JP2007260604A - Organic acid generation method, organic acid generation apparatus, and wastewater treatment facility - Google Patents

Abstract

An organic acid generation method, an organic acid generation apparatus, and a wastewater treatment facility capable of saving energy are provided.
An organic acid generator includes a temperature adjusting unit that adjusts the temperature of raw sludge, and a fermentation tank that anaerobically ferments the temperature-adjusted raw sludge to obtain an organic acid. The temperature adjustment unit 2 includes a heat pump 51 that uses treated water obtained by wastewater treatment using an organic acid as a heat source or a cold heat source, and heats or cools raw sludge using the heat pump 51.
[Selection] Figure 1

Description

  The present invention relates to an organic acid generation method, an organic acid generation apparatus, and a wastewater treatment facility using them, in which sludge is anaerobically fermented to generate an organic acid.

  Conventionally, denitrification or dephosphorization of sewage has been carried out by biological treatment methods to prevent the occurrence of abnormal algae and sea cucumbers due to eutrophication of rivers, seas, lakes, etc. Organic substances used in this biological treatment method In order to obtain sewage sludge, a method of anaerobically fermenting sewage sludge is known. An organic acid can be produced by an organic acid fermentation treatment using such sewage sludge as a raw material, and the produced organic acid can be effectively used as an organic source in a biological treatment method.

In such an organic acid fermentation treatment of sludge, it is necessary to optimize the temperature of the sludge during fermentation in order to increase the production rate of the organic acid used in the biological treatment method. Describes that fermentation of sewage sludge is efficiently performed at a predetermined temperature.
Research on practical application of advanced sewage treatment system using pre-coagulation and carrier, “2001 Annual Report on New Research Institute for Sewerage Technology”, New Organization for Sewerage Technology Promotion, October 2002, 2/2, P131-136

  However, the temperature of sewage sludge, which is a raw material for organic acids, varies depending on the influence of seasons and weather, such as high in summer and low in winter. Therefore, in the method of Non-Patent Document 1, in order to maintain the sewage sludge during fermentation at a constant temperature, it is necessary to heat or cool the inside of the fermenter according to the temperature of the introduced sewage sludge. And in an organic acid production | generation apparatus and a sewage treatment facility using the same, in order to attain energy saving, also when heating and cooling a sewage sludge, it is calculated | required to save required energy.

  Then, an object of this invention is to provide the organic acid production | generation method, organic acid production | generation apparatus, and waste water treatment equipment which can aim at energy saving.

  The organic acid production method of the present invention is an organic acid production method in which sludge is fermented anaerobically to produce an organic acid, a temperature adjustment step for adjusting the temperature of the sludge, and a sludge whose temperature is adjusted in the temperature adjustment step. A fermentation process for anaerobically fermenting to obtain an organic acid, and in the temperature adjustment process, using a heat pump that uses treated water obtained by wastewater treatment using an organic acid as a heat source or a cold source, Heating or cooling is performed.

  In this organic acid production method, the sludge can be adjusted to an appropriate temperature in the temperature adjustment step in order to improve the production rate of the organic acid. Moreover, in the temperature adjustment process, since the heat pump which uses treated water as a heat source or a cold heat source is used, heating or cooling using the thermal energy possessed by the treated water is possible. Accordingly, it is possible to effectively use the heat energy of the treated water that is originally discarded, and to save energy for adjusting the temperature of the sludge.

  Moreover, it is preferable that the organic acid production | generation method of this invention is further equipped with the washing | cleaning process which supplies process water to the sludge flow path in which sludge flows in a temperature adjustment process, and wash | cleans a sludge flow path. In the sludge flow path, there is a possibility that solids contained in the flowing sludge may accumulate, and the smooth flow of sludge is hindered by the accumulation of solids, which may reduce the temperature adjustment efficiency. However, according to this organic acid generation method, the sludge flow path is washed by the washing process, so that the accumulation of solid matter in the sludge flow path is suppressed, and as a result, the sludge is smoothly heated or cooled in the temperature adjustment process. To be done. Moreover, since the treated water originally discarded is effectively used for cleaning the sludge flow path, the cost of the cleaning water can be saved.

  Moreover, in the temperature adjustment step, it is preferable to adjust the temperature of the sludge so that the temperature of the sludge during fermentation in the fermentation step becomes 18 to 23 ° C. If the sludge is fermented at such a temperature, the organic acid production rate can be improved.

