JP2002143900A - Dehydration method for sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically improve a recovery rate of SS and to reduce the load of waste water treatment in a method of adding an inorganic flocculating agent to sludge, then adding an amphoteric polymer thereto, subjecting the resultant flocculated sludge to gravity dehydration and adding the inorganic flocculating agent to the gravity dehydrated sludge, then spin drying the sludge. SOLUTION: The inorganic flocculating agent is added to the raw mud to temper the sludge and to fix soluble phosphorus in a first reaction chamber 1. The tempered sludge in the first reaction chamber 1 is sent to a second reaction chamber 2 where the amphoteric polymer is added to the sludge and the sludge is granulated and flocculated. The granulated and flocculated sludge of the second reaction chamber 2 is subjected to gravity dehydration in a gravity spin drying machine 3. The inorganic flocculating agent is again added to the gravity dehydrated sludge in a third reaction chamber 4. The separated water of the gravity spin drying is received in a separated water tank 8 and the settled SS is admitted from the lower part of a submerged weir 12 into the third reaction chamber 4 where the sludge is subjected to flocculation treatment. The sludge of the third reaction chamber 4 is supplied by a sludge feed pump 5 to a centrifugal drier 6 and the amphoteric polymer is injected into the machine, by which the sludge is subjected to the dehydration treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dewatering sludge, and more particularly, to a method comprising adding an inorganic coagulant to sludge and then adding an amphoteric organic polymer coagulant (hereinafter referred to as "amphoteric polymer"). The present invention relates to a method for dewatering the obtained flocculated sludge by gravity dehydration, then adding an inorganic flocculant to the gravity dewatered sludge, and dewatering the sludge.

[0002]

2. Description of the Related Art Conventionally, as a method for treating organic sludge generated in a treatment step of sewage, human waste, or organic industrial wastewater, there are the following methods, but each has the following disadvantages. A method in which a cationic polymer is added to sludge and then dewatered with a belt press or a centrifugal dehydrator: The dewatering efficiency is poor, and good results cannot be obtained in terms of the treatment amount (the amount of sludge that can be processed) and the water content of the obtained dewatered cake. A method in which a cationic polymer is added to sludge for gravity dehydration, and a cationic polymer having a higher cation strength and an inorganic coagulant are added to the dewatered sludge and dewatered by a belt press or the like (Japanese Patent Publication No. 1-176060). It is not enough, and because two kinds of cationic polymers are used,
The line for dissolving and injecting the polymer becomes complicated. A method of adding an inorganic aggregating agent to sludge, adding an amphoteric polymer, granulating and coagulating or concentrating by granulation, and dewatering with a dehydrator (Japanese Patent Laid-Open No. 4-59100): Dewatering of granulated sludge with a centrifugal dehydrator In this case, the sludge floc is broken in the sludge supply section and the dehydration section in the centrifugal dehydrator, and sufficient dehydration cannot be performed. The required amount of the amphoteric polymer is large. Add the inorganic flocculant to the sludge and supply it to the centrifugal dehydrator,
Method of injecting amphoteric polymer into machine and dewatering: When treating sludge with low concentration and poor dewatering properties such as excess sludge, the amount of solids treated is small (since the liquid volume is rate-limiting), and moreover, it is sufficient. A dehydrated cake having a low water content cannot be obtained. A method of supplying sludge to a dehydrator, injecting a cationic polymer into the dehydrator, and dehydrating by a dehydrator: When the sludge concentration is low, the amount of liquid is rate-limiting, and the amount of solids treated is small, and the floc strength is weak. Therefore, the reduction of the cake moisture content becomes insufficient.

[0003] These problems can be solved to reduce the amount of coagulant used, increase the amount of solids treated, and reduce the water content of the dewatered cake. As a method of dewatering sludge capable of performing various treatments, the present applicant first added an inorganic coagulant to the sludge, then added an amphoteric organic polymer coagulant, and dewatered the obtained coagulated sludge by gravity. Then, after adding an inorganic coagulant to gravity dewatered sludge,
A method has been proposed in which a centrifugal dehydrator performs centrifugal dehydration while injecting an amphoteric organic polymer flocculant into the centrifuge.
No. 76000).

