JP2023162977A - Wastewater treatment system and wastewater treatment method - Google Patents

Abstract

To provide a wastewater treatment system and a wastewater treatment method that can reduce the cost required for dewatering treatment of digested sludge and secure the amount of activated sludge required for biosorption.SOLUTION: Inflowing sewage is separated from coarse solids in a sedimentation basin and a screen unit 1, and the separated coarse solids are treated in a methane fermentation unit 2 to produce digested sludge. The digested sludge is transferred to a dewatering unit 4 and a digested sludge conditioning apparatus 5, and the digested sludge is brought into contact in the digested sludge conditioning unit 5 with surplus sludge from a water treatment apparatus 8 and is conditioned. The conditioned sludge is then contacted in a contacting/mixing unit 6 with treated water from the sedimentation basin and the screen unit 1, and the organic matters contained in the treated water are adsorbed by the conditioned sludge. Sludge with adsorbed organic matters is separated in a separation and concentration unit 7, and the concentrated sludge is transferred to the methane fermentation unit 2. Separated water from the separation/concentration unit 7 is supplied to the water treatment unit 8, and organic matters contained in the wastewater are decomposed in the water treatment unit 8.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wastewater treatment device and a wastewater treatment method.

Conventionally, wastewater such as sewage containing impurities, organic matter, and moisture has been treated by a standard activated sludge method. For example, sewage discharged from homes, factories, etc. is transferred through a settling tank and a primary settling tank to a biological reaction tank containing activated sludge, and in the biological reaction tank, organic matter in the sewage is decomposed and removed by the activated sludge.

FIG. 4 is a diagram schematically showing a wastewater treatment device using the standard activated sludge method, which is generally implemented in medium- and large-scale sewage treatment facilities.

The wastewater treatment device in FIG. 4 includes a settling basin and pump well 41, a methane fermentation facility 42, an energy recovery facility 43, a dewatering facility 44, an initial settling tank 47, a biological reaction tank (aeration tank) 48, and a final settling tank 49. There is. First, sewage discharged from homes, factories, etc. is removed from coarse solids (sand and sludge) in a settling tank and pump well 41, and then transferred to a first settling tank 47, where solids ( The sludge is separated into treated water (pre-settled sludge) and treated water. Next, the initial settled sludge is transferred to the methane fermentation equipment 42 and subjected to methane fermentation treatment. Digestion gas (methane gas) and digested sludge are generated by the methane fermentation treatment of this initial settling sludge, the digested gas is transferred to the energy recovery facility 43, and the digested sludge is transferred to the dewatering facility 44. Thereafter, the digested sludge is subjected to a dehydration process in the dewatering equipment 44 to produce a dehydrated cake and a dehydrated filtrate.

On the other hand, the treated water in the first settling tank 47 is transferred to a biological reaction tank 48, where the organic matter in the treated water is aerobically decomposed by activated sludge. Next, the separated water flowing out from the biological reaction tank 48 is transferred to the final settling tank 49, where it is separated into sludge and treated water. A portion of the sludge separated in the final settling tank 49 is returned to the biological reaction tank 48 (return sludge), and the rest is transferred to the methane fermentation equipment 42 together with the first settled sludge separated in the first settling tank 47 (surplus sludge). be done. The treated water flowing out from the final settling tank 49 is sterilized in a sterilization tank and then released or put to effective use.

Incidentally, the adsorption of organic matter in inflowing sewage by activated sludge that has undergone aerobic oxidative decomposition has been known as biosorption. For example, in Patent Document 1, surplus sludge separated from an aerobic treatment tank is transferred to an adsorption tank into which raw water flows, and after solid-liquid separation of the surplus sludge that has adsorbed organic matter in the raw water, the separated sludge is subjected to anaerobic treatment. A method for recovering methane with high efficiency by introducing it into a digester is disclosed.

Japanese Patent Application Publication No. 2003-190997

However, since the digested sludge produced by methane fermentation treatment contains many very fine particles, it is more difficult to dewater than raw sludge (first-settled sludge and surplus sludge). Therefore, the dehydrated cake obtained by the dehydration treatment of digested sludge has a high moisture content, resulting in a large amount of dehydrated cake being generated, resulting in the problem of requiring a large amount of cost to dispose of the dehydrated cake. In addition, a flocculant is added during dewatering treatment, but since digested sludge contains many cationic low-molecular substances and has many charged sites on the sludge surface, many ionic sites of the flocculant are consumed. As a result, digested sludge has a higher rate of flocculant added than raw sludge, resulting in an increase in dewatering costs.
Furthermore, in the case of the method of adsorbing organic matter in wastewater using biosorption of surplus sludge (activated sludge) (Patent Document 1), the amount of surplus sludge generated in the aerobic treatment tank decreases, so the wastewater There was a problem in that as the treatment progressed, it became difficult to secure the amount of activated sludge necessary for biosorption.
Therefore, there has been a need for wastewater treatment that can reduce the cost required for dewatering digested sludge and ensure the amount of activated sludge necessary for biosorption.

