JP5882608B2 - Method and apparatus for dewatering organic sludge - Google Patents

Description

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

  In recent years, there has been a demand for reducing the amount of waste and reducing the environmental load, and dewatering technology for organic sludge discharged from wastewater treatment facilities is extremely important. Development is desired.

  In the case of dewatering organic sludge, after sludge is aggregated with a polymer flocculant, mechanical dehydration is performed (referred to as “one-component method”), or after adding an inorganic flocculant to the sludge. In general, a method of aggregating with a polymer flocculant and performing mechanical dehydration (referred to as “inorganic flocculant / pre-addition method”) has been generally performed.

  In recent years, as another dewatering method of organic sludge, the sludge is aggregated with a polymer flocculant, then concentrated by gravity, and further added with an inorganic flocculant to perform mechanical dehydration (“inorganic flocculant, later It is called “addition method”).

  For example, in JP-A-61-149300 (Patent Document 1), after adding and mixing a cationic organic polymer flocculant to organic sludge, the first step of generating floc while stirring the sludge, Next, there has been proposed a method for dewatering organic sludge comprising a second step of gravity filtering the sludge and a third step of adding iron salt to the sludge after gravity filtration, mixing and then dehydrating under pressure.

  Japanese Patent Application Laid-Open No. 9-24400 (Patent Document 2) discloses a step of adding a cationic polymer to digested sludge to agglomerate, a step of gravity dehydrating the agglomerated sludge, and an inorganic flocculant to the gravity dehydrated sludge. There has been proposed a method for dewatering digested sludge having a step of adding tempering and a step of adding an amphoteric polymer to the conditioned sludge and dehydrating with a dehydrator.

  Furthermore, in JP 2009-165964 A (Patent Document 3), a polymer flocculant is added to sludge generated from a wastewater treatment facility, and the mixture is slowly stirred to perform a primary flocculation treatment, and then the primary flocculation treatment. The sludge after the agglomeration treatment is concentrated at a high concentration, and then the polymer flocculant or inorganic flocculant is added to the sludge after the agglomeration treatment, followed by rapid agitation to perform the secondary agglomeration treatment. A processing method has been proposed.

JP-A-61-149300 Japanese Patent Laid-Open No. 9-24400 JP 2009-165964 A

  The object of the present invention is to further reduce the water content of the finally obtained dehydrated product in the dehydration method by the inorganic flocculant and post-addition method, and as a result, the amount of waste can be reduced. And a device for carrying out the same.

The present invention includes a coagulation step of adding a polymer flocculant to organic sludge to form the coagulation sludge, a coagulation sludge pressure dehydration step of pressing and dehydrating the coagulation sludge by pressurizing the coagulation sludge, and the coagulation sludge A slit forming step of forming a slit with a comb-like or lattice-shaped cutting blade in the dehydrated cake formed in the pressure dehydration step, an inorganic flocculant adding step of adding an inorganic flocculant to the dehydrated cake formed with the slit , and A mechanical dehydration process for mechanically dehydrating the dehydrated cake to which the inorganic flocculant has been added, and performing the aggregation process, the coagulated sludge pressure dehydration process, the slit forming process, the inorganic flocculant addition process, and the mechanical dehydration process in this order. We propose a characteristic method for dewatering organic sludge.

  According to the organic sludge dewatering method proposed by the present invention, in the inorganic flocculant and post-addition method, dewatering while aggregating sludge is pressurized, that is, by pressing the agglomerated sludge, for example, dewatering by its own weight. Compared with this, the dewatering of the coagulated sludge can be performed more effectively, and the sludge concentration in the dewatered cake can be remarkably increased, so that the moisture content of the finally obtained dewatered product can be further reduced. As a result, the amount of waste can be reduced.

It is the figure which showed an example of the apparatus structure for enforcing the processing method of the organic sludge which concerns on this invention. It is the figure which showed the modification of the apparatus structure shown in FIG. It is the schematic which showed an example of the sludge pressing machine. It is the schematic which showed an example of the slit forming machine. It is a figure for demonstrating the effect at the time of forming a slit in a dewatering cake, (A) is the perspective view which showed an example of the state which formed the slit in the dewatering cake, (B) is the state which does not form a slit It is the perspective view which showed an example.

  Next, the present invention will be described based on exemplary embodiments, but the present invention is not limited to the embodiments described below.

