JP4608900B2 - Biological treatment method of organic wastewater - Google Patents

Description

  The present invention relates to a biological treatment method for purifying wastewater by reducing organic matter in organic wastewater such as sewage and various industrial wastewater.

  As a technique for efficiently removing organic matter in organic wastewater such as sewage and various industrial wastewater, biological treatment methods represented by the activated sludge method are often used. In the biological treatment method, about 30 to 80% of the organic matter in the wastewater is oxidatively decomposed to become harmless as inorganic matter such as carbon dioxide and water. On the other hand, the remaining 20 to 70% of organic matter is synthesized into microbial cells, most of which is extracted as excess sludge out of the system, and part of it flows out as suspended matter (SS) in the treated water.

  The surplus sludge is usually a slurry having a suspended solid concentration of 5 to 20 g / L, which is further concentrated as necessary, then agglomerated by a polymer flocculant, etc., dehydrated by a dehydrator, and water content 70 About -86% dehydrated cake is disposed of as industrial waste. Before this dehydration operation, sludge may be reduced by a process such as aerobic digestion or anaerobic digestion. In addition, the dehydrated cake may be disposed of after being further reduced by incineration. Moreover, after making it into a dehydrated cake, it may be composted and used as a fertilizer or may be returned to green farmland.

  In recent years, surplus sludge has been subjected to reforming treatment such as ozone treatment to improve biodegradability and then returned to the aeration tank again, or sent to other aerobic digesters or anaerobic digesters. In addition, it has been devised to further biologically process and decompose surplus sludge into inorganic substances as much as possible.

  Thus, in order to dispose of surplus sludge generated by biological treatment of organic wastewater, it is necessary to treat and dispose of it by various methods, which requires labor and cost, and therefore a process that does not discharge surplus sludge as much as possible is desired. It is rare.

  As another method for reducing the amount of excess sludge discharged as much as possible, the use of uncoupling agents has been partially studied. The mechanism of action of this uncoupler is as follows.

  In order for microorganisms to grow using organic matter in wastewater, in addition to organic matter as a material constituting the cells, energy for processing this is required. As an energy source for cell synthesis, adenosine triphosphate (ATP), which is a high energy compound mainly generated by using energy obtained by oxidizing organic substances, is used.

More specifically, the energy when organic matter is oxidized in the cell pumps intracellular H ⁺ to the outside of the cell membrane. Since the cell membrane is usually substantially impermeable to H ^+, H ⁺ concentration gradient and the potential gradient is formed in the cell and out. Thus, the H ⁺ pumped out of the cell is taken into the cell again through the ATP synthase that penetrates the inside and outside of the cell membrane. At this time, the ATP synthase uses the energy when H ⁺ flows into the ATP synthase. Is synthesized.

That is, the chemical energy when the organic matter is oxidized is once converted into a form of H ⁺ concentration gradient inside and outside the cell membrane, and then converted into a high energy compound called ATP. A part of the taken-in organic substance is converted using the energy of ATP, the bacterial cell components are synthesized, and the bacterial cell grows. As a result, surplus bacterial cells are generated and become waste.

The uncoupler, the H ⁺ transported from the outside of the cell membrane to the cell membrane without passing through the ATP synthase, an agent that has an action to eliminate the H ⁺ concentration gradient.

For this reason, in the presence of the uncoupler, the oxidation of the organic matter proceeds as usual, and H ⁺ is pumped out of the cell. Most of this H ⁺ is passed through ATP synthase by the action of the uncoupler. The amount of ATP produced is reduced. As a result, it is difficult to obtain a sufficient amount of ATP for cell synthesis, the production amount of the bacterial cells is reduced, and the amount of surplus sludge generated is also reduced.

  Devices to reduce the amount of excess sludge generated include aerobic digestion and anaerobic digestion, incineration of dehydrated cake, and improvement of biodegradability of sludge as described above. There is a problem that operation management becomes complicated. In addition, depending on the process, for example, incineration increases costs for auxiliary fuel for combustion and exhaust gas countermeasures, and sludge reforming methods by ozone treatment increase the cost of ozone treatment. is there.

  In order to avoid such problems, the use of uncoupling agents is desired as a technique for suppressing the amount of surplus sludge generation itself, but it is still only at the laboratory level and has been put into practical use. Not.

  The present invention solves the problems of uncoupling agents and provides a technique for putting them into practical use. Organic substances in the organic substance intake process are aerobic by the action of microorganisms in the presence of uncoupling agents. It is an object of the present invention to provide a biological treatment method for organic wastewater that effectively reduces the amount of sludge generated by removing it.

