JP2012135736A - Sludge dehydration system and sludge dehydration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dehydrated cake in which a water content is sufficiently reduced.SOLUTION: A flocculant is supplied to sludge, flocks are formed by supply of the flocculant, and before supply of the flock-containing sludge to a dehydrator, the once formed flocks are suitably fined by a fining means so as to form fined sludge S. As the dehydrator, a filter cloth running type dehydrator 5 which squeezes a filter cloth 5V moving a prescribed circumferential orbit and the sludge supplied to the surface of the filter cloth 5V between confronted press rolls 5e, 5e to obtain a dehydrated cake M of a thin film is used, and the fined sludge S is supplied to the surface of the filter cloth 5V in the dehydrator 5. In the filter cloth running type dehydrator 5, since the thickness of the sludge upon the treatment is extremely thin, the force can be sufficiently conducted even when the flocks remain fine, and interstitial water can be easily extracted from the space between the fine flocks by the sufficient force, thus the water content can be sufficiently reduced.

Description

  The present invention relates to a sludge dewatering system and a sludge dewatering method for dewatering sludge.

  Conventionally, as a pretreatment for dewatering sludge, for example, an inorganic flocculant such as iron chloride or slaked lime or an organic polymer flocculant is supplied to the sludge to agglomerate fine particles in the sludge to form coarse particles. A technique for facilitating the disclosure is disclosed in Non-Patent Document 1 below. In this non-patent document 1, an inorganic flocculant is used for vacuum filtration and pressure filtration, and a polymer flocculant is often used for a screw press dehydrator, a belt press dehydrator, and a centrifugal dehydrator. (For example, refer nonpatent literature 1).

  Here, particularly in a mechanical dehydrator such as a screw press dehydrator, a belt press dehydrator or a centrifugal dehydrator for mechanical dehydration, a flocculant is supplied to sludge (generally, an inorganic flocculant is first supplied and then By supplying a polymer flocculant, a large and strong floc is formed, and this large floc is used to transmit a large force to sludge having a certain thickness, thereby making it easy to dehydrate. In this case, it is a general idea that if the floc is small and fine, the mechanical dehydrator hardly transmits the force to sludge, and the larger the flock, the higher the dewatering performance.

Pollution Prevention Technology and Regulations Editorial Committee “Pollution Prevention Technology and Regulations 2008 Water Quality II” published by Japan Industrial Environment Management Association 3.2.11 Sludge dewatering, (2) Sludge pretreatment

  However, as shown in FIG. 4, when the floc A having large particles is formed, the interstitial water B is easily confined between the large flocs A and A, and this interstitial water B is generated in the mechanical dehydrator as described above. It is difficult to remove and can only be dehydrated to a certain water content. In addition, the code | symbol C is sludge internal reserve water and the code | symbol D is capillary combined water.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a sludge dewatering system and a sludge dewatering method capable of obtaining a dewatered cake having a sufficiently reduced moisture content. .

  Here, as a result of intensive research, the present inventors used a filter cloth traveling type dehydrator optimal for obtaining a thin film dehydrated cake as the dehydrator, and the flocs once formed by supplying the flocculant. It has been found that when a floc-containing sludge containing finely divided flocs is supplied to a filter cloth traveling dehydrator, a dehydrated cake with a sufficiently reduced water content can be obtained.

  Therefore, the sludge dewatering system according to the present invention supplies flocculant to the sludge by the flocculant supply device, forms flocs by supplying the flocculant, and dewaters the floc-containing sludge containing the flocs with a dehydrator. In a sludge dewatering system for obtaining a dewatered cake, a filter cloth for obtaining a thin film dehydrated cake by pressing a dewatering machine between a filter cloth moving on a predetermined orbit and sludge supplied on the filter cloth between opposing press rolls. The traveling dehydrator is provided with subdividing means for subdividing the floc-containing sludge supplied to the filter cloth traveling dehydrator.

  The sludge dewatering method according to the present invention supplies a flocculant to sludge, forms flocs by supplying the flocculant, and dewaters the floc-containing sludge containing the flocs with a dehydrator to obtain a dehydrated cake. In the dehydration method, as a dehydrator, a filter cloth traveling type dehydrator that obtains a thin film dehydrated cake by pressing a filter cloth moving on a predetermined orbit and sludge supplied on the filter cloth between opposing press rolls. The floc-containing sludge used is subdivided by a subdividing means and then supplied onto the filter cloth of a filter cloth traveling dehydrator.

  According to such a sludge dewatering system and sludge dewatering method, flocculant is supplied to the sludge, flocs are formed by supplying the flocculant, and before the floc-containing sludge containing the flocs is supplied to the dehydrator The flocs once formed are moderately refined by the subdividing means. Here, since the thickness of the sludge when the filter cloth traveling type dehydrator is processed is very thin, the force can be sufficiently transmitted even with the fine flock, and pore water is generated between the fine flocks by this sufficient force. As a result, a dehydrated cake having a sufficiently reduced water content can be obtained.

