Note: Descriptions are shown in the official language in which they were submitted.
CA 02481956 2004-09-17
TERTIARY FILTER SEPTIC SYSTEM AND METHOD
Technical Field
[0001) This application relates to a system and method for filtering
wastewater derived from an effluent source;, such as an upstream
primary or secondary treatment plant. The invention employs peat or
some other hydrophilic material capable of transporting effluent by
capillary action.
Backgr,, ound
[0002] Various types of septic systems employing peat are known
in the prior art. Most prior art peat filtration devices load the effluent
from the top of the filter, and allow it to drain down through the peat in
order to effect filtration of the effluent. For example, Boyd et al. (US
5,049,265) entitled "Effluent Treatment System"discloses a system for
secondarily treating wasfiewater through a peat filter in which liquid
waste from a septic tank is pumped onto the top of a treatment medium
consisting of peat. The effluent is collected at the bottom of the peat
filter. The system incorporates peat-based organic fibrous material
having a relatively low absorptive capacity to promote drainage, and
also uses an effluent distribution system to distribute effluent over the
filter medium.
[0003] Festa et al. (US 6,620,321) entitled "Biofilter System and
Method For Treating Wastewater" describes a similar system in which
effluent is pumped onto the filter from the top through sacks containing
filtering material (often peat), and is allowed to drain out the bottom.
[0004] Albert (US 6,546;298) entitled "Biofiltering System for
Treating Wastewater Effluent" describes a method for treating effluent
that allows continuous treatment. The effluent flows onto the top of a
peat layer via a fluid flow regulator; and is 'permitted to drain into the
ground below. A fluid flow regulator and distribution system disposed
CA 02481956 2004-09-17
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upstream from the peat ensures that the wastewater flows through the
peat bed at a rate no greater than the peat bed biofiltering capacity.
[0005] Many effluent treatment systems which incorporate the use
of plants are also knowin the prior art. Simmering et al. (US 5,690,827)
entitled "Sewage Treatment System Using Peat and a Constructed
Wetland" discloses a three-stage method of sewage treatment consisting
of primary settling, passing the effluent through a peat filter, and then
passing the filtered effluent through a sub-surface constructed wetland.
In this method, the plants are used as a separate stage of treatment
following passage through the peat filter.
[0006] Winters (WO 98/21153) entitled "Device for Cleaning
Polluted Water" describes a method for treating water in a mobile
25 container filled with multiple layers, including porous layers at the
bottom of the container, a layer of peat, and then a layer of sand above
the peat. The method includes the use of plants for purification, partic-
ularly reeds. The container is mobile so that it may be easily replaced.
Effluent is pumped into a layer of sand near the top of the reservoir, and
is collected by a discharge pipe located in the base of the .container. The
container is flooded to a certain level to create an appropriate ground
water level to promote the activity of microorganisms at the interface
between wet and dry soil.
[0007] Rambeck (WO 99/32406) entitled "Improved Effluent
Treatment System" describes a two-stage treatment system, to treat both
solid and liquid portions of effluent. The treatment is provided by
gravel in layers, with microorganisms in the gravel, and plants. Solids
are retained on top of the filter body, to be transformed into a soil-peat
structure, while the liquid percolates through the filter for purification.
j0008] Wolverton (US 4,415,450) entitled "Method for Treating
Wastewater Using Microorganisms and Vascular Aquatic Plants"
describes a system in which supernatant ~rom a settling tank is pumped
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into the bottom of a container filled with racks, pea gravel, and vascular
aquatic plants for treatment. Effluent is purified by flowing upward
through the tank, during which time it is subject to processing by
anaerobic and facultative microorganisms; and the roots of at least one
vascular aquatic plant.
[0009] While numerous effluent treatment systems are known in
the prior art employing peat or vascular plants, they are not specifically
sized and configured for tertiary effluent treatment or to accommodate
both periodic surges in effluent flow and periods of low flow. Domestic
wastewater production is typically uneven, with peak flows in the
morning and early evening. Conventional treatment systems are
typically under loaded for most of the day and overloaded for brief
periods. Additionally, secondary treatment alone is insufficient to
remove microcontaminants and nutrients. The need has therefore
arisen for an improved tertiaxy filter system employing peat or other
peat-like organic or synthetic materials which can operate continuously
and passively, even duringperiods of low effluent inflow.
