CA1100240A - Method and apparatus for aerobic sewage treatment - Google Patents

Abstract

METHOD AND APPARATUS FOR AEROBIC SEWAGE TREATMENT
ABSTRACT
Method and apparatus for converting anaerobic leaching cesspools or drainfields to an aerobic sewage treatment process by reducing the size of floc particles in the presence of an oxygen-containing gas. Sewage is continuously withdrawn from the cesspool or drainfield by a submersible pump and injected into an elongated treatment vessel under conditions of hydraulic turbulence where the sewage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 said sewage is subjected to aerobic treatment and continuously returned to the cesspool or drainfield. Treatment continues until the cesspool or drainfield is functioning under aerobic conditions as measured by percolation of treated sewage into the surrounding soil.

Description

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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 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-. .

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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,-. . .

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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-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-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.

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Claims (5)

?HE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 size 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 aerobic 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.

2. An apparatus according to Claim 1 including means to introduce oxygen-containing gas into said submersible pump.

3. An apparatus according to Claim 1 wherein said compressor means includes a conduit between the compressor discharge and said treatment vessel adjacent said wastewater inlet and said conduit having therein a check valve to prevent backflow of wastewater into said compressor.

4. A method for cleaning clogged wastewater treatment vessels and drainfields subject to anaerobic wastewater treatment conditions 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.

5. A method according to Claim 4 wherein oxygen-containing gas is injected into said portion as it is withdrawn by said pump means.