  According to the study of the present inventor, in the short-term batch test, the sludge generation amount is decreased by the addition of the uncoupling agent, but in the continuous test, the sludge generation amount is not decreased, and the sludge used in this continuous test is also observed. When the batch test was performed again, it was found that the presence or absence of the uncoupler did not affect the amount of sludge generated. This was thought to be due to the fact that the properties of the sludge changed during the continuous test and resistance to the uncoupler was acquired.

  Therefore, the present inventor further studied to provide a method capable of effectively reducing the amount of sludge generated by the uncoupler even for sludge that has acquired resistance to the uncoupler, and as a result, in the vicinity of pH 5.5. It is found that the “true yield” described later is reduced, but the self-digestion rate is reduced under these conditions, and a significant reduction in sludge generation cannot be expected. It was found that by performing under the conditions, it is possible to reduce the true yield and the amount of generated sludge by self-digestion, thereby completing the present invention.

That is, the present invention relates to a biological treatment method in which organic matter in organic wastewater is removed aerobically by the action of microorganisms in the presence of an uncoupler, and the organic matter in the wastewater is ingested into the microbial cells. And a self-digestion step of self-digesting microorganisms that have ingested organic matter, and the self-digestion step is performed under a pH condition different from that of the organic matter intake step. It is characterized in that it is carried out in the range of ˜6.5 and the self-digestion step is carried out in the range of pH 7-9 .

  Here, the “true yield” is a yield when bacteria ingest organic matter to make a cell component, and is a yield that does not take into account self-digestion of the cell. Normally, sludge stays in activated sludge for about 5 to 30 days, and self-digestion proceeds during that time, so the actual sludge conversion rate is about 1/4 to 1/2 of the true yield.

The concept of such a true yield is, for example, the mathematical model ASM No. of activated sludge in the following literature. 1-No. 3 is also seen.
M. Henze, W. Gujer, T. Mino, MCM van Loosdrecht, "Activated sludge models ASM1, ASM2, ASM2d and ASM3. IWA Scientific and Technical Report No9, 2000", published by IWA Publishing. Although it was the maximum in the vicinity of 5, it was found that the true yield increased under these conditions, and a significant reduction in the amount of sludge generation could not be expected.

  Therefore, since the reaction of ingesting organic matter into the cell occurs relatively quickly, the pH is set to around 5.5 to reduce the true yield only when this reaction is mainly occurring, and the self that occurs thereafter In digestion, it was considered that the amount of sludge generated can be reduced by increasing the self-digestion rate by adjusting the pH to around 8.5. When the present inventors actually applied the uncoupling agent under such conditions, the amount of sludge generated was clearly reduced.

  Thus, the present invention has found that there is a pH suitable for reducing the amount of sludge generated in the organic matter intake process and the self-digestion process, even if the sludge has acquired resistance to the uncoupler. It was made by.

  For normal activated sludge to which no uncoupler is administered, the true yield and autolysis rate are hardly affected by pH. Therefore, such an influence of pH is considered to be a phenomenon peculiar when the uncoupler is used.

As described above, the detailed mechanism for changing the property of sludge sensitive to pH change due to the presence of the uncoupler is not clear. However, the uncoupler has a uniform H ⁺ concentration inside and outside the cell membrane. As described above, if there is no uncoupling agent, the cell membrane is H ⁺ impervious and is not easily affected by external pH changes, but in the presence of the uncoupling agent. It is considered that when the pH of the external environment varies, the intracellular pH varies, and some changes in cell metabolism are accompanied accordingly. That is, the phenomenon in which the influence of the external pH on the sludge metabolism in this way is highly likely to be common to drugs having an uncoupling action.

  According to the biological treatment method of the organic wastewater of the present invention, the problem that the sludge generation amount reducing effect is extremely low by simply adding the uncoupler is improved. A reduction effect can be obtained.

  The method of the present invention is a simple and inexpensive process that makes it possible to make a large change to the equipment simply by controlling the pH using an uncoupler, or to add a new process and complicate the operation. The problem of sludge can be solved, and it has a great effect on wastewater treatment cost reduction, workability improvement, and waste reduction.

  Hereinafter, preferred embodiments of the biological treatment method for organic wastewater according to the present invention will be described in detail.

