JPH046440B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for dewatering sludge sludge. Some of the digested sludge generated at sewage treatment plants is highly alkaline and contains a very large amount of solids.
In order to treat such sewage, it is known to use an organic flocculant to flocculate the sludge solid content in the sewage, and then dehydrate the concentrated sludge by compressing it under pressure with a filter press. However, in the method of flocculating sludge with the above-mentioned organic flocculant, in the case of precipitated sludge in which the organic component in the solid content of the sludge is less than 75%, the moisture content of the cake obtained by filter press is high, and the cake is subjected to combustion treatment. It is difficult to do so. As a solution to these problems, the sludge solids can be concentrated to 6-14% by weight by adding an organic flocculant to the settled sludge, which has been concentrated to 0.5-5.0% by weight by gravity sedimentation. , fine-grained coal or ash or a mixture thereof is added to this concentrated sludge, and before, simultaneously or after the incorporation of these additives, it is further treated with 2 to 8 kg of organic flocculant per ton of sludge solids, and then dewatered in a filter press. A method has been proposed to
(See Publication No. 117311). In this proposed method, the moisture content of the press cake is low and it can be incinerated sufficiently in a boiler, etc., but it requires a large amount of particulate coal or incineration ash additives, and the elapsed time in the filter press is long. Furthermore, since the organic flocculant is added in two steps, there is a problem that the operation becomes complicated. As a result of considering the above problem, the inventor has found that
This invention has been achieved. That is, in this invention, prior to adding an organic flocculant to precipitated sludge that has been concentrated by gravity sedimentation of sludge, pulverized coal or incinerated ash is first added, and then the organic flocculant is added and mixed and stirred. Water is removed through a screen, and the resulting concentrated sludge is mixed with 0.2~1 part by weight of sludge solids.
Secondary addition of 0.75 parts by weight of pulverized coal or incineration ash such that the total addition amount with the primary addition does not exceed 0.95 parts by weight, and compressing and dewatering the concentrated sludge settled by the above secondary addition by mechanical means. This is a method for dewatering sludge sludge. By gravity settling the sewage sludge in a settling tank, the sludge solids are concentrated to 0.5 to 5.0% by weight and a precipitated sludge is obtained. The amount of sludge solids in the settled sludge depends on the properties, concentration, settling time, etc. of the sludge contained in the sludge, but the above concentration range is suitable for post-process treatment. Prior to adding an organic flocculant to the above-mentioned precipitated sludge, pulverized coal or incinerated ash is first added and mixed and stirred. The amount of pulverized coal or incineration ash added is 0.2 to 0.75 parts by weight of sludge solids in the precipitated sludge.
Parts by weight are preferred, and if the amount added is less than 0.2 parts by weight, the overspeed of the concentrated sludge will decrease and the moisture content of the cake will increase, making it difficult to incinerate. If the amount added exceeds 0.75 parts by weight, the overspeed of the concentrated sludge will decrease, and the amount added will increase, resulting in high costs, and the processing capacity will increase, making operation difficult. An organic flocculant is added and mixed to the precipitated sludge to which pulverized coal or incinerated ash is primarily added and mixed and stirred.
As a result of the primary addition and mixing of the above pulverized coal or incineration ash,
The sludge is flocculated by an organic flocculant to form coarse particles with good water permeability, and these coarse particles are separated from the liquid as stable sludge flocs. The amount of the above organic flocculant added is 1 t of sludge solids.
2 to 12 kg (solid content) is preferable, and if it is less than 2 kg, the sludge will be difficult to separate, and if it exceeds 12 kg, the viscosity of the mother liquor will increase,
Also, when filtering the concentrated sludge, the cloth becomes clogged. The above-mentioned organic flocculant is preferably a cationic flocculant, but depending on the type of sludge, an anionic flocculant or a mixture of both types may be used. The above sludge flocs are separated from the liquid by a screen such as a wire mesh or cloth, and by further adding and mixing pulverized coal or incinerated ash to the sludge flocs, pulverized coal or incinerated ash is placed on top of the former flocs. It becomes a flocculent that drains well. The amount of pulverized coal or incineration ash added to the sludge flocs is 0.2 parts by weight per 1 part by weight of the sludge solids.
~0.75 parts by weight. The sum of the above primary addition amount and secondary addition amount is based on 1 part by weight of the sludge solids.
If the total amount of primary and secondary additives exceeds 0.95 parts by weight, the amount of additives will increase, resulting in high costs, and the processing capacity will increase, making processing operations complicated. The concentrated sludge is fed by mechanical means, such as a filter press, and passed through a cloth stretched across the plates of the filter press, solids being deposited in the form of a cake in the chambers between the cloths, and the filtration is completed. In this state, the cake is compressed by applying fluid pressure to remove water in the cake to form a compressed cake, and then the plate of the filter press is separated to take out the compressed cake. The moisture content of this compressed cake is approximately 40-65% by weight. The pulverized coal used in the method of this invention is
Pulverized coal produced as a by-product at a coal preparation factory or pulverized coal obtained by pulverizing coal is suitable. In addition, incineration ash obtained by incinerating cake at a sewage treatment plant is generally used. Pulverized coal and incineration ash are preferably placed under a sieve of 100 mesh or more. Mechanical means for compressing and dewatering the concentrated sludge include, in addition to the above-mentioned filter press, a vertical filter press, a box-type rotary press, a compression belt press, and the like. According to the method of this invention, the total amount of pulverized coal and incinerated ash added is smaller compared to the known method of adding the above-mentioned organic flocculant in two parts and adding pulverized coal and incinerated ash all at once. This reduces the cost, increases the overspeed of the settling sludge, shortens the elapsed time, and shortens the time for one cycle. Furthermore, since the amount of organic components in the cake increases, it becomes easier to burn and can be effectively used as a fuel. Furthermore, incineration ash from incineration is reduced. Examples of the present invention will be described below. Example Sludge in a domestic sewage final treatment tank was treated, and the sludge was made to have a sludge solid concentration of 3.1% by weight (of which 2.21% by weight was crude fiber dry solids), and the ignition loss of the sludge was 49.6 minutes
%, and the alkalinity is 8700mgCaCO ₃ /Kg
The pH of the liquid was 7.9. To the above sedimentation sludge, incineration ash passed through a 100 mesh sieve or pulverized coal (trade name Escor 15, volatile content 43%, ash content 15%, 40 to 60% by weight after passing through a 200 mesh sieve,
The particle size of the sludge is increased by first adding sludge (manufactured by Hokutan Kasei Kogyo Co., Ltd.) and stirring to increase the particle size of the sludge.Then, a cationic organic flocculant (product name: Zetatsuku 57, microbeads, manufactured by Allied Colloids, UK) is added to the sludge at a high concentration.
The sludge is added as a 0.2% aqueous solution and stirred to form a floc, and the floc is passed through a screen (60 mesh
Moisture was removed through a mesh), pulverized coal or incinerated ash similar to the above was added to this concentrated slurry as a secondary addition, and this concentrated sludge was fed to a single filter press. Overpressure of filter press is 4Kg/
cm ² and the elapsed time was 8 minutes, a cake was deposited between the cloth spread between the plates, and 20 kg/kg was deposited on this cake.
The moisture in the cake is removed by squeezing the cake by applying a compression pressure of cm ² for 20 minutes. Then, open the plate of the filter press and remove the compressed cake. In addition,
The time for one cycle using the filter press was 38 minutes. The primary addition amount of incineration ash or pulverized coal, the addition amount of organic coagulant, the secondary addition amount of pulverized coal or incineration ash, cake moisture content, back-calculated slurry concentration, net average overspeed of concentrated sludge, etc. in the above examples. are shown in the table below. In addition, a case where pulverized coal was mixed at once either before or after addition of the organic flocculant, and a case where the primary and secondary addition amounts were larger than a predetermined amount were shown as comparative examples.

