Note: Descriptions are shown in the official language in which they were submitted.
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RTnl;'IT.'l'r
The present invention relates to a filter for
use in the biological treatment of water in both aerobic
5 and anaerobic conditions.
The oldest well-known biofilters applied widely
in water treatment include biof ilters made of natural
materials, such a6 sand, gravel, or properly granulated
basalt or granite stones . Biof ilters have also been
10 filled with other natural materials, such as
blast-furnace coke or slag.
Another form of biofilter i5 a biochemical
reactor, in which biologically active material is
situated upon a spatially developed filter medium. These
15 have also been used in water treatment. In one
~mho~ nt a filter medium is made of porous blocks of
thin shaped plastic boards glued together. The blocks,
placed in layers on a grid within the biochemical reactor
(biofilter) serve as a base for a layer of micro-
20 organisms which take part in d~ ition and synthesisof chemical compounds.
Other extensively used biofilters are filled
with rings, balls or other g~ ~L ically shaped elements
made of ceramic materials or plastic . Floating f ibres,
25 coils, tapes and nets made of plastic have also been used
as biofilter fillings.
The previously known biof ilters, as a result of
the growth of microorganisms and biodegradation, become
excessively polluted and have to be cleaned or replaced
30 after a specific period of time. This task is difficult
and expensive, and requires a temporal shut-down of the
water treatment plant.
Water treatment plants have been usually built
as stationary units with biofilters of specific,
35 invariable dimensions. This narrows the possibility to
choose a water treatment plant according to the speciric
needs of recipients. Such water treatment plants are
generally lln~ cal as far as their size and
adjustment to individual needs are concerned.
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It i8 therefore an object of the present
invention to provide a filter that obviates or mitigates
the above disadvantages.
In general terms, the present invention
5 provides a filter that includes filter elements formed
from non-oriented plastic strips made of r~, ~ed,
preferably cut, waste plastic products with a surface
which constitutes a base for a layer of micro-organisms.
The strips are used as a f illing that is located within
10 flexible inelastic sleeves that may be flexed to adapt to
a cuboidal, preferably cubic configuration. A filter can
contain any number of such identical f ilter elements
a~sembled into modules that form a stiff, light-weight
structure .
It has been found that the plastic strips may
readily provide a surface area of between 60 ft2 and 90
ft2 for each 1 ft3 of filter to permit effective aerobic
or anaerobic operation.
In the preferred ~mhQrlir~-lt of the invention,
20 the utilization of fragmented waste plastic products
reduces the production costs of the biofilter, and at the
same time, if such biological reactors are widely used,
it will help protect the natural environment through
plastic waste disposal. Placing the filter elements in
25 modules permits the construction of biofilters suitable
in siÆe to the amount of f iltered water . This enables
one to choose the dimensions of a water treatment plant
according to individual requirements.
A biof ilter built of modules as described in
3o the preferred ~mhorlil lt can serve as a submerged ("wet")
or washed ("dry") biofilter and can be used in both
aerobic and anaerobic treatment methods. This
arrangement also facilitates construction from separate
containers that can be easily replaced when, due to the
35 growth of micro-organisms on the specific surface and
biodegradation, they become excessively polluted.
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The construction of a biof ilter according to
the preferred ~ t requires relatively small
illVeDi --L and provides low operating costs of treatment
plants .
An ~ nt of the invention will now be
described by way of example only with reference to the
;lr -nying drawings, in which:
Figure 1 is a schematic representation of a
waste water treatment system;
Figure 2 is a perspective view of a portion of
a biofilter used in the system of Figure l;
Figure 3 is a side view of a frame used in the
biof ilter of Figure 2;
Figure 4 is a view on the line 4-4 of Figure 3;
Figures 5a and 5b show the assembly of the
biofilter utilizing the frame of Figure 3;
Figure 6 is an end view of a filter element;
Figure 7 is a side view of a filter element;
and
Figure 8 is a curve illustrating the
performancQ of a waste water treatment system.
