Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Treating gas – emulsion – or foam
Reexamination Certificate
1999-07-07
2001-08-07
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Treating gas, emulsion, or foam
C435S299100
Reexamination Certificate
active
06271020
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to biofiltration processes and more particularly to a process and filter for increasing the biofilter efficiency in removal processes of sulfur-containing compounds.
BACKGROUND OF THE INVENTION
Environmental regulations are implemented to restrict the emission of pollutants into the atmosphere. Accordingly, it is necessary to reduce the amount of pollutants to their required level. Many chemical processes, such as fossil fuel conversion processes, release sulfur-containing compounds which must be removed from the effluent stream due to their negative environmental impact and high toxicity to most life forms. Hydrogen sulfide (H
2
S), for example, is one of the most common sulfur-containing compound which needs removal and disposal since this acid gas is extremely toxic and very corrosive in the presence of water. Other toxic sulfur-containing compounds which need to be removed from emitted effluents before entering the atmosphere include: carbon disulfide, sulfur dioxide, carbonyl sulfide, dimethyl sulfide, dimethyl disulfide, methyl mercaptan, and ethyl mercaptan.
In recent years, environmental concerns and the introduction of new environmental laws and regulations have brought about an increasing interest in more effective and economical decontamination processes.
The majority of the biological world derives energy from the oxidation of organic compounds. However, there exist some groups of microorganisms that derive metabolic energy and reducing equivalents for their biosynthesis from the oxidation of inorganic elements and compounds. Biofiltration processes make use of these types of metabolism to remove sulfur-containing compounds from effluent gas streams.
A biofilter is usually composed of an organic material, such as compost, peat or wood bark, having microorganisms attached thereto which are capable of decontaminating an effluent gas stream. The component of interest is degraded when the gas stream passes the biofilter through the metabolizing action of the microorganisms within the filter.
A number of microbial processes for the oxidation of hydrogen sulfide have been described in the patent literature. For example, JP Patent 02126917 describes a deodorizing method. The decontamination is carried out in two peat packing layers carrying microorganisms. Similarly U.S. Pat. No. 5,747,331 discloses a process and an apparatus for the removal of sulfur-containing compounds from waste gases with the aid of microorganisms. The invention described therein is also a two-stage biodegradation process wherein in the second stage the pre-purified gas is contacted again with the microorganisms to degrade any remaining sulfur-containing compounds. The publication in VDI Berichte 735, Biologische Abgasreinigung, VDI Verlag, Düusseldorf, pp. 129-138, 1989, also discloses the use of Thiobacillus spp. microorganisms for the degradation of hydrogen sulfide in waste gases.
Even though the above mentioned processes disclose biofiltration methods for the removal of toxic waste gases, there are still problems associated with the removal strategies, such as short biofilter age or incomplete decontamination.
The design of biofilters depends upon a number of criteria; some of which are the porosity of the filter material, the surface area available for the microorganisms in the organic material to attach to, the loft of the organic material and last but not least, the cost of the media.
It is apparent, that there is a need for effective and lasting biofilters in order to make biofiltration processes more cost effective. The methods disclosed in the prior art attack the problem of biofilter effectiveness by passing the waste gas through two or more biofilters to achieve satisfactory decontamination. Another approach is the post-cleaning or chemical “polishing” of the decontaminated gas stream by passing the purified waste gas through activated carbon. However, the biofilters have to be changed quite frequently due to the deposition of solid residues and physical collapse of the biofilter material. These deposits drastically reduce the capability of the biofilter to remove waste gases since the porosity and the surface area of the biofilter are significantly reduced because of pore blockage. Another aspect of this scenario is the economical disadvantage of the methods described above as the production of biofilters is costly and time consuming.
It is an object of this invention to provide an apparatus and a method for conducting efficient biofiltration processes which are also more cost effective.
It is another object of the invention to provide a method for increasing the lifetime of biofilters.
It is an object of one embodiment of this invention to provide a method and an apparatus for the effective removal of hydrogen sulfide.
The invention disclosed herein obviates this difficulty, by providing a method and an apparatus including two filtration stages with two different filters, a primary stage sacrificial filter and a secondary stage biofilter; a hybrid biofilter system.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a system having two filters serially interconnected, only one of the two filters being a biofilter having microorganisms placed therein for removing an unwanted sulfur-containing compound contained within a gas, a method for removing the sulfur-containing compound contained within the gas comprising the ordered steps of:
(a) passing the gas through a first of the two filters, the first filter being a primary stage sacrificial filter for removing elemental sulfur that is formed when the gas passes through the first filter, said first filter being stable at a pH<7; and subsequently
(b) passing the gas through the biofilter for forming a degradation product from the sulfur-containing compound, said biofilter being stable at a pH<7.
In accordance with the invention there is further provided a filter arrangement for forming a degradation product from a sulfur-containing compound contained within a gas having two sequential filters, only one of the two sequential filters being a biofilter having microorganisms placed therein, the filter arrangement comprising: (a) a first filter for removing elemental sulfur which is formed when the sulfur-containing compound passes through the first filter, said first filter being stable at a pH<7; and (b) a biofilter disposed in such a manner as to receive a remaining sulfur-containing compound from the first filter, the biofilter for degrading the remaining sulfur-containing compound to form the degradation product, said biofilter being stable at a pH<7.
Furthermore, in accordance with another embodiment of the invention there is provided a system having two sequential filters, only one of the two sequential filters being a biofilter for removing a sulfur-containing compound from a gas, a method for increasing a filter effectiveness and prolonging a lifetime of the biofilter comprising the steps of: (a) passing the gas containing the sulfur-containing compound through a first filter for removing elemental sulfur which is formed when the sulfur-containing compound passes through the first filter, the first filter being stable at a pH<7; (b) passing the gas containing a remaining sulfur-containing compound to the biofilter; and (c) passing the gas containing the remaining gaseous sulfur-containing compound through the biofilter for removing the remaining gaseous sulfur-containing compound from the gas, the biofilter being stable at pH<7.
Advantageously, the present invention provides a method and an apparatus for conducting efficient biofiltration processes which are also more cost effective. It is a further advantage of the invention to provide a method for increasing the lifetime of biofilters.
REFERENCES:
patent: 5510265 (1996-04-01), Monticello
patent: 5595910 (1997-01-01), Kant et al.
patent: 5635394 (1997-06-01), Horn
patent: 5747331 (1998-05-01), Hartikainen et al.
patent: 5798044 (1998-08-01), Strohmeier et al.
patent: 198 00 686 (1998-06-01), None
Alberta Research Council Inc.
Beisner William H.
Bennett Jones LLP
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