JP7254580B2 - Method and apparatus for treating organic sludge - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for treating organic sludge, and more particularly to a method and apparatus for treating difficult-to-dewater digested sludge.

In methane fermentation technology targeting waste biomass such as food processing residue, garbage, and sludge, increasing the concentration of raw materials input to equipment for the purpose of downsizing the equipment and improving the energy recovery rate of methane gas. It is known to reduce the driving power and improve the efficiency of energy recovery (high-concentration digestion method).

When the sludge concentration in methane fermentation for biomass increases, in addition to the inhibitory reaction of fermentation microorganisms, the equipment capacity and power cost increase during transfer, mixing, and agitation due to the increase in sludge concentration, and the sludge is difficult to dewater. problems such as conversion will occur. In particular, the TS concentration (total solids) of general anaerobic digestion sludge such as sewage sludge is 15 to 20 g / L, whereas the TS concentration of methane fermentation sludge for biomass is In the high-concentration digestion method of 20 g/L or more, appropriate mixing/stirring technology in the fermentation facility and technology for simple and stable sludge treatment of difficult-to-dehydrate fermented sludge are required. In the case of sludge with a TS concentration of 20 g/L or more, there is a strong tendency that the sludge becomes highly viscous and the solid-liquid separability is remarkably lowered, and a stable sludge treatment technology is required.

In the methane fermentation sludge treatment, a flocculating agent is injected to chemically flocculate the suspended solids in the sludge, followed by mechanical dehydration. At that time, for high-concentration sludge with a TS concentration of 20 g/L or more, a method of diluting the sludge with a diluent or the like and then dehydrating the sludge is adopted. Expensive amidine-based polymer flocculants are used as polymer flocculants for dehydration treatment of this high-concentration digested sludge. ) is required to be added at a high addition rate, the chemical cost is remarkably high. Compared to the fact that the polymer flocculant used for the dehydration treatment of general anaerobic digestion sludge for sewage sludge is an inexpensive non-amidine polymer flocculant with a chemical dosing rate of about 2 wt% (relative to TS concentration). Then, it is clear that the cost is remarkably high.

For example, in Patent Document 1, in order to improve the dewaterability of methane fermentation sludge, methane fermentation-treated digestion residue (digested sludge, or a mixed slurry of digested juice and digested sludge) is aerated with an oxygen-containing gas and then machined. A method of dehydration has been proposed. In this sludge treatment method, the amount of coagulant added to difficult-to-dewater digested sludge can be reduced, and high-concentration digested sludge can be stably dehydrated in a short time. Since the rate is about 79 to 81% at maximum, there is room for further improvement in dehydration.

Patent Document 2 provides an energy recovery system that obtains biogas at a high yield by methane fermentation of both solid sludge and food waste. This energy recovery system consists of a cogeneration engine that uses the obtained biogas as fuel to generate electricity and high-temperature, high-pressure steam; A proposal has been made in which a drying device is provided and the high-temperature, high-pressure steam generated by the cogeneration engine is supplied to the solubilization device, the drying device, and the methane fermentation tank. However, regarding the dehydration conditions for the difficult-to-dehydrate fermented sludge, the digested sludge with a water content of about 96% discharged from the methane fermentation tank is transferred to a dehydrator and dehydrated to obtain a solid state with a water content of about 80%. It is only described that it is discharged as sludge and desorbed liquid (water) (paragraph 0034), and since the water content of the dewatered sludge is about 80%, there is a large room for improvement.

Patent Document 3 describes a waste treatment method in which excess sludge is composted through a dehydration process and a drying process. Excess sludge and high-moisture organic waste are subjected to methane fermentation in a biogasification process to extract biogas. , The methane fermentation sludge discharged from the biogasification process is dehydrated in the dehydration process, and the dehydrated sludge obtained in the dehydration process is dried in the drying process. It has been proposed to feed the absorption chiller of the dryer used as a heat source. Then, the sludge dehydrated in the dehydration process has a water content of 70 to 87%, and the dehydrated sludge is further dried in a low-temperature dehumidifying dryer in the drying process to obtain dry sludge with a water content of 30 to 70%. there is However, no detailed description of the operating conditions in the dehydration process is disclosed at all, and the steam generated using biogas as fuel is supplied as a heat source to the absorption refrigerator of the drying apparatus used in the drying process, and is used in the dehydration apparatus. There is no treatment cost or performance improvement in the dehydration process.

In Patent Document 4, when dehydrating the sludge by a screw press method while heating the sludge by an indirect heating method, air is supplied to the sludge before it is introduced into the dehydration unit, thereby making the sludge an aerobic state. , the need for deodorizing equipment for deodorizing the exhaust air from the dewatering unit is eliminated. As a solution, an aerobic tank is installed between the digestion tank and the flocculation tank, and by blowing air into the digested sludge with a blower, the sludge is made into an aerobic state, and the hydrogen sulfide in the liquid is oxidized and reduced. A method has been proposed to do so. However, it is only described that the aerobic tank in this sludge treatment method is intended for sludge deodorization treatment.

In Non-Patent Document 1, in a dehydration method for night soil treatment sludge, the dehydrated cake dehydrated in the first stage belt press type dehydrator is re-dehydrated in the second stage screw press type dehydrator. , a two-stage dehydration method has been proposed in which the moisture content of the dehydrated cake is reduced to 65 wt% or less. In particular, in the second-stage screw press type dehydrator, steam heat can be effectively used during dehydration, so it is said that the water content of the dehydrated cake can be reduced more than other dehydrators. Considering operation management, there are many difficult aspects in reality.

WO2016/111324 JP 2009-34569 A JP-A-2005-131558 Japanese Patent No. 6216763

Ebara Infilco Jiho, No. 88, "Dehydration of night soil treatment sludge by screw press", Ebara Infilco Co., Ltd. "Ebara Infilco Jiho" editorial office, Bunshodo Printing Co., Ltd., March 28, 1983, p. 41-49

In view of the above problems, the present invention provides an organic sludge treatment method and treatment apparatus capable of achieving high dehydration efficiency at a lower cost.