FIG. 3 is a system diagram for explaining a method described in Japanese Patent Application Laid-Open No. 9-76000. In this method, first, in a first reaction tank 1, sludge to be treated (raw mud)
By adding an inorganic coagulant to the mixture and stirring the mixture, the charge of the sludge is neutralized, the sludge is refined, and the soluble phosphorus is fixed. The refined sludge from the first reaction tank 1 is further fed to the second reaction tank 2 and granulated and aggregated by adding and agitating the amphoteric polymer. The granulated and coagulated sludge in the second reaction tank 2 is gravity-dehydrated by a gravity dehydrator 3. The gravity dewatered sludge is then added to the third reaction tank 4 again with an inorganic coagulant and vigorously stirred to further neutralize the charge of the sludge. The sludge in the third reaction tank 4 is supplied to a centrifugal dehydrator 6 by a mud feed pump 5, and an amphoteric polymer is injected into the apparatus to perform dehydration treatment.

[0005] In this gravity dewatering machine 3, generally, the sludge concentration 6
It is dehydrated to ％ 10%, but in order to make the concentration of the third reaction tank 4 in the subsequent step a suitable concentration and to perform a stable supply by the mud feed pump 5, when the discharge amount of the mud feed pump 5 is set to a predetermined value. ,
If necessary, a part of the separated water overflows from the separation water tank 3A of the gravity dehydrator 3 into the third reaction tank 4 so that the liquid level in the third reaction tank 4 becomes constant.

In this method, after adding an inorganic coagulant to the sludge, the coagulated sludge obtained by adding the amphoteric polymer is subjected to gravity dehydration, so that a very high floc strength is not required. Can be drastically reduced (generally to about 2/3) as compared with the case of centrifugal dehydration.

[0007] Then, after adding an inorganic flocculant to gravity dewatered sludge pre-concentrated by gravity dewatering, it is supplied to a centrifugal dewatering machine to inject amphoteric polymer into the machine and perform centrifugal dewatering treatment. Since the floc strength is high and the water load is reduced, the sludge treatment amount is increased, and the water content of the obtained cake can be sufficiently reduced.

[0008]

However, the method described in JP-A-9-76000 has the following disadvantages. That is, the separation water SS of the gravity dehydrator 3 is settled in the separation water tank 3A. Sinking SS
Is concentrated in the lower part of the separation water tank 3A.
Most of S is discharged out of the system together with the separated water. As a result, the SS recovery rate is reduced, and the load of drainage treatment of the separated water discharged out of the system is also high.

The present invention solves the problem of the method described in Japanese Patent Application Laid-Open No. 9-76000, in which an inorganic aggregating agent is added to sludge, and then an amphoteric polymer is added. In a method of dewatering, and then adding an inorganic coagulant to gravity dewatered sludge and then dewatering, it is intended to provide a method of dewatering sludge which can significantly improve the recovery rate of SS and significantly reduce the load of wastewater treatment. Aim.

[0010]

According to the method for dewatering sludge of the present invention, after adding an inorganic coagulant to sludge, an amphoteric organic polymer coagulant is added, and the obtained coagulated sludge is dewatered by gravity. After adding the inorganic coagulant to the gravity dewatered sludge, in the method of dewatering, a separation water tank receiving the separated water obtained by the gravity dewatering sludge, and a reaction tank for adding the inorganic coagulant to the gravity dewatered sludge through a dive weir Communication.

In the present invention, the separation water tank for receiving the separated water obtained by gravity dewatering and the reaction tank for adding the inorganic flocculant to the gravity sludge are communicated through the submerged weir. SS flows under the submerged weir into the reaction tank, is subjected to coagulation treatment with an inorganic coagulant together with gravity dewatered sludge, and is fed to the dehydration step. On the other hand, the separated water that SS has settled in the separation water tank and has been clarified overflows from the separation water tank and is discharged out of the system.

In the present invention, the SS recovery rate can be significantly increased by introducing a portion of the gravity dewatered separated water having a high SS concentration into the gravity dewatered sludge as described above.

