Note: Descriptions are shown in the official language in which they were submitted.
"` llO~Z~O
BACKGROUND OF THE INVENTION
Field of the Invention
The pr-~sent invention relates to the field of sewage
treatment and, in particular, to coverting anaerobic sewage
treatment units such as leaching cesspools, cesspools, and
drainfields to aerobic processes. In particular, the
invention pertains to an aerobic sewage treatment unit having
optimum aeration efficiency used in conjunction with a
cesspool or drainfield to maintain aerobic conditions and to
facilitate percolation of the treated sewage effluent into
the surrounding soil.
Description of_the Prior Art
Cesspools employing the anaerobic process are widely
used in areas that do not have public sewage disposal
facilities. Modern cesspools consist of circular concrete
leaching drains installed in the soil with an access
manhole at or near grade level. Raw sewage flows by
gravity into the cesspool where the solids gravitate
or settle to the bottom of the pool and liquid sewage
discharges into the surrounding soil through openings in
the leaching drain, where, according to the theory of
cesspool treatment, the filtration effect of the solid will
result in purification of the liquid portion of the raw
sewage separated from the settled solids. Prior art
cesspools have been constructed with loose-fitting
materials such as stones, blocks, and in some cases logs
for a base; however, they are all intended to function in
a like manner.
j 1/ -1-
~k
``` 11~2~0
Although the cesspool and the conventional septic
tank and sub-surface drainfields associated with both
operate under anaerobic conditions, the septic tank was
developed as an improvement over the cesspool. In the
conventional septic tank, solids are collected in the
tank to avoid clogging of the drainfield and surrounding
soil by interposing a baffle or solid wall between the
accumulated solids and the liquid that eventually goes
into the drainfield for leaching into the soil. With
`10 either the cesspool or the septic tank, however, any
purification of liquid sewage is only effected by the
filtration effect of the solid and the anaerobic
digestion process.
One method and apparatus for providing an improved
sewage treatment utilizing a conventional septic tank is
disclosed in U.S. Patent 4,002,561. Patentee discloses
an apparatus and method for providing aerobic sewage
treatment in a conventional septic tank.
jl/ -2-
11C)t~2~0
SUMMARY OF THE INVENTION
In order to avoid the above-described problems, it
has been discovered that a conventional anaerobic leaching
cesspool and/or a clogged drainfield associated with a
leaching cesspool or conventional anaerobic septic tank
can be converted to aerobic processes for treating newly
generated raw sewage and accumulated raw sewage to provide
a more effective sewage treatment system. In the case of
a clogged drainfield, the aerobic process utilized according
to the present invention will enable the aerobically
treated sewage liquid to percolate into the surrounding
soil. With the method and apparatus of the present
invention, raw sewage is continuously drawn from the cesspool
or the drainfield by a submersible pump disposed within
the raw sewage. The sewage withdrawn from the cesspool or
drainfield is in;ected into an elongated treatment vessel
under conditions of hydraulic turbulence where the sewage -
! iS moved across a sharp surface in the presence of an
oxygen-containing gas so that the sewage is subjected to
aerobic t~eatment. The aerobically treated sewage is
continuously returned to the cesspool or drainfield and the
process continues until the cesspool or drainfield is
under`aerobic conditions. Sensors placed in the soil
surrounding the cesspool or drainfield will detect the
presence of liquid and serve as precise indicators that
the process is proceeding along
- 30
jl/ -3-
2~0
under aerobic conditions. Also, visible percolation into
the soild and a drop in the level of wastewater in the
cesspool are gross indicators that the system is aerobic.
