WO2000071222A2

WO2000071222A2 - Drainage sludge dehydration and dry system

Info

Publication number: WO2000071222A2
Application number: PCT/KR2000/000475
Authority: WO
Inventors: Se Jun Park
Original assignee: Se Jun Park
Priority date: 1999-05-20
Filing date: 2000-05-16
Publication date: 2000-11-30
Also published as: AU4619900A; JP2000354900A; WO2000071222A3; KR20000076920A; KR100308407B1; CN1171814C; CN1274687A

Abstract

The object of this invention is to provide a sludge dehydration and dry system. This system feeds sludge-laden waste liquid from a sludge inlet unit (10) to pressure vessels of an automatic pneumatic pump (20), and feeds waste liquid to a dehydration unit (30) by pressurizing the surface of waste liquid within the vessels using compressed air, thus dehydrating the sludge to form sludge cakes, and dries the sludge cakes at the filter plates (33) of the unit (30) using compressed air from a dry unit (18). The moisture content of the sludge cakes within the dehydration unit is reduced by inflating the membranes (90) with compressed air. After the sludge compression and dehydration process, the filter plates are separated from each other by a separation unit (34), and so the resulting sludge cakes are dropped from the filter plates onto a feeding conveyor (37) to be discharged from the system.

Description

DRAINAGE SLUDGEDEHYDRATIONANDDRYSYSTEM

Technical Field

The present invention is to provide a new drainage sludge dehydration and dry system by improving the structure of "The Drainage Sludge Dehydration System" disclosed in Korean Patent Application No. 99-18,302 applied by the inventor of this invention and designed to dehydrate sludge waste liquid generated from a variety of industrial processes, such as sewage treatment processes, chemical industrial processes or food industrial processes, to form sludge cakes. The drainage sludge dehydration and dry system of this invention is designed to feed sludge-laden waste liquid to an automatic pneumatic pump, consisting of one or two compression vessels, prior to feeding the liquid to a dehydration unit using compressed air, thus compressing and dehydrating the sludge-laden liquid by a plurality of filter plates to form sludge cakes and drying the sludge cakes using air and thereby remarkably reducing the moisture content of resulting sludge cakes, with such resulting sludge cakes being suitable for being recycled as a material of composts or a material of solid fuel.

Background Art

Several thousand tons of sewage sludge, organic sludge and industrial waste sludge are discharged from sewage treatment plants or a variety of factories every day. In most developing countries, the treatment of such sludge has been typically accomplished by burying under the ground within a dump yard or discarding onto the seabed. In accordance with the recent trend of installation or expansion of the sewage treatment plants for middle-sized cities and provinces, the quantity of sewage sludge generated from such plants may be quickly and extremely increased. Such conventional sewage sludge and industrial waste sludge are typically laden with a substantial amount of moisture, and so they may easily decay to form a great quantity of toxic liquid within a few hours when kept at room temperature. Due to such characteristics of the sludge, some developing countries cannot propose another method of treating the sludge in place of burying under the ground or discarding onto the seabed.

Such sludge may be incinerated through a combustion process in some countries. However, the combustion process of incinerating the sludge requires a consumption of a large quantity of energy and increases the sludge treatment cost. Particularly, in some countries regulated by the World Environmental Protection Law, such a burying of sludge under the ground or a discarding of sludge onto the seabed will be prohibited by law in the future, for example, from the year 2001 in the case of Korea, and so it is necessary for such countries to develop new methods of effectively treating such sludge or recycling the sludge without burying under the ground or discarding onto the seabed.

For example, The Sewage Treatment Plant of Seoul, Korea typically discharges about 1 ,200 tons of microbial sewage sludge, having a moisture content of about 76% - 83%, at every day. Such microbial sewage sludge may easily decay to form a great quantity of toxic liquid within a few hours when kept at room temperature. Therefore, the microbial sewage sludge has been treated by burying under the ground or discarding onto the seabed. In order to treat the sludge by forming sludge cakes prior to incinerating or recycling the sludge cakes, it is necessary to consume a great quantity of energy, labor and time.

Disclosure of the Invention

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a drainage sludge dehydration and dry system, which is designed to feed sludge-laden waste liquid from the storage tank of a sludge inlet unit to one or two predetermined scaled pressure vessels of an automatic pneumatic pump using atmospheric pressure or separate pumping pressure, and to feed the waste liquid to a dehydration unit by pressurizing the waste liquid within the pneumatic pump using compressed air, thus dehydrating the sludge to form sludge cakes, and to dry the sludge cakes within the filter fabrics of filter plates using highly compressed air supplied from a dry unit.

In an operation of the system according to this invention, the moisture content of sludge cakes within the dehydration unit is reduced by inflating the membranes, provided outside the fabric filters of the dehydration unit, with compressed air. After pneumatically compressing the sludge by inflating the membranes with compressed air, the interior of the pump is cleaned by compressed air. In addition, compressed air of the waste liquid discharging line passes through the sludge cakes within the dehydration unit, thus drying both the sludge cakes and the discharging line.

After the sludge compression and dehydration process at the dehydration unit is accomplished, the filter plates are separated from each other by a filter plate separation unit, and so the dehydrated and dried sludge cakes are dropped from the filter plates onto a sludge cake feeding conveyor prior to being discharged from the system. In such a case, the sludge, remaining in the fabric filters of the filter plates, is washed by pressurized washing water injected from the water injection nozzle of a fabric filter washing unit. In an operation of the sludge dehydration and dry system of this invention, sludge-laden waste liquid is primarily stored within the sludge inlet unit to allow sludge to be naturally deposited on the bottom of a sludge thickening tank. Thereafter, a sludge thickening agent is added to the sludge-laden waste liquid before the waste liquid is introduced from the tank into an automatic pneumatic pump. The waste liquid is forcibly fed from the pneumatic pump to the dehydration unit using pressure of compressed air, thus being dehydrated within the dehydration unit. In the dehydration unit, the sludge is compressed by membranes and is dried by a dry unit, thus forming dehydrated and dried sludge cakes. Thereafter, the filter plates of the dehydration unit are separated from each other by a filter plate separation unit, thus dropping the sludge cakes onto a sludge cake feeding unit which discharges the sludge cakes from the system. Thereafter, the fabric filters of the filter plates are washed by a washing unit. Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a circuit diagram, showing the construction of a drainage sludge dehydration and dry system in accordance with the primary embodiment of the present invention;

Fig. 2 is a circuit diagram, showing the construction of a drainage sludge dehydration and dry system in accordance with the second embodiment of the present invention; and

Fig. 3 is a circuit diagram, showing the construction of an automatic pneumatic pump included in a drainage sludge dehydration and dry system of the present invention.

