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Effect of Ferric Chloride Addition and Holding Time on Gravity Belt Thickening of Waste Activated Sludge

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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.

Keywords: blinding; ferric chloride; gravity belt thickening; phosphorus removal; sludge thickening

Document Type: Research Article


Publication date: February 1, 2011

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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