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Pilot scale evaluation of anaerobic codigestion of primary and pretreated waste activated sludge

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Pilot-scale (160 L) research on enhancement of anaerobic codigestion of combined primary sludge and waste activated sludge (WAS) was performed, using low-level alkaline solubilization of waste activated sludge. Solubilization was performed by the addition of 15 meq/L of calcium hydroxide or sodium hydroxide in the first part of the research (data already published), followed by the addition of 15.0, 12.5, or 10.0 meq/L of only sodium hydroxide in the next phase; mechanical anoxic mixing times of 5, 4, and 3 hours were employed. The previous work examined the effects of decreasing solids retention time (SRT) on digester operational efficiency; the subsequent research work examined the effects of different sodium hydroxide dosages and mixing times on digester efficiency. The overall performance of three pilot-scale digesters, including a control unit, was monitored. This research showed that solubilization of WAS did not have any appreciable effect on actual digester volatile mass reduction efficiency. However, better overall volatile mass reduction (solubilization process plus anaerobic digestion) was achieved in the chemically altered units. Better chemical oxygen demand (COD) removal was also observed in these units. Solubilization of WAS with sodium hydroxide also improved unit gas production (volume of gas produced per volatile mass removed in the digester). Overall, the experimental unit receiving WAS pretreated with different dosages of sodium hydroxide outperformed both the control and the other unit using calcium hydroxide (from previous work) as the solubilizing chemical. Waste activated sludge pretreatment allowed a decrease in digester SRT from 25 to 10 days, without major effects on process efficiency or effluent quality. It enhanced volatile mass reduction, COD removal, and unit gas production.


Document Type: Research Article


Publication date: July 1, 1995

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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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