JP6384168B2 - Sludge treatment method - Google Patents

Description

  The present invention relates to a sludge treatment method for treating sludge generated when treating sewage, waste water, waste water, sewage and the like.

  Conventionally, biological treatment by the activated sludge method has been widely used for the treatment of sewage, wastewater, wastewater, sewage, etc. (raw water) such as general wastewater such as domestic wastewater and human waste, factory / business groundwater wastewater, and agricultural / livestock wastewater. Has been done. In this biological treatment process, suspended substances in the raw water are first precipitated and removed as sludge in the sedimentation basin. The precipitated sludge is drawn out and transferred to the dehydration process through the subsequent concentration process in the gravity concentration tank. In this gravity concentrating tank, the sludge is concentrated by gravity over time. In this process, the activity of microorganisms in the sludge often progresses. As a result of the sludge rising due to the nitrogen gas generated by the sewage, the drainage of pollutants into the overflow water in the concentration tank, sludge concentration failure, sludge increase due to sludge increase due to sludge concentration failure and sludge dewaterability deteriorated There are many problems such as the generation of odor due to decay.

  In order to deal with such problems, for example, with regard to odor, measures such as covering the concentration tank and treating the odor separately have been taken.For sludge concentration reduction and dehydration deterioration due to poor concentration, Studies on the development of dehydrating drugs and studies on improving the efficiency of dehydrators are being conducted. In addition, as measures against solids flowing into the overflow water of the thickening tank, the promotion of operation management such as keeping sludge in the sedimentation basin and keeping the sludge zone in the thickening tank low is being promoted.

  Japanese Patent Application Laid-Open No. 2003-94094 describes a method of preventing odor by adding nitrite to sludge and performing solid-liquid separation, and further adding nitrite to the obtained dehydrated cake.

  Japanese Patent Application Laid-Open No. 2002-361300 discloses the effectiveness of nitrite for suppressing odor and sludge levitation.

  Japanese Patent Laid-Open No. 2006-305489 discloses a sludge levitation inhibitor containing a bacteriostatic agent and nitrite in order to suppress sludge levitation in a gravity concentration tank of raw sludge containing first sedimentation basin drawn sludge. It is described that it is added. Examples of the bacteriostatic agent include sodium pyrithione, sodium azide, 4,5-dichloro-1,2-dithiol-3-one, phosphonium compounds, and triazine compounds.

  In wastewater treatment facilities and sewage treatment facilities in factories, sedimentation basins and sedimentation tanks (or sedimentation tanks) are generally used for solid-liquid separation of suspended substances contained in wastewater and the supernatant water by sedimentation of wastewater (sewage). Pond) is provided. The suspended sediment is extracted and discharged as sludge (sediment sludge).

  In sewage treatment facilities, “sediment sludge” is sometimes referred to as “primary sludge” or “raw sludge”, but these are the same.

  In addition, the suspension is attached to and floats on bubbles blown into water, or is attached to bubbles generated by a surfactant and the like, and the suspended suspension is scraped and discharged out of the system. A levitation concentrator may be provided.

  In addition, a biological treatment tank that can purify organic substances in water using metabolic activities of microorganisms and bacteria is provided. Here, microorganisms and bacteria use part of the ingested organic matter for their life support activities, and emit carbon dioxide as a result of metabolism. On the other hand, microorganisms and bacteria grow. Microorganisms and bacteria that are present more than necessary in the system due to growth may reduce the purification capacity, and are controlled and managed so that the increased amount is discharged out of the system and maintained at a constant amount. This discharge can be done by draining a part of the system water directly from the biological treatment tank or by transferring a part or all of the system water to a tank capable of stationary sedimentation such as a sedimentation tank to increase the concentration in advance. It may be discharged as a turbid slurry. This discharged slurry is called “surplus sludge” because it discharges excess bacteria and microorganisms. Microorganisms and bacteria have a small specific gravity, and even if solid-liquid separation can be performed by standing for a short time, the concentration may not be sufficiently increased, and a concentrating device may be provided in order to further concentrate this. In this concentrating device, as described above, the levitation concentrating device that attaches to and floats on bubbles blown into water, or attaches to and floats on bubbles generated by a surfactant, etc. In some cases, a centrifugal concentrator for concentrating by concentration or a concentrator for increasing the concentration by filtration may be provided.

  As described above, precipitation sludge composed of a suspension separated from water and excess sludge composed of microorganisms and bacteria are usually dehydrated and often carried out as a dehydrated cake. The dehydration treatment is usually performed using a dehydrator, but may be performed by drying (dryer).

  In either case, the sludge to be treated is more uniform and more efficient when supplied at a high concentration. Therefore, the concentration concentration is increased in advance before the dehydration process, and a gravity concentration tank (precipitation) Pond) is provided.

