JPH0326120B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a sludge dewatering treatment method in which surplus sludge or the like generated in a sewage treatment plant is used as a material to be dehydrated, and this sludge is dehydrated by electroosmotic dehydration to form a cake.

[Prior art and its problems]

BACKGROUND ART Conventionally, a method has been widely adopted in which electroosmotic dehydration equipment is used to dewater sludge with a high water content generated in sewage treatment plants and the like. By the way, the nature of surplus sludge generated from sewage treatment plants is that it is hydrophilic and contains many substances with microscopic particle sizes in the colloidal range, and mechanical dewatering methods such as squeezing generally cannot separate the sludge particles. It is said that it is difficult to separate and dehydrate the interstitial water that exists between the two. Furthermore, sludge contains a large amount of electrolytes as well as organic and inorganic substances, and has a considerably high electric power. On the other hand, the electroosmotic dehydration method described above is a method that separates and dehydrates the sludge by applying electrical conductivity to the sludge and moving the pore water of the sludge to the cathode side using electric force. The amount of movement (amount of water removed) is proportional to the amount of current flowing through the sludge, so in order to dehydrate raw sludge with a high water content and turn it into a dehydrated cake with a low water content using an electroosmotic dehydrator, It consumes a lot of electricity to operate. For this reason, various methods have been attempted to achieve high dewatering efficiency with as little power consumption as possible than conventional methods. As an example, in the first step before raw sludge is introduced into an electroosmotic dewatering device, raw sludge is first washed with water to lower the electrolyte concentration, thereby lowering the electrical conductivity of the sludge, and then adding a polymer flocculant, etc. The same applicant has proposed a system in which sludge is subjected to a reforming process to coagulate and concentrate and then introduced into an electroosmotic dewatering apparatus (Japanese Patent Application No. 58-204478). Next, the dewatering method described above will be explained with reference to FIG.
In Fig. 3, 1 is a water washing device that constitutes a sludge washing process, 2 is a coagulation mixing device that is a preconcentration process, and 3 and 4 are a belt conveyor type pre-dewatering process in which a press belt 41 is combined with a filter cloth 31. gravity filtration dehydration equipment and low pressure dehydration equipment,
5 is an electroosmotic dehydration device. That is, raw sludge A generated in a sewage treatment plant or the like is first introduced into the washing water tank 11 of the water washing device 1, and while being stirred by the stirring device 12, the washing water is added to the washing water tank from the washing water supply line 13. The electrolyte concentration is diluted by washing the highly conductive sludge pore water contained in the sludge with water, thereby lowering the conductivity. The sludge adjusted to have a low conductivity in this way is sent by the sludge pump 14 to the next coagulation-mixing device 2, where a polymer flocculant 21 is added to coagulate and concentrate the colloidal particles. Subsequently, the sludge is pre-dehydrated via a belt conveyor-type gravity filtration dehydrator 3 and a low-pressure pressurized dewaterer 4, and then introduced into an electroosmotic dewaterer 5. The filtrate that has passed through the filter cloth 31 and been separated and dehydrated from the sludge in the pre-dehydration step is dripped into the drain tray 32 and discharged out of the system. On the other hand, the electroosmotic dehydration device 5 includes a rotary pressure drum 51 which also serves as an anode side electrode member, and a press belt which also serves as a cathode side electrode member and is stretched across a sprocket facing the circumferential area of the drum 51. 52, a filter belt 53 made of filter cloth or the like superimposed on the press belt, a DC power supply 54 that applies voltage between the drum 51 and the press belt 52, a drain tray 55, and the like. Such an electroosmotic dehydration device 5
The sludge that has been modified through the pre-treatment process is transferred to the pressurized drum 51 and the filter belt 5.
By supplying the sludge to the entrance of the sludge passage between
While the sludge is conveyed through the belt through the passageway, mechanical squeezing force is applied to the sludge, and electroosmotic dehydration is performed under the action of an electric field formed between opposing electrodes. As a result, the pore water contained in the sludge is positively charged and flows toward the cathode, passes through the filter belt 53, and is separated and dehydrated from the sludge. The filtrate that has passed through the filter belt 53 is dripped into a drain pan 55 and discharged from there to the outside of the system, while the electroosmotic dehydration turns the sludge into a dehydrated cake with a low water content, indicated by symbol B, at the exit of the device. It will be carried out. The dehydrated cake B is incinerated or composted and reused as fertilizer. In this way, instead of introducing sludge as raw sludge into the electroosmotic dewatering equipment, the sludge is modified to have a low conductivity in the pre-treatment washing process and then sent to the electroosmotic dehydrating equipment. This enables efficient dehydration with less power consumption. However, in the conventional dewatering method described above, in which raw sludge is washed with water in the first step as a pretreatment step and adjusted and reformed to reduce the electrical conductivity of the sludge, the following problems arise. In other words, surplus sludge generated in large quantities at sewage treatment plants has a high moisture content that is almost liquid phase, which increases the cleaning load in the washing process. This results in an increase in the consumption of water, resulting in higher equipment and operating costs for dewatering equipment.

[Purpose of the invention]

This invention was developed in consideration of the above points, and it improves the conventional dewatering method described above, reduces the washing load in the sludge washing process, downsizes the washing equipment, and reduces the amount of washing water consumed. Another object of the present invention is to provide a sludge dewatering method applied to electroosmotic dehydration that achieves high dewatering efficiency with low power consumption in the electroosmotic dewatering process.