<Flow>
The organic sludge dewatering method of the present embodiment (hereinafter referred to as “the present dewatering method”) includes a coagulation step of forming a coagulated sludge by adding a polymer flocculant to the organic sludge, and the coagulation formed in the above step. An agglomerated sludge pressurizing and dehydrating step for pressing and dewatering the agglomerated sludge by pressurizing sludge, an inorganic aggregating agent adding step for adding an inorganic aggregating agent to the dehydrated cake formed in the above step, and an inorganic aggregating agent are added. And a mechanical dehydration step of mechanically dewatering the dehydrated cake.

In the present dewatering method, it is preferable to insert a slit forming step for forming a slit in the dewatered cake, if necessary, between the coagulated sludge pressure dehydrating step and the inorganic coagulant adding step.
In addition, between the inorganic flocculant addition step and the mechanical dehydration step, by pressing the dewatered cake to which the inorganic flocculant has been added, the inorganic flocculant is dispersed in the dewatered cake or mixed gently. An inorganic flocculant dispersion step for dispersing the inorganic flocculant in the dehydrated cake can also be inserted.
Hereinafter, each of the above steps will be described sequentially.

<Organic sludge>
Organic sludge is organic sludge generated in sewage treatment, human waste treatment, various industrial wastewater treatment, and the like. For example, first sedimentation basin sludge, excess sludge, anaerobic digested sludge, aerobic digested sludge, septic tank sludge, digested and desorbed liquid and the like can be mentioned. The organic sludge may contain an inorganic substance.
Organic sludge has the characteristic that it is pH 6-8 normally.

<Aggregation process>
In this step, a polymer flocculant is added to the organic sludge to generate agglomerated flocs to form agglomerated sludge.
By performing the flocculation treatment using the polymer flocculant before adding the inorganic flocculant, the moisture content of the finally obtained dehydrated product can be effectively reduced, and the use of the inorganic flocculant is also possible. The amount can be reduced.

Examples of the polymer flocculant include a cationic polymer flocculant and an amphoteric polymer flocculant. It may be a mixture of a cationic polymer flocculant and an anionic polymer flocculant.
In this dehydration method, since an inorganic flocculant is used in the subsequent step, it is preferable to use an amphoteric polymer flocculant excellent in compatibility with the inorganic flocculant.
Among them, as shown in Examples described later, an amphoteric polymer flocculant having a cation degree at pH 4 of 3.0 meq / g or more from the viewpoint of further reducing the water content of the finally obtained dehydrated product. Among them, an amphoteric polymer flocculant having a cation degree of 3.5 meq / g or more at pH 4 is more preferable.

Examples of cationic polymer flocculants include acrylate polymer flocculants (also referred to as “DAA polymer flocculants”), methacrylate polymer flocculants (also referred to as “DAM polymer flocculants”), and amide groups. , Nitrile groups, amine hydrochlorides, formamide groups and the like, and polyvinylamidines (also referred to as “amidine polymer flocculants”), polyacrylamide Mannich modified products, and the like.
Examples of the amphoteric polymer flocculant include a copolymer of dimethylaminomethyl acrylate quaternary ammonium salt, acrylamide and acrylic acid, a copolymer of dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid, and dimethylaminomethyl. Examples thereof include a copolymer of acrylate quaternary ammonium salt, dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid.
However, the above is an example and is not limited thereto.

  Examples of the solvent in the polymer flocculant solution include pure water, tap water, industrial water, groundwater, treated water for various wastewater treatment, seawater, and the like. Is preferably pure water. On the other hand, from the viewpoint of economy, tap water, industrial water, ground water, and treated water for various wastewater treatment are preferable.

  When the polymer flocculant is added in an amount of 0.3% by mass or more with respect to TS of the organic sludge, the dehydration effect can be enhanced. It is useless. Therefore, from this point of view, it is preferable to add the polymer flocculant in an amount of 0.3 to 3.5% by mass with respect to TS of the organic sludge. It is even more preferable to add at a ratio of 0.5% by mass or less, particularly 0.5% by mass or more or 2.5% by mass or less.

<Aggregated sludge pressure dehydration process>
In this step, dewatering the coagulated sludge obtained in the above step while applying pressure makes it possible to dehydrate the coagulated sludge more effectively, and also concentrates the sludge to form a dewatered cake with a high sludge concentration. can do.