An object of the present invention is to provide a wastewater treatment device and a wastewater treatment method that can reduce the cost required for dewatering digested sludge and secure the amount of activated sludge necessary for biosorption.

In order to achieve the above object, the wastewater treatment device of the present invention is a wastewater treatment device that treats wastewater containing impurities, organic matter, and moisture, and includes a contaminant separation means that separates impurities from organic matter and moisture. , comprising a methane fermentation treatment means for methane fermenting the impurities separated by the impurity separation means, and a water treatment means for treating the treated water containing organic matter and water obtained by the impurity separation means. The wastewater treatment apparatus is characterized in that it has a digested sludge refining means for bringing at least a portion of the digested sludge obtained by the methane fermentation treatment means into contact with activated sludge in the presence of oxygen.

In order to achieve the above object, the wastewater treatment method of the present invention includes a contaminant separation step of separating the contaminants from the organic matter and water; a methane fermentation treatment step in which the impurities separated in the impurity separation step are treated with methane fermentation; a water treatment step in which treated water containing organic matter and moisture obtained in the impurity separation step is treated; and the methane fermentation treatment. The method is characterized by comprising a digested sludge conditioning step of bringing at least a portion of the digested sludge obtained in the step into contact with activated sludge in the presence of oxygen to condition the digested sludge.

According to the present invention, it is possible to reduce the cost required for dehydration treatment of digested sludge, and to ensure the amount of activated sludge necessary for biosorption to perform stable wastewater treatment.

1 is a diagram schematically showing a wastewater treatment device according to an embodiment of the present invention. It is a figure which shows the modification of the wastewater treatment apparatus of FIG. It is a figure which shows the modification of the wastewater treatment apparatus of FIG. 1 is a diagram schematically showing a wastewater treatment device using a standard activated sludge method.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram schematically showing a wastewater treatment device 10 according to an embodiment of the present invention.

The wastewater treatment device 10 in FIG. 1 includes a facility 1 comprising a settling basin and a screen, a methane fermentation facility 2, an energy recovery facility 3, a dewatering facility 4, a digested sludge conditioning facility 5, a contact mixing facility 6, and a separation/concentration facility 7. , water treatment equipment 8. First, sewage discharged from homes, factories, etc. is transferred to equipment 1 (impurity separation means), and in equipment 1, coarse solids (impurities) in the sewage are removed as sediment and sludge. As for the screen, it is preferable to use fine screen equipment with openings of 20 to 300 μm, preferably 50 to 200 μm, in order to remove coarse solids that are difficult to adsorb by activated sludge in contact mixing equipment 6, which will be described later. The equipment 1 is not particularly limited as long as it is capable of removing coarse solid matter (impurities) in sewage. Since the sediment separated in the settling pond contains sand, after the sand is removed by a sand cleaning device or the like, a portion is transferred to the methane fermentation equipment 2, and the remainder is disposed of or effectively utilized. On the other hand, the residue separated by the screen contains a large amount of organic matter and a small amount of sand, so after being crushed by a crusher, a portion is transferred to the methane fermentation equipment 2, and the remainder is disposed of or effectively utilized.

The methane fermentation equipment 2 (methane fermentation processing means) performs methane fermentation processing on the sediment after sand content removal, the residue after crushing, and the separated and concentrated sludge described below. Methane fermentation treatment is a treatment that uses a digestive reaction in which methane bacteria (anaerobic bacteria) decompose organic matter and produce digestive gas and digested sludge, mainly consisting of methane. Specifically, methane bacteria first hydrolyze organic matter to produce soluble amino acids and the like. Next, the produced amino acids and the like are taken into the cells of anaerobic bacteria and metabolically decomposed, producing acetic acid, hydrogen, carbon dioxide, and the like. Methane is then produced as biogas from acetic acid, hydrogen, and carbon dioxide. Digested sludge is the sludge that remains after organic matter in the sludge is decomposed by the action of methane bacteria and digestive gas is generated, and it contains methane bacteria. Since this digested sludge contains many very fine particles, it has a property of being more difficult to dewater than raw sludge (first-settled sludge and excess sludge).

Digestion gas discharged from the methane fermentation equipment 2 is transferred to the energy recovery equipment 3 and used as fuel as is, or transferred to a power generation device and used as electric power. Furthermore, part of the digested sludge flowing out from the methane fermentation equipment 2 is transferred to the digested sludge conditioning equipment 5, and the rest is transferred to the dewatering equipment 4. In the dewatering equipment 4, a flocculant is added to the digested sludge to perform dewatering treatment. Examples of flocculants added to digested sludge include organic polymer flocculants called polymers. Since digested sludge contains many cations and has a high alkalinity, a flocculant using an anionic polymer, an amphoteric polymer, or a combination of an anionic polymer and a cationic polymer is used.

By transferring a portion of the digested sludge to the digested sludge conditioning equipment 5 in this way, the amount of digested sludge supplied to the dewatering equipment 4 can be reduced, which reduces the amount of flocculant added to the dewatering process and the amount of dehydrated cake generated. It is possible to significantly reduce the cost required for dewatering digested sludge.

