KR20190050476A - Anaerobic digester and operating method of the same - Google Patents

Abstract

The present invention relates to a sludge digestion tank, which can promote sludge decomposition at an edge deposition part even when deposition occurs in an edge of a digestion tank, and performs a sludge pretreatment process and a sludge decomposition process to be integrated, and to an operating method thereof. The sludge digestion tank of the present invention comprises: a reactor (10) having a predetermined circular or polygonal shape; a sludge inlet (20) and a sludge outlet (30) formed at one side and the other side of the reactor (10), respectively; a heating means (40) for heating the reactor (10); a dead volume region (50) in which sludge is precipitated in the reactor (10) to be accumulated; an energy generating means (60) for radiating heat or sound waves to the reactor (10) and the dead volume region (50); and a power unit (70) for supplying power to the heating means (40) and the energy generating means (60).

Description

[0001] The present invention relates to an anaerobic digester and a method of operating the same,

The present invention relates to a sludge digestion tank and a method of operating the same, and more particularly, it relates to a sludge digestion tank and a method of operating the sludge digestion tank. More particularly, And a sludge pretreatment process capable of promoting the decomposition of sludge on the deposit site and a sludge digestion process.

Sludge is a secondary product that occurs in the sewage treatment process of a sewage treatment plant and can be defined as a form in which microorganisms and undissolved organic substances existing in domestic sewage, drinking waste water, livestock manure and sewage are present as solids together with moisture. The sludge is subjected to concentration and extinguishing processes, and after being dewatered into a cake form, it is transferred out of the sewage treatment plant. In this process, decomposition of the sludge is a very important factor in terms of sludge treatment efficiency and cost. The decomposition of sludge can be classified into an aerobic digestion method in which the digestion is carried out in the oxygen atmosphere during the digestion process of the concentrated sludge and an anaerobic digestion process in which oxygen is not necessary. Particularly, the pulmonary activated sludge is composed of microbial cells and extracellular polymer substances So that it is difficult to decompose by digestive microorganisms. Specifically, in the anaerobic digestion process, sludge produces substances such as organic acids, alcohols, ketones, carbon dioxide, hydrogen, and hydrogen sulfide through hydrolysis, acidogenesis and acetogenesis, Finally, methanogenesis takes place. The constituents of the sludge are combined with the extracellular polymeric substances (EPS) in the microbial metabolism to form a floc of a solid structure to dehydrate and decompose the sludge. It interferes. In addition, in order to protect the microorganism from osmotic pressure, it is difficult to hydrolyze the sludge of the anaerobic digestion tank having many microorganisms due to the outer wall of the microorganism composed of a hard layer. In order to achieve this, it is necessary to stay in the reactor for 20 ~ 30 days for a long time or increase the size of the reaction tank. Therefore, the device of the anaerobic digestion tank is more expensive than the aerobic digestion which is a relatively easy digestion process. Therefore, it is necessary to solubilize or reduce the amount of sludge for the anaerobic digestion process. In order to solubilize the sludge, it is necessary to physically, chemically and biological treat the microorganisms to destroy the cell wall to hydrolyze A variety of sludge pre-treatments have been developed. For example, Korean Patent No. 10-1367765 discloses a method of maximizing the efficiency of a digester by converting a polymer-type sludge into a low-molecular state that is easy to use in the digestion stage by a pretreatment process of the sludge, A technique of pre-treating sludge using the generated cavitation phenomenon has been proposed. However, there is a problem that a separate installation cost is required because the device is formed by separating the device from the front of the anaerobic digester. As another method, as disclosed in Korean Patent Laid-Open No. 10-2016-0117375, by increasing the temperature of the slurry flowing into the anaerobic digestion tank by 45 ° C or 30 ° C using heat, microbial growth can be smoothly carried out, However, it is difficult to maintain the temperature of the heated sludge because of the delay of the conveyance of the sludge because heat is transferred to the conveyed sludge by using the heat exchanger as an additional constitution, and a separate installation space is required There is a problem. In order to increase the digestion efficiency of the sludge which has been settled in the anaerobic digestion tank and precipitated in the anaerobic digestion tank, Korean Patent Registration No. 10-1696689 discloses a digestion tank in which rotation and guide vanes are installed to increase the efficiency of falling into sedimentation and sedimentation of the sludge However, since a rotary shaft driving device for stirring is installed separately and rotation and guide vanes are installed in the digester, a small amount of sludge may be introduced into the digester having the same size.

