Note: Descriptions are shown in the official language in which they were submitted.
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Description
On-Site Wastewater Treatment System
Technical Field
This invention relates to an on-site waste-
water treatment system and on-site method of treating
wastewater.
Background Art
On-site disposal of wastewater (sewage) from
single family residences and commercial establishments
in areas with no conventional sewer system has conven-
tionally been accomplished by a septic tank system where
the anaerobic effluent discharged from the septic tank,
after settling of the solids portion of the incoming
wastewater, is passed into a subsurface drainfield 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
drainfield exist. In many areas, soil conditions are
unsuitable for treatment of the effluent from septic
tanks. In such areas, one alternative is to utilize
small treatment plants which make use of chemical and/or
biological treatment means, such as primary, secondary
and sometimes tertiary treatment, to render the effluent
suitable for disposal. Such treatment plants are pro-
hibitively expensive, both to construct and operate,
unless there is a sufficiently dense population base or
industrial base for financially supporting the treatment
plant. Such treatment plants are generally not economi-
cally feasible for treatment of domestic sewage in rural
and semi-rural areas. Other alternative methods of on-
site waste treatment and disposal are known; however,
many of them have never been accepted by local health
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authorities because of insufficient treatment of the
wastewater.
Two alternative systems are illustrated in
Figs. 1 and 2 of the drawings. Fig. 1 illustrates a
system known as the intermittent sand filter system. In
the intermittent sand filter system, anaerobic effluent
from a septic tank is pumped into subsurface drains po-
sitioned in a sand filter. The effluent is generally
pumped into one of the subsurface drains in one area of
the filter bed for a period of time and then switched to
pump it into the other subsurface drain or drains of the
filter bed for a further period of time to allow regen-
eration of the bed around the first drain. In the in-
termittent sand filter, anaerobic slime builds up di-
rectly beneath the perforated drain pipes through whichthe effluent enters. The action of the intermittent
sand filter is primarily mechanical and the bacterial
count of effluent leaving the sand filter is not reduced
substantially. The only oxygen which reaches the efflu-
ent in the sand filter for aerobic degradation of thefecal bacteria is that which filters down through the
top layer of sand. A major disadvantage of the inter-
mittent sand filter is the physical size of the filter
required to treat a particular amount of effluent. For
example, to treat 450 gallons of effluent by such an in-
termittent sand filter would require a sand filter ac-
commodating two 50 foot subsurface drains.
Fig. 2 illustrates another alternative system,
known as the Hines-Favreau system. In the Hines-Favreau
system, effluent is discharged from the septic tank into
a recirculating tank from where it is pumped into per-
forated drain troughs positioned above the level of sand
in the filter bed. The effluent trickles down through
the sand filter, with a portion of the effluent reen-
tering the recirculation tank and a portion being dis-
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charged to a drain field. The portion entering the re-
circulation tank is again recirculated through the sand
filter. With the Hines-Favreau system, a high degree of
mechanical filtration occurs through the sand filter.
Clumps of algae, however, tend to build up directly be-
neath where the effluent trickles down onto the surface
of the sand filter. Over a period of time, this causes
channelization through the filter bed to occur and in-
efficient and ineffective treatment results. As is true
of the intermittent sand filter system, the bacterial
count of effluent discharged from the sand filter of the
Hines-Favreau system, although lower generally than that
discharged from the intermittent sand filter system, is
still too high to satisfy health authorities. After a
period of time with the Hines-Favreau system, the sand
filter becomes matted and clogged with filtered solids
and a bacteriological mat and must be cleaned and/or the
sand replaced. If not, the system fails to work effec-
tively.
In neither of the two prior art systems de-
scribed is there an effective retention/displacement
cycle of the effluent within the sand filter as occurs
in the system claimed. Because of the high ratio of re-
tention time to displacement which occurs in the media
bed of the system described and claimed in this applica-
tion, bacterial action occurs which results in substan-
tially lower bacteria counts in the discharged effluent.
Disclosure of Invention
For purposes of this application, the term
"media" used herein means an artificially constructed
environment conducive to the growth and maintenance of
aerobic soil organisms for the biological treatment of
wastewater.
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It is a primary object of this invention to
provide a dependable on-site wastewater treatment system
wherein wastewater, after solids separation, is passed
through particles of media in a bed, collected, and uni-
formly distributed a second time over the same mediabefore discharge.