In one particular aspect the present invention provides
in~a leaching cesspool system for collecting and treating
wastewater from residential, educational, health care, and
small commercial establishments, the improvement which
comprises in combination:
a submersible sewage pump disposed adjacent the bottom
of said leaching cesspool for withdrawing a portion of said
wastewater;
means for conducting the withdrawn wastewater into an
elongated generally cylindrical vessel, said vessel containing
a tangential inlet on one end and a tangential outlet on the
other end to cause the wastewater to circulate around the
circumference of said vessel and along its axis, thus
creating hydraulic turbulence in said fluid;
! sharp edged surface means including a knife-edged
baffle disposed within said vessel to contact and reduce the
si~e of the floc particles contained in said wastewater;
compressor means to introduce an oxygen-containing gas
into said vessel underneath and along said baffle and into
said wastewater in said vessel so that said wastewater is
exposed to aérobic processes and
means to continuously return effluent from said
tangential outlet in said vessel to said leaching cesspool;
whereby said leaching cesspool operates under aerobic
conditions to prevent formation of insoluble components or
bacteria to clog the soil surrounding the leaching cesspool.
In another particular aspect the present invention
provides a method for cleaning clogged wastewater treatment ~-
vessels and drainfields subject to anaerobic wastewater
~ J -4-
. .
24~
treatment condltions comprising the steps of:
disposing a submersible pump means adjacent the bottom
of said vessel or clogged field containing wastewater or
solid waste material;
utilizing said pump means to continuously withdraw a
portion of the wastewater or solid waste material adjacent
said pump;
injecting said withdrawn portion into a closed treating
vessel containing a sharp-edged surface through a tangential
inlet in said vessel so that said portion flows tangentially
through said vessel under conditions of hydraulic turbulence
so that floc particles in said portion are subjected to
shear forces by moving across said surface in said vessel;
simultaneously injecting an oxygen-containing gas into
said vessel so that said portion is subjected to aerobic
treatment as it is forced to a tangential outlet in said
vessel;
returning effluent from said outlet to said treatment
vessel or drainfield until said vessel or drainfield becomes
an aerobic treatment zone; and
continuing said steps until said vessel or drainfield
is cleared of solid particles preventing percolation of
treated wastewater into the surrounding soil.
BRIEF DESCRIPTION OF THE DRAWI~G
Figure 1 is a top plan view of a modern leaching
cesspool with the concrete cover partially broken away
to }eveal placement of the apparatus according to the
present invention.
Figure 2 is a view taken along line 2-2 of Figure 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Anaerobic sewage treatment processes are characterized
by the fact that the wastewater (raw sewage) is without
jl/~ -4a-
,~,
.
` dissolved oxygen and that no oxygen is brought in from
the air. If all the wastewater contains no dissolved
oxygen, sulfates serve as a source of oxygen for the
anaerobic bacterla. Elemental sulphur remains and
subsequently forms together with hydrogen the odorous
hydrogen sulfide (H2S). In most cases, the surrounding
soil contains iron compounds which react with the hydrogen
sulfide to form ferrous sulfide (FeS), the black
insoluble material which is
~ 4b-
;~
2~)
characteristic of soils exposed to anaerobic seepage or
soils surrounding leach beds. Ferrous sulfide forms small
solid particles which plug small soil pores. Additional
plugging occurs through excessive growth of anaerobic
bacteria. If biological conditions at the natural soil
interface are totally and constantly anaerobic, percolation
of the wastewater into the soil is thwarted and failure
of the wastewater (sewage) treatment system will occur
within one or two months after the anaerobic process begins.
A more detailed discussion of the anaerobic sewage treatment
process can be found in Volume 1 of "Treatment and Disposal
of Wastewater from Homes by Soil Infiltration and Evapotrans-
piration" by Dr. Alfred P. Bernhard, University of Toronto
Press, 1973.
The anaerobic sewage treatment process in general and
cesspools, in particular, fail by preventing percolation of
the liquid portion of the Sewage into the surrounding soils
thus necessitating the addition of new cesspools, which in
turn eventually fail until, in high density population areas,
there is literally no more room to install new cesspools.
