WO2002085798A1

WO2002085798A1 - Process and plant of the ubr formation for wastewater treatment

Info

Publication number: WO2002085798A1
Application number: PCT/KR2002/000709
Authority: WO
Inventors: Hong-Bok Choe; Jong-Won Kim; Jong-Phil Won; Kwang-Hyun Woo
Original assignee: Environmental Vision 21, Ltd.
Priority date: 2001-04-18
Filing date: 2002-04-18
Publication date: 2002-10-31

Abstract

An integral wastewater treatment plant includes a reaction tank for storing wastewater, the reaction tank being divided into plural spaces in a vertical direction, a thickening tank for settling sludge contained in the wastewater, the thickening tank being mounted under the reaction tank and provided with a wastewater intake tube and an air intake tube, an agitator for agitating the wastewater supplied from the thickening tank, allowing bubbles generated by air induced through the air intake tube to collide with each other to increase dissolved oxygen, and decomposing polluting material by aeration microorganism by extending a staying time of the bubbles, and a sludge separation tank for settling sludge contained in the wastewater exhausted from the reaction tank and returning the wastewater to the thickening tank.

Description

PROCESS AND PLANT OF THE UBR FORMATION FOR WASTEWATER

TREATMENT

BACKGROUND OF THE INVENTION

(a) Field of the invention

The present invention relates to a wastewater treatment plant and,

more particularly, to a wastewater treatment plant that can improve the

treatment efficiency of the wastewater by effectively supplying oxygen to

wastewater for the biological treatment of the wastewater by integrally

mounting agitating means on a reaction tank

(b) Description of the Related Art

Generally, a water treatment is a process for converting polluted

material into stable material through a microorganism or chemical

oxidation/reduction reaction

Accordingly, a water treatment technology is to stabilize organic

material or nutritive material in a variety of methods A biological

treatment method which is inexpensive is most widely used for the water

treatment However, since the treatment speed of the biological method

depends on the microorganism decomposition speed in a natural state,

the treatment speed is very slow and unstable.

Accordingly, the efficiency of the biological wastewater treatment

depends on how effectively supply the an energy source such as free

oxygen and bound oxygen, how effectively supply a carbon source such

as organic material, how properly maintain the conditions of the

microorganism, and how effectively agitate for the efficient contact

between the microorganism, the organic material and the nutritive

material.

Such a biological treatment is tested in a laboratory and then a

practical plant is installed and used at the field. However, the plant

installed in the field is a large scale, the actual flow of the fluid in the

practical plant may be different from that in the laboratory. Therefore, a

large amount of sludge may be accumulated around the reaction tank of

the plant, thereby reducing the active space for the microorganism.

This results in deteriorating the treatment efficiency. This problem is

inevitably appeared as the plant is large-sized, and there is a limitation in solving the problem even when the structure of the plant is im proved

SUM MARY OF TH E I NVENTION

Therefore, the present invention has been made in an effort to

solve the above-described problem It is an objective of the present

invention to provide a wastewater treatment plant that can prevent sludge

from accum ulating in a reaction tank and im prove agitation eff iciency by

installing an inclined blade assem bly in the reaction tank , through which

f luid can pass in a predeterm ined direction

It is another objective of the present invention to provide a

wastewater treatm ent plant that can effectively separate f irst-class water

from the sludge by m aking the f low direction of the f luid to be identical to

the direction of the gravity during a process for separating the sludge after

biologically treating the wastewater by connecting the reaction tank to a

sludge separation tank

It is still another objective of the present invention to provide a

wastewater treatm ent plant that can effectively settle solid material having

relatively high density and specif ic gravity by installing a wedge-shaped

guide blade at an inner-lower portion of a concentrating tank to form a difference in a fluid pressure around the guide blade .

It is another objective of the present invention is to provide a

wastewater treatment process using bio-reactor having a single reaction

tank that can resolve, settle and concentrate the organism in addition by

rotating sludge using rotational force generated by an upper blade

assem bly and directing sludge having a high specific gravity to a

lower-center of the reactor to accelerate the concentration of the sludge

To achieve the above objectives, the present invention provides an

integral wastewater treatment plant com prising a reaction tank for storing

wastewater, the reaction tank being divided into plural spaces in a vertical

direction by at least one partition , a thickening tank for settling sludge

contained in the wastewater, the thickening tank being integrally m ounted

under the reaction tank and provided with a wastewater intake tube and an

air intake tube, agitating m eans for agitating the wastewater supplied

f rom the thickening tank, allowing bubbles generated by air induced

through the air intake tube to collide with each other to increase dissolved

oxygen , and decom posing polluting material by aeration m icroorganism

by extending a staying tim e of the bubbles; and a sludge separation tank for settling sludge contained in the wastewater exhausted from the

reaction tank and returning the wastewater to the thickening tank, the

sludge separation tank being integrally connected to the reaction tank.