Su~,~of Invention
[0010] In accordance with the invention, an effluent treatment
apparatus is described comprising a fluid-impervious container; a
plenum positionable within the container; the plenum having a lower
fluid collection portion having a fluid holding capacity and an upper
fluid filter portion comprising a hydrophilic material capable of trans-
porting effluent by capillary action; an inlet for introducing fhe effluent
into the fluid collection portion; and a fluid wicking conduit containing
the hydrophilic material and extending into the fluid collection portion,
wherein the fluid wicking conduit wicks the effluent upwardly from the
fluid collection portion. In one embodiment the container may have a
bottom surface and the fluid collection portian is defined between the
bottom surface and the fluid filter portion. The fluid wicking conduit
may extend entirely or part-way between the fluid filter portion and the
CA 02481956 2004-09-17
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bottom surface. The fluid wicking conduit may be disposed, for exam-
ple, in a central portion of the plenum.
[0021) The hydrophilic material may comprise peat or a peat-like
organic or synthetic material; or a mixture thereof; capable of wicking
effluent. In one embodiment the fluid wicking conduit wicks effluent
upwardly when the volume of effluent in the fluid collection portion
exceeds a threshold :amount,: wherein the threshold amount is substan-
tially less than the fluid holding capacity of the fluid collection portion.
For example, the threshold amount may be less than 5 % of the fluid
holding capacity such that the apparatus operates substantially continu-
ously when effluent is introduced into the fluid collection portion
through the inlet.
[0012] Preferably the inlet is in fluid connmunication with an
upstream secondary treatment tank, such as a Nayadic~ plant, receiv-
ing effluent from an effluent source. The fluid holding capacity may be
sized to correspond with the maximum or average daily output of
effluent produced by the effluent source. For example; the fluid holding
capacity may be between 300 - 800 imperial gallons for an average
residential dwelling.
[0013] In one embodiment of the invention the plenum may
comprise one or more subcompartments for holding and stabilizing the
peat. The subcompartment(s) may be defined by wire frame elements.
[0014] The fluid filter portion may function as a vegetative tertiary
filter. For example, aquatic plants; such as T;ypJza Iatifoliu, may be
planted above the peat contained in the upper fluid filter portion. The
apparatus may further include a dispersal mound containing soil
disposed above or adjacent to the plenum; wherein at least some of the
soil contacts the peat disposed in the fluid filter portion.
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[0015] In one embodiment of the invention the fluid-impervious
container may be defined by a fluid-impervious fabric, such as a syn-
thetic rubber or plastic liner.: In another embodiment the container may
be a rigid structure, such as a concrete tank:
j0016] A method of treating effluent is also described comprising
the steps of:
(a) providing an effluent treatment apparatus having a lower
fluid collection portion having a fluid holding capacity and an
upper fluid filter portion comprising a hydrophilic material
capable of transporting effluent by capillary action;
{b) introducing effluent into the lower fluid collection portion;
and
{c) wicking effluent from the fluid collection portion to the
fluid filter portion.
Wicking of the effluent may occur when the volume of effluent in the
fluid collection portion exceeds a threshold amount, the threshold
amount being substantially less than the fluid holding capacify of the
fluid collection portion. In one embodiment the threshold amount is
sufficiently small such that wicking of effluent occurs substantially
continuously when effluent is introduced into the fluid collection
portion.
[0027] In accordance with the method, the effluent may be derived
from an upstream secondary treatment plant, such as a Nayadic~ plant.
At least some of the wicking may occur through a fluid wicking conduit
extending at least partway into the fluid collection portion. The wicking
may occur passively without the use of pumps.
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Brief Descr~tion of Drawings
[0028] In drawings which illustrate embodiments of the invention,
but which hould not be construed as restrictulg the spirit or scope of
the invention in any way,
[0019] Figure 1 is a schematic view showing an effluent source, a
primary pretreatment tank, a secondary treatment tank and a tertiary
effluent treatment apparatus constructed in accordance with the inven-
tion.
