JP2011206667A - Method and apparatus for treating organic waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for treating organic waste water which can reduce the volume of sludge.SOLUTION: The organic waste water is treated by using an organic waste water treatment apparatus which includes: a first solid-liquid separation tank 1 for removing primary settled sludge from the organic waste water; an acid fermentation treatment tank 3 for performing acid fermentation treatment of the primary settled sludge; an aeration tank 5 for performing activated sludge treatment of the organic waste water from which the primary settled sludge has been removed; a second solid-liquid separation tank 6 for removing surplus sludge from the treated liquid obtained after the activated sludge treatment; a solubilization treatment tank 8 for heating the surplus sludge to perform solubilization treatment thereof; a boiler 11, heating means Q2, Q3 for heating the surplus sludge and the primary settled sludge using heat of the boiler 11; a sludge mixing tank 4 for mixing the primary settled sludge obtained after the acid fermentation treatment and the surplus sludge obtained after the solubilization treatment and supplying the mixture to the methane fermentation tank; and the methane fermentation tank 9.

Description

  The present invention relates to an organic wastewater treatment method and treatment apparatus for treating organic wastewater such as sewage with activated sludge and treating methane fermentation of primary sludge and excess sludge discharged during the activated sludge treatment process.

  As a method for treating organic wastewater such as sewage, conventionally, the activated sludge treatment is performed by removing the first settling sludge from the organic wastewater, and the excess sludge is removed from the treated liquid after the activated sludge treatment. In addition, primary sludge and surplus sludge discharged in the activated sludge treatment process of organic wastewater is subjected to methane fermentation treatment to reduce the sludge volume.

  For example, Patent Document 1 below discloses that primary sludge and excess sludge are concentrated as necessary, and then heat-treated and then subjected to methane fermentation.

Japanese Patent Laying-Open No. 2003-305498 (see paragraph number 0030, FIG. 1)

  Since primary sludge is a sludge containing a large amount of hard-to-decompose components such as fibers, it cannot be modified to a state suitable for methane fermentation even if it is heat-treated. Could not improve.

  For this reason, when the mixed sludge of primary sludge and surplus sludge is heat-treated as in the above-mentioned Patent Document 1, a component having little heat treatment effect (hardly decomposable component) is also subjected to heat treatment. There was a problem that energy wasted, heat energy use efficiency was poor, and processing costs increased. Moreover, the methane fermentation treatment efficiency was not sufficient, and the volume reduction of sludge was not enough.

  Therefore, an object of the present invention is to provide an organic material that can efficiently reduce the volume of sludge by methane fermentation treatment of primary sludge and surplus sludge discharged during the process of treating organic wastewater with activated sludge. An object of the present invention is to provide a wastewater treatment method and a treatment apparatus.

  In achieving the above object, the organic wastewater treatment method of the present invention includes a primary sludge removal step for removing primary sedimentation sludge from the organic wastewater, and an activated sludge treatment for organic wastewater from which primary sedimentation sludge has been removed. An activated sludge treatment step, a surplus sludge removal step for removing excess sludge from the treated liquid after the activated sludge treatment, and a methane fermentation treatment step for introducing the initial settling sludge and the excess sludge into a methane fermentation tank to perform methane fermentation. A method for treating organic wastewater having an initial fermentation sludge treatment at 30 to 40 ° C. for 3 to 4 days, solubilizing the excess sludge at 60 to 90 ° C., and then mixing the two. Mixed sludge, and the mixed sludge is introduced into the methane fermentation tank.

The initial settling sludge in the present invention refers to settling sludge in an initial settling tank or the like of a treatment facility for organic wastewater such as sewage. The primary sedimentation sludge is sludge mainly containing hardly decomposable components such as fibers, and hardly decomposes even when heat-treated, but it is easily methane-fermented by acid fermentation treatment at 30 to 40 ° C. for 3 to 4 days. Modified to properties. Further, surplus sludge is sludge mainly containing organic matter such as microorganisms, and by heat treatment, cell membranes of microorganisms are destroyed, and the sludge is reformed to be easily methane-fermented.
According to the organic wastewater treatment method of the present invention, primary sludge and excess sludge are separately subjected to acid fermentation treatment for primary sedimentation sludge and solubilization treatment at 60 to 90 ° C for excess sludge. Therefore, the treatment suitable for each sludge is performed individually, and the initial settling sludge and excess sludge can be reformed to a property that can be efficiently subjected to methane fermentation treatment, and the heat energy and treatment time required for sludge reforming treatment can be reduced. Can be reduced. And since the sludge modified to the property that is easily treated with methane fermentation can be supplied to the methane fermentation tank, the methane fermentation efficiency of sludge can be improved and the amount of final sludge discharged can be reduced, and the sludge volume reduction is excellent. ing.

