JPH01111499A - Dehydration/dephosphorization process using water granulated slug as auxiliary - Google Patents

Abstract

PURPOSE:To lower the water content of dehydrated cakes and reduce the phosphorus concentration in filtrate by adding and mixing water granulated sludge as an auxiliary into sludge and then injecting a high molecular aggregating agent, agitating and mixing sludge therein and dehydrating. CONSTITUTION:First, sewage sludge (2.5%, 5m<3>/hr of slurry concentration) is stored in a sludge storage tank 1, while water crushed sludge [33% of SiO2, 13% of Al2O3, 40% of CaO, 4% of MgO, 0.06% of MnO and 1% of S (all weight %) and 1.2 of CaO/SiO2] is added to the sewage sludge in a sludge storage tank 1 through a feeder 2. The same is mixed and agitated by an agitator 3, with which an aggregating agent in an aggregating agent storage tank 4 is mixed by a pump 5 and fed to a mixing tank 6. The liquid mixed therein is separated into filtrate and dehydrated cakes by a belt press dehydrator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for dewatering sewage sludge and removing phosphorus contained in the sludge.

[Prior art] In the dewatering of sludge such as sewage, in order to increase the dewatering efficiency and obtain a dehydrated cake with a low water content, in addition to a polymer flocculant, an inorganic auxiliary agent is used to improve the compressibility of the sludge. This method has traditionally been widely used.

In this case, as the auxiliary agent, lime powder, pulverized coal, coke powder, perlite, diatomaceous earth, fine fibers, rice husks, wood chips, etc. are used.

Phosphorus in sludge, which has recently become a problem with eutrophication of lake water, can be removed by fixing it in a dehydrated cake using lime or iron chloride during dewatering. In this method, phosphorus is immobilized in a dehydrated cake to reduce the amount of phosphorus remaining in the filtrate and the amount of phosphorus that returns to the water treatment side.

Alternatively, the phosphorus remaining in the filtrate dehydrated using a polymer flocculant or the like in a conventional manner can be dephosphorized by: - A biological dephosphorization method in which the phosphorus is placed in an anaerobic state and immobilized in solid matter. There are ways to rinse.

[Problems to be Solved by the Invention] In dewatering the sludge, dephosphorization cannot be achieved by any method other than the method using lime powder. Lime is strongly alkaline and requires the use of iron chloride, etc., and although it can be used in filter presses and vacuum dehydrators, it is difficult to use in belt press dehydrators and centrifugal dehydrators.

There is also a method of using lime and a polymer flocculant in combination, but since the efficacy of the polymer flocculant decreases in a strongly alkaline region, the addition rate of lime cannot be made very high.

Therefore, this method has the disadvantage that the phosphorus removal effect cannot be very high.

Next, the above dephosphorization method using sludge lime or iron chloride can similarly be used in filter presses and vacuum dehydrators, but it is difficult to use in belt press dehydrators and centrifugal dehydrators.

Furthermore, the method of fixing phosphorus remaining in the dehydrated filtrate using a polymer flocculant requires dephosphorization equipment on the water treatment side in addition to dehydration, which is economically disadvantageous.

As described above, the conventional methods of dewatering sewage sludge and removing phosphorus contained in the sludge each have their own problems.

The object of the present invention is to develop and provide a method for dewatering sewage sludge and removing phosphorus contained in the sludge in order to solve these problems.

[Means for Solving the Problems] As a method for solving the above problems, the present invention involves adding and mixing granulated slag produced from blast furnaces in steel plants as an auxiliary agent to sludge, and then adding polymeric slag to the sludge. A dehydration/dephosphorization method using granulated slag as an auxiliary agent is provided, which is characterized in that a strong thionic polymer flocculant is injected as a flocculant and dehydrated by stirring and mixing.

The filter used for the dehydration is as follows:
It is preferable to use a belt press dehydrator, centrifugal dehydrator, filter press, or the like.

[Function] As shown in FIG. 1, the present invention stores sludge such as sewage in a sludge storage tank 1, and adds granulated slag to the sewage sludge in the sludge storage tank 1 via a feeder 2. Stirrer 3
The flocculant in the flocculant storage tank 4 is mixed with this using a pump 5, and the liquid is sent to a mixing tank 6, where the mixed liquid is then passed through a dehydrator 7 to separate it into a filtrate and a dehydrated cake. be.

The granulated slag used in the present invention has a high vitrification rate, is porous, and is produced by simultaneously refining and cooling the molten slag from the blast furnace using pressurized water in a conventional blast furnace of a steelworks. At the same time, it is a highly active slag with a markedly angular and uneven surface.

Its components (% by weight) are as shown below.

The reason why this granulated slag has dehydration and dephosphorization effects is thought to be due to the following reasons.

First, regarding the dewatering effect, in the process of coagulation → flocs → dewatering, granulated slag becomes the core of flocs and increases the strength of flocs in sludge, which has a positive effect on dewatering.

Regarding dephosphorization, CaO in the granulated slag reacts with P in the sludge to generate a compound of CaO and P, and P is removed.

Furthermore, the addition rate of the granulated slag used in the present invention (based on solids addition rate %) is preferably 20 to 50% for dewatering, and 50% for dewatering, as shown in the examples below. %
If it is less than 50%, the effect will be small, so it is preferably at least 50%.

