Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Biofiltering Device for Treating Wastewater
The present invention pertains to improvements in the field of
wastewater treatment. More particularly, the invention relates to a
biofiltering
device for treating wastewater discharged from a septic tank.
Small wastewater treatment systems are typically designed so that raw
wastewater generated by a residence is discharged directly into a septic tank.
Once discharged into the septic tank, the effluent is allowed to partially
settle
and is then passed into a dosing chamber. From the dosing chamber, the
effluent
is fed into a filtering medium, e.g. a trickling bed filter, and then
collected in a
central drain pipe. Once the effluent is collected in the central drain pipe,
it is
then dispersed to a plurality of parallel drain pipes positioned generally
equidistant from one another across a specified area underneath the ground.
Each drain pipe has a plurality of orifices which allow the effluent to be
released into the surrounding environment.
Various filtering media and devices have been proposed for treating the
wastewater discharged from a septic tank. For example, US Patent
No. 5,206,206 discloses the use of pre-treated peat in biofilters for
wastewater
treatment. The pre-treated peat comprises a mixture of pre-sieved peat with a
Fe-containing compound and lime. A filter-bed constituted of a layer of such a
pre-treated peat disposed between upper and lower layers of calcareous stones
is
arranged inside a filtration column. A rotary distribution system including a
perforated arm is used for distributing the wastewater to be treated on top of
the
filter-bed. Since the pressure of the incoming wastewater serves to displace
the
perforated arm and the wastewater entering the distribution system contains
suspended particles of organic and inorganic materials, the suspended
particles
often clog the rotation mechanism, thus rendering the distribution system
inoperative.
US Patent No. 5,618,414 also discloses a wastewater treatment system
utilizing peat as a filtering medium. Such a treatment system comprises a
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container having an upper portion, a lower portion, at least one waster water
inlet in the upper portion of the container for receiving the wastewater, and
an
opening in the lower portion of the container for allowing the treated water
to
escape the container. At least one elongated hollow casing is mounted within
the lower portion of the container. The casing has an open bottom surface and
defines at least two treatment chambers within the container, each of the
treatment chambers containing a bed of peat for treating the wastewater. At
least one distribution means is also provided for distributing the wastewater
entering the container through the wastewater inlet into at least one of the
treatment chambers. Each distribution means comprises a water inlet pipe
connected to the wastewater inlet and leading above the casing and a trough
tiltably mounted on top of a corresponding casing. The trough extends along
the
casing and has two opposite sides. It defines at least one wastewater
receiving
means on one of the two sides and it is tiltable between a first position
whereat
the wastewater receiving means receives wastewater exiting the water inlet
pipe
and a second position whereat the wastewater received in the receiving means
flows out of the same. The trough also has counterweight means on its other
side for holding it in the first position while it is filled up and for
bringing it
back from the second position to the first position after the at least one
wastewater receiving means has been emptied. In addition, at least one
distribution plate is mounted above the bed of peat in one of the treatment
chambers defined by the corresponding hollow casing. This at least one
distribution plate comprises a plurality of channels projecting from the
trough,
each of the channels having an end for receiving wastewater flowing from the
trough so that the wastewater is divided into a plurality of flows each
flowing in
a corresponding channel, each of the channels also having at least one opening
for letting the wastewater drip into the corresponding treatment chamber.
The use of the aforesaid tiltable trough in combination with the
distribution plate for distributing the wastewater over the bed of peat
presents
certain drawbacks. When the wastewater enters the container at a high flow
rate
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and a large amount of wastewater is continuously received in the trough over a
period of time, the trough rapidly tilts between the aforesaid first and
second
positions so that the wastewater flowing therefrom floods the channels defined
in the distribution plate and flows over the edges of the distribution plate
and
onto the bed of peat. There is thus flooding of the bed of peat. Since any
given
peat has a predetermined biofiltering capacity over which the peat will not
act
as a biofiltering medium, flooding of the bed of peat will cause the
wastewater
to flow through the bed of peat at a flow rate greater than the biofiltering
capacity of the peat, resulting in a non-efficient removal of both organic and
inorganic materials.
