APPARATUS FOR CLARIFYING A SLUDGE-CONTAINING EFFLUENT
The invention relates to apparatus for clarifying a
sludge-containing effluent, of the kind that includes:
5 - a clarification basin for clarification by
settling of sludge that is deposited on the bottom
of the basin while clarified water is evacuated at
the upper level of the basin;"
at least one arm able to move above the upper
10 level of the liquid in the basin to sweep all the
surface of the liquid;
at least one trough supported by the arm so that
it is immersed over part of its height in the
liquid in the basin;
15 - suction tubes held relative to the trough,
extending downwardly toward the bottom of the
basin, each suction tube including at the top a
vertically adjustable sleeve opening into the
trough at a level lower than the level of the
20 liquid in the basin, the downwardly extending
tubes enabling delivery into the trough of liquid
and sludge coming from the bottom of the basin,
and
means for evacuation of sludge from the trough.
25
The invention more particularly, but not exclusively,
concerns apparatus for clarifying an effluent produced
by the treatment and purification of waste water in
which the sludge is formed mainly by the purifying
30 biomass.
Apparatus for clarifying an effluent, known as a
clarifier, enables:
clarification of the effluents,
35 - separation of the purifying biomass and the most
dense particles of the treated effluent by gravity
settling,
WO 2014/057452 ~ 2 ~ PCT/IB2013/059265
thickening, that is to say dens if ication, of this
sludge,
collection and retention of sludge which must be
extracted:
5 - and recirculated upstream in the treatment
line,
and/or evacuated to the sludge treatment and/or
evacuation line.
10 The collection and the extraction of the sludge from
the bottom of the structure in a limited time is of
great economic and technical importance in claritiers.
In fact, if the extraction of sludge is insufficient
15 and/or unevenly effective over the whole of the surface
of the structure, sludge accumulates on the bottom of
the structure; portions of this sludge are deprived of
oxygen (prolonged anoxia), which causes their physical,
mechanical and biological deterioration and as a
20 consequence of this serious disturbances throughout the
treatment line, such as:
deterioration of the quality of the treated
water: increased contents of materials in
suspension and phosphorus,
25 - degraded settling of the sludge and therefore
the treatment capacity of the clarifier, i.e.
its technical/economical effectiveness,
degraded purification quality of the sludge and
therefore the effectiveness of treatment by the
30 whole of the purification line,
degraded treatability of the sludge,
all of which has an economic impact on the treatment
cost.
35 Moreover, the accumulation of sludge on the bottom of
the structure leads to high mechanical stresses on the
sludge take-up plant and underlying reliability
problems in respect of this plant, which:
WO 2014/057452 - 3 - PCT/IB2013/059265
reduces the availability of the structures, and
increases maintenance (labor) costs and plant
renewal costs.
A contrario, because the extracted flow of sludge is:
recirculated to the treatment line, including the
clarifier itself, it must be minimized in order to
limit:
the mass load per unit surface area of the
clarifier (kg of dry materials/m2. h) ,
the sludge extraction plant investment costs
(size of extraction and recirculation pumps)
and operating costs,
and/or evacuated to the sludge treatment unit, it
must be minimized in order to optimize the sizing
and the technical/economic operation of the sludge
line.
The efficacy, ruggedness and reliability of the device
for taking up sludge from the bottom of the structure
are therefore of great importance in sludge extraction:
necessary to limit the residence time of the
sludge in the structure, and
- sufficient not to increase the hydraulic and mass
loads on the structures and the treatment plant of
the water line and/or the sludge evacuation and
treatment line.
The clarification apparatus at which the invention is
30 aimed, also known as "sucked" clarifiers, is well
suited to large clarification structures, that is to
say to structures in which the basins, in theory
circular, have a diameter that is generally greater
than 25 m. The suction tubes are immersed directly in
35 the bed of the sludge that has settled on the bottom of
the structure and sweep the whole of the bottom
surface. These tubes open into the sludge take-up
10
20
25
WO 2014/057452 - 4 - PCT/IB2013/059265
trough on the surface, the hydraulic level of which is
kept lower than that of the clarifier.
