JP2007000758A - Method for treating organic substance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating an organic substance enabling an aeration not intermittent but continuous in treatment facilities which makes an aeration tank serve as a role of a denitrification tank and requires no separate denitrification tank. <P>SOLUTION: BOD of the organic substance and nitrogen in the aeration tank 12 are treated by aerating from an air diffuser pipe 14 mounted on an area having 30 to 70% of the bottom area and/or the volume of the aeration tank 12, preferably making the solution of this area aerobic having a dissolved oxygen concentration (DO) of 2 mg/L or more and preferably making the remaining area of the aeration tank 12 anaerobic having a dissolved oxygen concentration (DO) of 0.1 mg/L or less without aeration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  More specifically, the present invention relates to a method for treating organic waste such as food factory waste liquid, garbage, shochu waste liquid, and livestock manure.

  In recent years, the industry has developed rapidly, the population has been concentrated in the city, and lifestyles and agricultural forms have changed. Accordingly, a large amount of waste is generated intensively.

  When the amount of wastewater and waste generated from industry and daily life exceeds the natural purifying power, various problems in human health and environmental conservation occur, and so wastewater treatment and waste disposal are started. It was. For example, wastewater treatment including organic waste such as food factory waste liquor, shochu waste liquor, and livestock manure is generally biodegraded by microorganisms.

  There is an activated sludge method as a typical treatment method for performing wastewater treatment including the organic waste by using microorganisms (see, for example, Patent Document 1).

Among the pollutant loads contained in the waste water, nitrogen treatment includes the following treatment methods (a) and (b).
(a) Ammonia is nitrified in an aerobic state in an aeration tank, the nitrification solution is returned to the denitrification tank, and mixed with a solution containing BOD (or raw water) to be anaerobically denitrified.
(b) Nitrification and denitrification are performed by intermittently aeration of the aeration tank over time.
A typical processing flow example of these processing methods (a) and (b) is as shown in FIG.

  As a matter of course, the denitrification tank and the aeration tank need to have a tank capacity and an aeration amount (oxygen supply amount) capable of treating not only BOD but also nitrogen.

  In this nitrogen treatment, the nitrogen component contained in organic matter is converted to ammonia by microorganisms (what is present as ammonia in the first place), and further converted to nitrous acid and nitric acid by microorganisms under aerobic conditions (nitrification) In addition, it is denitrified by microorganisms in the presence of facultative anaerobic or anaerobic BOD.

  In the processing flow example (a) of FIG. 3, the raw contaminated water is received and stored in the raw water tank 22. This raw water is sent to the denitrification tank 26 via the adjustment tank 24. The adjustment tank 24 is provided to adjust the flow rate fluctuation. In the denitrification tank 26, a solution transferred from the adjustment tank 24 and a solution obtained by nitrifying ammonia in the aeration tank 28 (may be a solution returned directly from the aeration tank 28, transferred from the aeration tank 28 to the precipitation tank 30, and this precipitation tank 30. In this case, the nitrified nitrogen component is denitrified mainly in the presence of BOD transferred from the adjustment tank 24.

  The solution denitrified in the denitrification tank 26 is sent to the aeration tank 28. In the aeration tank 28, aeration processing (nitrification processing) is continuously performed. The aerated solution is sent to the precipitation tank 30 and separated into a sludge solution and a dischargeable supernatant. Part of the sludge solution in the precipitation tank 30 and part of the solution in the aeration tank 28 are returned to the denitrification tank 26.

  The processing flow example (b) in FIG. 3 is the same as the processing flow example (a) up to the raw water tank 32 and the adjustment tank 34. Unlike the processing flow example (a), the solution in the adjustment tank 34 is sent to the aeration tank 36 without passing through the denitrification tank.

  In the aeration tank 36, an intermittent aeration process (an aeration process in which BOD is biodegraded and a nitrification process is performed during aeration operation, and a nitrogen component is desorbed by microorganisms in the presence of BOD in an anaerobic or anaerobic state when aeration is stopped). A denitrification step of nitriding).

