How to operate an anaerobic treatment tank

Abstract

To provide a method of operating an anaerobic treatment tank, capable of shortening a start-up time.SOLUTION: The method of operating an anaerobic tank that anaerobically treats organic effluent by charging seed sludge thereinto at a time of start-up, is characterized by charging anaerobically digested sludge and aerobically treated sludge as seed sludge at a time of start-up so that the ratio of the amount of the aerobically treated sludge relative to the total amount of the sludge charged thereinto becomes 50 to 90% (weight ratio). Preferably, the seed sludge is charged into the tank at a time of start-up so that the sludge concentration in the tank becomes 10000 to 50000 mg / L.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for operating an anaerobic treatment tank for treating various types of organic wastewater, such as domestic wastewater, sewage, food factory wastewater, and paper factory wastewater, and more particularly to a method for operating the anaerobic treatment tank at the start-up stage. [Background technology]

[0002] Anaerobic treatment using an anaerobic treatment tank is used as a method for treating wastewater containing organic matter (organic wastewater). When starting the operation of the anaerobic treatment tank, seed sludge is supplied into the tank (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 56-38186 [Patent Document 2] JP 2012-110820 A Summary of the Invention [Problem to be solved by the invention]

[0004] Compared to aerobic treatment, anaerobic treatment has the advantage of reducing the amount of sludge generated, reducing the power required for aeration, and enabling the recovery of energy in the form of methane, but because the microorganisms involved grow slowly, it takes a long time to start up if the required amount of sludge cannot be secured. That is, when starting up an aerobic biological treatment tank, the retained sludge concentration is gradually increased from a low sludge concentration, but in the case of an anaerobic treatment tank, the sludge must be maintained at a high concentration or it will become inactivated, so it is necessary to store it until the required amount of sludge is reached, and then start passing the sludge through the tank to increase capacity, which takes a long time to start up.

[0005] An object of the present invention is to provide a method for operating an anaerobic treatment tank that can shorten the start-up time. [Means for solving the problem]

[0006] The method for operating an anaerobic treatment tank of the present invention is a method for operating an anaerobic treatment tank which anaerobically treats organic wastewater, and is characterized in that in the method for operating an anaerobic treatment tank in which seed sludge is added at the time of start-up, anaerobically digested sludge and aerobically treated sludge are added as seed sludge at the time of start-up so that the aerobically treated sludge accounts for 50 to 90% (weight ratio) of the total amount of sludge added.

[0007] In one embodiment of the present invention, anaerobic treatment is carried out using suspended sludge.

[0008] In one embodiment of the present invention, the anaerobically digested sludge is sludge collected from another anaerobic treatment tank treating organic wastewater of the same or similar composition.

[0009] In one embodiment of the present invention, seed sludge is added at the start-up so that the sludge concentration in the tank is 10,000 to 50,000 mg / L. Effect of the Invention

[0010] In the present invention, aerobically treated sludge is used as part of the seed sludge at the start of the system, and the flow of the sludge is started at a high sludge concentration. After the flow of the sludge starts, the amount of anaerobic microorganisms in the system increases over time, and the sludge becomes acclimated to the target wastewater.

[0011] Conventional methods for operating anaerobic treatment tanks required a period for securing the required sludge volume and a period for acclimatizing the sludge to the target wastewater. However, according to the present invention, securing the required sludge volume and acclimatizing the sludge are performed simultaneously, thereby significantly shortening the start-up period. [Brief description of the drawings]

[0012] [Figure 1] 1 is a configuration diagram of an anaerobic treatment apparatus to which a method for operating an anaerobic treatment tank according to an embodiment of the present invention is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Fig. 1 shows an anaerobic treatment apparatus to which the method of the present invention can be applied. Raw water (organic waste liquid) is supplied into anaerobic treatment tank 1. Anaerobic treatment tank 1 is provided with stirring blades 2, which stir the inside of the tank. A portion of the liquid in the tank is sent via piping 3 and pump 4 to raw liquid chamber 5a of membrane separator 5 outside the tank. Note that the inside of the tank may be mixed by circulation using a liquid sending pump without providing a stirrer.