Best Mode for Carrying Out the Invention

Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

Fig. 1 is a circuit diagram, showing the construction of a drainage sludge dehydration and dry system in accordance with the primary embodiment of the present invention. As shown in the drawing, the system of this invention comprises a sludge inlet unit 10, which has a sludge-laden waste liquid storage tank 1 for containing sludge-laden waste liquid therein. The above unit 10 also has a sludge thickening tank 3 connected to the waste liquid storage tank 1 through a waste liquid feed pipe 2. A pipeline 4 extends from the sludge inlet unit 10 to an automatic pneumatic pump 20, thus feeding the sludge-laden waste liquid from the unit 10 to the pump 20. A sludge thickening agent supply unit 80 is connected to both the sludge inlet unit 10 and the pipeline 4. In such a case, the sludge-laden waste liquid is fed from the sludge thickening tank 3 of the sludge inlet unit 10 to the pneumatic pump 20 using atmospheric pressure or separate pumping pressure.

The automatic pneumatic pump 20 of this system also has a liquid level sensing unit 24, which consists of upper and lower liquid level sensors 23 and 23' installed within each of the two pressure vessels 21 and 21 ' of the pneumatic pump

20 and are used for sensing upper and lower liquid levels within an associated vessel 21 or 21 ' when the waste liquid from the tank 3 is contained in the vessels

21 and 21 ' under the control of liquid inlet valves 28.

Each pressure vessel 21 or 21 ' of the pneumatic pump 20 also has a pressure sensing unit 25, a vacuum pump 26, an air compression solenoid valve

29, an air exhaust solenoid valve 29' and a muffler 27. The pressure sensing unit 25 consists of high and low pressure sensors 25' and 25" as best seen in Fig. 3.

The compression solenoid valves 29 are commonly connected to a compressed air supply unit 40, thus being selectively operated to pressurize the surface of liquid within the vessels 21 and 21 ' and to discharge the waste liquid from the pressure vessels 21 and 21 ' to a dehydration unit 30 through liquid outlet solenoid valves 28'.

An air pressure dispersing member 15 is installed within each pressure vessel 21 or 21' at an upper position around the compression solenoid valve 29 and disperses the compressed air, injected into the vessel 21 or 21 ' through the compression solenoid valve 29. The above air pressure dispersing members 15 of the two vessels 21 and 21 ' thus allow the compressed air from the valves 29 to uniformly pressurize the surface of waste liquid within the vessels 21 and 21 '.

The automatic pneumatic pump 20 further includes a liquid pressure dispersing member 15', which is installed within each vessel 21 or 21 ' at a lower position and disperses waste liquid injected into the vessel from the pipeline 4 under the control of the inlet valve 28.

In the system of this invention, the dehydration unit 30 is connected to the pneumatic pump 20 through a waste liquid discharging line 28a commonly extending from the two vessels 21 and 21 ' to the dehydration unit 30, with a buffer tank 70 being mounted to the line 28a. The above dehydration unit 30 cooperates with a dry unit 18, which is provided with a dry solenoid valve 18' for supplying compressed air to sludge cakes within the dehydration unit 30, thus compressing and drying the sludge cakes as will be described in more detail later herein.

In order to prevent an undesired knocking phenomenon caused by a water hammering action in the case of a closing of the liquid outlet solenoid valves 28' during an operation of the pneumatic pump 20, the buffer tank 70 is mounted on the discharging line 28a. The interior of this buffer tank 70 is partitioned into two chambers: first and second chambers 72a and 72b, by a partition wall 71.

A sub-tank 22 is connected to the exhaust solenoid valve 29', and so the exhausted compressed air from the pressure vessels 21 and 21 ' of the pneumatic pump 20 can be partially recycled for the operation of the compression solenoid valves 29, the exhaust solenoid valves 29', the liquid inlet valves 28 and the liquid outlet solenoid valves 28' of the pump 20. The sub-tank 22 also allows the remaining part of the exhausted compressed air from the vessels 21 and 21 ' to be usable as a pressure source for the other tools or machines within the plant equipped with the system of this invention.

The dehydration unit 30 comprises a fixed inlet terminal 31 and a movable plate 32, and so the pumped waste liquid from the pump 20 is introduced into the dehydration unit 30 through the fixed inlet terminal 31. In order to connect a plurality of inlet pipes to the dehydration unit 30, a plurality of inlet ports 31' are formed on the fixed inlet terminal 31. A plurality of filter plates 33, individually covered with a fabric filter 33', are regularly and movably set between the fixed terminal 31 and the movable plate 32. A membrane 90 is installed between each filter plate 33 and an associated fabric filter 33'. The membranes 90 of the filter plates 33 are commonly connected to a compressed air injection nozzle 36 of a compressed air supply line 40a extending from the compressed air supply unit 40.

The dry unit 18, having a dry solenoid valve 18', is connected to the liquid discharging line 28a, and so compressed air is supplied from the dry unit 18 to dehydrated sludge cakes within the dehydration unit 30 and is used for drying the sludge cakes.

A filter plate separation unit 34 is installed within the dehydration unit 30. This dehydration unit 30 also has a cylinder head 35, an oil pressure chamber 35', a piston rod 35", an oil pump 35a, and a check valve 35b, which are installed outside the movable plate 32.

The air supply line 40a, extending from an air compressor 41 and an air tank 42 of the compressed air supply unit 40, has the air injection nozzle 36 at its end. This air injection nozzle 36 is placed at a position under the filter plates 33 of the dehydration unit 30 and injects compressed air into the membranes 90 of the filter plates 33, thus inflating the membranes 90 with compressed air while compressing the sludge cakes to desirably reduce the moisture content of the sludge cakes. The filter plates 33 are separable from each other as desired by the filter plate separation unit 34 when it is desired to drop the dehydrated and dried sludge cakes from the filter plates 33 onto a sludge cake feeding conveyor 37 so as to discharge the resulting sludge cakes from the system.

In an operation of the system of this invention, sludge is compressed and dehydrated by the filter plates 33 of the dehydration unit 30, thus becoming sludge cakes. After the sludge compression and dehydration process is accomplished, the filter plates 33 are separated from each other by the filter plate separation unit 34, thus dropping the dehydrated and dried sludge cakes from the filter plates 33 onto the sludge cake feeding conveyor 37 prior to discharging the resulting sludge cakes from the system. In such a case, the sludge, remaining on the fabric filters

33' of the filter plates 33, is washed by pressurized washing water injected from the water injection nozzle 51 of a fabric filter washing unit 50. This washing unit 50 also comprises a washing water tank and a water pump. After the sludge washing process, the sludge-laden water is drained from the dehydration unit 30 to a separate sludge treatment facility through a water discharging pipe 52.

