JP2008142632A - Method for treating waste water biologically - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating waste water biologically which can allow an aeration tank to be miniaturized and in which BOD and extractive substances in normal-hexane can be treated at a high speed and the amount of the waste sludge to be generated is made small. <P>SOLUTION: The method for treating waste water biologically comprises the steps of: making raw waste water flow in a plurality of carrier-used aeration tanks connected in series to treat the raw waste water; finally treating the water treated in the plurality of aeration tanks in an activated sludge tank; and separating the finally-treated water in a precipitation tank while returning the return sludge from the precipitation tank to the activated sludge tank without returning the return sludge to the plurality of aeration tanks. The volume load of BOD in the activated sludge tank is ≤0.8 kg/m<SP>3</SP>-day. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wastewater treatment method for reducing the amount of excess sludge generated in a small space, and is particularly suitable for wastewater containing a normal hexane extract (hereinafter referred to as n-Hex) in a high concentration in the wastewater. Is.

Conventionally, the activated sludge method is often used as biological wastewater treatment. In the activated sludge method, an aeration tank and a sedimentation tank are formed, and a part of the sludge separated in the precipitation tank is returned to the aeration tank and extracted as surplus sludge, and the BOD volumetric load is 0.8 kg / m ³ · day to 1. Steady operation can be performed under conditions of about 5 kg / m ³ · day.

On the other hand, the development of a carrier capable of holding activated sludge at a high concentration is progressing. With the carrier method, operation with a high BOD volume load of ^{3 to 5} kg / m ³ · day is possible, and the aeration tank is downsized. be able to.

Recently, considering the optimization of the carrier method, a combined treatment method has been proposed in which the high-concentration part in the former stage is treated with the carrier method and the diluted part in the latter stage is treated with activated sludge (see, for example, Patent Document 1). ).
JP 2001-145894 A

However, in the activated sludge method, the BOD volume load is limited to about 0.8 to 1.5 kg / m ³ · day, and a large aeration tank is required when high concentration drainage is targeted. On the other hand, in the carrier method, it is possible to operate with a high load, and the aeration tank can be miniaturized. On the other hand, there is a problem in that fine sludge is produced by the treatment by the carrier method, and the conventional sedimentation tank does not settle easily. In addition, in the treatment of n-Hex, a high load treatment sometimes causes a problem in the carrier flow.

  Further, the carrier method will be described in detail. The carrier is not a micro floc such as activated sludge, but microorganisms are attached to a medium having a size of 3 to 10 mm. A big influence. A small carrier with a large specific surface area can have a relatively high processing performance, but it is necessary to reduce the screen width when separating the treatment liquid and the carrier. It becomes difficult. For this reason, a material having an optimum size of 3 to 10 mm is used depending on each carrier material and processing method.

  In addition, since the size of the carrier is larger than the floc of activated sludge, even if a large amount of sludge is attached to the carrier, if the substrate is diluted by the treatment, the diffusion of the substrate becomes rate limiting, and the treatment speed is increased. descend. In other words, in the carrier method, the diffusion rate of the substrate is generated, so that it becomes a primary reaction that depends on the concentration with respect to the zero-order reaction of activated sludge that does not depend on the concentration.

  The above-mentioned method of combining the carrier method and activated sludge can be processed even on a diluted substrate, which is a disadvantage of the carrier method, and by arranging the activated sludge treatment in the subsequent stage, fine sludge that is peeled off from the carrier can be removed. It can be co-precipitated. However, even in the method combining the carrier method and the activated sludge, surplus sludge is generated 30 to 50% of the removed BOD, and the generated surplus sludge has to be dehydrated and disposed of.

  An object of the present invention is to provide a method capable of reducing the size of a biological reaction tank and reducing the amount of excess sludge produced in a wastewater treatment method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that by arranging a plurality of aeration tanks to be treated in the preceding carrier method in series, the amount of sludge generation is reduced and the treatment accuracy is improved. The invention has been reached.