In addition, by transferring a portion of the digested sludge to the digested sludge conditioning equipment 5, the amount of tempered sludge (activated sludge) supplied to the contact mixing equipment 6 together with the treated water from the equipment 1 can be reduced, as will be described later. As a result, the amount of organic matter adsorbed to the conditioned sludge increases, and the amount of digestive gas generated by methane fermentation treatment can be increased. If the amount of energy recovered from the digestion gas increases, it is possible to provide a wastewater treatment device that can be energy independent if used for power generation or the like.

Furthermore, by transferring a part of the digested sludge to the digested sludge conditioning equipment 5, the digested sludge is conditioned and converted into aerobic activated sludge, as described later. The amount of activated sludge can be secured.

The digested sludge refining equipment 5 (digested sludge refining means) performs refining treatment on the digested sludge. Thermal treatment is a treatment in which digested sludge is brought into contact with activated sludge in the presence of oxygen. As a result, the activated sludge (aerobic microorganisms) decomposes and preys on the digested sludge (methane bacteria, anaerobic bacteria, etc.) and self-propagates, and the digested sludge becomes an aerobic activated sludge (conditioned microorganism) that has a biosorption effect. sludge), increasing oxygen dissolution efficiency. Activated sludge functions as a seed sludge for thermal refining treatment and enables thermal refining in a short time. Digested sludge contains reducing substances such as organic acids (propionic acid, butyric acid, valeric acid, etc.), ammonia, hydrogen sulfide, and sulfides, but these reducing substances in the digested sludge are also oxidized through tempering treatment. be done.

In this embodiment, activated sludge supplied to the digested sludge conditioning equipment 5 uses surplus sludge discharged from a water treatment equipment 8, which will be described later. In order to efficiently perform the refining process, it is necessary to have a sufficient amount of activated sludge present in the digested sludge refining equipment 5 relative to the digested sludge. The weight ratio of the digested sludge and surplus sludge supplied to the digested sludge conditioning equipment 5 is preferably within the range of 1:0.5 to 1:10. It is thought that this allows the conversion of digested sludge to activated sludge to proceed efficiently. In order to reduce the capacity of the digested sludge conditioning equipment 5, it is desirable to increase the ratio of surplus sludge to digested sludge. In addition, when the amount of excess sludge supplied to the digested sludge conditioning equipment 5 is small and the supply ratio of excess sludge to the digested sludge is small, carriers and contact materials for maintaining aerobic microorganisms may be transferred to the digested sludge conditioning equipment. It is effective to install it within 5. The concentration of the digested sludge supplied to the digested sludge conditioning equipment 5 is usually 1 to 2% by weight, and the concentration of activated sludge supplied to the digested sludge conditioning equipment 5 is usually 0.2 to 0.5% by weight. The concentration of the mixed sludge (digested sludge and activated sludge) in the mixed sludge digested sludge conditioning equipment 5 is 1% by weight or less, preferably 0.4 to 0.6% by weight, from the viewpoint of ease of conditioning. Better to maintain it. When the concentration of the mixed sludge exceeds 1% by weight, the viscosity of the sludge increases and the oxygen dissolution efficiency tends to decrease. The concentration of the mixed sludge can be adjusted, for example, by adding the dehydrated filtrate from the dewatering equipment 4 to the digested sludge conditioning equipment 5.

The contact between the digested sludge and the activated sludge can be carried out, for example, by arranging an aeration device in the digested sludge conditioning equipment 5 and aerating and stirring the digested sludge and activated sludge while aerating the air. Further, the contact between the digested sludge and the activated sludge can be carried out by, for example, line mixing using a stationary mixer (line mixer) such as a static mixer, in addition to aeration stirring. It is preferable to provide a sludge flow rate adjustment means in the digested sludge conditioning equipment 5, and the residence time of the mixed sludge (digested sludge and activated sludge) in the digested sludge conditioning equipment 5 is determined by the mixing ratio of the digested sludge and activated sludge, Although it varies depending on the capacity of the aeration equipment, the presence or absence of contact materials, etc., it is usually 3 to 12 days. The tempered sludge flowing out from the digested sludge conditioning equipment 5 is mostly activated sludge, and is transferred to the contact mixing equipment 6. When converting equipment for the standard activated sludge method to the membrane separation activated sludge method (hereinafter referred to as the MBR method), a part of the existing aeration tank (biological reaction tank) should be used as the digested sludge conditioning equipment 5. I can do it.

The contact mixing equipment 6 (contact means) is a means for contact-mixing the treated water of the equipment 1 and the tempered sludge transferred from the digested sludge refinement equipment 5 in an aerobic state. Contact mixing can be performed by arranging an aeration device in the contact mixing equipment 6 and performing aeration and stirring. Further, mechanical stirring can be additionally performed, for example, line mixing using a static mixer (line mixer) such as a static mixer can also be performed. Due to this contact mixing, soluble organic matter in the treated water transferred from the equipment 1 is adsorbed to the tempered sludge.