  The solution subjected to the intermittent aeration treatment is sent to the precipitation tank 38 and separated into a sludge solution and a supernatant that can be discharged. A part of the sludge solution in the sedimentation tank 38 may be returned to the aeration tank 36, but this is not intended for the nitrification / denitrification treatment of the nitrogen component, and the amount of activated sludge in the aeration tank 36 is reduced. The purpose is to adjust and activate sludge treatment without hesitation.

  Regarding the nitrogen treatment, regardless of whether the treatment flow method is the treatment flow example (a) or the treatment flow example (b), the necessary conditions are to supply the oxygen amount necessary for BOD oxidation and nitrogen nitrification in the aeration process, and In the denitrification step, an anaerobic or facultative anaerobic state is ensured in the presence of BOD.

  From this requirement, when using intermittent aeration, that is, in the case of the processing flow example (b), the time for placing in the facultative anaerobic state or anaerobic state (aeration stop time) is the ammonia, nitrous acid or the solution in the aeration tank after aeration. Depends on the concentration of nitric acid and the concentration of BOD present at the same time. Also in the case of the processing flow example (a), the effective residence time in the denitrification tank can be designed in principle with the same idea as the processing flow example (b).

  However, this design has the following problems.

  In the processing flow example (a), a denitrification tank is essential, and the entire equipment becomes large.

On the other hand, in the process flow example (b), since aeration is performed intermittently, the aeration time required for BOD oxidation / nitrification is reduced. It is necessary to increase the amount of aeration in comparison with the processing flow example (a) (the amount of oxygen required for nitrification is different although details such as denitrification from nitrous acid or denitrification from nitric acid are different) There is no big difference). As a result, in the processing flow example (b), since the electric capacity of the blower becomes high, the contract power has to be set to a high power value (high contract fee), so the efficiency is poor from the viewpoint of power use. However, the electricity usage fee does not change.
JP 2002-224696A (paragraph numbers [0002] to [0011])

More importantly, nitrogen treatment is not an essential issue in livestock wastewater treatment [see, for example, materials for training livestock environment advisor training (stock raising environment management organization, 2000), page 87], nitrogen The amount of oxygen required for processing is not included. However, after several years, it is obliged to meet the wastewater standard [TN (total nitrogen concentration) <100 mg / L] of the Ministry of the Environment. The Livestock Environment Management Organization is instructing to reduce the BOD volumetric load to 0.5 kg BOD / m ³ or less [see, for example, the material of the Livestock Environment Advisor Training Workshop (Livestock Environment Management Organization, 2000), page 86].

  In order to solve the above-mentioned problems, the present inventors have made various studies, and when treating the nitrogen component of the organic matter, a part of the aeration tank is continuously aerated to make it aerobic to nitrify nitrogen, and the remainder is aerated. By performing denitrification by making it anaerobic or facultative anaerobic, it was found that the following advantages were obtained, and the present invention was completed.

  That is, as compared with the processing flow example (a), the aeration tank also has the role of a denitrification tank, so that a separate denitrification tank is unnecessary (reduction of equipment costs), and compared with the processing flow example (b). Although the electricity charge does not change, the electric charge of the blower can be reduced to about half, so the contract charge can be reduced (reduction of the contract electric charge), and the blower required for oxygen supply in the processing flow example (b) The advantage of the present invention is that the blower / diffuser system can be reduced by half compared to the diffuser system (reduction of equipment costs).

  The capacity of the nitrification / denitrification tank required for nitrogen treatment is generally smaller than the aeration tank capacity required from the BOD volumetric load of the guidelines for livestock environment maintenance. From this, it has been found that it is possible to cope with future nitrogen treatment without changing the capacity of the aeration tank by adopting the method of the present invention.

  According to the guidelines of the Livestock Environment Management Organization, the efficiency of aeration (the dissolution rate of oxygen in the air) when determining the amount of aeration is 6%. Therefore, it has been found that if a diffuser tube with good aeration efficiency is used, oxygen necessary for nitrogen treatment can be supplied without changing the aeration capacity.

  From these facts, the present inventors have learned that the method of the present invention is a very simple modification method that can cope with future nitrogen treatment regulations.

  Accordingly, an object of the present invention is to provide a method for treating an organic substance that solves the above-described problems.

  The present invention for achieving the above object is described below.