Referring therefore to Figures L to 3, a waste
treatment system generally indicated to by reference
numeral 10 receives inf luent through a pipe 12 which is
stored in a surge tank 14. A pump 16 under the control
of a float valve 18 transfers influent from the surge
tank to an array 20 of reactors 22. In the specific
embodiment, the array 20 is provided by two parallel
banks 24,26 of reactors 22. The banks 24,26 are
connected to operate in series and with a corridor 25
between them. Each bank 24,26 in turn has two rows of
reactors 2 2 with the reactors 2 2 in each row connected in
series so that influent will pass through one row of
reactors of each bank before being discharged as
3 5 ef f luent . The rows in each bank theref ore operate in
parallel to divide the effluent flow. Other
configurations are of course possible.
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Each of the reactors 22 is supported over a
respectivc sump 28, which collects fluid flowing through
the reactors 22. Pumps 34 in each of the sumps 28
transfer the collected fluid to a spray head 35 over each
5 of reactors 22 for further treatment.
Effluent from the sumps 28 discharge over a
weir 36 and through a flocculating filter 38 into a
holding tank 40. EffIuent is discharged from the holding
tank through a pipe 42. Influent from the pipe 12 is
10 thus passed through a succession of filters 22 until the
required quality of effluent is achieved.
Each of the reactors 22 is formed from stacks
of filter modules 47 each of which includes filter
elements 44 which are retained within a frame indicated
15 to by reference numeral 46. The filter elements 44 are
similar in construction and will be described further
below. An air supply manifold 45 having an outlet
between each filter module 47 is also incoL~L~l_ed within
each reactor 22 to ensure a sufficient supply of oxygen
20 for aerobic operation.
It will be noted from Figure 2, that the filter
elements 44 within each filter module 47 extend laterally
in side-by-side relationship and abut one another along
opposed surfaces. The filter elements 44 in each filter
25 module 47 are oriented orthogonally to the elements
immediately above or below, that is the axis of the
filter elements alternate from level to level, and thus
avoid6 a direct path through the reactors 22.
Each of the elements 44 is formed from a
30 fragmented plastic, typically waste plastic which is
shredded to provide a nominal size that provides a
developed surface area of between 60 and 90 square feet
per cubic feet. Typically, shredded strips ~of between 1~"
and 3" wide provides the requisite range of densities and
35 it is found that such strips shredded from curved
articles such as bottles provide the requisite degree of
compressibility and separation of developed areas.
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Preferably for washed operation the plastic
strips are hydrophilic to promote adherence of the
effluent to the surface. Hydrophobic waste plastic may
be treated with acid solutions to etch the surface and
render it hydrophilic. In order to minimize intimate
contact between flat surfaces that would reduce the
developed area, it i8 preferred that closed curved loops
of waste material are used, e.g. slices of a cylindrical
bottle. Open-ended strips of material may be used
provided they have sufficient inherent .;uLv~u.a and
resilience to resist packing with other strips and to
maintain their surfaces separated from adjacent strips.
After shredding, the wa6te plastic is assembled
into the f ilter elements as shown in Figures 6 and 7 by
forming a cylindrical outer sleeve 48 of plastic mesh
that typically has a nominal size of 2". Shredded
plastic strips 50 are located within the sleeve 48 to
provide a random, non-oriented medium with the ends of
the sleeve 48 folded over to contain the plastic strips
50. The sleeve 48 contains sufficient of the strips 50
to provide the required developed surface area for the
volume of the sleeve with variations of the density being
provided within the reactor vessel. The plastic strips
are _ esued from their free body ahape within the
sleeves 48 with a 3 :1 ~ L e:ssion ratio being typical .
t'~ ession ratios of between 2 :1 and 4 :1 appear to be
suitable to provide the requisite developed area within
the filter elements 44 and still maintain separation of
the surfaces.
