Note: Descriptions are shown in the official language in which they were submitted.
wos4ll6999 21311 8 0 PCT~S93/00602
SECONDARY SEWAGE TREATMENT SYSTEM
FIELD OF THE INVENTION
This invention relates to on-site waste water treatment
systems, and more particularly to secondary treatment systems.
BAC~GROUND OF THE INVENTION
On-site disposal of waste water (sewage) from single
family residences and commercial establishments in areas with
no conventional sewer system has conventionally been
~ accomplished by a septic tank system. The anaerobic effluent
dîscharged from the septic tank, after settling of the solids
portion of the incoming waste water, is passed into a
subsurface drain field~for percolation into the surrounding
soil. Such a system works satisfactorily.if properly
installed and if proper soil conditions for disposal of the
effluent by the drain field exist. While most residential
septic systems work with harmony between the septic tank and
drain field, there are~increasing numbers of drain field
failures in~commercia;l~systems. Commercial systems where food
; preparation wastes are involved are particularly susceptible
20~ to ~ailure. The high strength and grease content related to
food preparation is beyond the capacity of the conventional
`
septic system.
In such systems,~heretofore, small treatment plants which
make use of chemical and/or biological treatment schemes to
25~ render the effluent suitable for disposal have been suggésted.
These treatment plants~usually are designed to replace the
conventional septic system~. Such treatment plants are
generally prohibitive~ly expensive to and generally not -;
economically feasible for~treatment of commerciàl sewage, as
~from restaurants, in rural and semi-rural areas.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a
secondary sewage treatment system intended to operate in
conjunction with a~conventional septic system. The system of
this invention is designed to be interposed between the septic
tank and drain field to provide a satisfactory ef~luent to the
drain field. In particular, the present system is specially
..
WO94/16999 h~ 0 PCT~S93/00602
designed for use in commercial treatment systems that must
handle food preparation wastes; and in this environment the
system provides an effluent comparable to that which would be
produced from a conventional residential septic tank.
Generally speaking, the system of this invention
biologically treats biodegradable wastes through aerobic
microbial growth on media resulting in the biological
oxidation of the waste products. The applied waste water
settles from the active aerobic zone, in which the media is
~lO contained, to an underlying anoxic treatment zone; and sludge
settles to a still lower anaerobic zone. The preferred
embodiment of this invention functions as an aeration tank,
settling tank and aerobic;~digester in a singe unit. This
invention uses buoyant;~media, as contrasted with fixed or
packed media, and consequently does not incur flocculent
build-up~during operation or the consequent clogging typical
of fixed or packed media treatment systems. In the present
invention, biological growth takes place in a mixing zone
fil}ed with a buoyant media. The buoyant media has a high
20~ ~ su~face area to volume~ratio, a low resistance to liquid flow
and a~surface condition réceptive to aerobic microbial growth.
; A preferred system~incorporates a series of modular media-
containing cages or ba~skets that float in the wastewater
undergoing treatment~within a mixing zone.
`25 ~ ~ Waste flow from~;a~septic tank enters~the system into a
turbulent zone above~the~mixing zone and begins a continuous
cycle, flowing down through the mixing zone and then upward
through draft tubes~from~which it is re-introduced to the
turbulent zone. The~mixing zone is fil~led with the buoyant
media and the waste flows gently down through the mixing zone
in contact with the buoyant media surfaces. The draft tubes
are free of buoyant media or any other surfaces on which
biomass can collect. ~The waste liquor is drawn turbulently up
through the draft tubes~and spills out above the mixing zone
into the turbulent zone The turbulent zone is likewise free
of buoyant media or any other surfaces on which biomass can
collect.
WO94/16999 ~Jl~ 0 PCT~S93/00602
Within the turbulent zone, the boiling action of the
liquor, including detergents and other foaming products,
produces a foam which accumulates in the area immediately
above the turbulent zone. This foaming action provides
additional treatment action, with bacteria being evident in
the foam, and also enables the system to tolerate occasional
overloading such as occurs during peak hours of operation in
food service establishments. When overloaded, the system
produces more foaming, in which a significant amount of
suspended solids and grease and oils are held, thereby
delaying treatment o these wastes until the system can
~tolerate them; at which time the foam settles through the
turbulent zone into the mixing zone and is incorporated in the
waste liquor.
The system provides an anoxic settling zone below the
mixing zone through which sludge may settle out for separate
removal and from which the~ treated liquor effluent may be
discharged into the~drain ~field. The treated liquor is
collected through a manifold positioned midway between the
~20~ bo~tom of the mixing zone;and the top of the sludge-collecting
zone. It then flows~through a riser into an outlet leading to
the septic system drain field.