  [1] The inside of the aeration tank is divided into an aerobic state region and an anaerobic state region, BOD treatment and nitrification treatment of organic matter are performed in the aerobic state region, denitrification treatment is performed in the anaerobic state region, and an aerobic state The processing method of the organic substance whose aeration tank inner bottom area ratio and / or capacity | capacitance ratio of an area | region are 30 to 70%.

  [2] The organic material processing method according to [1], wherein the number of divided regions is 2 or more.

  [3] The treatment of organic matter according to [1], wherein the dissolved oxygen concentration (DO) in the aerobic state region is 2 mg / L or more and the dissolved oxygen concentration (DO) in the anaerobic region is 0.1 mg / L or less. Method.

  According to the method of the present invention, the inside of the aeration tank is divided into an aerobic state region and an anaerobic state region, and the aeration step and the denitrification step are performed respectively, so that the processing equipment is simplified without the need for a separate denitrification tank. it can. Moreover, since aeration in the aerobic state region is not intermittent aeration, continuous aeration can be performed, so that the electric capacity of the blower can be reduced, and the contract fee can be reduced. In addition, the blower / air diffuser system can be reduced, and as a result, the processing equipment can be made inexpensive and simple.

  Hereinafter, the present invention will be described in detail. In the organic matter treatment method of the present invention, the region of 30 to 70% of the bottom area and / or capacity of the aeration tank is aerated to make it anaerobic, and the remaining area of the aeration tank is made anaerobic without aeration. , Treat organic BOD and nitrogen in the aeration tank.

  The ratio of the aerobic tank bottom area and / or capacity of the aerobic region in the range of 30 to 70% is determined by the ratio of the carbon concentration and the nitrogen concentration in the raw water. As a matter of course, in the aerobic region, oxygen is supplied in an amount necessary for BOD / nitrogen treatment. Regarding the setting of the necessary oxygen supply amount, it is not a matter of course that it is determined by known normal design conditions.

  It is necessary to achieve an aerobic state and an anaerobic state in the divided areas, and the number of divided areas is preferably 2 or more, more preferably 2 to 5, and even more preferably 2 or 3. .

  As the aeration tank used in the present invention, an apparatus that is an improvement of the existing apparatus shown in the schematic cross-sectional view of FIG. 1 and that is an improvement of the blower / aeration tube system shown in the schematic cross-sectional view of FIG. can do. In this case, the processing facility can be simplified.

  Hereinafter, the present invention will be described with reference to FIGS. 1 and 2.

  The aeration tank 2 (FIG. 1) and the aeration tank 12 (FIG. 2) are treatment tanks that perform air (oxygen aeration or mixed aeration) aeration in order to aerobically treat the pollutant load in biological treatment. In the aeration tank 2 (FIG. 1), the diffuser tubes 4a and 4b are arranged on the entire surface of the aeration tank 2 in two systems, as in a normal aeration tank. When aeration is performed in the above processing flow examples (a) and (b), the aeration tank can be uniformly aerobic.

  In contrast, the aeration tank 12 (FIG. 2) is characterized in that the air diffuser 14 is moved to one side (left side) in one system.

  In FIG. 1, what is indicated by a dotted line α in the middle of the aeration tank 2 is a mark for showing the difference between the left side area and the right side area in the aeration tank 2. However, in the conventional driving, either the left region or the right region is simultaneously aerobic, or simultaneously anaerobic or facultative anaerobic.

  In FIG. 2 as well, the middle of the aeration tank 12 is indicated by a dotted line β. However, unlike the aeration tank 2 of FIG. 1, the aeration tank 12 of FIG. 2 maintains the left side of the dotted line β in an aerobic state and maintains the right side of the dotted line β in an anaerobic or facultative anaerobic state.

  The air diffuser is a mechanism for dissolving oxygen in the air into the solution filled in the aeration tank when performing air aeration. There are various types of air diffusers, but any type can be used as long as oxygen necessary for treating the pollutant load can be supplied. However, higher oxygen dissolution efficiency is desirable.

  In FIG. 1, aeration blowers 6a and 6b are machines for producing pressurized air in order to dissolve oxygen in the air into the solution in the aeration tank 2. Air is sent from the blowers 6a and 6b to the diffuser tubes 4a and 4b by piping. Two systems of blowers 6a and 6b and air diffusers 4a and 4b are installed so that the left and right can be operated independently. However, in the conventional operation, both the left blower 6a and the right blower 6b are operated simultaneously or stopped simultaneously.

