JP2013111493A - Biological treatment method of organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological treatment method of organic wastewater capable of shortening the start-up period for a multistage biological treatment apparatus.SOLUTION: The biological treatment method of the organic wastewater has a start-up step for starting up the biological treatment apparatus having a first biological treatment tank 1 and a second biological treatment tank 2 to which raw water is made to flow in order during the normal operation. At starting up, a second biological treatment tank start-up step for supplying at least a part of the raw water to the second biological treatment tank 2 and starting up the second biological treatment tank 2 is performed, and then, water is made to flow from the first biological treatment tank 1 to the second biological treatment tank 2 in series, and the operation is shifted to the normal operation.

Description

  The present invention relates to a biological treatment method for organic wastewater that can be used for treatment of organic wastewater in a wide concentration range including domestic wastewater, sewage, food factories and pulp factories, and in particular, biological treatment equipment. The present invention relates to a biological treatment method for organic wastewater that can be launched in a short period of time.

The activated sludge method used when biologically treating organic wastewater is widely used for sewage treatment, industrial wastewater treatment, and the like because of its advantages such as good treated water quality and easy maintenance. However, since the BOD volumetric load in the activated sludge method is generally about 0.5 to 0.8 kg / m ³ / d, a large site area is required. Moreover, since 20 to 40% of the decomposed BOD is converted into microbial cells, that is, sludge, a large amount of excess sludge treatment is also a problem.

For high-load treatment of organic wastewater, a fluidized bed method in which a carrier is added to a reaction tank is known. According to this fluidized bed method, it is possible to operate with a BOD volume load of ³ kg / m ³ / d or more. However, this method has a disadvantage that the amount of generated sludge is about 30 to 50% of the decomposed BOD, which is higher than that of a normal activated sludge method.

  In Patent Documents 1 and 2, the organic wastewater is first treated with bacteria in the first treatment tank, the organic matter contained in the wastewater is oxidatively decomposed and converted into non-aggregating bacterial cells, and then the second treatment. It is described that the amount of excess sludge can be reduced by precipitating and removing the sticking protozoa in the tank.

  As a method of shortening the startup period of the apparatus from the start of raw water flow to the biological treatment apparatus until steady operation, Patent Document 3 added ammonium sulfate to the wastewater to be treated as raw water for startup. It describes the passage of raw water with a high substrate concentration. Patent Document 3 relates to a method for starting up a single tank type biological treatment tank in which only one treatment tank is installed, and there is no description about a method for starting up a multi-tank type biological treatment tank.

  Bacteria are fixed on the carrier. If the bacteria are fixed to a certain extent, the bacteria are fixed in layers on the carrier, so that the amount of cells retained increases rapidly. However, in multistage treatment, since the components flowing into the subsequent biological treatment are difficult to decompose, the growth of bacteria that directly settle on the carrier surface is slow, and as a result, the time to reach the target treated water quality (start-up time) is reduced. It will be slower than single tank type biological treatment. Even if microbes are fixed on the carrier for promoting sludge reduction, stable fixation is difficult unless bacteria are fixed on the surface of the carrier, and it takes time to exert the sludge reduction effect.

JP 2006-51414 A JP2008-36580 JP-A-8-71575

  An object of this invention is to provide the biological treatment method of the organic waste water which can shorten the starting period of a multistage type biological treatment apparatus.

  The biological treatment method for organic wastewater according to the present invention starts up a biological treatment apparatus having first to nth (n is an integer of 2 or more) biological treatment tanks through which raw water is sequentially passed during steady operation. In the biological treatment method for organic wastewater having a raising process, at the time of startup, at least a part of the raw water is supplied to the nth biological treatment tank, and the nth biological treatment tank is started up. It is characterized by performing.

  In the present invention, it is preferable to perform the n-th biological treatment tank startup process until the n-th biological treatment tank removes 90% or more of organic substances in the raw water.

  Moreover, in the n-th biological treatment tank startup process, it is preferable to supply raw water to the n-th biological treatment tank at a load of 20 to 50% of the raw water load on the biological treatment apparatus during steady operation.

  When the biological treatment apparatus is composed of two tanks, ie, a first biological treatment tank and a second biological treatment tank, the second biological treatment tank is first started, and then the first biological treatment tank and the second biological treatment tank in this order. Pass raw water and shift to steady operation. In this steady operation, the entire amount of raw water may be supplied to the first biological treatment tank, most of the raw water is supplied to the first biological treatment tank, and part of the raw water is supplied to the second biological treatment tank. May be.

