Sensitivity analysis for an elemental sulfur-based two-step denitrification model

A local sensitivity analysis was performed for a chemically synthesized elemental sulfur (S⁰)-based two-step denitrification model, accounting for nitrite (NO₂ ^-) accumulation, biomass growth and S⁰ hydrolysis. The sensitivity analysis was aimed at verifying the model stability, understanding the model structure and individuating the model parameters to be further optimized. The mass specific area of the sulfur particles (a*) and hydrolysis kinetic constant (k₁) were identified as the dominant parameters on the model outputs, i.e. nitrate (NO₃ ^-), NO₂ ^- and sulfate (SO₄ ^2-) concentrations, confirming that the microbially catalyzed S⁰ hydrolysis is the rate-limiting step during S⁰-driven denitrification. Additionally, the maximum growth rates of the denitrifying biomass on NO₃ ^- and NO₂ ^- were detected as the most sensitive kinetic parameters.