The contained sewage must then be pumped out and hauled away
to other sewage disposal sites, an expensive and odorous
alternative. Chemical products and enzymes have been
developed to aid in percolation of the liquid product from
the cesspools into the surrounding soil, however, they have
proved to be ineffective in eliminating 'the problem totally.
The extent of the problem is adequately summarized in
a December 1969 study on household waste authored by
Messrs. Bailey, Benoit, Dodson, Robb, and Wellman under a
contract from the Federal Water Quality Administration of
the Department of the Interior to the General Dynamics
Corporation (Contract No. 14-12-422). In their report, the
jl/ -5-
24~
uthors stated the following:
"In areas where the soil itself is suitable
for absorption systems, they are undesirable
because of high ground water levels such
that adequate filtration cannot be achieved
before the effluent enters the ground water.
The soil surface, or more accurately the
interface between the waste distribution and
the soil, is the key to clogging problems.
Under aerobic conditions, the ferric sulphate
is oxidized to a soluble ferric salt and
flushed through the soil, thus allowing
infiltration to continue. The aerobic
condition also relieves the surface clogging
as the organic solids are oxidized mo~e
rapidly. Aerobic unsaturated soil is
also an essential to the removal and
oxidation of detergents and other resistant
organic compounds. The problem is to obtain
and maintain these aerobic conditions. The
most effective technique for achieving these
aerobic conditions was to merely rest the
system and apply no more effluent. Un-
fortunately, the resting period required
to restore infiltration effectiveness is
much longer than now practical, often
several months."
If aerobic conditions can be maintained in the cesspool
as noted above, ferric iron compounds are formed which are
soluble in water. Consequently, the black color in the soil
disappears and the soil pores are reopened. The aerobes,
protozoa, rotifera, and nematoda can now reduce bacterial
j 1/ -6,-
. . .
24~
accumulations and percolation of the liquid portion of
the wastewater (sewage) into the soil is again facilitated.
The present invention enables a conventional leaching
cesspool or a drainfield having a pool or reservoir of
wastewater or sewage to function as a biological reactor.
In a conventional extended aeration plant, compartmented
tanks are used for treating wastewater. In the context
of this disclosure, wastewater is taken to mean the effluent
from the sanitary drainage system in a residence. Wastewater
consists of biological wastes as well as drain water from
sinks, showers, household washing machines, and the like.
Raw sewage (wastewater) in a conventional extended aeration
plant drains into a first compartment where it is aerated,
the mixed liquor from this compartment is forced into a
second settling compartment where the activated sludge
solids settle to the bottom of the compartment and the clear
liquor on the surface is discharged from the tank. The
activated sludge solids that have accumulated on the bottom
of the settling compartment are then pumped or otherwise
directed back into the aeration compartment for further
treatment at timed intervals.
The method and apparatus of the present invention
produces a flotation that is so complete, thus no activated
sludge solids are left on the bottom of the pool and digestion
is accelerated to such an extent that a single cesspool
employed as a biological reactor is all that is necessary to
treat residential, commercial, or light industrial wastewater
effluent. Conventional terms used in this specification
and in discussing the treatment of sewage are found in U.S.
Patent 4,002,561.
As will be hereinafter more fully disclosed, the
present invention utilizes an improved apparatus of the type
~ 7-
~, ,
2~0
disclosed in U.S. Patent 4,002,561. The improved apparatus
results from employing a liquid tangential flow across a
knife edge together with hydraulic turbulence in the treating
vessel (micro-liquefaction chamber), which produces great
shear forces across a knife edge. The turbulence is produced
by forceably injecting 120 gallons per minute (gpm) of
liquid and 2.2 cubic feet per minute (cfm) of air or other
oxygen-containing gas into a chamber with a volumetric
capacity of only 0.66 gallons. The flow rates of the liquid
in gallons and the air or other oxygen-containing gas is
directly proportional to the volumetric capacity of the
biological reactor (cesspool) being treated.