To enable individual adjustment of the suction rate of
5 each of the tubes, each tube is provided with a fixed
but adjustable telescopic sleeve at the overspill
level. This sleeve is installed at the outlet of each
suction tube and the liquid and the sludge overspill
over the upper end of the telescopic sleeve. This
10 difference between the liquid level in the clarifier
and the liquid level at the outlet at the top of the
sludge overspill telescopic tubes in the trough
provides the motive force for the suction and therefore
extraction of the sludge. The adjustment of the
15 position of each sleeve must ensure evacuation of the
sludge at the bottom of the structure such that there
is no accumulation and the bed of sludge has
substantially the same thickness over all of the
surface of the bottom of the structure.
20
In the prior art, the level of the upper edge of the
sleeves is adjusted by means of chains or threaded rods
or notched rods to which the sleeves are attached, the
chains or rods being themselves attached to a support.
25
The adjustment of the levels of each sleeve requires:
a laborious relatively long iterative manual
process of trial and error, taking of the order of one
day for a structure having a diameter equal to or
30 greater than 25 m, aiming to measure and to obtain a
necessary and sufficient sludge extraction mass flow
rate for each of the tubes,
- human intervention and manipulation on a turning
bridge generally constituting the mobile arm, with
35 risks of falling in that must be limited for reasons of
the safety of the operators and the plant.
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The flow rates of sludge to be evacuated are variable,
notably in the case of purification station sludge,
depending on atmospheric constraints, notably in the
event of storms. Under other conditions, however, the
5 flow rate of sludge to be evacuated can be much lower.
In practice, in prior art clarifiers, the levels of the
sleeves are adjusted for the highest flow rate to be
evacuated. The frequency of adjustment of the levels of
10 the sleeves is limited and in no case is the level of
the sleeves adjusted continuously and/or in real time
to suit the real requirements of the station.
The liquid level of the sludge in the take-up trough
15 must be maintained:
below the liquid level in the clarifier to enable
extraction of the sludge by the motive force
aspirating the sludge caused by the difference in
levels; and
20 - below the outlet levels of the suction tubes,
meaning that the tube must necessarily emerge
relative to the liquid level in the trough, so as
to be able to balance the flow rates through each
suction tube in order to obtain a good
25 distribution of the extracted mass flows between
the suction tubes; the flow rate through each
suction tube is inversely proportional to the
viscosity of the fluid conveyed' and therefore the
sludge concentration.
30
35
The differences in hydraulic levels are maintained
thanks to permanent external pumping to evacuate sludge
from the trough, constituting the means for evacuation
of this sludge.
The upper end of the sleeves of the suction tubes
should therefore be, at one and the same time:
WO 2014/057452 - 6 - PCT/IB2013/059265
continuously sufficiently high to emerge from the
liquid level in the trough regardless of the flow
rate at which the station is operating, and
as low as possible relative to the upper hydraulic
level in the basin of the clarif ier to ensure a
maximum flow rate through the suction tubes and to
enable extraction of the necessary and sufficient
masses of sludge when the station is functioning
at its maximum hydraulic and/or mass capacity.
To satisfy these two antagonistic constraints, the
outlet level of the sleeves of the suction tubes being
in theory adjusted once and for all, and not
continuously adjustable, this requires the pumping flow
rate in the trough to be permanently as high as
possible so that the adjustment of the sleeves of the
tubes is correct, that is to say with the sleeves
emerging from the water during rain and/or when the
station is operating with the maximum flow rate or
load.
Depending on these adjustments, and the resulting
operation of the apparatus, the sludge extraction and
recirculation flow rate is maintained constant and
25 maximum, with no possibility of regulation,
irrespective of the real hydraulic conditions under
which the station is operating and the real sludge
extraction requirements.