[0020] Figure 2(a) is s sectional view of the tertiary effluent treat-
ment apparatus of Figure 1.
j0021] Figure 2(b) is an enlarged sectional view of the fluid
wicking conduit portion of the effluent treatment apparatus of Figures 1
and 2.
[0022] Figure 3-is an enlarged; partially cut-away plan view of the
effluent treatment apparatus of Figures 1 and 2.
[0023] Figure 4 is a sectional view of a plurality of effluent treat-
ment apparatuses arranged in series in fluid communication with each
other for treating effluent derived from a common upstream effluent
source.
[0024] Figure 5 simplified cross-sectional view of an alternative
embodiment of the invention.
Description
[0025] Throughout the following description, specific details are
set forth in order to provide a more thorough understanding of the
invention. However, the invention may be practiced without these
particulars. In other instances, well known elements have not been
CA 02481956 2004-09-17
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shown or described in detail to avoid unnecessarily obscuring the
invention. Accordingly, the specification and drawings are to be re-
garded in an illustrative; rather than a restrictive, sense.
[0026] This application relates to an effluent treatment apparatus
for tertiary treatment of effluent derived from an effluent source 12
and a related treatment method. The overall effluent treatment train is
shown schematically in Figure 1. In the illustrated embodiment,
effluent source 12 is a residential dwelling.
[0027] Wastewater from effluent source 12 is first delivered to a
pre-treatment tank 14. Tank 14 performs several functions. First, it acts
as a trash tank receiving and holding recalcitrant material such as
plastics, excess paper and other contaminants that may be present in the
wastewater stream. Second, tank 14 functions to dilute any biologically
problematic substances such as disinfectants and anti-microbial soaps.
Third, tank 14 receives and holds effluent thereby smoothing water
flows somewhat. Finally, tank 14 receives and assists with the liquefac-
tion of particulate materials such as fibers.
[0028] The retention tune of effluent derived fxom effluent source
12 in tank 14 may vary, but it is typically on the order of 12 - 48 hours.
In one embodiment, tank 24 may consist of a sealed, two-chambered
septic tank. Tank 14 may be constructed from any suitable material.
For example; concrete tanks 14 are both reliable and cost-effective.
[0029] After pre-treatment in tank l4, effluent is then delivered to
tank 16 for secondary treatment. By way of example, tank 16 may
comprise a Nayadic~ aerobic treatment plant manufactured by Consoli-
dated Treatment Systems, Inc. Nayadic(~J treatment plants rely on
suspended growth and dixect oxidation principles to achieve organic
carbonaceous material reduction and to nitrify virtually all ammonical
nitrogen. The typical retention time of effluent in the Nayadic design is
on the order of 1.4 days. Nayadic~ trea~nent plants are certified under
CA 02481956 2004-09-17
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ANSI/NSF Standard 40,1999, Class 2, to produce an effluent having
less than 25 mg/L CBODS (five day carbonaceous biochemical oxygen
demand) and 30 mg/L TSS (total suspended solids) (National Sanitation
Foundation,1998). Nayadic~ extended aeration secondary treatment
plants are constructed from fiberglass. As will be appreciated by a
person skilled in the art, other advanced secondary treatment plants
could be substituted for the Nayadic~ design.
[0030] After secondary treatment in tank 16, effluent is then
delivered to the treatment apparatus 10 of the present invention for
tertiary treatment. Apparatus 10 includes a fluid-impervious container
18. In one embodiment container 18 may be defined by a fluid impervi-
ous liner placed within a cavity excavated at the septic field installation
site. For example, the liner could be constructed from ethylene
propylene dime monomer {EPD1VI) rubber or other synthetic rubber or
plastic sheeting. In the case of fluid impermeable soils such as clay, a
liner may not be required. In other embodiments container 18 may be a
rigid structure such a concrete or fiberglass tank. Container 18 is
preferably installed at a subterranean location, although above-ground
containers 18 could also be used. Surface placement minimizes soil
disturbance and soil compaction.