Korean Patent No. 10-1367765 Korean Patent Publication No. 10-2016-0117375 Korean Patent No. 10-1696689

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sludge digestion tank which is composed of a single integrated process without sludge pretreatment and sludge digestion as separate processes.

Another object of the present invention is to provide an anaerobic digester capable of promoting the decomposition of sludge on the edge-deposited site even if deposition of sludge occurs at the corner where two or more faces in the digester are crossed.

It is also intended to provide a digester with a relatively low energy consumption rate compared to pyrolysis technology, by removing the sludge treatment technology that has been made of pyrolysis center.

In order to solve the above problems, the sludge digestion tank of the present invention comprises a reactor having a predetermined shape of circular or polygonal shape; A sludge inlet formed at one side of the reaction tank and a sludge outlet formed at the other side; Heating means for heating the reaction tank; A dead volume region in which the sludge settles in the reaction tank to accumulate sludge therein; Energy generating means for emitting heat, plasma, shock waves, or ultrasonic waves to the dead volume region; And a power source for supplying power to the heating means and the energy generating means.

Here, the dead volume region is characterized in that it is constituted by 50% or less of the diameter of the reaction vessel from an edge where two or more faces cross each other.

Further, in the sludge digestion tank according to the present invention, it is preferable that the energy generating means is at least one of a heating element, an area heating element, a thermoelectric element, a plasma generator, and an ultrasonic generator using an electric resistance coil

The energy generating means may be a plasma generator, and may be selected from a corona plasma, an arc plasma, and a dielectric barrier plasma generator, and has a specific energy of 3400 kJ / kg TS or more and a temperature of 35 ^o C or more.

It is also preferable that the reaction tank is provided with a heat insulating means which can be selected from polyurethane foam, expanded polystyrene, phenol foam and lacquer.

A method of operating a sludge digester according to the present invention comprises: a first stage in which sludge is introduced into a reaction tank; A second step of operating the energy generating means located in the dead volume region in the reaction vessel until the temperature of the energy generating means reaches 35 DEG C while heating from an initial temperature of 15 DEG C to 35 DEG C; The energy generating means in the reaction tank and the heating means are turned off; Maintaining the temperature of the energy generating means at 35 degrees; And sludge outflow in the reaction tank.

Here, the dead volume region is characterized in that it is constituted by 50% or less of the diameter of the reaction vessel from an edge where two or more faces cross each other.

It is preferable that the energy generating means is at least one of a heating element, an area heating element, a thermoelectric element, a plasma generator, and an ultrasonic generator by an electric resistance coil.

The energy generating means may be a plasma generator, and may be selected from a corona plasma, an arc plasma, and a dielectric barrier plasma generator, and has a specific energy of 3400 kJ / kg TS or more and a temperature of 35 ^o C or more.

The sludge digestion tank and the operation method according to the present invention do not exist as a separate process of the sludge pretreatment and the sludge disassembly but are combined with one integrated process, resulting in an economical effect of space use and cost.

Further, the sludge digestion tank according to the present invention is capable of promoting the decomposition of sludge in the edge-deposited part even if the sludge is deposited on the edge where two or more faces in the digester are crossed, thereby increasing the sludge decomposition efficiency.

Further, the sludge digestion tank according to the present invention provides a sludge decomposition technique which has relatively low energy consumption rate compared with the existing pyrolysis process, so that the amount of sludge treatable per unit energy can be increased.

1 is a block diagram for explaining a sludge digester according to the present invention.
2 is a flowchart illustrating a method of operating a sludge digester according to the present invention.
3 shows changes in voltage and current at the time of plasma discharge.
4 shows the thermal efficiency of the sludge heating by the plasma discharge.
Fig. 5 shows the dissolution of the low concentration sludge by the plasma.
6 shows the dissolution of the high concentration sludge by the plasma.

Hereinafter, a sludge digestion tank and its operation method according to the present invention will be described with reference to the accompanying drawings.

The use of the terms "comprises", "having", or "having" in this application is intended to specify the presence of stated features, integers, steps, components, parts, or combinations thereof, But do not preclude the presence or addition of features, numbers, steps, operations, components, parts, or combinations thereof.