That is, according to the present invention, wastewater containing normal hexane extract material is treated by flowing into an aeration tank containing a carrier, and then treated by flowing into an activated sludge tank, and then sludge and treated water are separated in a sedimentation tank. A gist of the biological treatment method of wastewater is characterized in that wastewater is sequentially introduced into a plurality of aeration tanks arranged in series and treated, and sludge separated in the settling tank is returned to the activated sludge tank. Preferably, the carrier is one or more types of carriers selected from the group consisting of a gel carrier, a plastic carrier and a fiber carrier, and preferably BOD when flowing into the activated sludge tank In the biological treatment method for waste water described above, the treatment is performed while adjusting the volumetric load amount to 0.8 kg / m ³ · day or less.

  According to the present invention, the surplus sludge generation amount is 0 to 20%, which is smaller than the surplus sludge generation amount 30 to 40% of the conventional activated sludge method. Moreover, the installation area of the wastewater treatment facility can be reduced to about one third, and the initial cost can be reduced to 70 to 80% as compared with the activated sludge method.

  Hereinafter, the present invention will be described in detail.

  In the treatment method of the present invention, first, raw waste water is caused to flow into an aeration tank containing a carrier. At this time, it is necessary to arrange a plurality of aeration tanks in series and allow them to flow sequentially.

  In the present invention, by utilizing the concept of the primary reaction that is the removal characteristic of the carrier method, the tank in which the carrier is made to flow is finely divided, and the difference in concentration in the BOD concentration in each water tank is provided, thereby increasing the diffusion rate to the carrier. It speeds up and improves the removal speed. That is, BOD can be removed faster by treating wastewater of high concentration BOD with a carrier tank arranged in series than when treating with a single tank carrier method. The tank configuration arranged in series divided into a plurality is referred to as the number of stages. For example, the case of three tanks is referred to as three-stage processing.

  Further, by performing multistage processing, not only the BOD processing is speeded up, but also the amount of sludge generated is reduced. If the operation is performed with a low BOD load by the activated sludge treatment disposed at the subsequent stage of the carrier treatment, the self-decomposition of the sludge is further promoted. According to the properties of the raw water, there is a case where almost no excess sludge is generated, but as a result, it can be suppressed to a 10-20% excess sludge conversion rate. The excess sludge conversion rate is expressed as a ratio of the difference between the SS of raw water and treated water and the difference of BOD, and is about 30 to 40% in the activated sludge treatment.

  In the aeration tank according to the present invention, in order to minimize the aeration tank by utilizing the decomposition characteristics of BOD by the primary reaction of the carrier, there is a fixed bed-like treatment method in which the carrier is fixed and only the waste water flows through the plug flow. Although preferable, it is difficult when the carrier is flowing. Therefore, by dividing the aquarium and providing a screen for each aquarium, by preventing the carrier from going back and forth between the aquariums, the processing characteristics that combine the characteristics of the fluidized bed and the fixed bed are given, and the primary A reaction tank close to the reaction can be made.

  Drainage containing more than 300 mg / L of n-Hex concentration may make flow difficult due to accumulation of oil in the carrier. However, when n-Hex concentration is 300 mg / L or less, Determine the capacity and number of stages. The amount of sludge produced varies depending on the type of drainage and the SS / BOD load, but the sludge conversion rate is approximately 10 to 18%.

The capacity of the aeration tank varies depending on the type of wastewater, the raw water BOD concentration and the BOD load, but in the case of easily degradable food wastewater, wastewater with a soluble BOD (hereinafter referred to as s-BOD) concentration of 3000 mg / L or more If there is, the capacity can be determined with the first stage aeration tank as a BOD volumetric load of 10-15 kg / m ³ · day.

  As the BOD volumetric load is increased, the aeration tank can be reduced in size and the initial cost can be reduced. The idea of increasing the BOD volumetric load is a method of dividing the aeration tank of the present invention and arranging them in series. The higher the BOD concentration of raw water and the higher the ratio of s-BOD, the faster the diffusion rate and the smaller the size. Can do.

