Chemistry: molecular biology and microbiology – Apparatus – Bioreactor
Reexamination Certificate
2000-04-18
2001-07-03
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Bioreactor
C435S290100, C435S294100, C034S237000, C055S358000, C055S494000
Reexamination Certificate
active
06255102
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns removal of noxious odors and components from gases given off by a sewage treatment facility. More specifically, the invention concerns a modular support system for erecting a biofiltration support bed in virtually any size and shape desired.
Biological air pollution control has been used on an increasing basis in recent years to cleanse noxious and odorous gases, such as those emanating from a sewage treatment plant. The biological filtration systems, or biofilters utilize a bed of stacked biofilter material such as compost, tree bark, peat, heather or soil, generally about three feet or more deep. The containment gas from the sewage treatment plant or other sources is blown through the biofilter material in an upward direction. The material in the biofiltration bed provides an environment for a diverse culture of microorganisms, which degrade the gaseous pollutants as they pass through the biofilter.
Such biofiltration or biological treatment of the gases is an inexpensive treatment method, but the raw gas stream must generally meet certain conditions: The pollutants should be water soluble and biodegradable, and free of toxic components. Also, there must be sufficient concentration of oxygen. Further, the gas stream should nearly saturated with water (relative humidity at least about 95%), and at temperature between about 40° F. and 140° F. (more preferably between 50° F. and 100° F.). The odorous gas must also contain no more than small amounts of dust and grease.
These requirements usually dictate that the raw gas be preconditioned before entering into the biofilter bed. Preconditioning includes humidification, temperature control and removal of particulates.
In the biofilter itself, a biofilm covers the substrate of tree bark, peat, heather, etc. Water soluble air pollutants are absorbed into the biofilm and decomposed into carbon dioxide and water by the microbes. The filter beds are often built on a single level, but where area is limited, multiple level biofilters have been constructed, with the raw gas stream divided and fed in parallel to the various levels of the biofilter system.
Regarding sizing of the biofilter beds, the height of the filter bed, i.e. the stack of organic material as the medium, is generally in the range of about 1½ feet to 5 feet. Areas are up to tens of thousands of square feet. One rule of thumb regarding the calculation of needed area for a given waste air flow is that the “area load” or ratio between the waste gas flow rate and the filter area should be in the range of about 2.5 to 3.0 CFM/SF. The flow distribution and humidity of the inlet gas have to be carefully controlled, otherwise the filter bed will eventually clog and cease to function. Distribution throughout the area of the filter bed should be relatively even.
In addition to sewage treatment plants, biofilters are useful for treating the effluent gases from many other processes. These include factory farming, rendering plants, coffee roasters, foundries, composting plants, kraft paper drying and paint shops. The odorous emissions treatable include ammonia, hydrogen sulfide, amines, aldehydes, mercaptains, alcohols, disulfides, esters, fatty acids, unsaturated hydrocarbons, ketones, hexane, dichloromethane, formaldehyde, phenol, organic acids, acetone, toluene and others.
These biofilter systems are being used increasingly in treating the gases from sewage treatment processes and also some of the other processes listed above. There is a need for a relatively simple, inexpensive and modular approach for constructing a filter bed support for such biofilters.
Hallsten U.S. Pat. No. 5,454,195 discloses a modular containment system for preventing hazardous materials from leaching into the ground or otherwise escaping a defined containment area. That system includes peripheral modules and a liner to define the containment area, the modules being fillable by water or granular material, and the system has some relevance to the present invention described below.
SUMMARY OF THE INVENTION
The invention provides a very efficient and relatively inexpensive solution to erection of a biofilter support bed of desired area, on a single level or, in another embodiment, on multiple stacked levels. The system consists of modular components, quickly assembled on a flat site which may be unpaved ground, and with capability to produce many different sizes and rectangular shapes, as well as areas, of a filter bed support to retain and confine a biofilter medium.
The system of modules for construction of the support apparatus includes a series of peripheral modules or berm modules with means for assembling the modules end-to-end to form a free-standing peripheral frame surrounding a filtering area. A multiplicity of polygonal bed platform modules with generally planar top surfaces are shaped to be arranged side-by-side contiguously to cover the entire filtering area within the peripheral frame. In the bottom side of each bed platform module are leg-receiving recesses. At least some of the bed platform modules are perforated so as to allow gas to pass vertically through.
On the interior sides of the peripheral modules are module support means for engaging with and supporting edges of the bed platform modules to thereby provide partial support for those platform modules positioned at the periphery of the filtering area and adjacent to the peripheral frame. The system includes bed support legs having upper ends sized and shaped to be closely received in the leg-receiving recesses in the bottom sides of the bed platform modules, and of length sufficient to support and elevate the bed platform modules above a base surface, thus forming a plenum under the bed platform modules. The legs are assembled on-site into the platform modules.
The peripheral modules are substantially taller than the bed support legs, so that the assembled modular support apparatus forms a large open-topped tray for supporting the bed of biofilter medium, with the peripheral frame extending above the support surface to contain the bed and with the plenum below the support surface and also bordered by the peripheral frame.
In a preferred embodiment the module support means on the peripheral modules comprises a horizontally extending recess or slot in the interior side of each peripheral module, of a size to receive an edge of a bed platform module. Accordingly, no support legs are needed near the outer edges of the bed platform modules which are adjacent to the peripheral frame.
Since distribution of the gases in a relatively even manner throughout the area of the biofilter medium is important to efficiency of the process, the invention in one specific embodiment has vanes secured to at least some of the bed support legs within the plenum under the support bed, and these vanes are adjustable in orientation such that they can be oriented to direct gases to achieve a generally even distribution. To avoid collection of gas toward the periphery of the plenum, and to prevent gas flow up along the peripheral module walls (avoiding treatment), the outermost bed platform modules, those adjacent to and in contact with the peripheral frame, may be provided without perforations, or with reduced perforations.
To seal the gas plenum against the ground and against leakage at the peripheral frame, the system preferably includes a substantially gas-impermeable liner which lies on the ground or slab and on which the legs rest supporting the bed platform modules. The peripheral modules also rest on the liner, and in a preferred embodiment, these modules have a vertical slot extending up from the bottom side in such a way as to form a substantially continuous slot around the periphery, the liner being forced up into this slot or recess by a liner retainer block which is press fit against the liner and into the slot or recess. The peripheral modules are hollow and fillable with water or granular material, and when filled, they improve the seal with the liner.
One situation where the modular system of t
Beisner William H.
Freiburger Thomas M.
Hallsten Corporation
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