Also, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

The sludge digester according to the present invention shown in FIG. 1 comprises a reaction tank 10 having a predetermined shape of circular or polygonal shape, a sludge inlet 20 formed at one side of the reaction tank 10, a sludge outlet 30 formed at the other side, And a dead volume area 50 in which the sludge is settled in the reaction tank 10 and sludge is accumulated in the reaction tank 10 and the dead volume area 50, An energy generating means 60 for radiating heat, a plasma, a shock wave or an ultrasonic wave, and a power supply unit 70 for supplying power to the heating means 40 and the energy generating means 60. In the sludge digestion tank according to the present invention, the reaction tank 10 is a space for storing and extinguishing the sludge introduced from the outside in order to extinguish the sludge, and the heating means 40 and the energy generating means 60 . In the sludge digestion tank according to the present invention, the inlet 20 is a passage through which sludge flows into the reaction tank 10 from the outside. The sludge introduced from the side of the reaction tank 10 is mixed with sludge under digestion, Should be located. Generally, the sludge is introduced into the water near the center of the bath, or the small-scale digester uses a single inlet pipe, while the large-scale digester uses two or more inlet pipes to allow the sludge to mix evenly. In order to prevent the inflow pipe from being closed by the floating matters of the sludge, it is preferable to use a pipe having an inner diameter of 150 mm or more. It is more preferable that the inflow pipe can be backwashed by feeding the water with the pump. When the sludge is introduced into the reaction tank 10 through the inlet 20, the amount of sludge is 1,600 m 3 / day, and the water content of TS (solids) is 3% or more, about 95%.

In the sludge digester according to the present invention, the heating means 40 is a means for heating the sludge introduced from the outside through the inlet 20 and the reaction tank 10 as means for solubilizing the sludge and in the case of the anaerobic digestion tank, Heating is performed to the temperature. In the heating process, the temperature is not lowered by heating, so that the activity of the methane bacteria, which is highly influenced by the temperature in the anaerobic reaction, is not lowered, thereby preventing the generation of methane from being reduced. The reaction method according to the ordinary temperature is classified into a low temperature (cold tolerance) digestion at 10 to 15 ° C, a middle temperature (affinity) digestion at 31 to 38 ° C, and a high temperature (affinity) digestion at 50 to 56 ° C. The pretreatment rate of sludge increases with increasing temperature. However, in temperate regions such as Korea, the high temperature reaction is uneconomical. An important feature of the sludge digestion tank according to the present invention is that the sludge digestion tank 60 is provided with the energy generating means 60 capable of advancing the digestion of the sludge efficiently while proceeding with the digestion process through the heating means 40. As described above, sludge consists mostly of microorganisms and is composed of a glycan structure which acts as a solid layer to protect the microorganism from osmotic pressure. In addition, the extracellular polymeric substances , EPS) to form a floc, which is a microbial community, to prevent decomposition of the sludge through a mechanism of defense against degradation enzymes. Therefore, the digestion process takes considerable time and degradation efficiency becomes low. In addition, the large amount of bound water contained in the extracellular polymer material makes dehydration of the sludge difficult. The sludge digester according to the present invention comprises an energy generating means 60 for dissipating heat, plasma, shock wave or ultrasound to minimize decomposition of the glycan structure and degradation caused by microbial flocs And the energy source and output of the energy generating means 60 may be sufficient to decompose the glycan structure and the floc structure of the microorganism. The energy generating means 60 of the sludge digestion tank according to the present invention is preferably one or more of a heating element, an area heating element, a thermoelectric element, a plasma generator, and an ultrasonic generator using an electric resistance coil. In this case, the plasma generator may be selected from a corona plasma, an arc plasma, and a dielectric barrier plasma generator, and has a specific energy of 3400 kJ / kg TS or more and a temperature of 35 ° C or more.

The energy generating means 60 not only has the effect of pre-treating the sludge in the local high energy zone generated by the energy generating means 60 but also maintains the target operating temperature of the digester through the local high energy diffusion .

Another important feature of the sludge digestion tank according to the present invention is that the energy generating means 60 is installed in the dead volume region 50 where the circulation in the digester is low and sedimentation accumulation of solid components such as sludge takes place. That is, even if a certain level of flow circulation is generated in a digestion tank having a predetermined shape such as a circular shape or a polygonal shape, the flow circulation has a limit in continuously occurring in the entire digestion tank and accumulation of solid components such as sludge Which can not be achieved. In the sludge digestion tank according to the present invention, the dead volume region 50 may be a region in which the flow circulation in the digestion tank is small and sedimentation accumulation of sludge occurs. Preferably, Or less than 50% of the diameter of the reaction tank 10. In the case of the sludge digestion tank in which the conventional energy generating means 60 is not provided in the dead volume region 50, the heat which is to be transferred to the sludge due to the settled and deposited sludge in the dead volume region 50 is not normally transferred The microbes of the sludge in which the heat is not transferred are difficult to be solubilized in the outer wall, and thus the decomposition rate of the sludge is relatively low as compared with other portions heated. Accordingly, the energy generating means 60 of the sludge digestion tank according to the present invention dissipates heat or sound waves to the dead volume region 50 to facilitate decomposition of the sludge deposited in the dead volume region 50 and to accelerate the digestion of the sludge . In particular, in the case of anaerobic sludge, methane gas generation of methane bacteria is promoted.