  Aeration in the aeration tank supplies oxygen necessary for decomposition of BOD. When the amount of oxygen to be supplied is insufficient, oxygen becomes a limiting factor inside the carrier, and the decomposition of BOD is suppressed. In addition, if the decay of BOD progresses inside the carrier, the pH may decrease and the BOD decomposition rate may decrease. In consideration of the balance between the oxygen supply amount (rate-limiting) and the s-BOD concentration, the limit is about BOD concentration of about 5000 mg / L for a carrier having a size of about 8 mmφ and being easily porous. Thick drainage more than this may be diluted with dilute treated water and treated, and oxygen aeration is not limited to this and can be applied to higher drainage.

  Various known carriers can be used as the fluid carrier, but one kind of carrier selected from a gel carrier, a plastic carrier and a fiber carrier, or a combination of two or more of these carriers may be used. In particular, a fiber carrier having a porosity of 85%, good adhesion to sludge, and a large amount of sludge retained can be used in a range of 5 to 30% of the tank volume from the viewpoint of processability and fluidity. It is preferable that it is in the range of 10 to 20%.

  In the present invention, the water treated by the carrier method is treated by the activated sludge method.

Fine sludge generated in the aeration tank using the carrier is taken into the floc and has the effect of improving sedimentation. The purpose of the present invention is to reduce the amount of excess sludge to be generated. To reduce the amount of generated sludge, the BOD load of the wastewater containing microorganisms in the aeration tank using the carrier is 0.8 kg / m ³ · day or less. Is to design the aquarium. If the activated sludge tank becomes too large, it may be divided into a plurality of pieces and arranged in parallel. In other words, in the activated sludge tank closest to the sedimentation tank, it is necessary to adjust the amount of aeration so that flocs do not become extremely fine due to excessive aeration, so the parallel structure with simple control is superior to the serial structure where control is complicated .

  In this invention, the water processed by the activated sludge tank is introduce | transduced into a sedimentation tank, and it isolate | separates by settling sludge and obtains treated water. At this time, the entire amount of sludge settled in the settling tank or 80 to 90% is distributed and returned to the activated sludge tank.

  The wastewater to which the treatment method of the present invention can be applied is only required to have an n-Hex concentration of 300 mg / L or less. If it exceeds 300 mg / L, the flow of the carrier may be impaired. If it is 300 mg / L or less, the process is appropriately performed in each stage in designing the BOD volumetric load.

  Hereinafter, the present invention will be further described with reference to the drawings.

  FIG. 1 is a schematic flow diagram in which aeration tanks are arranged in three stages in series, and an activated sludge tank is disposed at the subsequent stage of the aeration tank. The first aeration tank 1, the second aeration tank 2 and the third aeration tank 3 are divided in three stages in series, and a screen 7 is provided in the upper part of each aeration tank, and the water treated in each aeration tank is a carrier. So that the treated water flows into the next tank.

The aeration tank using the carrier in the present invention varies depending on the type of waste water and the raw water BOD concentration. In the field of easily degradable food waste water, if it is raw water having an s-BOD concentration of 3000 mg / L or more, the first aeration tank The capacity can be determined as 1 BOD volumetric load of 10-15 kg / m ³ · day. The BOD removal rate of the first aeration tank 1 is empirically obtained to be about 40 to 50%. The inflow raw water of the second aeration tank 2 has a BOD concentration of 1500 to 1800 mg / L, and can be designed with a removal rate of 50 to 60% in a treatment of ^{5 to} 7 kg / m ³ · day as a BOD load. At this time, the treated water BOD of the second aeration tank 2 is 720 to 750 mg / L. The third aeration tank 3 has a BOD load of 3 to 4 kg / m ³ · day, and a BOD removal rate of 70 to 75% is obtained. The treatment water BOD concentration in the third aeration tank 3 is 180 to 220 mg / L, and the BOD concentration can be processed to 300 mg / L or less by serial three-stage treatment of the aeration tank in which the carrier is flowed.

  The sludge 9 settled in the settling tank 5 distributes and returns the entire amount or 80 to 90% to the activated sludge tank 4 depending on the type of drainage.