  In addition, recently, before the dehydration treatment, sludge is transferred to a tank that can be maintained in an anaerobic atmosphere, and the treatment of anaerobic bacteria is used to reduce the sludge (anaerobic digestion tank). . The organic matter contained in the precipitated sludge is consumed by anaerobic bacteria, and the volume of the sludge is reduced by the amount discharged as carbon dioxide or methane gas. Surplus sludge, on the other hand, is bacteria and microorganisms that were originally active under aerobic conditions, but they are killed and altered by being placed in an anaerobic atmosphere for a long time, and consumed as food for anaerobic bacteria. The volume of sludge becomes small.

  Anaerobic bacteria metabolize the ingested organic matter and emit carbon dioxide and methane. Anaerobic bacteria grow slowly and do not interfere with sludge volume reduction. In addition, the organic matter decomposition rate of anaerobic microorganisms is not so fast, and in such an anaerobic digestion tank, it is necessary to maintain the residence time in the digestion tank of the treated sludge for a long period of usually 10 days or more, When supplying low-concentration sludge, the volume of the reaction tank must be increased. On the other hand, if it is supplied at a lower concentration than designed, the residence time is shortened, so that undecomposed organic matter flows out, and the volume reduction rate of sludge is lowered. Furthermore, when the generated methane gas is used as a resource, the energy (calories) is reduced.

  For this reason, if the treated sludge is supplied uniformly and at a high concentration, the residence time in the digestion tank can be increased, the sludge volume can be reduced efficiently, and digestion gas can be obtained. Therefore, a gravity type concentration tank (sedimentation basin) and a sludge storage tank for increasing and homogenizing the concentration in advance are provided in the previous stage of the digestion process.

  However, precipitated sludge and excess sludge contain a large number of anaerobic or aerobic bacteria and microorganisms. For this reason, the activity of bacteria and microorganisms occurs in the gravity type concentration tank, and gas is generated to prevent the concentration, and sludge is floated / spilled out and returned to the water treatment system.

  When such sludge is returned to the water treatment system, it has poor sedimentation, so it flows out as it is, deteriorates the quality of the treated water, or becomes a load on the aerobic biological tank (activated sludge), and the power associated with aeration ( Power) costs increase. In addition, when active bacteria and microorganisms are returned, they act in a sedimentation tank (or sedimentation basin) that separates suspended solids contained in the wastewater, causing a solid-liquid separation failure.

  Solid-liquid separation failure has an adverse effect on sludge treatment (dehydrator, anaerobic digestion tank) and water treatment (solid-liquid separation, biological treatment), so solid-liquid separation management in this gravity concentration tank In addition, it is important to prevent microbial activity from causing concentration problems and levitation.

  The adhering of carbon dioxide bubbles discharged by the metabolism of anaerobic bacteria causes the sludge flocs, sludge mass, and sludge layer to rise. Anaerobic bacteria decompose organic substances step by step, and the pH is lowered by the organic acid discharged during the decomposition, resulting in an acidic atmosphere. For this reason, the solubility of carbon dioxide gas in water is lowered, the amount of bubbles expressed is increased, and the surface is more likely to rise.

  At this time, hydrogen sulfide gas may be generated at the same time, but the amount generated is different by one digit or more compared with carbon dioxide gas, usually by about two digits. This is due to the difference in the amount of substrate (retention) that is the source of generation.

  There are two types of anaerobic bacteria: facultative anaerobic bacteria, the environment in which facultative anaerobic bacteria are active is defined as “anoxic / anoxic atmosphere”, and the environment in which obligate anaerobic bacteria are active is “(absolutely ) Anaerobic state / (absolute) anaerobic atmosphere). “Anoxic state” is an environment where the redox potential is negative (reduction side) and ions such as molecular oxygen, nitric acid, and nitrous acid are present and oxygen can be used. Is a state where there is no such thing. If such a state is distinguished by “oxidation-reduction potential”, a state of 0 to −200 mV can be roughly divided into an anoxic state, and a state of −200 or less can be separated from an (absolute) anoxic state.

  Hydrogen sulfide gas is normally exhausted by obligate anaerobic bacteria. As described above, the (absolute) anaerobic state is an environment in which molecular and ionic oxygen is consumed after anaerobic conditions. Therefore, before hydrogen sulfide gas is generated by the obligate anaerobic bacteria, the activity of facultative anaerobic bacteria first occurs, and the discharge of carbon dioxide gas begins. For these reasons, most of the rising of sludge in sedimentation ponds and sludge storage tanks is due to carbon dioxide.

