JP6670192B2 - Organic sludge processing method and processing apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for treating organic sludge.

  Surplus sludge generated from sewage treatment plants is increasing with the spread of sewerage. Most of the sludge has been used effectively through methane fermentation, but sludge that has not yet been used is landfilled at a final disposal site after dewatering. In recent years, there is a social problem that it has become difficult to secure a final disposal site. Further, most of the anaerobic treated sludge generated by methane fermentation is hardly dewaterable sludge, and there is a problem that a large amount of a flocculant is required for the dewatering treatment, so that the operation cost is high. In addition, since the obtained dewatered cake has a high moisture content, the dewatered cake that cannot be burned has a problem that it is difficult to secure a final disposal site like the unused sludge.

  As a method for improving the dehydration property of the anaerobic treated sludge, the pH of the fermentation residue obtained by subjecting the organic waste to methane fermentation and other anaerobic organic compound-containing liquids is 5.5 or less, preferably 4.5 to 3.0. In addition, there has been proposed a method of performing solid-liquid separation of the treatment liquid after adjusting to 5 and contacting with an oxidizing agent (Patent Document 1). It is disclosed that pH adjustment is performed by adding an inorganic acid such as hydrochloric acid, sulfuric acid, and nitric acid. For contact with oxidizing agents, forcibly introduce air or oxygen into the fermentation residue by aeration to disperse the ammonia component out of the solution, or add hypochlorous acid or hypochlorite, etc. Is disclosed. In addition, it is described that when the pH of the fermentation residue is adjusted to 5.5 or less, intense foaming derived from carbon dioxide occurs.

  A method is proposed in which anaerobic digestion of organic waste capable of methane fermentation is performed, the digestion residue is aerated with oxygen-containing gas, and then the dewatered cake obtained by mechanical dehydration is dried with the heat of the air discharged from the aeration blower. (Patent Document 2). Patent Document 2 discloses that dehydration, which is insufficient only by aeration treatment, is compensated for by drying with heat.

  A method of dewatering anaerobic digested sludge has been proposed in which excess sludge is mixed after anaerobic digested sludge is aerated, a metal salt is added, an amphoteric organic polymer flocculant is added, and then dewatered. 3). Patent Literature 3 discloses that by aerating anaerobic digested sludge and degassing dissolved carbon dioxide gas, it was possible to prevent aggregation inhibition due to foaming of carbon dioxide gas when adding a flocculant. It is disclosed that when aeration was not performed, the moisture content of the dewatered cake increased due to aggregation inhibition due to foaming.

  After the organic sludge is anaerobically digested and solid-liquid separated, ozone or hydrogen peroxide is added to the digested sludge for solubilization, and furthermore, a method for reducing the amount of organic sludge to be anaerobically digested has been proposed ( Patent Document 4). Although the amount of ozone used can be reduced as compared with the conventional ozone oxidation treatment method, it is still a method of performing expensive ozone oxidation treatment, and the problem of cost reduction remains.

JP 2005-334713 A JP-A-60-38099 JP-A-08-206699 JP-A-09-085299

  The present invention suppresses the operation cost, improves the dewatering rate, and reduces the volume of organic sludge without using an expensive oxidizing agent such as ozone and without having to provide an additional facility such as a large blower. It is an object of the present invention to provide a simple organic sludge treatment method that can achieve the above.

  The present inventors have found that the viscous substances in the organic sludge are hardly dehydrated by being concentrated, and in the dehydration treatment of the organic sludge, the viscous substances in the organic sludge are decomposed before the coagulation treatment of the organic sludge. It has been conceived that dehydration can be easily performed by reducing the viscosity.

According to the present invention, there are provided the following methods and apparatuses for treating organic sludge.
[1] Before the coagulation and dehydration treatment of organic sludge, the organic sludge containing an iron compound is brought into contact with oxygen to generate hydroxyl radicals, and the viscosity of the organic sludge was measured at 35 ° C. and 60 rpm with a B-type rotational viscometer. A method for treating organic sludge wherein the viscosity is reduced at a viscosity reduction rate of 20 mPa · s / h or more.
[2] The total amount of iron compounds in organic sludge [Fe (mg / L)], TS (total solid: evaporation residue) [TS (mg / L)], and oxygen transfer capacity coefficient (kLa (h ⁻¹ )) )) And the following formula (1):

