JPS61257300A - Dehydrating method for sludge - Google Patents

Abstract

PURPOSE:To reduce water content in dehydrated cake and to reduce the cost for the treatment of sludge by dehydrating sludge with a dehydrator after adding an org. high molecular flocculant to the sludge, and dehydrating further in the dehydrator by adding an inorg. flocculant, then separating liquid from the sludge. CONSTITUTION:Solid or semisolid cake of sludge is obtd. by adding an org. high molecular flocculant 2 to the sludge 1, mixing both in a stirring tank 3 and dehydrating the formed floc in a dehydrator 4. Residual water in the cake of sludge 6 is removed by adding an inorg. flocculant 7 such as FeCl3, thus, the water content in the final dehydrated cake 9 is reduced. By this method, the water content of dehydrated cake obtd. by separating liquid from sludge is reduced, and the treating cost for the sludge is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for dewatering sludge generated in sewage, human waste, and various industrial wastewater treatment processes.

[Conventional technology]

Sludge generated in sewage, human waste, and various industrial wastewater treatment processes is
It is used for landfill, dried and incinerated for disposal. For this reason, sludge generated in sewage, human waste, and industrial wastewater treatment processes must be dehydrated to lower its water content.

An example of a conventional sludge dewatering method is explained with reference to FIG. 6. A cationic organic polymer flocculant (6) is added to the sludge (α), and the two are mixed in a stirring tank (c). The generated flocs were dehydrated by putting them into a dehydrator (d) such as a screw decanter type centrifugal separator, and were separated into a separated liquid (1) and a dehydrated cake (a). However, this dehydration method does not completely remove water from the flocs, resulting in a dehydrated cake (water content is 75-80% for digested sludge and 75-80% for surplus sludge). 86-8
5, has a high moisture content, and is not suitable for burial as a treatment process.
The processing costs for drying, drying, and incineration were high.

In addition, as another method of dewatering sludge that has been conventionally carried out, as shown in Figure 7, a cationic organic polymer flocculant (b) is added to the sludge (8), and the separated liquid is 6
) and dehydrated cake (1). This method uses a stirring tank (of the methods shown in Figure 6).
Although a) is omitted and is called the rain injection method, the same moisture content as the method shown in FIG. 6 can only be obtained.

Furthermore, as another dewatering method for sludge carried out in Jurai, as shown in Figure 8, a cationic organic polymer flocculant C6) is added to the sludge (c) in the first stage, and the first stage is agitation. The negative charges of the sludge particles are neutralized by rapid stirring in the tank (1), and then an anionic organic polymer flocculant (1) is added as the second stage.
rt) and stirred in the second stage stirring tank (A) to form a dense and large floc, and then put into the dehydrator (d) to separate the separated liquid (-) and the dehydrated cake (f). They were separated.

The method shown in Figure 8 is called the two-liquid method, but
Agglomeration.

The method of mixing the agent and sludge is difficult, and the appropriate stirring speed (
The control of rotation speed) and stirring time is complicated, and two types of expensive organic polymer flocculants are used, resulting in high chemical costs, and the moisture content of the dehydrated cake can only be improved by about 2 to 5 centimeters. Ta.

Furthermore, before or after adding the cationic organic polymer flocculant (b), an inorganic flocculant, such as ferric chloride,
Attempts have been made to improve flocculation or dewatering by adding sulfuric acid, polyaluminum chloride, etc. to sludge. In this method, it is said that when an inorganic flocculant is added after flocculating the sludge, the flocs will become finer but harder, improving dewatering performance, but the water content of the dehydrated cake will only improve by 1.
It was about 1.

[Problem that the invention seeks to solve]

As mentioned above, all conventional sludge dewatering methods are pre-addition methods in which a flocculant is added to the sludge and then dewatered, and the main focus is on the generation of coagulated flocs that have a dewatering effect. There are many points that are unclear as to whether a coagulating floc is good or not, and its ability to follow changes in sludge properties is poor, so sewage, human waste, and industrial wastewater treatment plants are currently searching for the selection of an appropriate coagulant.

The present invention aims to reduce the water content of a dehydrated cake obtained by separating a separated liquid from sludge, thereby reducing sludge treatment costs.

[Failure to solve the problem]

In the present invention, after adding an organic polymer flocculant to sludge, the sludge is dehydrated using a dehydrator to form solid or semi-solid cake-like sludge, and an inorganic flocculant is added to the cake-like sludge in the dehydrator. This is a sludge dewatering method that further dewaters cake-shaped sludge.

[For production]

The flocs produced by adding an organic polymer flocculant to the sludge settle or become compacted in the dehydrator, forming a cake-like shape.When an inorganic flocculant is added to this, the sludge becomes sludge due to its strong water removal ability. The residual moisture inside is removed, and the moisture content of the final dehydrated cake is reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows the system of the method according to the present invention, in which an organic polymer flocculant (2) is added to sludge (1), and the two are mixed in a stirring tank (3), resulting in flocculation. Put the flock into the dehydrator (4). , When the dehydrator (4) is of a type such as a belt press filter, filter press, or screw press, a stirring tank (3) in the first stage must be provided, but a screw decanter type centrifugal type described later as the dehydrator (4) must be provided. When a separator is used, the agitator (3) does not need to be installed because the aggregation reaction can occur within the dehydrator (4).