According to another aspect, the present invention provides an

integral wastewater treatment plant com prising a reaction tank for storing

wastewater, the reaction tank being divided into plural sections by at least

one partition , each of the sections being provided with a gas intake hole

and a gas collecting hole; agitating m eans f or agitating the wastewater

supplied from the thickening tank , allowing bubbles generated by gas

induced through the gas intake tube to collide with each other, and

decom posing polluting material by anaerobic m icroorganism by extending

a staying tim e of the bubbles; and a sludge separation tank for settling

sludge contained in the wastewater exhausted from the reaction tank and

returning the wastewater to the thickening tank, the sludge separation

tank being integrally connected to the reaction tank

BRI EF DESCRI PTION OF TH E DRAWI NGS

FIG . 1 is a schematic view illustrating an integral wastewater

treatm ent plant according to a f irst em bodim ent of the present invention; FIG. 2 is a sectional view of a reactor of a wastewater treatment

plant depicted in FIG. 1 ,

FIG. 3 is a partly enlarged view of a blade assembly of a

wastewater treatment plant depicted in FIG. 1;

FIG.4 is a sectional view of a blade assembly depicted in FIG 3;

FIG 5 is a sectional view taken along line A-A of FIG. 3;

FIG.6 is an enlarged sectional view taken along line B-B of FIG.1 ;

FIG. 7 is a schematic view illustrating an integral wastewater

treatment plant according to a second preferred embodiment of the

present invention,

FIG. 8 is a partly enlarged view of a blade assembly of a

wastewater treatment planet depicted in FIG. 7;

FIG. 9 is a perspective view of a blade assembly of a wastewater

treatment plant depicted in FIGS 3 and 7;

FIG. 10 is a schematic sectional view of an integral wastewater

treatment plant according to a third preferred embodiment of the present

invention;

FIG.11 is a top sectional view of a guide blade depicted in FIG.10; and

FIG. 12 is a bottom view of an exhaust hole depicted in FIG. 10.

DETAILED DISCLOSURE OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described

more in detail in conjunction with the accompanying drawings.

As shown in FIGS.1 to 4, an integral wastewater treatment plant of

a first embodiment comprises a first reactor 1 for primarily decomposing

polluting material in wastewater by use of aerobic microorganism through

a mixing process of the wastewater and air, a second reactor 2 connected

to the first reactor 1 to secondary decomposing the polluting material in

the wastewater introduced from the first reactor 1 , and a sludge

separating tank 3 for removing sludge by naturally settling the sludge

contained in the wastewater introduced from the second reactor 2.

In the above integral wastewater treatment plant, the first reactor 1

is formed in a cylindrical-shape and comprised of an aeration tank 4 in

which the wastewater is stored and a thickening tank 6 integrally mounted

under the aeration tank 6

Connected to a sidewall of the thickening tank 6 is a wastewater intake tube 7 which is connected to a pum p (not shown) so that the