In the sludge dehydration and dry system of this invention, the sludge inlet unit 10, the sludge thickening agent supply unit 80, the automatic pneumatic pump 20, the buffer tank 70, the dry unit 18, the dehydration unit 30, the membranes 90, the filter plate separation unit 34, the sludge cake feeding unit 37, the fabric filter washing unit 50, and the compressed air supply unit 40 consisting the compressor 41 and the air tank 42 are connected together using pipelines provided with a plurality of check valves and solenoid valves, thus being operated in conjunction with each other. In the system, the pneumatic pump 20 has a single or multi-stage pumping structure consisting of one or two pressure vessels 21 and 21 '. In the case of a multi-stage pneumatic pump 20 consisting of two pressure vessels 21 and 21 ', the two vessels 21 and 21 ' are alternately operated to allow the system to be continuously operated to produce desired sludge cakes. In the case of a single-stage pneumatic pump 20 consisting of one pressure vessel 21, the vessel 21 is intermittently operated under the control of a microcomputer 60.

The operational effect of the above-mentioned system will be primarily described herein below with reference to the embodiment of Fig. 1.

The sludge dehydration and dry system of this invention is preferably used for treating a variety of sludge-laden waste liquid, such as waste liquid from sewage treatment plants and a variety of industrial factories. In an operation of the system, sludge-laden waste liquid is mixed with a sludge thickening polymer within the sludge thickening tank 3, and so the sludge in the waste liquid is thus thickened. That is, the sludge-laden waste liquid within the storage tank 1 is primarily and naturally divided into water and sludge deposited on the bottom of the tank 1. The water is drained from the tank 1 into a separate reservoir through a drain port of the tank 1, while the deposited wet sludge is fed to the sludge thickening tank 3 through the feed pipe 2 and is thickened by a sludge thickening agent supplied from the sludge thickening agent supply unit 80.

The wet sludge is, thereafter, fed from the sludge thickening tank 3 of the sludge inlet unit 10 to the automatic pneumatic pump 20 through the pipeline 4 using atmospheric pressure or separate pumping pressure. When it is impossible to effectively thicken the sludge within the tank 3, the sludge thickening agent supply unit 80 supplies a sludge thickening agent to the sludge flowing through the pipeline 4.

In the automatic pneumatic pump 20, sludge-laden waste liquid is introduced into one or more pressure vessels 21 and 21 ' under the control of the liquid inlet valves 28. In such a case, the pump 20 has a single or multi-stage operational structure in accordance with the number of the pressure vessels 21 and 21 '. When the tank 3 of the sludge inlet unit 10 is positioned above the pressure vessels 21 and 21 ', liquid can be naturally fed from the tank 3 to the vessels 21 and 21 ' due to gravity. However, when the tank 3 is positioned under the pressure vessels 21 and 21 ', it is necessary to provide a separate pump on the pipeline 4 so as to forcibly feed the waste liquid from the tank 3 to the vessels 21 and 21'.

When the sludge-laden waste liquid is injected into the vessels 21 and 21 ' while being sprayed onto the upper level sensors 23 due to high pumping pressure, the pneumatic pump 20 may malfunction.

In order to overcome such a problem of malfunction, a liquid pressure dispersing member 15' cooperates with the liquid inlet valve 28 to disperse the liquid within each vessel 21 or 21 ' during an injection of waste liquid into the vessel. When the waste liquid reaches the upper level sensor 23 within a vessel 21 or 21 ', the sensor 23 outputs a signal to the microcomputer 60. In response to the signal from the sensor 23, the microcomputer 60 opens both the air compression solenoid valve 29 and the liquid outlet solenoid valve 28' while closing both the air exhaust solenoid valve 29' and the liquid inlet valve 28, thus feeding compressed air into the vessel 21 or 21 ' to pressurize the surface of the liquid within the vessel.

In such a case, the compressed air from the compression solenoid valves 29 may form a wave on the liquid surface within the vessels of the pump 20 to undesirably cause a malfunction of the pump 20.

In order to prevent such a problem, an air pressure dispersing member 15 having a paraboloidal shape is installed within each pressure vessel 21 or 21 ' of the pump 20 at an upper position so as to cover both the air compression solenoid valve 29 and the level sensing unit 24. This air pressure dispersing member 15 disperses the compressed air from the valve 29 laterally, thus allowing 3/4 of the inlet compressed air to be used for pressurizing the surface of the liquid within the vessel. When the level sensors 23 and 23' within each vessel 21 or 21 ' of the pump 20 are contaminated with sludge, it is impossible for the pump 20 to be optimally operated. Such sludge, contaminating the level sensors 23 and 23', also may unexpectedly stop the operation of the pump 20. Therefore, the air pressure dispersing member 15 disperses laterally the compressed air from the compression solenoid valve 29 so as to use 1/4 of the inlet compressed air for cleaning the sensors 23 and 23', thus finally preventing a malfunction of the sensors 23 and 23' due to the sludge deposited on the sensors. When compressed air is introduced into the pressure vessels 21 and 21 ', waste liquid is forcibly discharged from the vessels 21 and 21 ' by the pressure of the compressed air. When the waste liquid is discharged to reach the lower sensor 23', the supply of compressed air into the vessels is stopped, while the compressed air within the vessels is expelled from the vessels to the sub-tank 22 through an air pressure storage solenoid valve 29a, thus being stored within the sub-tank 22 prior to being discharged from the sub-tank 22 through the air exhaust solenoid valve 29'. In such a case, the internal pressure of each vessel 21 or 21 ' is sensed by the high and low pressure sensors 25' and 25". After sensing the internal pressures of the vessels 21 and 21 ', the pressure sensors 25' and 25" of each vessel output signals to the microcomputer 60 so as to allow the computer 60 to optimally control the internal pressure of an associated vessel 21 or 21 '.

When the sludge thickening tank 3 is positioned under the pressure vessels 21 and 21', it is necessary to provide a separate pump on the pipeline 4 so as to forcibly feed the sludge-laden waste liquid from the tank 3 to the vessels 21 and 21 '. In such a case, some kinds of sludge may be broken in their thickened states. When the thickened state of the sludge is broken as described above, the sludge forms a film thereon in the filter plates 33', and so it is almost impossible to dehydrate the sludge within the dehydration unit 30. In order to overcome the above-mentioned problem, the system of this invention is provided with a vacuum pump 26.