The filter elements 44 are contained within
frame 46 which as can be 3een from Figure 3 includes an
open rL, ~ with top and bottom rails 52, 54 and corner
posts 56. Int~ te bars 58 extend between the top
and bottom rails 52, 54 at intervals and diagonal braces
60 provides rigidity ~or the frame work.
The sleeves 48 are flexible but substantially
inelastic and are dimensioned to provide a snug f it of
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the filter elements 44 within the filter module 47. The
plastic strips 50 within sleeve 48 are sufficiently
~ :,sible that the cross-section of the sleeve may be
changed from circular as shown in Figure 5a to generally
5 rectangular as shown in Figure 5b. The e~ion of
the filter elements 44 ensures a close abutment along the
opposed edgeg of the sleeves to provide a reasonably
hl -,_..uus filter bed for the effluent within each frame
46 .
Each of the reactors 22 are formed from stacks
of frames 46 that are supported in a structural rL vLh
62 (Figures 3 and 4). The framework 62 includes vertical
pillars 64 that support rails 66. The lower end of each
of the corner posts 56 is slidably supported in the rails
66 so as to be laterally movable relative to the adjacent
frames 46. Accordingly, each filter module 47 may be
slid laterally into the corridor 25 80 that the filter
elements 44 may be serviced without interruption of the
flltration process.
A6 noted above, the strips 50 may be packed
within the sleeves 48 to provide different surface areas
for a given volume. Accordingly, the filter elements may
conveniently progressively increase in density and
developed area from the top of each reactor toward6 the
bottom to provide a progressive filtering action upon the
effluent. Typically, the filter elements 44 in the upper
frames 46 will have a developed area of 60 ftZ per ft3
plo~L.assively increasing to 90 ft2 per ft3 at the lower
level .
In operation, therefore, the effluent is
progressively passed through the reactors 22 where it
passe6 from top to bottom through the filter elements 44.
The plastic strips 50 within the elements 44 provide the
requisite developed surface for anaerobic or aerobic
action with progressively increasing density of filter
medium. The effluent received in each sump 28 i6 either
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recycled through the same reactor or passed to the next
reactor until it progresses to the effluent pipe 42.
If it becomes n~ pscAry to service the filter
elements 44, the frame 46 may be slid on the rails 66 out
of the reactors 22 to provide access to the filter
elements 44. In 60 doing, however, the reactors 22 may
continue to operate although with reduced efficiency due
to the removal of one of the f ilter modules . The f ilter
elements 44 may then be removed from the frame 46 for
cleaning or repl~ t and the refurbished filter module
r_LuLl.ed to thc reactor once service i8 complete.
The modular construction of the reactor 22 also
permits the performance of the waste treatment facility
to be adjusted to the particular needs. As seen in
Figure 8, the percentage of BODs removed by each reactor
is in the range of 7 . 5% after initial removal in the
first reactor. This performance is ~bf l;nP-l for a
reactor having 5 filter modules 47 each of nominal size
6 . 0 ft. by 6 . 0 ft. by 2 . 0 ft. and with a developed area
of between 60 and go ft2 per ft3. Obviously, additional
filter modules could be added to each reactor, or
additional reactors added to each bank or additional
banks added aB i8 most appropriate if additional removal
i8 required.
The reactors may be operated in a washed or
~dry" mode, as shown in Figure 1, or may be operated in a
submerged or ~wet" mode as required. When operating in
the dry mode, air may be supplied through the manifold 45
to promote the aerobic action on the developed surfaces.
The amount of air supplied will depend upon the
particular operating condition6 of each reactor and may
be adjusted to suit.
The use of the waste plastic strips 50 provides
an ~:XL.L~ -ly economical filter medium and is found to
have the nP~-Pcs~ry developed surface area per unit
volume. The inherent curvature found in many waste
products ensures that the ad~acent services of the strips
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remain separate to thereby maintain the required surface
area. Adjustment of the compression ratio and/or the
shredding size will also adjust the developed surface
area within each filter element. Accordingly, it will be
5 seen that a simple yet effective reactor is provided that
may be adapted in many conf igurations to suit the
particular needs.
