JPS6097011A - Dehydration treatment system of sludge - Google Patents

Abstract

PURPOSE:To efficiently dehydrate sludge with reduced power consumption, by adjusting the conductivity of raw sludge to a low value to modify the same before subjecting said sludge to electroosmosis dehydration. CONSTITUTION:Raw sludge is charged into a washing tank and mixed with washing water such as tap water sufficiently low in the concn. of an electrolyte under stirring. Sludge interstitial water high in conductivity contained in raw sludge is thinned in the concn. of the electrolyte thereof by this operation and conditioned so as to lower the conductivity thereof and excessive washing waste water is further separated from sludge and drained. Sludge adjusted to low conductivity by this method is sent into an electroosmotic dehydration process and subjected to dehydration treatment by an electroosmotic dehydrator to be recovered as a low moisture cake. Furthermore, pre-concn. due to the addition of a flocculant and pre-dehydration may be performed before sludge adjusted to low conductivity is sent to the electroosmotic dehydration process.

Description

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

The present invention relates to a sludge dewatering method in which excess sludge produced by activated sludge treatment in a sewage treatment plant or the like is dehydrated and turned into a cake by electroosmotic dehydration. When performing electroosmotic dewatering, it is desirable to be able to efficiently dehydrate sludge with as little power consumption as possible.

[Prior art and its problems]

For example, an electroosmotic dehydrator with a configuration as shown in Figure 1 is known as an electroosmotic dewatering machine that continuously dewaters sludge with a high water content generated in sewage treatment plants by applying the electroosmotic dewatering method. ing. In FIG. 1, 1 is a metal rotating drum that also serves as an anode side electrode member, and 2 is a metal rotating drum that also serves as a cathode side electrode member that is stretched across a sprocket 3 facing the circumferential surface of the drum 1. A press belt 4 is a filter belt for filter water permeation stretched over the press belt 2, 5
A sludge transport passage 6 is defined in the area where the drum 1 and the filter belt 4 face each other, and a sludge supply water tank 7 is installed on the entrance side of the sludge transport passage 6. This makes up the main body of the dehydrator. Further, a DC power supply device 9 is connected to the electrode drum 1 on the opposite electrode side, with the press belt 2 serving as the cathode electrode being on the ground side. Note that 10 is a filtered water receiving tray that communicates with the outside of the system, and 11 is a dehydrated cake collection container. With the configuration shown in FIG. 1 above, the sludge 12 as a material to be dewatered is sent from the hopper 7 to the sludge conveyance passage 6, and at the same time, the drive motor 5 is operated to move the sludge 12 in a sand winch shape within the conveyance passage. If power is supplied from the power supply device 9 while pinching the sludge and transporting it toward the exit in the direction of arrow I), in addition to the mechanical squeezing force, an electric field formed between the opposing electrodes acts on the sludge 12, causing the sludge to The water contained in 12 is positively charged and flows toward the cathode, and is discharged to this electrode member.
So-called electroosmotic dehydration, in which the water passes through the filter belt 4 and is dehydrated, will be performed. The filtrate that has passed through the filter belt 4 drips into the filtrate tray 10, from which it is drained out of the system. On the other hand, the dewatered sludge is turned into a cake and sent out from the outlet of the passage 6 as a dehydrated cake 12', and is collected into the collection container 11 via the scraper 13. As a result, sludge with a high water content is continuously dehydrated to become a dehydrated cake with a low water content. This dehydrated cake is incinerated or composted and reused as fertilizer.
By the way, the above-mentioned electroosmotic dehydrator consumes a lot of electricity to operate, and due to mechanical limitations, raw sludge with an extremely high water content, almost in the liquid phase, is directly introduced into the dehydrator to perform dewatering. Instead, as shown in Figure 2 or Figure 3, a flocculant is added to the raw sludge in the first step to concentrate it, and if necessary, the water content of the sludge is reduced through a pre-dehydration process using a compressor dehydrator, etc. A method is adopted in which the temperature is lowered as much as possible before introduction into the electroosmotic dehydrator. However, in colloidal regions such as sludge, which contain a large amount of hydrophilic substances and have small particle sizes of the solids that make up the sludge, it may be difficult to remove the interstitial water that exists between the solid particles. The actual situation is that the decrease in water content due to the pre-concentration and pre-dehydration steps described above is small, and does not have a significant effect on reducing power consumption in the electroosmotic dehydrator. On the other hand, regarding electroosmosis, as is well known, sufficient research has already progressed and the theory has been established, and the theoretical formula for the liquid iV transferred per unit time due to electroosmosis of slurry can be expressed by the following equation. well known. However, ζ: interfacial potential, D, η, λ: dielectric constant of liquid. Viscosity, electrical conductivity, I: current. In this way, in addition to the potential gradient between the electrodes and the iI current, factors such as η and λ, which represent the physical properties of the liquid described above, also affect electroosmosis. Among these, regarding the electrical conductivity λ of the liquid, since the sludge produced in sewage treatment plants contains electrolytes as well as organic and inorganic substances, it is thought that the electrical conductivity changes depending on the electrolyte concentration of the pore water. In order to investigate the relationship between the electrical conductivity of sludge and electroosmotic dewatering, the present inventor conducted a similar experiment. That is, a batch-type electroosmotic dehydration experimental device was used, and the experimental conditions were: the initial moisture content of the sludge to be treated was 90%, the amount of sludge was 400 g, and the compression pressure was 4 kg/
cTA, the voltage applied between the electrodes was set at 60 V, and the dewatering time was set at 20 minutes. The samples were subjected to electroosmotic dehydration, and the amount of power consumed in the experiment (W h ) and the amount of dehydrated filtrate per unit power consumption (m 7!/W h ) were calculated. The moisture content of the cake after dehydration was 5 for all samples.
It was 3-54%. The experimental results are shown in Figures 4 and 5.
As shown in the figure. As is clear from the results of this experiment, samples with lower conductivity of sludge pore water, which is a measure of the conductivity of sludge, consume less electricity for electroosmotic dehydration, and the amount of filtrate per unit power consumption is lower. There are many. In other words, it was confirmed that the relationship between the amount of moving liquid V and the electrical conductivity λ of the liquid in the theoretical formula for electroosmosis described above coincides with the experimental results.