[0014] Inside the membrane separator 5, a raw liquid chamber 5a and a permeate chamber 5b are formed by a separation membrane 5m. A UF ​​membrane is preferably used as the membrane 5m. The permeate that permeates the membrane 5m is taken out from the permeate chamber 5b as treated water. The liquid that does not permeate the membrane 5m is returned to the anaerobic treatment tank 1 through a pipe 6.

[0015] When the operation of the anaerobic treatment tank 1 is started, anaerobically digested sludge and aerobically treated sludge are stored in the anaerobic treatment tank 1 as seed sludge.

[0016] The anaerobic digestion sludge is preferably collected from another anaerobic treatment tank that treats organic wastewater or sewage sludge of the same or similar composition (e.g., proportion of solids, proportion of substances that can be directly utilized by methanogenic bacteria) or wastewater from food and beverage plants, but is not limited to these, as described below.

[0017] If the sludge concentration is low at the start-up stage when the organic wastewater effluent is introduced into the anaerobic treatment tank 1 and the treatment is started, the tank will not be in an anaerobic state and there will be less space for the symbiotic relationship between the anaerobic bacteria. Therefore, at the start-up stage, the VSS is preferably 10,000 mg / L or more, more preferably 15,000 mg / L or more, and even more preferably 20,000 mg / L or more and 50,000 mg / L or less. If the volume of the seed sludge cannot be secured to the effective volume of the tank, it may be diluted with water (industrial water, treated water, well water, etc.) to secure the required volume, provided that the required activity and VSS (10,000 mg / L or more) can be secured.

[0018] When the anaerobically digested sludge or aerobically treated sludge collected in another tank is dewatered sludge or granules, it is preferable to dilute it with water, crush and mix it with a crushing pump, process it into floating sludge, and then add it to the anaerobic treatment tank 1. In addition, when a membrane separation method is adopted, it is necessary to remove impurities using a separation screen or the like.

[0019] The biological treatment tank from which the seed sludge is collected is not limited to other biological treatment tanks at the same site, but may be biological reactors at other sites or laboratories. In the case of anaerobic digestion sludge, the amount that can be collected from other anaerobic treatment tanks at the same site is at most 200 m per tank. 3 If a larger initial sludge volume is required, sludge will be taken from a biological treatment tank at another site.

[0020] If a large amount of anaerobic digestion sludge is required initially, and if there is no similar facility nearby and it takes a long time to collect the required amount of anaerobic sludge, the sludge already collected may be stored for a long time, reducing the activity of the sludge, and it may take a long time to reach the target load even after start-up has begun.

[0021] Therefore, in the present invention, aerobically treated sludge is used as part of the seed sludge when starting up the anaerobic treatment tank. Aerobically treated sludge is disposed of in larger quantities than anaerobic digestion sludge, and it is easy to obtain a large amount of aerobically treated sludge. The aerobically treated sludge may be any of aeration tank sludge, thickened sludge, and dewatered sludge (which needs to be crushed). Another advantage of aerobically treated sludge is that it contains sufficient essential nutrients and a large amount of refractory organic matter, making it less likely to become rancid during the initial start-up stage.

[0022] The ratio of aerobically treated sludge to the amount of sludge initially charged (when the anaerobic treatment tank is started up) is preferably 50-90% (weight ratio; the same applies below), especially 80-90% (the amount of anaerobic digested sludge added is 10-50%, especially 10-20% of the amount of sludge initially charged). The organic decomposition activity should be 0.2 kg-COD Cr / kg-VSS·d or more, especially 0.3kg-COD Cr A rapid start-up is possible by adding sludge of 1 / kg-VSS·d or more.

[0023] The preferred type of anaerobic treatment is not the carrier method or granular method, but rather a floating-type anaerobic treatment.

[0024] FIG. 1 shows a membrane anaerobic process, but the present invention is also suitable for starting up a transient anaerobic process.

[0025] In the above embodiment, start-up of operation refers to the addition of new seed sludge to the anaerobic treatment tank and the start of the supply of raw water, but in the present invention, start-up also refers to the resumption of operation or operation under an increased load. EXAMPLES

[0026] The examples and comparative examples were carried out under the following experimental conditions.