wastewater can be pum ped by a predeterm ined pressure

The wastewater introduced into the thickening tank 6 is ascended

and directed into the reactor 1 , during which sludge having a relatively

high specif ic gravity spirally falls down to be settled and exhausted out of

the tank 6 At this point, by adjusting the pressure, the intake speed of the

wastewater can be also adjusted , thereby m aking it possible to control the

settling am ount and tim e of the sludge

In addition , as shown in FIG 6, since the wastewater intake tube is

disposed in a tangent line direction with respect to the thickening tank 6 ,

the intake wastewater is to rotate in the thickening tank 6 Connected to

an upper sidewall of the thickening tank 6 is an air intake tube 8

The wastewater and air are introduced into the first reactor 1

through the wastewater intake tube 7 and the air intake tube 8 ,

respectively At this point , the wastewater is gradually ascended in the

f irst reactor 1 by a predeterm ined pressure generated by the pum p

The aeration tank 4 is provided at its inside with plural partitions 1 3

and 20 by which the inner space can be vertically divided into plural spaces 36

Each of the partitions 13 and 20 is provided with a circular hole 13a

through which the wastewater is directed to the upper space

At this point, the wastewater collides with the bottoms of the

partitions 13 and 20 to form the returning flow and mixes with bubbles

formed by introduced oxygen, thereby decomposing the polluting material

contained in the wastewater by aerobic microorganism

Describing more in detail, the first and second partitions 13 and 20

is horizontally disposed in the aeration tank 4 in the vertical direction First

and second blade assemblies 9 and 19 are respectively mounted on the

first and second partitions 13 and 20 As the first and second partitions

13 and 20 are designed in an identical structure to each other, and the

first and second blade assemblies 9 and 19 are also designed in an

identical structure to each other, only the structures of the first partition 13

and the first blade assembly 9 will be described hereinafter

The circular hole 13a having a predetermined diameter is formed

on the center of the first partition 13 Part of the wastewater is directed

to the upper space through the circular hole 13a and the rest collides with the bottom of the first partition 13 and forms the returning flow. In

addition, bubbles are formed by the air introduced through the air intake

tube and the returning flow collides or mixes with the returning flow The

air increases the amount of dissolved oxygen and the treatment efficiency

is improved by buoyancy energy of the air.

The wastewater introduced through the circular hole 13a is directed

into the first blade assembly 9. The first blade assembly 9 comprises a

lower assembly 12 having a relatively small diameter and an upper

assembly 11 having a relatively large diameter.

The lower assembly 12 is formed in a cylindrical shape having a

predetermined diameter D, integrally coupled to an edge of the circular

hole 13a and projected upward The upper assembly 14 is mounted on

the upper end of the lower assembly 1

Accordingly, the wastewater induced through the circular hole 13a

is directed to the upper assembly 11 through the lower blade 14.

The upper assembly 11 comprises a cylindrical body 22 having a

diameter D1 greater than that of the lower assembly 11 and an upper

blade 16 mounted on the top of the cylindrical body 22. The lower assembly 12 is disposed on an inner-lower portion of the upper assembly

11 That is, plural connecting rods 15 are projected in a radial direction

from an outer circumference of the lower assembly 12 and coupled to an

inner circumference of the upper assembly 11 through, for example, a

welding process Accordingly, the upper and lower assemblies 11 and

12 are integrally coupled and the inner spaces thereof are communicated

with each other so that the wastewater flows there through

The volume difference between the upper and lower assemblies 11

and 12 makes it possible for the wastewater to be more effectively

agitated.

In addition, since the moving distance in horizontal and vertical

directions is increased, the agitation effect is improved by turbulence and

shearing force

In addition, as shown in FIG 9, each of the upper and lower

blades 16 and 14 has plural blades 23 partly overlapped on each other in

a circumference direction The overlapped area is more than 1/3 with

respect to whole area of the blades 16 and 14 One sides 24 of the

blades 23 are connected to each other at their middle portions, and the other sides of the blades 23 are coupled to the inner wall 21 a of the

cylindrical body 21 by a welding process The blades 23 are designed to

be inclined at 1 0-70 degrees so that spaces t between the blades 23

through which the wastewater flows can be form ed The wastewater

passing through the spaces t of the upper and lower blades 1 6 and 1 4 is

guided at a predeterm ined angle by the inclined blades 23 , thereby being

rotated in a spiral direction When the rotating wastewater collides with

bubbles , the surface area is increased to im prove the decomposing effect

of the polluting m aterial

Since the sludge settled during the above procedure may be

accum ulated on the partitions 1 3 and 20 , the accum ulated sludge should

be exhausted out of the plant through a periodic reverse washing process.

The wastewater passed through the f irst blade assem bly 9 is

directed to the second blade assem bly 1 9 and then identically treated and

purified as in the f irst blade assem bly 9.

The second reactor 2 is connected to the first reactor 1 through a

pipe 26 and has an identical structure to the f irst reactor 1 Therefore,

the wastewater primarily treated in the f irst reactor 1 is directed to the second reactor 2 through the pipe 26 and then identically treated as in the

first reactor 1

The sludge separation tank 3 is connected to the second reactor 2

through an intake tube 27 so that the sludge can be directed therein The

high quality water without sludge is exhausted out of the plant through an

exhaust tube 34

A section of the sludge separation tank 3 is a V-shaped so that the

sectional area is gradually decreased as it goes from the lower portion to

the upper portion , thereby m aking it possible to exhaust m ore than 50% of

the wastewater by sm oothly m oving the sludge downward The sludge

separation tank 3 is disposed such that a bottom line 29 is inclined at 1 0

degrees toward an exhaust hole 30 so that the f low speed of the

wastewater at the lower portion is faster than that at the upper portion

This allows the sludge to be m ore effectively settled and exhausted

Accordingly, the sludge m oved to the lower portion by the

V-shaped tank is directed to the exhaust hole 30 in a direction identical to

the gravity direction by the inclined bottom plane 29

An inclined plate 31 is attached on an upper portion of the sludge separation tank 3 and extended downward The inclined plate is preferably