BRIEF DESCRIPTION OF THE~DRAWINGS
Figure l is a vertical side elevation view, in cross
section, of an exemplary~embodiment illustrating the
principals of operation of the system of this invention;
Figure 2 is a top~plan view of a preferred embodiment of
the apparatus of this invention;
Figure 3 is a cross section view taken along the line 3 -
3 in Figure 2;
Figure 4 is a cross section view taken along the line 4 -
4 in Figure 2;
Figure 5 is a~top plan view of another embodiment of the
apparatus of this invention;
Figure 6 is a cross section view taken along the line 6 -
6 in Figure 5;
Figure 7 is a cross section view taken along the line 7 -
wo 94/16999 h 1 ~ ~ 1 8 0 PCT~S93/00602
7 in Figure 5;
Figure 8 is a detailed view of the draft tube segment of
the Figure 2 apparatus;
Figure 9 is a detailed view of the effluent outlet
manifold of the Figure 2 apparatus;
Figure lO is a partial view of the air discharge tube
employed in the Figure 8 draft tube segment;
Figure 11 is an isometric view of a preferred media-
containing cage or basket which may be used in place of the
integral structure shown in Figure 1;
Figure 12 is a top plan view of the Figure 11 cage;
Figure 13 is a side view of the Figure 11 cage,
illustrating the mixing action~of the process within an
individual cage;
Figure 14 is another isometric view of a cage similar to
the Figure 1~ cage but~having a different cage framework
construction;
~ Figure 15 is a partial view of a series of Figures 11&14-
; type cages arranged on the floor of a treatment vessel; and
~ Figure 16 is a partial v~iew of a series of Figures 11&14-
type cages ;floating~and in operation within a treatment
vessel.
DETAILED DESCRIPTION OF THE INYENTION
The on-site waste~water treatment system as herein
~25 described may be used for treatment of residential or
commercial wastes. However, its primary intended use is for
treating commercial~wastes which ordinarily cannot be treated
with~conventional septic systems. The typical effluent from
residential and commercial business establishments consists
primarily of human waste in admixture with biodegradable
materials such as food and other materials associated with
food preparation.~ The waste water to be treated generally
contains gravity settleable solids. While any means of
` effecting solid-liquid separation may be used, the most
commonly used method is a septic tank into which the waste
water is discharged and thè solids allowed to settle by
gravity. The effluent~leaving the septic tank, or other
WO94/169g9 ~ 3 ~18 ~ PCT~S93/00602
settling system, is directed into the system of the present
invention.
As shown in Figure 1, the system of the present invention
is provided in a concrete tank 1. The tank 1 has a lid 2, and
upper and lower halves 3 and 4. Within the upper half 3,
waste influent inlet 5 and waste liquor outlet 6 are provided.
Below the level of the inlet and outlet, a grating 7 is
provided that extends across the area of the tank interior,
from wall-to-wall. A plurality of draft tubes 8 are located
~lO and positioned in the tank such that they open at the top co-
planar with the top surface of the grating 7 and extend down
into the tank to open at their lower ends a distance below the
grating 7. The bottom of the tank 1 is sloped to provide a
centralized low point. This structure provides an anaerobic
sludge-collecting zone 9 at the bottom of the tank, an anoxic
settling zone lO extending above the sludge-collecting zone, a
media mixing and aerating~zone 11 extending above the settling
zone and generally defined by the length of draft tubes 8
~;~ inasmuch as it extends~from just below the bottom ends of the
20 ~ ~dra~t tubes to the grating 7, a turbulent zone 12 extending
;from the grating 7 to~the~elevation of the influent inlet 5,
and~a foam-collecting zone 13 above the turbulent zone 12. An
a~ir~delivery conduit~l4 de;livers air via a manifold 15
~ ~; embedded in the tank lid~2 to individual air delivery tubes
;~25 16~, one being provided for each draft tube 8. The air
delivery tubes 16 extend~axially down into the draft tubes 8 `~
and terminate above;thé bottom end of each respective draft
tube. A multiplicity~of~buoyant media, s~ch as spheres 17,
are contained within the tank below the grating 7. When the
systems is filled with waste fluid and operational, the tank l
is filled with waste~fluid up to the level of the outlet 6.
;The buoyant media 17 float and are ronfined beneath the
grating 7 within the media mixing and aerating zone 11; zone
11 being essentially filled with the media 17. The media are
preferably composed of buoyant hollow plastic spheres that
provide a high surface area to volume ratio on the order of 38
sq. ft./cu. ft. or more
.
