Clearstream Wastewater Systems, Inc., ("Clearstream") is the licensee of U.S. Patent No. 5,221,470 (the '470 patent), directed to a wastewater treatment apparatus utilizing aerobic bacteria to digest solid organic particles in wastewater. The claims describe a novel filtering system that includes a flexible air hose structure used in place of rigid conduit piping seen in the prior art. Use of the flexible air hose allows for ease of replacement and servicing of the air supply system in wastewater treatment plants.
Clearstream sued Hydro-Action, Inc. ("Hydro-Action") for infringement of the '470 patent. Hydro-Action filed a motion for summary judgment, contending non-infringement because its system lacked the "means for injecting air" limitations required by the disputed claims of the patent. Hydro-Action argued that the only possible corresponding structure for this means-plus-function limitation was the flexible-hose structure described in the patent, which Hydro-Action did not use. Clearstream argued that the '470 patent covers Hydro-Action's use of the prior art, rigid conduit structure as a corresponding structure or as a structural equivalent.
The U.S. District Court for the Southern District of Texas granted summary judgment of non-infringement in favor of Hydro-Action. The district court held that, because the patent discloses the disadvantages of the prior art structure and reveals novel features such as the flexible-hose system, the prior art could not be considered an equivalent structure for this mean-plus-function claim. Clearstream appealed, arguing that the district court erred by limiting its construction of the means-plus-function claim language to exclude from coverage a corresponding structure that was in the prior art. Clearstream further argued that the prosecution history supports such a claim construction as the patent application indicates that the point of novelty for the claims was the new filtering system, not the new flexible-hose aerating system.
The Federal Circuit noted that courts construing disputed claim limitations must consider the existence of combination claims, which can consist of new combinations of old elements or combinations of new and old elements. See, e.g., Intel Corp. v. U.S. Int'l. Trade Comm., 946 F.2d 821, 842, 20 USPQ2d 1161, 1179 (Fed. Cir. 1991). Thus, combination claims may, and often do, include old elements. The specification of the '470 patent points out the disadvantages of the rigid conduit system and the advantages of the flexible-hose structure. It does not, however, mandate the use of the new, flexible-hose system. Therefore, the court should construe the claim to include the prior art as a corresponding structure. If the specification described the prior art as being incapable of performing the function of the means-plus-function element, or if the means-plus-function element was the only new element in the claim for a non-novel combination, then the prior art would be excluded from the claim. Here, the prior art is not incapable of performing the contemplated function, and the aeration system is not the only novel element. When read as a whole, the patent covers a wastewater treatment plan that has a new filtering system and that may or may not have a new, flexible-hose aeration system. Because the district court's claim construction was erroneous, the Federal Circuit vacated the summary judgment of non-infringement and remanded the case for reconsideration.
Prepared by the liibulletin-patent Editorial Board.