In the contact mixing equipment 6, the amount of dissolved organic matter in the treated water transferred from the equipment 1 and the amount of tempered sludge transferred from the digested sludge conditioning equipment 5 are 1:0.5 to 1:1.5. It is preferable to maintain the weight ratio to be approximately the same, preferably 1:0.6 to 1:1.3. Thereby, in the contact mixing equipment 6, dissolved organic substances and fine solids in the treated water transferred from the equipment 1 are efficiently adsorbed to the tempered sludge.

The mixed liquid flowing out from the contact mixing equipment 6 contains tempered sludge that has adsorbed soluble organic matter and fine solid matter. Most of this mixed liquid is transferred to the separation/concentration facility 7, but a portion is transferred to the water treatment facility 8 via a bypass route without passing through the separation/concentration facility 7. By providing such a bypass path, the amount of the mixed liquid supplied to the separation/concentration equipment 7 and the amount of the mixed liquid transferred to the bypass path without passing through the separation/concentration equipment 7 can be adjusted, and the amount of the mixed liquid supplied to the separation/concentration equipment 7 can be adjusted. It becomes possible to easily control the amount of activated sludge supplied to the By installing such a bypass route, the MLSS (activated sludge suspended solids) concentration in the water treatment facility 8 can be quickly adjusted to the optimum range, and stable operation can be achieved even with daily load fluctuations. It becomes possible. Furthermore, when modifying equipment for the standard activated sludge method, a part of the initial settling tank can be used as the contact mixing equipment 6.

The separation and concentration equipment 7 (separation and concentration means) is a means for separating and concentrating tempered sludge that has adsorbed soluble organic matter and fine solids from the mixed liquid transferred from the contact mixing equipment 6, and is a means for separating and concentrating the tempered sludge that has adsorbed soluble organic matter and fine solids. The separation efficiency of organic matter is higher than that of ponds. In the separation and concentration process, it is possible to increase the separation efficiency of organic matter by adding iron-based or aluminum-based inorganic flocculants or organic flocculants, but the separation efficiency can be improved by using a pressure flotation device or a centrifugal separator. can be further increased. In particular, pressure flotation separation equipment is preferable because it can efficiently separate and concentrate solids of 20 to 50 μm or more in a short time of about 15 to 30 minutes without using a flocculant. sludge can be separated, further improving organic matter separation efficiency. Furthermore, phosphorus can be removed by using an inorganic flocculant containing aluminum or iron in the separation and concentration process. When modifying equipment for the standard activated sludge method, a part of the initial settling tank can be used as the separation and concentration equipment 7.

Through such separation and concentration treatment, most of the organic matter in the mixed liquid supplied to the separation and concentration equipment 7, both solid and soluble, is separated as thickened sludge, and the resulting separated water is transferred to conventional water treatment equipment. The content of organic matter is significantly reduced compared to the inflow water. By transferring this separated water to the water treatment facility 8 along with the mixed water via the bypass route, the amount of organic matter in the water treatment facility 8 is reduced, thereby significantly reducing the amount of power consumed by the water treatment facility 8. be able to.

The concentrated sludge separated in the separation and concentration equipment 7 and containing many organic substances is transferred to the methane fermentation equipment 2, where it is subjected to methane fermentation treatment together with the sand after sand removal and the residue after crushing, which were transferred from the equipment 1. The concentration of thickened sludge in the waste water transferred from the separation and concentration equipment 7 to the methane fermentation equipment 2 is usually 3 to 5% by weight, although it depends on the separation and concentration means. The digestibility of the thickened sludge in methane fermentation equipment 2 (the rate at which it is gasified into methane and carbon dioxide) is 60 to 90% by weight, so the rate at which the separated thickened sludge changes into digested sludge is 10 to 40% by weight. Become. Therefore, the concentration of digested sludge in the waste water discharged from the methane fermentation equipment 2 is usually 0.3 to 2.0% by weight.

The water treatment facility 8 performs water treatment to decompose soluble organic matter in the wastewater transferred from the separation and concentration facility 7 and the bypass route. As the water treatment equipment 8, for example, a standard activated sludge method or an MBR method is used, and organic matter in wastewater is oxidized and decomposed by activated sludge under aeration. Activated sludge is mainly microbial sludge that grows through aerobic oxidative decomposition of organic matter. In the present invention, it is preferable to use an MBR method that is compact, has high nitrogen removal performance, and can be operated in an energy-saving manner, particularly an apparatus using a membrane separation activated sludge method (hereinafter referred to as "B-MBR method") with a partition plate inserted. The MBR method and B-MBR method involve a nitrification reaction in which nitrifying bacteria convert ammonia contained in wastewater into nitrite and nitric acid in the presence of oxygen, and a nitrification reaction in which denitrifying bacteria convert nitrite and nitric acid into nitrogen in anoxic conditions. Denitrification reaction progresses. The B-MBR method equipment includes a dividing means that separates a nitrification reaction area for performing nitrification reaction and a denitrification reaction area for denitrification reaction, and a separation means installed in the nitrification reaction area to separate and remove solid content contained in wastewater. This is a wastewater treatment device having membrane separation means. In the water treatment facility 8, it is necessary to maintain the MLSS concentration at a predetermined concentration, and it is preferably maintained at 4500 to 5500 mg/L in consideration of aeration efficiency and BOD-MLSS load. After the water treatment is completed, the activated sludge is discharged from the water treatment equipment 8 as surplus sludge and transferred to the digested sludge conditioning equipment 5.