Hereinafter, the present invention will be described in detail by way of examples.
Example 1
BOD 2000 mg / L, SS by a wastewater treatment experiment apparatus comprising a 200 L raw water adjustment tank, 3 aeration tanks using a 100 L carrier, 200 L activated sludge tank, and 200 L sedimentation tank Food wastewater of 350 mg / L and n-Hex 200 mg / L was continuously processed at a flow rate of 600 L / day. The aeration tank using the carrier was filled with a fiber carrier with a bulk density of 20% with respect to the water tank capacity.

The flow in Example 1 is schematically shown in FIG. Based on the present invention, the BOD volumetric load of the first tank in the aeration tank using the carrier is 12 kg / m ³ · day, the second tank is 7.2 kg / m ³ · day, and the third tank is 4.1 kg / m ^3.・ It became day, and the operation was performed with the BOD load of the activated sludge tank being 0.66 kg / m ³ · day. The sludge was returned at 600 L / day, the same as the amount of raw water. As a result, the SS of the mixed solution flowing out from the third aeration tank 3 using the carrier was reduced to 180 mg / L. The activated sludge tank 4 has a BOD load of 0.66 kg / m ³ · day and a BOD-SS load of 0.17 kg / kg · day, so that the SS further decreases, and 15 mg / L of treated water leaks (sludge amount of 0. 009 kg / day). Further, n-Hex was 40 mg / L in the first aeration tank 1 using the carrier, and 3 mg / L in the second aeration tank 2.

Comparative Example 1
A wastewater treatment experiment apparatus comprising a raw water adjusting tank having a capacity of 200 L, an aeration tank 1 in which a carrier having a capacity of 600 L was flowed, an activated sludge tank 4 having a capacity of 200 L, and a sedimentation tank 5 having a capacity of 200 L, and Example 1 The same food wastewater was continuously treated at a flow rate of 600 L / day. The aeration tank 1 using the carrier was filled with a fiber carrier in a bulk volume of 20% with respect to the water tank capacity.

The flow in Comparative Example 1 is schematically shown in FIG. The BOD load in the aeration tank 1 using the carrier was 2 kg / m ³ · day. The activated sludge tank 4 was operated at a BOD volume load of 0.36 kg / m ³ · day. The sludge was returned at 600 L / day, the same as the amount of raw water.

As a result, SS flowing out from the carrier fluidized tank was 240 mg / L, which was slightly reduced from 350 mg / L of raw water SS. Activated sludge is operated with a BOD load of 0.36 kg / m ³ · day, a BOD-SS load of 0.12 kg / kg · day, SS is further reduced, and 20 mg / L leaks as treated water (0.012 kg / day). The sludge was not extracted as surplus sludge. n-Hex was 4 mg / L in the aeration tank 1 using the carrier and 0.7 mg / L in the activated sludge.

Comparative Example 2
Food wastewater similar to that of Example 1 was continuously processed at a flow rate of 600 L / day by a wastewater treatment experimental apparatus including a 200 L raw water adjusting tank, a 1000 L activated sludge tank 4, and a 200 L sedimentation tank 5. The sludge was returned at 600 L / day, the same as the amount of raw water. The flow in Comparative Example 2 is schematically shown in FIG. The activated sludge tank has a BOD load of 1.2 kg / m ³ · day, a BOD-SS load of 0.3 kg / kg · day, and 12 mg / L of SS flows into the treated water, resulting in an excess sludge of 0.57 kg / day. Sun sludge was generated. n-Hex was processed to 5 mg / L.

Comparative Example 3
Food wastewater similar to that of Example 1 was continuously processed at a flow rate of 600 L / day using a wastewater treatment experimental apparatus including a 200 L raw water adjusting tank, a 500 L activated sludge tank, and a 200 L sedimentation tank. The tank capacity was the same as the sum of the aeration tank and the activated sludge tank in which the carrier of Example 1 was flowed. The sludge was returned at 600 L / day, the same as the amount of raw water. The flow in Comparative Example 3 is the same as that in Comparative Example 2. The activated sludge tank has a BOD load of 2.4 kg / m ³ · day, a BOD-SS load of 0.6 kg / kg · day, 20 mg / L of SS flows into the treated water, and surplus sludge is 0.69 kg / Sun sludge was generated. n-Hex was processed to 15 mg / L.