It is a further object of this invention to
provide an on-site wastewater treatment system wherein
effluent, after solids separation, is passed intermit-
tently between a first area of particles of a media in abed and a separate area of the same media in the same or
a separate bed with the collected effluent then being
uniformly dispersed over the media in the bed through
which the effluent was initially passed.
It is a further object of this invention to
provide an on-site wastewater treatment system wherein
the fecal bacterial count of the discharged effluent is
reduced sufficiently to permit use of the effluent as
process water for toilets or urinals, for landscape ir-
rigation, or other purposes.
These and other objects are accomplished by a
method and system for on-site treatment of wastewater by
effecting solid-liquid separation of the gravity settle-
able solids portion of the wastewater, passing the ef-
fluent with the solids removed into a bed comprisingparticles of media which retain the effluent therein for
a period of time before displacement by additional ef-
fluent, collecting the displaced effluent, and uniformly
dispersing the displaced effluent over the media for
retention and displacement a second time by the media.
The effluent after retention and displacement a second
time through the media, is collected and discharged. In
order to allow continuous use of the media without in-
curring problems of matting and clogging, the waste-
water, after solids separation, is intermittently passed
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into a first subsurface area of the media for a periodof time and then passed into a separate subsurface area
of the media for a further period of time. The inter-
mittent use of different portions of the media allows
organic recovery of that portion of the media for subse-
quent use.
Brief Description of the Drawings
Figs. lA and lB are schematics of a prior art
intermittent sand filter treatment system and vertical
cross-section of the intermittent sand filter;
Figs. 2A and 2B are schematics of a typical
prior art Hines-Favreau treatment system and vertical
cross-section of the sand filter;
Figs. 3A and 3B are schematics of the treat-
ment system of this invention employing a media having
a single drain opening and vertical cross-section of the
media bed;
Fig. 4 is a vertical cross-section of a modi-
fied media;
Fig. 5 is a perspective view of an on-site
wastewater treatment system wherein the media basin in-
cludes multiple drain openings and wherein a portion of
the effluent displaced from the media is recirculated
through the media more than two times;
Fig. 6 is a top view of the media basin of
Fig. 5;
Figs. 7 and 8 are vertical cross sections of
the media basin of Fig. 2 illustrating positioning of
the distribution lines and drain lines in the media;
Fig. 9 is a an expanded, partial view of one
of the drain openings in the media basin; and
Fig. 10 is an elevation view of an enclosed
media basin.
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Best Mode of Carrying Out the Invention
The on-site wastewater treatment system as
herein described may be used for treatment of
residential or commercial wastes which contain no
significant amounts of heavy metals and/or synthetic
organics of the type discharged from chemical treating
and manufacturing facilities, electroplating industries
or metal working industries. The typical effluent from
residential and commercial business establishments
consists primarily of human waste in admixture with
biodegradable materials, such as food, etc.
The wastewater to be treated generally con-
tains gravity settleable solids. While any means of ef-
fecting solid-liquid separation may be used, the most
commonly used method is a septic tank into which the
wastewater is discharged and the solids allowed to set-
tle by gravity. The effluent leaving the septic tank is
anaerobic; i.e., it is not exposed to air or aeration.
The solids within the septic tank are subjected to par-
tial anaerobic degradation. Although septic tank de-
signs vary, the conventional septic tank is a vessel
containing a bottom wall and side walls, generally of
reinforced concrete, and a top wall having inspection
openings near the inlet and outlet of the vessel and a
central opening for inspection and pumping of the solids
from the tank when necessary. The tank is also general-
ly provided with baffles near the inlet and outlet to
prevent flow of solids from the outlet with the efflu-
ent.
The system described in this application com-
bines certain features of the intermittent sand filter
system and the Hines-Favreau system in a way to create a
more effective and efficient treatment system. As pre-
viously stated, the particulate media in the basin is a
material conducive to the growth and maintenance of aer-
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obic soil type organisms for the biological treatment of
wastewater. The media is preferably a material such as
sand; however, other irregularly shaped particulate
materials, such as particulate garnet, crushed glass,
etc., may be used. The particle size of the particulate
material making up the media should not be so large that
channeling of effluent through the bed occurs readily
nor so small that hydraulic compaction of the bed occurs
and prevents adequate drainage. The irregular-shaped
particles of sand or other particulate media within the
basin are separated by small interstices which hold
effluent by surface tension. The bed of media may be
evenly saturated with effluent and the effluent retained
within the interstices of the media bed for a
substantial retention time before its f eld capacity is
exceeded; i.e., the amount of water the bed of media
will hold until the surface tension between the particu-
late particles is overcome by the addition of additional
amounts of effluent and gravity. The retention~dis-
placement cycle which occurs in the system described inthis application does not occur to the same degree in
either the intermittent sand filter system of Fig. 1 or
the Hines-Favreau system of Fig. 2. In the intermittent
sand filter system, the action is primarily mechanical.