FIG. 2 is a diagram showing a modification of the wastewater treatment device shown in FIG. 1.

The wastewater treatment equipment in FIG. 2 transfers all of the digested sludge flowing out from the methane fermentation facility 2 to the digested sludge conditioning facility 5, and transfers not the digested sludge to the dewatering facility 4, but the tempered sludge flowing out from the digested sludge conditioning facility 5. The structure and functions are the same as those of the wastewater treatment apparatus shown in FIG. 1, except that a part of the wastewater treatment apparatus was transferred. Below, the points that are different from the wastewater treatment apparatus shown in FIG. 1 will be explained.

In FIG. 2, the entire amount of digested sludge flowing out from the methane fermentation facility 2 is transferred to the digested sludge conditioning facility 5. Since the amount of digested sludge transferred to the digested sludge conditioning equipment 5 is increased compared to the wastewater treatment equipment shown in FIG. The amount also increases, and as a result, the amount of organic matter adsorbed by the activated sludge in the contact mixing equipment 6 also increases. Therefore, compared to the wastewater treatment apparatus shown in FIG. 1, the wastewater treatment apparatus shown in FIG. 2 generates a larger amount of digestion gas (methane gas) in the methane fermentation equipment 2, and has higher energy recovery efficiency.

Further, most of the tempered sludge (activated sludge) flowing out from the digested sludge conditioning facility 5 is transferred to the contact mixing facility 6, but a portion of this tempered sludge is supplied to the dewatering facility 4. In this way, by supplying activated sludge with a low flocculant addition rate and a small amount of dehydrated cake to the dewatering equipment 4, rather than digested sludge with a high flocculant addition rate and a large amount of dehydrated cake generated, the dewatering equipment 4 can be dehydrated. The costs required for treatment and subsequent treatment can be significantly reduced.

FIG. 3 is a diagram showing a modification of the wastewater treatment device shown in FIG. 2.

In the wastewater treatment equipment shown in FIG. 3, the water treatment equipment 8 also serves as the digested sludge conditioning equipment 5, supplies digested sludge to the water treatment equipment 8, and dewaters some of the excess sludge discharged from the water treatment equipment 8. The structure and function are the same as those of the wastewater treatment apparatus shown in FIG. 2, except that the waste water was transferred to the equipment 4 and the rest was transferred to the contact mixing equipment 6. Below, points different from the wastewater treatment apparatus shown in FIG. 2 will be explained.

In the wastewater treatment equipment shown in FIG. 3, the digested sludge conditioning equipment 5 is not provided independently, and the water treatment equipment 8 functionally doubles as the digested sludge conditioning equipment 5. Digested sludge refining treatment is performed. That is, since activated sludge exists in the water treatment facility 8, the organic matter in the wastewater transferred from the separation and concentration facility 7 and the bypass route is aerobically decomposed by the activated sludge in the water treatment facility 8, and The digested sludge supplied to the water treatment facility 8 is refined by contacting activated sludge under aeration (in the presence of oxygen), and the digested sludge is converted into aerobic activated sludge with a biosorption effect. The amount of digested sludge supplied to the water treatment facility 8 per day is 1/40 to 1/30 of the amount of activated sludge in the water treatment facility 8, and there is a sufficient amount of activated sludge for the digested sludge. Sludge refining progresses easily. The capacity of the water treatment facility 8 is preferably larger than that of the water treatment facility shown in FIG. 2 in order to carry out the digested sludge refining treatment.

In the case of water treatment equipment 8 using the B-MBR method, nitrification reactions occur in which nitrifying bacteria convert ammonia contained in wastewater into nitrite and nitric acid in the presence of oxygen, and denitrifying bacteria convert nitrite and nitric acid in anoxic conditions. The denitrification reaction that converts nitrogen into nitrogen proceeds. The denitrification reaction requires organic matter as a hydrogen donor, but by supplying the digested sludge to the water treatment facility 8 as shown in FIG. 3, the organic matter in the digested sludge is utilized for the denitrification reaction. Due to such an apparatus configuration, the apparatus shown in FIG. 3 has a simpler structure as a whole than the apparatus shown in FIG. 2, and the wastewater treatment apparatus can be easily constructed by modifying the standard activated sludge method equipment.

In addition, surplus sludge (tempered sludge) that has been subjected to tempering treatment is discharged from the water treatment facility 8, but a part of the discharged surplus sludge (tempered sludge) is transferred to the dewatering facility 4, and the rest is Transferred to contact mixing equipment 6. As a result, the dewatering equipment 4 is supplied with tempered sludge (activated sludge) with a low flocculant addition rate and a small amount of dehydrated cake, rather than digested sludge with a high flocculant addition rate and a large amount of dehydrated cake generated. Therefore, the cost required for dehydration treatment and subsequent treatment of the dehydrated cake can be significantly reduced.