  There is no restriction | limiting in particular as an uncoupling agent used by this invention, It can apply to all conventionally well-known uncoupling agents. Practically, carbonyl cyanide phenylhydrazone derivatives such as carbonylcyanide-m-chlorophenylhydrazone and carbonylcyanide-p-trifluoromethoxyphenylhydrazone, which exhibit an uncoupling effect with a small addition amount, 2,6- Phenolic derivatives such as di-t-butyl-4- (2 ', 2'-dicyanovinyl) phenol, 3-chloro-N- (3-chloro-2,6-dinitro-4- (trifluoromethyl) phenyl) N-phenylpyridinamine derivatives such as -5- (trifluoromethyl) -2-pyridinamine, diallylamine derivatives such as 2'-chloro-2,4-dinitro-5 ', 6-di (trifluoromethyl) diphenylamine , Salicylanilide derivatives, and benzimidazole derivatives such as 2- (trifluoromethyl) -4,5,6,7-tetrachlorobenzimidazole. In particular, N-phenylpyridinamine derivatives, especially 3-chloro-N- (3-chloro-2,6-dinitro-4- (trifluoromethyl) phenyl) -5- (trifluoromethyl) -2-pyridine Amines and their analogs are suitable because they have a high sludge generation reduction effect.

  The amount of the uncoupling agent added to the raw water (organic waste water) varies greatly depending on the type of uncoupling agent used and the application conditions, but is usually added in the range of 0.01 to 100 mg / L, particularly 0.05 to 20 mg. / L, more preferably 0.1 to 5 mg / L, which is effective. If the amount of uncoupler added is too high, the cost of the drug will increase, and the COD value of the wastewater itself will increase to become a pollutant, generate a specific odor, and adversely affect the environment, especially aquatic organisms. This is not preferable because it may cause On the other hand, if the amount of uncoupler added is too small, the resulting sludge generation amount reducing effect is often small.

  The position at which the uncoupling agent is added is desirably the most upstream side of the biological treatment. This is because the uncoupling agent is most effective when microorganisms ingest and decompose organic substances because of its nature, and is considered to have little effect on reducing the cells that have already been generated. . Accordingly, also in the present invention, the uncoupler concentration in the organic substance intake process is relatively more important than the uncoupler concentration in the self-digestion process, and the uncoupler should be added in the organic substance intake process or upstream thereof. Is preferred.

  In general, a regulating tank is often installed on the upstream side of biological treatment, and aeration is often performed here for stirring. If the residence time in the adjustment tank is long, a part of the organic matter in the wastewater may be converted into cells in the adjustment tank. In this case, even if the uncoupling agent is added in the subsequent biological treatment, For some reason, the effect of reducing the amount of sludge generated by the uncoupling agent may be low. Therefore, in such a case, it is desirable to add at least a part of the uncoupling agent to the adjustment tank.

  In the present invention, in the biological treatment in the presence of such an uncoupler, the organic matter intake step and the subsequent autolysis step are performed under different pH conditions.

Here, the pH of the organic matter ingesting step is preferably in the range of 5 to 6.5, particularly in the range of 5.5 to 6.0. On the other hand, the pH of the autolysis process is 7 . The range of 0-9.0, especially 7.5-8.6 is good.

  If the pH of the organic matter intake process is lower than the above range, the organic matter intake (soluble BOD) is not sufficiently taken in the organic matter intake step, and the remaining organic matter will be taken in the subsequent self-digestion step. The effect cannot be obtained. If the pH is too high, for example, even if the pH is 9.5 or higher, a high effect cannot be obtained for the same reason. When the pH is near neutral, deterioration of the organic substance removal rate in the organic substance intake process is unlikely to occur, but when the pH is out of the above range, the sludge acquires resistance to the uncoupler as described above. The effect of reducing the true yield is reduced by the effect, and the sludge generation amount reducing effect according to the present invention cannot be sufficiently obtained. Moreover, even if the pH of the self-digestion step is higher or lower than the above range, the self-digestion rate cannot be increased, and the sludge generation amount reducing effect according to the present invention cannot be sufficiently obtained.

  Any known method may be used for pH adjustment in the organic matter intake process and the self-digestion process. In addition to adding an acid or alkaline pH adjuster, the pH may be adjusted by using an acid generation reaction or nitrification reaction by microorganisms as a method for lowering the pH, or by a decomposition reaction of organic acids by microorganisms as a method for raising the pH. Alternatively, a denitrification reaction or a deamination reaction may be used.

