FR2513239A1 - Partial draining of wet sludge partic. from sewage purificn. treatment - using inflatable bag to compress sludge against screening surface - Google Patents

Abstract

Sludge is poured into a strainer vessel of which a wall area is in the form of a screen through which water will pass while sludge particles are retained. An inflatable bag is fixed iisnside the vessel. The bag is inflated to compress the sludge against the interior of the vessel, forcing some of the water out of the sludge to pass through the screen. The bag is removed from the vessel and the partly drained residue of sludge is recovered from the inside of the vessel. Pref. sludge is poured gradually into the vessel to allow water to drain naturally by gravity alone from the sludge before pressure is applied by inflating the bag. Pref. the bag is inflated in several stages leading to max. expansion. Pref. the strainer vessel is of vertical cylindrical form, the curved wall comprising the screening area, and the inflatable bag is a cylindrical sock insertable coaxially into the strainer vessel. The strainer vessel is used to extract water from wet sludge, esp. surplus sludge from sewage purificn. treatment plants. The drained sludge can be spread as agricultural fertiliser.

Description

The present invention relates to a method and a device for the partial dewatering of sludge or the like.

The invention is more particularly suitable for partial dewatering, with a view to their recovery, of the sludges coming from installations for purifying waste water by bacteriological activation.

It is known that such water purification installations include in particular a settling tank at the bottom of which said sludge is deposited, while the upper part of the latter contains the liquid which may or may not undergo subsequent treatments in order to purify it. . The decanted sludge is for the most part recycled, while the rest must be eliminated from the installation. This surplus part requires a treatment aimed at ridding it of part of its water, in order to allow its transport, for later use, as a fertilizer for example.

Methods are already known which aim to extract part of the water contained in such sludge or the like.

A first method consists in spreading the sludge over a draining area provided with a collecting network and filtering materials. This technique requires a large instrument and labor and has a yield dependent on many factors and generally remaining low.

A second known method uses the principle of centrifugation. In addition to the fact that the initial investment is relatively high, this method involves significant energy consumption.

A third known method consists of depositing the sludge on an endless conveyor belt made of a filtering material and above which are placed means making it possible to exert pressure on said belt in order to compress the sludge and extract a part of the water they contain.

The known methods also have the common disadvantage of requiring significant investments which are only justified for installations intended to treat a large volume of wastewater.

In the case of low capacity wastewater treatment plants, such known devices for dewatering the mixture of sludge and water are disproportionate to the volume of mixture to be treated. It is therefore understandable that the partial dewatering of the surplus sludge from small wastewater treatment plants generally presents difficulties and requires costly and unprofitable investments.

The present invention overcomes these drawbacks and relates to a method and a device for its implementation, making it possible to carry out the partial dewatering of sludge in a simple and rapid manner. The method according to the invention makes it possible to adapt the device for its implementation to the volume of sludge to be treated.

This advantage is particularly important with regard to
concerns low-capacity wastewater treatment plants, which can thus use
dehydration devices adapted to their needs
and likely to be handled by personnel not
qualified.

To this end, according to the invention, the method for the
partial dewatering of sludge or the like is
characterized by the succession of the following stages
a) pouring said sludge into a container of which at least
a wall is permeable to water, while being able to
retaining mud particles;
b) an expandable body is introduced into said container;
c) causing the expansion of said body which compresses
then the sludge against the walls of the container, entrain-
the passage of part of the water through the
permeable walls;
d) the expandable body is removed, and the
partially dehydrated sludge from the container.

More specifically, the container is filled
gradually to allow a first draining
of the mixture, water naturally oozing on the face
external of the permeable wall.

Advantageously, the body is expanded
expandable in several stages.

The invention also relates to a device comprising
a container of which at least one wall is permeable to
water, while being able to retain particles
of mud, an expandable body able to penetrate
in said container, means for causing
the expansion of said body as well as its retraction, and means for extracting partially dehydrated materials contained in the container.

Advantageously, the expandable body is of shape substantially complementary to the internal volume of the container.
Preferably, the water permeable wall of the container consists of a sheet of woven or non-woven material of small thickness, and capable of retaining the particles of mud.