  In the present invention, at the time of start-up, at least a part of the raw water is directly supplied to the biological treatment tank at the subsequent stage. Then, after the bacteria have settled on the carrier to some extent, the operation shifts to a serial water passing operation in which water passes through the first biological treatment tank in order from the first biological treatment tank, and preferably the load is gradually increased. Thereby, colonization of the hardly decomposable organic matter-degrading bacteria and micro-animals in the biological treatment tank on the rear stage side can be promoted, and the start-up period in the entire biological treatment apparatus can be shortened.

It is explanatory drawing of the biological treatment method of the organic waste_water | drain which concerns on embodiment. It is explanatory drawing of the biological treatment method of the organic waste_water | drain which concerns on embodiment.

  Embodiments of a biological treatment method and apparatus for organic wastewater according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a system diagram showing a biological treatment method for organic wastewater according to the present invention. FIG. 1 (a) shows a start-up, FIG. 1 (b) shows another start-up, and FIG. 1 (c) shows a steady operation. .

  First, the steady operation will be described with reference to FIG. Raw water (organic wastewater) is introduced into the first biological treatment tank 1, and 70% or more, desirably 80% or more, more desirably 90% or more of the organic component (soluble BOD) is oxidatively decomposed by dispersible bacteria. The The pH of the first biological treatment tank 1 is 6 or more, preferably 8 or less. However, when the raw water contains a large amount of oil, the pH may be 8 or more.

BOD volume load to the first biological treatment tank 1 is 1 kg / m ³ / d or more, for example 1 to 20 kg / m ³ / d, and HRT (raw water residence time) is 24 h or less, for example 0.5 to 24 h. It is preferable because treated water predominated by dispersible bacteria can be obtained, and waste water having a low BOD concentration can be treated with a high load by shortening the HRT.

  In addition, the dissolved oxygen concentration in the first biological treatment tank 1 is preferably controlled to 1 mg / L or less, particularly 0.5 mg / L or less, particularly 0.1 mg / L or less. The dispersible bacteria become dominant, and these are rapidly preyed on by the small animals in the second biological treatment tank 2.

  A part of the sludge from the second biological treatment tank 2 or the subsequent solid-liquid separation tank may be returned to the first biological treatment tank 1.

  If the HRT of the first biological treatment tank 1 is longer than the optimum value, it leads to the predominance of filamentous bacteria and the formation of flocs, and bacteria that are difficult to be preyed on by the microanimals in the second biological treatment tank 2 at the subsequent stage. It will generate. Therefore, it is preferable to control the HRT of the first biological treatment tank 1 to be constant. Since this optimum HRT varies depending on the quality of raw water, it is preferable to obtain an HRT capable of removing 70 to 95% of organic components from a desktop test or the like. As a method of maintaining the HRT at an optimum value, when the raw water flow rate is reduced, a part of the treated water is returned and the amount of water flowing into the first biological treatment tank 1 is made constant, so that the first biological treatment tank 1 There are a method of stabilizing the HRT and a method of changing the water level of the first biological treatment tank 1 in accordance with the fluctuation of the raw water flow rate. It is desirable that the width for stabilizing the HRT of the first biological treatment tank 1 be within the range of 0.75 to 1.5 times the optimum HRT obtained by the desktop test.

  In addition, when dissolved organic matter is completely decomposed in the first biological treatment tank 1, flocs are not formed in the second biological treatment tank 2, and nutrients for microanimal growth are insufficient, and sludge with low compactness is used. Only becomes the dominant biological treatment tank. Therefore, it is preferable that the decomposition rate of the organic component in the first biological treatment tank 1 is not 100% but 95% or less.

  About the treated water (1st biological treated water) of the 1st biological treatment tank 1, it introduce | transduces into the 2nd biological treatment tank 2 of a back | latter stage, oxidative degradation of the remaining organic component, self-decomposition of dispersible bacteria, and a micro animal Reduction of excess sludge by predation.

  In the second biological treatment tank 2, it is preferable to use an operation condition and a treatment apparatus that allow the microanimal and the bacteria to remain in the system in order to utilize the action of the microanimal having a slower growth rate than the bacteria and the autolysis of the bacteria. . Therefore, it is desirable that the second biological treatment tank 2 increases the retained amount of the micro-animal in the tank by forming a fluidized bed in which the carrier is added in the aeration tank. The shape of the carrier added to the second biological treatment tank 2 is arbitrary such as a spherical shape, a pellet shape, a hollow cylindrical shape, a thread shape, a plate shape, and the size may be about 0.1 to 10 mm. The material of the carrier is arbitrary such as a natural material, an inorganic material, or a polymer material, and a gel material may be used.

