JPS5898199A - Dehydration of sludge - Google Patents

Abstract

PURPOSE:To dehydrate sludge to a high degree at a low cost without using a flocculant, by bringing the sludge formed in the purification of filthy water into contact with conc. salt water through a permeable membrane to utilize osmotic pressure derived from the salt water. CONSTITUTION:Sludge 3 formed in the purification of filthy water is supplied to a space between the endless belts 13 and 17 of belt conveyers 14 and 17, respectively, in an osmotic dehydrator 1. On the other hand, conc. salt water 4 is concurrently supplied to a space 14a surrounded with the belt conveyer 14 and brought into contact with the sludge through the endless belt 13 comprising a permeable membrane, so that the sludge is dehydrated by osmotic pressure derived from the salt water and discharged as dehydrated cake 5 having a water- retaining ratio below 60%. The permeating liquid 6 is separated into conc. salt water 4 and reverse osmosis-treated water 7 from which a salt part is removed in a reverse osmosis device 2. The conc. salt water 4 is fed to the osmotic dehydrator 1 again and cyclically used. In this way, the sludge can be dehydrated to a high degree by utilizing the osmotic pressure without using mechanical press or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dewatering sludge produced in a sewage treatment facility to facilitate post-treatment such as incineration.

Dewatering of sludge is done through operations such as pressure filtration or centrifugation, or because the sludge particles are fine and have a low specific gravity, large amounts of expensive flocculants must be used. It was impossible to reduce the water content of dehydrated sludge to 70% or less.

This invention utilizes 9 osmotic pressure instead of mechanical pressure to easily and inexpensively remove water without using a flocculant, and to a much higher degree than centrifugation. The purpose is to provide a method for dewatering sludge.

In the method of this invention, osmotic pressure from concentrated salt water is applied instead of pressurization or mechanical pressure such as centrifugal force as the pressure necessary to dewater the sludge. f, that is, the sludge comes into contact with concentrated salt water through a permeation membrane, and is dehydrated by forward osmosis at this time. The effective osmotic pressure for dehydration is
For example, even if a 5% concentration saline solution is used as the concentrated salt water, it will reach approximately 40'9 fAIIt, so it is possible to perform effective dewatering, and the water content of dehydrated sludge can be reduced to 5%.
Is it possible to -f below 0?

Next, an example of the steps of the method of this invention will be explained with reference to the drawings. In FIG.
indicate reverse osmosis equipment, respectively. The sludge to be concentrated is supplied to the osmosis dewatering device 1 through the thread path 3, and is dehydrated by forward osmosis between it and the concentrated salt water introduced through the thread path 4. The dehydrated sludge is discharged to the outside from the thread path 5, and the permeate liquid is introduced into the reverse osmosis device 2 through the thread path 6. #Shrinks. The concentrated salt water is returned to the osmosis dewatering device 1 through the yarn path 4 for circulation use, and the reverse osmosis treated water is discharged through the yarn path 7. By circulating concentrated salt water using the reverse osmosis device 2, it is possible to make little or no supplementary light for salt water necessary, or if salt water is easily available, K&', 11
．． , the reverse osmosis device 2 may be omitted. According to the law, P = RCT. However, R: Gas constant C: Solute concentration difference between the left and right sides of the permeable membrane T: Expressed as absolute temperature.In actual case of j at 20°C, approximately 40
It becomes about 9f1cm. This value is 10 KW/i given by a mechanical dewatering and concentrating device such as a belt press.
According to the experimental results, this means that the pressure is significantly higher than the pressure of about "st", and effective dehydration is carried out.
When the sludge was dehydrated using 5% saline, the moisture content of the dehydrated cake could be reduced to about 50%.

FIG. 2 shows an example of the configuration of the osmotic dewatering device t1.

In this example, a first conveyor 14 supports an endless belt 13 made of a permeable membrane between a pair of rotating bodies 11 and 12.
and a second conveyor 18 in which a normal conveyor belt 17 is similarly supported between a pair of rotating bodies 15 and 16, and concentrated salt water is supplied into the space 14a of the first conveyor 14. It has become. The endless belt 13 and the conveyor belt 17 are arranged so that their conveying surfaces face each other, run in the same direction at the same speed, and VC sludge is supplied between them. While being conveyed by the two conveyors 14 and 18, this sludge is dehydrated by coming into contact with concentrated salt water across the endless belt 13 made of a permeable membrane, and is dewatered from the end (3) of the conveyor 14.18. Sludge is discharged.

Further, in the example shown in FIG. 3, a plurality of permeation units 21 composed of cylindrical or box-shaped permeation membranes are arranged parallel to each other,
Concentrated salt water is supplied from one end of each osmosis unit 21 through a vibrator 22, and osmotic liquid is taken out from the other end through a vibrator 23. The sludge to be dewatered comes into contact with the outer peripheral surface of each infiltration unit 21, and is dewatered during this time. Note that as the permeation unit 21, a hollow fiber made of a permeation membrane can also be used.

As described above, according to the present invention, sludge is dehydrated using the forward osmosis effect of coarse salt water, so it is possible to dehydrate the sludge using a filter press or far IL. Compared to conventional methods such as separation, the dewatered cake can be produced at significantly lower i-.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of the steps of the method of this invention, and FIGS. 2 and 3 are schematic longitudinal sectional views showing an osmotic dewatering apparatus applicable to the invention. (4) 1... Osmosis dehydration device, 2... Reverse osmosis device, 3-7.
... Thread path, 11.12... Co-rotating body, 13... Endless belt, 14... - conveyor, 15.16... Turn & body,
17-...conveyor pel), 18-e conveyor, 21
...Unit, 22.23... Vice.

Claims (2)

[Claims] (1) A method for dewatering sludge, which comprises bringing sludge into contact with concentrated salt water through a permeation membrane, and transferring water in the sludge to the concentrated salt water by forward osmosis. (2) The osmotic liquid that has absorbed water by the forward osmosis is concentrated by the reverse osmosis, and the concentrated salt water obtained here is reused for the forward osmosis. Method of dewatering sludge.