The method for treating organic sludge according to [1], wherein the oxygen transfer capacity coefficient or the iron injection amount is controlled so that the following holds.
[3] When the injection amount (i) the volumetric oxygen transfer coefficient of the organic sludge precursor or an iron compound to organic sludge ^{(kLa (h -1))} is less than 0.12H ^-1 is, TS in organic sludge (Fe (mg / L)] / [TS (mg / L)] of the total amount of iron compounds per (total solid: evaporation residue) is 1.6 or more and 2.9 or less.
When (ii) the volumetric oxygen transfer coefficient (kLa ^{(h -1))} is less than 0.12H ^-1 than 0.28H ^-1 is, TS in organic sludge (total solid: evaporation residue material) iron compound per So that the ratio [Fe (mg / L)] / [TS (mg / L)] of the total amount is 0.9 or more and 2.9 or less.
To (iii) optionally an oxygen transfer capacity coefficient (kLa ^{(h -1))} is 0.28H ^-1 or more 5.7H ^-1 or less, TS in organic sludge (total solid: evaporation residue material) iron compound per Controlling the amount of iron injected into the organic sludge so that the ratio [Fe (mg / L)] / [TS (mg / L)] of the total amount becomes 0.6 or more and 2.9 or less. The method for treating organic sludge according to the above.
[4] An organic sludge containing an iron compound is brought into contact with oxygen to generate hydroxyl radicals, and a method for treating organic sludge for reducing the viscosity of the organic sludge at a viscosity reduction rate of 20 mPa · s / h or more. A processing device,
Iron compound injection means for injecting an iron compound into the organic sludge precursor or organic sludge,
An oxygen contact treatment tank that brings oxygen into contact with organic sludge containing an iron compound,
A coagulation tank for coagulating organic sludge discharged from the oxygen contact treatment tank,
A dehydrator for dehydrating the coagulated organic sludge,
A viscometer provided in the oxygen contact treatment tank or between the oxygen contact treatment tank and the coagulation tank,
A control device for controlling the oxygen transfer capacity coefficient or the iron injection amount of the contact treatment tank,
An apparatus for treating organic sludge, comprising:
[5] The contact treatment tank includes at least one of an aeration device, a stirring device, and an organic sludge injection switching valve, and at least one of the aeration device, the stirring device, and the organic sludge injection switching valve is the control device. The organic sludge treatment apparatus according to [4], which is electrically connected to the organic sludge.

  According to the present invention, before the coagulation and dehydration treatment of the organic sludge, the organic sludge containing an iron compound is brought into contact with oxygen, and the hydroxyl radical generated due to the autoxidation of iron causes the viscous substance in the organic sludge to be reduced. To reduce the viscosity of the organic sludge. When the viscous substance is concentrated in the organic sludge, the organic sludge is hardly dehydrated. Therefore, by reducing the viscosity, the hard dewatering can be prevented.

  Further, in a situation where it is difficult to increase the oxygen transfer capacity coefficient, it is possible to increase the amount of hydroxyl radical generated by increasing the injection amount of the iron compound into the organic sludge precursor or the organic sludge. Can increase the decomposition rate of the viscous substance.

  Furthermore, since a part of Fe (III) generated by the autoxidation of iron can be reduced to Fe (II) by the reducing power of the anaerobic treated sludge, for example, the amount is less than the theoretically necessary amount. Iron compounds can be injected, and the amount of iron compounds used can be reduced.

  Further, since the coagulation reaction due to Fe (III) generated by the autoxidation of iron and the oxidation reaction due to oxygen can be caused at the same time, the viscosity of the organic sludge can be more stably reduced.

Further, as a secondary effect, the load on the dehydration treatment, drainage treatment, desulfurization treatment and deodorization treatment can be reduced. More specifically, the following effects are obtained.
(1) By bringing organic sludge into contact with oxygen to oxidize Fe (II) contained in the organic sludge, Fe (III) can be used as a flocculant, and the flocculant in the subsequent flocculation step Can be reduced.
(2) By contacting organic sludge with oxygen, for example, coagulation inhibitory substances contained in anaerobic treated sludge such as polysaccharides, proteins, glycoproteins, nucleic acids, phospholipids, and polymeric substances such as humic acid are removed. Since it can be decomposed, it is possible to use an inexpensive non-amidine polymer flocculant or an inexpensive non-amidine polymer flocculant for anaerobic treated sludge that can only be coagulated with an expensive amidine polymer flocculant. Blend products mixed with amidine-based polymer coagulant can be used as coagulant, which can reduce coagulation cost, improve dewatering efficiency, and reduce water content of dewatered cake Becomes
(3) By injecting an excessive amount of an iron compound, sulfur contained in an organic substance is combined with iron, thereby suppressing the generation of hydrogen sulfide, and reducing the load in the subsequent desulfurization treatment and deodorization treatment. Becomes possible.
(4) When increasing the oxygen transfer capacity coefficient, the carbon dioxide gas dissolved in the anaerobic treated sludge can be removed, so that the foaming phenomenon when the coagulant is injected in the subsequent coagulation step is suppressed. It becomes possible.