  Here, when the floc diameter of the floc-containing sludge subdivided by the subdividing means is 1 to 2 mm, pore water can be more sufficiently removed in the filter cloth traveling dehydrator, and the water content is further reduced. A dehydrated cake can be obtained.

  As described above, according to the sludge dewatering system and the sludge dewatering method of the present invention, a dehydrated cake having a sufficiently reduced water content can be obtained.

It is a block diagram which shows the sludge dehydration system which employ | adopted the sludge dehydration method which concerns on one Embodiment of this invention. It is a block diagram which shows the pre-processing part in FIG. It is sectional drawing which shows the pressing and transferring part of the filter cloth traveling type dehydrator in FIG. It is a figure which shows the state which supplied flocculant to sludge and formed the floc.

  Hereinafter, preferred embodiments of a sludge dewatering system and a sludge dewatering method according to the present invention will be described with reference to FIGS. 1 is a block diagram showing a sludge dewatering system employing a sludge dewatering method according to an embodiment of the present invention, FIG. 2 is a block diagram showing a pretreatment unit in FIG. 1, and FIG. 3 is a diagram in FIG. It is sectional drawing which shows the squeeze transfer part of a filter cloth traveling dehydrator, and the sludge dewatering system of this embodiment is a system for dewatering sludge, such as excess sludge, generated by sewage treatment or the like.

  As shown in FIG. 1, the sludge dewatering system includes a filter cloth traveling dehydrator 5 as a main component, and a pretreatment unit 1 that performs pretreatment on sludge supplied to the filter cloth traveling dehydrator 5. Prepare.

  The pretreatment unit 1 is for supplying a suitable sludge to the filter cloth traveling dehydrator 5, and as shown in FIG. 2, the reaction tank 1a and the strong stirring tank are directed from the upstream side toward the downstream side. 1g in this order.

  The reaction tank 1a is for making sludge introduced into the tank into floc-containing sludge (flocculated sludge) by supplying a flocculant, and in the reaction tank 1a, inorganic flocs are formed in order to form floc-containing sludge. An inorganic flocculant supply device (coagulant supply device) 1b for supplying the agent and a polymer flocculant supply device (coagulant supply device) 1c for supplying the polymer flocculant are provided, and sludge and agglomerates in the tank. A stirrer 1f is provided in which the blade 1d immersed in the agent rotates at a low speed by driving of the drive source 1e, and the sludge and the flocculant are gently stirred, mixed, and reacted.

  The strong agitation tank 1g is for introducing floc-containing sludge (aggregated sludge) from the reaction tank 1a, crushing and subdividing, and the blade 1h immersed in the sludge in the tank is rotated at high speed by driving of the drive source 1i. A stirrer 1j that stirs and crushes sludge is provided.

  As shown in FIG. 1, the filter cloth traveling dehydrator 5 introduces the subdivided sludge S from the strong stirring tank 1 g and dehydrates it to obtain a dehydrated cake. The filter cloth traveling dehydrator 5 has a very thin sludge during processing, and is therefore suitable for obtaining a thin dehydrated cake. The filter cloth traveling dehydrator 5 moves endlessly in a predetermined orbit and forms a single filter cloth belt (filter cloth) 5V to which the sludge S from the strong stirring tank 1g is supplied. And a vacuum dewatering unit 5X that acts on the filter cloth belt 5V in order, a pressing and transferring unit 5Y, and a cleaning / dehydrating unit 5Z.

  The filter cloth belt 5V is an endless belt having a thickness of about 4 to 8 mm and a width of about 500 to 4200 mm. As shown in FIG. 3, the filter cloth belt 5V is made of a three-layered felt material. Specifically, the sludge S is filtered. An outer surface layer 5a composed of an ultrafine fiber layer, an intermediate layer 5b composed of a medium thin fiber layer that promotes moisture permeation, and an inner surface layer 5c composed of a base fabric layer that promotes water drainage. ing. The outer surface layer 5a, the intermediate layer 5b, and the inner surface layer 5c are joined so that fibers are entangled with each other by a process similar to the cotton-coating process without using an adhesive or the like. As shown in FIG. 1, the endless filter cloth belt 5V is stretched over a large number of rolls 5g, a lower press roll 5e, and a lower squeeze roll 5i (details will be described later). A predetermined orbit is moved in the clockwise direction of FIG. 1 at a moving speed of about 50 m.

  The vacuum dewatering unit 5X performs initial dewatering of the subdivided sludge S supplied to the upper surface side of the filter cloth belt 5V. For example, about 7 kPa at the first dewatering unit from the lower surface side of the filter cloth belt 5V with respect to the sludge S. And a vacuum device 5d for dehydrating by applying a suction negative pressure of about 25 kPa at the next dehydrating section.