The energy generating means 60 in the dead volume region 50 of the sludge digestion tank according to the present invention is capable of locally applying to the dead volume region 50 as described above and having an output capable of decomposing even the anaerobic sludge And it is advantageous to use plasma because there is a need to have a sufficient capacity to raise the temperature of the digestion tank as a whole. In this regard, the sludge digester according to the present invention preferably uses a plasma generator as the energy generating means 60 and can be selected from a corona plasma, an arc plasma and a dielectric barrier plasma generator, and has a specific energy of 3400 kJ / kg < / RTI > TS and a temperature of 35 DEG C or higher. When a high voltage is applied through the plasma generator, a discharge is generated between the two electrodes to form an electric field. At this time, a shockwave is generated together with a strong sound wave. The shock wave impacts the microbial cells to destroy solid cell walls. In this case, intracellular substances, that is, dissolved organic substances are eluted to increase the sludge decomposition efficiency of the dead volume region 50. In addition, due to the electrons generated in the plasma discharge, various kinds of radicals are produced by the reaction of water in Equation 1 and Equation 2. These radicals increase the degradation efficiency of sludge by decomposing cell walls and extracellular macromolecules.

Also, a high-temperature region having a very high temperature locally occurs in the plasma discharge channel. In the local high temperature region in the digester, the cell and extracellular polymer materials are pyrolyzed, and as the decomposition materials are diffused, the anaerobic microorganisms in the digester can be immediately used, so that the digester A high decomposition efficiency can be expected.

In the sludge digestion tank according to the present invention, the adiabatic unit is provided with the reaction tank (10) in order to stably and continuously maintain the temperature of the sludge heated through the heating unit (40) It is preferable to insulate using a material that can be selected from polyurethane foam, expanded polystyrene, phenol foam, and lacquer. As the temperature is kept stable, the degree of hydrolysis of the sludge is improved and solubilization is increased. As a result, acid production and methane production are increased, and reaction of the fermenting bacteria, acetic acid and hydrogen producing bacteria and methanogenic bacteria becomes active, The sludge decomposition rate can be improved.

The discharge port 30 is a passage through which sludge having undergone sludge digestion is discharged. Generally, the discharge sludge is located at the lower end of the reaction tank 10, and the digested sludge is deposited on the bottom of the digestion tank to discharge the concentrated sludge. When the sludge is discharged from the reaction tank 10 through the outlet 30, the amount of solids is 600 m 3 / day, the TS (solids) is 12% or less, and the volatile solids (VS) And remains.

In the sludge digester operation method according to the present invention, the sludge is introduced into the reaction tank 10 at a first stage, while the initial temperature is raised from 15 ° C to 35 ° C, The energy generation means 60 in the reaction tank 10 is turned off and the heating means 40 is turned off in the third step and the energy generation means 60 is used to operate the reaction tank 10 ) At 35 캜, and 5 steps of sludge discharge in the reaction tank 10.

Example 1 (Plasma generating device)

For the underwater plasma discharge, a plasma generator having a discharge cycle of 60 Hz composed of a 12-phase AC power supply, a capillary anode made of tungsten and ceramics, and a cathode made of platinum was used. As shown in FIG. 3, a plasma discharge having a discharge voltage of approximately 1200 to 1400 V and a discharge current of 1.7 to 2.0 A by the apparatus was measured in the sludge using an oscilloscope.

The apparatus also has the effect of Joule heating due to the movement of charge in the sludge and is very efficient compared to the conventional heating method which shows 70% energy efficiency compared to the theoretical energy requirement as shown in Fig. For example, microwave heating efficiency is known to be about 45% energy efficiency.