  The organic acid generator of the present invention is an organic acid generator that anaerobically fertilizes sludge to produce an organic acid. The temperature is adjusted by the temperature adjusting means for adjusting the temperature of the sludge and the temperature adjusting means. A fermenter that ferments sludge anaerobically to obtain an organic acid, and the temperature adjustment means has a heat pump that uses treated water obtained by wastewater treatment using the organic acid as a heat source or a cold source, Heating or cooling sludge is performed using a heat pump.

  In this organic acid generator, the sludge can be adjusted to an appropriate temperature by the temperature adjusting means in order to improve the production rate of the organic acid. Moreover, since the temperature adjusting means includes a heat pump that uses the treated water as a heat source or a cold heat source, it can be heated or cooled using the thermal energy held by the treated water. Accordingly, it is possible to effectively use the heat energy of the treated water that is originally discarded, and to save energy for adjusting the temperature of the sludge.

  Moreover, it is preferable that the organic acid generator of the present invention further includes a cleaning unit that supplies the treated water to the sludge flow path of the temperature adjusting unit through which the sludge flows to wash the sludge flow path. In the sludge flow path, there is a possibility that solids contained in the flowing sludge may accumulate, and the smooth flow of sludge is hindered by the accumulation of solids, which may reduce the temperature adjustment efficiency. However, according to this organic acid generator, since the sludge flow path is washed by the washing means, solid matter accumulation in the sludge flow path is suppressed, and as a result, the sludge is smoothly heated or cooled in the temperature adjusting means. To be done. Moreover, since the treated water originally discarded is effectively used for cleaning the sludge flow path, the cost of the cleaning water can be saved.

  Moreover, it is preferable that a temperature adjustment means adjusts the temperature of sludge so that the temperature of the sludge in fermentation in a fermenter may be 18-23 degreeC. If the sludge is fermented at such a temperature, the organic acid production rate can be improved.

  Moreover, the wastewater treatment facility of the present invention includes any one of the organic acid generators described above and a biological treatment tank that introduces wastewater and biologically treats the wastewater using the organic acid obtained by the organic acid generator. It is characterized by that. According to this wastewater treatment facility, the energy used for organic acid generation in the organic acid generator can be suppressed, so that energy for wastewater treatment can be saved.

  According to the organic acid generation method, the organic acid generation apparatus, and the wastewater treatment facility of the present invention, energy can be saved.

  Hereinafter, preferred embodiments of an organic acid generation method, an organic acid generation apparatus, and a wastewater treatment facility according to the present invention will be described in detail with reference to the drawings.

  A wastewater treatment facility 100 shown in FIG. 1 is employed in a sewage treatment plant, and is a facility that performs advanced treatment including biological nitrogen removal and biological phosphorus removal on sewage. As shown in the figure, the wastewater treatment facility 100 includes an organic acid generator 1 together with a first sedimentation tank 3, a biological treatment tank 5, and a final sedimentation tank 7.

  In the wastewater treatment facility 100, a solid substance having a relatively large particle size is settled and separated in a sand basin (not shown) of a sewage treatment plant, and sieves such as cloth, empty cans and vinyl are removed by a screen, and pumped from a pump well. The raised inflow sewage is introduced through the line L1. The inflowing sewage from the line L1 is first introduced into the settling basin 3 and separated into raw sludge and other supernatant liquid that sink to the bottom of the first settling basin 3 by gravity settling. The separated raw sludge is scraped to the sludge reservoir 3a by a sludge scraper (not shown), and a part thereof is sent to the organic acid generator 1 through the line L11, and the remainder is sludge treatment (not shown) together with the excess sludge. It is sent to the tank for processing. The supernatant liquid is sent to the biological treatment tank 5 through the line L2 as water to be treated. Although details will be described later, the organic acid generator 1 ferments the raw sludge, and discharges a fermentation broth containing an organic acid such as acetic acid, propionic acid, and butyric acid from the line L20.

