JP4002536B2 - Sludge drying method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sun drying method for wastewater sludge, particularly sludge discharged from a water purification plant. Specifically, the sludge freezing and thawing process is used to increase the efficiency of sludge drying in the sun. In the present invention, “raw sludge” is sludge that has been subjected to freezing / thawing treatment that is put into a sun-dried bed for drying, and “freezing / thawing sludge” is subjected to the above-described freezing / thawing treatment. It refers to sludge.
[0002]
[Prior art]
Usually, in water purification plants, wastewater treatment plants, etc., suspended substances contained in the taken raw water are concentrated and separated as sludge by installing a drainage pond or concentrating device, and the concentrated sludge is dried or dehydrated. After separating the coexisting water using, it is treated legally. The sun drying method is a means for drying the concentrated sludge, and generally, the raw sludge concentrated until the moisture content becomes about 2 to 5% by weight using a drainage pond, a concentrating device, or the like. This is a method in which the slurry is put into a sun-dried bed and allowed to stand, and the supernatant water and filtered water are removed to reduce the moisture content in the sludge, and further sludge drying is performed by natural evaporation such as sun. In many cases, the moisture content is dried to about 30 to 65% by weight for ease of transportation and use, and it is positioned as the final step in the sludge concentration and dehydration step. The sludge dried in this way can be effectively used as horticultural soil. The solar drying method is an excellent method that requires less equipment and operation costs and is easy to maintain and maintain compared to other dehydration methods when the frequency of waste mud is low, the location and weather conditions are suitable, and the site is easy to secure. It is.
[0003]
FIG. 1 is a plan view showing an example of a sun-drying bed, and FIG. 2 is a vertical sectional view of a portion A shown in FIG. The sun-dried floor is formed by dividing the inside of a pool-shaped concrete frame 1 with an open upper surface into dry floors 2 of an appropriate size, and collects filtered water at the bottom 3 of each dry floor. A water collecting main pipe 4 and a water collecting branch pipe 5 are provided if necessary. On the dry floor 2, gravel, quarry, etc. (generally about size 4 and gravel with different sizes may be layered in multiple layers) are spread as filter media, and river sand is spread on it. Sludge 8 is introduced from the surface of the filter medium 7 to about 150 cm. After the sludge is charged, the solid content is settled as it is, and the supernatant water is extracted through the supernatant water outlet 10 by a corner drop (a kind of overflow weir, which can be adjusted by sliding up and down) 9. The filtered water passes through the collecting pipes 5 and 4 and is discharged out of the dry bed from the drainage outlet 6 together with the supernatant water. The remaining sludge is naturally dried to become a dry sludge of about several tens of centimeters on the filter medium. The dried sludge is mechanically removed from the dry bed such as a shovel, pulverized, and used as, for example, gardening soil or buried soil. The filtered water and the supernatant water are returned to the raw water intake or treated legally and discharged into rivers.
[0004]
[Problems to be solved by the invention]
By the way, the sun drying method has the advantage that the cost for equipment and operation is small, but the weak point is that it takes time to dry and requires a large site. Normally, raw sludge has poor filterability, and its tendency is particularly remarkable in winter, and it may take 6 to 10 months for one drying. In addition, since the dried sludge has a thickness of several tens of centimeters, in order to effectively use the sun-dried sludge as horticultural culture soil, etc., it is taken out from the sun-dried bed and crushed into particles of about 2 to 5 cm. There is a need. However, the sun-dried sludge mass is generally hard and difficult to grind. The present invention has been completed as a result of repeated studies to solve the above-mentioned problems and to obtain an efficient sun drying method and a dry sludge that can be easily pulverized.
