facility may be newly installed for carrying out the present invention, but it can also be carried out by modifying an existing wastewater treatment facility.

Hereinafter, the present invention will be described in detail with reference to Examples. The following physical quantities described in Examples and Comparative Examples were measured by the following evaluation methods.

(Total BOD removal rate)
The total BOD of the water to be treated and the total BOD of the treated water in the aeration tank in which the carrier flows were measured and calculated by the following formula.
BOD removal rate (%)
= ({All BOD of treated water}-{All BOD of treated water}) ÷ {All BOD of treated water} × 100

(Soluble BOD removal rate)
The water-soluble BOD to be treated and the treated water-soluble BOD of the aeration tank in which the carrier flows were measured and calculated by the following formula.
Soluble BOD removal rate (%)
= ({Water-dissolved BOD to be treated}-{Water-dissolved BOD to be treated}) ÷ {Water-soluble BOD to be treated} × 100

(Example 1)
The water to be treated is food-based wastewater with a total BOD of 1000 mg / L, a soluble BOD of 400 mg / L, an SS concentration of 800 mg / L, and an inflow amount of 1 L / d. As the treatment device, a wastewater treatment device consisting of an aeration tank in which a carrier having a capacity of 1 L flows, an activated sludge tank having a capacity of 1 L, and a settling tank having a capacity of 5 L was used. 0.1 L of a polyvinyl alcohol crosslinked gel carrier (diameter 4 mm, specific gravity 1.025, pore diameter of communication holes in the carrier is 0.5 to 20 μm) was charged into the aeration tank in which the carrier flows. An aeration pipe is installed at the bottom of the aeration tank and activated sludge tank in which the carrier flows, and the water to be treated is aerated by the air sent from the blower connected to the air diffuser. In addition, a screen is installed at the outlet of the aeration tank through which the carrier flows to prevent the carrier from flowing out. The activated sludge that has flowed into the settling tank is separated into treated water and sludge, the treated water flows out due to the overflow, and the settled sludge is returned to the activated sludge tank. The aeration tank in which the carrier flows is controlled at a temperature of 25 ° C. ± 2 ° C., a pH of 6.0 to 6.2, and a DO of 3 to 6 mg / L. The activated sludge tank is controlled at a temperature of 25 ° C. ± 2 ° C., a pH of 6 to 7, a DO of 1 to 1.5 mg / L, and an MLSS concentration of 5000 to 6000 mg / L. The flow in Example 1 is schematically shown in FIG. When operated under these conditions, the total BOD volume load in the aeration tank in which the carrier flows is 1 kg / m ³ / d. The treated water in the aeration tank in which the carrier flows was 240 mg / L of total BOD and 24 mg / L of soluble BOD, and the total BOD removal rate was 76% and the soluble BOD removal rate was 98%. Therefore, the soluble BOD sludge load in the activated sludge tank is 0.002 kg-BOD / kg-MLSS / d, and the total BOD sludge load is 0.04 kg-BOD / kg-MLSS / d. The SS of the treated water was 20 mg / L, and good results were obtained. After operating for 13 days, 650 mg of excess sludge was generated.

(Comparative Example 1)
Biological treatment was carried out using the following water to be treated and the same treatment equipment as in Example 1. As the water to be treated, food wastewater was filtered using a 0.45 μm filter, and only soluble components were used. The filtered food-based wastewater has a total BOD of 400 mg / L and a soluble BOD of 400 mg / L, an SS concentration of 0 mg / L, and an inflow amount of 1 L / d. When operated under these conditions, the total BOD volume load in the aeration tank in which the carrier flows is 0.4 kg / m ³ / d. The treated water in the aeration tank in which the carrier flows was 40 mg / L of total BOD and 10 mg / L of soluble BOD, and the total BOD removal rate was 90% and the soluble BOD removal rate was 98%. Therefore, the soluble BOD sludge load in the activated sludge tank is 0.002 kg-BOD / kg-MLSS / d, and the total BOD sludge load is 0.007 kg-BOD / kg-MLSS / d. The SS of the treated water was 128 mg / L, and the cohesiveness of sludge deteriorated.

(Comparative Example 2)
Biological treatment was carried out using the following water to be treated and the same treatment equipment as in Example 1. As the water to be treated, the SS of food wastewater was separated by sedimentation by pretreatment. The pretreated food wastewater has a total BOD of 460 mg / L and a soluble BOD of 400 mg / L, an SS concentration of 80 mg / L, and an inflow amount of 1 L / d. The SS removed by the pretreatment was calculated as excess sludge. When operated under these conditions, the total BOD volume load in the aeration tank in which the carrier flows is 0.46 kg / m ³ / d. The treated water in the aeration tank in which the carrier flows was 50 mg / L of total BOD and 10 mg / L of soluble BOD, and the total BOD removal rate was 89% and the soluble BOD removal rate was 98%. Therefore, the soluble BOD sludge load in the activated sludge tank is 0.002 kg-BOD / kg-MLSS / d, and the total BOD sludge load is 0.01 kg-BOD / kg-MLSS / d. By operating for 13 days, 7600 mg of excess sludge was generated, and the amount of excess sludge generated increased.

1 Carrier fluid aeration tank 2 Activated sludge tank 3 Sedimentation tank 4 Organic wastewater 5 Return sludge 6 Excess sludge

Claims (5)

The process of treating water to be treated in an aeration tank equipped with a carrier,
The step of treating the water to be treated in the aeration tank in the activated sludge tank,
A step of separating the treated water treated in the activated sludge tank and the activated sludge in a settling tank,
It is equipped with a process to return a part of the sludge settled in the settling tank to the activated sludge tank.
The soluble BOD sludge load of the activated sludge tank is 0.01 kg-BOD / kg-MLSS / d or less, and the total BOD sludge load is in the range of 0.02 to 0.6 kg-BOD / kg-MLSS / d. , How to treat organic wastewater. The method for treating organic wastewater according to claim 1, wherein 70% or more of the soluble BOD of the water to be treated is removed in the step of treating in the aeration tank provided with the carrier. The method for treating organic wastewater according to claim 1 or 2, which does not include a precipitation step before the step of treating in an aeration tank provided with the carrier. The method for treating organic wastewater according to any one of claims 1 to 3, wherein the carrier is one or more types of carriers selected from the group consisting of a gel-like carrier, a plastic carrier and a fibrous carrier. The method for treating organic wastewater according to claim 4, wherein the carrier is a gel-like carrier, and the gel-like carrier is a polyvinyl alcohol cross-linked gel carrier.