[0027] <Experimental conditions> Flow: Fig. 1 (Anaerobic treatment tank volume 800m 3 The membrane used in the membrane separator is a UF membrane. Raw water: Food manufacturing wastewater (COD Cr =15000mg / L) ·Raw water supply amount: 300m 3 / d COD Cr Volume load: 6kg / m 3 / d - Target sludge concentration during steady state: 22000mg / L SRT=45d

[0028] [Example 1] The activity of COD was 0.2 kg-COD, which was collected from another anaerobic treatment tank that was treating the same raw water. Cr / kg-VSS·d, VSS=20,000mg / L anaerobic digestion sludge 80m 3 (1 day required to collect sludge) and 720 m of aerobic sludge with a VSS concentration of 20,000 mg / L collected from activated sludge treatment tanks of several food manufacturing plants. 3 (It took 3 days to collect sludge) and put it into the anaerobic treatment tank (total sludge input amount 800m 3 ) and 1 / 10 load (COD Cr Volume load 0.6kg / m 3We have started to launch the system from a base of approximately 1000GB / d.

[0029] As a result, the target load was reached in approximately 60 days, and the VSS concentration was constantly maintained at 20,000 mg / L or higher during the start-up period.

[0030] [Example 2] In Example 1, the anaerobic digestion sludge input amount was 160 m 3 The aerobic sludge input volume was set at 640 m 3 (Total 800m 3 ) and 1 / 8 load (COD Cr Volume load 0.7kg / m 3 The conditions were the same except that the start-up was started from a low of about 100m / d.

[0031] As a result, the target load was reached in about 45 days, and the VSS concentration was constantly maintained at 20,000 mg / L or higher during the start-up period.

[0032] [Example 3] In Example 1, the amount of anaerobic digested sludge input was 400 m 3 The aerobic sludge input volume is set at 400m 3 (Total 800m 3 ) and 1 / 5 load (COD Cr Volume load 1.2kg / m 3 The conditions were the same except that the start-up was started from a low load of about 1 / 5 because it took a long time to secure the anaerobic digestion sludge and the biological activity of the anaerobic digestion sludge that had been secured earlier and was waiting to be secured gradually decreased.

[0033] As a result, the target load was reached in about 40 days, and including the time required to secure sludge, it took a total of about 70 days to complete the start-up.

[0034] [Comparative Example 1] In Example 1, 800 m of anaerobic digestion sludge 3 (60 days to secure sludge) is put into the anaerobic treatment tank and 1 / 5 load (COD Cr Volume load 1.2kg / m 3The conditions were the same except that the start-up started from a low load of about 1 / 5 the load. Because it took a long time to secure the anaerobic digestion sludge, the biological activity of the anaerobic digestion sludge that had been secured earlier and was waiting for the start-up started from 1 / 5 the load.

[0035] As a result, the target load was reached in about 40 days, and including the period required to secure sludge, it took a total of about 100 days to complete the start-up.

[0036] [Comparative Example 2] In Example 1, 80 m of anaerobic digestion sludge 3 (1 day to secure sludge) and 720m of industrial water 3 and put into the anaerobic treatment tank, and the load is 1 / 10 (COD Cr Volume load 0.6kg / m 3 / d), but activity did not increase, and operation was stopped after 10 days due to rancidity. [Explanation of symbols]

[0037] 1 Anaerobic treatment tank 2 Stirring blade 5 Membrane separator 5m separation membrane

Claims

1. 1. A method for operating an anaerobic treatment tank for anaerobically treating organic wastewater, comprising the steps of: A method for operating an anaerobic treatment tank, characterized in that at the time of start-up, anaerobically digested sludge and aerobically treated sludge are added as seed sludge so that the aerobically treated sludge accounts for 50 to 90% (weight ratio) of the total amount of sludge added.

2. 2. The method for operating an anaerobic treatment tank according to claim 1, wherein anaerobic treatment is carried out using suspended sludge.

3. 3. The method for operating an anaerobic treatment tank according to claim 1 or 2, wherein the anaerobically digested sludge is sludge collected from another anaerobic treatment tank treating organic wastewater having the same composition.

4. 4. The method for operating an anaerobic treatment tank according to claim 1, wherein seed sludge is added so that the sludge concentration in the tank is 10,000 to 50,000 mg / L at the time of start-up.

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