It is a flowchart which shows the flow of the processing method of the organic sludge of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the apparatus structure for implementing the processing method of the organic sludge of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the apparatus structure for implementing the organic sludge processing method of this invention in anaerobic processing. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the apparatus structure for implementing the processing method of the organic sludge of this invention in aerobic processing. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the apparatus structure for implementing the processing method of the organic sludge of this invention in sewage aerobic processing. 4 is a graph showing a measurement result of a sludge viscosity in Example 1. 9 is a graph showing the results of measuring the viscosity of sludge in Example 2. 10 is a graph showing the measurement results of the SS recovery rate and the water content of the dehydrated cake corresponding to the iron concentration in Example 3. 14 is a graph showing the results of measuring the amount of flocculant added and the SS recovery rate during flocculation treatment in Example 4. 11 is a graph showing the results of measuring the amount of coagulant added and the water content of a dehydrated cake during the coagulation treatment in Example 4. 14 is a graph showing a change in a particle diameter average value due to an oxygen contact treatment in Example 5. 14 is a graph showing a change in median particle diameter due to oxygen contact treatment in Example 6.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.

  In the present invention, before the coagulation and dehydration treatment of organic sludge, an organic sludge containing an iron compound is brought into contact with oxygen to generate hydroxyl radicals, and the viscosity of the organic sludge is measured at 35 ° C. and 60 rpm with a B-type rotational viscometer. This is a method for treating organic sludge in which the viscosity is reduced at a viscosity reduction rate of 20 mPa · s / h or more.

  FIG. 1 is a flowchart showing the flow of an organic sludge treatment method of the present invention, FIG. 2 is a schematic diagram of an apparatus configuration for implementing the organic sludge treatment method of the present invention, and FIGS. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the apparatus structure for implementing the processing method of the organic sludge of this invention in anaerobic and aerobic treatment.

  As shown in FIG. 1, the treatment method of the present invention includes an oxygen contact treatment step of bringing organic sludge containing an iron compound into contact with oxygen prior to ordinary coagulation and dehydration treatment of organic sludge. The “organic sludge generation step” in FIG. 1 is, for example, a step until an anaerobic digestion sludge is formed in an anaerobic treatment tank shown in FIG. 3, and an excess sludge is formed in a biological reaction tank and a post-treatment tank shown in FIG. Until the surplus sludge is formed in the final sedimentation basin of the sewage treatment shown in FIG. The “oxygen contacting step” in FIG. 1 includes, for example, a step of bringing anaerobic digested sludge into contact with oxygen at a stage preceding the coagulation tank shown in FIG. 3, a step of bringing excess sludge into contact with oxygen at a stage preceding the coagulation tank shown in FIG. 5 means a step in which excess sludge is brought into contact with oxygen at a stage preceding the coagulation tank.

  In the present invention, “organic sludge” includes both digested sludge by anaerobic treatment and excess sludge by aerobic treatment, and is not limited to either anaerobic treatment or aerobic treatment. The `` organic sludge precursor '' may be any substance that forms organic sludge by anaerobic treatment or aerobic treatment.For example, in the case of anaerobic treatment, primary sludge or excess sludge generated in sewage treatment, Examples include excess sludge generated in various industrial wastewater treatments, food production residues and garbage, and solubilized liquids thereof. For example, in the case of aerobic treatment, sewage, digested sludge desorbed liquid, various industrial wastewaters, and the like are included. . Generally, organic sludge formed by anaerobic or aerobic treatment often contains a small amount of iron compounds. However, in the treatment method of the present invention, it is necessary that the organic sludge has a certain iron concentration described later. If the organic sludge does not have a sufficient iron concentration at the time of the oxygen contact treatment, an iron compound may be additionally injected into the organic sludge precursor or the organic sludge. What is necessary is just to be able to inject the organic sludge before the treatment. For example, when injecting into the anaerobic sludge shown in FIG. 3, the solubilization tank, the solubilized substance storage tank, the anaerobic treatment tank, the oxygen contact treatment tank, and the piping between them are optional. The iron compound can be injected at the point. For example, when injecting into the aerobic treated sludge including the biological treatment shown in FIG. 4, the post-treatment tank, the oxygen contact treatment tank, and the piping between them at the stage after the biological reaction tank and before the coagulation tank are optional. The iron compound can be injected at the point. For example, in the case of the sewage treatment shown in FIG. 5, it is possible to inject an iron compound into the final sedimentation tank and the oxygen contact treatment tank in the latter stage of the biological reaction tank and the previous stage of the coagulation tank, and in any part of the piping between them. it can.