30 Depending on these adjustments, and on the resulting
operation, the sludge extraction and recirculation flow
rate is, in fact, too high during periods of low
hydraulic and/or mass flow rate in the operation of the
station (nocturnal periods, periods of dry weather,
35 less polluted effluents leading to lower production of
sludge), causing in the water line:
overconsumption of pumping energy (by a
recirculation pump),
10
15
WO 2014/057452 - 7 - PCT/IB2013/059265
unnecessary wear of the pumping plant with
conseguences for maintenance costs and plant
renewal frequency,
~ mass hydraulic overloads on the clarifier that can
5 lead to the entrainment of materials in suspension
in the clarified treated water, i.e. deterioration
in the guality of the treated water,
an increased risk of entrainment of air bubbles
and therefore of unpriming of the device for
10 evacuating sludge from the trough.
Depending on these adjustments, and the resulting
operation, the concentration of the extracted sludge
is, in fact, lower than necessary most of the time, and
15 the volumes of sludge to be evacuated and treated are
therefore unnecessarily higher than necessary in
periods of low hydraulic and mass flov; rates in the
operation of the station, the consequence of which is
to induce in the sludge line:
20 - overconsumption of pumping energy,
hydraulic overloads of the sludge line (as a
result of degraded operating conditions), and/or
increased operating times of the treatment unit,
increasing electrical power consumption, plant
25 wear and labor costs,
substantial increases in consumption of reagents,
possible reduction of the dry content of the
treated sludge and therefore the volumes of sludge
treated, which leads to an increase in treated
30 sludge handling and evacuation/management costs.
Moreover, in the prior art, despite the usual
precautions in respect of the adjustment of the
sleeves, the risk of totally immersing some or all of
35 the suction tubes if the level in the take-up trough
rises above the overspill level of the sleeves is not
controlled in the case of:
exceptional hydraulic flov/ rates,
WO 2014/057452 ~ 8 ~ PCT/IB2013/059265
malfunctioning and/or stopping of the pump for
evacuation of sludge from the trough, which can
lead to the accumulation of fibrous waste and
chaff at the level of the devices for adjustment
5 of each of the telescopic sleeves equipping the
suction tubes, with resulting risks in respect of
the service life of the plant and the need for
time-consuming cleaning operations that are
hazardous for personnel and plant.
10
The most important object of the present invention is
to provide apparatus for clarifying sludge-containing
effluent of the type defined above that makes it
possible:
15 - to reduce the sludge extraction flow rate and to
improve the control of the residence time of the
sludge on the bottom of the structure of a
clarifier with suction tubes,
to reduce in this way the operating costs of the
20 clarifiers, in particular the sludge recirculation
pumping costs,
to reduce the times of operation of the pumping
plant and therefore the maintenance and
replacement costs for this plant.
25
More generally, the invention proposes to make more
reliable:
the operation of the clarifiers with suction
tubes, and therefore
30 - the operation of the water and sludge lines of a
station for treatment of urban and/or industrial
waste water.
In this context, the particular objectives set for the
35 invention are:
to adapt to the real requirements of the station
and in real time the flow rate of extraction of
WO 2014/057452 - 9 - PCT/IB2013/059265
sludge from a clarifier for at least one suction
tube, and
to eliminate the risk of totally immersing at
least one suction tube.
To this end, in accordance with the invention,
apparatus for clarifying a sludge-containing effluent
of the kind defined above is characterized in that the
sleeve of at least one suction tube is free to slide
vertically relative to the mobile arm supporting the
trough and to the tube and in that the sleeve has a
reserve of buoyancy necessary and sufficient for
keeping the overspill end of the sleeve in the trough
continuously out of the water so that the overspill
level of the sleeve adapts automatically relative to
the level of the liquid and sludge in the trough.
