The AST floating bead filters are designed to capture solids that sink. The low density polyethylene media commonly used in the floating bead filter has a specific gravity of 0.91-.92. The media floats. Although suspended particles that float will be captured by the bed, the internal solids separation of all the AST floating bead filters presume gravity separation of the sludge. Custom floating bead filters could be configured to remove floating solids, but standard units will just accumulate larger floatables in the bed. A few or small floatables like wood particles or small pieces of plastic eventually become covered with biofilm that will sink them as long term plastic accumulation has never been observed.

Standard and EN media are sized to capture particles above 50 microns on a single pass. These 1/8 inch diameter beads are selected to provide abrasion during a backwashing event the principal protection against biofouling. Particles below twenty microns are substantially reduced only when the filter solids capture mechanisms are enhanced (tuned) by lower flows (flux), by biofilm development, recirculation or coagulation/flocculation.

AST floating bead filters have limited tolerance of oils and greases. Oils that are liquid at room temperature will likely pass through the bed. Greases and oils that are solids at room temperature will likely adhere to the plastic media. Protection of the units by a clarifier, a dispersed or dissolved air flotation device (DAF) is recommended whenever large amounts of oils and greases are expected. Failure due to oiling has been seen only once over the last 20 years. This unit was unprotected on a catfish processing plant. No problems have been associated with units treating domestic or industrial wastes receiving domestic or industrial following minimal pretreatment to remove observable floating fats/greases.

The AST floating bead filters are not recommended as the final polishing/disinfection or principal treatment unit for domestic water supply. Although they have been used successfully in demonstration studies as a pretreatment device there have been no demonstrated studies confirming their ability to contain pathogens. So although they may produce a water that looks drinkable, it may not be.

The AST filters are not designed for the filtration of hot water. The polyethylene plastic used as a media can be presumed to deform at temperatures above 100 oC. The history of application is limited to a high of about 40 oC.

The AST floating bead filters should not be applied to filtration of water containing more than 1 percent (10,000 mg/L) of TSS. Although the bead bed may prove effective at reducing the high TSS (largely a flux adjustment) the internal sludge separation processes can be overwhelmed as it designed to produce a sludge concentration less than 4 percent solids. Studies continue to more precisely define this upper limit.

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