  The organic wastewater treatment method of the present invention preferably heats the excess sludge using biogas generated from the methane fermentation tank as a heat source, and then heats the mixed sludge using the residual heat.

  In the method for treating organic wastewater according to the present invention, it is preferable to heat the primary sludge directly or indirectly using the heat of the solubilized surplus sludge to perform acid fermentation treatment.

  According to each said aspect, effective utilization of a thermal energy can be aimed at, and organic waste water can be processed with a smaller thermal energy.

  Moreover, the organic wastewater treatment apparatus of the present invention includes a first solid-liquid separation tank that removes primary sedimentation sludge from the organic wastewater, an aeration tank that performs activated sludge treatment on organic wastewater from which primary sedimentation sludge has been removed, A second solid-liquid separation tank that removes excess sludge from the treated liquid after sludge treatment, a methane fermentation tank that performs methane fermentation treatment of the initial settling sludge and the excess sludge, and biogas generated from the methane fermentation tank An organic wastewater treatment apparatus comprising a boiler that generates a heat source, an acid fermentation treatment tank for acid fermentation treatment of the primary sedimentation sludge, and a solubilization treatment tank for heating and solubilizing the excess sludge The heating means for heating the excess sludge and the first settling sludge using the heat of the boiler, and the first settling sludge after the acid fermentation treatment and the excess sludge after the solubilization treatment are mixed and supplied to the methane fermentation tank Characterized by comprising a sludge mixing tank That.

  According to the organic wastewater treatment apparatus of the present invention, the primary sedimentation sludge is subjected to an acid fermentation treatment in an acid fermentation treatment tank, and the excess sludge is solubilized in a solubilization treatment tank, and then the primary sedimentation sludge after the acid fermentation treatment and The surplus sludge after the solubilization treatment is mixed in the sludge mixing tank and supplied to the methane fermentation tank. In this way, the initial settling sludge and surplus sludge are treated separately for each sludge in the acid fermentation treatment tank and the solubilization treatment tank. It can be reformed to be easily treated and supplied to the methane fermentation tank, and the thermal energy and processing time required for sludge reforming can be reduced. And since the sludge modified to the property that is easily methane-fermented can be supplied to the methane fermentation tank, the methane fermentation efficiency of the sludge can be improved and the final sludge discharge can be reduced, and the sludge volume can be reduced. Yes.

  The organic wastewater treatment apparatus of the present invention, as the heating means, a path between the first solid-liquid separation tank and the acid fermentation treatment tank or a first heat exchanger provided in the acid fermentation treatment tank, In the path between the second solid-liquid separation tank and the solubilization tank or the second heat exchanger provided in the solubilization tank, and the path between the sludge mixing tank and the methane fermentation tank A third heat exchanger provided, and at least part of the heat source generated from the boiler exchanges heat with the surplus sludge via the second heat exchanger, and then the third heat exchanger. And at least a part of the excess sludge after the solubilization treatment exchanges heat with the first settling sludge via the first heat exchanger, It is preferable to be configured to be introduced into the sludge mixing tank. According to this aspect, heat utilization efficiency is high, and organic wastewater can be treated with smaller heat energy.

  According to the present invention, the initial settling sludge and the excess sludge are treated separately for each sludge, and both are mixed and supplied to the methane fermentation tank. It can be modified to a property that is easily treated with methane fermentation, and the heat energy and processing time required for the reforming process can be reduced. And since the sludge modified to the property that is easily methane-fermented can be supplied to the methane fermentation tank, the methane fermentation efficiency of the sludge can be improved and the final sludge discharge can be reduced, and the sludge volume can be reduced. Yes.

It is the schematic of the organic wastewater treatment apparatus of this invention.

  One embodiment of the organic wastewater treatment apparatus of the present invention will be described with reference to FIG.

