Chemistry: molecular biology and microbiology – Apparatus – Bioreactor
Reexamination Certificate
1998-08-10
2001-01-09
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Bioreactor
C435S298100
Reexamination Certificate
active
06171853
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for treating volatile organic compounds (VOCs), air toxics, and odors in air emissions. A biofilter is a relatively new biological treatment device to convert VOCs and odor to carbon dioxide and water using biologically active soil, compost, or biofilm on a filter media. The existing biofilters have many drawbacks including frequent clogging and uneven distribution of water and air in the existing biofilter media. Water, nutrients, and air pass through only channels in the existing biofilter media using a limited volume of the media. Clogging often requires labor or energy intensive backwash or frequent replacement/turnover of the media. The object of the present invention is to develop an improved biofilter system that effectively treats VOCs, air toxics, and odor in air emissions by uniformly distributing nutrients, water, air pollutants, and oxygen to biomass grown on the entire volume of media and by eliminating frequent backwash or replacement of media.
BRIEF DESCRIPTION OF THE PRIOR ART
The use of soil beds for treating odorous server gases has been known for many years, as evidenced by the Pomeroy U.S. Pat. No. 2,793,096. A limited number of soil beds were used in the United States, primarily for odor control until the 1980s. In Europe, biofilters have been successfully used to treat VOCs and odors, and such use has been particularly cost effective for VOCs in low concentrations. Owing to more stringent environmental requirements, there has recently been renewed interest in biofilters in the United States.
A conventional biofilter includes beds of biologically active material, mixtures of compost, peat, or soil. Recently, other types of media with synthetic materials and ceramics were also used. When a contaminated air stream, often humidified, is vented through the biofilter with sufficient detention time, i.e. (on the order of tens of seconds to minutes), air contaminants will diffuse into the biofilm. The biofilm or biomass under aerobic condition will break down pollutants and nutrients into carbon dioxide and water. A variation of the biofilter is the biotrickling filter. In a biotrickling filter system, water with nutrients is sprayed on the biofilter media and a contaminated air stream is fed in co-current or counter-current directions with trickling water. The trickling water serves as a wetting agent as well as provides nutrients to the biomass.
In a conventional biofilter and a biotrickling filter, major problems are the clogging of voids in the filter and the difficulty with uniformly distributing the contaminated air stream, nutrients, and oxygen to the biomass. Air and trickling water streams often take the shortest path. With continued use, channels form through an irregular void. Consequently, water and air flow only through channels so that only a part of the total volume of media is used to treat the contaminated air. For the same reason, it is difficult to maintain an aerobic system throughout the entire bed and media can dry up. Frequently, media replacement or turn-over is needed. U.S. Pat. No. 5,413,936 discloses rotation of a cylindrical vessel having a horizontal, longitudinal axis filled with a biofilter medium for effective turn over.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the invention to provide an improved method and apparatus for removing pollutants from air emissions. The apparatus includes a housing having water arranged in a lower portion thereof and having an air emission supply in the upper portion. A biomass filter in the form of an endless element is displaced through the housing along a path wherein a section of the filter alternately passes between the upper and lower portions of the housing for air and water contact, respectively. When the filter section is in the housing upper portion, it withdraws pollutants from the air emissions and when the filter is in the housing lower portion, it receives moisture and nutrients from and releases pollutants into the water.
The biomass filter element preferably comprises a sponge-type foam material sandwiched between two layers of mesh with a frame at opposite ends. The frame is mounted on a chain which is driven by sprockets and around pulleys within the housing for continuous movement along a fixed path.
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