  In the second biological treatment tank 2, since a large amount of scaffolding for maintaining the micro-animal is required, the filling rate of the carrier to be added is 10% or more, desirably 20% or more, for example, 20 to 40%. Is desirable.

  In the present invention, when a large amount of organic matter remains in the first biological treatment water introduced into the second biological treatment tank 2, the oxidative decomposition is performed in the second biological treatment tank 2. However, when oxidative degradation of organic matter by bacteria occurs in the second biological treatment tank 2 in which a large amount of micro animals are present, it is known that the bacteria grow in a form that is difficult to be predated as a countermeasure to escape from predation of the micro animals. Thus, the bacteria that have grown in this way are not preyed on by the micro-animals, and their decomposition depends only on autolysis, which reduces the effect of reducing the amount of sludge generated.

  Therefore, as described above, in the first biological treatment tank 1, most of the organic components in the raw water, that is, 70% or more, preferably 80% or more of the raw water BOD, is decomposed and stably converted into cells. Is preferred. Therefore, it is desirable that the first biological treatment tank 1 be a fluidized bed type filled with a carrier. However, when the filling rate of the carrier added to the first biological treatment tank 1 is high, dispersible bacteria are not generated, and the bacteria adhere to the carrier or the filamentous bacteria grow. The filling rate of the carrier to be added is preferably 20% or less, desirably 10% or less, for example, 3 to 10%. This makes it possible to produce dispersible bacteria that are not affected by concentration fluctuations and are easy to prey. .

  In addition, there is no restriction | limiting in particular as a support | carrier filled with this 1st biological treatment tank 1, The thing similar to the support | carrier filled with the above-mentioned 2nd biological treatment tank 2 can be used.

  In addition, as described above, in the first biological treatment tank 1, most of the organic components in the raw water, that is, 70% or more, preferably 80% or more, more preferably 90% or more of the raw water BOD, is decomposed into cells. However, since an appropriate organic load is required even in the second biological treatment tank, a part of the raw water is directly introduced into the second biological treatment tank 2, and the second biological treatment tank 2 It is desirable to operate so that the sludge load due to the soluble BOD is 0.01 to 0.05 kg-BOD / kg-MLSS / d.

  Although illustration is abbreviate | omitted, the treated water (2nd biological treatment water) of the 2nd biological treatment tank 2 is introduce | transduced into a 3rd biological treatment tank, the organic substance which could not be decomposed | disassembled in the 2nd biological treatment tank 2, dispersible bacteria, You may make it aim at the reduction | decrease of sludge further by decomposing | disassembling the solid substance derived from raw | natural water. In this case, the third biological treatment tank is started up first, and then the second biological treatment tank is started by passing raw water in the order of the second biological treatment tank → the third biological treatment tank. Water is passed in the order of the biological treatment tank, the second biological treatment tank, and the third biological treatment tank, the first biological treatment tank is started up, and a transition is made to steady operation.

  In the present invention, in order to promote predation by micro animals, in the second and subsequent biological treatment tanks, particularly in the second biological treatment tank 2, the pH is set to 7 or less, for example, pH 5.5 to 6.5. It is preferable.

  In addition, even if the operating conditions are set to be suitable for the growth of micro-animals, the micro-animals will not proliferate and the sludge reduction effect will not improve unless the raw water contains essential ingredients for the micro-animal growth. . Therefore, a nutrient may be added to the second and subsequent biological treatment tanks, in particular, the second biological treatment tank 2 to stably maintain the micro animals, thereby stabilizing the sludge reduction effect. Moreover, when the 3rd biological treatment tank is installed, you may accelerate | stimulate the weight loss effect by adding a nutrient to a 3rd biological treatment tank. Nutrients include phospholipids, free fatty acids, lysophospholipids, sterols and lecithins containing these, liquid sugar, rice bran, beer pomace, vegetable oil pomace, soy extract, sugar beet bowl, shellfish powder, Nutrients effective in promoting the growth of metazoans such as eggshell, vegetable extract, fish meat extract, various amino acids, various vitamins, and the like can be used. These may be used alone or in combination of two or more.

  When these nutrients are added, the addition amount is preferably about 0.5 to 10% by weight of the amount of organic matter in the raw water.

  Next, the startup operation method will be described.