Based on the experience that the high-concentration digested sludge becomes difficult to dehydrate due to the highly concentrated colloidal sticky components remaining in the high-concentration digested sludge, the present inventors have found that the viscosity of the high-concentration digested sludge is It was found that the amount of coagulant to be added can be reduced by lowering the , and that the dehydration efficiency can be improved by blowing steam into the dehydrator to heat and dehydrate.

In one aspect of the method for treating organic sludge according to the embodiment of the present invention, which has been completed based on the above knowledge, an oxygen-containing gas is passed through difficult-to-dehydrate digested sludge after anaerobic treatment of organic sludge. This is a method for treating organic sludge, which comprises reducing the sludge viscosity of difficult-to-dewater digested sludge by aeration treatment, and then heating and dehydrating the sludge by blowing in steam.

In one embodiment of the organic sludge treatment method according to the embodiment of the present invention, the aeration treatment is carried out with an oxygen-containing gas at an aeration intensity of 0.05 to 0.3 m ³ /(m ³ min). The viscosity of the post-digested sludge is measured at 30° C. with a B-type rotational viscometer specified in the sewage test method until it decreases to 150 mPa·s or less.

In another embodiment of the organic sludge treatment method according to the embodiment of the present invention, 1.5 to 7% by mass of a polymer flocculant is added to digested sludge after aeration treatment to perform flocculation treatment.

In still another embodiment of the organic sludge treatment method according to the embodiment of the present invention, the heat dehydration treatment includes dehydration treatment by a press dehydrator using a polymer flocculant, and after aeration treatment A dehydrated cake having a moisture content of 78% or less is obtained by adjusting the amount of steam blown into the dehydrator based on the sludge viscosity of the digested sludge.

In still another embodiment, the organic sludge treatment method according to the embodiment of the present invention includes sludge drying treatment using a sludge dryer that heats and dries the dehydrated cake by blowing steam into it, and after aeration treatment By adjusting the amount of steam blown into the dehydrator and the sludge dryer based on the sludge viscosity of the digested sludge, a dry cake with a moisture content suitable for composting is obtained.

In still another embodiment of the organic sludge treatment method according to the embodiment of the present invention, the steam used for thermal dehydration is at least one of an incineration facility, a sewage sludge treatment facility, and a biomass methane fermentation facility. It is the steam obtained from the boiler equipment of the plant, or the steam obtained by converting the heat obtained from the power generation equipment.

In one aspect, an organic sludge treatment apparatus according to an embodiment of the present invention includes an anaerobic treatment tank for anaerobically treating organic sludge to form hard-to-dehydrate digested sludge, and an oxygen-containing gas for digested sludge. An aeration tank for aeration, a flocculation tank for forming flocculated sludge by adding a polymer flocculant to digested sludge after aeration treatment, an air volume control device for adjusting the aeration rate of the oxygen-containing gas supplied to the aeration tank, and flocculation The dehydrator that heats and dehydrates sludge by blowing steam to obtain dehydrated sludge, the dryer that dries the dehydrated sludge by blowing steam, and the blowing speed of the steam supplied to the dehydrator and dryer are adjusted. and a control device.

In one embodiment of the organic sludge treatment apparatus according to the embodiment of the present invention, at least one or more of an incineration facility that incinerates gas obtained by anaerobic treatment as a fuel, a sewage sludge treatment facility, or a biomass methane fermentation facility A steam supply line is provided for supplying steam obtained from the boiler facility or heat-converted steam obtained from the power generation facility.

According to the present invention, it is possible to provide a method and apparatus for treating organic sludge that can achieve high dehydration efficiency at a lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows an example of the processing method of the organic sludge which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic showing an example of the processing apparatus of the organic sludge which concerns on embodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings below, the same or similar parts are denoted by the same or similar reference numerals. The embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention. It does not specify anything. In this embodiment, "%" means "% by mass" unless otherwise specified.

In the organic sludge treatment method according to the embodiment of the present invention, as shown in FIG. After reducing the sludge viscosity of the difficult-to-dewater digested sludge by performing aeration treatment, steam is blown in in the dehydration step to perform heat dehydration treatment.

(A) Hard-to-dewater digested sludge The object to be treated in this embodiment is preferably hard-to-dewater digested sludge having a TS concentration of 20 g/L or more, preferably 20 to 60 g/L. In one embodiment, it has a TS concentration of 20 to 50 g / L, and in another embodiment, it is possible to treat a highly concentrated and highly viscous difficult-to-dewater digested sludge having a TS concentration of 25 to 40 g / L. More preferred. The sludge properties of the digested sludge are typically pH 6.5 to 8.0, and the sludge viscosity at 30 ° C. measured with a B-type rotational viscometer specified in the sewage test method is 200 to 2000 mPa s, It is preferably 400 to 1500 mPa·s, and the content of coarse suspended solids in SS is 3 to 20 wt%. The difficult-to-dewater sludge can have a SS concentration that is 5 g/L or more less than the TS concentration. In one embodiment, sludge with an SS concentration of 18 to 45 g/L, more preferably 20 to 40 g/L can be used.

Such difficult-to-dewater digested sludge is generated from a process of anaerobic treatment (methane fermentation treatment) of organic substances such as food manufacturing residue, garbage, and sludge. In general, an anaerobic process using a complete mixing methane fermentation tank or a dry methane fermentation tank that is operated under conditions of a retention period (HRT) of 12 to 40 days in a mesophilic fermentation region and a high temperature fermentation region at a processing temperature of 30 to 60 ° C. This is sludge that is discharged from the sludge treatment process.

(B) Aeration Treatment In the aeration treatment, difficult-to-dehydrate digested sludge is aerated with oxygen-containing gas, and sticky components remaining in the digested sludge are decomposed through biological and chemical reactions to reduce the viscosity of the sludge. Let In this aeration process, not only does the decarboxylation reaction of carbon dioxide gas dissolved in the sludge progress, but also sticky substances and organic substances formed by binding residual organic matter and inorganic matter in the sludge by cross-linking action. Adhesives and high-molecular-weight adhesives produced by the aeration treatment are reduced by biological and chemical reactions caused by the aeration treatment. In particular, high-molecular-weight substances having a molecular weight of 1,000,000 to 2,000,000 or more remaining in the digested sludge are reduced in molecular weight by the aeration treatment, thereby reducing the viscosity of the sludge.