  As shown in FIG. 1, a pipe L <b> 1 extending from a supply source of organic wastewater such as sewage is connected to the first solid-liquid separation tank 1.

  The first solid-liquid separation tank 1 in the present embodiment is an initial sedimentation tank in a treatment apparatus for organic wastewater such as sewage, and solid-liquid separates solids such as fiber components in the organic wastewater to perform initial sedimentation. This is a treatment tank that separates sludge and separated liquid. The first solid-liquid separation tank 1 is not particularly limited as long as it has a configuration capable of solid-liquid separation of organic waste water, and a solid-liquid separation apparatus such as a gravity precipitation tank can be widely used.

  A pipe L <b> 2 extends from the outlet of the first settling sludge in the first solid-liquid separation tank 1 and is connected to the first settling sludge storage tank 2. The initial sedimentation sludge storage tank 2 stores the initial sedimentation sludge sent from the first solid-liquid separation tank 1 and functions for adjusting the supply amount of the initial sedimentation sludge to the subsequent acid fermentation treatment tank 3 have.

  An acid fermentation treatment tank 3 is disposed downstream of the initial settling sludge storage tank 2, and is connected via a pipe L3 in which a heat exchanger Q1 is interposed. The acid fermentation treatment tank 3 is a treatment tank for acid-fermenting an organic substance by the action of anaerobic bacteria in the tank to produce an organic acid such as acetic acid, butyric acid, and propionic acid. A pipe L4 extends from the acid fermentation treatment tank 3 and is connected to the subsequent sludge mixing tank 4. In addition, you may make it provide the heat exchanger Q1 in the acid fermentation processing tank 3, and heat the inside of the acid fermentation processing tank 3. FIG. There is no limitation in particular as heat exchanger Q1. For example, a heat exchanger such as a spiral type in which the first settling sludge passes through a spiral pipe configured inside the heat exchanger, and the excess sludge heated outside the spiral pipe passes to exchange heat. Can be preferably used.

  A pipe L5 extends from the separation liquid discharge port of the first solid-liquid separation tank 1 and is connected to the aeration tank 5. The aeration tank 5 is a treatment tank that removes organic substances, nitrogen components, and the like by treating the organic waste water (separated liquid) from which the initial settling sludge has been removed with the action of microorganisms present in the tank. The aeration tank 5 is not particularly limited as long as activated sludge containing microorganisms stays in the tank and the activated sludge treatment of sewage can be performed by the action of microorganisms.

  A second solid-liquid separation tank 6 is disposed downstream of the aeration tank 5, and is connected via a pipe L6. The second solid-liquid separation tank 6 is a treatment tank for solid-liquid separation of organic waste water (hereinafter referred to as activated sludge treated water) treated with activated sludge in the aeration tank 5 into excess sludge and separated treatment liquid. The second solid-liquid separation tank 6 is not particularly limited as long as it has a configuration capable of solid-liquid separation of activated sludge treated water, and can be widely used, such as a gravity sedimentation tank, a membrane separation apparatus, and a centrifugal separation apparatus.

  A pipe L7 extends from the discharge port of the separation processing liquid in the second solid-liquid separation tank 6 and is connected to a drainage system (not shown). Further, a pipe L8 extends from the surplus sludge discharge port and is connected to the surplus sludge storage tank 7.

  The excess sludge storage tank 7 is a storage tank for storing excess sludge sent from the second solid-liquid separation tank 6, and a part of the excess sludge stored in the excess sludge storage tank 7 is aerated through the return pipe L16. It is returned to the tank 5 as return sludge, and the remainder is supplied to the subsequent solubilization tank 8. Moreover, the excess sludge storage tank 7 has a function for adjusting the supply amount of the excess sludge to the subsequent solubilization treatment tank 8.

  A solubilization treatment tank 8 is disposed downstream of the excess sludge storage tank 7, and is connected via a pipe L9 provided with a heat exchanger Q2. The solubilization processing tank 8 is a processing tank for solubilizing surplus sludge, and may have any heat insulation structure, and is not particularly limited. Moreover, a stirrer etc. may be provided and it may be comprised so that a shearing force can be applied to the excess sludge in a tank. The heat exchanger Q2 can be the same as the heat exchanger Q1 described above. In addition, the heat exchanger Q2 may be provided in the solubilization processing tank 8, and the inside of the solubilization processing tank 8 may be heated.

