WO2008068820A1

WO2008068820A1 - Method of treating excess active sludge for volume reduction

Info

Publication number: WO2008068820A1
Application number: PCT/JP2006/324089
Authority: WO
Inventors: Shinzo Ishikawa
Original assignee: Shinzo Ishikawa
Priority date: 2006-12-01
Filing date: 2006-12-01
Publication date: 2008-06-12

Abstract

A method of treating an excess active sludge (S) for volume reduction in which a significant reduction in water content can be expected and the energy efficiency in heating is satisfactory. An excess active sludge (S) discharged after a biological treatment is stored in a heat treatment tank (3). Water vapor (M) is directly supplied thereto to conduct a heat treatment at a given temperature for a given period. The excess active sludge (S) which has undergone the heat treatment is dehydrated, solidified, and further dried. The temperature in the heat treatment of the excess active sludge (S) is preferably 60-70°C, and the drying is preferably conducted in an atmosphere of 20-40°C.

Description

Specification

Reduction method of activated surplus sludge

Technical field

[0001] The present invention relates to a method for treating activated surplus sludge discharged by biological treatment from a sewage treatment plant, human waste treatment plant, or various production factories, and more particularly to a method for reducing the amount of activated surplus sludge.

Background art

[0002] Organic surplus sludge discharged from various wastewater treatment processes (hereinafter abbreviated as “active surplus sludge”) has its water content reduced by dehydration, recycled as fertilizer, or reduced by incineration. Then, landfill is processed as industrial waste.

[0003] However, such activated surplus sludge has a high moisture content of about 80% by weight, and the ratio of the solid content is so small that the entire capacity increases. For this reason, transportation costs to the treatment area or fuel costs for incineration were high. Therefore, it has been strongly desired to reduce the treatment cost by reducing the moisture content of the activated surplus sludge or to effectively use the decreasing land for disposal.

[0004] As a technique for reducing the amount of activated surplus sludge, there is, for example, the following: Patent Document 1 discloses that a biological acid tank power surplus sludge is extracted, transferred to a liquid container, and pH After adjusting the pH from 8 to 14 and heating at 110 ° C to 250 ° C for 10 seconds to 3 hours to make it capable of being decomposed by microorganisms, the treated sludge is adjusted to pH with a neutralizer. It is adjusted from 5 to 8 and returned to the bio-oxidation tank again to allow biodegradation again.

[0005] Prior to biological treatment of surplus sludge, Patent Document 2 first adds an acid to sludge to reduce the viscosity by heat treatment, and then either a proteolytic enzyme or a cell wall degrading enzyme or both. Is added as a hydrolytic enzyme to make excess sludge soluble, and then returned to the biological treatment tank for biological treatment.

[0006] In Patent Document 3, activated surplus sludge produced by biological treatment of wastewater is physically solubilized by ultrasonic treatment in an ultrasonic treatment tank to improve dispersibility and facilitate acid fermentation. The sludge Acid fermentation is efficiently performed in an acid fermenter to perform solubilization by biological reaction, and the solubilized processed product is returned to the activated surplus sludge processing tank through an acid fermentation processed product return line.

Patent Document 1: Japanese Patent Laid-Open No. 2003-245693

Patent Document 2: JP-A-2004-41925

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-321818

Disclosure of the invention

Problems to be solved by the invention

[0007] However, the technologies disclosed in these documents are not intended to reduce the weight. Actually, the process is complicated and lacks in processing efficiency. It was difficult and difficult to reduce processing costs.

[0008] For example, in Patent Document 1, after a process of heating excess sludge to a state in which it can be decomposed by microorganisms is performed, it is returned to the biological acid tank and reduced by microbial treatment. Eventually, the weight reduction depends on the biological treatment reaction of activated sludge. Therefore, a process of transferring excess sludge to a separate container for heat treatment is necessary and complicated, and the time required for the active treatment with microorganisms is governed by the activity of microorganisms. It was difficult to control directly.

[0009] Also in Patent Document 2, as a pretreatment, acid is added to the excess sludge and heat treatment is performed! Since the viscosity of the sludge is reduced, the hydrolytic enzyme is added and solubilized. As with Patent Document 1, there is a problem that the surplus sludge must be transferred and processed.