[Purpose of the invention]

The object of the present invention is to provide a method for dewatering sludge by electroosmotic dewatering, which achieves high dewatering efficiency with low power consumption, based on the analysis of the above-mentioned experimental results.

[Key points of the invention]

In order to achieve the above-mentioned object, the present invention reduces the sludge type conductivity of sludge as a material to be dewatered by lowering the electrolyte concentration of the sludge in a pre-treatment process, for example, by washing the sludge with water. The operating efficiency of the electroosmotic dehydrator is improved by sending it to the subsequent electroosmotic dehydration process for dehydration.

[Embodiments of the invention]

FIGS. 6, 7, and 8 show rη mud water treatment processes according to different embodiments of the present invention, and in each embodiment, sludge washing and washing water separation steps are performed as pretreatment steps. A new sludge-type conductivity reduction treatment process is incorporated. In this step, tap water with a sufficiently low electrolytic Ha level or runoff water purified at a sewage treatment plant is used as the cleaning water. For example, raw sludge is put into a cleaning tank and mixed with the cleaning water while stirring. The highly conductive sludge pore water contained in the primary sludge is modified by washing with water, the electrolyte concentration is diluted, and the conductivity is adjusted to lower, and the excess washing wastewater is Separate from sludge and drain. The sludge adjusted to have a low conductivity in this way can be processed directly as shown in Figure 6, or through a pre-concentration and pre-drying process by adding a flocculant as shown in Figures 7 and 8, and then subjected to an electroosmotic dewatering process. There, it is dehydrated using an electroosmotic dehydrator and recovered as a cake with a low moisture content. According to the above dewatering process, the sludge is introduced into the electroosmotic dewatering machine with its electrical conductivity reduced. The dehydrator can be operated efficiently with less power consumption than conventional methods. [Effect of the invention J As described above, according to the present invention, after the conductivity of raw sludge is adjusted and reformed to a low value through the sludge-type conductivity reduction treatment process, this sludge is introduced into the electroosmotic dewatering process. By performing the dewatering process, an excellent effect can be obtained in which highly efficient electroosmotic dewatering of sludge can be achieved with low power consumption.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an electroosmotic dehydrator, FIGS. 2 and 3 are flow charts showing a conventional sludge dewatering process, and FIG. Figure 5 is a characteristic diagram showing the relationship between the conductivity of sludge pore water, power consumption, and filtrate volume per unit power consumption obtained from electroosmotic dehydration experiment results, and Figures 6 to 8 are each 1 is a flowchart of a sludge dewatering process according to an embodiment of the invention. 1.2 - counter electrode member, 4-upper filter belt, 9 - power supply device, 12 - sludge, 12'... - dehydrated cake.

Claims (1)

[Claims] 1) After the conductivity of raw sludge as a material to be dehydrated is adjusted and modified to a low value through a sludge-type conductivity reduction process, this sludge is introduced into an electroosmotic dewatering process for dewatering. A sludge dewatering treatment method that is characterized by: 2. A sludge dewatering treatment method according to claim 1, wherein the sludge type conductivity reduction treatment step comprises a sludge washing step and a washing water separation step.