In this step, it is preferable to perform pressure dehydration so that the TS of the dehydrated cake is 100 to 150 g / L, and it is even more preferable that the TS of the dehydrated cake is 110 g / L or more or 140 g / L or less. preferable. “TS” means an evaporation residue, and in this case, the concentration of a substance remaining when sludge is evaporated to dryness at 105 to 110 ° C.
If the TS of the dewatered cake is lower than 100 g / L, the inorganic flocculant can be easily dispersed in the next step, but the inorganic flocculant flowing out to the dehydrated filtrate side increases, making it possible to effectively use the inorganic flocculant. The amount of agent added increases. For this reason, it is preferable to perform pressure dehydration so that the TS of the dewatered cake is 100 g / L or more. In general, in order to concentrate aggregated sludge to a TS of 100 g / L or more, gravity dehydration, that is, the method of dewatering by the weight of the aggregated sludge has insufficient dehydration pressure. There is. On the other hand, when the TS of the dehydrated cake is higher than 150 g / L, the dehydrated cake becomes close to a solid, the inorganic flocculant cannot be dispersed inside the dehydrated cake, and the effect of the inorganic flocculant cannot be sufficiently exhibited. The amount of inorganic flocculant added increases. From such a viewpoint, as described above, it is preferable to perform pressure dehydration so that the dehydrated cake has a TS of 100 to 150 g / L.

  What is necessary is just to adjust suitably the pressure applied to agglomerated sludge so that TS of a dewatering cake may become the said range. As a guideline for the pressure applied to the coagulated sludge, it is preferable to apply a pressure of 0.5 to 50 kPa to the dehydrated cake, particularly 1 kPa to 40 kPa, especially 3 kPa or more, or 30 kPa or less to the dehydrated cake. Even more preferred.

  The shape of the dehydrated cake formed in this step is not particularly limited. However, considering the dispersibility of the inorganic flocculant, it is preferably a flat plate shape.

<Slit formation process>
It is preferable to form slits in the dewatered cake formed in the coagulated sludge pressure dehydration step, and supply the dehydrated cake with the slits to the next inorganic flocculant addition step.

  Since the dehydrated cake formed in the above process is pressure dehydrated, it has lower fluidity than a dehydrated cake dehydrated by gravity, and in that state, the inorganic flocculant is uniformly permeated into the dehydrated cake. And difficult to disperse. Therefore, if the dewatered cake is stirred or kneaded to disperse the inorganic flocculant, the flocs formed by the flocculence by the polymer flocculant break, and the water content cannot be effectively reduced. . In contrast, by forming slits in the dewatered cake, the inorganic flocculant can permeate and disperse even from the end face with the slits, so that the inorganic flocculant can be efficiently dispersed in the sludge without breaking the flocs The effect of the inorganic flocculant can be enhanced and the amount of the inorganic flocculant used can be reduced.

FIG. 5A shows an example of the state of dispersion of the inorganic flocculant when slits are formed in the dehydrated cake, and FIG. 5B shows an example of the state of dispersion of the inorganic flocculant when slits are not formed. Show. The hatched area in the figure represents the area where the inorganic flocculant is dispersed.
As described above, when a plurality of slits are formed in the dewatered cake, the inorganic flocculant can be dispersed only on the upper surface of the dehydrated cake when the slits are not formed, whereas the inorganic flocculant reaches the inside of the dehydrated cake through the slits. Can be dispersed.

More specifically, a plurality of slits may be provided in the dehydrated cake, the dehydrated cake may be divided into a plurality of blocks, and the inorganic flocculant may be dispersed and infiltrated into the end face of each block.
The formation direction of the slit may be vertical or horizontal. If formed in the vertical direction, an inorganic flocculant can be added from above to disperse along the vertical cross section of the slit naturally.
In addition, the slits may be formed at appropriate intervals in the vertical direction or the horizontal direction when the dehydrated cake is viewed from the top, or may be formed in a lattice shape.

  With respect to the slit spacing, it can be considered that the slit spacing should be 1 cm or more in order to insert slits so as not to break the flocs formed by the polymer flocculant. On the other hand, if the interval between the slits is larger than 10 cm, the effect of forming the slits may be impaired. From such a viewpoint, the slit interval is preferably 1 cm to 10 cm, and more preferably 2 cm or more or 5 cm or less.

<Inorganic flocculant addition process>
In this step, the dewatering efficiency can be further increased by adding an inorganic flocculant to the dehydrated cake obtained in the previous step.

  Examples of the inorganic flocculant used include ferric chloride, aluminum sulfate, aluminum chloride, polyaluminum chloride, and polyferric sulfate.

Inorganic flocculants should be added to the dehydrated cake after diluting with dilution water from the viewpoint of reducing the viscosity and making it easier to impregnate and disperse in the dehydrated cake and increasing the volume by diluting to facilitate uniform dispersion. Is preferred.
From the above viewpoint, if the TS of the dehydrated cake is 100 to 150 g / L, the dilution factor of the inorganic flocculant is preferably 2 to 5 times. A more preferable dilution ratio is 3 to 4 times.

