The Village of Weston, OH utilizes four 0.070 MGD (70,000 GPD) rated aeration tanks and clarifiers in parallel for treatment of sanitary sewage. The original plant, built in 1968, consisted of two aeration tanks and two clarifiers with the additional two plants installed in 1981.
The older portion of the plant experienced frequent problems with the existing airlift pumps. These pumps were used to move the settled sludge in the clarifiers back to the head of the aeration tanks (Return Activated Sludge or RAS) or to waste. The problems included frequent clogging of the pumps or the pumps' inability to return enough solids during high flow events.
These problems ultimately led to the clarifier serving as more of a sludge storage tank rather than performing solids/ water separation. These problems also often limited operational control of the plants since optimum Mixed Liquor Suspended Solids (MLSS) concentrations could not be attained. The airlift pumps would not consistently pump the RAS at the optimum rate without clogging. Often an industrial type air compressor or a vacuum truck was required to unclog the airlift pumps or to remove the sludge from the clarifier.
IFM recommended the installation of two 4" Geyser Pumps in the older plants. The track record of problems with the airlift pumps at this facility served as a "worst case scenario" to test the effectiveness of this new wastewater treatment technology. The existing ductile iron piping that made up the existing airlift pumps was replaced with 4" SCH 80 PVC and the airline was replaced with 1" PVC braided tubing.
Since the installation of the Geyser Pumps in the original clarifiers, the MLSS, and Return Activated Sludge Suspended Solids (RASSS) concentrations have doubled, the Sludge Volume Index (SVI) has dropped and dissolved oxygen (DO) levels in the aeration tanks have increased. These results have been attained without having to take either of the tanks off-line for the removal of clogs or the pumping of solids from the clarifiers.
As a result of the marked improvement in the plants with the Geyser Pumps, the original airlift pumps in the remaining two clarifiers have also been replaced with new 4" Geyser Pumps. The installation of the Geyser Pumps in all four clarifiers has given the plant's biology a chance to mature to excellent settling floculated particles, leading to constant discharge compliance.