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Factors Affecting Floc Properties During Aerobic Digestion: Implications for Dewatering

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Laboratory aerobic digestion studies were conducted to determine the effect of divalent cations on the characteristics of aerobically digested activated sludge. Separate reactors were operated at two divalent cation concentrations. Characteristics examined included dewatering properties (cake solids, specific resistance to filtration, and capillary suction time), polymer conditioning requirement, floc strength, supernatant chemical oxygen demand (COD), supernatant turbidity, soluble cations (sodium, potassium, calcium, magnesium, and ammonium ions), soluble anions (nitrate and nitrite), and soluble exocellular polymers (proteins and polysaccharides). The reactor containing higher amounts of calcium and magnesium (1.25 mM each) exhibited better dewatering properties, higher floc strength, lower polymer conditioning requirement, lower soluble COD, lower supernatant turbidity, and lower soluble exocellular polymers than the reactor containing lower calcium and magnesium concentrations (0.40 mM each). Floc deterioration was associated with a release of soluble proteins and polysaccharides and monovalent cations (sodium and potassium) to the bulk solution. Divalent cations were not released to the bulk solution, indicating they may participate in floc binding. Mineralization of nitrogen was not affected, suggesting that aerobic digestion of activated-sludge solids (degradation rates) was not affected. These results imply that the addition of divalent cations improves aerobic digester performance with regard to floc properties, supernatant quality (implications for recycled COD), and dewatering performance.
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Document Type: Research Article

Publication date: 01 March 1999

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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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