On the other hand, a part of the system water in the biological reaction tank is discharged directly, or a part or all of the system water is transferred to a sedimentation tank etc. However, the cause of rising and running out of sedimentation ponds and sludge storage tanks is different from that of sedimentation sludge. The surplus sludge is originally activated sludge that is active in the aeration tank, and since the organic matter has been decomposed in an aerobic atmosphere, there is almost no organic matter that can be decomposed and metabolized in the slurry. In addition, since it is an aerobic bacterium, there is little ingestion or decomposition of organic matter in the absence of oxygen. Nonetheless, so-called “internal breathing” continues, and although carbon dioxide is exhaled even in anoxic conditions, it is clearly less than the amount exhaled when organic matter is decomposed. Moreover, since an organic acid is not discharged through an organic substance decomposition | disassembly process of an anaerobic bacterium in multiple steps, the fall of pH accompanying organic substance decomposition is slight. For this reason, even if a large amount of carbon dioxide is discharged due to endogenous respiration under the condition where the concentration is increased and the number of bacteria is increased, it becomes a form of dissolved carbon dioxide (HCO ₃ ⁻ , H ₂ CO ₃ ), and carbon dioxide gas. As a result, sludge levitation hardly occurs.

When a nitrogen component flows into the aeration tank, it is oxidized by nitrifying bacteria and NO ₂ ⁻ and NO ₃ ⁻ are generated. When denitrifying bacteria are present in the sludge, NO ₂ ⁻ or NO ₃ ⁻ is ingested under oxygen-free conditions, and nitrogen (N ₂ ) is discharged. This phenomenon due to microbial activity is called denitrification. The solubility of nitrogen in water is slight, and the generated nitrogen appears as nitrogen gas and gives buoyancy to the sludge. This often happens, not only in water treatment system sedimentation tanks, but also by taking advantage of this action to place aeration-oxygen-free tanks in series in water treatment systems. Reduction of the nitrogen component is performed. In such a system, when denitrification is not performed well, sludge may float in the sedimentation tank, or NO ₃ ⁻ or NO ₂ ⁻ may be brought into the surplus sludge. As mentioned above, sedimentation basins and sludge storage tanks are often oxygen-free. The cause of surplus sludge levitation in sedimentation ponds and sludge storage tanks is NO ₃ ⁻ (or NO ₂ ⁻ ) brought along with surplus sludge slurry, and denitrification occurs under oxygen-free conditions and is released. The levitation is caused by the generated nitrogen gas.

In some cases, the activity of bacteria decreases under environmental conditions such as a low water temperature, carbon dioxide and nitrogen gas are not discharged, and sludge does not float. Further, although the sludge floating in the settled sludge alone does not occur, NO ₃ ^- or the NO ₂ ^- to sometimes emerge together also settled sludge by denitrification by mixing the excess sludge containing a sludge precipitation sludge alone levitation will awake but, nO ₃ ^- and nO ₂ ^- in some cases floating falls by dilution effect by a mixture of excess sludge not containing.

Further, NO ₃ surplus sludge slurry ^- or NO ₂ ^- also contain, or if the denitrifying bacteria is no less or presence, even denitrifying bacteria sufficient exists, not meeting environmental (temperature, pH, ORP) In the case where the activity of denitrifying bacteria is reduced and surplus sludge alone is present in biological treatment tanks-sedimentation tanks and storage tanks, denitrification occurs by mixing with precipitated sludge even when sludge does not rise Sometimes.

  Until now, the cause of sludge levitation in sedimentation basins and sludge storage tanks has been attributed to hydrogen sulfide gas, but as a result of detailed investigation and verification, as described above, sludge levitation is not The surplus sludge was lifted by nitrogen gas. Therefore, the processing means for deodorizing hydrogen sulfide gas as a target is insufficient as a means for solving sludge floating due to the above causes and phenomena.

  As described above, under various conditions and conditions, the principle and mechanism of sludge levitation are different, and countermeasures corresponding to each are required.

  Japanese Patent Application Laid-Open No. 2005-265687, Japanese Patent Application Laid-Open No. 2011-13084, and Japanese Patent Application Laid-Open No. 2011-47761 describe an ultrasonic pulse reflection type interface level meter (in-vessel monitoring monitor) that can monitor the state in the vat.

JP 2002-361300 A JP 2003-94094 A Japanese Patent Laid-Open No. 2006-305489 JP 2005-265687 A JP 2011-13084 A JP 2011-47761 A

  An object of the present invention is to provide a sludge treatment method capable of effectively preventing sludge from rising in a step of concentrating precipitated sludge and excess sludge.

  In the sludge treatment method of the first invention, when the precipitated sludge and the excess sludge are concentrated in the same tank by natural sedimentation, before the precipitated sludge and the excess sludge are mixed, a flocculant, a bacteriostatic agent, a disinfectant, One or more chemical | medical agents chosen from a lysis agent and an oxidizing agent are added to each sludge, It is characterized by the above-mentioned.