[0031] Apparatus l0 further includes a plenum 20 which is
positionable within container 28: In the illustrated embodiment ple-
num 20 is constructed from plastic coated galvanized wire frame ele-
ments 22, best shown in Figure 3 The wire frame elements 22 define a
plurality of subcompartments including a central fluid wicking conduit
or "chimney" 24 (Figure 2{b)). In use, peat 26 or some other hydrophilic
material capable of transporting effluent by capillary action is placed
within an upper subcompartment or subcompartments of plenum 20 to
define an upper portion 28. As described further below, peat 26 or
other hydrophilic material is also placed within wicking conduit 24.
The wire frame elements 22 serve to contain and structurally support
peat 26, particularly aroundthe periphery. of plenum 20 and within
CA 02481956 2004-09-17
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wicking conduit 24. The IoWer portion 30 of plenum 20 below upper
portion 28 is open and constitutes a holding tank for receiving effluent
derived from the upstream effluent treatment train.
[0032] Tn one embodiment of the invention hydrophilic
geotechnical fabric is fitted vertically within wicking conduit 24 and
spread horizontally at the interface between upper portion 28 and lower
portion 30 before peat 26 is loaded into plenum 20 (Figure 2(b)). The
geotechnical fabric permits fluid effluent to; pass therethrough (i.e.
effluent wicking is not impeded) but prevents peat 26 from spilling
from wicking conduit 24 or 'upper portion 28 into lower portion 30.
[0033] Effluent is introduced into plenum louver portion 30
through an inlet 32 at one end of a fluid delivery conduit 34. The other
end of fluid delivery conduit 34 (not shown in Figures 2(a) and (b)) is
connected to the upstream secondary treatment tank 16.
[0034] In the illustrated embodiment inlet 32 is located at a side
location of container 18 and plenum 20. By introducing effluent into
plenum 20 via the sidewall; conduit burial does not need to be as deep
at the septic field installation site. Further; an inspection port may be
located directly above the secondary effluent entry point. That way, if
blockage occurs due to tree root intrusion or the Like, the effluent entry
point may be easily cleared and cleaned. Figure 5 illustrates an alterna-
five embodiment of the invention where the inlet 32 is located at a
cenixal bottom portion rather than a side portion of plenum 20.
[0035] Plenum 20 may be sized so that the volume of plenum
lower portion 30 is sufficiently large to accommodate anticipated
effluent flow .rates. Typically, for residential effluent sources 12, peak
water usage and effluent flow is in the morning and earlier evening.
Plenum lower pori~on 30 functions as a surge chambex which may be
sized to receive anticipated maximum, average, or between maximum
and average effluent flow rates, thereby accommodating irregular flow
CA 02481956 2004-09-17
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patterns: For example, plenum lower portion 30 may be sized to receive
and process effluent volumes on the order of between 300 - 800 Imperial
gallons per day based on an anticipated average daily flow of about 300
Imperial gallons per day for'a three bedroom dwelling. For example,
plenum lower portion 30 may be sized to accommodate approximately
a two day effluent residence time. As will be appreciated by a person
skilled in the art, the size of apparatus IO including plenum 20 may vary
without departing from the invention.
[0036] In one embodiment of the invention, best illustrated in
Figure 2(b); is wicking conduit 24 of plenum 20 extends at least part-
way into plenum lower portion 30 to contact effluent contained therein.
In the illustrated embodiment, wicking conduit 24 extends downwardly
to contact an interior bottom surface of container 18. As mentioned
above, wicking conduit 24 includes peat 26vue to the capillary
wicking action of peat 26, effluent in contact with wicking conduit 24
will contact peat 26 (and/ or the hydrophilic geotechnical fabric contain-
ing peat 26) and be drawn upwardly even if only a small volume of
effluent is present in plenum lower portion 30, for example, if the flow
rate of effluent through inlet 32 is low. Accordingly, effluent in lower
portion 30 does not need to rise to the Ievel of plenum upper portion 28
to begin the tertiary effluent filtering process (i.e. plenum lower portion
does not need to be full before any effluent will wick into peat 26).