  In the present invention, the "iron compound" is not particularly limited, and examples thereof include ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, ferric polysulfate, and ferrous polysulfate. Is preferably a divalent iron salt such as ferric sulfate or ferric chloride which can generate a hydroxyl radical by autoxidation of Fe (II) to Fe (III) with oxygen.

  By contacting organic sludge containing iron compounds with oxygen, in addition to the decomposition of viscous substances in organic sludge by oxygen, the decomposition of viscous substances in organic sludge by hydroxyl radicals generated by the autoxidation of iron occurs. Decomposition is promoted. When the organic sludge is surplus sludge after nitrification denitrification treatment or sludge after biological deodorization treatment, various aerobic microorganisms survive in spite of not having high decomposition activity of polymer components. These aerobic microorganisms can take up the sticky components remaining in the sludge in the anaerobic treatment process as a growth source and decompose them. As a result, the decomposition activity of the polymer component can be increased. Adhesive substances formed by the cross-linking of organic and inorganic substances remaining in the sludge, adhesive substances formed by the association of organic substances, and polymeric adhesive substances are caused by biological reactions by aerobic microorganisms and hydroxylation. Decomposed by chemical reaction due to radicals. In particular, sludge viscosity is greatly reduced by decomposing high molecular substances having a molecular weight of 1,000,000 to 2,000,000 or more remaining in digested sludge.

  Further, Fe (II) is automatically oxidized to Fe (III) by the contact between the iron compound in the organic sludge and oxygen. Fe (III) generated by the autoxidation of iron is surrounded (coagulated) by organic sludge containing decomposed viscous substances that are negatively charged, and also acts as a coagulant forming a basic floc. The base flocks grow into flocculated flocs in a subsequent flocculation step.

  In the present invention, oxygen only needs to be introduced into the organic sludge as a gas containing oxygen. For example, low-concentration and high-concentration odor gas containing odorous components generated from refuse receiving pits and refuse sorting facilities in treatment facilities where pure oxygen, air, and hardly dewaterable digested sludge are formed, and activated sludge of sewage Aerated exhaust gas generated from the processing equipment can be used. In the case where the dehydration treatment step includes a nitrification step of the dehydrated separated liquid after the dehydration treatment step, the exhaust gas from the nitrification step can be reused as an oxygen-containing gas. The exhaust gas from the nitrification step has a lower oxygen content than normal air, but contains sufficient oxygen for use in the oxygen contact treatment in the present invention. Oxygen can be introduced into the organic sludge using various known means, such as dissolution of oxygen into the liquid by gas-liquid contact by stirring, introduction of gas into the liquid by a microbubble generator or an aerator. However, in the treatment method of the present invention, it is necessary to make contact with a certain amount of oxygen described later, and it is preferable that the dissolved oxygen (DO) concentration is maintained at 1.0 mg / L or less.

  Regarding the quantitative relationship between the iron compound in the organic sludge and oxygen, the following formula (1):

(Where kLa (h ⁻¹ ) is the oxygen transfer capacity coefficient, [Fe (mg / L)] is the total amount of iron compounds in the organic sludge, and [TS (mg / L)] is the amount of the organic sludge. TS (total solid: evaporation residue).
The oxygen transfer capacity coefficient or the iron injection amount is controlled so that the following holds.

The oxygen transfer capacity coefficient kLa (h ⁻¹ ) is an index indicating the ability to supply oxygen from the gas phase to the liquid phase, and can be controlled by effective control factors such as aeration amount, stirring speed, liquid level, and oxygen partial pressure. it can. The control of the aeration amount can be performed, for example, by controlling the air volume of the aeration device. The stirring speed can be controlled by controlling the number of revolutions of a stirring means provided in the oxygen contact treatment tank, for example, a stirring blade. The liquid level can be controlled by controlling the flow rate of the organic sludge introduced into the oxygen contact treatment tank or the discharge amount from the oxygen contact treatment tank. The oxygen partial pressure can be controlled, for example, by controlling the amount of oxygen in a gas serving as an oxygen source.

As a simpler method, based on the design value of the oxygen transfer capacity coefficient of the oxygen contact treatment tank, the TS of the organic sludge and the actually measured values of the iron concentration, the iron compound to the organic sludge precursor or the organic sludge as described below. The injection volume can also be controlled. Here, [Fe (mg / L)] / [TS (mg / L)] is the ratio of the total amount of iron compounds per TS (total solid: evaporation residue) in organic sludge.
If (i) the volumetric oxygen transfer coefficient ^{(kLa (h -1))} is less than 0.12H ^-1 is, [Fe (mg / L) ] / [TS (mg / L)] is 1.6 or more 2 Iron injection amount to be 9 or less.
When (ii) the volumetric oxygen transfer coefficient ^{(kLa (h -1))} is less than 0.12H ^-1 than 0.28H ^-1 is, [Fe (mg / L) ] / [TS (mg / L)] Is the iron injection amount which becomes 0.9 or more and 2.9 or less.
To (iii) optionally an oxygen transfer capacity coefficient ^{(kLa (h -1))} is 0.28H ^-1 or more 5.7H ^-1 or less, [Fe (mg / L) ] / [TS (mg / L)] Is the iron injection amount at which 0.6 becomes 2.9 or less.