In the aeration treatment, the oxygen-containing gas is preferably aerated at an intensity of 0.05 m ³ /(m ³ ·min) or more, and the aeration time is preferably 4 to 48 hours. If the aeration intensity is less than 0.05 m ³ /(m ³ ·min), it is often difficult to aerate the entire sludge due to the high sludge viscosity. On the other hand, when the aeration intensity of the oxygen-containing gas is higher than 0.3 m ³ /(m ³ ·min) or when the treatment time is excessive, the foaming of the digested sludge becomes intense, and the sludge Not only the sticky components but also the decomposition of the sludge itself progresses to dissolve the bacterial components, or the properties of the sludge further change, which may adversely affect the flocculation treatment and dehydration treatment in the subsequent stage. The aeration intensity is preferably 0.1 to 0.25 m ³ /(m ³ ·min), more preferably 0.1 to 0.2 m ³ /(m ³ ·min), more preferably 0.1 ˜0.15 m ³ /(m ³ ·min).

In this embodiment, aeration is preferably performed until the viscosity of the digested sludge after aeration treatment is reduced to 150 mPa·s or less as measured at 30° C. using a B-type rotational viscometer specified in the sewage test method. Aeration times of 4 to 48 hours are typically used, more typically 6 to 24 hours. When the viscosity of the digested sludge after aeration treatment exceeds 150 mPa s, for example, even when the viscosity is about 200 mPa s, it may be possible to increase the dehydration rate of the dehydrated cake itself in the dehydration treatment described later. However, sludge adheres to the dewatering equipment used for dehydration, the conveyor that transfers and transports the dehydrated cake, and the inside of the drying equipment used for subsequent drying, reducing the sludge treatment speed and cleaning the dehydration equipment and drying equipment. Such maintenance may become complicated, and troubles may occur in the dewatering device and the drying device due to clogging during operation.

In order to minimize the addition of flocculants in the entire system and to improve the maintainability of each device with a high dehydration rate, the viscosity of the digested sludge after aeration treatment should be B-type rotational viscosity specified in the sewage test method. 150 mPa s or less, preferably 120 mPa s or less, more preferably 100 mPa s or less, still more preferably 80 mPa s or less, measured at 30 ° C. with a meter, until the aeration strength is reduced from 0.05 to 0.3 mPa s. It is preferable to aerate as slowly as possible in ³ /(m ³ ·min).

The temperature during the aeration treatment can be 10-50° C., and the pH can be 7-9. As the oxygen-containing gas used for aeration, there is no problem if it contains oxygen gas. Concentrated and high-concentration odorous gases, aerated exhaust gases generated from activated sludge treatment equipment for sewage, and the like can be used.

The dissolved oxygen (DO) concentration in the sludge during aeration treatment is maintained at 1.0 mg/L or less. The oxidation-reduction potential (ORP) of sludge is often around −400 to +100 mV. Aeration treatment is performed until the sludge pH is 7.5 to 9.5 and the sludge viscosity is 150 mPa s or less as measured at 30 ° C with a B-type rotational viscometer specified in the sewage test method. It is possible to improve the dehydration efficiency in the dehydration step while reducing the amount of flocculant used.

In order to promote the biological reaction by aeration treatment, sludge containing aerobic microorganisms (hereinafter referred to as "sludge containing aerobic microorganisms") may be added to difficult-to-dehydrate digested sludge before aeration treatment. Preferably, it is possible to positively decompose sticky components and reduce sludge viscosity. The sludge that can be added is preferably excess thickened sludge of activated sludge obtained from the nitrification and denitrification process, or sludge containing aerobic microorganisms such as composted sludge and biological deodorizing sludge. The amount of aerobic microorganisms-containing sludge to be added depends on the sludge concentration, but is 5 to 20 wt%, preferably about 5 to 10 wt% of the amount of anaerobic digestion sludge in consideration of the sludge retention time in the aeration tank. preferable.

(C) Aggregation Treatment In the aggregation treatment, a flocculating agent is added to the aerated digested sludge to form flocculated flocs, and the flocculated flocs are dehydrated (flocculation step). The flocculant is not particularly limited, but a polymer flocculant is used. Polymer flocculants include cationic, anionic, amphoteric, and the like, and include, for example, amidine-based flocculants, acrylamide-based flocculants, acrylic acid-based flocculants, and the like. In addition, a relatively inexpensive cationic polymer-based flocculant, such as an acrylic acid ester type, a methacrylic acid ester type, or an amphoteric type having a cationic degree higher than an anionic degree, can be used. As the acrylic acid ester-based flocculant, the molecular weight is preferably about 3 million to 6 million. The addition rate of the polymer flocculant during sludge aggregation is preferably 1.5-7 wt%, more preferably about 1.8-5 wt%, and in one embodiment, 1.9-2. 6 wt %. By this flocculation treatment, it is possible to form flocculated flocs having a diameter, that is, a floc diameter of about several millimeters, and having high sedimentation and separability.

In addition to using only a polymer flocculant, it may be effective to use an inorganic flocculating aid such as polyferric sulfate, aluminum sulfate, or PAC in combination with a polymer flocculant to improve the clarity of the separated liquid. be. However, when heating and dehydrating sludge by steam blowing as in the present embodiment, depending on the properties of the organic sludge, scale components such as gypsum components may be generated on the screen of the dehydrator. In addition, since the amount of generated sludge also increases due to the addition of the inorganic flocculation aid, it is necessary to determine the application of the inorganic flocculation aid depending on the properties of the sludge.

It is also preferable to dilute the aerated digested sludge prior to flocculation, which can reduce the flocculant injection rate. When diluting the digested sludge, a diluent having a TS concentration of 10.0 g/L or less can be added to the aerated digested sludge. This has the effect of diluting and washing macromolecular substances and colloidal components that remain in the digested sludge even after the aeration treatment and slow down the sludge flocculation reaction, and can promote the sludge flocculation reaction. It is preferable to add a diluent having a TS concentration of 6.0 g/L or less to the aerated digested sludge.

