Abstract

ABSTRACT: Anaerobic stabilization (AnS) is denned as difference between actual and theoretical oxygen use in activated sludge systems with anaerobic selectors. AnS-related oxygen savings translate into potentially lower aeration power costs. A comprehensive electron balance approach was developed for more accurate determination of AnS, along with procedures for in-situ oxygen uptake rate (OUR) measurement and analysis of dissolved gases by vacuum stripping.Lab-scale anaerobic/oxic (A/O) and anaerobic/anoxic/oxic (A2/O) systems operated under various conditions yielded AnS values of 15-55% of the theoretical oxygen requirement. Hydrogen and methane production together explained less than 1% of AnS, except when the A/O feed was supplemented with formate, in which case methane production explained about 19% of AnS. Stripping of reduced volatiles explained less than 1% of AnS in both systems. Kinetic limitations of the chemical oxygen demand (COD) test were not found to be significant in explaining AnS, but thermodynamic limitations were identified as potentially capable of explaining a significant fraction of AnS. Mechanisms are hypothesized that can partially explain AnS based on the results of this study.

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