[Table] In the above table, the primary addition amount of incinerated ash, pulverized coal, and secondary pulverized coal addition amount are weight % based on the sludge solids, the flocculant addition amount is ppm weight part based on 1 weight part of the sludge solid content, and the cake moisture content. is the moisture percentage in the wet cake, and the slurry concentration is calculated by the formula: cake dry weight/liquid volume + squeezed liquid volume + cake weight x 10
The concentration (%) of concentrated sludge calculated from 0,
The average overspeed is expressed as the net dry cake overweight per unit area and unit time of the filter press in units of Kg/m ² ·hour. As seen in the table above, each experiment No.
The average overspeed is larger than that of the comparative example. Even if the amount of organic flocculant added changes somewhat, as seen in Experiment No. 3 of the Examples, or if pulverized coal is used instead of incinerated ash as the primary additive, as seen in Experiment No. 4, There is also no significant difference in cake moisture content and average overspeed. As for secondary additives, even if incineration ash is used instead of pulverized coal, there is no significant difference in the moisture content of the cake or the average overspeed. Furthermore, as seen in Experiment Nos. 1, 2, and 3 of the comparative example, when a large amount of pulverized coal is added at once, either in the primary or secondary process, the average overspeed decreases. Further, as seen in Experiment No. 4 of the comparative example, when incinerated ash is added as the primary addition and pulverized coal is added as the secondary addition, the average overspeed decreases when the total amount is 95% by weight or more. Further comparative example experiments
As seen in No. 5, when a relatively small amount of incinerated ash is added as a secondary addition, the moisture content of the cake is large;
The average overspeed is significantly reduced.

Claims (1)

[Claims] 1. Prior to adding an organic flocculant to the precipitated sludge concentrated by gravity sedimentation of sludge, pulverized coal or incinerated ash was first added, and then the organic flocculant was added and mixed and stirred. After that, moisture is removed through a screen, and the resulting concentrated sludge is mixed with 0.2 to 0.75 parts by weight of pulverized coal or incinerated ash per 1 part by weight of the sludge solids, with the total addition amount not exceeding 0.95 parts by weight including the primary addition amount. A method for dewatering sludge sludge, which comprises performing secondary addition as described above, and then compressing and dewatering the concentrated sludge precipitated by the secondary addition using mechanical means. 2. The method for dewatering sludge sludge according to claim 1, wherein the primary addition amount of pulverized coal or incineration ash is 0.2 to 0.75 parts by weight per 1 part by weight of sludge solids.