It is therefore an object of the present invention to overcome the above
drawbacks and to provide an improved biofiltering device which utilizes peat
as
biofiltering medium and which can efficiently treat wastewater irrespective of
the flow rate thereof.
In accordance with the present invention, there is provided a biofiltering
device for treating wastewater, comprising a housing having inlet means for
receiving the wastewater to be treated and outlet means for discharging the
treated wastewater, a bed of peat disposed inside the housing between the
inlet
and outlet means, the peat defining a biofiltering medium having a
predetermined biofiltering capacity, and means for aerating the peat. The
device according to the invention further includes a fluid flow control system
arranged over the bed of peat and in fluid flow communication with the inlet
means, for distributing the wastewater through the bed of peat in a manner
such
that when the wastewater enters the system at a flow rate greater than the
biofiltering capacity of the peat, the wastewater discharged from the system
flows through the bed of peat at a flow rate no greater than the biofiltering
capacity.
According to a preferred embodiment of the invention, the fluid flow
control system comprises a fluid flow control unit having a chamber in fluid
flow communication with the inlet means and a plurality of spaced-apart
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discharge orifices in fluid flow communication with the chamber, the chamber
having a volume sufficient to permit accumulation of wastewater when the
wastewater enters the chamber at a flow rate greater than the biofiltering
capacity of the peat. The discharge orifices are adapted to discharge
wastewater
from the chamber to the bed of peat at a flow rate no greater than the
biofiltering capacity when the flow rate of the wastewater entering the
chamber
is greater than the biofiltering capacity.
Preferably, the chamber is a chamber of variable volume, the volume of
the chamber varying as a function of a difference between the flow rate of the
wastewater entering the chamber and the flow rate of the wastewater
discharged therefrom and increasing when the flow rate of the wastewater
entering the chamber is greater than the biofiltering capacity of the peat.
The
discharge orifices, on the other hand, each have a dimension selected so that
the wastewater discharged from the chamber flows through the bed of peat at a
flow rate substantially equal to the biofiltering capacity of t:he peat when
the
flow rate of the wastewater entering the chamber is equal to or greater than
the
biofiltering capacity.
In a particularly preferred embodiment, the fluid flow control unit
comprises an elongated, horizontally extending receptacle having upper and
lower walls formed of a flexible material, the lower wall being provided with
the aforesaid orifices and lying on the bed of peat. The chamber is defined
between the upper and lower walls with the upper wall being movable towards
or away from the lower wall in response to a decrease or increase in the
volume of the chamber. The receptacle further has a feed inlet in fluid flow
communication with the inlet means for feeding the wastewater into the
chamber. Preferably, the feed inlet is disposed at one end of the receptacle
and
wherein the lower and upper walls each have a predetermined width and the
orifices are formed in the lower wall at predetermined locations, the width
and
locations being selected so as to cause the wastewater discharged through each
orifice to flow at a substantially uniform flow rate. The orifices are
generally
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circular and each have a diameter ranging preferably from about 2 to about 8
mm. For example, when the peat used is sphagnum peat having a biofiltering
capacity of about 20 e/hr, the orifices each have a diameter of about 6 mm.
When using sphagnum peat having a biofiltering capacity of about 22 ~/hr, the
orifices each have a diameter of about 5 mm. In the case of sphagnum peat
having a biofiltering capacity of about 24 l'/hr, the orifices each have a
diameter of about 3 mm.
According to another preferred embodiment, the fluid flow control
system comprises first and second fluid flow control units with the first unit
being disposed on top of the second unit, the first fluid flow control unit
being
adapted to control the flow rate of the wastewater discharged therefrom and
the
second fluid flow control unit adapted to receive the wastewater discharged
from the first unit and cause the wastewater to flow throughout substantially
the entire bed of peat.