When the system of this invention is provided with such a vacuum pump 26, the system has to be designed to introduce compressed air into the pressure vessels 21 and 21 ' of the pump after containing waste liquid within each vessel until the liquid reaches the upper level within the vessel, with the valves of the compression tank being completely closed.

The sub-tank 22 is operated as follows. That is, since the pneumatic pump 20 is designed to pump up a large quantity of compressed air at every operational cycle, it is preferable to recycle the compressed air discharged from the pressure vessels 21 and 21' of the pneumatic pump 20 after every operational cycle of the pump 20. In order to accomplish the above object, the pressure storage solenoid valve 29a is provided at a side of each air exhaust solenoid valve 29'. In an operation of the pump 20, the pressure storage solenoid valves 29a are opened for a few seconds before an operation of the air exhaust solenoid valves 29', thus allowing the sub-tank 22 to partially store highly compressed air discharged from the vessels 21 and 21 '. In such a case, the remaining part of the compressed air discharged from the vessels 21 and 21 ' is exhausted to the atmosphere through the air exhaust solenoid valves 29'. The sub-tank 22 is provided with both a suction check valve 16 and an exhaust check valve 16', and so the inner pressure of the sub-tank 22 is appropriately controlled to be maintained at constant pressure. Due to such a sub-tank 22, the discharged compressed air from the vessels 21 and 21' can be preferably recycled for operating a variety of valves of the pump 20 or for operating the other machines or tools. It is thus possible for the system of this invention to preferably conserve energy in addition to remarkably reducing operational noise at the muffler 27 while exhausting the compressed air from the pump 20. In the system of this invention, the air supply line 40a is connected to the liquid discharging line 28a at a position near the dehydration unit 30. In addition, the dry unit 18, connected to another highly compressed air storage tank, is connected to the liquid discharging line 28a at a position near the dehydration unit 30. The dry solenoid valve 18' is provided on the dry unit 18 and is operable at an appropriate timing of drying the sludge cakes within the dehydration unit 30.

That is, the dry unit 18 supplies compressed air to the sludge cakes, thus drying the sludge cakes. When compressed air having a pressure of 10 kPa is introduced into the pump 20 and compressed air having a pressure of 12 kPa is supplied from the dry unit 18 into the dehydration unit 30 to dry the sludge cakes within the dehydration unit 30, it is possible to dry the sludge cakes by the compressed air of

12 kPa in addition to effectively removing sludge from the sludge inlet ports 31 ' of the fixed inlet terminal 31. Therefore, it is possible to additionally remove a process of separately removing the sludge from the ports 31 ' of the terminal 31 when separating the filter plates 33 from each other by the filter plate separation unit 34. In addition, since the highly compressed air passes through the sludge cakes within the filter plates 33, the compressed air collaterally allows an effective evaporation of moisture from the sludge cakes.

The dehydration unit 30, having such a dry unit 18, is advantageous in that it preferably reduces the moisture content of resulting organic sludge cakes to a level of not higher than 50%) different from a conventional dehydration unit, which does not have any dry unit and only dehydrates organic sludge cakes to a moisture content of 60% at the maximum. In the case of inorganic sludge cakes, the dehydration unit 30 of this invention preferably reduces the moisture content of resulting sludge cakes to a level of not higher than 10% different from the conventional dehydration unit only producing inorganic sludge cakes having the moisture content of 20% - 30%.

In an operation of the pneumatic pump 20 of this invention, an undesired knocking phenomenon may be caused by a water hammering action in the case of a closing of the outlet solenoid valves 28', thus generating operational noise at the valves. Such a knocking phenomenon is caused when a high-speed liquid flow is suddenly stopped within the system. In order to prevent such a knocking phenomenon, the buffer tank 70 is mounted on the liquid discharging line 28a extending from the pressure vessels 21 and 21 '. The interior of this buffer tank 70 is partitioned into the first and second chambers 72a and 72b by a partition wall 71. The dehydration unit 30 has the fixed inlet terminal 31 and the movable plate 32, and so the pumped sludge from the pump 20 is introduced into the dehydration unit 30 through the fixed inlet terminal 31. In order to connect a plurality of pipes to the dehydration unit 30, a plurality of inlet ports are formed on the fixed inlet terminal 31. A plurality of filter plates 33, individually covered with a fabric filter 33', are regularly and movably set between the fixed inlet terminal 31 and the movable plate 32. A membrane 90 is installed between each filter plate 33 and an associated fabric filter 33'. The membranes 90 of the filter plates 33 are commonly connected to the air injection nozzle 36 of a compressed air supply line 40a extending from the air supply unit 40, and so the sludge cakes within the dehydration unit 30 are compressed to be reduced in their moisture content.

The filter plate separation unit 34 is installed at a side of the dehydration unit 30, while the cylinder head 35' is installed at a side of the movable plate 32. The filter plates 33 are compressed by oil pressure output from an oil pump. In order to prevent a leakage of sludge-laden liquid from the gap between the filter plates 33 during a sludge compression process, the piston rod 35" compresses the movable plate 32 to compress the filter plates 33. However, when the pneumatic pump 20 is exceedingly high, the pressure of the oil pump 35 may be reduced or the cylinder head 35' may allow a leakage of pressurized oil. In such a case, the piston rod 35" may be unexpectedly retracted. When the piston rod 35" is unexpectedly retracted as described above, the filter plates 33 are undesirably separated from each other, thus allowing the sludge to leak from the gaps between fabric filters 33' of the filter plates 33. Furthermore, sludge-laden liquid under high pressure may leak from the dehydration unit 30 to the working area, thus seriously contaminating the area. In order to overcome the problem, a check valve 35b is provided within the dehydration unit 30. The above check valve 35b reliably prevents unexpected leakage of oil from the oil pressure chamber 36' to the oil pump 35a until the filter plates 33 are completely separated from each other by the separation unit 34. This finally prevents an unexpected reduction of oil pressure within the dehydration unit 30 during an operation of the system.