  The pressing and transferring unit 5Y compresses the sludge S from the vacuum dehydrating unit 5X to obtain a dehydrated cake M, and a pair of upper and lower opposing press rolls 5e and 5e that squeeze and dewater the sludge S together with the filter cloth belt 5V. And a scraper 5f that peels and scrapes off the dewatered cake M transferred to the peripheral surface of the upper press roll 5e by pressing and dewatering in the vicinity of the downstream side of the upper press roll 5e. And the press pressure by the press rolls 5e, 5e is set to a pressure of about 100 to 600 kPa.

  The washing / dehydrating unit 5Z is for washing and squeezing the filter cloth belt 5V from the pressing and transferring unit 5Y, and includes a washing pool 5h for bathing the filter cloth belt 5V in washing water, and this washing pool 5h. Is provided with a flush shower 5j for injecting washing water onto the filter cloth belt 5V, and a pair of upper and lower opposing squeeze rolls 5i for squeezing the washed filter cloth belt 5V on the downstream side of the washing shower 5j. 5i.

  Next, the sludge dewatering method of the sludge dewatering system configured as described above will be described.

  As shown in FIG. 2, the sludge is introduced into the reaction tank 1a. First, an inorganic flocculant such as PAC or polyiron is supplied from the inorganic flocculant supply apparatus 1b into the tank, and the sludge and the inorganic flocculant are mixed by the stirrer 1f. The agent is mixed by gentle stirring, and a small floc is formed by the coagulation action. Next, a polymer flocculant such as anion and cation is supplied from the polymer flocculant supply device 1c into the tank, and the sludge and the polymer flocculant are mixed by being gently stirred by the stirrer 1f. Small flocs are gathered to form large flocs.

  The floc-containing sludge is introduced into 1 g of the strong stirring tank and is vigorously stirred by the stirrer 1j. As a result, the large flocs once formed are subdivided and appropriately made fine. And the diameter of the floc of the fragmented floc containing sludge shall be 1-2 mm.

  Here, the crushing force is applied to the flocs by mechanical strong stirring in 1 g of the strong stirring tank, and the crushing force is applied to the flocs by strong stirring by the flow of gas or liquid. It may be made finer, or it may be made fine by applying a crushing force such as pressing force or squeezing force to the flock, or it may be made finer by using a chemical, In short, any means for subdividing floc-containing sludge can be used.

  Then, the subdivided sludge S in the strong stirring tank 1 g is introduced into the filter cloth traveling dehydrator 5 through the sludge supply line L as shown in FIG.

  In the filter cloth traveling dehydrator 5, the subdivided sludge S is supplied onto the filter cloth belt 5V, and in the vacuum dewatering section 5X, a negative vacuum pressure is applied to the sludge S from the lower surface side of the filter cloth belt 5V by the vacuum device 5d. Acts, and moisture in the sludge S permeates the filter cloth belt 5V. At that time, the outer surface layer 5a composed of the ultrafine fiber layer of the filter cloth belt 5V allows only the moisture to permeate through the capillary phenomenon to surely filter the sludge S, and the intermediate layer 5b composed of the medium thin fiber layer permeates the moisture due to the capillary phenomenon. The inner surface layer 5c made of the base fabric layer promotes water drainage. Therefore, the filter cloth belt 5V efficiently performs initial dehydration of the sludge S without causing clogging. The moisture sucked by the vacuum device 5d is collected in a collection tank (not shown).

  The sludge S that has been initially dewatered is squeezed and dewatered by these rolls 5e and 5e when passing between the press rolls 5e and 5e together with the filter cloth belt 5V in the pressing and rolling part 5Y. At that time, as described in the vacuum dewatering unit 5X, the outer surface layer 5a permeates only moisture to reliably filter the sludge S, the intermediate layer 5b promotes moisture permeation, and the inner surface layer 5c is drained. Facilitate.

  At the time of pressing with the press rolls 5e, 5e, since the sludge S is very thin, it is possible to sufficiently transmit the force even with fine flocks. Can be easily removed, and a dehydrated cake M having a moisture content of about 70% or less is formed with a thin film of about 1 to 2 mm.

  The dewatered cake M is transferred to the peripheral surface of the upper press roll 5e, scraped off by the scraper 5f, and collected. The recovered dehydrated cake M has a flake shape.

  The filter cloth belt 5V that has passed through the pressing and transferring unit 5Y and from which the dewatered cake M has been peeled off is washed in the washing / dehydrating unit 5Z by bathing in the washing water of the washing pool 5h, and then washed by the washing shower 5j. Then, when passing between the squeeze rolls 5i and 5i, the rolls 5i and 5i are squeezed and dehydrated to return to the original state.