  According to the treatment method of the present invention, when the oxygen transfer capacity coefficient or the viscosity reduction rate of the iron injection amount is measured by a B-type rotational viscometer at 35 ° C. and 60 rpm, it is 20 mPa · s / h or more, preferably 30 mPa · s / h or more. , More preferably at least 45 mPa · s / h, it is possible to prevent the organic sludge from being hardly dehydrated. As the viscosity reduction rate is higher, the viscosity of the organic sludge can be reduced by a short contact treatment, or the viscosity can be reduced to a lower viscosity by a long contact treatment. The viscosity is preferably measured in an oxygen contact tank or in a pipe between the oxygen contact tank and the coagulation tank.

  The sludge whose viscosity has been reduced by the treatment method of the present invention is then formed into a dewatered cake by a coagulation treatment in a coagulation tank and a dehydration treatment in a dehydrator. The coagulation treatment and the dehydration treatment are not particularly limited, and ordinary treatment can be performed. However, the amount of the coagulant added may be about 90% or less of the necessary amount in the case of ordinary treatment.

  Next, an outline of each device configuration of FIGS.

  FIG. 3 is an outline of an apparatus configuration when the treatment method of the present invention is applied to anaerobic treated sludge. Anaerobic sludge formed by solubilizing organic matter in the solubilization tank and anaerobic treatment in the anaerobic treatment tank is introduced into the oxygen contact treatment tank before the coagulation treatment. The iron compound can be injected into any part of the organic matter before the solubilization treatment, the solubilization tank, the solubilized substance storage tank, the anaerobic treatment tank, the oxygen contact treatment tank, and the piping therebetween.

  FIG. 4 is a schematic view of an apparatus configuration when the treatment method of the present invention is applied to excess sludge of aerobic treatment. The excess sludge formed when the organic wastewater is subjected to the aerobic treatment in the pretreatment and the biological reaction tank, and the excess sludge formed when the treated water from the biological reaction tank is post-treated are subjected to coagulation treatment. Is introduced into the oxygen contact treatment tank. The iron compound can be injected into the excess sludge from the biological reaction tank and the excess sludge from the post-treatment tank or the oxygen contact treatment tank. Note that the pre-processing may not be performed.

  FIG. 5 is a schematic view of an apparatus configuration when the treatment method of the present invention is applied. Sewage or organic wastewater is separated into solid and liquid in the settling basin and first settling basin, the supernatant is sent to the biological reaction tank for aerobic treatment, and the excess sludge separated in the final settling tank is solidified. Before being treated, it is introduced into an oxygen contact treatment tank. The iron compound can be injected into a final settling basin, excess sludge or an oxygen contact treatment tank.

  The oxygen contact treatment tank is provided with means for supplying organic sludge, aeration means for supplying an oxygen-containing gas, and means for extracting sludge after the oxygen contact treatment. Examples of the aeration means include an aeration type, a mechanical stirring type, and a combination type of an aeration type and a mechanical stirring type. A diffuser-type aerator is composed of a diffuser and a blower. Examples of the diffuser include a diffuser plate, a diffuser tube, a perforated tube, and a sparger. The aeration means is preferably provided so that air bubbles can be supplied from the bottom of the aeration tank to the sludge in the aeration tank. The aeration tank preferably includes a pH meter, a DO meter, an ORP meter, and a viscometer as measuring devices for operation management. Further, in order to control the pH of the sludge in the aeration tank, it is preferable to provide an acid injection unit or an alkali injection unit.

  The coagulation tank is provided with a means for supplying the organic sludge after the oxygen contact treatment, a means for injecting the coagulant, a means for mixing the organic sludge and the coagulant, and a means for extracting the coagulated sludge. Further, two or more coagulation tanks may be provided, and the coagulant may be dividedly injected. For example, when two or more coagulation tanks are provided, an inorganic coagulant may be injected in the first coagulation tank, and a polymer coagulant may be injected in the second and subsequent coagulation tanks to form coagulated sludge. The polymer flocculant may be injected into the first flocculation tank, and the polymer flocculant may be injected into the second and subsequent flocculation tanks. When three or more coagulation tanks are provided, the inorganic coagulant may be dividedly injected into the first coagulation tank, and the polymer coagulant may be dividedly injected into the second coagulation tank and the third and subsequent coagulation tanks. The injection amount and the number of injections of the coagulant can be appropriately set according to the properties of the sludge to be treated and the number of coagulation tanks.