  The biological treatment tank 5 is a treatment tank that performs biological treatment by an anaerobic-anoxic-aerobic method, and includes an anaerobic tank 5a, an anaerobic tank 5b, and an aerobic tank 5c in this order. Water to be treated, which is a supernatant liquid introduced from the line L2 into the anaerobic tank 5a, is sent in the order of the anaerobic tank 5a, the anaerobic tank 5b, and the aerobic tank 5c, while anaerobic treatment and anaerobic treatment are performed in each tank After the aerobic treatment, the final settling tank 7 is sent through the line L3. At this time, the denitrification reaction or the dephosphorization reaction of the to-be-processed water in the biological treatment tank 5 is accelerated | stimulated by supplying the fermented liquor containing an organic acid from the organic acid production | generation apparatus 1 to the anaerobic tank 5a through the line L20. It will be. Further, the aerobic tank 5c is provided with an air diffuser 5d, and the water to be treated in the aerobic tank 5c is aerated by the air sent from the blower 5e. Further, the staying liquid in the aerobic tank 5c is sent to the anoxic tank 5b through the line L4 by the circulation pump 5f and circulated. Here, the fermentation liquid may be supplied from the line L20 to the anoxic tank 5b.

  The biologically treated water sent to the final settling basin 7 is discharged through the line L5 after the suspended activated sludge is settled and separated. A part of the discharged treated water is sent to the organic acid generator 1 through the line L8, and the rest is discharged to a river or the like after tertiary treatment and sterilization treatment are performed in an unillustrated facility. The activated sludge settled in the final sedimentation basin 7 is discharged from the activated sludge reservoir 7a through the line L6. A part of the discharged activated sludge is returned to the anaerobic tank 5a of the biological treatment tank 5 through the line L7, and the rest is processed through a sludge treatment process in a facility (not shown).

  The organic acid generator 1 will be described in more detail. As described above, the organic acid generator 1 is an apparatus that uses raw sludge separated from inflow sewage as a raw material, and an organic matter in the raw sludge is anaerobically fermented by acid-producing bacteria to obtain an organic acid. As shown in FIG. 1, the organic acid generator 1 includes a sludge storage tank 23, a strainer 26, a sludge temperature adjustment unit (temperature adjustment means) 2, an acid fermentation tank 27, a concentration tank 43, and a fermentation liquid storage tank 49. ing. Raw sludge as a raw material is introduced into the apparatus 1 through the line L11, first stored temporarily in the sludge storage tank 23, and stirred by the sludge stirrer 25 provided in the sludge storage tank 23. The raw sludge that has been stirred to a uniform sludge concentration passes through the strainer 26 that removes contaminants and the like, and is then introduced into the temperature adjustment unit 2 through the line L12 by the sludge supply pump P1. The raw sludge heated or cooled in the temperature adjusting unit 2 and adjusted to a temperature of 18 to 23 ° C. is introduced into the acid fermentation tank 27 through the line L13. Details of the temperature adjusting unit 2 will be described later.

  The sludge storage tank 23 and the strainer 26 may not be provided, and the raw sludge from the line L11 may be directly introduced into the acid fermentation tank 27. Moreover, when the sludge density | concentration of the raw sludge introduced into the sludge storage tank 23 is too low, it is preferable to introduce | transduce into the sludge storage tank 23 or the acid fermentation tank 27, after pre-concentrating with a sludge concentration tank separately.

  The acid fermentation tank 27 is a tank that ferments the introduced raw sludge to produce an organic acid. The acid fermentation tank 27 includes an acid fermentation stirrer 29 for stirring the fermentation sludge S staying in the tank, a pH sensor 31 for measuring the pH of the fermentation sludge S, a temperature sensor 33 for measuring the temperature of the fermentation sludge S, and the fermentation sludge S. ORP sensor 34 for measuring the oxidation-reduction potential of pH, and pH adjusting device 35 for adjusting the pH of fermentation sludge S by introducing an acid agent (for example, hydrochloric acid) or an alkali agent (for example, sodium hydroxide) into the tank. ing. Moreover, although not shown in figure, the acid fermentation tank 27 may be equipped with the air supply apparatus for adjusting the oxidation-reduction potential of the fermentation sludge S. In the acid fermentation tank 27, fermentation conditions such as pH in the tank are appropriately controlled based on information obtained from the pH sensor 31, temperature sensor 33, and ORP sensor 34, and acid producing bacteria are in the fermentation sludge S. Organic acid fermentation reaction that decomposes the organic matter to produce an organic acid proceeds. Suitable fermentation conditions for the acid fermenter 27 are, for example, a temperature of about 20 ° C., an ORP of about −300 to −200 mV, and a pH of about 4 to 6.5.