  In the present invention, in the organic matter ingestion step, which is a step in which microorganisms ingest organic matter in wastewater, any one of the steps provided on the downstream side (self-digestion step, precipitation) It is preferable to return the required amount of sludge from the tank, digestion tank, etc., to make the reactor a chemostat system, hold the carrier with microorganisms attached in the reactor, or to return the carrier with microorganisms attached from the downstream side. These methods can also be combined.

  In the organic matter ingesting step, it is desirable to retain the cells so that 60% or more, more preferably 80% or more, and still more preferably 90% or more of the dissolved BOD that flows in is removed. In order to achieve this condition, depending on the retention method of microorganisms, the type of organic matter flowing in, the water temperature, and other conditions, for example, the solubility BOD per VSS for VSS retained in the organic matter intake process The load is 0.1 to 12 kg-BOD / kg-VSS / d, more preferably 0.5 to 6 kg-BOD / kg-VSS / d, and still more preferably 1.2 to 4.0 kg-BOD / kg-VSS / d. It is good to be d.

  Soluble BOD that cannot be removed in the organic matter ingestion process will be removed in the subsequent self-digestion process, but in the self-digestion process, the pH is adjusted to optimize the self-digestion rate. This is a relatively high condition. As a result, the sludge conversion rate of the BOD removed in the self-digestion step becomes a value close to the sludge conversion rate in the conventional method, and the sludge generation amount increases. That is, the effect of the present invention is mainly to reduce the amount of microbial cells generated from the soluble BOD ingested in the organic matter ingestion process. Therefore, it is effective to make sludge ingest as much soluble BOD as possible in the organic matter ingestion process. Is.

  On the other hand, in the self-digestion step, which is a step of self-digesting microorganisms that have ingested organic matter in the organic matter ingestion step, it is necessary to cause the cells that have flowed out of the organic matter ingestion tank to stay for a certain period of time to perform self-digestion. Usually, as shown in FIG. 1 to be described later, a self-digestion tank that receives almost all of the treated water from the organic matter intake process is provided, and the treated water in the self-digestion tank is solid-liquid by means such as precipitation, levitation concentration, and membrane separation. After separation, only the supernatant liquid is discharged as treated water, and the concentrated sludge is returned to the organic matter intake tank or self-digestion tank.

  Thus, the BOD load per VSS is 0.05 to 1.0 kg-BOD / kg-VSS / d, preferably 0.1 with respect to the total amount of VSS retained in the organic matter intake process and the self-digestion process. ~ 0.6kg-BOD / kg-VSS / d, more preferably 0.15-0.4kg-BOD / kg-VSS / d, the water tank volume, solid-liquid separation means, sludge return rate, etc. It is preferable to determine. In addition, the VSS held in the self-digestion process should be 40% or more, desirably 60% or more, more desirably 80% or more with respect to the total amount of VSS retained in the organic matter intake process and the self-digestion process. . That is, as shown in FIG. 4 to be described later, when the ratio of sludge retained in the organic matter intake process increases, the self-digestion rate in the organic matter intake process is not so fast, so the amount of sludge that is self-digested decreases, The amount generated increases.

  It is preferable to mainly use floating activated sludge floc for the microorganisms that work in the organic matter intake process (organic matter intake tank). In order to always hold a certain amount of microorganisms or more and stabilize the BOD removal rate, it is also effective to use a fluid carrier or a fixed carrier in combination in the organic matter intake process. Although the fluid carrier can be circulated between the subsequent self-digestion process (self-digestion tank), the structure of the device is slightly complicated, and a certain amount of ingenuity is required for transporting the carrier. It is preferable to keep it in the tank. Even in this case, the present invention is effective because the microbial cells that have grown and detached on the fluid carrier are self-digested in the subsequent self-digestion tank.

  The purpose of the self-digestion tank (self-digestion process) is to self-digest microorganisms that have ingested organic matter in the organic matter intake tank (organic matter intake process). It is less desirable to do. In other words, these carriers rather occupy space in the self-digestion tank to secure the cells flowing in from the organic matter intake tank, reduce the residence time available for self-digestion, and generate a small amount of sludge. Leads to an increase in

  On the other hand, in the self-digestion tank, if the uncoupling agent is not added directly, the uncoupling agent added in the organic matter intake tank is adsorbed or decomposed into sludge, etc., and the uncoupling agent concentration is reduced. Wastewater purification is easy to proceed. That is, in the presence of the uncoupling agent, the BOD removal rate and the COD removal rate tend to be slightly inferior, but if such a carrier is provided in the self-digestion tank, these carriers are directly uncoupled in the organic matter intake tank. Since it is not affected by the agent, a biological species having relatively superior BOD removal ability and COD removal ability is given priority over the carrier surface. Furthermore, depending on the type of uncoupler, biodegradation of the uncoupler itself can be expected.