Also the expandable body consists of a pocket whose walls are elastically deformable, being capable of containing air under pressure and provided with a member, such as a valve, allowing the escape of the contained air and thus the retraction of said pocket.

Advantageously, the container consists of a cylinder forming the water-permeable wall, said cylinder being closed at one of its ends by a sealed bottom, while the other end is open and allows the introduction of the expandable body. of substantially cylindrical shape, said body being integral with a cover capable of closing after its introduction, the open end of the container.

According to an alternative embodiment, the water permeable wall consists of two half-cylinders articulated along one of their common generatrices connecting the edge respectively of the bottom and of the container lid, sealing means on the one hand , and on the other hand closing, being provided to ensure in closed position of the device a tight closure, the open position of the two half-cylinders allowing the extraction of partially dehydrated sludge adhering to the internal faces of said half-cylinders.

According to another embodiment, the expandable body comprises nipples of substantially annular shape, projecting with respect to the external surface of the deformable flanks of said body, and of sufficient rigidity to come to carry the expanded state of the latter by their point. against the internal face of the permeable walls of the container, the relative movement in translation of the container and of the body ensuring, by scraping of said points on the internal face of said walls, the extraction of dehydrated sludge from the container.

 The invention will be clearly understood in the light of the appended figures which represent the device according to the invention applied to the partial dehydration of a mixture of water and sludge from a wastewater treatment installation by bacteriological activation.

Figures 1 and 2 show, in perspective, an embodiment of the permeable container according to the invention.

FIG. 3 shows the expandable body and the complementary cover of the container of FIGS. 1 and 2.

Figure 4 shows, in perspective, the container and the associated expandable body.

Figures Sa, 5b and 5c are diagrams showing the three stages of partial dewatering of the sludge.

Figures 6,7,8,9a and 9b show different embodiments of the sludge extraction means
partially dehydrated
Figures 10 and 11 show another embodiment of the container and its means for extracting dehydrated sludge.

Figures 12a, 12b and 12c show an alternative embodiment of the expandable body and the extraction means.

The device for implementing the method according to the invention is shown according to an exemplary embodiment in FIGS. 1 to 4, and is composed of a container 1 of cylindrical shape capable of receiving an expandable body 2.

The container 1 is open at one of its ends -3, while the other end is provided with a sealed bottom 4 by which the container rests on a support or on the ground. The vertical walls 13 of the cylinder consist of a sheet of water-permeable material, such as a woven or a nonwoven, stretched between vertical frames 5 connecting the bottom 4 of the container and the upper flange 6. L the open end 3 is capable of being closed off by a circular cover 7 secured to the expandable body 2.

The upper flange 6 and said cover 7 have corresponding slots, capable of being traversed by fastening members, such as bolts for example.

The permeable material forming the side walls 13 of the container 1 are capable of allowing free passage to water while retaining the mud particles.

The expandable body 2 is formed of an inflatable pocket of elastically deformable material, such as rubber, and of substantially cylindrical shape. The air comes from a source of pressurized air via a pipe 8, possibly provided with a valve 9. The expandable body 2 is shown in Figures 3 and 4 in the retracted state.

The cover 7 has on its upper face a filling orifice 10 associated with a pipe II connected to the source of the sludge which it is desired to partially dehydrate. Said orifice 10 is eccentric relative to the expandable body 2.

The method according to the invention comprises several stages shown diagrammatically in FIGS. 5a, 5b and 5c which represent in section the embodiment of the device shown in FIGS. 1 to 4.

First, the expandable body 2 is introduced, in the retracted state, into the container 1 and the cover 7 and the flange 6 are secured. Then the sludge 12 is poured through the filling orifice 10 in container 1 (figure Sa).

Said sludge 12 occupies a volume equal to that of the container minus that of the retractable expansible body 2. It is noted that, from this first stage, part of the water 14 contained in the sludge 12 crosses, by natural drainage, the permeable walls 13 of said container 2. Thus, the progressive filling of the container already makes it possible to reduce the water content. of the volume of sludge 12 initially poured.