[0010] Patent Document 3 differs from Patent Documents 1 and 2 in that ultrasonic waves are used, but it is the same in that the activated surplus sludge must be transferred and treated, which is complicated. O

[0011] Further, in Patent Documents 1 to 3, sludge is reduced by dehydration after these steps, and water is evaporated by heating as a general method of dehydration. However, since a large amount of microorganisms remain active in the activated surplus sludge after biological treatment and contain a large amount of moisture in the cells, most of the heating energy removes the moisture in the cells. It will be consumed as latent heat. Therefore, it is difficult for the temperature of activated surplus sludge to rise. The energy efficiency is very bad.

[0012] As a result, the amount of heat necessary to evaporate water is also greater than the amount of heat that the dried sludge has (generally 5, OOOkcalZkg to 6, OOOkcal Zkg). Therefore, the utilization of dry sludge is low, and it was only used as cement raw material, incineration residue as soil conditioner, or melt processed and used as civil engineering or construction material. . On the other hand, when incinerated, the transportation cost to the incineration plant is high, and if the combustion temperature at the time of incineration is low, there is a strong concern about the impact on the environment due to the generation of dioxin. The fuel cost was high.

[0013] Therefore, the present invention has been made paying attention to the above problems, and destroys the cell walls of microorganisms present in the activated surplus sludge discharged from a treatment plant or a factory to drain water inside the cells. The present invention discloses a method by which the moisture content can be drastically reduced and the temperature of activated surplus sludge can be increased efficiently by being drawn out. Means for solving the problem

[0014] In order to solve the above-described problems, a method for reducing the amount of activated surplus sludge according to the present invention is configured as follows.

That is, the heat treatment is performed by directly supplying a heat medium to the activated surplus sludge contained in the organic wastewater discharged by the biological treatment. In this specification, the activated surplus sludge subjected to the heat treatment is referred to as “heat-treated sludge”.

[0015] The heat treatment is preferably performed in a heat treatment tank having means for directly supplying a heat medium, and it is preferable to use water vapor as the heat medium. In the heat treatment, it is preferable to maintain the temperature of the activated surplus sludge in the range of 40 ° C to 90 ° C. It is more preferable to maintain the temperature in the range of 60 ° C to 70 ° C.

[0016] In addition, it is preferable to dehydrate the heat-treated sludge after heat treatment to obtain a sludge that is solidified by dehydrating the heat-treated sludge (this is commonly referred to as "dehydrated cake"). It may be allowed. A compression technique may be used for dehydration. As a compression method, a conventional method is used, but conventional techniques such as mechanical compression, centrifugal compression, and natural compression may be used.

[0017] The dehydrated cake can be dried by heat drying or by room temperature drying without active heating. Both may be performed. Also, break the dehydrated cake and dry it.

[0018] When drying by heating, it is preferably performed in an atmosphere of a temperature of 10 ° C or higher and 120 ° C or lower, more preferably 20 ° C or higher and 40 ° C or lower.

[0019] In the case of drying at room temperature, it may be left alone! /, But it may be carried out while circulating air using an air supply means.

The invention's effect

The present invention has the following effects by the above-described configuration.

Since the heat medium is directly supplied to the activated surplus sludge, the microorganisms have more opportunities to directly contact the heat medium or water heated by the heat medium, and can effectively destroy the cell membrane of the microorganism cells. In addition, since most of the heat quantity of the heat medium is used to raise the temperature of the activated surplus sludge, the activated surplus sludge can be efficiently heated, and the heating cost can be reduced.

[0021] Further, since the structure for directly supplying the heat medium can simplify the structure, maintenance management with little influence of the deposits on the pipe line becomes extremely easy, and durability and practicality are improved. be able to.

Brief Description of Drawings

FIG. 1 is a conceptual diagram of an apparatus used for a processing method according to an embodiment of the present invention.