It is preferable to dilute the diluted digested sludge so that the M alkalinity is 4000 mg/L or less, more preferably 2500 mg/L or less by adding a diluent. The electrical conductivity of the diluted digested sludge is preferably adjusted to 1200 mS/m or less, more preferably 750 mS/m or less.

As a diluent, in addition to normal drinking water, properties that do not affect flocculation and dehydration, such as process water with a low concentration of soluble components, or in advanced treatment facilities that perform biological treatment after dehydration Process water in a treatment plant can be used if it has properties that do not affect biological treatment, eg, pH 5-9, NH ₄ --N 1000 mg/L or less, hexane extractables 500 mg/L or less.

Specifically, activated sludge treated water, biologically treated water such as biological deodorizing equipment waste liquid, dewatered and separated water discharged from sludge dehydration, boiler wastewater, on-site washing wastewater, composting condensed wastewater, miscellaneous wastewater, etc. should be used. can be done.

(D) Concentration Treatment The flocculated flocs formed by the flocculation treatment (not shown in FIG. 2) may be subjected to solid-liquid separation before the dehydration treatment to obtain a digested sludge concentrate, and then the dehydration treatment. By the concentration treatment, the flocculated floc is solid-liquid separated into a digested sludge concentrate and a separated liquid. Sludge concentrated to a TS concentration of 8 to 12 wt% can be dewatered more efficiently.

(E) Dehydration Treatment In the dehydration treatment, solid-liquid separation is performed on the flocculated floc of the digested sludge that has undergone flocculation treatment or flocculation treatment and concentration treatment into dewatered cake and separated water. In this dehydration treatment, steam is blown into the dehydrator to heat and dehydrate the cake, thereby obtaining a dehydrated cake with a moisture content of 78% or less, which is lower than the moisture content of the dehydrated cake obtained by conventional general dehydration treatment.

The supply steam pressure is set to 0.15 to 0.25 MPa, and the blowing speed of the steam is adjusted by adjusting the pressure by opening and closing the electric valve. Examples of the dehydrator used for the dehydration treatment are not particularly limited. Among them, by using a heat dehydration treatment with a press type dehydrator using a polymer flocculant, it is possible to suppress the increase in size of the equipment and to increase the efficiency. Hot dehydration treatment can be performed. As the polymer flocculant used in the heat dehydration treatment using a press dehydrator, the same materials as those used in the flocculation treatment described above can be used. The amount of polymer flocculant to be added can be appropriately adjusted.

The amount of steam blown into the dehydrator is preferably adjusted based on the sludge viscosity of digested sludge after aeration. The adjustment of the steam blowing amount may be performed manually by an operator, or may be automatically controlled by a control device having a calculation means for automatically calculating the optimum steam blowing amount. For example, as shown in FIG. 2, measuring devices such as a pH meter 32, a DO meter 33, an ORP meter 34, and a viscometer 35 are arranged in the aeration tank 3, and based on the measurement results of these measuring devices, the moisture content of the dehydrated cake is determined. The amount of steam blowing can be adjusted so that the processing conditions are such that the rate is 78% or less.

According to the processing method according to the present embodiment, the water content of the dehydrated cake can be reduced to 72 to 78% or less, which enables recycling such as composting, carbonization, and fuel conversion. On the other hand, the dehydrated separated water obtained by the dehydration treatment has an SS concentration of 100 to 2000 mg/L, an M alkalinity of 1000 to 2000 mg/L, and an electrical conductivity of 200 to 500 mS/m, so it can be used as a diluent for digested sludge. can.

(F) Drying Treatment In the drying treatment, the dehydrated cake having a moisture content of 78% or less obtained by the dehydration treatment is heated and dried to obtain a dry cake. In the drying treatment, it is preferable to perform a sludge drying treatment using a sludge dryer for heating and drying the dehydrated cake by blowing steam into it. As a result, the drying efficiency of the dehydrated cake can be lowered to suppress adhesion of sludge to the inside of the apparatus, and a process with excellent maintainability of the dryer can be provided.

The supply steam pressure is set to 0.4 to 0.7 MPa, and the blowing speed of the steam is adjusted by adjusting the pressure by opening and closing the electric valve. The amount of steam blown into the drying process is preferably adjusted based on the sludge viscosity of the digested sludge after the aeration process. The adjustment of the steam blowing amount may be performed manually by an operator, or may be automatically controlled by a control device having a calculation means for automatically calculating the optimum steam blowing amount.

It is also preferable to adjust the amount of steam blown in the drying process according to the moisture content of the dehydrated cake obtained in the dehydration process. By appropriately adjusting the amount of steam blown in the drying process according to the properties of the dehydrated cake, it is possible to optimize the amount of steam used and obtain a more efficient treatment system.

According to the treatment method according to the present embodiment, the moisture content of the dry cake is about 30 to 55%, and the dry cake can be obtained with a moisture content suitable for the subsequent composting treatment. This dry cake is heated and fermented for a predetermined period in the composting step described later to obtain good quality compost, which is useful in that organic sludge can be effectively used as a resource.

(G) Composting treatment The dry cake with a moisture content of 30 to 55% obtained by the drying treatment can be composted at an aeration rate of 0.1 to 0.2 m ³ /(m ³ · min) without any auxiliary materials for moisture adjustment. Stable aerobic fermentation is possible. Compost with a water content of 20 to 30% is obtained by this composting treatment.

(H) Waste water treatment The dehydrated and separated water obtained in the dehydration treatment may be subjected to nitrification and denitrification treatment. Specific examples of the digestive denitrification treatment are not particularly limited. The treated water obtained by nitrification and denitrification may be discharged to the outside and a part thereof may be circulated to digested sludge after aeration treatment.

(I) Incineration treatment, biomass methane fermentation, power generation treatment Whether the steam used for dehydration treatment and drying treatment is steam obtained from at least one or more boiler equipment of an incineration treatment facility, a sewage sludge treatment facility, or a biomass methane fermentation facility. , or steam obtained by converting heat obtained from a power generation facility. Among them, for example, methane gas obtained by anaerobic digestion is supplied as an auxiliary fuel to the combustion chamber of the incineration treatment for incinerating organic substances, and the heat obtained by combustion is converted into steam by boiler equipment. By sending the extracted steam to the dehydration process and the drying process respectively, the methane gas obtained in the anaerobic digestion process can be used as it is as auxiliary fuel, so the gas obtained in the anaerobic digestion process can be effectively used without loss. .