  As described above, in this embodiment, flocculant is supplied to sludge, flocs are formed by supplying the flocculant, and floc-containing sludge containing the flocs is once formed before being supplied to the dehydrator. While the floc was appropriately finely divided by 1 g of a strong stirring tank (subdividing means) to obtain a subdivided sludge S, the dehydrator was supplied onto a filter cloth 5V moving on a predetermined orbit and the filter cloth 5V. Using the filter cloth traveling dewatering machine 5 that squeezes the sludge between the opposing press rolls 5e, 5e to obtain a thin film dehydrated cake M, the above-mentioned subdivided sludge S is placed on the filter cloth 5V of the filter cloth traveling dewatering machine 5. To supply. In this filter cloth traveling dehydrator 5, since the thickness of the sludge during processing is very thin, the force can be sufficiently transmitted even with the fine flock, and the gap between the fine flocks can be obtained with this sufficient force. Water can be easily drained, and as a result, a dehydrated cake M with a sufficiently reduced water content can be obtained.

  In the present embodiment, since the floc diameter of the subdivided floc-containing sludge is 1 to 2 mm, pore water is more sufficiently removed in the filter cloth traveling dehydrator 5, and the water content is further reduced. A dehydrated cake M can be obtained.

  In addition, if the diameter of the flocculant supplied in the reaction tank 1a is about the same as that of the subdivided floc, a stronger shearing force is generated during the squeezing in the filter cloth traveling dehydrator 5, and the cell membrane and the cell wall are separated. It can be destroyed, thereby removing the water held in the cells, and as a result, the water content can be further reduced.

  The present invention has been specifically described above based on the embodiment. However, the present invention is not limited to the above embodiment. For example, in the above embodiment, an inorganic flocculant is supplied in the reaction tank 1a. Then, after supplying the polymer flocculant, the floc is subdivided by the subdividing means, but when supplying only the inorganic flocculant without supplying the polymer flocculant, or supplying the inorganic flocculant The present invention can also be applied to the case where only the polymer flocculant is supplied, and in any case, the flocculant is supplied and then subdivided by the subdividing means.

  Moreover, the dewatering cake which further reduced the moisture content can be obtained by mixing a dehydrating auxiliary agent with sludge in the front | former stage of the pre-processing part 1. FIG. As the dehydration aid to be mixed, a substance having a particle size of about 0.1 to 1 mm, such as combustion ash, coal, and wood chips, can be used. In addition, since a floc containing sludge becomes difficult to subdivide when a dehydrating aid is mixed with sludge, it is preferable to subdivide by mechanical strong stirring.

  DESCRIPTION OF SYMBOLS 1 ... Pretreatment part, 1a ... Reaction tank, 1b ... Inorganic flocculant supply apparatus (coagulant supply apparatus), 1c ... Polymer flocculant supply apparatus (coagulant supply apparatus), 1d ... Reaction tank blade, 1e ... Reaction Tank drive source, 1f ... reaction tank stirrer, 1g ... strong stirring tank (subdividing means), 1h ... strong stirring tank blade, 1i ... strong stirring tank drive source, 1j ... strong stirring tank stirrer, DESCRIPTION OF SYMBOLS 5 ... Filter cloth traveling dehydrator, 5e ... Press roll, 5V ... Filter cloth belt (filter cloth), 100 ... Sludge dewatering system, M ... Dehydrated cake, S ... Subdivided sludge.

Claims (3)

In the sludge dewatering system in which flocculant is supplied to sludge by a flocculant supply device, flocs are formed by supplying this flocculant, and floc-containing sludge containing this floc is dehydrated by a dehydrator to obtain a dehydrated cake.
The dehydrator is a filter cloth traveling dehydrator that obtains a thin film dehydrated cake by pressing the filter cloth that moves along a predetermined orbit and sludge supplied on the filter cloth between opposing press rolls,
A sludge dewatering system comprising a subdividing means for subdividing the floc-containing sludge supplied to the filter cloth traveling dehydrator.   The sludge dewatering system according to claim 1, wherein the subdividing means subdivides the floc diameter of the floc-containing sludge into 1 to 2 mm. In the sludge dewatering method of supplying flocculant to sludge, forming floc by supplying this flocculant, and dehydrating floc-containing sludge containing this floc with a dehydrator to obtain a dehydrated cake,
As the dehydrator, using a filter cloth traveling dehydrator that obtains a thin film dehydrated cake by pressing the filter cloth moving on a predetermined orbit and sludge supplied on the filter cloth between opposing press rolls,
The sludge dewatering method, wherein the floc-containing sludge is subdivided by a subdividing means and then supplied onto the filter cloth of the filter cloth traveling dehydrator.

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