The air supply line 40a, extending from the air compressor 41 and the air tank 42 of the compressed air supply unit 40, has the air injection nozzle 36 at its end. This air injection nozzle 36 is positioned under the filter plates 33 of the dehydration unit 30 and injects the compressed air into the membranes 90 of the filter plates 33, thus inflating the membranes 90 with compressed air while compressing the sludge cakes and reducing the moisture content of the sludge cakes. The filter plates 33 are separable from each other as desired by the filter plate separation unit 34 when it is desired to drop the dehydrated and dried sludge cakes from the filter plates 33 onto the sludge cake feeding conveyor 37 so as to feed the resulting sludge cakes from the dehydration unit 30. That is, during an operation of the system of this invention, sludge is compressed and dehydrated by the filter plates 33 of the dehydration unit 30, thus becoming sludge cakes. After the sludge compression and dehydration process is accomplished, the filter plates 33 are separated from each other by the filter plate separation unit 34, thus dropping the dehydrated and dried sludge cakes from the filter plates 33 onto the sludge cake feeding conveyor 37 so as to discharge the resulting sludge cakes from the system. In such a case, the sludge, remaining in the fabric filters of the filter plates 33, is washed by pressurized washing water injected from the water injection nozzle 51 of the fabric filter washing unit 50. This washing unit 50 also has the washing water tank and the water pump. After the sludge washing process, the sludge-laden water is drained from the dehydration unit 30 to a separate sludge treatment facility through the water discharging pipe 52.

In a brief description, during an operation of the sludge dehydration and dry system according to the primary embodiment of this invention, sludge-laden waste liquid is primarily fed from the sludge inlet unit 10 to the automatic pneumatic pump 20 through the pipeline 4 using atmospheric air or separate pumping pressure. In such a case, a sludge thickening agent is added to the sludge-laden liquid from the sludge thickening agent supply unit 80. In the pump 20, compressed air, acting as a conventional piston, pumps the sludge-laden liquid while highly pressurizing the liquid, thus feeding the liquid to the dehydration unit

30. Within the dehydration unit 30, the sludge-laden waste liquid is dehydrated by the fabric filters 33' of the filter plates 33, and is compressed by the membranes 90, and is dried by the highly pressurized air at the dry unit 18, thus becoming sludge cakes. The sludge cakes are dropped onto the conveyor 37 so as to be discharged from the dehydration unit 30. In the system of this invention, the dehydration unit 30, the fabric filter washing unit 50, and the compressed air supply unit 40 consisting the compressor 41 and the air tank 42 are connected together using a pipeline provided with a plurality of check valves and solenoid valves.

Fig. 2 is a circuit diagram, showing the construction of a drainage sludge dehydration and dry system in accordance with the second embodiment of the present invention. As shown in the drawing, in an operation of the system according to the second embodiment, sludge-laden waste liquid is fed from the sludge inlet unit 10, consisting of the storage tank 1 and the sludge thickening tank 3, into the pressure vessels 21 and 21 ' of the automatic pneumatic pump 20 through the liquid inlet valves 28. When the waste liquid reaches the upper level sensor 23 within each vessel 21 or 21 ', the sensor 23 outputs a signal to the microcomputer 60. In response to the signal from the sensor 23, the microcomputer 60 opens both the air compression solenoid valve 29 and the liquid outlet solenoid valve 28' while closing both the air exhaust solenoid valve 29' and the liquid inlet valve 28, thus feeding compressed air into the vessel 21 or 21 ' so as to pressurize the surface of the liquid within the vessel. Therefore, the sludge- laden waste liquid under pressure is fed from the vessels 21 and 21 ' of the pump 20 to the dehydration unit 30.

When the sludge-laden liquid is not effectively thickened irrespective of the addition of the sludge thickening agent supplied from the unit 80 into the liquid, compressed air is introduced into the vessels 21 and 21 ' through the aerating valves 19' of aerators 19 at the same time of the introduction of liquid into the vessels 21 and 21 ', thus allowing the waste liquid to swirl along the sidewalls of the vessels 21 and 21 '. In such a case, the swirling liquid forms vortexes along with air bubbles, and is actively mixed and agitated within the vessels 21 and 21 ', thus being effectively thickened. The aerators 19 are respectively installed within the pump 20 at positions around the inlet valves 28 for the vessels 21 and 21 '.

In such a case, the air exhaust solenoid valve 29' and the liquid inlet valve 28 of each vessel 21 or 21' are closed, while both the air compression solenoid valve 29 and the liquid outlet solenoid valve 28' are opened. In addition, the dry solenoid valve 18' of the dry unit 18, which is mounted on the air supply line 40a connected to the liquid discharging line 28a, is closed.

During such an operation of the system of this second embodiment, sludge thickening polymer may be preferably added from the thickening agent supply unit 80 to the pipeline 4 extending from the sludge inlet unit 10 to the liquid inlet valves 28 of the pressure vessels 21 and 21 ' of the pump 20. The sludge thickening polymer may be also preferably added from the unit 80 to the sludge thickening tank 3 of the sludge inlet unit 10. At any rate, the sludge-laden liquid is preferably thickened within this system.

When the aerators 19 are installed at the pressure vessels 21 and 21 ' of the pneumatic pump 20 as described above, the aerators 19 collaterally increase the amount of dissolved oxygen within the waste liquid in addition to effectively agitating, mixing and thickening the liquid. In the system according to the second embodiment, the sludge-laden waste liquid is fed from the pressure vessels 21 and 21 ' of the pneumatic pump 20 to the dehydration unit 30 by the compressed air after it is effectively aerated by the aerators 19 within the vessels 21 and 21 '.

In the system according to the second embodiment, a buffer tank 70 is mounted on the waste liquid discharging line 28a. The interior of this buffer tank 70 is partitioned into the first and second chambers 72a and 72b by a partition wall 71. When the outlet solenoid valves 28' of the two pressure vessels 21 and 21 ' are entirely closed, the hydraulic pressure is moved into the second chamber 72b of the buffer tank 70 in the case of a water hammering within the pump 20, since the liquid outlet port of the tank 70 is connected to the liquid discharging line 28a extending to the sludge inlet ports 31 ' of the fixed inlet terminal 31 of the dehydration unit 30. Therefore, the hydraulic pressure is completely removed at the air occupying the upper portion within the tank 70, thus effectively thickening the sludge-laden waste liquid within the pressure vessels 21 and 21 ' of the pump 20 in addition to allowing the pump 20 to be almost completely free from any knocking phenomenon caused by such a water hammering.

The dehydration unit 30 comprises the fixed inlet terminal 31 and a movable plate 32, and so the pumped sludge from the pump 20 is introduced into the dehydration unit 30 through the fixed inlet terminal 31. In order to connect a plurality of inlet pipes to the dehydration unit 30, a plurality of inlet ports 31' are formed on the fixed inlet terminal 31. A plurality of filter plates 33, individually covered with a fabric filter 33', are regularly and movably set between the fixed inlet terminal 31 and the movable plate 32. A filter plate separation unit 34 is installed within the dehydration unit 30 at a position around the filter plates 33.