  As the diluting liquid, pure water, tap water, industrial water, ground water, treated water for various wastewater treatment, seawater, etc. can be used, but from the economical viewpoint, industrial water, groundwater, treated water for various wastewater treatment are preferable. .

  If the inorganic flocculant is added in an amount of 1.0% by mass (Fe conversion) or more with respect to TS of the organic sludge, the dehydration effect can be enhanced. It is a waste of inorganic flocculants. Therefore, from such a viewpoint, it is preferable to add the inorganic flocculant in an amount of 1.0 to 10% by mass (converted to Fe) with respect to the organic sludge. It is even more preferable to add at a ratio of 8.0% by mass (Fe conversion) or less, of which 2% by mass (Fe conversion) or more or 6.0% by mass (Fe conversion) or less.

<Inorganic flocculant dispersion process>
After the inorganic flocculant addition step and before the mechanical dehydration step, the dewatered cake to which the inorganic flocculant has been added is pressurized or gently mixed as necessary to convert the inorganic flocculant into the dehydrated cake. You may make it disperse | distribute.

  As described above, since the dewatered cake formed in the coagulated sludge pressure dehydration process is pressure dewatered, it has lower fluidity than the dewatered cake dehydrated by gravity, It is difficult to uniformly penetrate and disperse the flocculant in the dehydrated cake. When the dehydrated cake is rapidly stirred to disperse the inorganic flocculant, the flocculent flocs formed by the agglomeration by the polymer flocculant are broken, and the water content cannot be effectively reduced. Therefore, by pressurizing or gently mixing the dehydrated cake to which the inorganic flocculant has been added, the inorganic flocculant can be dispersed in the sludge without breaking the floc floc, and the effect of the inorganic flocculant Can be increased.

<Mechanical dehydration process>
The dehydrated cake to which the inorganic flocculant is added can be mechanically dehydrated to obtain a dehydrated product.
According to the present dehydration method, the water content of the dehydrated product can be reduced to 80% or less, preferably 75% or less, and more preferably 70% or less, so that the amount of waste can be reduced.

<Device configuration>
As one aspect of the apparatus configuration for carrying out this dehydration method, a coagulation tank that mixes organic sludge and a polymer flocculant to form coagulated sludge, a sludge press that depresses and dehydrates the coagulated sludge, The structural example provided with the inorganic flocculent addition machine which adds an inorganic flocculant to a dewatering cake, and a dehydrator can be mentioned.

  More specifically, as shown in FIG. 1, a polymer flocculant dissolution tank 1, an inorganic flocculant storage tank 2, a flocculant tank 3, a sludge press 4, a slit forming machine 5, an inorganic flocculant addition machine 6, and a dehydrator 8 may be mentioned.

With such an apparatus configuration, as shown in FIG. 1, a polymer flocculant is prepared in the polymer flocculant dissolution tank 1, and this polymer flocculant is transferred from the polymer flocculant dissolution tank 1 to the flocculence tank 3. On the other hand, the organic sludge is put into the coagulation tank 3, and the organic sludge and the polymer coagulant are mixed in the coagulation tank 3 to form the coagulated sludge (coagulation step). Is supplied to the sludge press 4.
In the sludge pressing machine 4, the agglomerated sludge is pressed and dehydrated by pressurizing the agglomerated sludge, and a dehydrated cake is formed (aggregated sludge pressure dehydration step) and supplied to the slit forming machine 5.
In the slit forming machine 5, a plurality of slits are put in the dehydrated cake (slit forming step) and conveyed to the inorganic flocculant adding machine 6.
In the inorganic flocculant adding machine 6, an inorganic flocculant is added to the dehydrated cake with slits formed (inorganic flocculant adding process), and the dehydrated cake is mechanically dehydrated to obtain a dehydrated processed product. (Mechanical dehydration process).

  Further, as shown in FIG. 2, after the dehydrated cake to which the inorganic coagulant is added by the inorganic coagulant adding machine 6 is supplied to the inorganic coagulant dispersing machine 7, the inorganic coagulant is dispersed in the dehydrated cake. The dehydrator 8 may be supplied.

  Hereinafter, the sludge pressing machine 4, the slit forming machine 5, the inorganic flocculant adding machine 6, and the inorganic flocculant dispersing machine 7 will be further described.

(Sludge press 4)
As shown in FIG. 3, for example, as shown in FIG. 3, the sludge pressing machine 4 includes a sludge charging hopper 11, a sludge moving means 12, a pressurizing means 13 provided above the sludge moving means 12, and a lower part of the sludge moving means 12. The thing of the structure provided with the water collection means 14 provided in can be illustrated.

