Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2001-07-17
2003-06-10
Prince, Fred (Department: 1723)
Liquid purification or separation
Processes
Treatment by living organism
C210S614000, C210S747300, C210S139000, C210S170050, C210S221200, C210S260000, C210S532100, C405S043000, C405S051000
Reexamination Certificate
active
06576130
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to drainfields and, in particular, this invention relates to a process for renovating failed septic tank soil absorption systems or maintaining functioning septic tank soil absorption systems.
2. Background
A typical on-site septic system is disclosed in
FIGS. 1-3
generally at
20
and includes a hydraulic system
21
and an absorption field
22
. Sewage is generated from a facility, such as a house
23
, and flows through a sewer line
24
into a settling tank, such as a septic tank
26
. Upon being conveyed to the septic tank
26
, solid materials are allowed to settle out of the sewage and the separated liquid effluent (wastewater) then flows through line
28
to the absorption field
22
via a system designated generally at
30
.
The system
30
depicted in
FIG. 1
is a trench system and will be more particularly described hereinbelow. However, the present method is contemplated to be applicable to bed systems, seepage pits, mound systems, or any other system using an underlying soil profile to absorb and detoxify wastewater. These and other disposal systems are disclosed in
Onsite Wastewater Treatment and Disposal Systems,
Design Manual No. 35, U.S.E.P.A. (January 1980), hereby incorporated by reference Each of these disposal systems uses an absorption field defined in a soil profile to dispose and purify wastewater. While the following discussion addresses primarily a trench system, the problem of maintaining and reclaiming soil absorption systems is common to each method of wastewater disposal and the present
The trench system depicted in
FIGS. 1-3
includes distribution boxes
32
,
34
, and
36
, lines
38
and
40
, and laterals
42
,
44
,
46
,
48
,
50
, and
52
. Wastewater is conveyed from the septic tank
26
through the line
28
to the distribution box
32
. The distribution box
32
usually divides wastewater flowing therein between the laterals
42
and
48
and the line
38
. The line
38
conveys wastewater to the distribution box
34
. The distribution box
34
divides the wastewater flowing therein between the laterals
44
and
50
and the line
40
. The wastewater flowing through the line
40
flows into the distribution box
36
, where the waste water is divided between laterals
46
and
52
. Each of the distribution boxes
32
,
34
, and
36
may include valves or the like to further control the flow and distribution of wastewater. For instance, the distribution box
34
could contain a valve controlling the flow or the amount of flow, to the laterals
44
and
50
, as well as the line
40
.
The entire disposal system
20
is usually buried. However, for the sake of clarity, the absorption system
30
is shown as being buried within a trench system
54
. With the exception of the permeable laterals
42
,
44
,
46
,
48
,
50
, and
52
, the entire disposal system is usually impermeable to fluid egress. The laterals usually contain perforations or other openings to allow egress of wastewater into the soil profile.
Referring to
FIGS. 4 and 5
, the exemplary trench system
54
is present within a soil profile
60
. The soil profile
60
may arbitrarily be considered to include an upper portion
62
and a lower portion
64
. A trench
66
is excavated in the soil profile
60
and is defined by sidewalls
68
and
70
and a bottom
72
. The sidewalls
68
and
70
are defined by the upper soil profile portion
62
and the bottom is defined by the lower soil portion
64
. As can be seen, one of the laterals
52
has been installed within the trench
66
. A multiplicity of perforations
76
for wastewater egress can be seen in the lateral
52
. A layer
80
of aggregate, such as gravel, is laid in the trench
66
so as to more or less evenly cover the bottom
72
to a desired height (e.g., four inches). The lateral
52
is then laid atop the gravel layer
80
and another gravel layer
82
is poured in to cover the lateral
52
to a desired height (e.g., six inches). A usually semi-permeable barrier
84
covers the gravel layer
82
and backfill
86
is used to fill the remainder of the trench
66
. The barrier
84
prevents the backfill from penetrating, and plugging, the gravel layers
80
and
82
and may also shed moisture percolating down from the surface of the soil profile
60
. Shedding moisture thusly may be desirable to prevent the gravel layers
80
and
82
from being filled by water percolating from the surface. Wastewater egresses the lateral
52
via the perforations
76
and enters the interstitial spaces between the gravel particulates in layers
80
and
82
. From the layers
80
and
82
, the wastewater enters the soil profile
60
by being absorbed through an infiltrative surface
87
formed by the sidewalls
68
and
70
and bottom
72
. The direction of the wastewater flow through the soil profile
60
is generally down as indicated by arrows
88
, but may be somewhat lateral as depicted by arrow
90
. The texture and water content are two major factors determining the extent and direction of the travel of the wastewater entering the soil profile
60
. Upon entering the soil profile
60
, the wastewater is exposed primarily to bacteria disposed on the surface of the soil particulates. These bacteria detoxify the wastewater by decomposing undesirable compounds dissolved or suspended therein. When the portion of the soil profile
60
surrounding the trench
66
becomes saturated with wastewater, wastewater pools within the gravel layers
80
and
82
until soil conditions allow for wastewater entry and percolation.
Initially, wastewater flows relatively freely into the soil profile
60
. However over time, the soil profile
60
loses the ability to absorb the wastewater. When the hydraulic loading rate of the system exceeds the wastewater infiltration of the soil profile, the wastewater begins to pond, or accumulate, in the system. If this situation continues, the net result is wastewater backing up into the home or appearing the above the ground surface above the absorption field
30
. In either event, the septic system is considered to have failed. Remedies for restoring absorption fields which will no longer absorb sufficient amounts of wastewater include discontinuing use of the system, use of hydrogen peroxide or other oxidizing agents such as ozone in the disposal field, reduction of the BOD of effluent leaving the settling tank, or installing a new absorption field. Moreover, maintaining the equipment necessary to produce hydrogen peroxide or ozone can be time consuming and costly as well. Discontinuing use of septic systems is usually not feasible. Moreover, applying hydrogen peroxide or other oxidizing agents to the soil profile has often not renovated the system and has been observed to be deleterious to the soil structure. Reducing BOD and suspended solids in wastewater being conveyed to an absorption field is frequently expensive and requires continual monitoring and maintenance.
While not desiring to be limited to any particular theory, a layer called a biological mat or biomat
94
(
FIG. 5
) forms proximate the soil infiltrative surface (i.e., proximate sidewalls
68
and
70
and bottom
72
). The biomat may be anaerobic residues as well as undecomposed solids from wastewater, bacteria, and bacterial extracelluar polymers which clog the soil pores within the biomat layer
94
. Due to the lack of available oxygen, an almost exclusively anaerobic environment is created within the portion of the soil profile
60
being infiltrated by wastewater, especially so proximate where the biomat layer
94
forms. A nonlimiting listing of anaerobic microbes often present in soil include bacterial genera Sphaerotilus, Pseudomonas, Escherichia, Salmonella, Shigella, Klebsiella, Enterobacter, Aeromonas, Desulfovibrio, Clostridium, Streptococcus, and Methanobacterium, and other microbial genera Nocardia and Streptomyces. A nonlimiting listing of aerobic bacterial genera often present in soil includes Rhodospirillum, Chlorobium, Beggiatoa, Flexibacter, T
North American Wetland Engineering, Inc.
Patterson Thuente Skaar & Christensen P.A.
Prince Fred
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