  If the flow rate of raw water is small at the time of start-up, or the organic matter concentration in raw water is low and the load is low, first, as shown in FIG. The processing tank 2 is started up. When the flow rate of raw water is high or the organic matter concentration in the raw water is high and the load is high, a part of the raw water is directly flowed into the second biological treatment tank 2 to promote the initial colonization of the bacteria and the remaining raw water is used as the first organism. It is preferable to introduce into the treatment tank 1.

  The raw water load flowing into the second biological treatment tank 2 is preferably equal to or less than the assumed raw water load × (second biological treatment tank volume / total volume of the first and second biological treatment tanks). The assumed raw water load is the raw water load (the product of the raw water flow rate and the dissolved organic matter concentration) during steady operation. After positively applying a load to the subsequent stage in this way, after obtaining an organic substance removing ability capable of removing 90% or more, preferably 95% or more of organic substances in the raw water at a load of 20% or more, preferably 30 to 50% of the assumed raw water load. By shifting to the multistage serial operation of steady operation, colonization of the bacteria is promoted, and the period until the target organic matter removal ability and sludge reduction rate at the assumed load are achieved can be shortened.

  If a third or later biological treatment tank is installed, start up with the highest load on the most downstream biological treatment tank first, and then start up the upstream biological treatment tank sequentially. Just drive.

  When starting up the 2nd biological treatment tank 2, you may supply a part of raw | natural water to the 1st biological treatment 1 like FIG.1 (b). In this case, the raw water load flowing into the second biological treatment tank 2 is 20% or more of the assumed raw water load, preferably 30 to 50%, and the raw water supply amount supplied directly to the second biological treatment tank 2 is the first. The raw water supply flow rate to the one biological treatment tank 1 is increased (for example, 1.2 to 5 times the amount).

  When starting up the second biological treatment tank 2, as shown in FIG. 2, the effluent water of the second biological treatment tank 2 is introduced into the coagulation tank 3, and an inorganic coagulant such as ferric chloride and PAC and a polymer coagulant. May be introduced into the sedimentation tank 4 for solid-liquid separation, the supernatant water may be taken out as treated water, and a part of the concentrated sludge that has settled may be returned to the second biological treatment tank 2. Thereby, the start-up time can be further shortened. Further, the solid-liquid separation may be a pressure floating separation.

  The following Examples and Comparative Examples were performed using food processing wastewater (BOD 800 mg / L, pH 6) as raw water.

Example 1 (FIG. 1)
Startup was carried out by the water flow method shown in FIG. The capacity of the first biological treatment tank 1 (without sludge return) is 2.5L, and the capacity of the second biological treatment tank 2 (without sludge return) is 4.4L. The first biological treatment tank 1 was operated with DO of 0.5 mg / L, and the second biological treatment tank 2 with DO of 2-3 mg / L. Further, a fluidized bed having a carrier filling rate of 5% was formed in the first biological treatment tank 1, and a carrier was added to the second biological treatment tank at a filling rate of 40% to obtain a fluidized bed. Both carriers are 5 mm square urethane foam. Before starting water flow, 500 ml of wastewater treatment plant sludge (MLSS 2000 mg / L) was added to each tank as seed sludge.

From the start of operation to the fifth day, raw water was passed through the second biological treatment tank 2 only at a flow rate of 0.22 L / hr (30% of the assumed raw water load). Five days after the start of operation, the dissolved organic matter removal rate reached 90% or more, so the raw water flow rate was 0.43 L / hr (60% of the assumed raw water load) from the first biological treatment tank 1 to the second biological treatment tank 2. Series water was passed. Since dissolved organic matter removal rate of 90% or more was reached on the 2nd day (7th day after the start of operation) after the series water transfer, the raw water flow rate was 0.72L / hr (100% of the assumed raw water load) on the 8th day after the start of the operation. And BOD volumetric load of the first biological treatment tank 1 5.5 kg-BOD / m ³ / d, HRT 3.5 h, overall BOD volumetric load 2.0 kg-BOD / m ³ / d, HRT 9.6 h Drove in. After 10 days from the start of operation, the soluble organic matter removal rate was always maintained at 95%, and the sludge conversion rate was 0.20 kg-MLSS / kg-BOD. Therefore, the number of days required to obtain the predetermined performance (the number of days required for starting up the entire biological treatment apparatus) was 10 days.

Example 2 (FIG. 2)
In Example 1, when the second biological treatment tank 2 is started up, treated water flowing out from the second biological treatment tank 2 is introduced into the coagulation tank 3 as shown in FIG. After 200 mg / L of PAC was added, it was introduced into the sedimentation tank 4 and separated into solid and liquid, the supernatant water was taken out as treated water, and a part of the sludge was returned to the second biological treatment tank 2. Other conditions were the same as in Example 1 and start-up was started.