There is no even dispersion of effluent over the surface
of the filter media. The same is true of the Hines-Fav-
reau system, wherein a high degree of mechanical filtra-
tion and channelization of the filter bed occurs without
the retention/displacement cycle of the effluent. The
sand material should preferably fall within the follow-
ing ranges with a uniformity coefficient of about 2.5;
however, other media material having different grain
size distributions which accomplish the results desired
herein may also be used.
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Percentages
Passing a 3/8" sieve........ 100
Passing a No. 4 sieve....... 80-100
Passing a No. 10 sieve...... 35-80
Passing a No. 30 sieve...... 10-60
Passing a No. 50 sieve...... 0-30
Passing a No. 100 sieve..... 0-5
Referring to Fig. 3, wastewater flowing into a
septic tank 1 is discharged into line 2 where it flows
by gravity to the media basin 3 througb two perforated
subsurface drain lines 4 extending substantially the
length of the basin 3. The basin has a sloped bottom
wall and a single drain opening at the apex of the
sloped floor of the basin. The perforated drain lines 4
are placed about 6 inches below the top surface of the
media and are surrounded with a layer of round rock. In
like manner, the drain opening is surrounded with a lay-
er of round rock. Effluent is displaced from the coarse
sand media 5 in the basin through drain opening and
drain line 6 into a recirculating tank 7 which includes
a submersible pump 8 which pumps the displaced effluent
through a valve and line 9 leading back into the basin 3
where it is evenly dispersed by sprinkling through a
sprinkler head over the top surface of the media 5 in
the media basin 3. The effluent distributed uniformly
over the surface of the media is retained by the media
before being displaced again through drain line 6 into
recirculation tank 7. Effluent is discharged from the
recirculation tank through a line leading to a drain-
field or otherwise disposed of. The submersible pump 8
in the recirculation tank is preferably provided with a
clock timer for intermittent operation and may also in-
clude high water and low water controls (not shown1 for
safety purposes.
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Fig. 4 illustrates a modification of the media
basin of Figs. 3A and 3B wherein the media basin 3 is
separated into two sections 3a and 3b by a central wall
3c. Each section of the media basin includes a drain
opening which connects to the recirculation tank 7.
With this modification, a valve is provided in the line
2 to direct effluent coming from the septic tank ini-
tially through one of the subsurface drain lines 4a or
4b, thereby allowing the other drain line to remain
inactive for a period of time for rejuvenation of the
media to occur. Likewise, the line leading from the
recirculation tank may be bifurcated and valved to
uniformly disperse the recirculated effluent through
sprinkler heads over the surface of the media whose sub-
surface drain 4a or 4b is not being used at that time toreceive effluent from the septic tank.
Referring again to Fig. 3B, it is preferable
to alternate use of discrete areas of the media by means
of valving ~not shown) for delivery of effluent through
one of the drain lines 4a for a period of time, then
closing off that line to flow of effluent and delivering
effluent for another period of time only through the ad-
jacent line 4b. By doing so, mat buildup and clogging
of the media around the perforated drain lines 4a and 4b
are prevented through degradation of the organic materi-
al by aerobic bacteria which receive oxygen as a result
of the recirculated effluent distributed over the top
surface of the media which carries dissolved oxygen and
some free oxygen into the media.
Figs. 5 through 10 illustrate a system similar
to that previously described except that the media basin
has multiple drain openings. The system illustrated in
Figs. 5-10 and the media basin thereof is designed so
that effluent discharged into the media basin must trav-
el through the media basin at least twice before dis-
charge.
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Referring to Fig. 5, effluent, after separa-
tion of the gravity settleable solids, is discharged
through line 10 and flows into a wet well 11 where it is
pumped by either submersible pump 12 or 13 to a basin 2Q
as will be described. If it is possible to locate the
basin at a lower elevation than the line 10, flow of the
effluent to the basin may be by gravity, thus eliminat-
ing the need for the wet well 11 and the pumps. Timed
valving may be used to distribute effluent between the
subsurface lines 35 and 36.