  Thus, after introducing raw sludge into the temperature adjustment part 2 and adjusting temperature, it introduce | transduces into the acid fermentation tank 27, and the raw sludge in the acid fermentation tank 27 becomes temperature suitable for fermentation, such as 18-23 degreeC. . As a result, in the fermenter 27, the organic acid production rate is improved by an efficient organic acid fermentation reaction. And the fermented sludge containing the organic acid produced | generated by this fermentation reaction is sent to the concentration tank 43 through the line L14.

  The concentration tank 43 has a circular cross section, and includes a scraper 47 having a scraping blade 47a that rotates at the lower part of the tank. The fermented sludge introduced into the concentration tank 43 through the line L14 is solid-liquid separated by gravity sedimentation. A part of the solid component that has been gravity settled by the solid-liquid separation is returned to the acid fermentation tank 27 by the pump P2 through the line L16 as concentrated sludge and subjected to fermentation treatment again. The remainder of the solid component that has been gravity settled is discharged out of the equipment 100 through the line L17 as surplus sludge, and is incinerated or digested by the equipment (not shown) together with the fermentation residue and the like generated in the acid fermentation tank 27. Here, instead of the concentration tank 43 that performs solid-liquid separation by gravity sedimentation, a membrane separation tank that performs solid-liquid separation with a separation membrane may be employed.

  On the other hand, the fermented liquid separated as the supernatant in the concentration tank 43 is sent to the fermented liquid storage tank 49 through the line L15, and once stored in the fermented liquid storage tank 49, the fermented liquid containing the organic acid through the line L20. As discharged. And as above-mentioned, this fermentation liquid discharged | emitted through the line L20 is supplied to the biological treatment tank 5 as an organic source of an anaerobic-anoxic-aerobic method. Note that the fermentation solution storage tank 49 may be omitted, and the fermentation solution from the concentration tank 43 may be directly supplied to the biological treatment tank 5.

  In such a wastewater treatment facility 100, in order to efficiently perform dephosphorization treatment and denitrification treatment of water to be treated in the biological treatment tank 5, the organic acid production rate in the organic acid production apparatus 1 is improved. is required. In this apparatus 1, the fermented sludge S contains not only acid producing bacteria but also methanogenic bacteria. Therefore, in the fermented sludge S of the acid fermentation tank 27, the acid producing bacteria change the sludge into an organic acid. The acid fermentation reaction and the methane fermentation reaction in which the methanogenic bacteria change the generated organic acid into methane gas proceed simultaneously. For this reason, in order to improve the production rate of the organic acid, it is appropriate to set the temperature of the fermentation sludge S to 18 to 23 ° C. in consideration of the balance of the activity of the organic acid fermentation reaction and the methane fermentation reaction. If the temperature of the fermented sludge S is lower than 18 ° C, the activity of the organic acid fermentation reaction is low, so that the production of the organic acid itself is too little. If the temperature of the fermented sludge S is higher than 23 ° C, the activity of the methane fermentation reaction is high. This is because a large amount of organic acid produced is changed to methane gas because it is high.

  However, since the temperature of the sewage introduced into the wastewater treatment facility 100 changes depending on the season, the temperature of the raw sludge separated from the sewage also changes. For example, the temperature of raw sludge in winter is about 15 ° C., and the temperature of raw sludge in summer is about 25 ° C. Thus, since the temperature of raw sludge is not constant depending on the season and may fall outside the above range suitable for organic acid generation, as described above, the organic acid generator 1 heats raw sludge or A temperature adjusting unit 2 for cooling is provided.

  And this temperature adjustment part 2 has the heat pump 51 in order to make the energy required for heating or cooling of raw sludge as small as possible, The temperature adjustment part 2 uses this heat pump 51, and is an acid fermenter. The raw sludge before being introduced to No. 27 is heated or cooled.