In the present invention, the step of dewatering the gravity dewatered sludge to which the inorganic coagulant has been added is preferably performed, for example, as follows. The gravity dewatered sludge to which the inorganic flocculant has been added is centrifugally dewatered by the centrifugal dehydrator while the amphoteric organic polymer flocculant is injected into the centrifugal dehydrator. An amphoteric organic polymer coagulant is further added to the gravity dewatered sludge to which the inorganic coagulant has been added, and dewatered by a mechanical dehydrator.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIGS. 1 and 2 are system diagrams showing an embodiment of the present invention.

In the method shown in FIG. 1, an inorganic coagulant is added to a sludge to be treated (raw mud) and stirred in a first reaction tank 1 to neutralize the charge of the sludge and to condition the sludge. And at the same time, immobilize soluble phosphorus.

The refined sludge in the first reaction tank 1 is further fed to the second reaction tank 2, where the amphoteric polymer is added and stirred to be granulated and aggregated.

In the present invention, the inorganic coagulant added to the first reaction tank 1 includes ferric chloride, aluminum sulfate,
Aluminum chloride, polyaluminum chloride (PAC),
Examples thereof include polyiron sulfate.

The amount of the inorganic coagulant added to the first reaction tank 1 depends on the type of the compound used, but is 5 to SS of the sludge.
It is preferable to set it to 15% by weight.

On the other hand, the amphoteric polymer has a colloid equivalent value (a value) of from 1.0 to 3.0 as determined by colloid titration at pH 3 indicating the amount of cationic constituent units (cation groups) (hereinafter referred to as “cation amount”). The colloid equivalent value (b value) determined by colloid titration at pH 7 showing the difference between the amount of the anionic structural unit (anion group) (hereinafter, referred to as “the amount of anion”) and the amount of the cationic structural unit is -1. 7-0.
It is preferably 7 meq / g, and the value of (ab) / a indicating the ratio of the amount of anion / the amount of cation is in the range of 0.8 to 1.8.

Examples of such amphoteric polymers include a copolymer of an anionic monomer component and a cationic monomer component, a copolymer of an anionic monomer component, a cationic monomer component and a nonionic monomer component, Alternatively, a Mannich modified product or a Hoffman decomposition product of a copolymer of an anionic monomer component and a nonionic monomer component can be used.

Here, examples of the anionic monomer component include acrylic acid (AA), sodium acrylate (NaA), methacrylic acid, sodium methacrylate and the like. Examples of the cationic monomer component include dimethylaminoethyl acrylate, dimethylaminoethyl (meth) acrylate (DAM),
Examples thereof include dimethylaminopropyl (meth) acrylate and quaternized products thereof. Specific examples of the quaternary compound include dimethylaminoethyl acrylate quaternary compound (DAA). Also,
Dimethylaminopropylacrylamide hydrochloride (DA
PAAm) may be used. Examples of the nonionic monomer component include acrylamide (AAm), methacrylamide, and N, N′-dimethyl (meth) acrylamide. Specific examples of the copolymer of these compounds include DAA / AA / AAm copolymer, DAM / AA / AAm copolymer, and DAPAAm /
AA / AAm copolymer, DAA / AA copolymer, or N
Mannich-modified aA / AAm copolymers can be mentioned.

The amount of the amphoteric polymer added to the second reaction tank 2 is preferably 0.4 to 1.2% by weight based on the sludge SS.

The granulated coagulated sludge in the second reaction tank 2 is gravity-dehydrated by a gravity dehydrator 3. As the gravity dehydrator 3, an inclined screen (wedge wire screen), a filter cloth traveling type (belt press), a rotary screen type, or the like can be used.

The gravity-dewatered sludge is introduced into the third reaction tank 4 by the shooter 9, and in the third reaction tank 4, the inorganic coagulant is again added and vigorously stirred to perform the charge neutralization of the sludge at a higher level. . On the other hand, the separated water for gravity dehydration is supplied to a separated water tank 8 from a water receiving section 7 provided below the gravity dehydrator 3.

In FIG. 1, the separation water tank 8 has a bottom surface inclined downward toward the third reaction tank 4, and the separation water tank 8 and the third reaction tank 4 have a dive weir 1.
1, 12 and 14 and overflow weirs 13 and 15 are provided.
The lower weirs 11, 12, and 14 are open at the lower part and form a communication part at the open part. The overflow weirs 13, 15 are erected from the bottom of the tank, and water can overflow to the upper part. It forms a partition.