  The dewatering apparatus is not particularly limited, and preferably includes a means for applying pressure to the coagulated sludge or the concentrated sludge, and a means for separating the solid matter and the dewatered separation liquid. Examples of the dehydrating apparatus include a belt press, a screw press, a centrifugal dehydrator, a filter press, a multiple disk type dehydrator, a multiple disk type screw press, a rotary press, and the like. Further, it may be provided in a dehydrator integrated with the coagulation tank. Examples of such a dehydrator include some centrifugal dehydrators, and such a centrifugal dehydrator has an area corresponding to a flocculation tank therein, and mixes sludge and a flocculant by centrifugal force, Form coagulated sludge.

  The present invention will be specifically described with reference to Examples and Comparative Examples.

[Example 1]
In a 500 mL plastic bottle containing 250 mL of TS34 800 mg / L digested sludge (iron concentration 232 mg / L), an aqueous solution of FeSO ₄ having an iron concentration of 120 g / L was prepared, and the injected iron concentration was 0 mg / L (total iron concentration 232 mg / L). L, [Fe] / [TS] = 0.6), 40 mg / L (total iron concentration 272 mg / L, [Fe] / [TS] = 0.8), and 80 mg / L (total iron concentration 312 mg / L) , [Fe] / [TS] = about three 0.9), two oxygen transfer shaking speed of each 120rpm (kLa = 0.12h ^-1) and 200rpm (kLa = 3.28h ^-1) As a sample of the capacity coefficient, the mixture was shaken and stirred at a temperature of 35 ° C., and a sample was collected at an arbitrary elapsed time of stirring to measure the viscosity. The viscosity was measured at 35 ° C. and 60 rpm using a B-type rotational viscometer (the same applies to the following examples). The viscosity reduction rate was determined from the initial viscosity and the viscosity of the sample taken in 5 hours. The results are shown in Table 1 and FIG.

When the oxygen transfer capacity coefficient kLa is 0.12 h ⁻¹ , the ratio [Fe (mg / L)] / [TS (mg) of the total amount of iron compounds per TS (total solid: evaporation residue) in the organic sludge. / L)] of 0.6 and 0.8, the viscosity reduction rate was less than 20 mPa · s / h, but [Fe (mg / L)] / [TS (mg / L)] was 0.9. The viscosity reduction rate was 20 mPa · s / h or more. When the oxygen transfer capacity coefficient kLa is 3.28 h ⁻¹ , the viscosity reduction of [Fe (mg / L)] / [TS (mg / L)] is 0.6, 0.8 and 0.9, respectively. The speed became 20 mPa · s / h or more.

[Example 2]
In a 500 mL plastic bottle containing 250 mL of TS34800 mg / L digested sludge (232 mg / L of iron), 120 g / L and 240 mg / L of FeSO ₄ aqueous solution (Fe (FeSO ₄ ) 120 ppm and Fe (FeSO ₄ ) 240 ppm) and 60 mg / L and 120 mg / L aqueous ferric polysulfate solutions (referred to as 60 ppm Fe (P) and 120 ppm Fe (P), respectively) were prepared and the injected iron concentration was 0 mg / L (total iron). Concentration 232 mg / L, [Fe] / [TS] = 0.6), 60 mg / L (total iron concentration 292 mg / L, [Fe] / [TS] = 0.8), 120 mg / L (total iron concentration 352 mg) / L, [Fe] / [TS] = 1.0) and 240 mg / L (total iron concentration 472 mg / L, [Fe] / [TS] = 1.4). It was injected, respectively. The mixture was shaken and stirred at a shaking speed of 200 rpm (kLa = 3.28 h ^-1 ) and a temperature of 35 ° C., a sample was collected at an arbitrary stirring time, and the viscosity was measured. The viscosity reduction rate was determined from the initial viscosity and the viscosity of the sample taken in 4 hours. Table 2 and FIG. 7 show the viscosities as a control without iron injection and without shaking (total iron concentration 232 mg / L, [Fe] / [TS] = 0.6, kLa = 0 h ^-1 ). The measurement results are also shown. When shaking is not performed, oxygen may be dissolved from the gas phase to the liquid phase at the gas-liquid contact interface, but the oxygen does not move into the liquid under the interface. Since there is no oxygen transfer capacity coefficient, it is treated as 0h- ¹ .