Since the sludge-laden liquid under high pressure is fed from the pneumatic pump 20 to the dehydration unit 30, with the filter plates 33 being forcibly compressed by the piston rod 35b of the cylinder head 35 installed at a position around the movable plate 32, sludge-laden waste liquid is removed from the fabric filters 33' while forming sludge cakes.

After the sludge within the dehydration unit 30 is compressed and dehydrated as described above to form sludge cakes, the air compression solenoid valves 29 of the pressure valves 21 and 21 ' are opened under the control of the microcomputer 60 with both the air exhaust solenoid valves 29' and the liquid inlet valves 28 being closed. In such a case, compressed air passes through the liquid outlet solenoid valves 28' and through the interior of the dehydration unit 30 by way of the air supply line 40a, thus being finally exhausted to the atmosphere. Therefore, it is possible to remove the sludge-laden liquid from both the interior of the pressure vessels 21 and 21 ' and the inlet ports 31 ' of the dehydration unit 30, thus cleaning both the interior of the pressure vessels 21 and 21 ' and the inlet ports

31 ' of the dehydration unit 30 in addition to drying the sludge cakes in the unit 30.

When it is impossible to allow compressed air to pass through the pressure vessels 21 and 21 ' of the pneumatic pump 20, the system of this invention is designed to inject compressed air into the inlet ports 31 ' of the dehydration unit 30 by closing the liquid outlet solenoid valves 28 and opening the dry solenoid valve

18' of the dry unit 18. In such a case, the dry unit 18 is connected to the air supply line 40a communicating with the liquid discharging line 28a.

In the above system, the dehydration unit 30 desirably dries the sludge cakes positioned between the filter plates 33 to reduce the moisture content of the sludge cakes, and cleans the inlet ports 31 '.

After the sludge cakes are desirably dehydrated, the dry solenoid valve 18' is closed. In addition, the hydraulic pump 35a is started with the check valve 35b being inactivated, and so the piston rod 35" is retracted to allow the filter plate separation unit 34 to separate the filter plates 33 from each other, thus finally dropping the dehydrated and dried sludge cakes onto the conveyor 37 to discharge the resulting sludge cakes from the system. The resulting sludge cakes may be recycled or separately treated by an additional treatment facility.

In the primary embodiment of Fig. 1, the system includes both an air injection nozzle 36 used for inflating the membranes 90 with compressed air and a water injection nozzle 51 used for washing the fabric filters 33' of the filter plates 33 after dropping the resulting sludge cakes onto the conveyor 37.

Different from the embodiment of Fig. 1, the system according to the second embodiment of Fig. 2 does not have such membranes 90 and such an air injection nozzle 36, but injects compressed air to the inlet ports 31' from the dry unit 18, thus cleaning the pipes of the dehydration unit 30 in addition to drying the sludge cakes within the dehydration unit 30 using the compressed air.

Conventional sludge dehydration systems may be typically changed in their construction in accordance with the kinds of sludge to be treated by the systems. For example, some sludge-laden waste liquid may be effectively dehydrated to form sludge cakes having a desired moisture content using only such a dry unit 18 without using membranes 90. However, some sludge-laden waste liquid cannot be dehydrated to form sludge cakes having a desired moisture content even when the system is provided with the membranes 90.

However, the sludge dehydration and dry system of this invention is commonly usable for treating various types of sludge. That is, the membranes 90 installed within the dehydration unit 30 are somewhat expensive and are somewhat difficult to use, but they have to be selectively used for treating some kinds of sludge. Therefore, the system of this invention is provided with both such membranes 90 and such a dry unit 18 in the dehydration unit 30. In a brief description, the system of this invention may be selectively operated while activating only the dry unit 18 or both the membranes 90 and the dry unit 18 as desired. Most sewage sludge, ceramic sludge and food sludge may be effectively dehydrated only by the dry unit 18 without using the membranes 90 to form sludge cakes having a desired moisture content. Therefore, the system of this invention saves the processing cost and conserves energy while treating sludge to form sludge cakes. In the dehydration unit 30 included in the system of this invention, highly compressed air is used for drying sludge cakes within the dehydration unit 30. A check valve 35b is provided between the oil pressure chamber 35' and the oil pump 35a for preventing the filter plates 33 from being undesirably separated from each other in the case of an unexpected reduction in oil pressure or an unexpected deterioration in the operational performance of the oil pump.

Due to the check valve 35b, it is possible to almost completely prevent an unexpected retraction of the piston rod 35" into the cylinder head due to a leakage of oil pressure from the oil pump 35a during a sludge dehydration process of the dehydration unit 30. Each of the systems of Figs. 1 and 2 effectively dehydrates sludge to form sludge cakes having a moisture content of not higher than 50%. When organic sludge is dehydrated to form sludge cakes having a moisture content of about 50%, the resulting sludge cakes have a dry and compressed solid state as expected from sesame dregs, and so such organic sludge cakes may be preferably recycled or incinerated while remarkably reducing the processing cost and remarkably conserving energy. For example, when dehydrating one hundred tons of sludge cakes having a moisture content of 75% to form sludge cakes having a moisture content of 50% using a system of this invention, it is possible to reduce the total weight of the sludge cakes from one hundred tons to twenty five tons, thus remarkably conserving energy and reducing the processing cost while incinerating the resulting sludge cakes at a separate incineration facility.

Microbial sludge, generated from biological sludge treatment facilities, typically includes plenty of organized ferments. Therefore, when such microbial sludge is dehydrated to form sludge cakes having a moisture content of about 65 % prior to supplying oxygen to the resulting sludge cakes at a barnyard, the sludge cakes are easily and appropriately fermented while being increased in temperature to 65°C - 70°C. When microbial sludge cakes, produced by a compression and dehydration process of the filter plates 33 included in the system of Fig. 1, have a moisture content of about 65%, the resulting sludge cakes may be preferably recycled as composts in place of being incinerated. In addition, when sludge is compressed by the filter plates 33 and dried by the dry unit 18 of the system of Fig. 2 so as to form sludge cakes having a moisture content of 50% - 60%, the resulting sludge cakes may be easily incinerated while conserving energy. When such sludge includes plenty of oil, it is possible to recycle the resulting sludge cakes as a material of solid fuel. In addition, any system of this invention is easily and appropriately controllable to accomplish a desired moisture content of resulting sludge cakes by controlling the amount of compressed air used in the process of the system and the processing time while forming dehydrated sludge cakes. That is, the operational performance of the sludge dehydration and dry system including the automatic pneumatic pump of this invention is remarkably improved in comparison with the other systems provided with conventional high-pressure pumps as expressed in the following Table 1.

