ABSTRACT
Phosphorus removal using ferric chloride (FeCl3) addition was demonstrated at the Egan Water Reclamation Plant. Concurrently, sludge thickening performance problems occurred in the gravity belt thickeners (GBTs). Blinding problems and polymer demand change were attributed to FeCl3 and long sludge holding times. Laboratory tests were conducted to gain insight to the GBT problems. Sludge holding time effects before polymer conditioning and thickening and prolonged contact of the solids with FeCl3 were evaluated via modified time-to-filter and blinding tests developed for this study. The tests assessed the sludge filterability under polymer and FeCl3 conditioning treatments and varying sludge holding and FeCl3 contact times. It was determined that fresh sludge was the easiest to thicken compared with sludge stored for any length of time. The FeCl3 improved thickening; however, when both the FeCl3 and polymer were used as conditioners, higher FeCl3 concentrations resulted in thickening inhibition compared with polymer alone.