Specifically, 500 ml of wastewater treatment plant sludge (MLSS 2000 mg / L) is added to each tank as seed sludge before the start of water flow, and the raw water flow rate is the same as in Example 1 for the first day from the start of operation. It was supplied only to the second biological treatment tank 2 at 0.22 L / hr (30% of the assumed raw water load). From the second day after the start of operation, 2000 mg-SS / L of concentrated sludge separated into solid and liquid in the sedimentation tank 4 was returned to the second biological treatment tank 2 at 200 mL / hr. Three days after the start of operation, the dissolved organic matter removal rate reached 90% or more, so the raw water flow rate was 0.43 L / hr (60% of the assumed raw water load) from the first biological treatment tank 1 to the second biological treatment tank 2. Series water was passed. The concentrated sludge was returned in the same manner. After the transition to series water flow, 90% or more of the soluble organic matter removal rate was achieved, so the raw water flow rate was set to 0.72 L / hr (100% of the assumed raw water load) on the fifth day after the start of operation. The tank 1 was operated under the conditions of BOD volumetric load 5.5 kg-BOD / m ³ / d, HRT 3.5 h, overall BOD volumetric load 2.0 kg-BOD / m ³ / d, HRT 9.6 h. Thereafter, a soluble organic matter removal rate of 95% was always maintained, and the sludge conversion rate was 0.20 kg-MLSS / kg-BOD. Therefore, the number of days required to obtain the predetermined performance (the number of days required for starting up the entire biological treatment apparatus) was 5 days.

Comparative example 1 (start-up by serial water flow)
In Example 1, raw water was passed in series from the first biological treatment tank 1 to the second biological treatment tank 2 immediately after the start of operation. In addition, like Example 1, DO of the 1st biological treatment tank 1 was 0.5 mg / L, and DO of the 2nd biological treatment tank 2 was 2-3 mg / L. In addition, a carrier is added to the first biological treatment tank 1 and the second biological treatment tank 2 under the same conditions as in Example 1, and each wastewater treatment plant sludge (MLSS 2000 mg / L) is used as seed sludge before the start of water flow. 500 ml each was added to the tank.

  Immediately after the start of operation, it was operated at a raw water flow rate of 0.22 L / hr (30% of the assumed raw water load), and 7 days after the start of operation, the dissolved organic matter removal rate reached 90% or more, so the raw water flow rate was 0.43 L / hr. Shifted to water flow (60% of assumed raw water load). After that, since the dissolved organic matter removal rate reached 90% or more on the 7th day (14 days from the start of operation), the raw water flow rate changed to 0.72 L / hr (100% of the assumed raw water load) on the 15th day from the start of the operation. The number of days required to maintain the removal rate of soluble organic matter of 95% after the transition to the assumed raw water load of 100% was 10 days. In addition, it took 15 days after 100% water flow for the sludge conversion rate to be 0.20 kg-MLSS / kg-BOD. Accordingly, the required startup time for obtaining the predetermined performance was 30 days.

1 First biological treatment tank 2 Second biological treatment tank 3 Coagulation tank 4 Sedimentation tank

Claims (4)

In an organic wastewater biological treatment method having a startup process of starting up a biological treatment apparatus having first to nth biological treatment tanks (n is an integer of 2 or more) through which raw water is sequentially passed during normal operation ,
Biological treatment of organic wastewater characterized by performing an nth biological treatment tank start-up step of supplying at least part of raw water to the nth biological treatment tank and starting the nth biological treatment tank at the time of start-up Method.   2. The biological treatment method for organic wastewater according to claim 1, wherein the nth biological treatment tank is started up until the nth biological treatment tank removes 90% or more of organic matter in the raw water.   In claim 1 or 2, in the n-th biological treatment tank start-up step, the raw water is supplied to the n-th biological treatment tank at a raw water load of 20 to 50% of the raw water load to the biological treatment apparatus during steady operation. A biological treatment method for organic wastewater.   In any 1 item | term of Claim 1 thru | or 3, n is 2, and in the steady operation after the starting process of a 2nd biological treatment tank, whole quantity of raw | natural water is supplied to a 1st biological treatment tank, or raw | natural water is used. A biological treatment method for organic wastewater, characterized by being supplied to a first biological treatment tank and a second biological treatment tank.

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