Each suction tube is preferably equipped with a sleeve
free to slide vertically relative to the mobile arm and
20 to the tube and each sleeve preferably has a reserve of
buoyancy necessary and sufficient for keeping the
overspill end of the sleeve in the trough continuously
out of the water.
Each sleeve may be made from a material the density of
which is higher than that of the liquid in the trough
and to provide the reserve of buoyancy the sleeve
includes a floating device that is immersed in the
liquid in the trough and that holds the upper edge of
the sleeve at a constant distance above the liquid
level in the trough. The sleeves and the suction tubes
may be made of polyvinyl chloride.
The floating device may consist of a float that
35 surrounds the corresponding sleeve. The float may have
the shape of a ring or a torus. Each float may be made
of expanded polystyrene.
10
25
30
WO 2014/057452 - 10 - PCT/IB2013/059265
The floating device is advantageously adjustably
mounted on the sleeve so that its position is
adjustable in the heightwise direction.
5 The various floating devices equipping the suction
tubes of the same clarifier may differ in terms of size
and/or the density of the materials so that the
positions of the overspill ends of each of the sleeves
can vary from one tube to another and thus enable
10 individual adjustment of the aspiration capacity of
each suction tube.
The apparatus may include a vertical guide device for
the movement of each sleeve free to slide vertically
15 relative to the mobile support arm.
The apparatus advantageously includes a vertical guide
device for the movement of each sleeve free to slide
vertically relative to the mobile support arm. The
20 guide device may include a flat part similar to a
ladder the lower portion of which is forceps-shaped
with two branches that engage in diametrically opposite
holes at the upper end of the sleeve, the vertical
plane of the part being oriented at a right angle to
25 the radial direction of the arm and the trough, guide
plates fixed to the arm including a slot through which
the part passes vertically and which guides it. The
slot may be equipped with a shoe made from a material
having a low coefficient of friction.
30
Alternatively, each sleeve may be made from a material
the apparent density of which is less than that of the
liquid in the trough and the basin and is equipped with
an adjustable ballast weighing on the guide system,
35 notably a guide rod, for the adjustment of the position
of the upper overspill end of the sleeve in the trough.
WO 2014/057452 - 11 - PCT/IB2013/059265
The floating device providing the reserve of buoyancy
is optimized to facilitate the free vertical movement
of the sleeve and not to disturb the horizontal flow of
sludge evacuated from the trough.
5
Apart from the features explained above, the invention
consists in a certain number of other features
described more explicitly hereinafter with reference to
the appended drawings, which are in no way limiting on
10 the invention. In these drawings:
Figure 1 is a partial diagrammatic vertical section of
clarification apparatus in accordance with the
invention, the mobile arm not being represented.
Figure 2 is a perspective view, with parts removed, of
a trough with four sleeves below a mobile arm of
clarification apparatus in accordance with the
invention.
Figure 3 shows in elevation a sleeve provided with its
float and vertical guide means.
Figure 4 is an exploded view in elevation of the
25 elements from figure 3, and
Figure 5 is a diagrammatic perspective view from above
of part of the trough and the sleeves of clarification
apparatus in accordance with the invention.
30
Referring to figure 1 of the drawings, there can be
seen apparatus A for clarifying effluent 1 v/hich in the
embodiment represented arrives via a pipe in the lower
part of the apparatus A, v/hich includes a clarification
35 basin 2. The basin 2 is generally circular and its
diameter is at least 20 m for the kind of clarifier to
which the invention more particularly relates. Only
half of the basin 2 is represented in figure 1, the
15
20
WO 2014/057452 - 12 - PCT/IB2013/059265
other half being symmetrical with respect to the
vertical geometrical axis Y-Y of the circular basin.
Sludge is deposited on the bottom of the basin to form
5 a layer 3 and clarified water 4 is evacuated at the
upper level of the apparatus over an overspill weir 5
and is collected in a gully 6 to be recovered by means
that are not represented. In accordance with the figure
1 embodiment/ the bottom 2p of the basin 2 has a more
10 or less pronounced slope or is horizontal.