  Hereinafter, the temperature adjusting unit 2 will be described. The temperature adjustment unit 2 includes the heat pump 51, a treated water flow path 53a through which treated water introduced from the line L8 flows, a sludge flow path (sludge flow path) 53b through which raw sludge introduced from the line L12 flows, And a circulation channel 53c through which water circulates. Furthermore, the temperature adjustment unit 2 includes a heat exchanger 52c that performs heat exchange between raw sludge flowing through the sludge flow path 53b and water flowing through the circulation flow path 53c. The heat pump 51 includes a circulation channel 51r through which a condensable working fluid such as hydrocarbon and ammonia circulates, and a compressor 51s and an expansion valve 51t provided on the circulation channel 51r. Furthermore, the heat pump 51 includes a heat exchanger 52a that performs heat exchange between the circulation channel 51r and the treated water channel 53a. The heat pump 51 also includes a heat exchanger 52b that performs heat exchange between the circulation channel 51r and the circulation channel 53c. Various types of heat exchangers 52a, 52b, and 52c can be used. Here, for example, a shell-and-tube heat exchanger having a solid wall heat transfer surface can be employed.

  Based on such a configuration, the heat pump 51 can cause heat transfer between the treated water in the treated water channel 53a and the water in the circulation channel 53c. In addition, by switching and controlling a four-way valve (not shown) provided in the circulation channel 51r and controlling the flow direction of the working fluid, it is possible to cause such heat movement to be performed in both directions. .

  For example, in the winter season, when the temperature of the raw sludge in the line L12 is lower than 18 ° C., the heat exchanger 52a functions as an evaporator and the heat exchanger 52b functions as a condenser. Control the flow direction. In this case, due to the operation of the heat pump 51, the temperature of the treated water in the treated water channel 53a moves to the water in the circulation channel 53c via the working fluid of the heat pump 51. Further, the temperature of the water in the circulation channel 53c moves to the raw sludge in the sludge channel 53b in the heat exchanger 52c, so that the temperature of the raw sludge increases. In this way, warming of the raw sludge is achieved, and the temperature of the raw sludge is set to 18 to 23 ° C. suitable for organic acid production. At this time, the treated water in the treated water channel 53a is cooled, discharged to the line L9, and merged with the line L5.

  Further, for example, in the summer, when the temperature of the raw sludge in the line L12 is higher than 23 ° C., the circulation channel is configured so that the heat exchanger 52a functions as a condenser and the heat exchanger 52b functions as an evaporator. The flow direction in 51r is controlled. In this case, due to the operation of the heat pump 51, heat is transferred in the reverse order to the above, and the temperature of the raw sludge is lowered. In this way, cooling of the raw sludge is achieved, and the temperature of the raw sludge is set to 18 to 23 ° C. suitable for organic acid production. At this time, the treated water in the treated water flow path 53a is heated, discharged to the line L9, and joined to the line L5.

  Thus, since the organic acid production | generation apparatus 1 uses the treated water generated in large quantities in the installation 100 as a heat source or a cold heat source, it is not necessary to prepare the heat source from the outside. In addition, due to the action of the heat pump 51, the raw sludge can be heated or cooled from a state where there is almost no temperature difference between the raw sludge and the treated water. Therefore, although a large amount of treated water was originally sent to the subsequent process as it is, the thermal energy possessed by this treated water can be used effectively, and the energy required for temperature adjustment of raw sludge can be saved. it can. In addition, by adjusting the temperature of the raw sludge, the production rate of organic acid is improved regardless of the seasonal change in the sewage temperature, and the dephosphorization treatment and denitrification treatment of the treated water in the biological treatment tank 5 are performed. It is done efficiently.

  In the temperature adjusting unit 2, since raw sludge containing solids flows through the sludge flow path 53b, scale and slime are likely to adhere to the sludge flow path 53b. By such a deposit, the smooth flow of raw sludge in the sludge channel 53b is hindered, and the heat transfer surface of the sludge channel 53b in the heat exchanger 52c in which heat exchange is performed is covered with the deposit. The heat exchange efficiency of the heat exchanger 52c will decrease. Further, in the vicinity of the heat transfer surface, the flow path may be narrow in order to improve the heat exchange efficiency, and therefore the flow path is likely to be blocked. Therefore, the organic acid generator 1 includes cleaning lines (cleaning means) L61 and L62 for cleaning the sludge flow path 53b.