Table 1

As well known from the above Table 1 , there is a remarkable difference in operational performance between the system including the automatic pneumatic pump of this invention and the systems including the conventional high-pressure pumps. In addition, the operational efficiency of the automatic pneumatic pump of this invention is also remarkably improved in comparison with such conventional high-pressure pumps as expressed in the following Table 2.

Table 2

Comparison of the performance of the pneumatic pump of this invention with a conventional high pressure dehydration Pumps

Conventional pumps: Pneumatic pump of this

No. 1. Diaphragm type pump invention using compressed air,

2. Volute type pump and designed to allow the

As described above, the sludge dehydration and dry system including the automatic pneumatic pump of this invention is remarkably improved in its operational performance, operational efficiency and economic efficiency in comparison with another system including any one of the conventional high- pressure pumps.

The automatic pneumatic pump 20, used for feeding sludge-laden waste liquid to the dehydration unit 30 in the sludge dehydration and dry system of this invention, may be also preferably used for supplying compressed air to a variety of pneumatically operated machines or tools requiring compressed air for operation.

Conventional pneumatically operated machines or tools typically use low-pressure air of not higher than 3 kPa. Therefore, recycled compressed air stored in the sub-tank 22 of this pump 20 is preferably used for operating such pneumatically operated machines or tools without causing any problem. The pump 20 of this invention thus maximizes energy efficiency. Of course, the recycled compressed air stored in the sub-tank 22 may be also returned to the pressure vessels 21 and 21 ' of the pump 20 so as to be recycled as operational air at the initial stage of the operation of the pressure vessels 21 and 21 ' requiring low-pressure air at such an initial stage. In addition, the operational performance of the filter press used as the dehydration unit according to this invention is remarkably improved in comparison with a conventional belt press designed to dehydrate sludge by compressing the sludge on fabric filters as expressed in the following Table 3.

Table 3

As well known from the above Table 3, the filter press used as the dehydration unit of this invention is advantageous in that it can effectively treat a large amount of sludge while accomplishing a desired moisture content of resulting sludge cakes and is preferably reduced in its maintenance cost and processing cost in comparison with the conventional belt press that has to be continuously operated every day while being cycled 9.6 times every day. In addition, it is also possible for the filter press of this invention to easily control moisture content and total weight of resulting sludge cakes as desired, and so the filter press is remarkably improved in its operational performance in comparison with the conventional belt press that is not designed to control moisture content or total weight of resulting sludge cakes. Therefore, the resulting sludge cakes produced by the filter press of this invention are more effectively treated by a separate treatment facility than those of the conventional belt press as expressed in the following Table 4 showing a treatment of such sludge cakes by burying under the ground. Table 4

From the above Table 4, it is well known that the resulting sludge cakes of this filter press can be more easily and cheaply treated than those of the conventional belt press. The sludge dehydration and dry system of this invention provided with such a specifically designed automatic pneumatic pump and a specifically designed dehydration unit will be more preferably used for producing sludge cakes from a variety of sludge, such as sewage sludge, industrial waste sludge, microbial sludge of sewage treatment plants, ceramic sludge and food industrial sludge.

In the system according to the second embodiment of this invention, it is possible to effectively dehydrate and dry the sludge cakes using a dry unit along with another pressure pump in place of using the automatic pneumatic pump. In such a case, the dry unit is provided on a waste liquid discharging line and is operated in conjunction with a compressed air supply line. In an operation of the above system, sludge is dehydrated by a dehydration unit and is dried by the dry unit to form desired sludge cakes. This system is also preferably used for dehydrating and drying a variety of sludge to produce sludge cakes having a desired moisture content.

Industrial Applicability

As described above, the present invention provides a sludge dehydration and dry system. This system is designed to dehydrate a variety of sludge, such as sewage sludge or industrial waste sludge, to form sludge cakes while controlling moisture content of the resulting sludge cakes as desired. Therefore, the resulting sludge cakes, produced by the system of this invention, may be preferably recycled as a material of solid fuel, a material of feedstuff, or a material of organic composts without performing any additional drying process for the resulting sludge cakes. The system of this invention thus preferably and remarkably reduces the processing cost of such sludge. Furthermore, since the sludge cakes produced by the system of this invention can be recycled for various purposes as described above, it is possible to prevent soil contamination caused by burying the sludge under the ground, air pollution caused by incinerating the sludge and water pollution caused by discarding the sludge into a river or a sea. Particularly, this system is more preferably used in the future in some countries, for example, Korea, regulated by the World Environmental Protection Law, which prohibits a burying of sludge under the ground or a discarding of sludge onto the seabed. Another advantage of this system resides in that it is preferably used for treating a variety of sludge while reducing the installation cost and maintenance cost of such a system. This finally minimizes environmental pollution caused by such sludge.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A drainage sludge dehydration and dry system, comprising: a sludge inlet unit; an automatic pneumatic pump connected to said sludge inlet unit through a pipeline and receiving sludge-laden waste liquid from the sludge inlet unit using atmospheric pressure or separate pumping pressure, said pneumatic pump consisting of: one or more pressure vessels commonly connected to said sludge inlet unit through the pipeline to receive the waste liquid from the sludge inlet unit, said vessels being alternately operated to allow the pneumatic pump to be continuously operated during an operation of the system; a liquid inlet valve mounted on the pipeline extending to each pressure vessel for controlling an inflow of waste liquid into each vessel; a liquid level sensing unit consisting of upper and lower level sensors installed within each pressure vessel for sensing upper and lower levels of waste liquid within each vessel; an air compression solenoid valve provided at each vessel for injecting compressed air into each vessel; an air exhaust solenoid valve provided at each vessel for exhausting compressed air from each vessel; a liquid outlet solenoid valve provided at each pressure vessel for controlling an outflow of waste liquid from each vessel; an air pressure dispersing member provided within each pressure vessel at an upper position around the air compression solenoid valve for dispersing the compressed air injected into each vessel; and a liquid pressure dispersing member provided within each pressure vessel at a lower position around the liquid inlet valve for dispersing the waste liquid injected into each vessel; a buffer tank commonly connected to said pressure vessels and used for preventing a water hammering of said pneumatic pump in the case of a closing of said liquid outlet solenoid valve during an operation of said pneumatic pump; a dehydration unit connected to said pneumatic pump, said dehydration unit consisting of: a fixed inlet terminal having a plurality of inlet ports so as to be connected to a plurality of inlet pipes; a movable plate positioned opposite to said fixed inlet terminal so as to be movable relative to the inlet terminal; a plurality of filter plates regularly and movably set between the fixed inlet terminal and the movable plate, said filter plates being individually covered with a fabric filter; a membrane provided between each filter plate and an associated fabric filter; a compressed air injection nozzle connected to the membranes so as to inflate the membranes with compressed air for compressing sludge by the membranes, thus forming sludge cakes between the filter plates and dehydrating the sludge cakes in cooperation with the fabric filters so as to reduce the moisture content of the sludge cakes; and a filter plate separation unit connected to said movable plate so as to move the movable plate relative to the fixed inlet terminal, thus separating the filter plates from each other when necessary to allow the sludge cakes to be removed from the filter plates; a dry unit connected to a liquid discharging line extending from said buffer tank to the inlet terminal of the dehydration unit, thus supplying compressed air from a compressed air supply unit to the dehydrated sludge cakes within the dehydration unit so as to dry the sludge cakes; a sludge cake feeding conveyor installed at a position under said dehydration unit so as to receive and feed sludge cakes dropped from the filter plates when the filter plates are separated from each other by the filter plate separation unit; a fabric filter washing unit used for washing sludge remaining in the fabric filters of the filter plates by injecting pressurized washing water from its water injection nozzle to the fabric filters after dropping the sludge cakes from the filter plates onto the sludge cake feeding conveyor, said washing unit also having a washing water tank and a water pump, with sludge-laden washing water being drained from the dehydration unit to a separate sludge treatment facility through a water discharging pipe; and a microcomputer controlling an operation of the system.