  The sludge treatment method of the second invention is one in which the precipitated sludge and the excess sludge are concentrated by natural sedimentation in separate tanks, and one or more chemicals selected from a flocculant, bacteriostatic agent, bactericidal agent, bactericide and oxidizing agent Are added to the sludge, respectively.

  The sludge treatment method of the third invention is a sludge treatment method in which the precipitated sludge is concentrated by natural sedimentation, and the excess sludge is concentrated by mechanical concentration without being concentrated by natural sedimentation. One or more chemical | medical agents chosen from a flocculant, a bacteriostatic agent, a disinfectant, a bactericide, and an oxidizing agent are added only to the sedimentation sludge before settling.

  In the first invention, in the method of concentrating precipitated sludge and surplus sludge by natural sedimentation, the agent (flocculant, bacteriostatic agent, bactericide, bacteriolytic agent) is added before the precipitated sludge and surplus sludge are mixed in the same tank. Or an oxidizing agent) is added to each sludge.

  In the second invention, the precipitated sludge and the excess sludge are respectively concentrated in the individual tanks by adding chemicals and spontaneous sedimentation.

  In 3rd invention, a chemical | medical agent is added only to precipitation sludge, it concentrates by natural sedimentation, and it concentrates mechanically, without performing the concentration by natural sedimentation about excess sludge.

  Generally, precipitated sludge contains a lot of anaerobic bacteria, and excess sludge contains a lot of aerobic bacteria.

  Precipitated sludge is rich in minerals and has a large specific gravity, so it has excellent sedimentation and consolidation properties. Since most of the excess sludge is bacteria or microorganisms, it is mainly organic matter, has a small specific gravity, and has lower sedimentation and consolidation properties than sedimentation sludge.

  As described above, the properties of the precipitated sludge and the excess sludge are different, and the chemical components and the addition amount for improving the sedimentation property are often different. For example, in a biological treatment apparatus that performs nitrogen treatment (nitrification denitrification), the bacteriostatic action of nitrous acid and nitrite is effective for the initial sedimentation sludge. On the other hand, excess sludge contains denitrifying bacteria and is present in large quantities with high activity, so nitrous acid and nitrite are immediately denitrified and converted to nitrogen gas. Nitrous acid and nitrite are not effective, and rather the generated nitrogen gas may promote sludge levitation.

  Since excess sludge has poor sedimentation properties, it is possible to improve the consolidation and concentration by adding flocculant to increase the floc particle size to increase the sedimentation rate, or by adding a lysing agent when there are many filamentous bacteria. Can do.

  When the activity of microorganisms contained in the precipitated sludge is very active, the activity can be lowered using a bacteriostatic agent or a bactericide according to the situation and state. In addition, when there are a lot of fibers and hair and steric hindrance has caused poor consolidation, an oxidizing agent can be added to weaken this.

  Therefore, as in the first invention, when the precipitated sludge and the excess sludge are concentrated by natural sedimentation in the same tank, by adding appropriate chemicals respectively before the precipitated sludge and the excess sludge are mixed, Sludge can be concentrated efficiently.

  In the second invention, each sludge can be efficiently concentrated in each tank by adding chemicals suitable for the properties and properties of the precipitated sludge and surplus sludge.

  In the third invention, the precipitated sludge is concentrated by natural sedimentation by adding a chemical, and the excess sludge is concentrated by mechanical concentration. Thereby, each sludge can be concentrated efficiently.

  One kind of drug may be used, or two or more kinds may be used. In this case, they may be added simultaneously, a premixed solution may be added, or they may be put in order. Or you may change the place to add. Alternatively, different drugs may be added in the first half and the second half. An appropriate addition method may be arbitrarily selected in consideration of the effect and interaction for each drug.

It is a flowchart of the sludge processing method which concerns on embodiment. It is a timing chart which shows inflow of sludge. It is a timing chart which shows inflow of sludge and chemical injection. (A) is a flowchart of the sludge processing method which concerns on embodiment, (b) is sectional drawing of a gravity concentration tank. It is a flowchart of the sludge processing method which concerns on embodiment. It is a flowchart of the sludge processing method which concerns on embodiment. It is a flowchart of the sludge processing method which concerns on embodiment. It is a flowchart of the sludge processing method which concerns on embodiment. It is a flowchart of the sludge processing method which concerns on embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 shows a flow of a sludge treatment method according to the first embodiment, and here, a flow of a sewage treatment facility will be taken up and described as a representative example. The raw water is first introduced into the sedimentation basin 1 and the primary sedimentation sludge is settled and separated. First, the supernatant water of the sedimentation basin 1 is introduced into the aeration tank 2 and subjected to aerobic treatment by air aeration from the air diffuser 2a. The liquid in the aeration tank 2 is introduced into the final sedimentation basin 3 and separated into settling sludge and supernatant water, and the supernatant water is taken out of the system as treated water.