The second step consists in causing the expansion of the expandable body 2 by introducing pressurized air. Said body 2, increasing in volume, then presses the sludge 12 against the permeable walls 13 through which the water 14 flows. The introduction of pressurized air is also carried out gradually, in order to allow the gradual passage of the and the uniform distribution of pressure.

Sludge 12 ′ is thus obtained having abandoned part of their water (Figure 5b). The reduction in volume obtained between the initial volume 12 and the partially dehydrated volume 12 ′, can reach the ratio 3 or 4, for a container with a capacity of a few tens of liters.

The last step consists in bringing the expandable body into the retracted state by causing the exit of the pressurized air, then in removing said body from said container (FIG. 5c), in order to allow the extraction of the partially dehydrated sludge 12 'out of the container.

The removal of said sludge is capable of being carried out using extraction means of which FIGS. 6 to 12 give exemplary embodiments
A first possibility consists in removing the bottom 4 of the container 1 and in exerting a longitudinal pressure on the volume in the form of a cylindrical ring, sludge 12 ′ adhering to the permeable wall 13 of the cylindrical container. This pressure can be exerted by means of a rotating disc provided with a brush on its periphery (Figure 6), or a rotary and movable member in translation in the form of an Archimedes screw (Figure 7); in both cases the partially dehydrated sludge 12 ′ is collected in a receptacle 19.

FIG. 8 shows another embodiment of the device according to the invention, in which the permeable walls 13 consist of two half-cylinders 15 and 16 articulated along a common generator connecting the bottom 4 and the cover 7 of the container 1. The process of obtaining sludge. partially dehydrated 12 'is the same as shown in Figures 5a, 5b and 5c; the cover 7 and the body 2 do not then need to be removed. The semi-cylinders 15 and 16 are then pivoted in order to separate them, and the sludge 12 'adhering to the walls is then removed by scraping (mechanical or manual).

Another possibility of extracting the mixture consists in providing the container 1 with walls deformable by longitudinal pressure (FIGS. 9a and 9b, arrow f); this deformation causes detachment of the constitutive crust by the de-hydrated sludge and adhering to said walls. The opening of the container then makes it possible to extract the sludge 12 '.

Figures 12a, 12b and 12c show an alternative embodiment of the expandable body 2. Said figures are sectional views of the cylindrical container 1 in which the expandable body 2 is placed, the sludge 12 being poured. Figure 12a shows the body 2 in the retracted state comprising nipples 18, forming rings (or a thread) and projecting from the surface of said body 2. The introduction of pressurized air causes the body to expand (FIG. 12b) and said nipples 18 are rigid enough to come to bear against the internal wall of the container 1, the body 2 being in the expanded state. This is obtained in the same manner as described above, by compressing the volume
initial sludge 12 which loses part of its water flowing through permeable walls 13, sludge 12 'partially dehydrated. FIG. 12c shows the removal of these same dehydrated sludge 12 ′ from the container 1 by the longitudinal translation of the inflated body 2, which, thanks to the nipples 18, makes it possible to scrape the internal surface of said container 1 and thus to take off the dehydrated sludge 12 'adhering to said internal face.

The embodiments described show a container and a body of cylindrical shape, but it is understood that any shape can be suitable; the only obligation results from the complementarity of form between the body and the container so that the space left for the dare pressed sludge has a thickness as homogeneous as possible.

Figures 10 and 11 show in perspective a parallelepiped container whose lateral faces made of permeable material, each pivot around the edge separating it from the upper face 17 of the container 1. The pivoting of said faces, after a mixture filling cycle and swelling of the expandable body, allows the removal by scraping of the partially hydrated sludge 12 adhering to the internal face of said permeable faces.

The method according to the invention, and the device for its implementation, make it possible to treat variable amounts of sludge. Indeed, for a container of given volume, it will be possible to carry out several cycles in order to dehydrate the necessary quantity of sludge; It is also possible to produce the container with a volume such that it allows the treatment of the quantity of sludge at one time.

It can be seen that the device according to the invention adapts to the volume of sludge to be dewatered. This is particularly advantageous with regard to the treatment of surplus activation sludge from a wastewater treatment installation, in particular of modest size. In fact, this volume to be treated is generally small and the method according to the invention is perfectly suited to this situation in view of the low investment which it implies for its implementation.