The basin 20 is an open air basin, generally
of reinforced concrete or other suitable material, hav-
ing a bottom wall 21 and side walls 22a, b, c and d.
Side wall 22a has openings 23 therein at an appropriate
level for entry of the distribution lines for the efflu-
ent as will be described. The basin is sized to accept
the amount of effluent to be discharged. The bottom
wall of the basin is provided with spaced central drain
openings 25 and spaced periphery drain openings 26 and
27 adjacent to side walls 22b and 22d, as illustrated in
Fig. 2. Between the central drains and the periphery
drains 26 and 27, the portion 28 of the bottom wall 21
of the basin is sloped upward to a mid-rise point 29
from which it slopes downwardly to the respective drain
openings 26 and 27. The central drain openings 25, as
well as the drain openings 26 and 27, may be connected
by shallow trenches 30, 31 and 32, as illustrated by
Figs. 5, 6 and 7. Other means than sloping bottom walls
for the basin may be used to separate the effluent, such
as curbing.
The effluent is delivered into a subsurface
area of the media in the media basin by pumping or by
gravity through subsurface inlet lines 33 and 34, which
enter the media basin through side wall openings 23.
The effluent is distributed into the particles of the
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11
media bed through perforated pipes 35 and 36, each of
which is capped at their respective ends by suitable cap
members 37. The distribution lines 35 and 36 are pro-
vided with perforations along their entire length, pre-
ferably all of the perforations being on one side andpositioned to point upwardly. Referring to Fig. 7, the
basin is filled with particles of a media 38, such as
sand, of the type previously described to a depth of
about two-thirds the depth of the basin. The area
around the distribution lines 35 and 36 is packed with
coarse rock 39 averaging about 3/4" to 1-1/2~ in size or
other material, such as anthracite coal or activated
charcoal. A shallow layer of sand 40 covers the coarse
material 39. The basin may be exposed to the open air
or enclosed as illustrated in Fig. 10 and is rested on a
suitable foundation 41 placed on undisturbed natural
ground. As illustrated in Fig. 7, the areas surrounding
drains 25, 26 and 27, as well as the slots 30, 31 and
32, are preferably packed with a coarse particulate ma-
terial 42, such as round rock.
Referring to Fig. 5, the lines 33 and 34,leading from the wet well 11, are provided with suitable
valving, such as gate valves, to control discharge of
the effluent to the distribution lines 35 and 36. Check
valves may also be provided in lines 33 and 34. If de-
sired, the submersible pumps 12 and 13, which pump ef-
fluent from the wet well 11 into lines 33 and 34, may be
provided with a clock timer, high and low limit switches
and alternating relay, or all of the above, for automat-
ically alternating flo of the effluent between distribu-
tion lines 33 and 34. By so doing, matting and clogging
of the media in the basin is deterred b allowing rest
periods for bacterial action to take place. Depending
on climatic conditions and other factors, it may be de-
sirable to enclose the basin in a structural enclosure
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12
43 (see Fig. 10). An enc~osure over the basin may beused to control the ambient air temperature around the
basin to ensure optimum operating conditions as well,
the enclosure incorporating light filters to prevent
plant growth on the surface of the media. Heat lamps
irradiating the surface of the media in the basin, heat
tapes in the basin, a heater in the recirculation tank
for the effluent, or other means may be used to maintain
the media in the basin at an optimum temperature for
bacterial action.
The effluent exiting through the perforations
in distribution lines 35 and 36 is retained by the media
until the surface tension between the effluent and par-
ticles of the media is overcome by additional effluent
and the effect of gravity. The effluent displaced col-
lects in the center trench 31 for exit through drain
openings 25. Each of the drain openings 25, as illus-
trated in Figs. 5 and 7, connects with a common drain
line 44 which carries the effluent by gravity to a re-
circulation tank 50.
The recirculation tank is illustrated in Fig.5 and is preferably submerged below the level of the
basin so that the effluent from the basin flows into the
recirculation tank by gravity. Sizing of the recircula-
tion tank depends on the capacity and sizing of the ba-
sin. The recirculation tank 50, as illustrated in Fig.