Next, the wastewater treatment method of this embodiment will be explained according to the wastewater treatment apparatus shown in FIG.

The wastewater treatment equipment 10 in FIG. 1 includes equipment 1 consisting of a settling basin and screen equipment, methane fermentation equipment 2, energy recovery equipment 3, dewatering equipment 4, digested sludge conditioning equipment 5, contact mixing equipment 6, and separation and concentration equipment. 7. Equipped with water treatment equipment 8.

First, sewage discharged from homes, factories, etc. is continuously supplied to equipment 1, and coarse solids (sand and sludge) are separated using a settling basin and a screen (impurity separation step). The sand separated in the sand settling pond is transferred to the methane fermentation equipment 2 after sand content is removed by a sand washing device or the like. On the other hand, the residue separated by the screen is crushed by a crusher and then transferred to the methane fermentation equipment 2. In the methane fermentation equipment 2, methane fermentation processing is performed on the settled sand after sand content removal, the residue after crushing, and the above-mentioned separated and concentrated sludge transferred from the separation and concentration equipment 7 (methane fermentation processing step). This methane fermentation process produces digested gas and digested sludge. The digested gas is transferred to the energy recovery facility 3, and part of the digested sludge is transferred to the digested sludge conditioning facility 5 and the rest to the dewatering facility 4. The treated water separated from coarse solids in equipment 1 is transferred to contact mixing equipment 6.

In the digested sludge conditioning equipment 5, conditioning treatment is performed in which the digested sludge comes into contact with surplus sludge (activated sludge) transferred from the water treatment facility 8 in the presence of oxygen. As a result, the digested sludge is converted into aerobic activated sludge (tempered sludge) that has a biosorption effect (digested sludge conditioning step). Next, the tempered sludge flowing out from the digested sludge conditioning equipment 5 is transferred to the contact mixing equipment 6, where it is contacted and mixed with the treated water from the equipment 1 under aeration (contact step). As a result, soluble organic matter and fine solid matter contained in the treated water are adsorbed to the tempered sludge. Thereafter, part of the mixed liquid containing tempered sludge with soluble organic matter and fine solid matter adsorbed is transferred to the bypass route, and the remaining part is transferred to the separation and concentration equipment 7.

The separation and concentration equipment 7 uses a pressurized flotation separator to concentrate the tempered sludge to which soluble organic matter and fine solid matter have been adsorbed and separate it into thickened sludge and separated water (separation and concentration step). The separated thickened sludge is transferred to the methane fermentation equipment 2 (thickened sludge supply step), and is subjected to methane fermentation treatment in the methane fermentation equipment 2 together with the coarse solids transferred from the equipment 1 (methane fermentation treatment step).

The separated water flowing out from the separation and concentration equipment 7 is supplied to the water treatment equipment 8 together with the liquid mixture from the contact mixing equipment 6 which passes through the bypass route. The water treatment facility 8 accommodates activated sludge, and the activated sludge decomposes soluble organic matter in the wastewater transferred from the separation and concentration facility 7 and the bypass route under aeration (water treatment step). Thereafter, excess sludge (activated sludge) discharged from the water treatment facility 8 is transferred to the digested sludge conditioning facility 5.

On the other hand, an organic polymer-based flocculant is added to the digested sludge flowing out from the methane fermentation equipment 2 and transferred to the dehydration equipment 4, and dehydration processing is performed. The dehydration process produces a dehydrated cake and a dehydrated filtrate, and the dehydrated filtrate is transferred to equipment 1.

As described above, by transferring part of the digested sludge discharged from the methane fermentation equipment 2 to the digested sludge conditioning equipment 5, the amount of digested sludge supplied to the dewatering equipment 4 can be reduced. As a result, the addition rate of the flocculant and the amount of dehydrated cake produced in the dehydration equipment 4 can be reduced, and the cost required for dehydration treatment can be significantly reduced.

Further, by transferring a portion of the digested sludge to the digested sludge conditioning equipment 5 and converting it into activated sludge (tempered sludge), the amount of activated sludge supplied to the contact mixing equipment 6 can be increased. As a result, the amount of organic matter adsorbed to the conditioned sludge and transferred to the methane fermentation equipment 2 after separation and concentration increases, and the amount of digested gas generated by the methane fermentation process in the methane fermentation equipment 2 can be increased.

Furthermore, by transferring a part of the digested sludge to the digested sludge conditioning equipment 5, the digested sludge is conditioned and converted into aerobic activated sludge, so the amount of activated sludge necessary for biosorption is sufficient. It becomes possible to secure the following.

Next, examples of the present invention will be described.

Wastewater treatment of sewage was performed using the wastewater treatment apparatus 20 shown in FIG. However, as equipment 1, a fine screen (opening: 15 mm) and a fine screen (opening: 250 μm) were used. First, inflow sewage with a daily maximum amount of 100,000 m ³ /day and an average daily amount of 75,000 m ³ /day was continuously supplied to equipment 1, and coarse solids were separated using a screen. Next, the coarse solids separated in equipment 1 were crushed by a crusher and then transferred to methane fermentation equipment 2, where methane fermentation treatment was performed. Digested gas and digested sludge were generated by this methane fermentation process, and the digested gas was transferred to the energy recovery facility 3, and the entire amount of the digested sludge was transferred to the digested sludge conditioning facility 5. The treated water separated from coarse solids in equipment 1 was transferred to contact mixing equipment 6.