The apparatus A includes at least one mobile arm 7 that
can be seen in figure 2 but is not represented in
figure 1. The arm 7 extends radially from the central
15 area of the basin 2 where it is supported and driven in
rotation by a central or peripheral motor (not
represented) . The radially outermost end of the arm 7
is supported by a support leg, not represented,
provided in its lower part with a rolling member
20 resting on a rolling track 2b integral with the
cylindrical wall of the basin 2, optionally projecting
radially outward. The arm 7 constitutes a turning
bridge, represented diagrammatically, which enables
sweeping of all the surface of the liquid in the basin
25 2 by a 360° rotation. The arm 7 is designed to allow an
operator to move safely on the arm to carry out the
necessary adjustments of the apparatus.
Although clarification basins are generally circular,
30 the invention applies equally to rectangular basins
surmounted by an arm mobile in translation along one
dimension of the basin, notably the length.
At least one trough 8 is supported by the arm 7, for
35 example with the aid of tie-rods that are not
represented, so that it is immersed over a portion of
its height in the liquid in the basin 2. The trough 8
has a substantially rectangular cross section open at
WO 2014/057452 - 13 - PCT/IB2013/059265
the top and closed on all its other sides. In figure 2,
a longitudinal wall of the trough is opened up to
expose the interior of the trough. The upper edge 8b of
the wall of the trough is above the upper level 4a of
5 the clarified water, that is to say above the upper
level of the liquid in the basin 2.
The bottom 8c of the trough is substantially horizontal
from the radially outermost end to a well 8d provided
10 at the radially innermost end of the trough 8. A
vertical branch 9a of a siphon 9 dips into the well 8d
and the other vertical branch 9b of the siphon
constitutes a mobile hydraulic seal. A vertical pipe 10
is connected to the hydraulic seal for the evacuation
15 of sludge taken up from the bottom of the well 8d via
the siphon 9. The maximum motive head because of the
difference in liquid level for the evacuation of sludge
in the pipe 10 is equal to the head difference between
the upper level 4a of the clarified water in the basin
20 and the outlet level of the suction tubes above the
level in the trough.
The pipe 10 is connected to a sludge take-up ditch 11.
The ditch 11 is divided into two compartments 12, 13 by
25 a partition 12a forming an overspill weir. The sludge
arrives in the compartment 12 and the pump 14 is in the
other compartment 13 into which the sludge overspills.
The pump 14 constitutes means for evacuation of the
sludge to an aeration basin that is not represented.
30 The flow rate of the pump 14 is regulated. The feed
pipe 1 for effluent to be treated is connected to a
cylindrical vertical part la around the pipe 10.
Suction tubes Tl, T2 are secured to the underside of
35 the trough 8 and extend downwardly toward the bottom of
the basin 2 so that their lower end enters the bed 3 of
sludge. The tubes Tl, T2 are at different radial
distances from the geometrical axis Y-Y and there is a
WO 2014/057452 - 14 - PCT/IB2013/059265
sufficient number of them to ensure satisfactory
evacuation of the deposited sludge. In accordance with
the embodiment represented in figure 1, for simplicity,
only two tubes Tl, T2 have been represented, but the
5 number of tubes may be greater than this and as high as
20 or more. The tubes Tl, T2 may be fixed under the
bottom 8c of the trough, which includes orifices in
line with the tubes Tl, T2.
10 Each tube Tl, T2 includes in its upper part a sleeve
Bl, B2 that opens into the trough 8 at a level 15 lower
than the level 4 a of the liquid in the basin. The
difference between the liquid level 4a in the clarifier
and the level 15 at which sludge overspills into the
15 trough at the outlet from the sleeves provides the
motive force for suction and extraction of the sludge
from the bottom of the clarifier 2. The sleeves Bl, B2
are of cylindrical tubular shape and are enqaged inside
the tubes Tl, T2.