  A part of the sludge settled in the final sedimentation basin 3 is sent to the gravity concentration tank 7 by the sludge pump 4 and the pipe 5 as surplus sludge, and the remaining sludge is returned through the sludge return pipe 6 branched from the pipe 5. It is returned to the aeration tank 2 as sludge. Instead of branching the pipe 6 from the pipe 5, a part of the sludge settled in the final sedimentation basin 3 may be directly returned to the aeration tank 2 by a return-only pipe.

  The initial sedimentation sludge that has settled in the sedimentation tank 1 can be introduced into the gravity concentration tank 7 through the pipe 8.

  The drug A is added by the chemical injection device 20 to the first settling sludge introduced into the gravity concentration tank 7 from the pipe 8. Moreover, the medicine B is added by the chemical injection device 21 to the excess sludge introduced into the gravity concentration tank 7 from the pipe 5.

  In the gravity concentration tank 7, the sludge is separated into supernatant water and concentrated sludge by gravity. The supernatant water is first returned to the sedimentation basin 1 through the pipe 15.

  The concentrated sludge is extracted from the bottom of the gravity concentration tank 7 and introduced into the anaerobic digestion tank 10 through the pipe 9.

  In this embodiment, the anaerobic digestion tank 10 includes a primary tank 10a and a secondary tank 10b, and the concentrated sludge is introduced into the secondary tank 10b after being anaerobically digested in the primary tank 10a. It is configured to be further anaerobic digestion. Digestion gas generated by anaerobic digestion in the tanks 10 a and 10 b is taken out of the system through the pipe 11.

  Digested sludge taken out from the secondary tank 10b is sent to the dehydrator 13 through the pipe 12, dehydrated, and the resulting dehydrated cake is taken out of the system. The dehydrated filtrate is first returned to the settling basin 1 via the pipe 14.

  As the drugs A and B, one of a flocculant (an inorganic coagulant, an organic coagulant, an organic coagulant, or a combination thereof), a bacteriostatic agent, a bactericide, a lysing agent, and an oxidizing agent. Or 2 or more types are mentioned. The same drugs A and B may be added, or different drugs A and B may be added.

  Two or more chemical injection devices may be provided in the pipes 5 and 8, and different chemicals may be added thereto. Specifically, for example, a flocculant and a bacteriostatic agent are added to the initial sedimentation sludge, and a flocculant and a bacteriostatic agent are also added to excess sludge. In addition, there is an example in which a bacteriostatic agent is first added to the initial settling sludge, and then the flocculant is added, and the flocculant is added to the surplus sludge and then switched to the bacteriostatic agent.

  When the sludge decays in the first sedimentation basin, a bacteriostatic agent is added to the sludge immediately after extraction, that is, the initial sludge flowing into the gravity concentration tank, and a flocculant is added to the place where the concentration in the latter half is low. Thus, the concentration can be increased, the sedimentation rate can be increased, and the pressure density can be increased.

  Since excess sludge has a slow sedimentation rate and the sludge may soar, a flocculant is added to the sludge at the beginning of the inflow to increase the sedimentation rate and promote solid-liquid separation. Can be added to suppress the ascent of the sludge in the latter half.

  As another method of chemical injection, flocculant and bacteriostatic agent are added to the first settling sludge with separate chemical injection devices, and bacteriostatic agent and flocculant are added to the excess sludge with separate chemical injection devices. Examples of addition and examples of changing the addition position are given.

  The inflowing sludge changes depending on the treatment facility, the inflowing time zone, and the season, and the chemicals that effectively act on the sludge also change. Therefore, it is preferable to select the sludge from time to time.

  It is preferable to predetermine the kind and addition amount of the drug by a desktop test or the like.

  As the inorganic coagulant, for example, aluminum chloride, polyaluminum chloride (PAC), ferric chloride, polyiron, calcium chloride, silicon compound and the like are used. Examples of organic flocculants that can be used include cationic polymer flocculants, anionic polymer flocculants, nonionic polymer flocculants, and amphoteric polymer flocculants.

  In addition, since the flocculant mainly composed of inorganic components increases the amount of sludge, the amount of dehydrated cake increases when used in large amounts. In addition, a flocculant mainly composed of inorganic components and containing aluminum may reduce the activity when the concentrated sludge is led to an anaerobic digester. Those containing iron may activate the activity of anaerobic bacteria and increase the generation of gas in the gravity concentration tank.

  In the flocculant mainly composed of organic components, when bubbles are generated in the formed floc, the bubbles are unlikely to come out of the floc and may cause sludge to float. In particular, the cationic polymer flocculant easily attracts bubbles in an electric charge, and the sludge easily floats.