When the oxygen transfer capacity coefficient kLa = 3.28 h ⁻¹ , [Fe (mg / L)] / [TS (mg / L)] is 0.6, 0.8, 1.0, and 1.4. In each case, the viscosity reduction rate was 20 mPa · s / h or more. On the other hand, when the oxygen transfer capacity coefficient kLa = 0 h ⁻¹ , even if iron was present, the viscosity was maintained at 400 mPa · S / h or more and did not decrease.

  In the case without stirring, the influence of only the iron injection amount was examined by increasing the iron injection amount. As a result, no effect of decreasing the viscosity by increasing the iron injection amount was observed in the sample collected after 2 hours.

[Example 3]
A coagulant: Ebagulose (registered trademark) CS-374D (manufactured by Mizu-ing Co., Ltd.) was added to 200 mL of each sample collected at the 14th hour in Example 2 (135 mL) (the TS injection rate was 4.9%). Flock was formed and dewatered by a belt press dehydrator to produce a dehydrated cake of each sample. For the dewatering test, a belt press batch dewatering tester was used, and the dewatering conditions were the filter cloth tension of a real machine DRP-P type dehigh roll (registered trademark, manufactured by Mizu-ing Co., Ltd.) = 4.9 kN / m, the filter cloth speed = It was set to 1.0 m / min. Table 3 and FIG. 8 show the relationship between the iron concentration (or Fe / TS) injected, the SS recovery rate, and the water content of the dehydrated cake. It was confirmed that the SS recovery rate and the dehydration property were improved as the concentration of the injected iron was increased.

[Example 4]
In the same manner as in Example 3, samples of a non-iron-injection system and an iron-injection system (injection of 120 mg / L FeSO ₄ in terms of iron) were subjected to a polymer flocculant: Ebagulose (registered trademark) CS-374D (water ing The SS recovery rate and the water content of the dehydrated cake when the injection rate of (2.5 g / L) was changed were determined, and the results are shown in FIGS. 9 and 10. Although it is based on a belt press tester, it was confirmed that the amount of the polymer flocculant used in the dehydration step can be reduced by about 10% by injecting iron.

[Example 5]
The sample collected at the 14th hour in Example 2 was diluted 10-fold, and then filtered through two types of filters. Three types of filter fractions (oxygen-contact-treated sludge, filtrate of 7 μm or less, filtrate of 0.45 μm or less) ) Was prepared, and the change in particle size distribution was measured. Table 4 shows the identifiers of the filter fractions of the digested sludge before and after the oxygen contact treatment, FIG. 11 shows the change in the average particle diameter of each filter fraction, and FIG. 12 shows the change in the median particle diameter of each filter fraction. . Both the average value and the median of the particle size in the filter fraction are reduced by the oxygen contact treatment, and in the system in which iron is injected, the size is further reduced.The digestion sludge is decomposed and refined by the iron and oxygen contact, It was clarified that there was no aggregation.

[Example 6]
The excitation fluorescence matrix of the filter fraction of the sample of Example 5 was measured, and the change in the excitation fluorescence matrix when iron was injected during the oxygen contact treatment for any of the filter fractions was smaller than when no iron was injected. It has been confirmed that it has changed greatly. It was also confirmed that the finer the filter fraction, the greater the change in the excitation fluorescence matrix. Separately, the results show that the values of soluble TOC (total organic carbon), COD (chemical oxygen demand), and Kj-N (Kjeldahl nitrogen: the sum of organic nitrogen and ammonium nitrogen) are also increased. Therefore, it is considered that by subjecting digested sludge to oxygen contact treatment in the presence of a predetermined amount of iron, organic substances such as proteins, polysaccharides, nucleic acids, and corrosive acids in organic sludge were eluted. .

[Example 7]
Construct a hydroxyl radical detection system using terephthalic acid as a chemical probe, inject terephthalic acid into digested sludge so as to have a final concentration of 1 mM, carry out oxygen contact treatment, sample at any elapsed time, Excitation fluorescence matrix measurement was performed. Since the detection of 2-hydroxyterephthalic acid was confirmed, it was confirmed that hydroxyl radicals were generated by the oxygen contact treatment of the digested sludge containing iron. In addition, it was confirmed that 2-hydroxyterephthalic acid was stable in digested sludge for 20 hours.

  Based on the results of Examples 5 to 7, by treating organic sludge in the presence of predetermined amounts of iron and oxygen, Fe (II) is automatically oxidized from Fe (II) to Fe (III), and hydroxyl radicals are generated. Organic substances such as proteins, polysaccharides, nucleic acids, and corrosive acids in organic sludge are decomposed and eluted, and Fe (III) acts as a coagulant to form fine coagulated flocs. It is thought to decrease.