  In this way, when priority is given to reducing sludge generation, it is desirable not to install a carrier in the self-digestion tank. On the other hand, to improve the quality of treated water and to prevent the uncoupler from flowing into treated water In some cases, it is preferable to install a carrier.

  Of course, if the installation area and cost allow, after the self-digestion process and the solid-liquid separation process, further biological treatment using a fluid carrier or a fixed carrier can further reduce the treated water BOD and COD, It is also possible to reduce the concentration of the conjugate agent.

  As shown in FIG. 2 described later, the self-digestion process may be provided for the concentrated sludge after the solid-liquid separation. In this case, the volume of the self-digestion process between the organic matter intake process and the solid-liquid separation process is increased. It is possible to reduce the size or to omit it. If the self-digestion process between the organic substance intake process and the solid-liquid separation process is downsized or omitted, the solubility BOD of the treated water after the solid-liquid separation becomes slightly higher, or the sludge before the solid-liquid separation process In some cases, the SS concentration of treated water becomes slightly high due to insufficient flocking, but it can be applied when the required level of treated water quality is relatively low, and the conditions of the organic matter intake process Further, by devising solid-liquid separation means, it is possible to minimize the deterioration of treated water quality.

  Thus, when providing a self-digestion tank with respect to concentrated sludge, since the sludge density | concentration in a self-digestion tank can be made high, a water tank volume can be reduced in size and construction cost can be reduced. Moreover, since the amount of the alkaline agent added to adjust the pH suitable for self-digestion described above to the concentrated sludge is small, the chemical cost can be reduced.

  In the present invention, the organic matter intake process and the self-digestion process are not necessarily spatially separated, and may be switched in time within the same water tank. That is, in the organic matter intake step, the pH is adjusted within a predetermined range and waste water is allowed to flow, and after a predetermined soluble BOD removal rate is obtained, the pH may be adjusted to a pH suitable for the self-digestion step. The processing conditions described above can be applied.

  Even when this method is applied to such batch activated sludge, sludge is settled and separated before the self-digestion process or during the self-digestion process, and the resulting supernatant is discharged as treated water. And you may perform a self-digestion process with respect to the concentrated sludge which remained in the tank. By performing such an operation, the amount of the alkaline agent added in the self-digestion step can be reduced.

  In the present invention, the organic matter intake process and the self-digestion process are not necessarily performed in the presence of dissolved oxygen, and may be performed in the presence of nitrate or nitrite. In particular, if the nitric acid respiration is actively generated in the self-digestion process and the denitrification reaction proceeds, the pH increases due to the denitrification reaction, so the amount of the alkali agent added from the outside can be reduced, Economical.

  In the present invention, organic matter decomposition is performed using microorganisms mainly composed of heterotrophic bacteria. However, the present invention can also be applied to a method for organic matter decomposition mainly using yeast or mold.

  By the way, as another method for reducing surplus sludge, as described above, surplus sludge is modified to be readily biodegradable by ozone treatment, etc., and re-introduced into the aeration tank as a substrate for activated sludge to perform biodegradation. A method of decomposing excess sludge is known. Even when such a method is used, since the sludge newly proliferates using the modified sludge as a substrate, it is necessary to perform a reforming treatment on an excessive amount of sludge rather than the original excess sludge generation amount. However, by using the method of the present invention in combination with such a method, not only the amount of excess sludge to be treated itself is reduced, but also the amount of sludge that grows using the modified sludge as a substrate is suppressed. The amount of sludge required for reforming can be greatly reduced. As a result, the sludge reforming process can be performed at a low construction cost and operation cost, and the amount of sludge generated can be reduced relatively inexpensively.

  In particular, when it is necessary to obtain a high sludge reduction rate, even if the present invention is adopted, it is difficult to achieve a desired sludge reduction rate only by the action of the uncoupler, but in such a case, as described above By combining the sludge reforming / substrate conversion method and the method of the present invention, a high sludge reduction rate can be achieved at a low cost.

  Hereinafter, embodiments of the biological treatment method for organic wastewater according to the present invention will be described in more detail with reference to the drawings. 1 and 2 are system diagrams showing an embodiment of the biological treatment method for organic wastewater according to the present invention.