20
In accordance with the invention, for at least one
suction tube, and preferably for each suction tube, the
sleeve Bl, B2 is free to slide vertically relative to
the associated tube and the mobile arm 7. The vertical
25 sliding movement between the sleeve Bl, B2 and the
associated tube Tl, T2 is almost completely sealed by
means of appropriate seals.
Each sleeve Bl, B2 has a reserve of buoyancy necessary
30 and sufficient to maintain the upper, overspill end El,
E2 of the sleeve continuously above the water in the
trough. The overspill level of the sleeve is
automatically adjusted relative to the level 16 of the
liquid and the sludge in the trough 8.
35
To provide this reserve of buoyancy, the sleeve Bl, B2
is advantageously provided with a floating device
consisting of a float Fl, F2 that is immersed in the
WO 2014/057452 - 15 - PCT/IB2013/059265
liquid in the trough 8 and maintains the upper edge of
the sleeve at a constant distance above the level 16 of
liquid in the trough. As can be seen in figures 2 to 4,
the floats can have a ring or torus shape to surround
5 the corresponding sleeve Bl, B2.
Each float is mounted on the sleeve so as to be
adjustable in the vertical direction, in particular by
screwing it relative to said sleeve, by means of a
10 helicoidal open clamping ring J fastened to the sleeve
(figure 4) so that its position is easily adjustable in
the heightwise direction.
The floats Fl, F2 may be made from expanded polystyrene
15 or some other material of lower density than the liquid
in the trough 8. With such a float, the corresponding
sleeve may be made from a material the density of which
is higher than that of the liquid in the trough. The
sleeves Bl, B2 and the tubes Tl, T2 are advantageously
20 made of polyvinyl chloride (PVC).
Alternatively, each sleeve may be produced with an
apparent density lower than that of the liquid in the
trough and the basin, in which case the reserve of
25 buoyancy is inherent to the sleeve itself. For the
adjustment of the position of the upper overspill end
of the sleeve in the trough, there is then provided an
adjustable ballast acting on the sleeve to weigh on the
mobile guidance system, notably a guide rod. In
30 accordance with this variant the inherent density of
the material of the sleeve may be either less than that
of the liquid or greater than the.latter, in which case
closed voids are provided in the material to reduce the
apparent density.
35
The various floating devices, or floats Fl, F2,
equipping the suction tubes Tl, T2 of the same
clarifier may differ in terms of size and/or the
WO 2014/057452 - 16 - PCT/IB2013/059265
density of the material used so that the overspill ends
El, E2 of each of the sleeves can vary from one tube to
another and therefore allow individual adjustment of
the aspiration capacity of each suction tube.
5
As shown in figures 2 to 4, each sleeve such as Bl is
equipped with a vertical guide device 17 adapted to
retain the sleeve Bl along its vertical geometrical
axis of movement within the suction tube Tl fixed
10 relative to the trough 8 and the arm 7.
In accordance with the embodiment of figures 2 to 4,
the guide device 17 includes a flat part 18 similar to
a ladder, the lower portion 19 of which is forceps-
15 shaped with two branches that engage in diametrically
opposite holes at the top end of the sleeve Bl. The
upper end 20 of the part 18 is of closed semicircular
shape to constitute a handle facilitating grasping of
the part 18 for vertical movement. The vertical plane
20 of the part 18 is oriented at a right angle relative to
the radial direction of the arm 7 and the trough 8.
Guide plates 21 (figures 2 and 5) fixed under the arms
7 include a slot 22 orthogonal to the radial direction.
The part 18 passes vertically through this slot 22,
25 which guides it. The slot 22 is advantageously equipped
with a shoe 23 made from a material with a low
coefficient of friction, notably
polytetrafluoroethylene (PTFE), making it possible to
limit the risk of abrasion and to render the device
30 long-lasting. The shoes 23 may be made from any
material identified for its properties of low friction
and mechanical strength.
This being the case, the adjustment and the operation
35 of clarifying apparatus in accordance with the
invention are as follows.