  A bacteriostatic agent is a drug that inhibits the growth or growth of bacteria. In the method of the present invention, a drug generally referred to as a bactericide can also be used as a bacteriostatic agent by developing a bacteriostatic action when used at a low concentration. Examples of the bacteriostatic agent used in the method of the present invention include nitrite, hypochlorite, quaternary ammonium salt, ethanol, formaldehyde, pyrithione or derivatives thereof, and sorbic acid. Among these, nitrite and pyrithione or derivatives thereof can be suitably used. Examples of nitrites include ammonium nitrite, lithium nitrite, sodium nitrite, potassium nitrite, rubidium nitrite, cesium nitrite, magnesium nitrite, calcium nitrite, strontium nitrite, barium nitrite, nickel nitrite, Examples thereof include zinc nitrate and thallium nitrite. Examples of pyrithione or derivatives thereof include pyrithione, sodium pyrithione, zinc pyrithione, and dipyrithione.

  Into the gravity concentration tank 7, the initial settling sludge and the excess sludge may be introduced simultaneously or separately.

  FIGS. 2A and 2B show an example of a pattern in which the initial settling sludge and the excess sludge are intermittently introduced into the gravity concentration tank 7, respectively. In this case, the introduction of the initial settling sludge and the introduction of the excess sludge may not overlap as shown in FIG. 2B, and the introduction of the excess sludge as shown in FIG. It may overlap with the introduction of the first settling sludge.

  When primary sedimentation sludge and surplus sludge are mixed in the gravity concentration tank 7, biological activities become active, the effect of the drugs to be added decreases, or drugs react with each other. As shown in FIG. 2B, it is preferable not to overlap the introduction of the first settling sludge and the introduction of the excess sludge at all. In this case, after the initial settling sludge is introduced, the surplus sludge is introduced after the time for the initial settling sludge to sufficiently settle and concentrate, and after the time for the surplus sludge to sufficiently settle and concentrate, the initial settling sludge is removed. It may be preferable to introduce. By taking a sufficient settling time in this way, it is possible to avoid mixing of the settling sludges, or to prevent sludge from being newly introduced before the settling is completed and rolling up before the settling is completed. For sufficient settling time, the inflow may be controlled in advance by investigating the time, or the interface level may be measured to determine the end of settling and the next inflow control may be performed.

  The addition of the chemical may be performed during the period from the start of sludge introduction to the end of the introduction, and may be performed before or after the introduction. An example is shown in FIGS.

  In Fig.3 (a), the addition of the chemical | medical agent A is started with the introduction start of initial sludge, and the addition of the chemical | medical agent A is complete | finished with the introduction start of surplus sludge. Moreover, the addition of the chemical | medical agent B is started with the introduction start of surplus sludge, and the addition of the chemical | medical agent B is complete | finished with the introduction start of surplus sludge.

  In FIG.3 (b), the chemical | medical agent A (a kind is not limited) is added at the time of introduction | transduction of primary sedimentation sludge, and only chemical | medical agent A or a bacteriostatic agent is added for a while after completion | finish of introduction | transduction of primary sedimentation sludge. Moreover, the chemical | medical agent B (a kind is not limited) is added at the time of the introduction of surplus sludge, and after completion | finish of introduction | transduction of a surplus sludge, only the chemical | medical agent B or a bacteriostatic agent is added for a while.

  In this case, the bacteriostatic agent may be added for a predetermined time, or a predetermined amount of the bacteriostatic agent may be added according to the volume of the concentration tank. The predetermined time may be controlled by a timer with a predetermined time, or may be determined by measuring the sludge interface and checking the sedimentation state.

  In FIG.3 (c), only a bacteriostatic agent or the chemical | medical agent A is added prior to the start of introduction | transduction of first sedimentation sludge, and the chemical | medical agent A (a kind is not limited) is added at the time of sludge introduction | transduction. Prior to the start of the introduction of excess sludge, only the bacteriostatic agent or the drug B is added, and the drug B (the type is not limited) is added when the sludge is introduced.

  The addition of the bacteriostatic agent before the start of the introduction of the sludge may be performed for a predetermined time, or a predetermined amount may be added according to the volume of the concentration tank. The predetermined time may be timer-controlled at a predetermined time.

  In FIG. 3 (d), only the bacteriostatic agent or the drug A is added prior to the start of the introduction of the initial settling sludge, and the drug A (the type is not limited) is added when the sludge is introduced, and the introduction of the initial settling sludge is completed Thereafter, the bacteriostatic agent alone or the drug A is continuously added for a while. Prior to the start of surplus sludge introduction, only bacteriostatic agent or drug B is added, and drug B (the type is not limited) is added at the time of sludge introduction. Add drug alone or drug B.

  As shown in FIG. 2 (b) and FIGS. 3 (a) to 3 (d), after the initial sludge and the excess sludge are introduced at different times, the previously introduced sludge has been settled and accumulated. The advantages of allowing the next sludge to flow in and preventing each sludge from mixing are as follows.

