It had been determined that volumetric measurement would not work in this application, as the de-watered sludge expands over time. A simple test indicated an approximate increase in volume of 15% just one hour after leaving the V-Ram  system. Historical data showed that weight per cubic foot immediately after centrifugation was fairly constant (around 62 lbs.), so that figure was used as a baseline for establishing a tons-per-hour formula.

Unfortunately, the originally installed meter did not meet the required ±5% accuracy standards. AFTCO was confident its UniMag flowmeter could provide the desired accuracy, and offered to provide a 6-inch diameter UniMag and AFTCO 4404 Converter for testing. It was agreed to leave the existing meter on-line to allow a direct comparison between brands.

UniMag accuracy confirmed

Figures generated by both meters, and a belt scale, were compared to the weight recorded on the landfill truck scale when the sludge load was dumped. Results showed the UniMag mass result averaged 4.54% greater than the landfill scale results. This was well within the Millcreek WWTP requirements, and a more accurate figure than was obtained from either the belt scale or the original magmeter.

As a footnote, visual inspection showed that a substantial amount of sludge (estimated at 250-500 lbs.) remained in the sludge transport truck after it had been weighed as empty.  Correcting for this would bring the UniMag result even closer to the landfill scale result.

The AFTCO UniMag proved capable of exceeding the accuracy requirements.