  Since the aeration blower 16 in FIG. 2 is one system with respect to the aeration blowers 6a and 6b in FIG. 1, the operation is naturally performed only in the aerobic region (left side).

  As described above, the aeration tank of the best mode used in the present invention is an apparatus shown in the schematic plan view of FIG. 2, and is an improved apparatus having a blower / aeration tube system only on one side. However, although the processing equipment is not simplified, the existing apparatus shown in the schematic plan view of FIG. 1 can also be used. In this case, since the aeration blowers 6a and 6b are alternately switched between the blower operation side and the blower stop side to operate only one of the blowers, either one of the aeration blowers 6a and 6b is biased and the continuous operation is continued for a long time. It has the feature which can avoid becoming.

  During normal aeration blower operation, a shower system for defoaming is installed.

  Even if the aeration treatment tank is operated only on one side, the input raw water (contamination load) is naturally distributed throughout the treatment tank. If at least part of the left and right solutions are not interchanged, the anaerobic BOD is not oxidized or takes time to be oxidized. If such wastewater is discharged to the outside as treated water, the BOD oxidation treatment is not sufficiently performed, causing environmental destruction.

  In order to prevent this, the transfer pump 8a on the left side in FIG. 1 is designed to suck the solution on the left side of the processing tank and discharge the left side solution to the solution on the right side of the processing tank from a discharge port (not shown) installed on the right side of the processing tank. Has been. When the left transfer pump 8a is used as a defoaming pump, the defoaming place is a portion on the right side of the processing tank.

  The right defoaming pump (transfer pump) 8b is designed to defoam the left side solution. Since the defoaming pump (transfer pump) 18 in FIG. 2 is installed on the right side, it is naturally designed to defoam only the solution on one side (left side).

  In FIG. 1, the aeration tank 2 of this example is provided with a barrier at the center, that is, at the position indicated by the dotted line α in order to increase the structural strength. This barrier allows the liquid to move freely in the section 1 m below the surface of the water. On the flat plate surface of the barrier, a window having a height of 1 m and a width of 2 m is bored at substantially the center, and the liquid is designed to be freely exchanged therethrough. In the example of FIG. 2 as well, a barrier is similarly provided at the dotted line β in the middle of the aeration tank 12.

  If there is no barrier, it is necessary to install a stirrer instead of the transfer pump and exchange the left and right liquids appropriately. The dissolved oxygen values (DO) of the left and right treatment tanks are 2 mg / L or more on the side where the aeration is performed in FIG. 1 (on the side where the diffuser is installed in FIG. 2) when the treatment state is stabilized, FIG. Then, the capacity of the stirrer is selected so that it can be maintained at 0.1 mg / L or less on the side not aerated from the diffuser (on the side where the diffuser is not installed in FIG. 2). Since the capacity of the agitator varies depending on the shape of the aeration tank, it cannot be generally formulated.

  If the solution foams when aerated, it must be defoamed with a shower. In this case, in FIG. 1, the solution on the side not aerated from the diffuser (in FIG. 2, the side where the diffuser is not installed) is pumped up and the aerated side (in FIG. 2 where the diffuser is installed). The solution on the side) is showered and defoamed, and at the same time, the left and right solutions are replaced. In this case, it is necessary to determine the capacity of the pump so that the left and right DOs approach the above values.

  In addition, in the example of FIG. 2, if the pumping capacity is too high and there is no difference between the left and right DOs, and defoaming is required, install the necessary defoaming pump on the side where the air diffuser is installed. It is possible to control the replacement of the left and right liquids.

  When changing the left and right liquids, if the left and right DO values are less than the above difference, a barrier is provided between the left and right tanks to maintain the difference in DO values. In this case, the replacement of the liquid can be easily achieved by using a transfer pump. When the aeration tank is divided into a plurality of parts, the difference in the DO values may be maintained by the return pump. In the present invention, the barrier is not an indispensable condition but an indispensable condition is that there is a predetermined difference in DO value.