Explanation of symbols

[0023] 1 ... Biological treatment tank, 2 ... Precipitation tank, 3 ... Heat treatment tank, 31 ... Liquid temperature sensor, 4 ... Jet pipe, 4 1 ... Steam outlet, 5 ... Steam Supply pipe 51 ··· Open / close valve, 6a… Dehydrator (belt press type), 6b… Dehydrator (roller type), 7 ··· Drum rotary dryer, W… Organic waste water, S… Activity surplus Sludge, M ... water vapor (heat medium), H ... heat treated sludge, C ... dehydrated cake, F ... flocculant BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best embodiment of the method for reducing the surplus activity according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a conceptual diagram of an apparatus used for a processing method according to an embodiment of the present invention. [0025] In the figure, reference numeral 1 denotes a biological treatment tank. The biological treatment tank 1 is, for example, treated with microorganisms in various plants such as a sewage treatment plant, a human waste treatment plant, or a chemical factory, or a food factory. This is to temporarily store the organic wastewater W that has been discharged. In the biological treatment tank 1, biological treatment is still in progress. Then, a predetermined amount of organic waste water W is transferred from the biological treatment tank 1 to the precipitation tank 2, and solid-liquid separation is performed by precipitation separation by standing for a predetermined time. As a result, the activated surplus sludge S contained in the organic wastewater W is precipitated. The precipitation here is natural precipitation, but if necessary, the precipitation may be accelerated by using an appropriate flocculant.

Next, the activated surplus sludge S precipitated in the lower part of the settling tank 2 is transferred to the heat treatment tank 3. At this time, the water content of the activated surplus sludge S is usually 90% by weight or more, and the active microorganisms account for 96% to 99% by weight.

[0027] The heat treatment tank 3 has, for example, a cylindrical shape having a capacity of about lOOt (not limited to this), and is transferred intermittently or continuously from the precipitation tank 2 in accordance with its treatment capacity. 50 to 60 tons of activated surplus sludge S is stored. It is effective to transfer the activated surplus sludge S by a batch method (batch method) from the upper part of the heat treatment tank 3. At the bottom of the heat treatment tank 3, an ejection pipe line 4 is provided as a supply means for directly supplying the heat medium into the activated surplus sludge S in the tank.

[0028] A large number of jets 41 are formed in the jet pipe 4, and a steam supply pipe 5 for supplying the steam M from an external supply source (for example, a once-through boiler, not shown) to the jet pipe 4. Are connected via an on-off valve 51. It is preferable to arrange a liquid temperature sensor 31 in the heat treatment tank 3 and adjust the water vapor M supplied by adjusting the on-off valve 51 based on information from the liquid temperature sensor 31. If necessary, a stirrer (not shown) may be provided inside the heat treatment tank 3 to promote internal heat convection.

[0029] Under such a configuration, steam M as a heat medium is directly supplied into the activated surplus sludge S stored in the heat treatment tank 3 via the steam outlet 41 of the ejection pipe 4. In this way, the activated surplus sludge S is heat-treated to actively destroy the cell walls of the activated microorganisms. The intracellular water leaks from the destroyed cells. The activated surplus sludge S is heated to 40 ° C or more and 90 ° C or less by steam M, and this temperature is started from 18 hours. It is preferable to maintain for about 20 hours. The more preferable heating temperature of the activated surplus sludge S is 60 ° C or higher and 70 ° C or lower. In this example, for example, the activated surplus sludge S was set to about 60 ° C., the steam M was set to a set gauge pressure of 1 kgZcm ² , and the steam amount was set to 5 Okg per surplus sludge It.

[0030] After heating at the above-mentioned predetermined temperature for a predetermined time, for example, the heat-treated sludge H is transferred to a belt press type dehydrator 6a equipped with a compression filtration means and dehydrated by solid-liquid separation. The heat-treated sludge H is compressed and filtered by the dehydrator 6a to become a dehydrated cake C. If necessary, an inorganic or polymer flocculant F may be added to improve the efficiency of solid-liquid separation. The dewatering device 6a used in this example is, for example, a heat-treated sludge H charged at 7.5 tons per hour and a filter cloth width of 1.5 m by compression filtration at a belt speed of 0.45 m / min. Has the ability to form.

[0031] The dehydrated cake C is, for example, formed into a plate having a thickness of about 22 mm by compression filtration at a speed of 50 cm per minute. In this case, the moisture content is from 63% to 68% by weight. Furthermore, if this dewatered cake C is left in the form of a plate at room temperature without being actively heated, for example, at room temperature (“naturally left”), after about 40 hours, depending on the season and environmental temperature, It was confirmed that the moisture content decreased from 20% to 25% by weight.