Referring to the drawing, Figure 2 shows a conventional
leaching cesspool consisting of a dome section 10 and ring
section 12 containing a plurality of sanitary drain rings
14 and 16 having therein a plurality of drain openings 18.
The drain rings 14 and 16 are in a vertically nested
relationship and sit on a base 20 which can be a solid
concrete platform or a bed of gravel, stones, or other
porous material having some structural stability for the soil.
Disposed on top of ring 16 is a dome 22, which may have
drain openings 18. In some structures, it may be preferable
to omit the drain openings 18 from dome 22. Dome 22 is
closed at its uppermost end by an adaptor ring 24 and cover
26 as is conventional in the art. The sanitary drain rings
14 and 16, dome 22, and related closure are offered for sale
by Andrew Carlson & Sons, Inc. of Kings Park, New York.
According to the present invention, a base plate 30 of
aluminum or other structural metal having an opening 32 is
fitted underneath the cover 26. Disposed on the one side of
base plate 30 are a pair of structura~ supports 34 and 36
which are adapted to hold a microliquefaction chamber 38,
~ 8-
240
such as disclosed in U.S. Patent 4,002,561. The chamber
38 contains an inlet 40 and an outlet 42 with associated
piping as will hereinafter be more fully described. Fitted
in the top of chamber 38 is a sample port and associated
hardware shown generally as 50 for withdrawing a sample of
the material undergoing treatment in chamber 38, Inlet
fitting 40 is connected to a conduit 52 which in turn is
connected to a submersible sewage pump 54 disposed at the
bottom 20 of the leaching cesspool 10, 12. The submersible
pump 54 has the necessary electrical lead 56 which also can
be associated with an air conduit and a lifting line 58 so
that the pump can be made accessible for service. Cha~ber 38
includes an air or oxidizing gas inlet adaptor 60 including
a check valve (not shown). A conduit 62 entering through dome
22 serves to provide access for the electrical leads 56 and
air hose 63 for providing electricity to power the motor of
the submersible pump 54 and to provide air or other oxidizing
I gas to chamber 38. Air is supplied to conduit 63 by means
of a small air compressor (not shown) as discussed in the
'561 Patent.
In operation, raw sewage is pumped by means of a
submersible pump from the bottom of the cesspool 10 through
conduit 52 into the microliquifaction chamber 38. The
microliquefaction chamber 38 has disposed therein a knife
edge (not shown) along its central axis disposed generally
above the inlet fitting 60. As the sewage is pumped through
conduit 52 into the mlcroliquefaction chamber 38, it is
caused to circulate around the chamber with hydraulic
turbulence. As it circulates throughout the chamber, it is
caused to pass over the knife edge where the floc particles
are reduced in size and exposed to air or other oxygen-
containing gas entering the chamber 38 underneath the knife
j 1/ _9_
2~
edge as is disclosed in the '561 Patent. As the treated
wastewater moves toward the discharge conduit 42, it has
undergone aerobic treatment and under aerobic conditions
is discharged through pipe or conduit 70 back into the
leaching cesspool or leach (drain) field. The process
continues until the cesspool or drainfield is under aerobic
conditions.
Liquid sensors can be placed in the soil at various
soil depths and at locations adjacent to the leaching
cesspool or drainfield and will indicate when aerobic
treatment has been effected in the wastewater to the point
where the surrounding soil ha~ been unclogged and the soil is
once again effective to filter the liquid portion of the
wastewater effluent. The use of sensors is expensive and
only necessary where it is difficult or impossible to view
- the cesspool or drainfield. If sensors are not used, the
level of effluent in the cesspool will drop measurably under
aerobic conditions.
Actual experience has shown that the aerobic effluent
from a treatment tank would clean up a drain field that has
previously been blocked by anaerobic discharge from the
anaerobic digestion process so that the drainfield will
again percolate liquid wastewater and accept effluent as
it did when the drainfield was originally installed.