[0005]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the present invention provides a sludge ceiling characterized by mixing raw sludge to be sun-dried with sludge that has been subjected to freezing and thawing treatment, putting it into a sun-drying bed, and drying it. Provide sun drying method. Furthermore, the present invention provides a sun drying method for sludge, characterized in that at least one layer of frozen and thawed sludge and raw sludge are alternately put into a sun drying bed. In the above-mentioned sun drying method, the ratio of the frozen / thawed sludge in the sludge to be put into the sun drying bed is preferably adjusted to a range of 30 to 100% by weight. In addition, if the frozen / thawed / concentrated sludge is used after the frozen / thawed sludge is frozen / thawed, the frozen / thawed sludge is precipitated and the supernatant water is separated and concentrated. Sun drying can be performed efficiently.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail and specifically. The raw sludge to be dried using the present invention may be organic or inorganic, and may be sludge that has been separated by settling, or sludge that has been further concentrated by some method. The water content of the sludge in the present invention (wt%), after completely dried for sludge weight W ₁ in a hot air circulating dryer at 105 ° C., a dry weight W ₂ was measured {(W ₁ -W ₂ ) / W ₁ } × 100% was calculated.
[0007]
Now, in the present invention, if the raw sludge to be dried is mixed with the sludge that has been subjected to freezing and melting treatment, and put into a dry bed and sun-dried, the number of days required for drying is greatly reduced, and drying is performed. By finding the effect that the sludge does not harden and harden as in the prior art, it can be easily pulverized. Thus, the present invention has been completed as a means for solving the above-mentioned problems in the sun drying method. Raw sludge and frozen / dried sludge may be mixed and charged in advance, or at least one layer may be alternately charged and stacked. In the latter case, the frozen / thawed sludge layer is preferably the lowest layer. The amount of frozen / thawed sludge in the sludge to be put into the sun-dried bed is generally preferably 30 to 100% by weight, particularly preferably 40 to 80% by weight, although it depends on the characteristics and operating conditions of the sludge to be handled. . If it is 30% by weight or less, the effect of freezing / thawing sludge becomes small, and if it is too much, the cost of freezing / thawing sludge increases and the economic advantage is lost.
[0008]
For freezing / thawing of sludge, for example, a freezing / thawing tank in which heat transfer tubes are arranged inside the tank is used. The sludge from the concentrating tank is put into the freezing / thawing tank, and the introduced sludge is frozen by flowing the refrigerant through the heat transfer tube. Freezing conditions are often determined based on the structure of the apparatus, the characteristics of the sludge to be treated, the supply temperature, etc., and preliminary tests and experience. In general, cold brine at −10 to −30 ° C. is passed through a heat transfer tube or the like for 1 to 3 hours and frozen. The sludge is frozen and thawed by switching the refrigerant to a heat medium after the predetermined freezing treatment to melt the frozen sludge. The sludge for freezing and thawing generally uses raw sludge to be dried, but is not limited thereto. It is also effective to melt the frozen sludge, set the sludge, discharge the supernatant water out of the system, concentrate the sludge, freeze / thaw / concentrate sludge, and reduce the load in the drying process. is there.
[0009]
When the sludge is frozen, the water taken into the solid is drawn out to the cooling surface of the heat transfer tube and becomes ice, and the solids agglomerate. That is, by freezing the water in the sludge, the sludge is microscopically separated from the water and agglomerates to improve filterability and dewaterability, and after drying, the frozen sludge is not hardened and solidified. By mixing aggregated frozen / melted sludge with raw sludge, the filterability and dewaterability of raw sludge are improved, and solidification due to drying of raw sludge is prevented. Furthermore, the frozen / thawed sludge itself contains about 20 to 30% by weight of Al ₂ O ₃ , and has the same effect as a coagulation precipitation aid on the raw sludge in the same manner as aluminum sulfate and polyaluminum chloride. It is thought that it contributed to the improvement of the characteristics of the mixed raw sludge.
[0010]
The mixed sludge of frozen / thawed sludge and raw sludge treated in this way is not only improved in sedimentation and fast and easy to separate from the supernatant water, but also improved in sludge filtration characteristics and dehydrated sludge. It has the effect of reducing the residual moisture content. Further, the trouble of clogging of the filter medium (filter cloth) is reduced, and the sludge after dehydration is not hardened unlike conventional dry sludge and can be easily pulverized. In addition, separation from the filter medium (filter cloth) becomes easy.
