INVESTIGATION OF HYPOTHESIZED ANAEROBIC STABILIZATION MECHANISMS IN BIOLOGICAL NUTRIENT REMOVAL SYSTEMS

Anaerobic stabilization (AnS) is defined 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 d eveloped for more accurate determination of AnS, along with procedures for in-situ oxygen uptake rate (OUR) measurement and analysis of diss olved gases by vacuum stripping. Lab-scale anaerobic/oxic (A/0) and an aerobic/anoxic/oxic (A2/0) systems operated under various conditions y ielded AnS values of 15-55% of the theoretical oxygen requirement. Hyd rogen and methane production together explained less than 1% of AnS, e xcept when the A/0 feed was supplemented with formate, in which case m ethane production explained about 19% of AnS. Stripping of reduced vol atiles explained less than 1% of AnS in both systems. Kinetic limitati ons of the chemical oxygen demand (COD) test were not found to be sign ificant in explaining AnS, but thermodynamic limitations were identifi ed as potentially capable of explaining a significant fraction of AnS. Mechanisms are hypothesized that can partially explain AnS based on t he results of this study.