Example 2
Food wastewater similar to that in Example 1 by using a wastewater treatment experiment apparatus comprising a raw water adjustment tank having a capacity of 200 L, three aeration tanks using a carrier having a capacity of 100 L, an activated sludge tank having a capacity of 150 L, and a 200 L sedimentation tank. Was continuously processed at a flow rate of 600 L / day. The aeration tank 1 using the carrier was filled with a fiber carrier in a bulk volume of 20% with respect to the water tank capacity.

The BOD volume load of the first aeration tank using the carrier is 12 kg / m ³ · day, the second aeration tank 2 is 7.2 kg / m ³ · day, and the third aeration tank 3 is 4.1 kg / m ³ · day. The activated sludge tank was operated at a BOD load of 0.88 kg / m ³ · day. The return was performed at 600 L / day, the same as the amount of raw water. As a result, the SS of the mixed solution flowing out from the third aeration tank 3 using the carrier is 180 mg / L, which is lower than the raw water SS. The activated sludge tank 4 is operated with a BOD load of 0.88 kg / m ³ · day, a BOD-SS load of 0.22 kg / kg · day, 15 mg / L leaked as treated water (sludge amount 0.009 kg / day), surplus sludge 0.06 kg / day of sludge was generated. Further, n-Hex was 40 mg / L in the first aeration tank 1 using the carrier, and 5 mg / L in the second aeration tank.

  Table 1 shows a summary of the water tank capacity, sludge generation amount, and n-Hex treatment results of each Example / Comparative Example.

In Example 1, the removal rate of 40 to 50% or more of BOD is obtained in the first aeration tank using a carrier, and 300 mg / L or less for raw water with a raw water BOD concentration of 2000 mg / L. a three-stage process, then, following 0.8 kg / ^{m 3} · day BOD load in the activated sludge tank 4, which was carried out at 0.2 kg / kg · day following design in BOD-SS load is the most sludge The amount was small and the processing apparatus was compact, and n-Hex was also relatively low at 3 mg / L.

In Comparative Example 3, which is an activated sludge treatment with the same capacity, the amount of sludge generated was the largest, and the n-Hex treatment was also poor. In order to make the n-Hex treatment at the same level in the activated sludge treatment, twice the water tank capacity was required as in Comparative Example 2, but the amount of sludge generated was not equivalent. In order to reduce the amount of generated sludge, a combination with an aeration tank using a carrier as in Examples 1 and 2 and Comparative Example 1 is required. In the case of Comparative Example 1 in which a single-stage aeration tank and an activated sludge tank were combined, twice as many carrier tanks were required as compared with the treatment in the three-stage aeration tank in series. Further, even in the same three-stage aeration tank as in Example 1 as in Example 2, the BOD load of the activated sludge tank after the treatment exceeds 0.8 kg / m ³ · day, and the BOD-SS load is 0.2 kg. / Kg · day, the amount of sludge generated tended to increase.

It is a schematic explanatory drawing which shows one embodiment of the biological treatment method of the waste_water | drain of this invention. It is a schematic explanatory drawing which shows the biological treatment method of the waste_water | drain in the comparative example 1. It is a schematic explanatory drawing which shows the biological treatment method of the waste_water | drain in the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st aeration tank 2 2nd aeration tank 3 3rd aeration tank 4 Activated sludge tank 5 Sedimentation tank 6 Carrier 7 Screen 8 Blower 9 Sludge

Claims (3)

In a treatment method in which wastewater containing normal hexane extract material is treated by flowing into an aeration tank containing a carrier and then flowing into an activated sludge tank for treatment, and then separating sludge and treated water in a sedimentation tank. A biological treatment method for wastewater, characterized in that wastewater is sequentially introduced into a plurality of aerated tanks for treatment, and sludge separated in the settling tank is returned to the activated sludge tank. The biological treatment method of waste water according to claim 1, wherein the carrier is at least one carrier selected from the group consisting of a gel carrier, a plastic carrier and a fiber carrier. The biological treatment method for wastewater according to claim 1 or 2, wherein the treatment is carried out while adjusting the BOD volumetric load when flowing into the activated sludge tank to be 0.8 kg / m ³ · day or less.