  That is, since the sludge that has flowed into the gravity concentration tank settles in the clarified phase (supernatant water) in the gravity concentration tank 7, the sedimentation speed is high and solid-liquid separation is performed efficiently. Since the sludge that has settled the clarified phase is deposited on the sludge accumulation layer that has previously settled, the accumulated sludge is not mixed with each other, and the effect of each added chemical agent is stably exhibited for a long period of time.

  The chemical injection rate (chemical injection speed) of the chemical may be proportional to the introduction speed of the sludge slurry introduced into the gravity concentration tank 7 from the pipe 5 or 8, and when the introduction speed is high, it is larger than the proportional chemical injection amount. It is good also as a medicine dosage. That is, if the introduction flow rate of the sludge slurry is increased, the time for mixing and diffusing with the drug cannot be taken, or the effect of the drug may be diminished due to a decrease in contact efficiency, particularly when the pipe is injected. In such a case, when the sludge slurry flow rate increases, it may be preferable to set a chemical injection rate higher than a preset chemical injection rate (reference value).

  Similarly, when the concentration of sludge flowing in is high, it is sometimes preferable to increase the chemical injection rate. The drug injection rate may be adjusted by increasing / decreasing the addition amount (volume) with a preset drug concentration, or may be adjusted by increasing / decreasing the concentration without changing the addition amount. You may change with the capability of facilities, such as a chemical injection device.

  Another embodiment will be described with reference to FIGS.

  FIG. 4A shows the gravity concentration tank 7 provided with measuring means 30 in the inside of the tank.

  The measuring means 30 may be an interface level sensor that measures the height of the sedimentation sludge accumulation layer or the distance from the water surface to the upper surface of the sludge accumulation layer, that is, the sludge interface level. When the sludge interface level in the gravity concentration tank 7 is higher than a preset value, the sludge is extracted from the gravity concentration tank 7 to adjust the sludge interface level. FIG. 4B is a longitudinal sectional view schematically showing the state of sludge accumulation in the gravity concentration tank 7. As described above, solid-liquid separation is not performed well if there is no clarified phase (supernatant water) in the gravity concentration tank. For this reason, it is desirable to adjust the sludge interface level in advance so that the clarified phase is above the sludge accumulation layer.

  The measuring means 30 may be an ultrasonic pulse reflection type interface level meter (in-tank monitoring monitor) having a function of detecting the sludge interface level and detecting bubbles in the tank. The in-vessel monitoring monitor may be one described in Patent Documents 4 to 6. Sludge extraction is performed so that the interface level detected by the ultrasonic pulse reflection type interface level meter becomes a set value. Also, when sludge flows up into the gravity concentration tank 7, when sludge rises are detected, the sludge in the upper part of the sludge accumulation layer is pulled out so as not to be affected by the inflowing water flow to lower the interface level, Adjust the inflow rate. Further, when the ultrasonic pulse reflection type interface level meter detects bubbles in the tank, the sludge is extracted by a predetermined amount, the sludge interface level is lowered by a predetermined amount, or bacteriostatic against sludge to be introduced to the gravity concentration tank 7 next time. Increase the dose rate or dose of agents, fungicides, lysing agents or flocculants.

  In FIG. 5, a measuring device 31 for measuring the water quality characteristic value of the supernatant water flowing out from the gravity concentration tank 7 is provided in the pipe 15. The measuring device 31 measures turbidity, SS concentration, MLSS concentration, transparency, particle diameter or particle size distribution in the supernatant water, and based on the measured values, the bacteriostatic agent, bactericidal agent, lysing agent or flocculant Determine the rate or amount of addition and control the dosing.

  In FIG. 6, a measuring instrument 31 is provided in the pipe 15 as shown in FIG. 5, and a measuring instrument 32 that measures water quality characteristic values is also provided in the lower part of the gravity concentration tank 7. The measuring device 31 measures the M alkalinity or redox potential (ORP) of the supernatant water, and the measuring device 32 measures the M alkalinity or redox potential (ORP) of the sludge slurry accumulated in the gravity concentration tank 7. To do. And based on the measured value of the one or both of the measuring devices 31 and 32, the addition rate or addition amount of a bacteriostatic agent, a bactericide, a bactericide, or a flocculant is determined, and a chemical injection is controlled.

  In addition, a nitrous acid concentration measuring device is installed as the measuring devices 31 and 32, and the nitrous acid concentration of one or both of the supernatant water and the sludge slurry in the gravity concentration tank 7 is measured, and the nitrous acid concentration after a predetermined time is determined in advance. Compared with the threshold value, adjust the addition rate, addition amount or concentration of nitrite, nitrite, nitrite containing chemicals or nitrite containing chemicals added to the sludge to be introduced into the gravity concentration tank 7 next time. You may be allowed to inject medicine.