WO~4/16999 ~ 131 18 0 ` PCT~S93/00602
Each draft tube ~ air delivery conduit assembly comprises
an air diffuser 18 through which air is ejected into the
system without disturbing the surrounding media mixing and
aerating zone ll. During operation of the system, influent
entering the tank l is circulated through the media 17 by the
pumping action of the air diffusers 18. As air is discharged
into the draft tubes 8, it aerates the liquor within the draft
tubes as it rises. The waste liquor is churned and pumped
along with the rising air up;and out of the draft tubes into
the turbulent zone 12.
As waste influent enters the system, the liquor flows
gently down through the mixing zone ll, passing through the
buoyant media 17 (i.e. around the individual spheres that make
up the media). From the bottom of the mixing zone ll, the
liquor passes vertically through the separate passageways,
provided by the draft tubes 8, between the bottom and top of
~; the mixing zone ~l. The air forced into the draft tubes
induces a pumping action while aerating the liquor passing
upward in the draft tubes.~ Uniike the gentle flow in the
20 ~ mi~ing zone ll, the~flow within these vertical passageways is
~; relatively turbulent.~ The volume of air used and the
proximity of the vertical flow passageways is such that the
outlet circles 19 of~flow turbulence between adjacent draft
~tubes overlap. Consequently, the liquor is continuously
circulated in a flow path~, including the mixing zone ll and
the vertical flow passageways, at a flow rate and under
conditions suitable for promoting thorough mixing of the
liquor with the buoyant media, and suitable for maintaining
aerobic microbial growth on the buoyant media. If the flow
rate of the liquor through the mixing zone ll is too
turbulent, microbial growth will be washed off the buoyant
media. On the other hand, if the flow rate through the
buoyant media is too slow, excessive microbial growth will
accumulate and may cause clogging. When the flow rate is
correct, excessive microbial growth falls off the buoyant
media and is naturally recycled. Because the media is not
fixed or packed, the individual buoyant elements that make up
WO94/16999 ~ 13118 0 PCT~S93100602
the buoyant media can rotate and tip over as growth builds up.
The buoyant media is thus self- cleaning. Dead growth will
fall from the buoyant media and settle through the settling
zone lO, forming sludge in the sludge-collecting zone 9.
Periodically the sludge may be pumped out and discarded or
recycled.
One preferred embodiment that incorporates the features
of the Figure 1 system and functions in accordance with the
description of the Figure 1 system is shown in Figures 2 - 4.
lO; A similar system is shown in Figures 5 - 6.
Another preferred embodiment provides a series of modular
media-containing cages or baskets, rather than an integral, or
built-in, mixing zone~structure. The modular cage feature, as
shown in Figures 11 - 16,~functions in the same manner and in
accordance with the same principles as the Figure 1 system
heretofore described.~ ~
With reference to Figures 2 - 4, this embodiment
:
oomprises a cast concrete tank 101 having top and bottom
halves 103 and~104 joined at a circumferential seam, and a lid
~lO~. ~The lid is provided with a plurality of air diffuser
~; ~ openings arranged in two rows, each opening being closed by a
traffic-bearing clean-out cover 120, and a pair of access
openings located between the two rows of air diffuser
openings. The access`openings are closed by traffic-bearing
2;5~ steel~doors 121 - 122. The access openings are separated by a
mid-span lid portion that contains a~sludge pu~p-out opening
closed~by a traffic-bearing clean-out cover 123.
An influent inlet conduit 105 enters from the side of the
tank lOl and branches at~a Tee toward the center of the tank
~ to provide two influent discharge openings into the tank's
interior. An ef~luent discharge conduit 106 enters from one
end of the tank lOl~and is connected to a liquor-collecting
manifold 124 by a riser 125. Manifold 124 is located between
the bottom of the settling zone and the top of the sludge-
collecting zone.
A grating 107 is positioned within the tank's interiorand fastened to the tank inner wall by brackets 126. The
:
WO94/16g99 ~13 ~ PCT~S93100602
grating 107 is positioned just below the elevation of the
outlet conduit 106 as shown. Axially below the air diffuser
openings, the grating 107 is provided with apertures for the
draft tubes 108. Draft tubes 108 are provided that extend
from the lid air diffuser openings and downward through the
grating 107 into the tank's interior. The draft tubes are
secured to the lid at their respective lid openings and
stabilized by the grating 107. Each draft tube is provided
with longitudinal cut-out openings 127 in it's side wall,
above the grating 107, that span the turbulent zone's depth to
provide for liquor flow from the draft tube interiors into the
turbulent zone. An air inlet conduit 114 connects to a
manifold conduit 115 embedded in the tank lid. Individual air
delivery tubes 116 are connected to the manifold conduit 115
and extended down into the draft tubes to provide, in
conjunction with the~ draft tubes, the multiple air diffuser
as~semblies 118 required~by this invention. As shown in Figure
lO, the bottom end of each air delivery tube 116 is capped and
proYided wîth radial apertures 129 through the cap 128 and the
tube wall for discharge of air into the draft tube passageway.