When the method and apparatus of the invention are
used to create an aerobic cesspool, the pool is always in
an aerobic condition so the aerobic digestion process takes
place constantly and is not dependent upon flow from the
building it is supporting.
All residential or commercial on-lot sewage systems
are intended to dispose of the liquid portion of the
wastewater into the surrounding soil. Aerobic cesspools
j 1 / -10-
Z~
according to the present invention accomplish this in an
exemplary manner by keeping the cesspool inventory in a
constant aerobic condition so that the liquid portion can
percolate into the soil down to the level of a pressure
switch which can be connected to the pump which will, in
turn, turn off the treatment unit until more liquid enters
the cesspool, thus actuating the unit to repeat the cycle.
This action can be automatic without the need for an
attendant and the unit can operate only as long as necessary
to maintain the cesspool in an aerobic condition so that
the liquid portion of the wastewater will percolate into
the surrounding soil where the filtering action of the 50il
accomplishes the final clean-up before the liquid enters
any surrounding ground water.
The method and apparatus of the present invention
were installed on two on-lot sewage treatment sites having
similar problems in that there was not enough land
! available to install additional sub-surface drainfields to
accomodate effluent from the primary collection vessel. The
soil properties at the test sites were vastly different --
one, located in a heavy clay, hard pan area with very poor
percolation; and the other, in an area with natural sand
and gravel with excellent percolation.
The test site in the clay soil area consisted of a -
stone cesspool installed in 1908 which serviced a bank
building until approximately three years ago when the
building was sold and converted into three large apartments.
The anaerobic discharge eventually blocked the soil and the
sewage backed up into the plumbing in the building. The
owner has no possibility of installing additional cesspools
on the lot. A system according to the present invention
was installed in the existing cesspool and it converted the
j 1 / - 1 1 -
Q2~
contents of the cesspool by aerobic processes to a liquid
that was able to percolate the soil within two days after
the unit was installed. The installation is still in
operation and is servicing the apartments even though the
occupants have installed automatic laundry equipment which
increases the flow considerably. To date, no surface
discharge has been detected.
The second test site is located near the seashore and
services a large restaurant. The restaurant owner had
installed new cesspools annually over several years until
there was no land area to install new leaching cesspools.
- In periods of high usage when the liquid portion of the
sewage would not percolate into the soil, the cesspools
has to be pumped and the sewage hauled away generally on
a weekly schedule. Two systems according to the present
invention were installed in blocked cesspools and the
liquid began percolating into the surrounding sand and
gravel and soil within two days. A twelve-hour composite
sample of the influent sewage indicated BOD5 of greater than
1,160 ppm and suspended solids greater than 890 ppm. This
sewage was meted into one cesspool for twelve hours; and 180
gallons per hour were meted into the other cesspool for a
twelve-hour period. There was no overflow from the pools,
no odors, and the liquid percolated into the soil.
The system according to the present invention in the
restaurant operated an entire summer under conditions of
high ground water level, high ambient temperature, high
grease and fat content, BOD~ in excess of 1,160 ppm, flows
in excess of 12,000 gallons per day, hourly flows of up to
1200 gallons per hour, and in the presence of chemicals
which cause bacterial degradation. Proof of drainfield
clean out in this application and the use of less leaching
jlj -12-
240
area was shown by the fact that during the hurricane of
1976 that struck the East Coast, power to the treatment
units was cut. One eight foot by eight foot cesspool
located in the water table leached the entire effluent
for at least two days. There was no evidence of backing
up or of clogging of the cesspools or drainfields. At
this site, the use of cesspools was decreased from 14 - 4,
less drainfield area is required and the cesspools no longer
have to be pumped and the effluent carted away.
According to the foregoing description and the
discoveries made herein, it was heretofore unknown than
an apparatus such as disclosed in U.S. Patent 4,002,561
could be used to convert a cesspool to an aerobic, biological
reactor and to clean out clogged cesspools, drainfields,
and the like.
~ 13-
