Anaerobic Digestion of Waste Activated Sludge

by James M. Gossett, (M.ASCE), Asst. Prof.; Environmental Engrg. Dept., Hollister Hall, Cornell Univ., Ithaca, N.Y. 14853,
Roy L. Belser, Sr. Engr.; Environmental Activities, General Motors Assembly Div., General Motors Corp., North Tarrytown, N.Y.,

Serial Information: Journal of the Environmental Engineering Division, 1982, Vol. 108, Issue 6, Pg. 1101-1120

Document Type: Journal Paper


The purpose of this laboratory study was to evaluate, and model the effect of solids retention time in the activated sludge process (θcAS) on the performance of anaerobic digesters fed the resulting waste sludges. Activated sludge systems were operated over a range of θcAS values, with the waste sludges used as feed sources for batch and semi-continuous anaerobic digestion studies. Previous models for aerobic biodegradability of activated sludges were found to accurately predict ultimate anaerobic digestibility. However, conventional kinetic models of digestion over-estimated actual performance with this substrate. An activated-sludge anaerobic digestion model is proposed which includes a first-order rate mechanism for preliminary conversion of viable activated sludge biomass into available anaerobic substrate. Decreasing θcAS results in increased sludge solids for digestion. However, the solids are of sufficiently greater digestibility that both the quantity of digested solids for ultimate disposal, as well as the cost of digestion, are virtually independent of θcAS.

Subject Headings: Waste treatment | Anaerobic processes | Activated sludge | Laboratory tests | Model accuracy | Substrates | Industrial wastes | Solid wastes

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