Respirometric evaluation of S0/X0 ratio effect on the kinetic and stoechiometric parameters of activated sludge

Respirometry is the measurement of the biological oxygen consumption rate under well-defined conditions. This technique is generally employed to determine the kinetic and stoechiometric parameters of biological processes, such as: the oxygen transfer coefficient K_La, the endogenous oxygen uptake rate OUR_end, exogenous oxygen uptake rate OUR_exo, the total oxygen uptake rate OUR_t; the substrate affinity constant (K_S), the maximum growth rate (μ_max) and the yield (Y_X/S). According to the literature, there is a large variability in the estimation of these kinetic and stoechiometric parameters, attributed to three key factors: the culture history, the parameter identifiability and the initial substrate to biomass ratio (S₀/X₀). KLa, depends on endogenous oxygen uptake rate OUR_end, is a key constant in evaluating respirogramme-specific parameters. Generally, OUR_end is assumed constant during dissolved oxygen variation. The effect of S₀/X₀ ratio on kinetic and stoechiometric parameters has only been partially studied. The goal of this study was to assess respirometrically the effect of various S₀/X₀ ratios (in the range of 0.01 to 0.23) on the kinetic and stoechiometric parameters of a heterotrophic activated sludge biomass (presence of ATU a nitrification inhibitor) and for both heterotrophic-autotrophic activated sludge biomass.