JP3692331B2 - Filtration / dehydration method and system for sludge - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an efficient filtration / dehydration method and system for sewage sludge, septic tank sludge, human waste, or hardly dewaterable sludge discharged in the treatment of industrial wastewater or landfill wastewater.
[0002]
[Prior art]
The sludge usually contains a solid component in a large amount of water, so several solid-liquid separation methods such as sedimentation and filtration are combined to separate and remove a large amount of water sequentially from the solid component. The solid content obtained by concentrating and finally dewatering is composted, or final disposal such as landfill and incineration is performed. However, these sludges have extremely poor sedimentation and filterability and are difficult to separate from water, and it takes a long time to concentrate and dehydrate. In order to improve this, usually, an inorganic dehydration aid such as lime is added to facilitate dehydration. However, the addition of these dehydrating aids has increased the amount of sludge to be disposed of, and recently the possibility of environmental pollution has been discussed.
[0003]
[Problems to be solved by the invention]
Therefore, a sludge dewatering method for concentrating and dewatering sludge without using a chemical such as a dehydrating aid has been studied, and a so-called non-chemical injection sludge dewatering method has been developed. An example of a system using this method is shown in a flow sheet in FIG. In this example, the raw water 21 containing sludge is guided to the settling basin 22 to settle and separate the sludge, and then fed into the concentration tank 23 and blown with water vapor 24 to heat the sludge to reduce the viscosity and improve the dewaterability of the sludge. . This sludge is sent to the filter dehydrator 25 for dehydration. Although it is a preferable method from the viewpoint of environmental protection, there is a problem that it takes a long processing time and usually requires 8 hours or more for the filtration / dehydration operation.
[0004]
In addition, for the purpose of improving sludge filtration and dewaterability, a freeze / thaw treatment method has been proposed in which sludge is frozen and thawed. An example of a sludge dewatering system using this method is shown in a flow sheet in FIG. In this example, the raw water 31 containing sludge is guided to the settling basin 32 to settle and separate the sludge, and then the settled sludge is fed into the concentration tank 33 to be separated and concentrated. The concentrated sludge is frozen and thawed in the freezing / thawing tank 34 to improve the dehydration property and the like, and is sent to the filtration / dehydrator 35 for dehydration. Although it is thought that sludge is microscopically separated from water by freezing the water in the sludge, the equipment cost and operation cost required for freezing sludge are high. In addition, if a centrifuge is introduced in the previous process, the amount of sludge to be concentrated and frozen and thawed can be reduced, but the electrical cost is increased. As a means for reducing costs, a temporary effect can be obtained by taking a measure to reduce the amount of treated sludge in a dehydrator by performing a sedimentation treatment after freezing / thawing treatment to extract the supernatant water. However, the present invention was completed as a result of diligent research on the sludge dewatering method, particularly non-chemical dewatering of sludge, which is easy to operate, completes the dewatering operation in a short time, and is low in cost. It has been done.
[0005]
[Means for Solving the Problems]
The present invention is a frozen, thawed sludge, or a frozen / thawed sludge after freezing and thawing to separate and remove the supernatant water, which is excellent in dehydration, less clogging the filter cloth, after dehydration, As a result of finding advantageous properties such as good releasability from filter cloth, and using it as a measure to finish conventional sludge dehydration, especially non-chemical injection dehydration, in a short time. It has been done.
[0006]
As a means for solving the above-mentioned problems, the present invention provides a sludge filtration / dehydration method in which frozen / thaw sludge obtained by the sludge freezing / thawing method is pre-coated on a filter, and the sludge to be dehydrated after pre-coating is described above. We provide a method for filtering and dewatering sludge by supplying it to a filter and filtering and dewatering. More preferably, the frozen / thawed sludge obtained by the sludge freezing / thawing method is clarified to separate the supernatant water, and the remaining frozen / thawed sludge is pre-coated on a filter. A pressure filter is suitable for the filter used in the sludge filtration / dehydration method. The present invention is particularly filtration and dehydration process sludge without using a dehydrating aid, effective as a so-called no-drug poured dewatering sludge treatment method.