  Here, the sludge moving means 12 includes a belt 16 and a belt driving device 21. The entire upper surface (conveying surface) of the belt 16 is horizontally moved by the belt driving device 21 and sludge can be moved to the horizontal sludge discharge port side, and the agglomerated sludge is filtered while moving on the belt 16. The liquid falls to the lower water collecting means 14.

  The pressurizing means 13 has a pressurizing plate 13A obliquely installed so as to provide a gap between the sludge discharge port 17 of the sludge moving means 12 and the belt 16, and the sludge is sludged in the horizontal direction by the sludge moving means 12. When it moves to the discharge port side, it is pressurized from above when passing through the gap between the pressure plate 13A and the belt 16.

One or more pressure plates 13A may be provided, and the pressure plate 13A may be provided so that the installation angle is fixed, or may be provided so that the installation angle can be changed as needed. Further, it can be pivotally supported so as to be swingable up and down.
By changing the angle of the pressure plate 13A and the size of the gap with the belt 16, the pressure applied to the coagulated sludge can be adjusted, and the dewatering efficiency can be adjusted.
Further, instead of the pressure plate 13A, for example, a roller can be installed.

  The water collecting means 14 is provided below the sludge moving means 12 so that water falling from the sludge moving means 12 can be collected and drained from a waste water outlet.

Next, operation | movement of the sludge pressing machine 4 provided with such a structure is demonstrated.
When the aggregated sludge is charged into the sludge charging hopper 11, the aggregated sludge is moved to the horizontal sludge discharge port side by the sludge moving means 12 and is transported horizontally on the upper surface of the belt 16. The agglomerated sludge is dehydrated during the conveyance process, and is pressurized and further dehydrated when passing through the gap between the pressure plate 13A and the belt 16, and is sent out from the sludge discharge port 17 as a plate-shaped dehydrated cake. . The dehydrated water falls from the sludge moving means 12, is collected by the water collecting means 14, and is drained from the waste water outlet.

  As the sludge press 4, in addition to the sludge press 4 having such a configuration, a sludge press used for conventional sludge dehydration, such as a centrifugal concentrator, a screw concentrator, an elliptical plate type concentrator, etc. It is also possible to adopt. Moreover, the machine of the structure which pressurizes a dewatering cake with a flat plate can also be used.

(Slit forming machine 5)
FIG. 4 shows an example of the slit forming machine 5. This figure is an enlarged view of a part of the sludge discharge port of the sludge press 4.
As shown in this example, the slit forming machine 5 is configured such that the comb-shaped cutting blades 20 are arranged at appropriate intervals in the horizontal direction at the sludge discharge port 17 of the sludge pressing machine 4 so that the blades are in the vertical direction. Can be configured.
With such a comb-shaped cutting blade, a vertical slit can be formed in the dewatered cake extruded from the sludge press 4.

  However, the slit forming machine 5 is not limited to the above configuration. For example, a cutting blade assembled in a lattice shape when viewed from above, or a cutting blade assembled at an appropriate interval in the length or width direction of the dewatered cake when viewed from above, is raised and lowered from above. It is also possible to use devices that can.

(Inorganic flocculant addition machine 6)
As the inorganic flocculant addition machine 6, an arbitrary configuration can be adopted. For example, a method of adding an inorganic flocculant using a nozzle or a spray, a method of dropping the inorganic flocculant from a V-shaped or U-shaped notch, and the like can be mentioned.

(Inorganic flocculant disperser 7)
In order to further promote the dispersion of the inorganic flocculant into the dehydrated cake, an apparatus that can pressurize the dehydrated cake to which the inorganic flocculant has been added to disperse the inorganic flocculant in the dehydrated cake, or mix gently to make inorganic As an apparatus that can disperse the flocculant in the dehydrated cake, any apparatus can be adopted.
As a machine for pressurizing the dehydrated cake, any apparatus provided with a pressurizing means can be employed. For example, a machine of the same type as the sludge press 4 can be used. Moreover, the machine of the structure which pressurizes a dewatering cake with a flat plate can also be used.
Examples of the apparatus for gently mixing the dehydrated cake to which the inorganic flocculant is added include a vertical mixer, a drum mixer, and a spatula.

  However, in the inorganic flocculant disperser 7, a filtrate containing the inorganic flocculant is generated from the dehydrated cake by pressurization, but it is preferable that this filtrate is not discharged out of the system. When the filtrate is discharged out of the system, the inorganic flocculant is discharged out of the system together with the filtrate. Therefore, the inorganic flocculant cannot be used efficiently, and the amount of the inorganic flocculant used increases.