The method of the present invention is characterized by the simultaneous progress of dehydration and dephosphorization using granulated slag generated from ironworks and the like.

This results in low moisture content and dephosphorization of the dehydrated cake.

For dehydration, use a belt press dehydrator.

Centrifugal dehydrators, filter presses, etc. are used.

Granulated slag is inexpensive and can be stably supplied in large quantities from steel works.

Next, examples of the present invention will be described.

[Example] FIG. 1 shows a process flow diagram in an example of the present invention. In the figure, 1 is a sludge storage tank, 2 is a feeder, 3 is an agitator, 4 is a flocculant storage tank, 5 is a pump, 6 is a mixing tank, and 7 is a belt press dehydrator.

Next, according to the process diagram in Figure 1, sewage sludge (slurry concentration 2.5%, 5 m3/h) was first stored in the sludge storage tank 1, while granulated slag (composition double weight %) was stored in the sludge storage tank 1.

SiO: 33%, AI O: 1B%, Cab:
40%, MgO: 4%, MnO: 0.6%, S: 1
%, CaO/SiO: 1.2) is added to the sewage sludge in the sludge storage tank 1 via the feeder 2, mixed and stirred by the stirrer 3, and added to the flocculant in the flocculant storage tank 4. The agents are mixed by a pump 5 and sent to a mixing tank 6. The mixed liquid is then transferred to a belt press dehydrator (effective filter cloth width 0).
．． 5m) 7 to separate into filtrate and dehydrated cake.

Using such sewage sludge treatment equipment, granulated slag was added to the sludge stock solution, and a strong thionic polymer flocculant (Diafloc Kp201G) was added and mixed as a flocculant, and a dehydration test was conducted using a belt press dehydrator. .

The test conditions in this case are shown in Table 1, and the dehydration results are shown in Table 2 as the apparent moisture content (%).

Table 1 Test conditions Table 2 Dewatering results (apparent water content %) However, 1: When granulated slag was added to the sludge stock solution and a coagulant was added at a ratio of 0.61% to solids.

(2): When granulated slag was added to the sludge stock solution and a flocculant was added at a solids addition rate of 0.76%.

(2): This is the case in which granulated slag was added to the sludge stock solution and a flocculant was further added at a rate of addition of 1.14% to solids.

The results in Table 2 are illustrated in terms of the absolute amount of water in the dehydrated cake as shown in FIG.

As shown in Figure 2, under conditions (I) and (n), the absolute amount of water in the dehydrated cake was reduced by adding granulated slag to the sludge stock solution, and the absolute amount of water in the dehydrated cake was reduced by adding granulated slag to the sludge stock solution. The effect is clearly visible.

The boundary water content in the figure is the calculated water content when the solid content in the dehydrated cake increases by the amount of the added granulated slag. If the moisture content in the test result is lower than the boundary moisture content, it can be determined that the moisture content has been reduced by adding the granulated slag.

Next, Table 3 shows the phosphorus concentrations in the dewatered filtrate when granulated slag was used as an auxiliary agent and when pulverized coal was used in the above test.

When pulverized coal is added, the phosphorus concentration in the dewatered filtrate does not change, but when granulated slag is used as an auxiliary agent, the phosphorus concentration decreases.

P- in the stock solution was 321 (mg/kg), but most of this was carried away in the dehydrated cake.

Furthermore, when granulated slag is used as an auxiliary agent, the P concentration remaining in the dewatered filtrate is reduced, and when 100% granulated slag is added, the residual P concentration is about 1/4. P''
Almost the same thing can be said if we discuss the absolute amount of ``.'' The granulated slag has the effect of reducing the amount of P in the dewatered filtrate.

Table 3 Auxiliary agent and P-concentration in dehydrated filtrate [Effects of the invention] According to the dehydration/dephosphorization method using the granulated slag of the present invention as an auxiliary agent, the following effects are achieved.

(1) Since granulated slag is added to the auxiliary agent, the water content of the dehydrated cake can be reduced.

(2) The phosphorus concentration in the filtrate can be reduced.

(3) The method of the present invention can be used regardless of the type of dehydrator.

(4) Granulated slag is inexpensive and can be stably supplied in large quantities from steel mills.

(5) Even if granulated slag is used in combination with a polymer flocculant, the effectiveness of the polymer flocculant does not decrease.

(6) No dephosphorization equipment is required on the dehydrated filtrate side.

(7> If phosphorus is fixed in sludge on the water treatment side and extracted to the sludge dewatering equipment side and dewatered using the method of the present invention, no dephosphorizing equipment is required.

(8) The method of the present invention is an effective dewatering process in places where the total amount of phosphorus is strictly regulated, such as in final treatment plants where water is discharged into lakes.

[Brief explanation of the drawing]

FIG. 1 is a process flow diagram in an embodiment of the present invention. FIG. 2 is a comparison diagram of the absolute water content of the dehydrated cake when the coagulant addition rate is changed. In the figure, 1: sludge storage tank, 2: feeder. 3: Stirrer, 4: Coagulant storage tank, 5: Pump, 6: Mixing tank, 7: Belt press dehydrator.

Claims (1)

[Claims] A dehydration/dephosphorization method using granulated slag as an auxiliary agent, which is characterized by adding and mixing granulated slag as an auxiliary agent into sludge, then injecting a polymer flocculant, stirring and mixing, and dewatering.