  In FIG. 1, a self-digestion tank 2 is provided on the downstream side of the organic matter intake tank 1, raw water is introduced into the organic matter intake tank 1, and effluent water from the organic matter intake tank 1 is introduced into the self-digestion tank 2. The outflow water of the self-digestion tank 2 is solid-liquid separated in the sedimentation tank 3, the supernatant water is discharged out of the system as treated water, and the separated sludge is returned to the organic matter intake tank 1 by the pump P as return sludge. Moreover, the sludge of the self-digestion tank 2 is discharged out of the system as excess sludge as necessary. An uncoupling agent is added to the organic matter intake tank 1. Further, in order to adjust the inside of the tank to a predetermined pH, the organic substance intake tank 1 is provided with an acid addition means such as HCl and a pH meter 1A, and the self-digestion tank 2 is provided with an alkali addition means such as NaOH and a pH meter. 2A is provided. In this method, the soluble BOD in the raw water is ingested by the activated sludge in the organic matter intake tank 1 and partly decomposed. The treated water in the organic matter intake tank 1 is fed to the self-digestion tank 2, and sludge is reduced by self-digestion.

In FIG. 2, the self-digestion tank 2 is provided in the subsequent stage of the settling tank 3, the effluent water from the organic matter intake tank 1 is solid-liquid separated in the settling tank 3, and the supernatant water is discharged out of the system as treated water and separated sludge ( discharged from the system as excess sludge optionally a part of the concentrated sludge) is fed to the self-digestion tank 2 and the remainder by a pump P _2. Outflow sludge autolysis tank 2, a portion is discharged from the system as excess sludge if necessary, the remainder is returned to the organic matter intake tank 1 as return sludge by the pump P _1.

  In the method of FIG. 2, soluble BOD in raw water is ingested by microorganisms in the organic matter intake tank 1 and partially decomposed. Thereafter, solid-liquid separation is performed, the supernatant is discharged as treated water, and the sludge is concentrated and sent to the self-digestion tank 2. In order to obtain a pH suitable for self-digestion in the self-digestion tank 2, an alkali agent (NaOH aqueous solution in the figure) is introduced in conjunction with the pH controller, but the sludge concentration is 1.5-7 compared to the flow of FIG. It is concentrated about twice, so that the alkaline agent can be saved 1.5 to 1/7. Moreover, the volume of the self-digestion tank 2 can also exhibit an equivalent performance in 1.5-7 times compared with the thing of FIG. Alternatively, if the volume of the self-digestion tank is increased, for example, if the volume is the same as that of the self-digestion tank in the flow of FIG. This will be further reduced.

  On the other hand, in this flow, the reaction time for removing the soluble BOD is shortened, which may result in treated water having a high soluble BOD concentration. In order to prevent this, it is effective to appropriately set and manage the BOD volume load and MLVSS concentration of the organic matter ingestion tank 1, but if the soluble BOD removal rate is prioritized too much, the organic matter ingestion tank 1 becomes large. In some cases, the effect of reducing the amount of generated sludge cannot be fully exhibited. In such a case, by providing the organic matter intake tanks 1 in series in multiple stages, the soluble BOD removal rate can be increased even if the entire organic matter intake tank has the same volume.

  Further, in this flow, the generated bacterial cells may not be sufficiently taken into the floc and may flow out into the treated water to increase the SS concentration and turbidity of the treated water. Even in such a case, the multi-stage organic matter intake tank may be effective. Further, as another method, it can be coped with by using an organic or inorganic flocculant in combination, or further treating the treated water by coagulation precipitation or filtration.

  In the method of FIG. 2, concentrated sludge that is relatively easy to self-digest, and that has not passed much time after ingesting organic matter into the cells, can be obtained. Therefore, when anaerobic digestion is used as a treatment method for excess sludge, anaerobic digestion is performed with concentrated sludge before being sent to the self-digestion tank, thereby reducing oxygen consumption in the self-digestion tank and increasing methane generation during anaerobic digestion. You can expect the effect. On the other hand, when the excess sludge is dehydrated without performing a special weight reduction treatment, the sludge after self-digestion is easier to prevent the decay of the sludge and is effective in preventing odor in the dehydration process.

