Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2002-04-25
2004-11-23
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S617000, C210S747300, C210S151000, C210S170050, C210S532200, C405S043000
Reexamination Certificate
active
06821424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wastewater treatment, and particularly to wastewater treatment systems for onsite applications.
BACKGROUND OF THE INVENTION
The disposal and/or treatment of waste is as old as civilization itself. The waste products of human activity take many forms, and present numerous disposal and sanitation issues. Of particular importance in the last half century has been the preservation and conservation of our natural resources, including groundwater and land, in particular.
The treatment of wastewater is not a new art, and involves essentially three broad aspects: conveyance, treatment, and disposal. Conveyance is more often associated with large systems, such as municipal sewage treatment systems, and involves transporting the wastewater, with associated solids, to a treatment location.
Various treatment systems are known, including large-scale treatment, common to municipalities, which involve activated sludge processing and/or surface discharge to a river or lake. An onsite wastewater system, however, typically involves a septic tank in combination with a dispersal field. Septic tanks were first introduced in the late 1800's when municipal treatment systems had not yet become an established part of the infrastructure of growing towns and cities. The advent of the Environmental Protection Agency and the population growth in urban areas gave rise to the development of large scale sewer and treatment systems. In recent years, the Environmental Protection Agency has changed its philosophy of placing all homes on large treatment systems with surface discharge, to onsite systems with subsurface dispersal. This has been prompted by increased suburban growth.
Septic systems have not radically changed over the past 100 years. A conventional septic system comprises a septic tank that receives wastewater from a residence, and a dispersal field wherein partially treated wastewater drains into a bed of gravel and soil. The most widely used parameter for estimating the organic pollution of wastewater is the biochemical oxygen demand (BOD). BOD involves the measurement of the dissolved oxygen used by micro-organisms in the biochemical oxidation of organic matter. The higher the number, the greater the organic pollution. Another parameter used in characterizing the degree of pollution is the total suspended solids (TSS). The greater the BOD and TSS, the greater is the formation of a biomat in the drainfield. The biomat, or growth layer of organic matter, accumulates over a period of time and eventually leads to ultimate failure of the drainfield. Thus, measures which reduce BOD and TSS lead to slower growth of the biomat, and thus prolonged life of the septic system. The conventional septic tank generally produces a BOD of about 250 mg/l and a TSS of about 150 mg/l.
As is generally recognized in the art, there are two key factors that reduce the BOD and TSS levels in wastewater: (1) maximizing the oxygen present over a short duration, usually through super-saturation, or (2) increasing the time of treatment. While these principles work well for surface treatment systems, commonly known as activated sludge processes, there has not been a satisfactory and reliable solution for septic systems. There are known septic dispersal systems that incorporate standpipes, or vents, to provide for some natural circulation of air through the dispersal field, but these systems have had little practical effect in reducing the BOD and/or TSS of the waste stream.
SUMMARY OF THE INVENTION
The present invention is directed to a simple and economical wastewater treatment and dispersal system that addresses the problems described above. That is, the treatment and dispersal system is of the type used in conjunction with a septic tank and is directed at lengthening the time of treatment, maximizing the amount of air/oxygen in contact with the wastewater, or a combination thereof, in the dispersal field to minimize BOD and TSS.
The two prominent aspects, induced air and extended treatment time, are somewhat interchangeable, meaning that when one is increased the other may be decreased. In one embodiment, the present invention includes multiple wastewater conduits and at least one pump for forcing air through each of the conduits. Each of the conduits has at least one discharge opening therefrom, and each of the conduits so configured and the discharge openings, or perforations, so sized and positioned that wastewater flowing into the conduits will stand in each of the conduits below the level of the discharge openings until the desired level of effluent BOD is obtained. The conduits may be configured in a conventional dispersal field arrangement with an inlet header, a series of dispersal conduits branching off of the inlet header, and one or more effluent ends. In this embodiment, the effluent end comprises an effluent header in communication with each of the multiple conduits.
The header end of the system is interconnected to a conventional septic tank so that it receives wastewater flowing from a riser or the like, from the septic tank. The connection to the septic tank may consist of more than one line, but is generally just a single inlet. The header end is configured as a manifold; i.e., a main conduit from which a number of individual treatment and dispersal lines branch outward.
While the number of conduits, in and of itself, is not important to the present invention, an important consideration is the total volume of the combined conduits forming the treatment and dispersal field. Conventional conduits are typically dimensioned as approximately 4 inch diameter lines, but as described in greater detail below, the conduits of the present invention are a minimum of 4 inches in diameter and may be dimensioned up to about 48 inches in diameter, or more. One of the underlying considerations of the present invention is the concept of “retention time”. As used herein, “retention time” refers to the total time that the wastewater remains within the treatment system before being dispersed. As will be appreciated by those skilled in the art, the longer the retention time, the greater the duration of biological activity within the system, and the lower the BOD and TSS of the discharged water.
Conventional drainfield conduits are PVC piping or the like, having discharge openings typically aligned and positioned so that the wastewater disperses through the bottom of the piping into the underlying dispersal bed. As has been discussed, this configuration has been used for many years, but does not provide a sufficient retention time or adequate mixing with air/oxygen. As a result, the typical wastewater treatment system comprising a septic tank disperses a treated water having a BOD of about 250 mg/l, or higher.
The conduits of the present invention each have at least one discharge opening that is so positioned to ensure that there will be wastewater standing in a about one half of the volume of each of the conduits. Depending upon whether the system is configured to lengthen the time of treatment or maximize the amount of air/oxygen in contact with the wastewater, or both, the one or more discharge openings may be formed in the upper portion of the conduit or may be formed in a cap, or the like, at the end of the conduit, or a combination thereof. With discharge openings formed in this way, the retention time of the wastewater within the system is maximized, while maximizing the exposure of the wastewater to air, either ambient or forced. Where the one or more discharge openings are formed in the upper portion of the conduit itself, the wastewater eventually rises until it seeps out the discharge openings. Where the one or more discharge openings are formed in an end cap, or flange, the wastewater must travel the full length of the conduit before seeping out, which also maximizes the retention time within the system.
In a second embodiment, using the same or similar conduits, the treatment and dispersal system of the present invention uses forced air through the wastewat
Upton Christopher
Womble Carlyle Sandridge & Rice PLLC
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