[0032] Next, the dewatered cake C that has been subjected to compression filtration may be transferred to a roller-type dewatering device 6b that is opposed to a contact type and processed into a thin plate of lmm to 3mm with a roller for a peripheral speed of 10mZ. . When dehydrated cake C was allowed to stand for about 30 minutes after being thin, the moisture content decreased to 15% by weight or less due to the spontaneous release of moisture.

[0033] In addition, the dehydrated cake C may be subdivided with various cross-sections such as small grains or strings to increase the surface area per volume. Subdivision is preferable because the area of contact with the air increases and the efficiency of spontaneous emission increases. Further, it is preferable not to simply leave the dehydrated cake C, but to dry it while actively circulating air, since it can be dried more efficiently.

[0034] Power! In order to bring the moisture content close to 'zero', the dehydrated cake C may be dried using a dryer such as the drum rotary dryer 7. The drum of the drum rotary dryer 7 In addition to forced air circulation, dry air or hot air may be used. Yes. When heating, a temperature atmosphere of 10 ° C or more and 120 ° C or less is preferred. A temperature atmosphere of 20 ° C or more and 40 ° C or less is more preferred. The specifications of the rotary drum dryer 7 used in this example are, for example, drum diameter φ: 0.38 m, drum length: 2.42 m, rotary drum rotation speed: 10 rpm, blowing air temperature: 25 ° C Ventilation air volume: 30 (m ³ Z min).

[0035] Under this condition, when the dehydrated cake C was dried for 10 minutes, the water content of the dehydrated cake C was 5% by weight or less. This drying step is not essential in the present invention. If the desired moisture content can be achieved only by the dehydration step, it can be omitted.

[0036] In this way, when the activated surplus sludge S is heat-treated and then subjected to compression filtration, the moisture content of the dewatered cake C changes to a property that the drying proceeds naturally in a short time. This is because the microbial cell wall was crushed by supplying the heat medium directly to the activated surplus sludge S, and the water inside the cells leaked out. In this way, it was found that the water content of dehydrated cake C was drastically reduced in a short time by a simple operation.

[0037] By the way, the temperature of the activated excess sludge generated after the wastewater treatment is 30 ° C to 35 ° C unless heat treatment is performed. The moisture content of the dehydrated cake obtained under these conditions was 82% by weight when the water was separated by the dehydrator 6a. The dehydrated cake 6b was thinned by the dehydrator 6b, and the dehydrated cake was put into a dryer and aerated to dry. Even after further water separation in the second stage, the water content was 81.5% by weight.

Industrial applicability

[0038] The sludge processed by the water separation treatment according to the present treatment method can be used as a carbon-neutral boiler fuel. Therefore, unlike fossil fuels such as heavy oil and city gas, it becomes a new fuel that does not have to worry about the emission of global warming gas.

[0039] In this way, surplus sludge can be brought close to "zero" in the sludge moisture content simply by adopting an easy method of heating, maintaining and separating water. It is very big.

Claims

The scope of the claims

[1] A method for reducing the amount of activated surplus sludge, comprising directly supplying a heat medium to the activated surplus sludge contained in organic wastewater discharged by biological treatment and performing heat treatment.

[2] The method for reducing activated surplus sludge according to claim 1, wherein the heat treatment is performed in a heat treatment tank having means for directly supplying a heat medium.

[3] The method for reducing the amount of activated surplus sludge according to claim 1, wherein water vapor is used as the heat medium.

[4] The method for reducing activated surplus sludge according to claim 1, wherein the activated surplus sludge is heated to 40 ° C or higher and 90 ° C or lower by the heat treatment.

[5] Perform dehydration after the heat treatment! 2. The method for reducing the amount of activated surplus sludge according to claim 1, wherein a dewatered cake is formed.

[6] The method for reducing the amount of activated surplus sludge according to claim 5, wherein the dehydrated cake is further dried.

7. The method for reducing the amount of activated surplus sludge according to claim 6, wherein the dehydrated cake is subdivided and at least one of heat drying and room temperature drying is performed.

[8] The method for reducing the amount of activated surplus sludge according to claim 6, wherein the dehydrated cake is dried in an atmosphere at a temperature of 10 ° C to 120 ° C.

[9] The method for reducing the amount of activated surplus sludge according to claim 6, wherein the dehydrated cake is dried at room temperature while circulating air.