Title page for ETD etd-02152006-140516


Type of Document Master's Thesis
Author Webb, Jared A
URN etd-02152006-140516
Title A Comparative Study of Anaerobic Digestion Processes for Sewage Sludge
Degree Master of Science
Department Environmental Engineering
Advisory Committee
Advisor Name Title
Novak, John T. Committee Chair
Boardman, Gregory D. Committee Member
Randall, Clifford W. Committee Member
Keywords
  • biosolids
  • organosulfur
  • anaerobic
  • digestion
  • sludge
  • shear
Date of Defense 2006-02-07
Availability restricted
Abstract
The Blue Plains Wastewater Treatment Plant in Washington, D.C. is in the process of updating its anaerobic digesters, with a completion date set for 2008. This research was undertaken to aid designers at Blue Plains by evaluating alternative digestion approaches. The technologies applicable to the plant included thermophilic anaerobic digestion, acid/gas phased digestion, and temperature phased anaerobic digestion. To obtain design data, a year long study was conducted using bench scale digestion systems operating at different solids retention times (SRT) and organic loading rates (OLR). The digesters were fed with mixed primary and secondary waste (50/50 by weight) from the Blue Plains wastewater treatment facility. The digesters were operated until they reached steady state as observed by volatile solids reduction (VSR), methane production, and volatile fatty acid (VFA) levels. At this point, samples of digested waste sludge were analyzed for residual biological activity, dewatering properties and headspace organo-sulfur production. Results from the study demonstrated that the TPAD digestion process had the lowest residual biological activity (RBA) after digestion, and that the single stage thermophilic digesters had the highest RBA. Sludge from single stage mesophilic digestion had the highest odor potential, with headspace gas tests generating over 1400 mg organo-sulfur per m3 of headspace gas, while both single stage thermophilic and TPAD systems generated less than 400 mg/m3 at all SRTs studied.
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