[0007]
The present invention includes a sludge freezing and thawing device 1 and a precoat type filter 2, and a line for guiding the sludge to be dewatered to the freezing and thawing device and the filter by switching the destination. 3 and the freezing / thawing apparatus includes a line 4 for sending frozen / thawed sludge to the filter and a line 5 for sending supernatant water clarified from the frozen / thawed sludge to the outside of the system. A sludge filtration / dehydration system is provided.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described with reference to the drawings. FIG. 1 is a flow sheet showing an example of an embodiment using the present invention. In the description of the present invention, frozen / thawed sludge refers to sludge treated by the freezing / thawing method. The sludge to be dehydrated by the present invention may be organic or inorganic, and may be raw sludge that has not been concentrated or sludge that has been concentrated by some method. In the description of the present invention, the “non-chemically injected sludge dewatering method” refers to a dehydration aid such as slaked lime that has been used in the dehydration process to improve the sludge filterability (note: sludge used in the sludge concentration process). It is a dehydration method that does not use a coagulant and the like. The embodiment shown here is illustrated for easy understanding of the present invention, and does not limit the present invention.
[0009]
In the present invention, sludge is dehydrated by utilizing the properties of the frozen / thawed sludge. In the sludge freezing and thawing method, the sludge is frozen, so that the water in the sludge liquid phase and the water incorporated in the solid content are frozen and separated from the solid content in the sludge. The supernatant water obtained by melting and clarifying frozen sludge is discharged out of the system. The supernatant water can be separated in advance to reduce the processing amount, and the load on the dehydrator can be reduced.
[0010]
In the process illustrated in FIG. 1, first, the sludge 6 to be dewatered is guided to the settling basin 7 to cause the sludge to gravity settle, and the precipitated sludge is sent to the concentration tank 8 for secondary concentration. The sludge concentrated by the switching operation of the line 3 is sent to the freezing / thawing tank 1 to be frozen, thawed and clarified, and the supernatant water is discharged out of the system via the line 5. The remaining frozen / thawed sludge is pumped to the filter 2 via the line 4 and pre-coated. Precoated frozen / thawed sludge rarely causes clogging of the filter cloth.
[0011]
The type of the filter 2 used in the present invention may be a filter that can adopt the precoat method, and for example, a pressure filter, a vacuum filter, and a centrifuge can be used. In particular, a filter press is suitable. Pre-coating conditions are often determined empirically and experimentally depending on the characteristics and state of the sludge, but generally a thickness of 1 to 2 mm is appropriate, and the amount of frozen / thawed sludge is usually dehydrated. The amount of sludge is about 10 to 50% by weight.
[0012]
When the required precoat layer is formed on the filter 7, the line 3 is switched, and in this example, the concentrated sludge is directly pumped to the filter. The sludge sent under pressure is filtered and dewatered by the precoat, but a large amount of sludge can be dehydrated in a much shorter time than the pressure filtration using sludge that has not been frozen or thawed. The moisture content is low. Moreover, the sludge after the dehydration has a good peelability from the filter cloth and the like, and the removal work is easy. The sludge to be treated according to the present invention is preferably subjected to a certain concentration treatment before treatment, but the concentration treatment is not an essential requirement.
[0013]
The method for filtering and dewatering sludge according to the present invention is particularly effective when the sludge to be dewatered is difficult to filter sludge using a large amount of sludge flocculant. The sludge dewatering performance in the filter is improved, the processing capacity that has been a problem in the conventional chemical-free sludge dewatering method is improved, the sludge removal after dehydration is facilitated, and the work efficiency is also improved. It can contribute to the spread of pollution sludge dewatering treatment.
[0014]
Instead of pre-coating frozen and thawed sludge on the filter, mixing with the sludge to be dehydrated and filtering and dehydrating can also increase the throughput of the filter and remove dehydrated sludge after dehydration. Operation can be facilitated. However, the effect is that it is necessary to mix at least 10 parts by weight, preferably 50 parts by weight, of sludge to be dehydrated with respect to 100 parts by weight of sludge to be dehydrated. It does not extend to the method of pre-coating the filter.
[0015]
【Example】
In order to understand the present invention specifically, examples will be given below. However, neither FIG. 1 nor examples limit the scope of the present invention.