[Key points of the invention]

In order to achieve the above object, the present invention performs each pretreatment process of adding a flocculant to raw sludge, a gravity filtration dewatering process, and a sludge washing process in the above order to reduce the electrical conductivity of sludge. After adjusting and reforming this sludge, this sludge is introduced into the electroosmotic dewatering process and subjected to electroosmotic dehydration treatment, which improves the separation between raw sludge sludge and filtrate in the first flocculation and mixing process, and then In order to easily reduce the volume of sludge in the filtration and dewatering process, thereby reducing the washing load in the next washing process, and adjusting and reforming the sludge to a low conductivity, the washing equipment can be downsized and a small amount of washing water can be used. The electrical conductivity of the sludge can be adjusted efficiently, and this pretreatment process allows high dewatering efficiency to be obtained with low power consumption in the electroosmotic dewatering process.

[Embodiments of the invention]

FIG. 1 is a block diagram of a sludge dewatering apparatus according to an embodiment of the present invention, and FIG. 2 is a flowchart of FIG. 1. In FIG. 1, the same members as in FIG. There is. That is, according to the illustrated embodiment, raw sludge A is first introduced into the flocculating mixer 2 as a first pretreatment step, and a polymer flocculant 21 is added thereto to flocculate and concentrate the sludge.
Next, the sludge is sent to a belt conveyor-type gravity filtration and dehydration device 3, and gravity filtration and dewatering is performed in the process of conveying it on a filter cloth belt. On the other hand, a cleaning water supply line 13 is arranged opposite to the downstream area of the gravity filtration and dehydration area on the filter cloth belt, and a nozzle at the tip of the water supply line 13 sprays cleaning water onto the sludge conveyed by the belt. The sludge is then washed with water, thereby diluting the electrolyte concentration of the highly conductive pore water contained in the sludge and reforming it into sludge with low conductivity. The washed sludge is pre-dehydrated in a low-pressure dehydrator 4 and then sent to an electroosmotic dehydrator 5, where it is subjected to electroosmotic dehydration and recovered as a dehydrated cake B with a low water content. The above dehydration process is shown in a flowchart as shown in Figure 2. That is, as described above, as a pretreatment step for the electroosmotic dewatering step, a flocculant is first added to the raw sludge to flocculate the sludge, thereby increasing the separability between the sludge and the filtrate. Therefore, the concentration of sludge can be easily increased by separating and dewatering the filtrate in the next step of gravity filtration and dehydration, and the volume of sludge can be significantly reduced. As a result, the cleaning load in the next water washing process is significantly reduced compared to the conventional water washing process shown in Figure 3, and the sludge is efficiently washed with water and adjusted to a low conductivity with a small amount of water supplied during the washing process. It becomes possible to do so. Note that the above-mentioned washing process is not limited to the method of spraying washing water onto the sludge as shown in the illustrated example, but according to this washing water spraying method, a washing water tank like the conventional method shown in Fig. 3 can be used. This has the advantage that a stirring device and the like can be omitted and the equipment can be simplified. Further, the low-pressure dehydration step performed after the water washing step may be omitted depending on the case. By introducing the sludge into the electroosmotic dewatering process after adjusting and reforming the sludge to have a low conductivity through the pretreatment process, the electroosmotic dewatering device 5 can efficiently perform electroosmotic dewatering with less power consumption. You will be able to do this.

【Effect of the invention】

As described above, according to the present invention, the pretreatment steps of the coagulation mixing step of adding a flocculant to raw sludge, the gravity filtration dewatering step, and the sludge washing step are performed in the above order to reduce the electrical conductivity of the sludge. After adjusting and reforming the sludge, this sludge is introduced into the electroosmotic dehydration process and subjected to electroosmotic dehydration treatment.The action of the flocculant in the first flocculation and mixing process improves the separation of raw sludge sludge and filtrate. Therefore, the volume of sludge is easily reduced in the next step of gravity filtration and dewatering. This reduces the cleaning load in the next washing process, and makes it possible to efficiently wash sludge with a small amount of washing water and adjust and improve its conductivity to a low value, compared to conventional methods. equipment costs and operating costs can be reduced. Furthermore, in the electroosmotic dehydration step at the final stage, highly efficient electroosmotic dehydration can be achieved with less power consumption due to the above-mentioned pretreatment.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a sludge dewatering facility according to an embodiment of the present invention, FIG. 2 is a flowchart of the dewatering process in FIG. 1, and FIG. 3 is a system diagram of a conventional dewatering facility. In the figure, A: Raw sludge, B: Dehydrated cake, 2: Coagulation-mixing device, 21: Flocculant, 3: Gravity filtration dehydration device, 1
3: Washing water supply line for washing, 4: Low pressure dehydration device, 5: Electroosmotic dehydration device.

Claims (1)

[Scope of Claims] 1. A sludge dewatering treatment method in which sludge generated in a sewage treatment plant, etc. is dehydrated and turned into a cake, which includes a coagulation-mixing process in which a flocculant is added to raw sludge, a gravity filtration dewatering process, and sludge. Dewatering of sludge characterized by carrying out the treatment steps in the above order to adjust and reform the sludge to a low conductivity, and then introducing the sludge into an electroosmotic dewatering step for electroosmotic dehydration treatment. Processing method. 2. A sludge dewatering method according to claim 1, characterized in that a low pressure dehydration step is incorporated between the sludge washing step and the electroosmotic dehydration step.