In a preferred embodiment, the first fluid flow unit has a chamber in
fluid flow communication with the inlet means and a plurality of spaced-apart
discharge orifices in fluid flow communication with the chamber, the chamber
having a volume sufficient to permit accumulation of wastewater when the
wastewater enters the chamber at a flow rate greater than the biofiltering
capacity of the peat. The discharge orifices are adapted to discharge
wastewater
from the chamber to the second fluid flow control unit at a flow rate no
greater
than the biofiltering capacity when the flow rate of the wastewater entering
the
chamber is greater than the biofiltering capacity.
Preferably, the chamber is a chamber of variable volume, the volume of
the chamber varying as a function of a difference between a variation of the
flow rate of the wastewater entering the chamber and the flow rate of the
wastewater discharged therefrom and increasing when the flow rate of the
wastewater entering the chamber is greater than the biofiltering capacity of
the
peat. The discharge orifices, on the other hand, each have a dimension
selected
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so that the wastewater discharged from the chamber flows through the bed of
peat at a flow rate substantially equal to the biofiltering capacity of the
peat
when the flow rate of the wastewater entering the chamber is equal to or
greater than the biofiltering capacity.
In a particularly preferred embodiment, the first fluid flow control unit
comprises an elongated, horizontally extending receptacle having upper and
lower walls formed of a flexible material, the lower wall being provided with
the aforesaid orifices and lying on the second fluid control unit. The chamber
is
defined between the upper and lower walls with the upper wall being movable
towards or away from the lower wall in response to a decrease or increase in
the volume of the chamber. The receptacle further has a feed inlet in fluid
flow
communication with the inlet means for feeding the wastewater into the
chamber.
According to a further preferred embodiment, the second fluid flow
control unit comprises an elongated, horizontally extending porous membrane
having upper and lower surfaces with the lower surface contacting the peat,
the
lower wall of the receptacle lying on the upper surface of the membrane. The
membrane is capable of spreading the flow of the wastewater discharged from
the receptacle as the wastewater flows through the membrane from the upper
surface to the lower surface, and into the bed of peat. Preferably, the
membrane
is a multilayered membrane comprising upper and lower layers formed of non-
woven fibers and each having a predetermined density, and an intermediate
layer disposed between the upper and lower layers and formed of the non-
woven fibers, the intermediate layer having a density less than the
predetermined density. The upper and lower layers each have a plurality of
spaced-apart apertures extending therethrough and formed, for example, by
piercing the upper and lower layers with needles.
According to still a further preferred embodiment, the housing has a
bottom opening defining the outlet means and a metal grating covers the
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bottom opening to support the bed of peat inside the housing while enabling
the treated wastewater to flow through the bottom opening.
According to yet another preferred embodiment, the biofiltering device
further includes sampling means enabling a sample of the treated wastewater to
S be collected for analysis. Preferably, the sampling means comprise a
horizontal
tray-like member disposed inside the housing adjacent a sidewall thereof and
the bottom opening, and a guide member connected to the tray-like member
and extending through an aperture formed in the sidewall. The tray-like
member has a main fluid-receiving surface extending along an inclined plane
for causing drops of the treated wastewater received on the main surface to
flow in a direction towards the sidewall and the guide member has a guide
channel arranged to receive the drops of treated wastewater from the main
surface for guiding the drops through the apertures and exteriorly of said
housing. The tray-like member preferably has two secondary fluid-receiving
sufaces disposed opposite one another and each extending along an inclined
plane for causing drops of treated wastewater received on the secondary
surfaces to flow in a direction towards the main surface.
The biofiltering device according to the invention enables one to
efficiently treat incoming wastewater irrespective of the flow rate thereof.