According to the method for treating organic sludge according to the embodiment of the present invention, steam is blown into the sludge of which the sludge viscosity of difficult-to-dehydrate digested sludge has been reduced by performing aeration treatment by aerating an oxygen-containing gas. By heating and dehydrating while heating, it is possible to obtain a dehydrated cake with a low moisture content of 78 wt % or less while minimizing the addition of a flocculant in the entire system. By treating low-viscosity sludge, troubles in the dehydrator used for dewatering treatment can be reduced, so maintenance labor can be reduced and more efficient treatment can be performed.

FIG. 2 is a schematic diagram showing an example of an organic sludge treatment apparatus according to an embodiment of the present invention. The organic sludge treatment apparatus includes an anaerobic treatment tank 2 for anaerobically treating the organic sludge to form hard-to-dehydrate digested sludge, an aeration tank 3 for aerating the digested sludge with an oxygen-containing gas, and A flocculation tank 4 for adding a polymer flocculant to digested sludge to form flocculated sludge, an air volume control device 31 for adjusting the aeration speed of the oxygen-containing gas supplied to the aeration tank 3, and aggregating the flocculated sludge by steam blowing. A dehydrator 6 that obtains dehydrated sludge by thermal dehydration, a drying device 7 that dries the dehydrated sludge by blowing steam, and a control device 10 that adjusts the blowing speed of the steam supplied to the dehydrator 6 and the drying device 7. and A raw water tank 1 for storing organic sludge (organic substances) is arranged upstream of the anaerobic treatment tank 2 .

(a) Anaerobic treatment tank As the anaerobic treatment tank 2, known anaerobic treatment tanks such as complete mixing methane fermentation tanks and dry methane fermentation tanks generally used in waste biomass treatment facilities and sewage treatment facilities are used. Can be used without restrictions. In the anaerobic treatment tank 2, stirring is essential in order to homogenize the liquid in the tank and uniformize the temperature distribution, and also to prevent scum from being generated. It is also effective to attach a pump agitation system or a gas agitation system depending on the facility environment and processing conditions. Furthermore, if the fermentation treatment tank has a watertight and airtight structure that satisfies these requirements, it may be made of either reinforced concrete or steel plate. In addition, the anaerobic treatment tank 2 includes a solubilization/acid fermentation treatment tank for solubilizing and acid fermentation treatment of the target biomass, and an anaerobic treatment tank 2 for fermenting the treated material in the tank. is also possible.

(b) Aeration tank Aeration tank 3 generally used in water treatment facilities etc. can be used without restriction, means for introducing difficult-to-dehydrate digested sludge (such as methane fermentation sludge), and introducing oxygen-containing gas into digested sludge Equipped with an air volume control device 31 consisting of an aeration means such as a blower or a diffusion means, an aerated sludge extraction means, and a pH meter 32, a DO meter 33, an ORP meter 34, and a viscometer 35 as measuring instruments for operation management. is preferred. The air volume control device 31 is preferably provided so as to introduce air bubbles into the difficult-to-dehydrate digested sludge in the aeration tank 3 from the bottom of the aeration tank 3 . Furthermore, a sludge dispersing device such as a high-speed dispersing machine may be provided upstream of the aeration tank 3 . In this case, a slurry state in which the difficult-to-dewater digested sludge is uniformly dispersed can be maintained, and the capacity of the aeration tank 3 can be reduced.

(c) Coagulation tank Any coagulation tank 4 generally used in water treatment facilities can be used without limitation. The coagulation tank 4 includes a post-aeration sludge supply pipe for supplying digested sludge after aeration treatment in the aeration tank 3, a coagulant supply pipe for adding a coagulant to the sludge, and a coagulant formed by the coagulation treatment. A flocculated sludge pipe is connected to send the flocculated sludge to the thickener.

(d) Thickening Tank A thickening tank 5 is provided as a solid-liquid separation device for solid-liquid separation of the flocculated flocs formed in the flocculating tank 4 to form concentrated flocculated flocs. The thickening tank 5 is not particularly limited, and may be a simple tank to which the gravitational concentration method is applied, a centrifuge to which the centrifugal concentration method is applied, a separator to which the flotation concentration method is applied, a separator using a screen, or the like. mentioned. Among them, a slit-type concentrator having a slit plate having a large number of slits through which the liquid component passes and a large number of discs having a peripheral surface protruding from the slit plate is preferable. In a slit-type concentrator, for example, the processed material received by a slit plate is sent to the discharge side on the slit plate by a large number of discs on the slit plate that rotate eccentrically in the direction of discharge of the processed material. Liquid components fall through the gap with the disk and are filtered, and solid components in the processed material are separated and collected. Furthermore, a mechanical structure in which a back pressure plate is provided on the slit plate to compress and concentrate the collected matter on the slit plate by rotating in the discharge direction of the processed material in close proximity to the upper surface of the slit plate can also be preferably used. .

(e) Dehydrator A dehydrator 6 is provided for receiving and dehydrating flocculated flocs from the flocculating tank 4 or concentrated flocculated flocs from the thickening tank 5 . The dehydrator 6 is not particularly limited. It is preferable to provide a filtration means that is permeable to liquid and retains digested sludge aggregates. Examples of filtering means include a screen having an opening diameter of 0.1 to 2.5 mm.

Means for applying stress include a press, centrifugation, and the like. A screw press type dehydrator is more suitable than other dehydrators in that it can dehydrate while heating sludge. Also, the higher the temperature of the sludge, the lower the viscosity of the water in the sludge, the more easily the water is separated, and the easier the dewatering tends to be. Steam is supplied during thermal dehydration by inflowing from the steam inlet provided on the screw shaft of the screw press type dewatering machine, and by heating the screw shaft, it is possible to heat the sludge, resulting in a lower water content than before. A dehydrated cake having a moisture content of 78% or less is obtained.