One advantage of this design is that apparatus 10 will operate passively
25 and continuously so long as at least some flow of effluent is introduced
into apparatus 10 from the upstream effluent treatment train or some
effluent remains present in plenum 20. This capacity for "24/ ~" opera-
tion is an improvement over prior art effluent filtering designs. At the
same time,~as mentioned above, apparatus 10 can accommodate surges
30 in effluent flow caused, for example, by diurnal increases in water
consumption. By contrast, conventional systems may be underloaded
for most of the day and overloaded for brief periods.
CA 02481956 2004-09-17'
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j0037] In one embodiment of the invention, the threshold volume
of effluent required to be contained within apparatus 10 before it will be
wicked upward through wicking conduit 24 is very low. For example,
the threshold amount could be less than 5 % of the total fluid holding
capacity of plenum lower portion 30 (i.e. less than 1 cm of fluid depth).
In one embodiment of the invention plenum 20 rnay be configured so
any effluent entering lower portion 30 flows, such as by gravity, toward
the Iower portion of wicking conduit 24.
[0038] As will be appreciated by a person skilled in the art,
wicking conduit 24 may be alternatively disposed other than in a central
portion of plenum 20. For example, if apparatus 10 were installed on a
sloped site, wicking conduit 24 could be disposed near a downslope
edge of plenum 20 to wick up any effluent which flows into its vicinity
by gravitational forces.
[0039] In another alternative embodiment of the invention, the
amount of effluent flowing into treatment apparatus 10 may be con-
trolled by a flow regulator. For example, a surge chamber could be
provided upstream from apparatus 10. This arrangement may be
particularly advantageous in the case of large installations. A pump
controlled by a timer could be employed to periodically introduce
effluent from the surge chamber into inlet 32 at a constant or near
constant rate. In this embodiment, the volume of lower portion 30 of
plenum 20 could be reduced since it is not required to function as a
surge chamber. This embodiment may enhance the efficiency of the
fermentation process taking place within plenum 20 since the microor-
ganisms present in peat 26 will receive nutrients at a relatively consis-
tent rate. On the other hand, systems employing pumps or other
mechanical flow regulators are more vulnerable to mechanical break-
down than purely passive systems.
[0040] The volume of peat 26 required for effective operation of
plenum upper portion 28 and wicking conduit 24 may be determined
CA 02481956 2004-09-17
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depending upon expected hydraulic retention times. Peat 26 provides
positive physical filtration, adsorption, a plethora of fixed film attach-
ment sites and supplies carbon for denitrification. The myriad of flow
pathways through peat 26 ensures long effluent residence times and
multiple contacts with microphagous organisms. For example, as
shown in Figure 2(b), effluent has a relatively long flow path through
peat 26 present in wicking conduit 24 and/ or upper portion 28 before it
migrates to the surrounding environment. As will be appreciated by a
person skilled in the art, other hydrophilic materials capable of trans-
porting effluent by capillary action may be substituted for peat 26 or
mixed with peat 26 in alternative embodiments of the invention: Such
other materials may include organic materials having wicking proper-
ties similar to peat and hydrophilic synthetic materials such as
geotechnical fabric. By way of further example; sawdust may be used
as part of the wicking material.
(0041] As illustrated in the drawings, vascular aquatic plants 36
may be planted in peat 26 contained within plenum upper portion 28.
Various species of aquatic emergent plants may be used, such as Typha
latcfolia. Plants 36 fulfill a number of roles including replenishment of
peat 26, phytoremediation, ; maintaining fluid channels open, direct
nutrient uptake, evapotranspiration and providing a large surface area
for microbial film attachment on root surfaces. Of course; plants 36 may
also be species selected to be-aesthetically pleasing. Once established,
the roots of plants 36 will grow into and stabilize peat 26 and provide
structural integrity to the entire effluent treatment apparatus 10.