An aeration device was installed in the digested sludge conditioning equipment 5, and excess sludge (activated sludge) discharged from the water treatment equipment 8 was supplied thereto. In the digested sludge conditioning equipment 5, conditioning treatment was performed in which the digested sludge and excess sludge (activated sludge) were mixed under aeration and brought into contact with each other. At this time, the weight ratio of the digested sludge and excess sludge supplied to the digested sludge conditioning equipment 5 was 1:0.66. This tempering treatment converted the digested sludge into aerobic activated sludge (tempered sludge). Next, a part of the tempered sludge (tempered sludge concentration: 6,576 mg/L) flowing out from the digested sludge conditioning equipment 5 was transferred to the dewatering equipment 4, and the remaining tempered sludge was transferred to the contact mixing equipment 6 ( Amount of tempered sludge injected into contact mixing equipment 6: 570 m ³ /day).

An aeration device is installed in contact mixing equipment 6, and the treated water and digested sludge from equipment 1 are stirred and mixed under aeration, and the soluble organic matter and fine solids contained in the treated water are adsorbed into the tempered sludge. Ta. In the contact mixing equipment 6, the amount of soluble organic matter in the treated water transferred from the equipment 1 was approximately the same as the amount of tempered sludge transferred from the digested sludge conditioning equipment 5. Thereafter, part of the liquid mixture containing tempered sludge with soluble organic matter and fine solid matter adsorbed was transferred to a bypass route, and the remaining part was transferred to separation and concentration equipment 7.

The separation and concentration equipment 7 used a pressurized flotation separator to concentrate the tempered sludge to which soluble organic matter and fine solid matter had been adsorbed and separate it into concentrated sludge and separated water. The separated thickened sludge (13,350 kg/day, concentration: 4% by weight) was transferred to methane fermentation equipment 2, where it was subjected to methane fermentation treatment along with the coarse solids transferred from equipment 1. Input sludge: ^394m3 /day). The entire amount of digested sludge (3,270 kg/day) flowing out from methane fermentation equipment 2 was transferred to digested sludge conditioning equipment 5.

The separated water flowing out from the separation and concentration equipment 7 was supplied to the water treatment equipment 8 together with the liquid mixture from the contact mixing equipment 6 that had passed through the bypass route. Water treatment equipment 8 (BOD-MLSS load: 0.043 kg/kg/day, MSLL concentration: 5,000 mg/L) is a B-MBR method equipment that accommodates activated sludge, and activated sludge is separated and concentrated equipment 7 and bypass route Dissolved organic matter in the wastewater transferred from the plant was decomposed under aeration. Thereafter, excess sludge (activated sludge) (2,160 kg/day) discharged from the water treatment facility 8 was transferred to the digested sludge conditioning facility 5.

On the other hand, in the dewatering facility 4 to which the conditioned sludge is transferred from the digested sludge conditioning facility 5, organic polymer flocculant (17 kg/day) is added to conditioned sludge (dehydrated sludge amount: 255 m ³ /day). ) was dehydrated. The dehydration process produced a dehydrated cake (7.6 m ³ /day) and a dehydrated filtrate, and the dehydrated filtrate was transferred to equipment 1, and the dehydrated cake was discharged or effectively utilized.

In addition, when inflowing sewage with the same daily maximum sewage volume and daily average sewage volume is treated using the conventional standard activated sludge method equipment (Figure 4), the amount of flocculant added to the dewatering equipment 4 is 87 kg. /day, and the amount of dehydrated cake produced is 29.2m ³ /day. By using the wastewater treatment equipment shown in Figure 2, the amount of flocculant used will be reduced by 70 kg/day and the amount of dehydrated cake produced will be reduced by 21.6 m ³ /day, significantly reducing the cost required for dewatering digested sludge. I was able to do that.

Table 1 below shows the capacity and residence time (HRT) of each equipment used in this example.

Table 2 below shows the quality of inflowing sewage and treated water from each facility.

When inflowing sewage with the same daily maximum sewage volume and daily average sewage volume as in this example was treated using the standard activated sludge method equipment (Figure 4), the BOD of the treated water after water treatment was 14 mg/L, Since D-BOD (soluble BOD) is 8 mg/L and SS (suspended solids) is 12 mg/L, the wastewater treatment equipment shown in Figure 2 has better water quality than equipment using the conventional standard activated sludge method. I was able to get water.

From the above results, the digested sludge flowing out from the methane fermentation equipment 2 is transferred to the digested sludge conditioning equipment 5 and brought into contact with the excess sludge from the water treatment equipment 8, and part of the tempered sludge (activated sludge) is By transferring the sample to the dehydration equipment 4, it was possible to reduce the amount of flocculant used and the amount of dehydrated cake produced, and the cost required for dehydration treatment could be significantly reduced.