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For any flow rate of effluent to be treated arriving
via the pipe 1 and to which there corresponds a level
16 in the trough 8 and a bed 3 of sludge, the operator
adjusts the position of the sleeves Bl, B2 by adjusting
5 the position of the floats Fl, F2. For each sleeve,
this adjustment is effected so that the upper overspill
end El, E2 of the sleeve is at an appropriate level,
lower than the level 4a, of course, to ensure a
satisfactory flow rate of evacuation of the sludge via
10 the corresponding tube Tl, T2.
When this adjustment has been carried out, a variation
in the height of the level 16 leads to a corresponding
variation in the height of the upper ends El, E2, which
15 therefore remain at a constant distance above the level
16, so that there is no other adjustment to be carried
out when the level in the trough 8 varies.
In accordance with the invention, the overspill level
20 of the suction tubes and the sleeves therefore depends
on the level of sludge in the trough 8 and consequently
becomes intrinsically linked to the flow rate of
evacuation of sludge from the trough. As a result of
this the flow rate of evacuation of sludge from the
25 trough 8, already controlled and/or being easily
controllable in real time according to the real
requirements of the station, enables optimum control in
real time of the flow rate of extraction of sludge from
the clarifier with no automation additional to that
30 already existing and without human intervention.
Moreover, the present invention advantageously
eliminates all risk of totally immersing the suction
tubes Tl, T2 and the sleeves Bl, B2 the overspill end
35 of which remains above the level 16 of liquid in the
trough 8 by virtue of their buoyancy.
WO 2014/057452 - 18 - PCT/IB2013/059265
In contrast to this, in a conventional clarifier not
using the invent! on, the sleeves would be fixed
relative to the arm 7. When an adjustment of the
position of the upper end has been carried out, this
5 position relative to the arm 7 and to the bottom of the
trough 8 remains fixed. If the level 16 of liquid in
the trough varies, the distance between the overspill
end of the sleeve and the liquid level in the trough
varies, whereas in accordance with the invention this
10 distance remains constant and enables self-regulation
of the level 16 of liquid in the trough 8. In fact, in
accordance with the invention, if the level 16 falls,
the overspill end of the sleeve also falls, which
increases the motive hydraulic head and increases the
15 flow rate of sludge aspirated via the suction tube Tl,
T2 to cause the liquid level in the trough 8 to rise.
Conversely, if the level in the trough 8 rises, the
overspill end of the sleeves also rises, which reduces
the motive hydraulic force.
20
The means proposed by the invention are:
simple,
rugged,
of relatively low cost to purchase,
25 - very easy to fit to an existing clarifier.
They do not necessitate any modification of civil
engineering structures and/or plant that would impact
on the warranties of the structures. They do not lead
to additional maintenance costs. They require little if
30 any modification of existing automatic control and
regulation systems in treatment stations.

CLAIMS
1. An apparatus for clarifying a sludge-containing
effluent, comprising:
5 - a clarification basin (2) for clari fleation by
settling of sludge that is deposited on the
bottom of the basin while clarified water is
evacuated at the upper level (4a) of the basin;
at least one arm (7) able to move above the
10 upper level of the liquid in the basin to sweep
all the surface of the liquid;
at least one trough (8) supported by the arm,
so that it is immersed over part of its height
in the liquid in the basin;
15 - suction tubes (Tl, T2) held relative to the
trough, extending downwardly toward the bottom
of the basin, each suction tube including at
the top a vertically adjustable sleeve (Bl, B2)
opening into the trough at a level (15) lower
20 than the level (4a) of the liquid in the basin,
the downwardly extending tubes enabling
delivery into the trough of liquid and sludge
coming from the bottom of the basin, and
means for evacuation of sludge from the trough,
25 characterized in that the sleeve (Bl, B2) of at least
one suction tube (Tl, T2) is free to slide vertically
relative to the mobile arm (7) supporting the trough
and to the tube (Tl, T2) and in that the sleeve (Bl,
B2) has a reserve of buoyancy necessary and sufficient
30 for keeping the overspill end (El, E2) of the sleeve in
the trough (8) continuously out of the water so that
the overspill level of the sleeve adapts automatically
relative to the level (16) of the liquid and sludge in
the trough.