Further features and advantages of the invention will become more
readily apparent from the following description of preferred embodiments as
illustrated by way of examples in the accompanying drawings, in which:
Figure 1 is a top plan view illustrating a plurality of biofiltering devices
according to a preferred embodiment of the invention, arranged downstream of
a distributor box in fluid flow communication with a septic tank (not shown),
for treating the wastewater discharged from the septic tank;
Figure 2 is a sectional view of one of the biofiltering devices shown in
Fig. 1;
Figure 3 is a sectional view taken along line 3-3 of Fig. 2;
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Figure 4 is a bottom plan view of a receptacle used as a first fluid flow
control unit in the biofiltering device shown in Fig. 2;
Figure 5 is a partial sectional view of a membrane used as a second fluid
flow control unit in the biofiltering device shown in Fig. 2;
Figure 6 is a sectional view of another one of the biofiltering devices
illustrated in Fig. 1, shown provided with a sampling system enabling a sample
of the treated wastewater to be collected for analysis;
Figure 7 is a top plan view of the sampling system used in the
biofiltering device shown in Fig. 6;
Figure 8 is a side elevational view of the sampling system shown in Fig.
7; and
Figure 9 is an end elevational view of the sampling system shown in Fig.
7, taken from the left-hand side of Fig. 7.
Figure 1 shows a plurality of biofiltering devices 10,10' arranged
downstream of a distributor box 12 and connected thereto by means of conduits
14. The distribution box 12 is connected by conduit 16 to a dosing chamber
(not
shown) in fluid flow communication with a septic tank (also not shown). The
devices 10,10' serve to treat the wastewater discharged from the septic tank.
As shown in Figures 2 and 3, each biofiltering device 10 is disposed in a
hole dug in the ground 18 and rests on a bed of gravel stones 20. The device
10
comprises a housing 22 having four sidewalk 24, 26, 28 and 30 and a topwall
32 which are integral with one another and formed of concrete. The housing 22
further has a bottom opening 34 which is covered with a metal grating 36 sup-
porting a bed of peat 38 inside the housing. The peat defines a biofiltering
me-
dium having a predetermined biofiltering capacity. The sidewall 24 is provided
with an inlet 40 connected to the conduit 14 (shown in Fig. 1) for feeding
into
the housing 22 the wastewater to be treated. A fluid flow control system 42 in
fluid flow communication with the inlet 40 is arranged on top of the bed of
peat
38 for distributing the wastewater through the bed of peat 38 in a manner such
that when the wastewater enters the system 42 at a flow rate equal to or
greater
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than the biofiltering capacity of the peat, the wastewater discharged from the
system flows throughout substantially the entire bed of peat 38 at a flow rate
substantially equal to the biofiltering capacity.
The fluid flow control system 42 comprises an elongated, horizontally
extending receptacle 44 and an elongated, horizontally extending porous mem-
brane 46, the receptacle 44 being disposed on top of the membrane 46. As best
shown in Figures 3-5, the receptacle 44 has an upper wall 48 and a lower wall
50 formed of a flexible material with a chamber 52 (shown in Fig. 6) of
variable
volume defined therebetween. The receptacle 44 further has a feed inlet 54
connected to the inlet 40 for feeding the wastewater into the chamber 52. The
lower wall 50 is provided with a plurality of spaced-apart discharge orifices
56
in fluid flow communication with the chamber 52 and facing the membrane 46.
The volume of the chamber 52 varies as a function of the difference between
the flow rate of the wastewater entering the chamber 52 and the flow rate of
the
wastewater discharged therefrom and increases when the flow rate of the
wastewater entering the chamber 52 is greater than the biofiltering capacity
of
the peat. The upper wall 48 thus moves towards or away from the lower wall 50
in response to a decrease or increase in the volume of the chamber 52. The dis-
charge orifices 56 each have a dimension selected so that the wastewater dis-
charged from the chamber 52 and flowing through the membrane 46 flows
through the bed of peat 38 at a flow rate substantially equal to the
biofiltering
capacity of the peat when the flow rate of the wastewater entering the chamber
52 is equal to or greater than the biofiltering capacity. The walls 48 and 50
of
the receptacle 44 have a width which decreases from the inlet end to the
opposite end and the orifices 56 are disposed adjacent the longitudinal edges
of
the wall 50, thereby causing the wastewater discharged through each orifice 56
to flow at a substantially uniform flow rate.