In the case where said volume to be treated varies (for a given treatment installation), the invention allows a constant correlation between the needs and the means of satisfying them. In fact, if the volume increases, it will be possible either to treat the sludge in several cycles, or to make a container of larger size.

 A range of devices of different sizes can be designed which can be combined with one another to cover the necessary requirements for installations of different capacities.

The device according to the invention is particularly easy to make and use; the investment is then reduced to a minimum and is therefore quickly amortized.

Similarly, the type of permeable material used, the ratio of the total internal surface to the permeable surface as well as the ratio of the volumes or container and of the expandable body, allow numerous combinations depending in particular on the type of sludge to be treated.

Claims (12)

1 - Process for the partial dewatering of sludge or the like characterized by the succession of the following steps a) the said sludge 12 is poured into a container 1 of which at least one wall 13 is permeable to water, while being capable of retaining the mud particles b) an expandable body 2 is introduced into said container 1; c) causing said body 2 to expand which then compresses the sludge 12 against the walls 13 of the container 1, causing part of the water 14 to pass through said permeable walls 13; d) the expandable body 2 is removed, and the partially dehydrated sludge 12 ′ is extracted from the container 1. 2 - Method according to claim 1, characterized in that the filling of the container 1 is carried out gradually in order to allow a first drainage of the mixture, the water naturally seeping on the external face of the permeable wall 13. 3 - Method according to one of claims 1 or 2, charac terized in that one realizes the expansion of the expandable body 2 in several stages. 4 - Device for implementing the method according to one of claims 1 to 3, characterized in that it comprises a container 1 of which at least one wall 13 is permeable to water, while being capable of retaining the mud particles, an expandable body 2 able to penetrate into said container 1, means for causing the expansion of said body as well as its retraction, and means for extracting the partially dehydrated sludge contained in the container.  5 - Device according to claim 4, characterized  in that the expandable body 2 is of substantially complementary shape to the internal volume of the container 1.  6 - Device according to one of claims 4 or 5, characterized in that the permeable wall 13 to water of the container 1 consists of a sheet of woven or non-woven material of small thickness, and capable of retaining the mud particles. 7 - Device according to one of claims 4 to 6, characterized in that the expandable body 2 consists of a pocket whose walls are elastically deformable, being capable of containing air under pressure and provided with a member 19, such as a valve authorizing the escape of the contained air and thus the retraction of said pocket 2. 8 - Device according to one of claims 4 to 7, characterized in that the container consists of a cylinder forming the wall 13 permeable to water, said cylinder being closed at one of its ends by a sealed bottom 4, while the other end is open - and allows the introduction of the expandable body 2 of substantially cylindrical shape, said body 2 being secured to a cover 7 capable of closing after its introduction the open end of the container 1. 9 - Device according to claim 8, characterized in that the permeable wall 13 to water consists of two half-cylinders 15,16 articulated along one of their common generatrices connecting the edge respectively of the bottom 4 and the cover 7 of the container 1, sealing means on the one hand, and closing means on the other hand, being provided in order to ensure the closed position of the device, a sealed closure, the open position of the two half-cylinders 15,16 allowing the extraction of partially dehydrated sludge adhering to the internal faces of said half-cylinders 15,16. 10-- Device according to claim 8, characterized in that the expandable body 2 comprises nipples 18 of substantially annular shape, projecting relative to the external surface of the deformable sides of said body 2 and of sufficient rigidity to come to bring the expanded state of the latter by their point against the internal face of the permeable walls 13 of the container 1, the relative movement in translation of the container 1 and of the body 2 ensuring, by scraping said points on the internal face of said walls 13, the extraction of dehydrated sludge 12 'from the container.  11 - Device according to one of claims 4 to 7, characterized in that the container 1 is formed of a parallelepiped, one of the faces constituting the opening through which is introduced the expandable body 2 of substantially complementary shape. 12 - Device according to the preceding claim, characterized in that the permeable faces of the parallelepiped paral are able to pivot each along the edge connecting said permeable face to one of the lower or upper faces of the container 1 in the form of a parallelepiped.