Example 2 (Dissolution of sludge by plasma)

Sludge having a solid concentration of 1.6% and a chemical oxygen demand (COD) of 17,000 mg / L was subjected to plasma treatment using the plasma generator of Example 1. The dissolution rate versus the input energy was measured by measuring the dissolved oxygen demand (soluble COD, SCOD) and the experimental results are shown in FIG.

The theoretical energy required to heat the 15 ° C sludge at 1.6% solids to the mid-temperature extinguishing temperature of 35 ° C is approximately 5200 kJ / kg TS. Considering the thermal efficiency of 70% of the plasma generator used in this experiment, it is necessary to input energy of 7500 kJ / kgTS. As a result of the experiment, it was confirmed that more than 10% of COD was dissolved in the sludge at the time of energy input.

In addition, over 10% of the sludge is dissolved over a very short time (<30 min) compared to the hydraulic retention time (15-30 days) inside the digester of the sludge, and the rate constant of hydrolysis by the plasma is 5.6 d ^-1 Respectively. This is 10 times faster than the biological hydrolysis rate of 0.5 d ^-1 . The anaerobic digestion efficiency of the sludge can be improved considerably by promoting the rate-limiting hydrolysis in the anaerobic digestion of the sludge using plasma.

Example 3 (Sludge Dissolution Rate for Dead Volume Region 50)

Sludge having a COD of 220 mg / L and a solid concentration of 5% was subjected to plasma treatment using the plasma generating apparatus of Example 1. The dead volume region 50 in the digester was simulated through the sludge having a high solid content concentration which does not smoothly stir the sludge.

6 shows that the sludge solubilization rate of 10% or more was solved in the same manner as in Experimental Example 1, even in the case of high concentration sludge in which agitation was not smooth. Therefore, the dissolution of the sludge in the dead volume inside the digester can be promoted by the plasma discharge.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. These changes and modifications may be made without departing from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

10: Reactor 50: dead volume area
20: inlet 60: energy generating means
30: exhaust port 70:
40: Heating means 80: Insulation

Claims (9)

A reaction tank 10 having a predetermined shape of a circular or polygonal shape;
A sludge inlet 20 formed at one side of the reaction tank 10 and a sludge outlet 30 formed at the other side;
Heating means (40) for heating the reaction tank (10);
A dead volume region 50 in which sludge is settled in the reaction tank 10 and sludge is accumulated;
Energy generating means 60 for dissipating heat, plasma, shock waves or ultrasonic waves to the reaction tank 10 and the dead volume region 50;
And a power supply unit (70) for supplying power to the heating means (40) and the energy generating means (60). The sludge digester
2. The sludge digester according to claim 1, wherein the dead volume region (50) is constituted by 50% or less of the diameter of the reaction vessel (10) from an edge where two or more faces intersect.
2. The sludge digestion apparatus according to claim 1, wherein the energy generating means (60) is at least one of a heating element by an electric resistance coil, an area heating element, a thermoelectric element, a plasma generator,
The method according to claim 1, wherein said energy generating means (60) are plasma generators, corona plasma, arc plasma, and may be selected from a dielectric barrier plasma generators, non-energy (specific energy) 3400 kJ / kgTS above, temperature 35 ^o or more C A sludge digester
2. The sludge digester according to claim 1, wherein the reaction tank (10) is provided with a heat insulating means which can be selected from polyurethane foam, expanded polystyrene, phenol foam,
A first stage in which sludge flows into the reaction tank 10;
A second step of operating the reactor 10 until the temperature of the reactor 10 reaches 35 ° C by using the energy generating means 60 located in the reactor 10 and the dead volume region 50 while heating the reactor 10 from an initial temperature of 15 ° C to 35 ° C;
The energy generating means 60 in the reaction tank 10 and the heating means 40 are turned off;
A fourth step of maintaining the temperature of the reaction tank 10 at 35 degrees using the energy generating means 60;
And sludge outflow in the reaction tank (10).
[7] The sludge digestion apparatus according to claim 6, wherein the dead volume area (50) is configured to be 50% or less of the diameter of the reaction tank (10)
7. The sludge digester operation method according to claim 6, wherein the energy generating means (60) is at least one of a heating element, an area heating element, a thermoelectric element, a plasma generator, and an ultrasonic generator by an electric resistance coil
According to claim 6, wherein said energy generating means (60) are plasma generators, corona plasma, arc plasma, and may be selected from a dielectric barrier plasma generators, non-energy (specific energy) 3400 kJ / kgTS above, temperature 35 ^o or more C A method of operating a sludge digester

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