(Dehydrator 8)
For the dehydrator 8, a conventionally known dehydrator can be used. For example, a screw press dehydrator, a belt press dehydrator, a centrifugal dehydrator, a vacuum dehydrator, a filter press dehydrator, a multiple disk dehydrator, and the like can be given.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.

(Test 1)
In this test, it was examined whether the moisture content of the finally obtained dehydrated product could be reduced by pressurizing the coagulated sludge to dehydrate and concentrate it.

Two types of anaerobic digested sludge (A, B) were used for the test. The TS of sludge A and sludge B were 13.1 g / L and 19.3 g / L, respectively, and the pH was 7.2 and 7.3, respectively.
TS is an evaporation residue and is a concentration of a substance remaining when sludge is evaporated to dryness at 105 to 110 ° C. The measuring method was based on the sewage test method.

In the test of sludge A, an amphoteric polymer flocculant (a copolymer of dimethylaminomethyl acrylate quaternary ammonium salt, dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid, cation degree 2.0 meq / g at pH 4) In the sludge B test, a cationic polymer flocculant (a mixture of a DAA polymer flocculant and a DAM polymer flocculant) was used.
In both tests, a stock solution of polyferric sulfate was used as an inorganic flocculant.

In addition, the measurement method of the cation degree in pH4 was performed in the following procedure (it is the same also in another test).
The polymer flocculant was dissolved in pure water to prepare a 500 mg / L aqueous polymer flocculant solution. Next, 90 mL of pure water and 10 mL of the polymer flocculant solution were mixed and adjusted to pH 4 with 0.1 N hydrochloric acid aqueous solution. Toluidine blue was added thereto and titrated with 1/400 N potassium polyvinyl sulfate. In the titration, the end point was the time when the color changed from blue to magenta and held for 15 seconds or longer. The degree of cation was calculated from the following formula.
Cation degree (meq / g) = Titration volume (mL) / 2

The test procedure is as follows.
In the test of sludge A, 1.9% by mass (vs. TS) of the polymer flocculant with respect to 19.6 kg / h (TS conversion) of organic sludge is added to the agglomeration tank together with the organic sludge, and the agglomerated sludge is stirred and mixed. Formed. Next, the coagulated sludge was dehydrated using the following sludge press and concentrated to form a dehydrated cake (thickness 30 to 40 mm). Next, using the following inorganic flocculant addition machine, a stock solution of 5.8% by mass (converted to Fe, vs. TS) of ferric sulfate was added dropwise from above the dehydrated cake as described later. Thereafter, the dehydrated cake was dehydrated with a screw press dehydrator, and the moisture content of the obtained dehydrated product was measured.

  In the sludge B test, 2.4% by mass (vs. TS) of polymer flocculant is added to the coagulation tank together with the organic sludge for 17.5 kg / h (TS conversion) of organic sludge, and agglomerated sludge by stirring and mixing. Formed. Next, the coagulated sludge was dehydrated using the following sludge press and concentrated to form a dehydrated cake (thickness 30 to 40 mm). Next, using the following inorganic flocculant addition machine, a stock solution of 5.8% by mass (converted to Fe, vs. TS) of ferric sulfate was added dropwise from above the dehydrated cake as described later. Thereafter, the dehydrated cake was dehydrated with a screw press dehydrator, and the moisture content of the obtained dehydrated product was measured.

As the sludge squeezing machine, a sludge squeezing machine 4 provided with a pressure plate 13A as shown in FIG. 3 was used. A 25 kg weight was placed on the pressure plate 13A.
As an inorganic flocculant addition machine, a plastic pipe with a plurality of holes is installed at the sludge discharge port 17 of the sludge squeezing machine 4, and polyferric sulfate is supplied to this pipe to dehydrate it. Polyferric sulfate was added dropwise to the cake.

As a comparative test, a similar test was performed using a sludge press (referred to as “gravity concentrator”) having a configuration in which the pressure plate 13A is not installed in the sludge press 4 shown in FIG.
The test results are shown in Table 1.

When the sludge press 4 was used, the TS of the dewatered cake was 120 to 130 g / L. On the other hand, in a comparative test, TS of the dehydrated cake when using a gravity concentrator was 60 to 70 g / L.
By using the sludge squeezing machine 4, the moisture content of the dehydrated product was reduced by 0.7 points for sludge А and 1.8 points for sludge B.

(Test 2)
In this test, it was examined whether the moisture content of the finally obtained dehydrated product can be reduced by adding a diluted solution of an inorganic flocculant to the dehydrated cake.

For the test, anaerobic digested sludge C was used. Sludge C had a TS of 18.6 g / L and a pH of 7.3.
Further, as a polymer flocculant, an amphoteric polymer flocculant (a copolymer of dimethylaminomethyl acrylate quaternary ammonium salt, dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid, pH 4 cation degree 3.6 meq / g) It was used.

