This invention relates generally to filters, and more specifically to a filter bottom construction employed to support filter media in liquid filters.
Multi-block filter bottoms of the type disclosed in U.S. Pat. No. 3,110,667, issued to Stuppy, have been employed with success in liquid filter systems, e.g., water and wastewater filter systems. The blocks are disposed next to each other in parallel adjacent rows, and then are cemented or grouted in place to form a support structure for gravel and/or other finely divided filter media.
The upper walls of the blocks are provided with passages through which liquid can pass during both the filtering and backwashing operations. The interior of each block is divided into upper and lower laterals separated by a horizontal partition, but interconnected by a plurality of vertical ports formed through the partition.
The above-described multi-block construction is commonly employed in a filter structure having a central flume extending below a concrete bottom wall upon which the multi-block construction is secured. The blocks that are vertically aligned with the flume have at least a portion of their bottom walls removed to provide openings into the lower laterals. These lower laterals communicate with the flume through connecting ports formed through the concrete supporting structure.
During conventional filtration the influent moves in a downstream direction through the filter media, and then through the passages formed in the top walls of the blocks forming the filter bottom. The liquid then moves from the upper laterals into the lower laterals throught the vertical ports in the horizontal partitions, and then along the lower laterals to the cut out regions in the blocks overlying the central flume. At this location the effluent (i.e., the filtered liquid) passes into the flume through the connecting ports in the concrete supporting structure, and then out of the filter.
During backwashing the backwash liquid is introduced into the flume and passes through the connecting ports in the concrete supporting structure into the cut out regions in the blocks overlying the flume. At this point the liquid moves into, and is distributed laterally along the lower laterals. The distributed backwash liquid passes through the ports in the horizontal partitions separating the upper and lower laterals in the various blocks, and then through the passages in the top walls of the blocks and through the filter media to provide the backwashing function.
Although the above-described prior art system provides excellent liquid distribution during backwashing, while permitting the desired flow of influent during filtration, a problem does exist in the repair and maintenance of the system in the event that one or more of the blocks become clogged. For example, if the liquid distribution ports formed in the horizontal partition between the upper and lower laterals in one or more of the blocks become blocked, or if the laterals themselves become blocked, the distribution of backwash liquid can be adversely affected. This can cause uneven flow of backwashing liquid through the filter media, resulting in an undesired disruption of the media bed. Unfortunately, it is not always easy to determine exactly where the blockage exists merely by visually observing the movement of the backwash liquid. In fact, in attempting to locate a blockage it is not uncommon to actually break out one or more blocks that are perfectly good, on the mistaken belief that those blocks actually were the ones that were malfunctioning.
Thus, although the multi-block filter bottom constructions of the prior art are well suited for use during filtering and backwashing operations, they do not permit the easy, non-destructive detection of blockages therein.