  In the cleaning process of the sludge flow path 53b, the valve V1 of the temperature adjustment unit 2 is closed and the valve V2 is opened, whereby the treated water in the treated water flow path 53a flows into the sludge flow path 53b through the cleaning line L61. In this case, by closing the valves V3 and V4 and opening the valve V5, the inflowing treated water flows through the sludge flow path 53b in the heat exchanger 52c and is discharged from the cleaning line L62. And the deposit | attachment of the sludge flow path 53b peels by such a flow of treated water, and the heat-transfer surface of the sludge flow path 53b in the heat exchanger 52c is wash | cleaned. Therefore, coupled with the smooth flow of raw sludge in the sludge flow path 53b, the heat exchange efficiency on the heat transfer surface can be maintained well. As a device for removing deposits on the heat transfer surface, a sponge ball circulation device and a brush cleaning device are known. However, the cleaning means in the organic acid generator 1 has facilities and operations as compared with these devices. Has the advantage of being simple. The cleaning process as described above can be performed, for example, by operating the valves V <b> 1 to V <b> 5 every predetermined operation time of the facility 100.

  In the above-described cleaning process, if a gas such as air or nitrogen is introduced from the line L63 so as to join the cleaning line L61, and the sludge flow path 53b is cleaned with a mixed fluid of treated water and gas, the cleaning effect is further improved. Can be increased. In the above cleaning means, the treated water flows through the sludge flow path 53b in the direction opposite to the normal raw sludge flow direction, but the treated water flows in the same direction as the normal raw sludge flow direction. However, the same effect can be obtained. Alternatively, two heat exchangers 52c may be provided, and the normal operation and the cleaning process may be alternately performed in each heat exchanger 52c. If it does in this way, in the heat exchanger 52c, the temperature adjustment of raw sludge can be performed continuously.

  The present invention is not limited to the embodiment described above. For example, the sludge as the raw material of the organic acid introduced into the organic acid generator 1 is not limited to the sludge generated in the first settling basin 3 but may be sludge generated in the final settling basin 7 or the first settling basin. 3 and the sludge of the final sedimentation basin 7 may be used in combination.

It is a figure which shows one Embodiment of the waste water treatment facility which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic acid production | generation apparatus, 3 ... Temperature adjustment part (temperature adjustment means), 5 ... Biological treatment tank, 27 ... Acid fermentation tank, 51 ... Heat pump, 53b ... Sludge flow path (sludge flow path), 100 ... Waste water treatment equipment , L61, L62 ... cleaning line (cleaning means), S ... fermented sludge.

Claims (7)

In the organic acid production method in which sludge is anaerobically fermented to produce an organic acid,
A temperature adjusting step for adjusting the temperature of the sludge;
A fermentation step of anaerobically fermenting the sludge whose temperature has been adjusted in the temperature adjustment step to obtain the organic acid,
In the temperature adjustment step, the sludge is heated or cooled using a heat pump that uses the treated water obtained by the wastewater treatment using the organic acid as a heat source or a cold source. Method.   The organic acid generation method according to claim 1, further comprising a cleaning step of supplying the treated water to a sludge flow path in which the sludge flows in the temperature adjusting step to wash the sludge flow path. In the temperature adjustment step,
The method for producing an organic acid according to claim 1 or 2, wherein the temperature of the sludge is adjusted so that the temperature of the sludge during fermentation in the fermentation step is 18 to 23 ° C. In an organic acid generator that produces an organic acid by anaerobically fertilizing sludge,
Temperature adjusting means for adjusting the temperature of the sludge;
A fermentor for anaerobically fermenting the sludge whose temperature is adjusted by the temperature adjusting means to obtain the organic acid,
The temperature adjusting means includes a heat pump using a treated water obtained by the waste water treatment using the organic acid as a heat source or a cold heat source, and heats or cools the sludge using the heat pump. An organic acid generator.   5. The organic acid generator according to claim 4, further comprising a cleaning means for supplying the treated water to a sludge flow path of the temperature adjusting means through which the sludge flows to wash the sludge flow path. The temperature adjusting means is
The organic acid generator according to claim 4 or 5, wherein the temperature of the sludge is adjusted so that the temperature of the sludge during fermentation in the fermenter is 18 to 23 ° C. The organic acid generator according to any one of claims 4 to 6,
A wastewater treatment facility comprising: a biological treatment tank that introduces wastewater and biologically treats the wastewater using an organic acid obtained by the organic acid generator.

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