  A pipe L10 extends from the solubilization treatment tank 8 and is connected to the sludge mixing tank 4 disposed at the subsequent stage of the solubilization treatment tank 8 through the heat exchanger Q1 described above.

  The sludge mixing tank 4 includes an acid fermented primary sedimentation sludge (hereinafter also referred to as a modified primary sedimentation sludge) sent from the acid fermentation treatment tank 3 and a solubilization treatment sent from the solubilization treatment tank 8. The obtained excess sludge (hereinafter also referred to as reformed excess sludge) is mixed and stored, and has a function for adjusting the supply amount of the mixed sludge to the methane fermentation tank 9 at the subsequent stage.

  In the subsequent stage of the sludge mixing tank 4, a methane fermentation tank 9 connected via a pipe L11 provided with a heat exchanger Q3 is arranged. The heat exchanger Q3 can be the same as the heat exchanger Q1 described above.

  The methane fermentation tank 9 is a treatment tank in which the mixed sludge supplied into the tank is anaerobically treated by the action of anaerobic microorganisms such as methane bacteria and decomposed into biogas such as methane gas. The methane fermentation tank 9 is provided with a stirring device (not shown) for stirring the fermentation liquid in the tank. A methane fermentation liquid extraction pipe L12 extends below the methane fermentation tank 9 and is connected to a sludge treatment system (not shown). Further, from the upper part of the methane fermentation tank 9, a biogas extraction pipe L <b> 13 extends and is connected to the gas holder 10.

  The biogas stored in the gas holder 10 is supplied to the steam boiler 11 connected via the pipe L14 and burned to heat the heat medium flowing in the circulation path L15. Then, the heat medium heated by the steam boiler 11 passes through the heat exchanger Q2 and the heat exchanger Q3 in this order and is heated in the order of excess sludge and mixed sludge, and then returned to the steam boiler 11 again.

  Next, the organic wastewater treatment method of the present invention will be described by taking the case of using the treatment apparatus shown in FIG. 1 as an example.

  First, organic wastewater such as sewage sent from an organic wastewater supply source is supplied to the first solid-liquid separation tank 1, and solids such as fiber components in the organic wastewater are subjected to solid-liquid separation. Separated into primary sludge and separated liquid. The water temperature of this initial sedimentation sludge is approximately 10 to 20 ° C., although it varies depending on the outside air temperature. In addition, the amount of primary sludge discharged varies depending on the properties of the organic wastewater to be treated and various treatment conditions, but the initial sludge: surplus sludge = 6: 4-5 in a solid content ratio with surplus sludge described later. : 5 in many cases.

  The organic waste water (separated liquid) from which the initial settling sludge has been removed is sent to the aeration tank 5 through the pipe L5, where it is treated with activated sludge to remove organic substances and nitrogen components. Then, the activated sludge treated water is withdrawn from the aeration tank 5 through the pipe L6 and is sent to the second solid-liquid separation tank 6 to be separated into the excess sludge and the separated treatment liquid. The water temperature of this excess sludge is approximately 10 to 20 ° C., although it varies depending on the outside air temperature.

  The separation treatment liquid is sent to a drainage system (not shown) through the pipe L7, and is drained out of the system as it is or after being purified by adding chemicals or the like as necessary.

  The surplus sludge is sent to the surplus sludge storage tank 7 through the pipe L8 and is temporarily stored here. A part of the excess sludge stored in the tank is returned to the aeration tank 5 through the return pipe L16 and used for the activated sludge treatment. In addition, the pipe L9 is pulled out from the pipe L9 by a certain amount, and is heated by exchanging heat with the heat medium heated by the steam boiler 11 in the heat exchanger Q2. In the heat exchanger Q2, the flow rate of the excess sludge and the flow rate of the heat medium are adjusted so that the excess sludge is heated to 60 to 90 ° C, preferably 70 to 80 ° C.

  Excess sludge heated to a predetermined temperature in the heat exchanger Q2 is sent to the solubilization tank 8 and can be used at a temperature of 60 to 90 ° C, preferably 70 to 80 ° C for 1 to 4 hours, preferably 2 to 3 hours. Perform solubilization. Further, during the solubilization treatment, a shearing force may be applied such as stirring the excess sludge stored in the tank. Surplus sludge is sludge mainly containing organic substances such as microorganisms, and by performing solubilization treatment in this way, the cytoplasm of microorganisms and the like are destroyed, and the sludge is modified to a property that is easily subjected to methane fermentation treatment. Moreover, fluidity arises and it becomes easy to distribute | circulate the inside of piping.