disposed at less than 45 degrees with respect to the top plane of the

sludge separation tank 3 Accordingly, the wastewater induced through

the intake tube 27 is directed downward by contacting the inclined plate

31 , thereby m oving the m axim um am ount of the sludge to the bottom

A plate 32 is m ounted on the sludge separation tank 3 and spaced

away f rom the inclined plate 31 The plate 32 is provided with protruded

portions 33 at its upper end The high quality water is exhausted through

the exhaust tube 34 over the protruded portions 33

The wastewater containing the sludge settled in the sludge

separation tank 3 is returned to the thickening tank 6 through the exhaust

hole 30 , the returning tube 28, and the wastewater intake tube 7 and goes

through the above described processes

FIGS 7 to 9 show a reactor of an integral wastewater treatm ent

plant according to a second preferred em bodim ent of the present

invention As shown in the drawing , the reactor of this em bodim ent

relates to a biological reactor for inducing an anaerobic digestion

A gas intake tube 1 01 instead of the air intake tube is connected to a reactor 100 The reactor 100 is provided with a gas collecting hole 107

for collecting gas generated in each section

A blade assembly 102 comprises a funnel-shaped partition 103, a

cylindrical body 104 coupled on an edge of a circular hole formed on a

central portion of the partition 103 and extended downward, and a blade

105 mounted on the circular hole

Accordingly, the wastewater supplied to the reaction tank 100

passes through the cylindrical body 104 and a space of the blade 105

During this procedure, the wastewater spirally rotates Then, the

wastewater collides with the bottom 106 of the partition to form the

returning flow

At this point, by supplying anaerobic gas such as methane gas and

nitrogen gas, the agitating effect in the reactor can be improved In

addition, gas generated at each section is collected through the gas

collecting hole 107, during which the wastewater at the upper portion is

moved to the lower portion by pressure difference caused by the gas

exhaustion, thereby obtaining reverse agitation effect

During the above procedure, the anaerobic gas can be selectively injected in the reaction tank That is, the agitation effect may be

obtained by supplying only wastewater without injection the gas in the

reaction tank

Such a reactor is an upward flow type reactor Therefore, since

most of the anaerobic microorganism is disposed on the lower portion,

the loss of the microorganism can be minimized

Except the above, the operation of this embodiment is identical to

that of the first embodiment

FIGS 10 to 12 show a third preferred embodiment of the present

invention This embodiment is identical to the first and second

embodiments except for the thickening tank That is, a thickening tank

201 of this embodiment has a guide blade 205 for more effectively

exhausting solid material contained in wastewater

Describing more in detail, the thickening tank 201 comprises a

case 203, a guide blade 205 disposed in the case 203, an air intake tube

207 for supplying air to the case 203, a wastewater intake tube 209, and

exhaust tubes 211 for exhausting solid material

The case 203 is preferably formed in a cylindrical-shape The guide blade 205 is form ed in a wedge-shape and supported by plural

supports 226 on an inner wall of the case 203 Therefore , the intake air

ascends along an inclined surface 21 3 of the guide blade 205

In addition , the exhaust tubes 21 1 , as shown in FIG 1 2 , are

extended in an opposite direction The exhaust tubes 21 1 are also

extended in a tangent direction with respect to the thickening tank 201 ,

thereby increasing the exhaustion eff iciency of the wastewater

In the above-described thickening tank, the wastewater is supplied

through the wastewater intake tube 209 and filled in the whole inner space

of the thickening tank 201 and the reactor

At this point, when the air is injected through the air intake tube 207 ,

the air is m ixed in the wastewater and generates bubbles The bubbles

contact the inclined surface 21 3 of the guide blade 205 and ascend in a

direction of a first arrow The bubbles provide kinetic energy to the

wastewater so that polluting material contained in the wastewater can be

m oved upward

As the bubbles ascend along the inclined surface 21 3 of the guide

blade 205 , the fluid pressure in the vicinity of the lower space of the inclined surface 213 is instantaneously reduced. Therefore, heavy

wastewater moves to the lower space in a direction of a second arrow 217.