5, includes a bottom wall 51, side walls 52 and a top
wall 53. Access to each section of the recirculating
tank is through openings in the top wall. A recirculat-
ing pump 56 is set in a housing 57 resting above on thetop wall 53, as illustrated in Fig. 5. The inlet of the
pump is connected to a suction line 58 extending down
into the tank. The outlet of the pump is connected to a
recirculation line 59 which pumps the effluent through a
series of lines 60 connecting with a plurality of noz-
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13zles 61. The array of nozzles illustrated in Fig. 5 is
exemplary. Other arrays may be used. What is desired
is to inject the effluent into the air above the basin
for even distribution of the effluent over the entire
surface of the media in the basin. The nozzles are
sized and adapted to cover the entire surface of the
media, effect optimum droplet size and application rate.
High water and lower water alarms of a conventional na-
ture, such as floating mercury switches, are preferably
provided to activate and shut off the pump as necessary.
Primary control of the pump is by a clock timer. About
one-third of the recirculated effluent, as it is dis-
placed from the media in the basin a second time, col-
lects in trenches 30 and 32 and exits through drain
openings 26 and 27 connected to drain lines 62 and 63.
These drain lines are connected together by line 64
leading to a wet well 65. If desired, a gate valve 66
may be provided to control effluent entering the wet
well. The effluent discharged from the basin into the
wet well may be discharged directly into a subsurface
drainfield, discharged to a land application site or
used as process water for landscape irrigation, for
toilets, urinals or other such uses. The wet well 65,
if at a level below that needed for disposal of the ef-
fluent, is provided with submersible pumps 67 for pump-
ing of the effluent through lines 68 and 69.
As previously described, sizing of the basin
recirculation tank, pumps, nozzles and other components
of the system is dependent on the amount of wastewater
entering the system. The following is an illustration
of the system of Figs. 5 to 9 but is not intended to be
limiting in any manner.
Fig. 5 illustrates a reinforced concrete basin
26 feet x 26 feet having side walls approximately 6 feet
high filled with medium sand having a particle size as
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14
previously described. The top surface of the sand was
about 18 inches below the top of the side wall of the
basin. The distribution lines 35 and 36 were set in the
coarse rock layer 39 about 9 inches below the surface of
the sand 40 and about 2 inches below the top surface of
the rock 39 surrounding the distribution lines. The
layer of rock was about 12 inches in depth. The trenches
30 and 32 in the basin were about 6 inches wide and 2
inches deep while the center trench 31 was 8 inches wide
and 2 inches deep. All of the trenches are connected
with 6 inch drain openings and 6 inch drain lines, the
center drain line 44 leading to the recirculation tank
50 and the drain lines 62, 63 and 64 leading to wet well
65. The recirculation tank 50 of reinforced concrete
was about 115 inches wide, 72 inches long and 62 inches
high, the tank having a capacity of about 1500 gallons.
The pump housing atop the recirculating tank was pro-
vided with a suction line 58 positioned about 8 inches
from the bottom wall of the recirculating tank 50. Two
recirculating pumps were utilized, together with a con-
trol system including a high water and low water sensing
means and an alarm system for indicating failure of one
or both of the pumps. Two pumps were used in the event
that one pump failed to operate satisfactorily. The
outlet of the pump recirculated the effluent back
through lines 59 and 60 and nozzles 61, which sprayed
the effluent into the air above the media in the basin
for even distribution of the effluent over the top sur-
face of the media. The recirculated effluent was re-
tained by the media a sufficient time for the aerobicbacteria in the media to reduce the bacterial count sub-
stantially before being displaced by additional effluent
applied onto the top surface of the media. Referring to
Fig. 7, when the recirculated effluent displaced from
the media contacted the sloping bottom wall of the ba-
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15sin, about one-third of the effluent flowed to the outer
drain openings 26 and 27 and out through drain lines 62
and 63 for disposal. The portion of effluent contacting
the sloping wall 28 again exited through the central
drains 25 of the basin and was again recirculated. Oxy-
gen dissolved in the recirculated effluent and free
oxygen carried with the recirculated effluent into the
media promoted bacterial degradation of the suspended
solids held by the media and promoted oxidation of the
BOD so that the effluent discharged was not only free of
suspended solids and other contaminants but had a low
bacterial count.
For possible control of nitrates in the efflu-
ent, a vessel containing pieces of anthracite coal may
be positioned to receive the untreated an anaerobic ef-
fluent discharged from the septic tank. The effluent is
preferably introduced into the vessel holding the coal
near the lower end, with exit of the effluent near the
upper end so as to provide a holding time of the en-
treated effluent within the vessel in contact with thecoal. The effluent, after passage through the coal, then
flows to the media basin for distribution therein.
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