2. A drainage sludge dehydration and dry system, comprising: a sludge inlet unit; an automatic pneumatic pump connected to said sludge inlet unit through a pipeline and receiving sludge-laden waste liquid from the sludge inlet unit, said pneumatic pump consisting of: one or more pressure vessels commonly connected to said sludge inlet unit through the pipeline to receive the waste liquid from the sludge inlet unit, said vessels being alternately operated to allow the pneumatic pump to be continuously operated during an operation of the system; a liquid inlet valve mounted on the pipeline extending to each pressure vessel for controlling an inflow of waste liquid into each vessel; a liquid level sensing unit consisting of upper and lower level sensors installed within each pressure vessel for sensing upper and lower levels of waste liquid within each vessel; an air compression solenoid valve provided at each vessel for injecting compressed air into each vessel; an air exhaust solenoid valve provided at each vessel for exhausting compressed air from each vessel; a liquid outlet solenoid valve provided at each pressure vessel for controlling an outflow of waste liquid from each vessel; an air pressure dispersing member provided within each pressure vessel at an upper position around the air compression solenoid valve for dispersing the compressed air injected into each vessel; and a liquid pressure dispersing member provided within each pressure vessel at a lower position around the liquid inlet valve for dispersing the waste liquid injected into each vessel; a buffer tank commonly connected to said pressure vessels and used for preventing a water hammering of said pneumatic pump in the case of a closing of said liquid outlet solenoid valve during an operation of said pneumatic pump; a dehydration unit connected to said pneumatic pump, said dehydration unit consisting of: a fixed inlet terminal having a plurality of inlet ports so as to be connected to a plurality of inlet pipes; a movable plate positioned opposite to said fixed inlet terminal so as to be movable relative to the inlet terminal; a plurality of filter plates regularly and movably set between the fixed inlet terminal and the movable plate, said filter plates being individually covered with a fabric filter and compressing sludge so as to form sludge cakes and dehydrate the sludge cakes in cooperation with the fabric filters so as to reduce a moisture content of the sludge cakes; and a filter plate separation unit connected to said movable plate so as to move the movable plate relative to the fixed inlet terminal, thus separating the filter plates from each other when necessary to allow the sludge cakes to be removed from the filter plates; a dry unit connected to a liquid discharging line extending from said buffer tank to the inlet terminal of the dehydration unit, thus supplying compressed air to the dehydrated sludge cakes within the dehydration unit so as to dry the sludge cakes; a sludge cake feeding conveyor installed at a position under said dehydration unit so as to receive and feed sludge cakes dropped from the filter plates when the filter plates are separated from each other by the filter plate separation unit; and a microcomputer controlling an operation of the system.

3. A drainage sludge dehydration and dry system, comprising: a sludge inlet unit; an automatic pneumatic pump connected to said sludge inlet unit through a pipeline and receiving sludge-laden waste liquid from the sludge inlet unit, said pneumatic pump consisting of: one or more pressure vessels commonly connected to said sludge inlet unit through the pipeline to receive the waste liquid from the sludge inlet unit, said vessels being alternately operated to allow the pneumatic pump to be continuously operated during an operation of the system; a liquid inlet valve mounted on the pipeline extending to each pressure vessel for controlling an inflow of waste liquid into each vessel; a liquid level sensing unit consisting of upper and lower level sensors installed within each pressure vessel for sensing upper and lower levels of waste liquid within each vessel; an air compression solenoid valve provided at each vessel for injecting compressed air into each vessel; an air exhaust solenoid valve provided at each vessel for exhausting compressed air from each vessel; a liquid outlet valve provided at each pressure vessel for controlling an outflow of waste liquid from each vessel; an air pressure dispersing member provided within each pressure vessel at an upper position around the air compression solenoid valve for dispersing the compressed air injected into each vessel; an liquid pressure dispersing member provided within each pressure vessel at a lower position around the liquid inlet valve for dispersing the waste liquid injected into each vessel; and an aerator installed within each pressure vessel at a lower position around the liquid inlet valve, said aerator supplying compressed air into each vessel at the same time of inflow of waste liquid into the vessel, thus allowing the waste liquid to swirl along the sidewall of the vessel while forming vortexes along with air bubbles and thereby allowing the waste liquid to be actively mixed, agitated and thickened within the vessel; a buffer tank mounted to the outlet line commonly extending from said pressure vessels, with the interior of said buffer tank being partitioned into first and second chambers by a partition wall; and a microcomputer controlling an operation of the system.

4. The system according to claim 1 or 2, further comprising: means for preventing a leakage of oil pressure from an oil pump of said dehydration unit or an unexpected retraction of a piston rod of a cylinder head during an operation of said pneumatic pump after the filter plates are completely compressed by the piston rod actuated by oil pressure output from said oil pump.

5. The system according to claim 1 or 2, further comprising: means for dehydrating the sludge cakes within said dehydration unit using pressure supplied from another pressure pump in place of using said automatic pneumatic pump and drying the sludge cakes by injecting compressed air from the air supply line of said compressed air supply unit into the inlet ports of the fixed inlet terminal of said dehydration unit.