Abstract: An improved method for constructing filter underdrain systems may be provided which uses prefabricated underdrain cells. The prefabricated underdrain cells may have a one piece construction having side walls and a bottom. The side walls may include a porous plate support ledge with a ridge at the center of the ledge. The ridge helps ensure that the sealant forms a uniform and effective gasket when the porous plates are installed.

Abstract: A completely new type of filtration system uses a traveling plenum that travels through granular filtration media in a filter tank and backwashes a portion of the media a little at a time. A pump forces backwash water into the traveling plenum, and porous plates mounted on the top of the plenum allow the water to come to the surface of the media and loosen solids deposited at the surface during a filtration cycle. A washwater hood and waste water pump removes the loosened solids from the surface of the media. Porous plates mounted on the sides of the traveling plenum allow backwash water to fluidize surrounding media and promote the transportation of the traveling plenum in the media. Thus, filter construction is reduced to creating a tank with influent and effluent openings without the complicated cell and plenum construction of conventional traveling bridge filters. Effluent plugs, installed across effluent openings, are designed to allow water to exit the tank but retain media inside the tank.

Abstract: The present invention comprises apparatus and a method of automatically controlling the permeability of filter beds. In particular, this invention directs itself to filter beds or tanks that are divided into a plurality of contiguous compartments or cells, each compartment containing a filtering media substrate, which substrate is cleansed or backwashed, periodically, when necessary, by a traveling bridge backwash mechanism. The duration and frequency of backwashing is automatically controlled to maintain a desired overall permeability and throughput performance of the filter bed. Permeability control is dynamic to maintain optimum performance under all conditions, i.e. changing in response to fluctuating filter bed hydraulic or solids loading rates.