The test procedure is as follows.
With respect to 15.7 kg / h (TS conversion) of organic sludge, 2.2% by mass (vs. TS) of the polymer flocculant was added to the agglomeration tank together with the organic sludge, and stirred and mixed to form agglomerated sludge. Next, the coagulated sludge was dehydrated using the same sludge press as in Test 1, and concentrated to form a dehydrated cake (thickness 30 to 40 mm, TS 100 to 120 g / L).
Next, slits were formed in the dewatered cake at intervals of 15 mm by the slit forming machine 5 shown in FIG. Next, as in Test 1, a 2.3 mass% (Fe equivalent, vs. TS) dilute dilute solution (dilution ratio of 3 to 5) was dropped from above the dehydrated cake with slits formed. Added. Finally, the dehydrated cake was dehydrated with a screw press dehydrator, and the water content of the dehydrated product obtained was measured.
In addition, the water which carried out the sand filtration process of the treated water of an activated sludge process was used for the dilution water of a polyferric sulfate.

As a comparative test, a similar test was performed using a ferric sulfate sulfate stock solution.
The test results are shown in Table 2.

  By using the 3-fold diluted solution and 5-fold diluted solution, the water content of the dehydrated product could be reduced by 1.1 and 0.6 points, respectively.

(Test 3)
In this test, it was examined whether the moisture content of the finally obtained dehydrated product could be reduced by using various polymer flocculants.

  For the test, anaerobic digested sludge D was used. Sludge D had a TS of 17.3 g / L and a pH of 7.3.

The test procedure is as follows.
2.4% by mass (vs TS) amphoteric polymer flocculant a (dimethylaminomethyl acrylate quaternary ammonium salt and dimethylaminomethyl methacrylate quaternary ammonium salt and acrylamide) with respect to 16.6 kg / h (TS conversion) of organic sludge And a copolymer of acrylic acid, a cation degree of 3.6 meq / g at pH 4) were added together with organic sludge to a coagulation tank, and mixed by stirring to form coagulated sludge. Next, using the same sludge press as in Test 1, the coagulated sludge was dehydrated and concentrated to form a dehydrated cake (thickness 30 to 40 mm, TS 120 to 130 g / L). Next, as in Test 1, a 5.8 mass% (Fe equivalent, vs. TS) polyferric sulfate stock solution was added dropwise from above the dehydrated cake. Finally, the dehydrated cake was dehydrated with a screw press dehydrator, and the water content of the obtained dehydrated product was measured.

As a comparative test, two kinds of cationic polymer flocculants (b, c) were used and the same test was performed. The composition of the polymer flocculant is a mixture of a DAA polymer flocculant and a DAM polymer flocculant. The cationic degree of the cationic polymer flocculants b and c at pH 4 is 4.4 meq / g and 3.1 meq / g, respectively.
The test results are shown in Table 3.

  It was confirmed that the water content of the dehydrated product can be reduced by using the amphoteric polymer flocculant.

(Test 4)
In this example, it was examined whether the water content of the finally obtained dehydrated product could be reduced by using amphoteric polymer flocculants having different cation degrees at pH 4.

Two types of anaerobic digested sludge (E, F) were used for the test. The TS of sludge E and sludge F were 13.5 and 20.2 g / L, respectively, and the pH was 7.6 and 7.3, respectively.
Two types of amphoteric polymer flocculants (a, d) were used in the test. The composition of the amphoteric polymer flocculant is a copolymer of dimethylaminomethyl acrylate quaternary ammonium salt, dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid. The cationic degree of the amphoteric polymer flocculants a and d at pH 4 is 3.6 meq / g and 3.0 meq / g, respectively.

The test procedure is as follows.
In the sludge E test, 1.3% by mass (vs. TS) of the amphoteric polymer flocculant was added to a 200 mL beaker together with the organic sludge with respect to 100 mL of organic sludge, and agglomerated sludge was formed by stirring and mixing. Next, the coagulated sludge was concentrated to form a dehydrated cake (TS 100 to 110 g / L). Next, 4.0 mass% (Fe equivalent, vs. TS) polyferric sulfate stock solution was added dropwise from above the dehydrated cake in the same manner as in Test 1, and gently mixed using a spatula. Finally, the dehydrated cake was dehydrated with a piston type pressure dehydrator, and the water content of the obtained dehydrated product was measured.