(f) Drying Device A drying device 7 for receiving and drying the dehydrated cake from the dehydrating device 6 is provided. The drying device 7 is not particularly limited, and includes a means for feeding the drying device 7, a blower for supplying a carrier gas (air), a blower heater for heating the carrier gas to maintain the temperature in the drying device 7, and an exhaust. and a wet dust collector for collecting and cooling the exhaust gas sent from the blower, and a wet dust collector circulation pump.

Drying methods include a direct drying method and an indirect drying method. In the indirect drying method, dried sludge can be produced while still containing organic matter, which can then be effectively used as compost or the like. In addition, among the indirect drying methods, the conduction electric heat dryer supplies the amount of heat required for drying by conduction electric heat from the main body and blades, so drying can be performed efficiently. The dehydrated cake fills between the surface of the casing of the main body and the hollow stirring blades, and the friendly contact with the electric heating surface is successively repeated to efficiently perform the heat exchange process. Evaporated moisture is accompanied by a carrier gas sent by an air blower, is exhausted outside the machine, and is collected and cooled by a wet dust collector.

The steam pressure used is 0.4 MPa to 0.7 MPa, and by changing the steam pressure, the dehydrated cake with a moisture content of 78% or less is dried to a moisture content of 30 to 55%, more specifically to a moisture content of 40 to 55%. .

(g) Composting device When a composting device (not shown) is further provided, the dried cake from the heat drying device 7 is received and composted by aerobic fermentation. A dry cake having a water content of 30 to 55% dried according to the present embodiment can be stably maintained at an aeration rate of 0.1 to 0.2 m ³ /(m ³ min) even without auxiliary materials for moisture adjustment. Aerial fermentation is possible, and compost with a moisture content of 20 to 30% can be obtained. Fermentation processing time of the composting equipment is 2 to 7 days for rotary fermenters and multi-level fermenters, about 20 to 40 days for plowing method, and about 30 days for open-air method (pile method). can do. In this embodiment, since it is possible to stably heat and dehydrate only with a polymer flocculant without using an iron-based flocculant as a flocculant for digested sludge, in that case, the product compost is derived from an iron agent. Since the compost does not have a reddish tinge, it is possible to obtain high-quality compost that does not look strange.

(h) Nitrification and denitrification tank A nitrification and denitrification tank 8 for nitrifying and denitrifying the dehydrated and separated water from the dehydrator 6 may be provided. A circulation type nitrification and denitrification tank, a high-load denitrification tank, and a membrane separation type high-load nitrification and denitrification tank, which are generally used in water treatment facilities, can be used without limitation. In the case of a circulating nitrification and denitrification tank, two tanks are installed: a denitrification tank in an anaerobic environment and a nitrification tank in an aerobic environment using aeration, etc. Nitrates produced by aerobic microbial reactions in the nitrification tank are transferred to the denitrification tank. Nitrification and denitrification are carried out by the circulation method in the method of returning and denitrifying by anaerobic or facultative anaerobic microbial reaction. In the case of high-load denitrification by membrane separation, the nitrification and denitrification tank is divided into an anaerobic section and an aerobic section, adopting the biological flotation method, and performing solid-liquid separation of activated sludge and flocculated sludge with an ultrafiltration membrane. .

(i) Diluent supply pipe A diluent supply pipe 81 for adding the treated water from the nitrification and denitrification tank 8 to the aerated digested sludge may be provided. The diluent supply pipe 81 is preferably connected to a pipe connecting the aeration tank 3 and the coagulation tank 4 . The diluent supply pipe 81 may be connected to a diluent supply pipe 61 that feeds part of the dehydrated and separated water from the dehydrator 6 .

(j) Steam supply control device Steam is supplied from the incinerator of the adjacent waste incineration treatment facility, or the steam obtained from the incineration, power generation, boiler equipment 9 of the sewage sludge treatment facility, biomass methane fermentation facility, etc. By transferring via line 12a and controlling steam supply valve 11, the required pressure can be obtained. During steam supply, the amount of steam blown into the dehydrator 6 is adjusted by the steam supply valve 11 based on the sludge viscosity of the sludge in the aeration tank 3, and the sludge is discharged from the dehydrator 6 through the steam supply line 12b. It is possible to control the amount of steam blowing so that the moisture content of the dehydrated cake is 78% or less.

Furthermore, in the drying process of heating and drying the dehydrated cake obtained in the dehydrator 6 by blowing steam, the amount of steam blown into both the dewatering device 6 and the drying device 7 is adjusted based on the sludge viscosity of the sludge in the aeration tank 3. It is also possible to individually control the amount of steam blowing so that the moisture content of the discharged dry cake is adjusted and dried to 30 to 55%. The control device 10 is connected to measuring devices including a pH meter 32, a DO meter 33, an ORP meter 34, and a viscometer 35 that measure the properties of the sludge in the aeration tank 3, and the optimum can be controlled to supply a predetermined amount of steam having a pressure of . The control device 10 is also connected to an air volume control device 31 that controls the aeration volume in the aeration tank 3, and adjusts the aeration intensity for the difficult-to-dewater digested sludge.

According to the organic sludge treatment apparatus and treatment method according to the embodiment of the present invention, the TS concentration of methane fermentation sludge generated by anaerobic treatment is 20 to 50 g / L, preferably 25 to 40 g / L. It is possible to efficiently dehydrate highly viscous, difficult-to-dewater digested sludge at low cost.

Furthermore, according to the organic sludge treatment apparatus and treatment method of the present invention, the difficult-to-dewater digested sludge is aerated to reduce the viscosity of the sludge and improve the flocculation action and dehydration efficiency of the flocculant. As a result, chemical costs and dehydration costs can be significantly reduced. The reduction in sludge viscosity is thought to be due to the reduction of colloidal sticky components due to aeration. It is possible to

Conventionally, when flocculating and dehydrating highly viscous, difficult-to-dewater digested sludge, it has been necessary to reduce the viscosity by dilution. As a result, the volume of sludge to be treated has increased, placing a burden on the treatment. According to this method, dilution is not required during flocculation and dehydration treatment, or a low dilution rate is sufficient. As a result, the cost of the diluent can be reduced, and the separation membrane filtration cost and the sewage discharge cost in the biological treatment process for purifying the dehydrated and separated water can also be reduced.