Dehydration in the dehydrator (4) consists of pre-dehydration (5) and post-dehydration (6).
The inorganic flocculant (7) is added during post-dehydration. A dehydrator (4) separates the flocs into a separated liquid (8) and a dehydrated cake (9) and discharges them.

As the inorganic flocculant (7) added in the post-dehydration (6), ordinary iron salts such as ferric chloride, ferrous sulfate, and ferric sulfate, or polymeric coagulants such as polyferrous sulfate can be used. A dehydrated cake (9) is obtained as a final product by using iron salts, etc., and removing residual water inside the sludge with its strong water removal power.
Reduces the moisture content of

Next, an example in which a screw decanter type centrifugal separator is used as the dehydrator (4) will be described.

In FIG. 2, QG is an outer shell, αυ is an inner shell, and the outer shell a is supported by a bearing az and rotates at high speed. The inside of the inner body αυ is divided into a chamber a3 and a chamber α. A feed pipe a9 is inserted into the center of the chamber (13).A feed pipe (15) has an outer pipe αe, an inner pipe αη It is a double tube consisting of, and the inner tube αη is
A flocculating floc α mallet produced by adding an organic polymer flocculant (2) (see Figure 1) to the sludge (1) is sent to the outer tube a.
An inorganic flocculant (7) is supplied to e through a side pipe α9 from a pump (not shown).

The flocculation side enters the chamber α through the inner pipe aη and is discharged from the discharge port (A) into the outer shell a.
The centrifugal force caused by the high-speed rotation of [[] separates the separated liquid (8) and the sludge deposit Qυ into pre-dehydration (5) (see Figure 1).
The separated liquid (8) overflows from Oriswiss Co., Ltd. and is discharged from the outer shell α. Sludge deposit (2
1) is compacted by centrifugal force and subjected to post-dehydration (see FIG. 1), and after water is further removed as described below, it is scraped out of the discharge port Q4).

The inorganic flocculant (7) supplied to the outer tube αe enters the chamber a3 from the outlet (c) of the outer tube αe, and is further discharged into the outer shell α from the outlet (a). and sludge deposit Q that has become solid or semi-solid cake-like due to consolidation.
It is sprayed on the surface of υ and penetrates inside. As a result, the water remaining inside the sludge deposit 6D is removed, added to the separation liquid (8), and discharged. The sludge deposit I21) whose water content has been reduced in this way is scraped out of the discharge port (24) as described above. Conventionally, when adding an inorganic flocculant, the inorganic flocculant was added to slurry-like sludge, so the inorganic flocculant reacted with the liquid part before reacting with the solid particles of the sludge. The inorganic flocculant did not work effectively and there was a loss of work, but in the method of the present invention, the inorganic flocculant is added to the cake-like sludge with a low moisture content that has been pre-dehydrated (5) (see Figure 1). ,
There is no reduction in efficiency due to reaction with the liquid part, and an effective dewatering effect is exerted on the sludge particles. (C) in Figure 2 is a screw.

Table 1 shows an experimental example of sludge dewatering using the screw decanter centrifugal separator shown in FIG. 2 above, using polyferric sulfate as an inorganic flocculant.

Table 1 Experimental examples of dehydration with the addition of iron polysulfate Experimental conditions Dehydrator Screw decanter type centrifugal separator Sludge
Sewage anaerobic digested sludge flocculant (1) Organic polymer flocculant (cationic) Diafloc KP-201B (rJ, 5T aqueous solution) (2) Inorganic polymer flocculant polyferric sulfate (commercial product stock solution) Operating conditions Experiment 1 Centrifugal effect 1,800G, differential speed 10 days p-inertia 1, liquid depth 2
2.5sg wealth, flow rate 1.0111”/hr, flocculant addition amount (1) 2.15//Chicken 11 (2) 20.7
/ Inasumu.

Experiment 2 Centrifugal effect 4,000 G, differential speed 15.5 r, p-rn
-1 liquid depth 15.5iaw, flow rate l], 5rrL7hr1
Amount of flocculant added (1) α67 l! /waits.

(2) 10itl/fILin.

In both Experiments 1 and 2 above, the effect of adding an inorganic flocculant was clear, with a water content reduction of 5.0 to 5.5 inches compared to the case without addition.

To explain the example of the case where a belt press filter is used in the dehydrator (4) i in Fig. 1, the endless furnace cloth @ is connected to the rollers (to), (to), (to), o
The hooks are passed through C121, (To), (B), (To), and (To), and are being driven in circulation in the direction of the arrow.