  Then, the reformed surplus sludge is extracted from the solubilization treatment tank 8 by a certain amount through the pipe L10, passed through the heat exchanger Q1, and sent to the sludge mixing tank 4.

  On the other hand, the first settling sludge is sent to the first settling sludge storage tank 2 through the pipe L2 and temporarily stored therein. Then, the initially settled sludge stored in the tank is pulled out from the pipe L3 by a certain amount, heated in the heat exchanger Q1 by exchanging heat with the above-described reformed excess sludge. The reformed surplus sludge drawn out from the solubilization tank 8 has a high fluidity, and thus smoothly flows through the piping in the heat exchanger. Moreover, since the water temperature of the modified surplus sludge is approximately 60 to 90 ° C., the initial sludge is heated by exchanging heat between the initially settled sludge and the modified surplus sludge. In the heat exchanger Q1, the flow rate of the first settling sludge and the flow rate of the excess surplus sludge are adjusted so that the first settling sludge is heated to 25 to 45 ° C, preferably 30 to 40 ° C. In addition, when the initial settling sludge cannot be heated to a desired temperature only by heat exchange with the reformed surplus sludge, an auxiliary heat source such as a heater may be installed to compensate for the insufficient heating amount with these auxiliary heat sources.

  The initial settling sludge heated to a predetermined temperature by the heat exchanger Q1 is sent to the acid fermentation treatment tank 3 and carried out at 30 to 40 ° C. for 3 to 4 days. Further, during the acid fermentation treatment, a shearing force may be applied, for example, stirring the initially settled sludge stored in the tank. Primary sedimentation sludge is a sludge that mainly contains difficult-to-decompose components such as fibers, and hardly decomposes even when heat-treated, but by acid fermentation treatment, the primary sedimentation sludge is modified to a property that is easy to be subjected to methane fermentation treatment. Is done.

  Then, the modified initial settling sludge is extracted from the acid fermentation treatment tank 3 by a certain amount through the pipe L4 and sent to the sludge mixing tank 4.

  In the sludge mixing tank 4, the modified initial sedimentation sludge sent from the acid fermentation treatment tank 3 and the modified excess sludge sent from the solubilization treatment tank 8 are mixed, and crushed, pulverized, etc. as necessary. Perform the process. Then, a certain amount of the mixed sludge in the tank is drawn from the pipe L11 and heated in the heat exchanger Q3 with the heat medium after heat exchange with the excess sludge to heat the mixed sludge, and then to the methane fermentation tank 9. send. In the heat exchanger Q3, the flow rate of the mixed sludge is adjusted so that the mixed sludge is heated to 40 to 50 ° C, preferably 50 to 60 ° C.

  In the methane fermentation tank 9, the supplied mixed sludge is subjected to anaerobic treatment by the action of anaerobic microorganisms and decomposed into biogas such as methane gas. The fermented liquid after methane fermentation is sent to a sludge treatment system (not shown) through the pipe L12, and is treated by dehydration, incineration, etc. by adding chemicals as necessary. In addition, the biogas generated by methane fermentation is recovered by the gas holder 10, burned by the steam boiler 11, and heats a heat medium (such as high-pressure steam) that circulates in the circulation path L15. The heat medium heated by the steam boiler 11 heats the excess sludge to a predetermined temperature in the heat exchanger Q2, and then heats the mixed sludge to the predetermined temperature with the remaining heat in the heat exchanger Q3. Will be returned. The heat medium returned to the steam boiler is heated again by the steam boiler 11 and flows through the circulation path L15 to heat excess sludge and mixed sludge.

  According to the organic wastewater treatment method of the present invention, primary sedimentation sludge and excess sludge are separately subjected to acid fermentation treatment in the acid fermentation treatment tank 3 for primary sedimentation sludge and acceptable for excess sludge. Since the solubilization treatment is performed in the solubilization treatment tank 8, the treatment suitable for each sludge is performed individually, and the initial settling sludge and the excess sludge can be efficiently modified to a property that can be easily subjected to methane fermentation treatment. The required thermal energy and processing time can be reduced. The methane fermentation tank 9 can be supplied with sludge that has been modified to be easily methane-fermented, so that the methane fermentation efficiency of the sludge can be improved and the final sludge discharged can be reduced, thereby reducing the sludge volume. Are better.

