Liquid purification or separation – With gas-liquid surface contact means – With separator
Reexamination Certificate
2000-11-06
2002-08-06
Upton, Christopher (Department: 1724)
Liquid purification or separation
With gas-liquid surface contact means
With separator
C210S170050, C210S259000, C210S299000, C210S532200
Reexamination Certificate
active
06428691
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a compact, environmentally benign biological waste water treatment and disposal system.
BACKGROUND OF THE INVENTION
Waste water, or sewage, produced from residential and commercial sources must be treated to remove environmentally adverse components prior to introduction into ground or surface waters. Significant health risks arise from human exposure to untreated waste water predominantly resulting from the presence of fecal coliform. While most cities and towns treat waste water by processing it through an active mechanical and chemical wastewater treatment plant, many “on site” residential treatment systems, primarily septic tanks, are used in rural or remote settings.
The first stage of “on site” treatment occurs at the septic tank, which serves as combined settling and skimming tank in which primary treatment of residential wastewater occurs. When water tight and structurally sound, a septic tank acts as an unheated, unmixed anaerobic digestion chamber where bacteria attacks and decomposes solids and particulate matter suspended in the waste water. The primary purpose of the septic tank is to separate solids, or sludge, from the liquids, and to provide storage for the sludge during the active decomposition process. As separation of the solids occurs, the liquid, or effluent, is passed to a secondary treatment stage.
A variety of secondary treatment systems have been used in conjunction with septic tanks, including, but not limited to: disposal fields, lateral lines, intermittent sand filters, recirculating granular-medium filters, and shallow-trench, sand-filled, pressure-dosed disposal fields. By far, the most common secondary septic treatment includes subsurface-soil absorption. A subsurface-soil absorption system, or leach field, consists of a series of narrow, relatively shallow trenches filled with a porous medium such as gravel. Porous material provides structure to the leach field, increases effluent water treatment, distributes effluent to the infiltrative soil surfaces and provides temporary storage capacity during peak flows.
Septic tank effluent is transported and applied to the disposal field by intermittent gravity flow or by periodic dosing by hydraulic pump or dosing siphon. Effluent discharged to the disposal field infiltrates into the soil primarily through the side-walls of the trench. Once effluent enters the unsaturated soil zone between the ground surface and the groundwater or bedrock, known as the vadose zone, flow is dictated by soil and bedrock conditions. Gravity will force the effluent over soil particle surfaces and within capillary pores where the effluent eventually finds its way into groundwater courses.
Groundwater contamination commonly occurs because effluent does not receive enough “treatment” between the septic tank and the groundwater course. It is common to find high fecal coliform levels in groundwater near septic tanks, leach fields and lateral lines. Typical disposal field treatment occurs as the effluent flows over and through the porous medium used in the disposal field trenches and as it infiltrates and percolates through the soil. Generally, the porous medium of the leach field acts as a submerged anaerobic filter under continuous inundation of effluent, and as an aerobic trickling filter under periodic application of effluent.
Intermittent gravity flow application of effluent in the leach field causes a biomat to develop progressively on any infiltrative surfaces. Once the biomat is in place, it serves as a biological treatment unit and as a mechanical and biological filter. Under this condition, the leach field environment is usually anaerobic due to relatively high organic and solid loading of the leach field. However, biological treatment occurs more rapidly under aerobic conditions than under anaerobic conditions. Therefore, it is usually desirable to use periodic dosing of waste water onto a large area leach field to prevent accumulation of a dense biomat. Periodic dosing facilitates maximum effluent treatment, under aerobic conditions, as the effluent moves through the coarse leach field material in a thin layer and through the soil vadose zone under unsaturated flow conditions.
Another effluent treatment method utilizes sand filters. Particularly, intermittent sand filters are shallow beds of sand provided with a surface oriented effluent distribution system and an underlying drainage system. Effluent from the septic tank is periodically applied across the surface of the sand bed where gravity pulls it downward through the sand where it undergoes physical, chemical and biological transformation. Suspended solids are removed by mechanical straining and sedimentation. Bacteria colonized within the sand grows by autofiltration and increases removal of suspended solids from the effluent. Microorganisms in the sand beds convert ammonia to nitrate and remove biological oxygen demand (BOD) under aerobic conditions. Anaerobic bacteria which coexist in the aerobic environment also bring about denitrification (conversion of nitrate to nitrogen gas) which results in significant loss of nitrogen from the effluent. While effective in secondary treatment of waste water, sand bed are difficult to maintain due to particulates clogging the filter which affects the aerobic condition of the site.
Lateral lines are yet another secondary effluent disposal method, quite similar in application to a leach field. Rather than having a leach field, trench or pit, pipes are connected to the septic tank and channel effluent into contact with the soil vadose zone. Usually, the lateral lines are filled with a porous medium such as gravel, and operate under the same principles as the leach field, albeit over a greater area. Due to the relatively small diameter of a lateral line pipe, typically 4 to 8 inches, it is often necessary to install a significant linear footage of the pipe to achieve the same magnitude of treatment which can be expected in a leach pit.
Often, between 200 and 500 linear feet of lateral line will be necessary to obtain acceptable treatment levels of septic tank effluent. This often requires accessing the land of an adjacent landowner to satisfactorily install and maintain lateral lines. Soils which are too porous provide insufficient treatment time and can result in contaminated effluent reaching groundwater. Soils which are not porous enough can diminish treatment effectiveness and result in incompletely treated sewage reaching the surface. Due to the endless variations of backyard soil conditions throughout the world, none of the currently available secondary treatment methods can be uniformly applied.
Quite often a shallow layer of soil over bedrock makes a leach pit or sand filter impractical. Likewise, a high groundwater table may make any of the conventional treatment methods undesirable and unsafe. Overflowing the treatment area will decrease the effectiveness of treatment and may result in diminishing microbial growth. Small parcels of property, such as are often found in rural towns financially incapable of installing and maintaining a treatment plant, may make lengthy lateral lines undesirable. Further, each of the conventional methods of treatment requires extensive excavation not only at the installation phase, but also in the event of failure, or for necessary periodic maintenance.
Further, each of these conventional disposal fields, leach fields, lateral lines and sand filters, tend to adversely impact the environmental under certain conditions, including: shallow soil over bedrock, exceeding quick or slow soil percolation rates, high groundwater levels, on steep slopes and where treatment must occur in a limited area. Under any of these conditions, effluent might reach the surface or groundwater before treatment occurs. The present invention achieves unexpected levels of treatment when compared to traditional systems.
It is desirable to have a system which is easy to repair and which needs little maintenance. Further, it is desirable to have a secondary treatmen
Lathrop & Gage L.C.
Upton Christopher
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