35
2. The apparatus as claimed in claim 1, characterized
in that each suction tube (Tl, T2) is equipped
with a sleeve (Bl, B2) free to slide vertically
WO 2014/057452 - 20 - PCT/IB2013/059265
relative to the mobile arm (7) and to the tube
(Tl, T2) and in that each sleeve has a reserve of
buoyancy necessary and sufficient for keeping the
overspill end of the sleeve (Bl, B2) in the trough
5 {8) continuously out of the water.
3. The apparatus as claimed in claim 1 or 2,
characterized in that each sleeve (Bl, B2) is made
from a material the density of which is higher
10 than that of the liguid in the trough (8) and that
to provide the reserve of buoyancy the sleeve (Bl,
B2) includes a floating device that is immersed in
the liquid in the trough and that holds the upper
edge of the sleeve at a constant distance above
15 the liquid level (16) in the trough (8).
4. The apparatus as claimed in claim 3, characterized
in that the sleeves (Bl, B2) and the suction tubes
(Tl, T2) are made of polyvinyl chloride.
20
5. The apparatus as claimed in claim 3 or 4,
characterized in that the floating device consists
of a float (Fl, F2) that surrounds the
corresponding sleeve (Bl, B2) .
25
6. The apparatus as claimed in claim 5, characterized
in that the float (Fl, F2) has the shape of a ring
or a torus.
30 7. The apparatus as claimed in claim 5 or 6,
characterized in that each float (Fl, F2) is made
of expanded polystyrene.
8. The apparatus as claimed in any one of claims 3 to
35 7, characterized in that the floating device is
adjustably mounted on the sleeve (Bl, B2) so that
its position is adjustable in the heightwise
direction.
WO 2014/057452 - 21 - PCT/IB2013/059265
9. The apparatus as claimed in any one of claims 3 to
8, characterized in that the various floating
devices equipping the sleeves (Bl, B2) of the same
5 clarifier differ in terms of size and/or the
density of the materials so that the positions of
the overspill ends of each of the sleeves can vary
from one tube to another and thus enable
individual adjustment of the aspiration capacity
10 of each suction tube.
10. The apparatus as claimed in any one of the
preceding claims, characterized in that it
includes a vertical guide device (17) for the
15 movement of each sleeve (Bl, B2) free to slide
vertically relative to the mobile support arm (7).
11. The apparatus as claimed in claim 1 or 2,
characterized in that each sleeve is made from a
20 material the apparent density of which is less
than that of the liquid in the trough and the
basin and is equipped with an adjustable ballast
weighing on the guide rod for the adjustment of
the position of the upper overspill end of the
25 sleeve in the trough.
12. The apparatus as claimed in any one of the
preceding claims, characterized in that it
includes a vertical guide device (17) for the
30 movement of each sleeve (Bl, B2) free to slide
vertically relative to the mobile support arm (7).
13. The apparatus as claimed in claim 12,
characterized in that the guide device (17)
35 includes a flat part (18) similar to a ladder the
lower portion (19) of which is forceps-shaped with
two branches that engage in diametrically opposite
holes at the upper end of the sleeve (Bl) , the
2014/057452 - 22 - PCT/IB2013/059265
vertical plane of the part (18) being oriented at
a right angle to the radial direction of the arm
(7) and the trough (8), guide plates (21) fixed to
, the arm (7) including a slot (22) through which
the part (18) passes vertically and which guides
it.
14.The apparatus as claimed in claim 13,
characterized in that the slot (22) is equipped
with a shoe (23) made from a material having a lov;
coefficient of friction.