[0042] Apparatus 10 further includes a dispersal field 38 covering
or adjacent to (e.g. surrounding) upper portion 28 of plenum 20. Dis-
persal field 38 may comprise permeable topsoil placed over peripheral
portions of container 18 and plenum 20. This ensures intimate contact
between peat 26 and the topsoil. Unlike sand, topsoil includes resident
soil organisms and may be sodded with a deep-rooted grass such as
perennial turf rye grass. Water will infiltrate into the sod at the edge of
CA 02481956 2004-09-17
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container 18 via capillary action and hence into other regions of the
dispersal field 38 having a lower moisture concentration. The present
invention has been shown to be very effective in producing effluent
having very low to non-detectable suspended solids, biological oxygen
demand and fecal coliform bacteria.
[0043] Figure 4 illustrates an alternative embodiment of the
invention wherein a plurality of effluent treatment apparatuses 10 as
described above are arranged in series. In this embodiment apparatuses
10 are in fluid communication (i.e. they are co~:mected by a common
fluid delivery conduit 34). Thus the incoming effluent may be distrib-
uted amongst a plurality of plena 20. The size of the lower portion 30 of
each plenum 20 may be accordingly reduced (i.e. the surge chamber is
effectively distributed at multiple locations). dewed from the surface
the vascular aquatic plants 36 may cover the entire dispersal field
installation region and it will not be apparent that multiple subterra-
neap effluent treatment apparatuses 10 are installed.
[0044] Figure 5 describes an alternative embodiment of the inven-
Lion where fluid-impervious container 18 is a concrete tank and effluent
is introduced into plenum 20 from a lower portion rather than a side
portion of container 18. A shut-off valve 40 may be provided for regu-
lating flow through the upstream fluid delivery conduit 34. In this
embodiment plenum 20 must be full to capacity with effluent before
effluent will wick into the overlying layer of peat 26 and there is a
diminished capacity to accommodate effluent surges compared to the
embodiments described above.
j0045] In operation, the effluent treatment illustrated in Figure 1
may opexate passively by gravity flow. This decreases capital and
operational costs and enhances reliability. Alternatively, one or more
pumps and/ or valves could be used to regulate effluent flow. For
example, a pump could be employed in the case of a negative slope
CA 02481956 2004-09-17
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between the primary treatment tank 14 or secondary treatment tank 16
and the effluent treatment apparatus 10 at the installation site (Figure 1).
(0046] In an alternative embodiment of the invention, effluent
treatment apparatus l0 may receive effluent from a primary rather than
a secondary treatment source: For example, apparatus 10 may be used
as a temporary replacement for a pre-existing septic field. Many exist-
ing septic fields fail to operate as intended due to gradual formation of
an anaerobic biomat therein. This failed or failing state can be reversed
by allowing the septic field to dry out; such as over the summer months.
As the water dissipates; oxygen is drawn in to replace it. This is turn
allows aerobic organisms to replace the anaerobic biomat, thereby
restoring permeability to the septic field. In order to enable the existing
septic field to dry out, apparatus 10 may be connected to the primary
treatment tank. In this case apparatus 10 will function as both a second-
ary treatment apparatus removing carbon and a tertiary treatment
apparatus removing nutrients and microcontaminants. Unless supple-
mentary oxygen is provided to apparatus 10; apparatus 10 may eventu-
ally become plugged up with an anaerobic biomat. However, by this
time (e.g. at the end of thQ summer season) the rejuvenated existing
septic field may be bxought back into service.
[0047] In the illustrated embodiments: described above, the por-
tion 28 of plenum 20 containing peat 26 or other hydrophilic material
exhibiting capillary action is disposed above the plenum portion 30
functioning as a fluid collection chamber . As will be apparent to a
person skilled in the art, in other embodiments of the invention portions
28, 30 could be disposed side by side or in some other geometric rela-
tion. In such embodiments, effluent could be initially wicked away
from plenum portion 30 horizontally rather than vertically. Such an
arrangement may permit enhanced effluent throughput since wicking
would not be occurring in a direction directly opposite gravitational
forces.
CA 02481956 2004-09-17
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[0048] As will be apparent to those skilled in the art in the light of
the foregoing disclosure, many alterations and modifications are possi-
ble in the practice of this invention without departing from the spirit or
scope thereof. Accordingly, the scope of the invention is to be con-
s strued in accordance with the substance defined by the following
claims.