At this point, solid material having high density and high specific gravity is

firstly moved to the bottom.

Accordingly, the solid material contained in the wastewater is

moved downward in an opposite direction to a direction where the air

moves.

The above described procedure occurs identically in the first and

second blade assemblies 220 and 222, thereby further improving the

settling effect of the solid material contained in the wastewater.

The wastewater having the high density has high viscosity tending

to adhere to the inner wall 224 of the thickening tank 201. As a result,

the thickening tank 201 remains relatively low density at its center portion

and relatively high density at its inner wall 224. Therefore, to exhaust the

high density wastewater primarily, the two exhaust holes 211 are opened

in turn.

As the wastewater treatment plant is operated, sludge may be

attached on the inner wall 224 of the thickening tank 201 , resulting in the deterioration of the treatment efficiency. To prevent this , a large amount

of concentration water may be supplied in a direction opposing to the

exhaustion direction and then exhausted through the wastewater intake

hole 209 so as to rem ove the sludge attached on the inner wall 224

The operation of the wastewater treatm ent plant according to a

preferred em bodiment of the present invention will be described m ore in

detail in conjunction with the accom panying drawings

As shown in FIGS 1 to 9, wastewater is supplied to the thickening

tank 6 through the wastewater intake tube 7 At this point, wastewater

returned f rom the sludge setting tank 3 is also joined in the thickening tank

6. The wastewater flows in a tangent direction to spirally rotate around

the center of the thickening tank. This spiral m ovem ent is further

enhanced by the rotational force of the first blade assem bly 9 During this

procedure , the solid m aterial contained in the wastewater and the returned

sludge can be easily concentrated and settled by biological absorption .

As the sludge m ay be continuously exhausted under the partitions , the

high density solid m aterial can be separated before the biological

treatment is performed . The wastewater ascended in the thickening tank 6 is directed in the

lower assembly 12 of the first blade assembly 9 through the circular hole

I 3a of the first partition 13. As the wastewater passes through the lower

assembly 12, it rotates in a spiral direction to be agitated At this point,

the air induced through the air intake tube 8 is mixed with the wastewater

to generate bubbles that collide with each other

The wastewater and bubbles passed through the lower assembly

12 is directed to the upper assembly 11 having the larger volume for the

more active agitation and collision between the bubbles The larger

volume extends the staying time of the bubbles, thereby improving the

dissolution of gas.

The wastewater and bubbles passed through the upper assembly

I I is directed to the upper space 36 and collide with the bottom 20a of the

second partition 20. As a result, the wastewater moves downward in the

upper space 36, thereby forming over flow.

As the over flow is formed and the collision between the bubbles

are actively realized, the decomposing efficiency of the polluting material

can be further improved At this point, part of the wastewater is directed to the second blade

assem bly 1 9 and treated as in the f irst blade assem bly 9.

The treated wastewater in the first reactor 1 is directed to the

second reactor 2 through the pipe 26 and further treated as in the f irst

reactor 1 .

The wastewater exhausted f rom the second reactor 2 is directed to

the sludge separation tank 3 and m oved downward as it contact the

inclined plate 31 . During this procedure, the sludge is settled on the

bottom 29. The settled sludge is directed to the exhaust hole along the

inclined surface of the bottom 29 As the sludge separation tank 3 is

form ed in the V-shape such that the flow speed at the lower portion is

higher than at the upper portion , the sludge can be m ore effectively

directed to the exhaust hole 30. Sludge separated high quality water

m oves over the protruding portions 33 of the plate 32 and is then

exhausted outside through the exhaust tube 34

The wastewater induced through the exhaust hole 30 is returned

to the wastewater intake tube 7 through the returning tube 28 and treated

again as in the above . The test result of the treatment efficiency obtained through the

above-described procedure is as follows

The integral wastewater of the present invention has following

advantages.

First, since the moving distance of fluid in horizontal and vertical

directions is increased, the agitation effect is improved by turbulence and

shearing force.

Second, the accumulation of the sludge in the reactor can be

controlled, enough time for treating wastewater by the microorganism

while maintaining high density microorganism.

Third, the agitation effect can be maximized by the buoyancy energy of the air, thereby reducing the treatm ent costs.

Fourth , when the treatm ent is an anaerobic digestion , since the

gas can be collected at each section , the gas can be easily separated and

collected .

Fifth , since the reactor is an upward f low type , the loss of the

m icroorganism can be m inim ized as it is disposed at the lower end .

Sixth , since the thickening tank is integrated in the reactor, a

special thickening tank is not required .