The membrane 46 has upper and lower surfaces 58,60 with the lower
surface 60 contacting the peat. The lower wall 50 of the receptacle 44 lies on
the upper surface 58 of the membrane. The membrane 46 is a multilayered
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membrane comprising upper and lower layers 62,64 formed of non-woven
polypropylene fibers and having a density of about 0.1 g/cm3, and an
intermediate layer 66 also formed of non-woven polypropylene fibers, but hav-
ing a density of about 0.05 g/cm3. The upper and lower layers 62,64 each have
a
plurality of spaced-apart apertures 68 extending therethrough and formed by
piercing the layers 62,64 with needles. The membrane 46 is capable of spread-
ing the flow of wastewater discharged from the receptacle 44 as the wastewater
flows through the membrane from the upper surface 48 to the lower surface 50,
and into the bed of peat 38. Thus, the receptacle 44 constitutes a first fluid
flow
control unit adapted to control the flow rate of the wastewater discharged
there-
from, whereas the membrane 46 constitutes a second fluid flow control unit
adapted to receive the wastewater discharged from the receptacle 44 and cause
the wastewater to flow throughout substantially the entire bed of peat 38. The
treated wastewater is discharged from the device 10 through the bottom opening
34 and flows through the metal grating 36. The peat filters suspended
particles
of organic and inorganic materials present in the wastewater. 'The anti-
microbial
properties of the peat combined with those of fungi and actinomycetes present
in the peat contribute to eliminating fecal coliforms.
The membrane 46 is optional. Where use is not made of such a
membrane 46, the receptacle 44 lies directly on the bed of peat 38.
Means are provided for aerating the peat. As shown in Figure 2, the
topwall 32 of the housing 22 has an aperture 70 which is closed with a
removable cover 72 provided with an orifice 74. A removable cap 76 having a
plurality of vent orifices 78 is disposed in the orifice 74. The aperture 70
and
orifices 74,78 define an air inlet permitting atmospheric air to enter into
the
housing 22. In addition, as shown in Figure 3, the membrane 46 has lateral and
end edges which are each spaced from a respective sidewall 24,26,28,30 by a
respective gap 80. The gaps 80 also permit aeration of the peat.
The biofiltering device 10' shown in Figure I and illustrated in more
detail in Figure 6 is similar to the device 10, except that the device 10' is
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provided with a sampling system 82 enabling a sample of the treated
wastewater to be collected for analysis and the housing 22' has a sidewall 26'
provided with a column 84 having sampling hole 86. The sampling system 82
comprises a horizontal tray-like member 88 disposed adjacent the sidewall 26'
and resting on the metal grating 36, and a guide member 90 connected to the
tray-like member 88 and extending through an aperture 92 formed in the
sidewall 26'. As shown in Figures 7-9, the tray-like member 88 has a main
fluid-receiving surface 94 extending along an inclined plane for causing drops
of the treated wastewater received on the main surface 94 to flow in a
direction
towards the sidewall 26' (shown in Figs. 1 and 6). The guide member 90, on the
other hand, has a guide channel 96 arranged to receive the drops of the
treated
wastewater from the main surface 94 for guiding the drops through the aperture
92 and into the sampling hole 86. The tray-like member 88 further has two
secondary fluid-receiving surfaces 98,100 disposed opposite one another and
l5 each extending along an inclined plane for causing drops of treated
wastewater
received on the secondary surfaces 98,100 to flow in a direction towards the
main surface 94.
The sampling hole 86 is closed with a removable cover 102. Removal of
the cover 102 enables one to gain access to the sampling hole 86 and, by using
an elongated spoon-shaped sampling instrument, one can take a sample of the
treated wastewater dripping into the hole 86 for analysis of the sample.
As it is apparent, the biofiltering devices 10 and 10' enable one to
efficiently treat incoming wastewater irrespective of the flow rate thereof.
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