  The methods of FIGS. 1 and 2 may be used simultaneously. That is, in FIG. 1, a second self-digestion tank can be provided in the middle of returning sludge from the settling tank. Since the second self-digestion tank can hold sludge at a high concentration, similar to the self-digestion tank in FIG. 2, it is highly effective even with a small volume. In addition, since the amount of water is small, the consumption of the alkali agent can be relatively reduced even when an additional alkali agent is added to achieve a high pH suitable for self-digestion.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. For convenience of explanation, a comparative example is given first.

Comparative Example 1: Control Test Using No Uncoupler As shown in FIG. 3, a continuous test of activated sludge was performed using a 30 L aeration tank 11 and a 6 L capacity sedimentation tank 12. The aeration tank 11 was aerated by an aeration means (not shown) so that the dissolved oxygen (DO) was 1 mg / L or more. The activated sludge that has flowed out of the aeration tank 11 is guided to a cylindrical feed well in the center of the precipitation tank 12, and is separated into solid and liquid by gravity sedimentation. The settled sludge is collected at the center of the lower cone of the settling tank 12 by a rake rotating at 1 to 2 rpm, and returned to the aeration tank 11 by the pump P as return sludge. The amount of sludge returned was the same as the amount of raw water flowing in.

Vegetable extract as raw water, fish extract, liquid sugar, methanol using a synthetic wastewater consisting mainly of, _{COD Cr} concentration was adjusted to 600 mg / L. This raw water was passed through the aeration tank 11 at a flow rate of 60 L / day so that the COD _Cr volumetric load in the aeration tank 11 was 1.2 kg-COD _Cr / m ³ / d. The water temperature of the aeration tank 11 was 20 ° C., and the pH was 6.5 to 7.5. Further, sludge was periodically extracted and discharged out of the system so that the MLVSS concentration in the aeration tank 11 was 4 kg / m ³ .

The amount of generated sludge was defined as the total of the VSS increase in the aeration tank and the sedimentation tank, the VSS pulled out of the system, and the VSS flowing out into the treated water. On the other hand, COD _Cr treated in the system was obtained by subtracting soluble COD _Cr in treated water from COD _Cr in raw water. The sludge conversion rate is obtained by dividing the amount of generated sludge by the amount of COD _Cr processed in the system.

  The sludge conversion rate when no uncoupling agent was added was 0.23 g-VSS / g-COD.

Comparative Example 2: Test with uncoupling agent added in conventional flow The uncoupling agent was continuously added in the flow shown in FIG. 3 to examine the effect of the uncoupling agent. As the uncoupler, 3-chloro-N- (3-chloro-2,6-dinitro-4- (trifluoromethyl) phenyl) -5- (trifluoromethyl) -2-pyridinamine is used against the raw water. It added to the aeration tank 11 so that it might become 3 mg / L. The uncoupler was prepared as a 500 mg / L concentrated solution and added at a flow rate of 360 mL / day. As a result, the sludge conversion rate was about 0.15 g-VSS / g-COD for about 2 weeks after the start of addition, and there was an effect of reducing the sludge generation amount of about 35%, but after that, the sludge conversion rate was 0.20 g-VSS. / G-COD, and the sludge generation reduction effect was about 13%.

Comparative Example 3: Test in which only pH was changed by conventional flow In Comparative Example 2, the pH of the aeration tank 1 was adjusted to 5.5 to 6.0 and the sludge conversion rate was determined to be 0.21 g. -VSS / g-COD. Moreover, when it adjusted so that it might become pH 8.3-8.7 and the sludge conversion rate was calculated | required, it was set to 0.19g-VSS / g-COD. That is, it was found that only by changing the pH, the sludge conversion rate hardly changed.

Example 1: Test of the Present Invention As shown in FIG. 1, treated in Comparative Example 1 using a 4.5 L organic substance intake tank 1, a 30 L self-digestion tank 2 and a 6 L capacity sedimentation tank 3. A continuous test of activated sludge passing raw water was conducted.

  Assuming that the sludge concentrations in the organic matter intake tank 1 and the self digestion tank 2 are almost equal, the organic matter intake tank 1 has a volume of 13% of the whole, and the self digestion tank 2 holds 87% of the VSS. .

  In order to change pH in the organic matter intake tank 1 and the self-digestion tank 2, a pH controller is installed, respectively. In the organic matter intake tank 1, a 6 wt% HCl aqueous solution is injected, and in the self digestion tank 2, an 8 wt% NaOH aqueous solution is injected. The pH of the organic matter intake tank 1 was adjusted to 5.6 to 5.9, and the pH of the self-digestion tank 2 was adjusted to 7.8 to 8.6.