[0011]
【Example】
In order to confirm the effect of this invention, it experimented using the experimental sludge sun drying bed, and it demonstrates with reference to FIG.3 and FIG.4. FIG. 3 is a sectional view of the experimental sludge drying bed. For the experiment, six dry floors with outer dimensions of 50 × 50 × 90 (depth), in which the side wall and bottom plate of the steel plate container 21 were covered with a heat insulating material 22 having a thickness of 5 cm, were used, all 10 cm from the bottom. 10 to 20 mmφ gravel 23, 10 cm to 4 cm 6 mm gravel 24, 5 cm to 1 to 2 mm φ gravel 25, and 10 cm thick Laying river sand 26. A discharge port 27 for continuously discharging filtered water was attached to the bottom plate. The treated sludge capacity of this dry bed was about 0.125 m ³ .
[0012]
On the other hand, about 0.6 m ³ of raw sludge is put into a 0.6 m ³ freezing / melting tank (not shown) with a built-in heat transfer coil, and a -20 ° C refrigerant flows through the heat transfer coil for 100 minutes. After freezing, the refrigerant was switched to a heating medium at 30 ° C. and flowed for 90 minutes to melt the frozen sludge to obtain frozen / thawed sludge.
[0013]
In the above experimental sludge drying bed, freezing and thawing sludge is respectively 0: 1, 2), 20: 40, D: 60, E: 80, and F: 100 with respect to 100 parts by weight of the total amount of sludge. 6 types of mixed sludge 28, with the remainder and raw sludge as raw sludge, were mixed in 0.125 m ³ units and placed in each dry bed. The water content of the input sludge was 96% by weight. The filtrate outlet at the bottom was always open, and the supernatant water was discharged to the sludge surface once every two days. FIG. 4 shows the daily change in the sludge / supernatant water interface height together with the moisture content after about 60 days. In addition, among the obtained dried sludge, ha to f were hard enough to collapse easily when the lump was strongly pressed with a finger.
[0014]
【The invention's effect】
Utilizing the present invention, the number of days required for sun-drying can be shortened by adding sun sludge frozen / thawed or frozen / thawed / concentrated to the raw sludge and sun-drying. The treatment efficiency of the sun-drying bed is improved, and the amount of mechanical dewatering is reduced, and the wastewater treatment cost is reduced. In addition, the sun-dried sludge according to the present invention is not hard and hardened like the conventional sun-dried sludge, so it can be easily pulverized and easily pulverized to about 2 mmφ, so that it can be effectively used as horticultural soil. .
[Brief description of the drawings]
FIG. 1 is a plan view showing an example of a sun-drying bed,
2 is a vertical cross-sectional view of part A shown in FIG. 1. FIG. 3 is a cross-sectional view of an experimental sludge drying bed. FIG. 4 is a result of an example (sludge with a mixing ratio of frozen and thawed sludge as a parameter). / Graph showing the interfacial height of the supernatant water and the sludge moisture content.
1: Pool-like concrete frame with open top surface 2: Dry floor 3: Dry floor bottom 4: Water collection main pipe for discharging filtrate out of the floor 5: The same water collection branch 6: Supernatant water, filtered water Discharge port 7: Filter medium (gravel, quarrying, etc.) 8: River sand, etc. 9: Sludge 10: Corner drop 11: Clear water outlet 12: Partition groove 21: Steel plate container 22: Insulating material 23: Gravel with 10-20 mmφ 24: 4-6mmφ gravel 25: 1-2mmφ gravel 26: River sand 27: Outlet of supernatant water and filtered water 28: Blended sludge

Claims (4)

A sludge sun drying method characterized by mixing raw sludge to be sun dried with sludge that has been subjected to freezing and thawing treatment, putting it into a sun drying bed, and drying. A method for drying sludge in the sun, wherein the sludge that has been subjected to freezing and thawing treatment and the raw sludge are alternately put into a sun-drying bed in layers. The method for drying sun of sludge according to claim 1 or 2, wherein the ratio of frozen and thawed sludge in the sludge to be put into the sun drying bed is adjusted to a range of 30 to 100% by weight. Instead of the sludge that has been subjected to the above-mentioned freezing / thawing treatment, the frozen / thawed / sludge sludge that has been frozen / thawed, precipitated, separated from the supernatant and concentrated, is used. The sun drying method of the sludge of Claim 1, 2, or 3.

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