Th~is capped feature~prevents buoyant media elements from
accidentally becoming lodged in the draft tubes, as might tend
to occur while th~e tank is being filled for example. As in
Figure l, the mixing zone is substantially filled with the
25~ buoyant media elements~117.
The bottom outlet~manifold conduit 124 is provided with
several downward-opening inlets 130 as shown in Figures 2 and
3. These large openings;~prevent the manifold from becoming
anaerobic. Along the~length of the mànifold conduit,
moreover, the semi-clarified effluent liquor passes through a
plurality of apertures 131. These apertures, as shown in
Figure 9, are located below the mid-line of the manifold
conduit so that settling particulates will not fall into the
apertures.
Air is supplied to the system by air pumping system 135,
comprising a fan 136 and an air pressure and volume regulator
137. Excess air is vented from the tank 107 through air vent
WO94/16999 PCT~S93/00602
" ~1.,~t~18~
conduit 138 extending into the foam collecting zone.
A sludge removal conduit 140 extends downward from the
top lid clean-out opening to the bottom of the tank for
removal of sludge from the sludge-collecting zone. Side
openings are provided in the bottom removal conduit 140, as
shown in Figures 3 and 4 to facilitate sludge removal.
A 1680 gallon tank sized as shown in Figures 2 - 4 would
conveniently hold 100 cubic feet of 3.5 inch diameter Jaeger
Tri-Pak Polypropylene media elements. This media has a ratio
~ of 38 square feet of area per cubic foot of volume. This
would yield 3800 square feet of media area. Compressed air
could be supplied by a 2.5 horsepower Gast model R5125-1 fan
at 160 cfm free air. A unit of this capacity could handle 700
gallons of waste water from a restaurant per day and yield
household-type effluent to the drain field after a 58 hour
; retention time at maximum hydraulic capacity. If lower waste
strength is desiredf the unit could be operated at a lower
flow rate or two such units could be connected in series
between ths septic tank~and the drain field. This unit has
;2~0 demonstrated that it has~the capacity to cope with shock
loading, whether due~to increases in waste strength or
ydraulic loading or both. ~In normal operation, the unit does
not accumulate~sludge in the sludge-collecting zone and there
will~be little;or no~need for periodic pump outs.
~ The embodiment~shown~in Figures 5 - 6 is similar in most
structural~respects to the Figures 2 - 4 embodiment. In this
embodiment, however, the grating 207 and the draft tubes 208
are supported in a~different manner within the tank 201.
Also, thé draft tubes~208 do not extend above the turbulent
1 30 zone inasmuch as they are supported from below, rather than
~from the overhead tank lid as in the Figures 2 - 4 embodiment.
... . .
In the present embodiment, the grating 207 is supported on
~ brackets 250 that also extend inward to enclose one of the
;~ draft tubes 208 at~their outer ends, as shown in Figure 7.
Also in this embodiment, the tank lid is configured
differently. The lid is provided with a longitudinal
rectangular maintenance opening covered by a non-metallic
WOs4/16s99 PCT~S93/00602
~3~180
walkway cover 251. A tank cover having a pair of triangular
end walls 252 and 253, and with hinged panels 254 and 255 that
overlap at their apex to form a weather-tight roof. The end
panels are vented at 256 so that excess air from the tank 207
can escape through the walkway 251 to the atmosphere. Roof
mounting hinge sets 257 and 258 are attached to tank 207 as
shown in Figure 7. The roof structure may be made of light
weight material such as fiberglass so that installation is
convenient.
~10 ~ With reference to Figures 11-12, the media cage or basket
300 comprises a frame such as the top flotation ring 302, a
media-containing screen 304 that covers all sides of the cage
300,; a draft tube 306 centered in the cage and supported
therein such as by cross-bracing 308 from ring 302, an air
15~ delivery tube 310 extending into the draft tube 306, and
buoyant media 312. The draft tube 306 extends at least
through the top and bottom surfaces of the screen covering
304, and may extend slightly above and below these screen
sur~faces. In Figure 11, the media screen surface acrosæ the
:
~ top~of the cage is broken away for the purpose of better
revealing the support~structure for the draft tube 306. In
Figure 13, the media screen is broken away from the central
and left-hand portions~of the view for the purpose of better
revealing the presence~of the~buoyant media and the cross-
25~ section of the draft~tube configuration.