  Moreover, in this embodiment, using the heat medium heated with the steam boiler 11, the excess sludge is heated to a temperature suitable for the solubilization treatment, and the mixed sludge is further converted to a temperature suitable for methane fermentation using the residual heat. And heat the reformed surplus sludge to heat the primary sludge to a temperature suitable for acid fermentation treatment, so the heat utilization efficiency is high, and organic wastewater is produced with less heat energy. Can be processed.

  In this embodiment, the reformed surplus sludge is passed through the heat exchanger Q1, and the initial settling sludge is directly heated using the heat of the reformed surplus sludge. For example, the solubilized with the heat exchanger Q1 is used. A heat medium circulation path may be provided between the treatment tank 8 and the heat of the reformed excess sludge may be used to indirectly heat the first settling sludge via the heat medium. By doing in this way, the utilization efficiency of a heat | fever can be improved and an organic waste water can be processed with a smaller thermal energy.

1: First solid-liquid separation tank 2: Initial settling sludge storage tank 3: Acid fermentation treatment tank 4: Sludge mixing tank 5: Aeration tank 6: Second solid-liquid separation tank 7: Surplus sludge storage tank 8: Solubilization treatment tank 9: Methane fermentation tank 10: Gas holder 11: Steam boiler

Claims (5)

Initial sludge removal process to remove primary sludge from organic waste water, activated sludge treatment process to treat organic waste water from which primary sludge has been removed, and excess sludge from the treatment liquid after activated sludge treatment A wastewater sludge removal step, and a method of treating organic wastewater having a methane fermentation treatment step of introducing the initial sludge and the surplus sludge into a methane fermentation tank to perform methane fermentation treatment,
The initial settling sludge is subjected to acid fermentation treatment at 30 to 40 ° C. for 3 to 4 days, the surplus sludge is solubilized at 60 to 90 ° C., and then mixed to form mixed sludge. An organic wastewater treatment method characterized by being introduced into a tank.   The method for treating organic wastewater according to claim 1, wherein the surplus sludge is heated using biogas generated from the methane fermentation tank as a heat source, and then the mixed sludge is heated using the surplus heat.   The method for treating organic wastewater according to claim 1 or 2, wherein the heat of the solubilized surplus sludge is used to heat the primary sedimentation sludge directly or indirectly for acid fermentation treatment. A first solid-liquid separation tank that removes primary sedimentation sludge from organic wastewater, an aeration tank that treats organic wastewater from which primary sedimentation sludge has been removed, and excess sludge from the treatment liquid after activated sludge treatment Organic having a second solid-liquid separation tank, a methane fermentation tank that performs methane fermentation treatment of the initial settling sludge and the excess sludge, and a boiler that generates a heat source by burning biogas generated from the methane fermentation tank A wastewater treatment device,
An acid fermentation treatment tank for acid fermentation treatment of the initial settling sludge, a solubilization treatment tank for heating and solubilizing the excess sludge, and heating the excess sludge and the initial settling sludge using heat of the boiler An organic wastewater treatment apparatus comprising: a heating means that performs mixing, and a sludge mixing tank that mixes the first settling sludge after acid fermentation treatment and surplus sludge after solubilization treatment and supplies the mixed sludge to the methane fermentation tank. As the heating means, a path between the first solid-liquid separation tank and the acid fermentation treatment tank or a first heat exchanger provided in the acid fermentation treatment tank, the second solid-liquid separation tank, and the acceptable A path between the solubilization tank or the second heat exchanger provided in the solubilization tank, and a third heat exchanger provided in the path between the sludge mixing tank and the methane fermentation tank. Have
At least a part of the heat source generated from the boiler exchanges heat with the surplus sludge via the second heat exchanger, and then exchanges heat with the mixed sludge via the third heat exchanger. Configured,
The at least part of the excess sludge after the solubilization treatment is configured to be introduced into the sludge mixing tank after heat exchange with the first settling sludge via the first heat exchanger. 4. The organic wastewater treatment apparatus according to 4.