Examples of the present invention are presented below along with comparative examples, which are provided for a better understanding of the invention and its advantages and are not intended to be limiting of the invention.

Based on the flow diagram of FIG. 1, various food manufacturing wastes were mixed and subjected to methane fermentation treatment under the treatment conditions shown below. As the gas for aeration, the air containing highly concentrated odor is sucked from processing equipment such as raw material receiving hoppers, crushers, sorters, solubilization tanks, and composting fermentation tanks, and is introduced from the diffuser at the bottom of the aeration tank. bottom.

(Processing conditions)
・Methane fermentation tank (vertical mechanical agitator) Effective volume: 1,700 m ³ × 2 tanks Amount of waste (solubilized liquid) input to methane fermentation tank: Average 157 m ³ /day Fermentation temperature: 38°C
・Aeration tank effective volume 70m ³
Amount of methane fermentation sludge input to aeration tank: 160 m ³ /day Aeration intensity: 0.15 m ³ /(m ³ ·min)
Fermented sludge retention time 6 to 24 hours Oxygen-containing gas: Air containing highly concentrated odorous components in the facility / flocculation tank (vertical mechanical agitator) Effective volume 0.6 m ³
Diluted solution (nitrified denitrified water of dehydrated and separated water) 70 m ³ /day TS concentration 5610 mg/L, SS concentration 6 mg/L, pH 7.3, M alkalinity 213 mg CaCO ₃ /L, NH ₄ —N 22 mg/L, chloride substance ion 1940mg/L
Flocculant ・One-liquid method of cationic polymer flocculant (Ebergrose HE-100B) or
・2-liquid method of cationic polymer flocculant (Evergulose HE-100B) + iron-based inorganic flocculant (polyiron) ・Slit-type concentrator (screen slit width 1.0 mm, with back pressure plate)
・Thermal dehydrator (screw press type dehydrator, amount of solids processed: about 280 kgDS/h)
Screw rotation speed 0.15 to 0.25 rpm
Supply steam pressure 0.2 MPa
Sludge temperature 65-80℃
・Membrane separation type nitrification and denitrification tank for dehydrated and separated water Effective volume: 1080 m ³
Amount of nitrified and denitrified sludge input to aeration tank: 270 m ³ /day pH: 7.1
・TS 17,600mg/L
・VS 9,380mg/L
・MLSS 9,770mg/L
・MLVSS 8,590mg/L
・_NH4 -N 26 mg/L
・NO ₃ -N not detected

Table 1 shows the properties of the digested sludge obtained after methane fermentation (methane fermentation sludge) and the digested sludge after aeration treatment.

Each analysis item was based on the following analysis methods.
・ TS (Total solids, total evaporation residue); 105 ° C evaporation residue weight (JIS K 0102)
・ VS (Volatile total solids, ignition loss); 600 ° C. ignition loss (JIS K 0102)
・SS (Suspended solids); Sediment weight after 10 minutes at 3,000 rpm in a centrifuge (JIS K 0102)
・ VSS (Volatile suspended solids, volatile suspended solids); 600 ° C ignition loss of suspended solids (JIS K 0102)
・M alkalinity: Titrate the supernatant with a 0.1 mol/L hydrochloric acid solution to pH 4.8 at 3,000 rpm in a centrifuge for 3 minutes (sewage test method)
・Colloidal charge amount: surface charge amount of sludge, equivalent weight measured by colloid titration method (sewage test method)
・ Content of crude suspended solids; loss on ignition analysis of residue with nominal size 74 μm sieve (sewage test method)
・ Sludge viscosity; measured at 30 ° C. using a B-type rotational viscometer (sewage test method)
• Dehydration test; cationic polymer flocculant Evergulose HE-100B was used.
・ Stickiness: Evaluation of sludge stickiness (stickiness) when dewatered sludge is touched with the palm (none: smooth and no stickiness, weak: slightly sticky, strong: strong stickiness that adheres to the palm) )

Table 2 shows the treatment conditions and treatment results of Examples 1 to 3 and Comparative Examples 1 to 4.

As shown in Examples 1 to 3, highly viscous anaerobic digested sludge with a sludge viscosity of 200 mPa s or more is subjected to aeration treatment to reduce the sludge viscosity to a level of 70 mPa s, and the aerated sludge is steamed. It can be seen that sludge with a water content of 72 to 75% in the dehydrated cake can be stably obtained by heating and dehydrating by blowing. Furthermore, in Examples 2 and 3, by adding a polymer without adding an inorganic coagulant such as an iron-based coagulant, a dehydrated cake with a low moisture content can be obtained and the scale adhesion of the dehydrator can be suppressed. is made.

As shown in the test results of Comparative Example 1, even if the sludge viscosity is reduced to 73 mPa s by performing aeration treatment, stable sludge treatment is possible with normal dehydration treatment of aerated sludge, but the water content of the dehydrated cake is 79. %, and it can be seen that the dehydration property is slightly inferior.

In addition, as shown in the test results of Comparative Example 2, if the sludge is heated and dehydrated with high viscosity without aeration, the sludge flocculation flocs are easily broken in the dehydrator. The water content of the dewatered cake was 83%, and the amount of sludge treated was low.

As shown in the test results of Comparative Examples 3 and 4, in normal dehydration treatment with high sludge viscosity without aeration treatment, the dosing rate of the polymer flocculant is at least twice as high as in the example, Even with the addition of polyiron, the moisture content of the dewatered cake was about 83%, the amount of sludge treated was low, and stable dehydration was not possible.

