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Improving Aerobic Digestion by Prethickening, Staged Operation, and Aerobic–Anoxic Operation: Four Full-Scale Demonstrations

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Four full-scale aerobic digesters were studied to determine the effects of prethickening, staged operation, and aerobic–anoxic operation on digester performance. Prethickening is expected to enhance aerobic digestion by reducing hydraulic flow rates, thereby allowing increased solids retention time (SRT) values and temperature elevation. Staged operation increases the plug flow characteristic of the digester, resulting in increased solids stabilization and pathogen destruction. Aerobic–anoxic operation results in denitrification, which can provide approximately neutral pH that enhances nitrification, digestion, and nitrogen removal. Results demonstrate that staging enhances digestion and reduces the SRT necessary to produce stabilized solids (i.e., one with a volatile solids reduction efficiency greater than 38% or a specific oxygen uptake rate less than 1.5 mg O2/g volatile suspended solids h). Effective pathogen destruction is also observed. Aerobic–anoxic operation at several facilities resulted in maintenance of approximately neutral pH values, enhanced digestion, near-complete nitrification, and nitrogen removal. Prethickening resulted in autoheating at the Paris, Illinois, site, caused by the high concentration of biodegradable volatile solids in the digester feed, and at the Los Lunas, New Mexico, facility, which was specifically designed to maintain specified temperatures. The oxygen transfer capacity of the first stage must be adequate to meet the increased process oxygen requirement in that stage to allow increased digestion rates. A combination of low temperature and high solids concentration may interfere with oxygen transfer capacity. Excessive foaming can occur if adequate oxygen transfer capacity is not provided. Excellent performance can be achieved at SRT values in the 20- to 40-day range at operating temperatures of 20 °C or greater.


Document Type: Research Article


Publication date: 2000-05-01

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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.

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