  The raw water can be fed into the aeration tank in the case of batch processing, either on the left side or the right side of the aeration tank. However, if possible, the side of the aerated tank in FIG. 1 (the diffuser pipe is installed in FIG. 2). It is better to put it on the other side. In the case of a continuous type, it is preferable that the drainage is not discharged to the outside such as a precipitation tank.

  In FIG. 1, measuring devices 10a and 10b such as a DO meter, an oxidation-reduction potential (ORP) meter, a pH meter, and a liquid temperature meter are installed in the aeration tank in order to grasp the processing status of the aeration tank, and are constantly monitored by a computer. is doing. Similarly in FIG. 2, measuring instruments 20a and 20b are installed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely and in detail, this invention is not limited by an Example.

Comparative Example 1
As an aeration tank, an aeration tank 2 whose equipment arrangement is shown in FIG. 1 was used, and organic matter treatment was performed under the following conditions. The design quantities of the aeration tank 2 are as follows.

  The aeration tank 2 has a rectangular parallelepiped shape, dimensions of 8 m in length, 5 m in width, 5 m in depth, and an effective water depth of 4.5 m. The quantities of the device shown in this example are not a requirement. As long as the standard activated sludge method is adopted, the design quantities of septic tanks such as aeration tanks are basically common to all countries.

The pollution load of the raw effluent is effluent = 11.2 m ³ / day, BOD = 75 kg / day, SS = 80 kg / day, TN = 25 kg / day. Since the design of the aeration tank is BOD volume load = 0.4 kg BOD / m ³ , the amount of the solution containing microorganisms in the aeration tank is 187.5 m ³ , and therefore the capacity of the aeration tank is designed to be 200 m ³ . Since MLVSS during normal operation is 8000 mg / L, the BOD sludge load is 0.05 kgBOD / kgMLVSS.

As a result of this design, the nitrogen sludge load necessary for nitrogen treatment is 0.017 kgN / kgMLVSS, which is smaller than the generally required nitrogen sludge load of 0.04 kgN / kgMLVSS, so that the nitrogen treatment can be performed. ing. The total amount of oxygen required for the pollutant load BOD, nitrogen treatment and endogenous respiration is 170 kg O ₂ / day.

In order to supply this oxygen from the air, air is sent from the two blowers to the diffuser at a rate of 4.4 m ³ / min / blower. In this aeration tank 2, aeration was carried out for 12 hours to perform BOD treatment and nitrification. Subsequently, the nitrified nitrous acid and nitric acid were denitrified by anaerobic for 12 hours. The blower and the diffuser have two identical systems.

  As described above, Table 1 shows the results of nitrogen treatment in which nitrification and denitrification were performed by batch-type aeration for 12 hours and anaerobic for 12 hours.

  As can be seen from this result, the total nitrogen concentration is reduced from 2500 mg / L to 59 mg / L by the batch aeration method. The treated water BOD at this time was 70 mg / L. Through this nitrogen treatment experiment, the ORP is about -300 mV, the DO is about 0 mg / L, and the pH is about 8 immediately after the raw water is charged. These values vary depending on the magnitude of the load. When aeration is started, oxidation of BOD / nitrogen begins, ORP and DO rise, and pH decreases.

  BOD treatment and nitrogen nitrification treatment were completed 8 to 12 hours after the start of aeration. From the start of aeration to the end of nitrogen treatment, ORP was +100 mV, DO was 2 mg / L or more, and pH was about 6.5. At this stage, BOD treatment and nitrification of nitrogen are almost completed. When the aeration is stopped here, both the ORP and DO are rapidly lowered and the aeration tank becomes anaerobic.

  In this state, denitrification of nitrous acid and nitric acid is performed using BOD adhering to sludge or residual BOD in the solution in the aeration tank. As a result, foaming that seems to be nitrogen gas is observed in the aeration tank. When the concentration of nitrous acid and nitric acid is high at the end of aeration, the denitrified nitrogen gas is adsorbed on the sludge, and sludge levitation may be observed. In that case, if sludge is beaten with a defoaming pump, sludge will settle. When the denitrification is completed, the ORP is -300 mV or less, the DO is almost 0 mg / L, and the pH is restored to 7 to 7.5.