  The same uncoupling agent as that used in Comparative Example 2 was used, and it was put into the organic matter intake tank 1 so as to be 3 mg / L with respect to the raw water. The organic substance intake tank 1 and the self-digestion tank 2 were aerated by using aeration means (not shown) so that DO becomes 1 mg / L or more. The activated sludge that has passed through the organic matter intake tank 1 and the self-digestion tank 2 is guided to a cylindrical feed well at the center of the precipitation tank 3 and is separated into solid and liquid by gravity sedimentation. The sedimented sludge is collected at the center of the lower cone of the sedimentation tank 3 by a rake rotating at 1 to 2 rpm, and returned to the organic matter intake tank 1 by the pump P as return sludge. The amount of sludge returned was the same as the amount of raw water flowing in.

The raw water was passed at 69 L / day so that the COD volumetric load was 1.2 kg-COD / m ³ / day with respect to 34.5 L in total of the organic matter intake tank 1 and the self-digestion tank 2. The water temperature of the organic matter intake tank 1 and the self-digestion tank 2 was 20 ° C. Further, in the self-digestion tank 2, sludge was periodically extracted and discharged out of the system so that the MLVSS concentration was 4 kg / m ³ .

  As a result, the sludge conversion rate was 0.12 g-VSS / g-COD, and this value was continuously obtained for at least 2 months. This value is a 48% reduction in sludge generation compared to Comparative Example 1.

  From this result, it was shown that sludge generation amount can be effectively reduced by using the uncoupler according to the present invention.

  In addition, when the relationship between the ratio of the sludge retention amount in the organic matter intake tank, the soluble BOD removal rate, and the sludge conversion rate was obtained by calculation, the results shown in FIG. 4 were obtained. Here, the horizontal axis represents the ratio of the amount of VSS held in the organic matter intake tank to the total amount of VSS held in the organic matter intake tank and the self-digestion tank.

COD _Cr ingested in the organic substance intake tank is assumed to be converted into cells with a true yield of 0.32 g-VSS / g-COD _Cr , and COD _Cr ingested in the autolysis tank has a true yield of 0. .49 g-VSS / g-COD _Cr was converted into cells. The self-digestion rate in the organic substance intake tank was 0.07 day ⁻¹ , and the self-digestion rate in the autodigestion tank was 0.25 day ⁻¹ . For the calculation, the activated sludge model described in the above-mentioned literature and its standard parameters were used.

The COD _Cr volumetric load was 1.5 kg-COD / m ³ / d with respect to the whole organic matter intake tank and the self-digestion tank, and all soluble and easily degradable COD _Cr flowed in. The COD _Cr removal rate in the organic substance intake tank was 8 kg-COD _Cr / m ³ / d.

  From this result, the point of minimizing the sludge conversion rate is within the range where the soluble BOD removal rate in the organic matter intake tank almost reaches the upper limit (0.2 or more horizontal axis in the figure, soluble BOD removal rate ≈ 100%). It can be seen that the ratio of the self-digestion tank is as large as possible, and it is particularly important to increase the BOD removal rate in the organic matter intake tank.

It is a systematic diagram which shows embodiment of the biological treatment method of the organic wastewater of this invention. It is a systematic diagram which shows other embodiment of the biological treatment method of the organic wastewater of this invention. It is a systematic diagram which shows the test apparatus used in Comparative Examples 1-3. It is a graph which shows the relationship between the ratio of the sludge retention amount of an organic matter intake tank, soluble BOD removal rate, and sludge conversion rate.

Explanation of symbols

1 Organic substance intake tank 2 Self-digestion tank 3 Precipitation tank

Claims (2)

In a biological treatment method in which organic matter in organic wastewater is removed aerobically by the action of microorganisms in the presence of an uncoupling agent,
An organic substance ingesting step for ingesting organic matter in the wastewater into the microbial cells, and a self-digesting step for self-digesting the microorganism ingesting the organic matter, wherein the self-digestion step is performed under a pH condition different from that of the organic matter ingesting step A way to do ,
A biological treatment method for organic wastewater, characterized in that the organic substance ingesting step is carried out in the range of pH 5 to 6.5, and the self-digestion step is carried out in the range of pH 7 to 9 . The biological wastewater according to claim 1, wherein VSS retained in the self-digestion step is 80% or more based on a total of VSS retained in the organic matter intake step and the self-digestion step. Processing method.

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