The dive weir 11 is provided substantially at the center of the separation water tank 8, and the dive weir 12 and the overflow weir 13 are separated from the separation water tank 8 by the third
It is provided at the boundary with the reaction tank 4. The dive weir 14 is provided between the overflow weir 13 and the stirrer in the third reaction tank 4, and the overflow weir 15 is provided between the wall of the third reaction tank 4 on the sludge discharge side and the stirrer. It is provided in.

Separation water of gravity dewatering is supplied to a water area 22 surrounded by dive weirs 11 and 12 of the separation water tank 8, SS in the separation water settles down in this water area 22, and an inclined surface of the bottom surface 8 A of the separation water tank 8. Down from the lower communication part of the dive weir 12 to the water area 23
And overflows the overflow weir 13 and flows into the water area 24 of the third reaction tank 4. Then, the water flows into the water area 25 from the lower communication portion of the dive weir 14 together with the gravity dewatered sludge introduced into the water area 24 from the shooter 9 and the inorganic coagulant injected into the water area 24, where it is coagulated together with the gravity dewatered sludge under stirring. Agglomeration treatment is performed by the agent. The flocculated sludge overflows the overflow weir 15 and reaches the water area 26, is pulled out by the mud feed pump 5, and is sent to the centrifugal dehydrator 6.

On the other hand, the separated water whose SS has settled in the water area 22 and whose clarity has been enhanced is discharged out of the system through the water area 21 from the lower communication part of the dive weir 11.

In the present invention, generally, the gravity dehydrator 3
Is dewatered to a sludge concentration of 6 to 10%.
As described above, when the discharge amount of the mud feed pump 5 is set to a predetermined value, as described above, the SS concentration from the separation water tank 8 is high in order to make the reaction tank 4 a suitable concentration and to perform stable supply by the mud feed pump 5. By allowing the separated water to flow into the third reaction tank 4,
It is preferable to adjust the concentration of gravity dewatered sludge pulled out of the third reaction tank 4 by the sludge pump 5 to be 3 to 5%.

The inorganic coagulant to be added to the third reaction tank 4 can be the same as the inorganic coagulant to be added to the first reaction tank 1 described above. Is preferably 3 to 7% by weight.

The discharge amount of the sludge pump 5 is appropriately adjusted so that the sludge concentration in the third reaction tank 4 is within the above-mentioned preferred range. It is necessary to set a value larger than the amount of dewatered sludge. The difference between the discharge amount of this mud feed pump and the amount of gravity dewatered sludge settles in the separation water tank 8, passes through the lower part of the dive weir 12 from the separation water tank 8, overflows the overflow weir 13, and flows into the third reaction tank. S flowing into 4
It corresponds to the amount of S. Specifically, when the raw mud concentration is 0.8% and the raw mud supply amount is 20 m ³ / hr, the discharge amount of the mud feed pump 5 is set so that the sludge concentration in the third reaction tank 4 is 4%. Is 4
It is about m ³ / hr.

The sludge in the third reaction tank 4 is supplied to a centrifugal dehydrator 6 by a mud feed pump 5, and an amphoteric polymer is injected into the apparatus to perform a dehydration treatment. As the amphoteric polymer to be injected into the centrifugal dehydrator 6, preferably, the same amphoteric polymer as that added to the above-described second reaction tank 2 is used.
It is preferable that the amount be about 0.2 to 0.6% by weight based on the SS of the sludge.

In this centrifugal dewatering treatment, the sludge to be supplied is already sufficiently concentrated, and the strength of the floc is strong. Therefore, the solid processing amount is large, and the water content of the cake can be sufficiently reduced.

In the method shown in FIG. 2, instead of centrifugally dewatering the sludge from the third reaction tank 4 while injecting the amphoteric polymer in the centrifugal dehydrator 6, an amphoteric polymer is added in the fourth reaction tank 10. After that, the point of dehydration by a mechanical dehydrator is different from the method shown in FIG. 1, and otherwise the same processing is performed. 2, members having the same functions as those shown in FIG. 1 are denoted by the same reference numerals.