  In the said embodiment, although the anaerobic digester 10 is provided, you may abbreviate | omit the anaerobic digester 10 in this invention. FIG. 7 shows such a flow, and the concentrated sludge taken out from the bottom of the gravity concentration tank 7 is directly introduced into the dehydrator 13 by the pipe 9.

  In the above embodiment, the first settling basin 1, the aeration tank 2 and the final settling basin 3 are provided in only one series, but a plurality of series may be provided. FIG. 8 shows an example when two systems are provided.

  In FIG. 8, the first settling basin 1, the aeration tank 2 and the final settling basin 3 and the first settling pond 1A, the aeration tank 2A and the final settling pond 3A are installed, and the first settling sludge in each of the first settling ponds 1 and 1A. Is introduced into the gravity concentration tank 7 via the pipes 8, 8 </ b> A, and excess sludge in the final sedimentation tank 3 is introduced into the gravity concentration tank 7 via the pipe 5.

  A part of the excess sludge in the final sedimentation basin 3A is returned to the first sedimentation basin 1A via the pump 4A and the pipe 5A, and the remaining surplus sludge in the final sedimentation basin 3A is returned to the aeration tank 2A via the pipe 6A. Will be returned. Chemical injection is performed on the pipes 5, 8, and 8A by a chemical injection device (not shown).

  The supernatant water of the gravity concentration tank 7 is introduced into the first sedimentation basin 1 and 1A through the pipe 15, and the concentrated sludge is anaerobically treated by the primary tank 10a and the secondary tank 10b of the anaerobic digestion tank 10 through the pipe 9. The digestion gas is taken out via the pipe 11.

  The digested sludge is introduced into the dehydrator 13 through the pipe 12, dehydrated, the dehydrated cake is taken out of the system, and the dehydrated filtrate is first returned to the settling basin 1, 1A.

  In the flow of FIG. 8, excess sludge from the final sedimentation basin 3 </ b> A may also be introduced into the gravity concentration tank 7.

  In the above embodiment, surplus sludge from the final sedimentation basin 3 is introduced into the gravity concentration tank 7, but in FIG. 9, this surplus sludge is introduced into the mechanical concentrator 40 and mechanically concentrated without adding any chemicals. .

  The liquid separated by mechanical concentration is first introduced into the sedimentation basin 1 through the pipe 42. The sludge concentrated by the mechanical concentrator 40 is sent to the anaerobic digester 10 through the pipe 41.

  Other configurations are the same as those of the embodiment of FIG. 1, and the same reference numerals denote the same parts. As in the case of FIG. 1, the first settling sludge is gravity concentrated in the gravity concentration tank 7, and the supernatant water is introduced into the first settling tank 1 via the pipe 15, and the concentrated sludge is added to the anaerobic digestion tank 10 via the pipe 9. To be introduced.

  As the mechanical concentrator 40, a centrifugal concentrator, a belt-type pressure concentrator, an electroosmotic dehydrator, a granulating concentrator, a pressure levitation concentrator, an atmospheric levitation concentrator, or the like can be used.

  In FIG. 9, only the first settling basin 1, the aeration tank 2 and the final settling basin 3 are provided, but two or more series may be provided.

  In the above embodiment, the chemical pouring for the precipitated sludge and the excess sludge is performed by piping, but the chemical pouring may be performed for the gravity concentration tank 7.

DESCRIPTION OF SYMBOLS 1,1A First sedimentation basin 2,2A Aeration tank 3,3A Final sedimentation basin 7 Gravity concentration tank 10 Anaerobic digestion tank 13 Dehydrator 20,21

Claims (3)

In the sludge treatment method of introducing and concentrating the sediment sludge generated by the sedimentation treatment before the biological treatment and the excess sludge into the gravity concentration tank ,
A sludge treatment method that repeats a step of introducing one of precipitated sludge and excess sludge into the gravity concentration tank and terminating the sedimentation, and then introducing the other to terminate the sedimentation,
To the settled sludge and excess sludge, respectively flocculants, bacteriostatic agents, bactericidal agents, sludge treatment method, which comprises added pressure to the one or more agents selected from the lysing agent and the oxidizing agent. According to claim 1, with the addition of agents to the sludge when introducing the sludge into the gravity concentration tank, at least one of after introducing the before and sludge introducing sludge into the heavy force concentration tank, a predetermined time, the A sludge treatment method comprising adding a bacteriostatic agent to a gravity concentration tank. In Claim 1 or 2 , the generation | occurrence | production of the bubble from the sedimentation sludge in the said gravity concentration tank is monitored, and if bubble generation is detected, the addition speed | rate or addition amount of the chemical | medical agent will be increased when sludge is introduced next time. A sludge treatment method characterized in that

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