Patent Application
20070284294
Referring now to
Referring now to
The profile of the preferred embodiment of the biomass carrier (10) has a substantially hollow rectangular body with rounded corners (18), (20), (22) and (24). For the sake of reference, the biomass carrier comprises four walls: top (26), bottom (28), left (30) and right (32). The body is hollow to permit mass transfer there through. Inside these four walls are equally spaced vertical parallel partitions (34) (36), (38), (40) and (42) and a single transverse support member (44). The intersection of the partitions and the support member results in the formation of a plurality of cells (46) within the carrier body (10) having a reticulated matrix pattern. The distance (41) between the vertical parallel partitions is uniform. In other embodiments of the invention there may be additional parallel partitions and transverse support ribs to provide appropriate control on the dimensions of the cells (46) according to production methods and requirements. The cells have a width (47) and a length (49).
Referring now to
Referring to
The bio-film thickness on conventional biomass carriers in conditions anticipated for this invention would be expected to be in the range of 0.3 mm to 0.8 mm, with a typical value of 0.5 mm. With the present invention and under similar operating conditions, the bio-film thickness (86) in the separation areas will be considerably thicker than this, ranging from 0.6 mm to 1.3 mm while the thickness (88) of the bio-film in the projection areas is expected to be close to the typical value of 0.5 mm. Consequently, my biomass carrier will carry more biomass than an equivalent projected area of a conventional (flat) carrier surface under the same operating conditions. In addition, bio-film in well protected separation areas (80) will tend to slough at a slower frequency than projection areas (76) allowing the development of an older bio-film with higher autotroph populations (to facilitate nitrification) as well as anoxic regions to promote de-nitrification.
The depth and width and shape of separations must be optimized to balance several considerations:
Appropriate dimensions for the separation (80) under typical operating conditions are as follows: maximum depth (84) of 1 mm, with separations bounded by projections such that separations have a width (82) of approximately 1.4 mm. Variations in these dimensions are appropriate depending on the specific process application, however, the height of the projections (78) should be within the range of 0.5-2 mm with the ratio of separation width (82) to depth (84) falling in the range of 1.2:1 to 3:1.
All three surface morphologies depicted in
The next consideration is the placement of defined morphologies in my biomass carrier (10). Many carriers employ a general tubular shape with one or more concentric rings and several radial partitions. This results in apertures that have a low aspect ratio (square-like or pie shaped). As with a pipe cross section, as bio-film grows, it reduces both the diameter for flow as well as the area of interface between the bio-film and the bulk liquid. Flow in tubular conduits (or apertures in this case) is proportional to the square of the diameter. As the diameter of the pipe decreases the rate and amount of bio-film growth also decreases due to: (1) a reduction in the flow diameter (and therefore flow velocities); and, (2) a reduction in the area for diffusion between bulk liquid and bio-film. With my biomass carrier the intention is to develop bio-films that are thicker, on average, than those possible with prior art carriers while at the same time maximizing the mass flow through the biomass carrier. However, with the use of a plurality of rectangular cells (46) there would normally be severe mass transfer problems through the carrier as the bio-film increased in thickness. To overcome this, I have introduced the benefits of flow between parallel plates, namely, the parallel walls of the cells (46). By introducing the projections (78) inside of each cell, the mass flow through each cell is optimized without the deleterious effects caused by an increase in bio-film thickness. For example, in the preferred embodiment (10) (momentarily ignoring the prominences), each cell (46) has a width (47) of approximately 4.1 mm and a length (49) of approximately 10 mm. This has the same hydraulic radius as a circular aperture 5.8 mm in diameter. In addition, as bio-film thickness increases, the deleterious effect on total bio-film/bulk fluid contact area is less pronounced than with lower aspect ratio apertures. In summary, for the intended application of this invention, surfaces can be most tightly spaced if apertures between the surfaces are elongated. This results in the ability to achieve higher specific surface area values without counterproductive mass transfer effects. It follows that opposing projections should be spaced apart as much as possible to maintain an open channel, to the extent possible.
The preferred embodiment (10) has spacing between the partitions (42) (ignoring projections) of 4.1 mm, however, values in the range of 3 to 6 mm are feasible for this embodiment depending on the specific process application and the dimensions selected for projections.
Finally, we address the overall configuration of the carrier (10). The overall size and aspect ratio of the carrier is based on several considerations:
Consideration of the above factors in the light of practical experience has led to the selection of an overall size of 28.6 mm in length (50) by 21.9 mm in width (48). The cut thickness is dependant on the specific application and can vary from approximately 10 mm to 25 mm. Variations in the cross-sectional dimensions are permissible by including more or fewer of the patterned cells (46). For example, cells can be added to the length (50) of the profile.
The predetermined first aspect ratio of length to width is approximately 1.3:1, however, ratios up to 3:1 are considered to be practical. For example, a carrier designed on the basis of the upper or lower half of the preferred embodiment as depicted, would be acceptable and would have an aspect ratio of approximately 2.6:1.
The cells (46) should have high aspect ratios. However, there are practical limitations imposed by the manufacturing process such as the need for rigidity and uniform distance (41) between the vertical partitions in the carrier. In the preferred embodiment, the predetermined second aspect ratio is approximately 3:1. Values between 2.5 and 4.0 are acceptable and feasible. However, the distance (41) must conform to the guidelines stated above.
The carrier is preferably made from a plastic such as HDPE. However, the composition may optionally be amended by the addition of a UV retardant such as carbon black as well as other amendments designed to optimize the specific gravity. In recent experimental work, I have observed that the specific gravity of a biomass carrier has significant impact on the ability of the carrier to be entrained by water circulating throughout bioreactors. This effect is most pronounced at start-up before the media has wetted out and developed a significant bio-film or in process situations where bio-films are ordinarily thin. As bio-film develops, the natural buoyancy of the carrier is reduced and motion is enhanced. Nonetheless, there are numerous situations with conventional carriers where the amount of air required to move the media satisfactorily exceeds the amount required to fulfill biochemical requirements, resulting in a significant incremental expenditure of energy. An example would be a nitrification application, where the invention's large surface area and well protected niches will be advantageous for the growth of nitrifying bacteria but where average bio-film thickness can be expected to be small. In such situations, a carrier with optimized specific gravity can result in significant energy savings. Practical experience by this inventor has indicated that a specific gravity in the range of 0.975 and 0.995 with a preferred value of 0.985 being close to ideal for most applications.
Although the description above contains much specificity, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,550,121 | Jun 2006 | CA | national |