The media cage screen covering may have structuralstrength sufficient~to~be self-supporting such that only the
framework 302 shown in Figure~ 11 will be sufficient.
Alternately, as shown in Figure 14, the framework may be
provided in the form of top and bottom rectanguIar frames 301,
303 connected by at least one vertical strut 305 per side, and
the screen covering may be provided as a flexible mesh. In
either case, the screen covering has an open mesh
configuration small enough to retain the media and large
enough to enable sloughed bio-mass to pass through. The upper
surface of the screen covering provides the same function as
the grating 7 in the Figure 1 system, the wastewater flowing
WO94/16999 ~ 3 ~18Q PCT~S93/00602
11
therethrough and translating from a turbulent state into a
free-flowing non-turbulent state required for passage through
the floating media. The draft tube 306 may be cylindrical, as
shown in Figure 11, or may have a venturi-tube configuration,
as shown in Figure 13. The air delivery tube 310 may be
provided with a flexible coupling member 311, as shown in
Figure 13, for coupling to an air delivery manifold 313 as
shown in Figure 16.
In Figure 16, four of the Figure 14-type cages are shown
floating in a treatment vessel 315 with the air delivery
manifold extended across the top of the vessel 315 and with
four flexible couplings 311 connecting the manifold with the
air delivery tubes~. In operation, as heretofore described and
shown with reference to Figure 1, aerated wastewater flows
turbulently out of the top of each draft tube as illustrated
in Figure 16 and i5 distributed across the surface of the four
cages. The so-called turbulent zone is that zone between the
top surface of the cages and the top of the treatment vessel
aasing wall. Appropriate wastewater inlet and outlet conduits
ar~ provided for the treatment vessel, but are not shown in
Figure 16.
As shown in Figure 15, several cages may be arranged to
fit any particular treatmeDt vessel configuration. They may
be installed on the~vessel~floor, as shown, and then connected
to the air delivery system. Wastewater may then be charged
into the vessel to~f~loat the cages and then the system process
; started. The cages need not be secured to the treatment
~; vessel nor to one another, although they may be is so desired.
The aeration modules of the Figures 11 - 16 type may be
30 used in any treatment process configuration, if desired.
There are particular advsntages in using them in the Figure 1
type of processing system, but other processes can benefit
from use of these modular aeration structures. Any treatment
system wherein unstable waste loading can degrade the
treatment process effectiveness can benefit from the
installation of these modular aeration structures.
The Figures 11 - 16 cages shown may be 32 inches square
WO94/16999 ~ 80 I PCT~S93100602
and 22 inches high. The framework may be constructed of
plastic or fiber glass material. The screen covering may also
be constructed of plastic or fiber glass material. The draft
tube for each cage may be supported from the top, as shown in
Figure ll, or from the top and the bottom as shown in Figure
14.
In summary:
A secondary sewage treatment system is provided with
verticalIy-aligned foam collecting, turbulent, mixing,
settling, and sludge collecting zones. A grating defines the
boundary between the turbulent and mixing æones. Beneath the
grating, a buoyant media, such as hollow plastic spheres, are
ontained and occupy~substantia}ly all of the mixing zone.
Air diffùsers including~elongated draft tubes extend from the
turbulent zone down through the mixing zone for introduction
of~air to aerate~waste water liquor and to cause the aerated
liquor~to recirculate up into the turbulent zone, thereby
creating a circulation of waste water liquQr from the
;turbulent zone, ~down~throuqh~the mixing zone and around the
~; 2~0 ~; buo~ant media, and up through the draft tubes to the turbulent
zone.
While the preferred~embodiments of the invention have
been described herein,~ variations in the design may be made.
For example,;various~feature of the two embodiments described
25~ herein~may be substituted for one another or combined, as
appropriate. As another example, the secondary treatment
system~apparatus~of this invention might be~incorporated into
a combination treatment tank that would have a first section
that would function as;~a conventional septic tank and a~second
:
~section that would function in accordance with the principles
described herein. The scope of the invention, therefore, is
only to be limited by the claims appended hereto.
The embodiments of the invention in which an exclusive
proper~y is claimed are~defined as follows:
~ ::
.