[0016]
Example 1
Using the filtration / dehydration apparatus having the same configuration as shown in FIG. 1, the raw river water was guided to the settling basin, and the sludge was gravity precipitated and concentrated, and the settled sludge was further concentrated to about 4% by weight in the concentration tank. This sludge was freeze-concentrated at a brine temperature of −20 ° C. in a batch-type freeze concentration tank with a treatment capacity of 600 liters to obtain a freeze-concentrated sludge having a sludge concentration of 15% by weight. About 50 kg of this freeze-concentrated sludge was precoated on a filter press having a filtration area of 1.59 m ² . As the filter cloth, ordinary filter cloth N856 was used. 200 kg of sludge to be treated with a moisture content of about 4% by weight which is not frozen and filtered is supplied and filtered and compressed. After 0.8 hours, the sludge concentration is measured, and a compressed sludge with a water content of 62% by weight can be obtained. . The filtration rate at this time was 3 kg / m ² hr. Cake peeling and recovery was extremely easy.
[0017]
Comparative Example 1
The same apparatus as used in Example 1 was used, except that 200 kg of the same water content of about 4% by weight as sludge filtered in Example 1 was supplied without pre-coating the freeze-concentrated sludge, followed by filtration and compression. . When the sludge concentration was measured after about 3 hours, a compressed sludge having a water content of 70% by weight was obtained. The filtration rate at this time was 0.3 kg / m ² hr.
[0018]
【The invention's effect】
By utilizing the present invention and pre-coating freeze-concentrated sludge, the sludge release property from the dehydrator is improved, and clogging of filter cloth and the like is less likely to occur. Dehydration is improved and the dehydration operation time is shortened. These effects are also observed when freeze-concentrated sludge is added to the concentrated sludge, but it is not as effective as the present invention . Compared to the case of dehydration after freezing and concentrating all the conventional amounts that have been obtained, both the equipment and operating costs are economical. The pre-coating method is an existing equipment introduction type and can be introduced into many dehydration systems regardless of whether it is newly installed or existing. With the present invention, the spread of pollution-free sludge dewatering is expected.
[Brief description of the drawings]
FIG. 1 is a schematic flow sheet illustrating sludge treatment using the sludge filtration / dehydration system of the present invention. FIG. 2 is a schematic flow sheet illustrating conventional sludge treatment using a non-chemically poured sludge dewatering method.・ Outline flow sheet exemplifying conventional sludge treatment using melting method [Explanation of symbols]
1: Freezing / thawing tank 2: Filter 3: Line for switching sludge between freezing / thawing device and filter 4: Line for sending frozen / thawed sludge to the filter 5: Line for sending supernatant water out of the system 6: Sludge to be dehydrated 7: Sedimentation basin 8: Concentration tank 21: Raw water containing sludge 22: Sedimentation pond 23: Concentration tank 24: Steam 25: Filtration dehydrator 31: Raw water containing sludge 32: Sedimentation basin 33: Concentration Tank 34: Freezing / thawing tank 35: Filtration / dehydrator

Claims (5)

          In the sludge filtration / dehydration method, pre-coating the sludge freezing / thawing sludge obtained by the sludge freezing / thawing method on the filter, supplying the sludge to be dehydrated after pre-coating to the filter, and filtering / dehydrating. A sludge filtration and dehydration method characterized by           The frozen sludge obtained by the sludge freezing and thawing method is clarified, the supernatant water is separated, and the remaining frozen and thawed sludge is pre-coated on a filter. Dehydration method. 3. The sludge filtration / dehydration method according to claim 1, wherein a pressure filter is used as the filter. Sludge to be dewatered is, filtration and dehydration process sludge according to 請 Motomeko 1, 2 or 3, characterized in that a sludge containing no dehydrating aid.           A line that includes a sludge freezing / thawing device (1) and a precoat-type filter (2), and leads the sludge to be dewatered to the freezing / thawing device and the filter by switching the delivery destination ( 3) and a freezing and thawing device, a line for sending frozen and thawed sludge to the filter (4), and a line for sending supernatant water clarified from the frozen and thawed sludge to the outside of the system (5) And a sludge filtration / dehydration system.

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