An overflow weir 15 and a dive weir 16 are provided at the boundary between the fourth reaction tank 10 and the third reaction tank 4, and are provided between the wall of the fourth reaction tank 9 on the sludge discharge side and the stirrer. Is provided with an overflow weir 17.

The sludge from the third reaction tank 4 overflows the upper part of the overflow weir 15 and flows into the water area 26.
Flows into the water area 27 through the lower communication part, and is further coagulated by the amphoteric polymer. The flocculated sludge overflows the overflow weir 17, is drawn out of the water area 28 by the mud feed pump 5, and is fed to a subsequent mechanical dehydrator to be dewatered.

As the amphoteric polymer to be injected into the fourth reaction tank 9, the same amphoteric polymer as that added to the second reaction tank 2 is preferably used. Is preferably about 0.2 to 0.6% by weight.

Further, as the mechanical dehydrator, a centrifugal separator, a screw press, a multiple disc dehydrator and the like can be used.

In the method shown in FIG. 2, a good processing effect can be obtained as in the method shown in FIG.

According to such a sludge dewatering method of the present invention, even in the treatment of sludge having poor dewaterability, the sludge treatment amount is doubled as compared with the conventional method using only a cationic polymer. The resulting cake moisture content can be reduced by 4% or more. Also, after adding an inorganic flocculant, adding an amphoteric polymer and performing gravity dehydration, further adding an inorganic flocculant, then adding an amphoteric polymer, and performing sludge treatment compared to a method of belt press dehydration or centrifugal dehydration. While increasing the amount by 60% or more, the obtained cake moisture content can be reduced by about 1 to 2%. Further, regarding the SS recovery rate, as shown in FIG.
As is clear from the results of Examples and Comparative Examples described later, it is possible to increase 5 to 9% in the gravity dewatering section and 4 to 8% in the whole system as compared with the method of JP-A-76000.

The method for dewatering sludge according to the present invention can be applied to excess sludge, mixed sludge, and the like generated in the treatment of sewage and wastewater.
It is effective for dewatering treatment of digested sludge.

[0043]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Comparative Examples and Examples, but the present invention is not limited to the following Examples unless it exceeds the gist of the invention.

In the following examples and comparative examples, raw sludge was treated with excess sludge (concentration: 0.6%) by the sewage oxidation ditch method. The following were used as the inorganic coagulant, amphoteric polymer and cationic polymer. Inorganic flocculant: PAC amphoteric polymer: colloid equivalent at pH 3 (a) 2.6 meq / g, colloid equivalent at pH 7 (b)
DAA / with a value of 0 meq / g and a value of (ab) / a of 1
AA / AAm copolymer was used. Cationic polymer: "Crifix CP604" manufactured by Kurita Water Industries Ltd.

The following were used as a belt press type dehydrator and a centrifugal dehydrator as gravity dehydrators. Belt press type dehydrator: "Hide Press PA1250" manufactured by Kurita Kogyo Co., Ltd .: Effective filter cloth width: 1.0 m Centrifugal dehydrator: "PM-35000" manufactured by Tomoe Kogyo Co., Ltd .: Nominal capacity 10 m ³ / hr (60 kg / hr)

Comparative Example 1 (Method described in Japanese Patent Application Laid-Open No. 9-76000) The raw mud was dehydrated by the method shown in FIG. 3 under the following conditions. [Treatment conditions] Sludge supply amount: 20 m ³ / hr Inorganic flocculant addition amount to the first reaction tank: 1 to sludge SS
0 wt% Amphoteric polymer addition amount to second reaction tank: 0.8 wt% based on sludge SS Amount of inorganic coagulant added to third reaction tank: 5 based on sludge SS
Amount of amphoteric polymer injected into centrifugal dehydrator 6: 0.4% by weight based on sludge SS Supply amount of SS: 120 kg / hr (= 20 m ³ / hr ×
(0.6% × 1000) Gravity dewatered sludge concentration: 8% Sludge concentration supplied to dehydrator: 4% Sludge amount supplied to dehydrator (discharge amount of mud pump): 3 m ³
/ Hr Separated water discharged from the separation water tank to the outside of the system: 17 m ³ / h
r (= 20 m ³ / hr-3 m ³ / hr) SS recovery rate of the centrifugal dehydrator: 95% Dewatered cake water content: 78%