Seventh , since the sludge is exhausted at the lower end of the

sludge iseparation tank, the settling speed of the sludge can be increased

Eighth , since the guide blade is m ounted in the thickening tank, the

sludge having high density and high specif ic gravity can be effectively

settled by the difference in the fluid pressure

Although the invention has been described above with reference to the

embodiment of the invention, the invention is not limited to the embodiment

described above Various modifications and variations of the embodiment

described above will occur to those skilled in the art, in light of the above

teachings.

Claims

WHAT IS CLAI M ED IS

1 An integral wastewater treatm ent plant com prising

a reaction tank for storing wastewater, the reaction tank being

divided into plural spaces in a vertical direction by at least one partition ,

a thickening tank for settling sludge contained in the wastewater,

the thickening tank being integrally m ounted under the reaction tank and

provided with a wastewater intake tube and an air intake tube,

agitating means for agitating the wastewater supplied from the

thickening tank, allowing bubbles generated by air induced through the air

intake tube to collide with each other to increase dissolved oxygen , and

decom posing polluting material by aeration m icroorganism by extending a

staying time of the bubbles, and

a sludge separation tank for settling sludge contained in the

wastewater exhausted from the reaction tank and returning the wastewater

to the thickening tank, the sludge separation tank being integrally

connected to the reaction tank

2 An integral wastewater treatm ent plant com prising

a reaction tank for storing wastewater, the reaction tank being divided into plural sections by at least one partition , each of the sections

being provided with a gas intake hole and a gas collecting hole,

agitating m eans for agitating the wastewater supplied f rom the

thickening tank, allowing bubbles generated by gas induced through the

gas intake tube to collide with each other, and decom posing polluting

m aterial by anaerobic m icroorganism by extending a staying tim e of the

bubbles, and

a sludge separation tank for settling sludge contained in the

wastewater exhausted from the reaction tank and returning the wastewater

to the thickening tank, the sludge separation tank being integrally

connected to the reaction tank

3 A plant of one of claim s 1 and 2 wherein a reactor is further

provided between the reaction tank and the sludge separation tank

4 A plant of claim 1 wherein the agitating means com prises a

blade assem bly including a lower assem bly for firstly agitating the

wastewater induced through a circular hole form ed on the partition , the

assem bly being m ounted on an edge of the hole and an upper assem bly

for secondary agitating the wastewater passed through the lower assem bly, the upper assem bly being mounted on a top of the lower

assem bly.

5 A plant of claim 4 wherein the lower assem bly com prises a

cylindrical portion mounted on the edge of the circular hole and a lower

blade m ounted on a top of the cylindrical portion to agitate the

wastewater

6 A plant of claim 4 wherein the upper assem bly com prises a

cylindrical portion having a diameter larger than that of the cylindrical

portion of the lower assem bly so that the cylindrical portion of the lower

assem bly can be disposed in the cylindrical portion of the upper assem bly

and an upper blade m ounted on the cylindrical portion of the upper

assem bly to agitate the wastewater

7 A plant of claim 2 wherein the agitating means com prises a

blade assem bly including a funnel-shaped partition , a hollow body

connected to an edge of a circular hole form ed on a central portion of the

partition , and a blade m ounted on the circular hole

8 A plant of any one of claim s 5 to 7 wherein each of the upper

and lower blades has plural blades overlapped on each other in a circum ference direction , the blades being designed to be inclined so that

spaces between the blades through which the wastewater flows can be

form ed .

9. A plant of one of claim s 1 and 2 wherein the sludge separation

tank com prises a body having a sectional area that is reduced at it goes

from an upper portion to a lower portion , an inclined plate m ounted on the

body to direct the wastewater downward , a plate m ounted in the body and

spaced away from the inclined plate , the plate being provided with a

protrude portion through which sludge separated high quality water passes,

and an exhaust hole form ed on a corner of a bottom of the body to return

the wastewater to the wastewater intake tube .

1 0. A plant of claim 9 wherein the bottom of the sludge separation

tank is inclined toward the exhaust hole such that settled sludge can be

m oved to the exhaust hole.

1 1 . A plant of claim 1 wherein the thickening tank com prises a

case, a guide blade disposed in the case , an air intake tube for supplying

air into the case , a wastewater intake tube for supplying wastewater, and

an exhaust hole f or exhausting solid m aterial .

12. A plant of claim 11 wherein the guide blade is formed in a

wedge-shape so that the air induced through the air intake tube can be

moved upward along an inclined surface of the guide blade.