Next, with the apparatus configuration shown in FIG. 2, operation was performed under the processing conditions shown in Table 1 while adjusting the amount of steam blown into the dehydrator and the sludge dryer. In this test operation, the aeration strength of the aeration tank was 0.1 to 0.15 m ³ /(m ³ ·min), and the flocculant was the macromolecular flocculant Evergulose HE-100B, a one-liquid method. The conditions for the sludge drying equipment and composting equipment are as follows.
・Sludge drying equipment (solid matter processing amount 5000kgDS/day)
Moisture evaporation 750kg/h
Supply steam pressure 0.5 to 0.6 MPa
Supply steam temperature 160°C
・Composting equipment 60 m ³ × 2 tanks Air supply blower speed 0.1 m ³ /(m ³ · min)
No secondary materials added for moisture adjustment

As in Examples 4 to 9, for difficult-to-dewater anaerobic digested sludge with a sludge viscosity of 200 mPa s or more, the aeration intensity of the aeration tank was adjusted to reduce the sludge viscosity to 70 to 120 mPa s. By heating and dehydrating the aerated sludge by steam supply control operation, followed by drying, it is possible to operate the sludge treatment with a dehydrated cake moisture content of 72 to 78% and a dry cake moisture content of 33 to 47% almost stably. I understand. The dried cake thus obtained could be composted by aerobic fermentation without using secondary materials, and compost with a water content of 22 to 25% was obtained.

As described above, according to the present embodiment, the difficult-to-dewater digested sludge obtained by methane fermentation treatment of organic waste at a high concentration is subjected to aeration treatment before dehydration treatment, thereby significantly increasing the viscosity of the sludge. can be reduced, and flocculation performance and dewatering efficiency can be improved. According to the treatment method of the present embodiment, the amount of coagulant to be added can be reduced (low chemical dosing rate), and heat dehydration treatment of difficult-to-dewater, high-concentration digested sludge by steam blowing becomes possible. The dehydrated cake having a moisture content of 78% or less obtained by this embodiment has a lower moisture content than conventional dehydrated cakes, has no stickiness, and does not have a particular unpleasant odor. It is also suitable for recycling such as.

REFERENCE SIGNS LIST 1 raw water tank 2 anaerobic treatment tank 3 aeration tank 4 coagulation tank 6 dehydration device 7 drying device 8 nitrification and denitrification tank 9 incineration, power generation, boiler equipment 10 control device 11 steam supply valve 31 ... Air volume control device 32 ... pH meter 33 ... Dry cake moisture content 33 ... DO meter 34 ... ORP meter 35 ... Viscometer 61 ... Diluent supply pipe 81 ... Diluent supply pipe

Claims (9)

For difficult-to-dewater digested sludge having a TS concentration of 20 g/L or more after anaerobic treatment of organic sludge, a sludge viscosity of 200 to 2000 mPa s , and a coarse suspended matter content rate for SS of 3 to 20 wt%, After reducing the sludge viscosity of the hard-to-dewater digested sludge by performing an aeration treatment with an oxygen-containing gas, the hard-to-dewater digested sludge is coagulated and supplied based on the sludge viscosity of the hard-to-dewater digested sludge after the aeration treatment. A method for treating organic sludge, which includes heat dehydration treatment at a steam pressure of 0.15 to 0.25 MPa while adjusting the amount of steam blowing. In the aeration treatment, the oxygen-containing gas is applied at an aeration intensity of 0.05 to 0.3 m ³ /(m ³ · min), and the viscosity of the digested sludge after the aeration treatment is the B-type rotational viscosity specified in the sewage test method. 2. The method for treating organic sludge according to claim 1, wherein the organic sludge is treated until it decreases to 150 mPa.s or less when measured at 30[deg.] C. with a meter. 3. The method for treating organic sludge according to claim 1, wherein 1.5 to 7% by mass of a polymer flocculant is added to the digested sludge after the aeration treatment to carry out flocculation treatment. The heat dehydration treatment includes dehydration treatment by a press dehydrator using a polymer flocculant, adjusting the amount of steam blown into the dehydrator based on the sludge viscosity of the digested sludge after the aeration treatment, and The method for treating organic sludge according to any one of claims 1 to 3, characterized in that a dehydrated cake having a rate of 78% or less is obtained. Sludge drying treatment using a sludge dryer that heats and dries the dewatered cake by blowing steam into it, and blowing steam into the dehydrator and the sludge dryer based on the sludge viscosity of the digested sludge after the aeration treatment. 5. The method for treating organic sludge according to claim 4, wherein a dry cake having a moisture content of 30 to 55% suitable for composting is obtained by adjusting the amount. The steam used for the heat dehydration treatment is steam obtained from at least one or more boiler equipment of an incineration treatment facility, sewage sludge treatment facility, or biomass methane fermentation facility, or steam obtained by converting heat obtained from a power generation facility. The method for treating organic sludge according to any one of claims 1 to 5, characterized in that Anaerobic treatment of organic sludge to form hard-to-dewater digested sludge having a TS concentration of 20 g/L or more, a sludge viscosity of 200 to 2000 mPa s , and a coarse suspended matter content of 3 to 20 wt% relative to SS. a sex treatment tank;
an aeration tank for aerating the hard-to-dehydrate digested sludge with an oxygen-containing gas;
a flocculation tank in which a polymer flocculant is added to digested sludge after aeration treatment to form flocculated sludge;
an air volume control device that adjusts the aeration speed of the oxygen-containing gas supplied to the aeration tank;
a dehydrator for obtaining dehydrated sludge by heating and dehydrating the flocculated sludge by steam blowing at a supply steam pressure of 0.15 to 0.25 MPa;
a drying device for drying the dewatered sludge by blowing steam;
a control device that adjusts the blowing speed of the steam supplied to the dehydrator and the drying device and adjusts the amount of steam blown into the dehydrator based on the viscosity of the digested sludge after the aeration treatment; An organic sludge treatment device characterized by: Steam obtained from at least one boiler facility of an incineration facility that burns the gas obtained by the anaerobic treatment, a sewage sludge treatment facility, or a biomass methane fermentation facility, or steam obtained by converting heat obtained from a power generation facility 8. The organic sludge treatment apparatus according to claim 7, further comprising a steam supply line for supplying the organic sludge. 7. The method according to any one of claims 1 to 6, wherein the aeration treatment reduces the sludge viscosity of the hard-to-dewater digested sludge to 70 to 120 mPa s, and the sludge is subjected to the heating dehydration treatment. A method for treating organic sludge as described.

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