Another endless furnace cloth 07) is the roller (to), (to)
, 顛, (c).

The hook is passed to 翰 (to) 0υ, and the roller is 1CI'
A cloth (5) is overlapped between l, CI, and Gυ, and is also driven to circulate in the direction of the arrow. An organic polymer coagulant (2) (see Figure 1) is added to the sludge, and the flocs α produced in the stirring tank (3) pass through the feed pipe 0D to the gravity dewatering section (4). and is pre-dehydrated (5) by gravity dehydration (see Figure 1).

The cake-like sludge that has been subjected to gravity dewatering in the gravity dewatering section <43 is placed on a furnace cloth between rollers (c) and (to), and after an inorganic flocculant is added by a sprayer or dripper 03, the cake-like sludge is (To), (To), (To), 09
Between F cloth (3) and C3? ) and are compressed.

After being dehydrated (6) (see Figure 1), the roller (33
It is removed as a dehydrated cake.

Figure 4 shows the relationship between centrifugation time and water content when 22g of dehydrated cake obtained by the conventional* method of digested sewage sludge using a screw decanter centrifuge was used as a sample in a laboratory using a tabletop centrifuge. This is the graph shown. The moisture content of the sample placed in the tabletop centrifuge was 77.3%, and one experiment used the dehydrated cake as it was, and the other experiment used the sample to which 1 rttl of iron polysulfate was added. In each case, the sample was placed in a cylindrical test dehydration container with a small hole, and centrifugal effect 1. This shows the case of centrifugal dehydration at s 20 G. As can be seen from Fig. 4, when polyferric sulfate is added, the water content decreases significantly, for example, when centrifugation time is 30 seconds, it is 75.5-71. A decrease in water content of Q = 4.5' was observed, and at a centrifugation time of 5.5 minutes, it was 74.6-65.
It can be seen that the water content decreased by 5=9.1 h, and the dehydration effect by adding the inorganic flocculant was large.

All of the inorganic flocculants are inexpensive, with prices ranging from s 1 /20 to 1/40 of that of organic polymer flocculants. Assuming that the price of polyferric sulfate is 50 yen/IcFI and the price of organic polymer flocculant is 1,500 yen/kg, the sludge flow rate is 1 m37 hr.
The cost of the flocculant required for this is as follows:

In the case of polyferrous sulfate, the amount of polyferrous sulfate added is 20 tnl/mis = 29
g/m1n (specific gravity 1.45) Ki5 yen/kg -da (sludge concentration 1.8%) In the case of organic polymer flocculant, if the dissolved concentration is α3chi, the amount added is 2.13//sacrifice i% becomes.

=32PVkg-da (sludge concentration 1.8chi) Next, when incinerating the dehydrated cake, the fuel (heavy oil) unit price is 70 yen/kF/-OU, the higher calorific value of the % combustible content is s,
Assuming o a o heat/ky, the relationship between the water content of the dehydrated cake and the auxiliary fuel cost is as shown in FIG. The auxiliary fuel cost when incinerating the dehydrated cake in Experiment 1 in Table 1 is shown in Figure 5 as follows.

Moisture content of cake with addition of polyferric sulfate 72.7ch Auxiliary fuel cost 6 yen - oitA9 da Cake moisture content without addition of iron polysulfate 77.7ch Auxiliary fuel cost 13 yen - 9 da for oil/coagulant cost and auxiliary fuel cost The total cost of sludge disposal is shown in Table 2.

Table 2 As shown in Table 2, the sludge incineration cost when polyferric sulfate is added is 2 yen/9-9-
The cost will be reduced by da.

〔Effect of the invention〕

The present invention has the following effects.

(J) Since an inexpensive inorganic flocculant is used for dewatering the dewatered cake and is added to the sludge in the form of a solid or semi-solid cake, the amount of flocculant used is small and the water content is reduced. big.

(4) Moisture content can be reduced simply by partially modifying a conventional dehydrator and adding an inorganic flocculant addition mechanism.

(m) Like the two-liquid addition method of cations and anions,
The dehydrator can be easily operated without strictly setting mixing and stirring conditions.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the system of the method of the present invention, Figure 2 is a sectional view when a screw decanter type centrifuge is used as a dehydrator, and Figure 3 is a diagram when a belt press filter is used as a dehydrator. Figure 4 shows centrifugation time and desorption. Figure 5 is a graph showing the relationship between the water content of the water cake and the auxiliary fuel cost.
8 through 8 are block diagrams showing the system of the conventional method. In the figure, (1) is sludge, (2) is organic polymer flocculant, and (4 is
) is a dehydrator, (7) is an inorganic flocculant, (8) is a separation liquid, (
9) indicates a dehydrated cake. Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1) After adding an organic polymer flocculant to the sludge, the sludge is dehydrated in a dehydrator to form a solid or semi-solid cake-like sludge, and an inorganic flocculant is added to the cake-like sludge in the dehydrator. A method for dewatering sludge, comprising further dewatering the cake-like sludge.