Further, by transferring the digested sludge to the digested sludge conditioning equipment 5 and converting it into activated sludge (tempered sludge), the amount of activated sludge supplied to the contact mixing equipment 6 could be increased. As a result, the amount of organic matter adsorbed to the conditioned sludge and transferred to the methane fermentation equipment 2 after separation and concentration increased, making it possible to increase the amount of digestion gas generated by the methane fermentation process. That is, by providing the digested sludge conditioning equipment 5 that brings digested sludge and surplus sludge into contact and refines them, the amount of digestion gas generated in the methane fermentation equipment 2 is increased, thereby providing a wastewater treatment device with a high energy recovery rate. I was able to do that.

Furthermore, by transferring the digested sludge to the digested sludge conditioning equipment 5, the digested sludge is conditioned and converted into aerobic activated sludge, so that the amount of activated sludge (surplus sludge) necessary for biosorption is sufficient. were able to secure it.

The wastewater treatment device 20 shown in FIG. 2 used in this example can be constructed by modifying an existing device using the standard activated sludge method. For example, the contact mixing equipment 6 and the separation concentration equipment 7 are constructed by modifying the initial settling tank, and the digested sludge conditioning equipment 5 and water treatment equipment 8 (B-MBR method) are constructed by modifying the biological reaction tank (aeration tank). be able to. Furthermore, by using the wastewater treatment apparatus of this embodiment, it is possible to construct an apparatus that does not have a primary settling tank with low organic matter removal efficiency.

Although the present invention has been described above using the embodiments described above, the present invention is not limited to the embodiments described above.

1 Sediment basin and screen equipment 2 Methane fermentation equipment 3 Energy recovery equipment 4 Dewatering equipment 5 Digested sludge conditioning equipment 6 Contact mixing equipment 7 Separation and concentration equipment 8 Water treatment equipment 10, 20, 30, 40 Wastewater treatment equipment

Claims (13)

A wastewater treatment device that processes wastewater containing impurities, organic matter, and moisture,
a contaminant separation means for separating contaminants from organic matter and moisture;
Methane fermentation processing means for methane fermentation processing of the impurities separated by the impurity separation means;
A wastewater treatment device comprising a water treatment means for treating treated water containing organic matter and water obtained by the impurity separation means,
A wastewater treatment device comprising a digested sludge conditioning means for conditioning at least a portion of the digested sludge obtained by the methane fermentation treatment device by contacting it with activated sludge in the presence of oxygen. The wastewater treatment apparatus according to claim 1, further comprising contact means for contacting and mixing the tempered sludge obtained by the digested sludge conditioning means and the treated water obtained by the impurity separation means. The wastewater treatment apparatus according to claim 2, further comprising separation and concentration means for separating the mixed liquid obtained by the contacting means into thickened sludge and separated water. 4. The wastewater treatment apparatus according to claim 3, further comprising a bypass path for supplying a part of the liquid mixture obtained by the contacting means to the water treatment means without passing through the separation and concentration means. The wastewater treatment apparatus according to claim 3, wherein the concentrated sludge separated by the separation and concentration means is supplied to a methane fermentation treatment means. The wastewater treatment device according to claim 1, wherein the foreign matter separation means is a settling basin and/or a screen device. The water treatment means is a means using an activated sludge treatment method, and the activated sludge brought into contact with the digested sludge in the digested sludge conditioning means is surplus sludge discharged from the water treatment means. The wastewater treatment device according to claim 1. The wastewater treatment apparatus according to claim 1, wherein the weight ratio of the digested sludge and the activated sludge supplied to the digested sludge refining means is 1:0.5 to 1:10. The wastewater treatment apparatus according to claim 3, wherein the separation and concentration means is a pressure flotation separator. The wastewater treatment device according to claim 1, wherein the wastewater treatment device does not have a primary settling tank. In the wastewater treatment method using the wastewater treatment device according to any one of claims 1 to 10,
a contaminant separation step of separating the contaminants from the organic matter and moisture;
a methane fermentation treatment step in which the impurities separated in the impurity separation step are subjected to methane fermentation;
a water treatment step of treating the treated water containing organic matter and water obtained in the impurity separation step;
a digested sludge conditioning step in which at least a portion of the digested sludge obtained in the methane fermentation treatment step is conditioned by contacting it with activated sludge in the presence of oxygen;
A wastewater treatment method characterized by having the following. a contacting step of contacting and mixing the tempered sludge obtained in the digested sludge conditioning step and the treated water obtained in the impurity separation step;
a separation and concentration step of separating the liquid mixture obtained in the contacting step into thickened sludge and separated water;
a thickened sludge supplying step of supplying the thickened sludge separated in the separation and concentration step to the methane fermentation treatment step;
The wastewater treatment method according to claim 11, characterized by comprising: A claim characterized in that the water treatment step is a step using an activated sludge treatment method, and the activated sludge that is brought into contact with the digested sludge in the digested sludge conditioning is surplus sludge discharged from the water treatment step. The wastewater treatment method according to item 11.

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