  In the test of sludge F, 1.9% by mass (vs. TS) of amphoteric polymer flocculant was added to 100 mL of organic sludge together with organic sludge in a 200 mL beaker, and agglomerated sludge was formed by stirring and mixing. Next, the coagulated sludge was concentrated to form a dehydrated cake (TS 100 to 110 g / L). Next, 4.0 mass% (Fe equivalent, vs. TS) polyferric sulfate stock solution was added dropwise from above the dehydrated cake in the same manner as in Test 1, and gently mixed using a spatula. Finally, the dehydrated cake was dehydrated with a piston type pressure dehydrator, and the water content of the obtained dehydrated product was measured.

As a comparative test, the same test was performed using the amphoteric polymer flocculant e. The composition of the amphoteric polymer flocculant e is a copolymer of dimethylaminomethyl acrylate quaternary ammonium salt, dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid. The degree of cation at pH 4 of the amphoteric polymer flocculant e is 2.0 meq / g.
The test results are shown in Table 4.

  In order to reduce the water content of the dehydrated product, it has been found that it is preferable to use an amphoteric polymer flocculant having a cation degree at pH 4 of 3.0 meq / g or more.

(Test 5)
In this test, after adding an inorganic flocculant, it was examined whether the moisture content of the dehydrated product as the finally obtained dehydrated product could be reduced by pressurizing the dehydrated cake.

  For the test, anaerobic digested sludge G was used. Sludge G had a TS of 19.8 g / L and a pH of 7.3.

The test procedure is as follows.
1.8% by mass (vs. TS) amphoteric polymer flocculant (copolymerization of dimethylaminomethyl acrylate quaternary ammonium salt, dimethylaminomethyl methacrylate quaternary ammonium salt, acrylamide and acrylic acid to 250 mL of organic sludge And a cation degree of 3.6 meq / g at pH 4 were put into a 1 L beaker together with organic sludge, and stirred and mixed to form agglomerated sludge. Next, the coagulated sludge was pressurized with a flat plate (pressure 10 kPa) and concentrated. Next, a stock solution of 3.2% by mass (Fe equivalent, vs. TS) of polyferric sulfate was dropped onto the top surface of the dehydrated cake. Next, the dehydrated cake was again pressed with a flat plate. Finally, the dehydrated cake was dehydrated with a belt press dehydrator, and the water content of the obtained dehydrated product was measured.

As a comparative example, a test in which no pressurization was performed after dropping ferric sulfate was conducted in the same procedure.
The test results are shown in Table 5.

  It was confirmed that the water content of the dehydrated product can be reduced by 1.0 point by performing the pressure dispersion step.

Claims (6)

A coagulation step in which a polymer flocculant is added to organic sludge to form coagulated sludge;
An agglomerated sludge pressurizing and dehydrating step of pressing and aggregating the agglomerated sludge to dehydrate
A slit forming step of forming a slit with a comb-like or lattice-like cutting blade in the dewatered cake formed in the coagulated sludge pressure dehydration step;
An inorganic flocculant addition step of adding an inorganic flocculant to the dehydrated cake with slits formed;
A mechanical dehydration step of mechanically dehydrating the dehydrated cake to which the inorganic flocculant has been added,
An organic sludge dewatering method comprising performing a coagulation step, a coagulation sludge pressure dehydration step, a slit formation step, an inorganic coagulant addition step, and a mechanical dehydration step in this order.   The organic sludge dewatering method according to claim 1, wherein an amphoteric polymer flocculant having a cation degree at pH 4 of 3.0 meq / g or more is added in the aggregation step.   The method for dewatering organic sludge according to claim 1 or 2, wherein in the inorganic flocculant addition step, a 2 to 5 times diluted solution of the inorganic flocculant is added.   An inorganic flocculant dispersion step, wherein the inorganic flocculant is dispersed in the dewatered cake by pressurizing the dewatered cake to which the inorganic flocculant is added between the inorganic flocculant addition step and the mechanical dehydration step. The method for dewatering organic sludge according to any one of claims 1 to 3, wherein the method is inserted.   A coagulation tank for mixing organic sludge and a polymer flocculant to form coagulated sludge, a sludge press for depressing the coagulated sludge to dehydrate to form a dehydrated cake, and a comb or lattice on the dehydrated cake An organic sludge dewatering device comprising: a slit forming machine that forms a slit with a chopping blade; an inorganic flocculant adding machine that adds an inorganic flocculant to the dewatered cake on which the slit is formed; and a dehydrator. The sludge squeezer comprises a sludge charging hopper, sludge moving means, pressurizing means provided above the sludge moving means, and water collecting means provided below the sludge moving means, and wherein the sludge outlet of the sludge transportation Ru provided with a slit forming machine, dehydrator of organic sludge of claim 5.

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