  From the above, it was confirmed that BOD / nitrogen could be treated by intermittent aeration without providing a denitrification tank.

Example 1
The following organic substance treatment was performed using the aeration tank 12 whose arrangement is shown in FIG. 2 as an aeration tank. The design quantities of the aeration tank 12 are basically the same as the design quantities of the aeration tank 2 of FIG. The difference between the equipment arrangement of the aeration tank 12 in FIG. 2 and the equipment arrangement of the aeration tank 2 in FIG. 1 is that the right blower / aeration tube system is not used. Since the amount of oxygen required for BOD oxidation and nitrification of nitrogen is the same, the aeration time is doubled to 24 hours.

  Table 2 shows the results of the BOD / nitrogen treatment performed in the aeration tank 12 having such a device arrangement together with the results of Comparative Example 1 of the BOD / nitrogen treatment performed in the aeration tank 2 before deformation. The data shown here is the quality of the treated water discharged to the outside.

  The modified modified aeration tank 12 in FIG. 2 has a variation in the total organic carbon concentration (TOC), but the average value is not much different from that of the pre-deformation aeration tank 2 in FIG. The total nitrogen concentration (T-N) is rather reduced. In particular, nitrous acid and nitric acid concentrations are often low. This phenomenon is thought to be because, if ammonia moves to the right side after nitrification on the left side, it can be immediately denitrified there. The DO value was always 2 mg / L or more on the aerobic side and 0.1 mg / L or less on the anaerobic side during the treatment.

  In addition, it is necessary to evaluate how equipment costs and running costs change due to improved deformation of the aeration tank.

  By improving and deforming the aeration treatment tank, the BOD volume load, BOD sludge load, and nitrogen sludge load, which are basic design conditions, do not change. In other words, the tank construction costs are the same. In other words, the construction cost of the barrier may be imposed, but if it is not necessary for strength, it can be regarded as unchanged. Further, the point that the denitrification tank is unnecessary is the same as before the aeration treatment tank is modified.

  The oxygen supply, which is the basis for aerobic treatment, does not change. It is aeration time that changes fundamentally. Table 3 compares the facility costs and electricity charges for aeration in the case of the experiment shown above.

  The equipment cost of the aeration equipment (blower and diffuser) is halved. If the scale of the facility is increased, the cost will be considerably reduced. For example, since the blower / aeration pipe / pipe construction cost / equipment installation cost in the aeration tank equipment used in Comparative Example 1 is about 3.4 million yen, the deformation of the aeration tank used in Example 1 is about 1.7 million. It will be a reduction of the equipment that covers the circle. Generally, the equipment cost is considered to be proportional to the BOD / nitrogen load of raw water. Given that, this reduction is not negligible.

  Regarding the electricity charge, the usage fee remains the same, but the contract fee is halved. In this case as well, the running cost is considerably reduced as the scale increases.

It is a plane schematic sectional drawing which shows the aeration tank used in the comparative example 1. It is a plane schematic sectional drawing which shows the aeration tank used in Example 1. FIG. It is a schematic flowchart which shows the typical processing flow example of the processing method (a) and (b) of the nitrogen component in wastewater treatment.

Explanation of symbols

2, 12, 28, 36 Aeration tank 4a, 4b, 14 Aeration tube 6a, 6b, 16 Aeration blower 8a, 8b, 18 Transfer pump 10a, 10b, 20a, 20b Measuring instrument 22, 32 Raw water tank 24, 34 Adjustment tank 26 Denitrification tank 30, 38 Precipitation tank α, β Dotted line indicating the middle of the aeration tank

Claims (3)

The inside of the aeration tank is divided into an aerobic state region and an anaerobic state region, BOD treatment and nitrification treatment of organic matter are performed in the aerobic state region, denitrification treatment is performed in the anaerobic state region, and aeration in the aerobic state region The processing method of the organic substance whose tank bottom area ratio and / or capacity | capacitance ratio are 30 to 70%. The organic matter processing method according to claim 1, wherein the number of divided regions is 2 or more. The method for treating an organic substance according to claim 1, wherein the dissolved oxygen concentration (DO) in the aerobic state region is 2 mg / L or more, and the dissolved oxygen concentration (DO) in the anaerobic region is 0.1 mg / L or less.

Images