In this treatment, the SS concentration of the separated water discharged from the separation water tank to the outside of the system is 600 mg / L, and the SS contained in the separated water and discharged to the outside of the system is calculated by the following equation. And 10.2 kg / hr. SS discharged outside the system = 17 x 600/1000 = 1
0.2kg / hr

Accordingly, the SS recovery rate of the gravity dewatering section is 92% as calculated by the following equation from the SS supply rate to the gravity dehydration section of 120 kg / hr and the SS discharge rate of 10.2 kg / hr. is there. SS recovery rate of gravity dewatering unit = (120-10.2) / 12
0 × 100 = 91.5%

Further, since the SS recovery rate of the centrifugal dehydrator is 95%, the SS recovery rate of the entire system is 87.4% as calculated by the following equation. SS recovery rate of the entire system: 91.5 × 95/100 = 86.
9%

Example 1 Sludge treatment was carried out under the same conditions as in Comparative Example 1, except that a separation water tank provided with a partition wall shown in FIG. 1 was used.

As a result, the SS concentration of the separated water discharged from the separation water tank to the outside of the system is 50 mg / L, and the SS contained in the separated water and discharged to the outside of the system is calculated by the following equation. , 0.85 kg / hr. SS discharged outside the system = 17 x 50/1000 = 0.8
5kg / hr

Therefore, the SS recovery rate of the gravity dewatering section is 99.3 as calculated from the following formula based on the SS supply rate to the gravity dehydration section of 120 kg / hr and the SS discharge rate of 0.85 kg / hr. %. SS recovery rate of gravity dewatering unit = (120-0.85) / 12
0 × 100 = 99.3%

Since the SS recovery of the centrifugal dehydrator is 95%, the SS recovery of the entire system is 94.3% as calculated by the following equation. SS recovery rate of the entire system: 99.3 × 95/100 = 94.
3%

The results of Comparative Example 1 and Example 1 are summarized in Table 1.

[0055]

[Table 1]

[0056]

As is clear from the results of Example 1 and Comparative Example 1, according to the sludge dewatering method of the present invention, an amphoteric polymer is added to the sludge and then the amphoteric polymer is added. In the method in which the flocculated sludge is gravity-dewatered, and then the inorganic flocculant is added to the gravity-dewatered sludge and then dewatered, the SS recovery rate can be greatly improved, and the load of wastewater treatment can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a sludge dewatering method of the present invention.

FIG. 2 is a system diagram showing another embodiment of the sludge dewatering method of the present invention.

FIG. 3 is a system diagram showing a method described in JP-A-9-76000.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st reaction tank 2 2nd reaction tank 3 Gravity dehydrator 4 3rd reaction tank 5 Sludge pump 6 Centrifugal dehydrator 7 Water receiver 8 Separation water tank 9 Shooter 10 4th reaction tank 11, 12, 14, 16 13,15,17 Overflow weir

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tatsuya Kobayashi F-term (reference) 4D059 AA01 AA03 BE07 BE08 BE26 BE31 BE38 BE55 BE56 BE57 BE60 BE61 BE65 CA21 DA16 DB24 DB25 DB26 DB28

Claims (3)

[Claims] After adding an inorganic flocculant to the sludge, adding an amphoteric organic polymer flocculant, gravity-drying the resulting flocculated sludge, and then adding an inorganic flocculant to the gravity-dewatered sludge,
In the method of dewatering, dewatering of sludge, wherein a separation water tank for receiving the separated water obtained by the gravity dewatering and a reaction tank for adding an inorganic coagulant to the gravity dewatered sludge are communicated via a submerged weir. Method. 2. The method of claim 1, wherein the gravity dewatered sludge to which the inorganic coagulant is added is centrifugally dewatered by the centrifugal dehydrator while injecting an amphoteric organic polymer into the centrifugal dehydrator. Dehydration method. 3. The sludge dewatering method according to claim 1, further comprising adding an amphoteric organic polymer flocculant to the gravity dewatered sludge to which the inorganic flocculant has been added, and dehydrating the sludge with a mechanical dehydrator. Method.