Claims (4)

Before the coagulation and dehydration treatment of the organic sludge, the organic sludge containing an iron compound is brought into contact with oxygen to generate hydroxyl radicals, and the viscosity of the organic sludge is measured at 35 ° C. and 60 rpm with a B-type rotational viscometer at 20 mPa. A method for treating organic sludge reduced at a viscosity reduction rate of s / h or more,
The total amount of iron compounds in the organic sludge [Fe (mg / L)], TS (total solid: evaporation residue) [TS (mg / L)], oxygen transfer capacity coefficient (kLa (h ^-1 )) During the following equation (1):
A method for treating organic sludge, wherein the oxygen transfer capacity coefficient or iron injection amount is controlled so that the following holds. Before the coagulation and dehydration treatment of the organic sludge, the organic sludge containing an iron compound is brought into contact with oxygen to generate hydroxyl radicals, and the viscosity of the organic sludge is measured at 35 ° C. and 60 rpm with a B-type rotational viscometer at 20 mPa. A method for treating organic sludge reduced at a viscosity reduction rate of s / h or more,
If the injection amount (i) the volumetric oxygen transfer coefficient of the organic sludge precursor or an iron compound to organic sludge ^{(kLa (h -1))} is less than 0.12H ^-1 is, TS in organic sludge (total solid : Fe (mg / L) / [TS (mg / L)] of the total amount of iron compounds per (evaporation residue) is 1.6 or more and 2.9 or less.
When (ii) the volumetric oxygen transfer coefficient (kLa ^{(h -1))} is less than 0.12H ^-1 than 0.28H ^-1 is, TS in organic sludge (total solid: evaporation residue material) iron compound per So that the ratio [Fe (mg / L)] / [TS (mg / L)] of the total amount is 0.9 or more and 2.9 or less.
To (iii) optionally an oxygen transfer capacity coefficient (kLa ^{(h -1))} is 0.28H ^-1 or more 5.7H ^-1 or less, TS in organic sludge (total solid: evaporation residue material) iron compound per The method for treating organic sludge, wherein the ratio [Fe (mg / L)] / [TS (mg / L)] is controlled to be 0.6 or more and 2.9 or less. A treatment apparatus for carrying out an organic sludge treatment method for bringing an organic sludge containing an iron compound into contact with oxygen to generate hydroxyl radicals and reducing the viscosity of the organic sludge at a viscosity reduction rate of 20 mPa · s / h or more. So,
Iron compound injection means for injecting an iron compound into the organic sludge precursor or organic sludge,
An oxygen contact treatment tank that brings oxygen into contact with organic sludge containing an iron compound,
A coagulation tank for coagulating organic sludge discharged from the oxygen contact treatment tank,
A dehydrator for dehydrating the coagulated organic sludge,
A viscometer provided in the oxygen contact treatment tank or between the oxygen contact treatment tank and the coagulation tank,
A control device for controlling the oxygen transfer capacity coefficient or the iron injection amount of the contact treatment tank,
Equipped with,
The control device, when the viscosity reduction rate obtained based on the viscosity measurement value from the viscometer is less than 20 mPa · s / h,
(A) The total amount of iron compound in organic sludge [Fe (mg / L)], TS (total solid: evaporation residue) [TS (mg / L)], and oxygen transfer capacity coefficient (kLa (h ⁻¹ )) )) And the following formula (1):
The oxygen transfer capacity coefficient or the iron injection amount is controlled so that
(B) Determine the amount of iron compound injected into the organic sludge precursor or organic sludge.
If (i) the volumetric oxygen transfer coefficient (kLa ^{(h -1))} is less than 0.12H ^-1 is, TS in organic sludge: the ratio of the total amount of (total solid evaporation residue material) iron compound per [Fe (Mg / L)] / [TS (mg / L)] is from 1.6 to 2.9.
When (ii) the volumetric oxygen transfer coefficient (kLa ^{(h -1))} is less than 0.12H ^-1 than 0.28H ^-1 is, TS in organic sludge (total solid: evaporation residue material) iron compound per So that the ratio [Fe (mg / L)] / [TS (mg / L)] of the total amount is 0.9 or more and 2.9 or less.
To (iii) optionally an oxygen transfer capacity coefficient (kLa ^{(h -1))} is 0.28H ^-1 or more 5.7H ^-1 or less, TS in organic sludge (total solid: evaporation residue material) iron compound per Is controlled so that the ratio [Fe (mg / L)] / [TS (mg / L)] of the total amount is 0.6 or more and 2.9 or less.
An organic sludge treatment apparatus , characterized in that: The contact treatment tank includes at least one of an aeration device, a stirring device, and an organic sludge injection switching valve, and at least one of the aeration device, the stirring device, and the organic sludge injection switching valve is electrically connected to the control device. The organic sludge treatment apparatus according to claim 3 , wherein the apparatus is connected to an organic sludge.