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Abstract: A new kinetic model is developed to describe the microbial storage process under anoxic conditions in activated sludge. The accumulation of nitrite in denitrification is taken into account in this model. The formation of storage polymers under anoxic conditions is coupled with energy generation and anoxic respiration, and their formation rate is found to be proportional to the substrate utilization rate. The sensitivity of the nitrogen uptake rate toward the stoichiometric and kinetic coefficients of the established model is analyzed by using an “absolute–relative” sensitivity function implemented in software AQUASIM. Batch denitrifying experiments were conducted to calibrate and validate the established model. The model is compared with ASM1 and ASM3, the two commonly used activated sludge models. Results show that the kinetic model established in this work is able to better describe the microbial storage processes under anoxic conditions. [Copyright &y& Elsevier]

Abstract: In the widely used Activated Sludge Models (ASMs) for biological wastewater treatment, denitrification is assumed as a single-step process, which is not true for some cases where a considerable amount of nitrite is build-up in system. This causes limitation to the application of ASMs. In this work, with a consideration of denitrification on both nitrite and nitrate, and an introduction of the simultaneous storage and growth concept, a two-step ASM3-based denitrification model is established. The sensitivity of the effluent chemical oxygen demand, and concentrations toward the stoichiometric and kinetic coefficients is analyzed. Model calibration is performed by comparing the measured and predicted values for model components. Thereafter, this model is evaluated with the experimental results of four different case studies on denitrification and compared with the original ASM3. The evaluation and comparison results demonstrate that the developed model is able to better and more mechanistically describe the denitrification process in the activated sludge systems. [Copyright &y& Elsevier]

Nitrate contamination of groundwater has been recognized as a significant environmental problem world widely. Sulfur-driven mixotrophic denitrification has been demonstrated as a promising groundwater treatment process, which though plays an important role in nitrous oxide (N 2 O) emissions, significantly contributing to the overall carbon footprint of the system. However, the current process optimizations only focus on nitrate removal and excess sulfate control, with the N 2 O emission being ignored. In this work, an integrated mathematical model was proposed to evaluate the N 2 O emission as well as the excess sulfate production and carbon source utilization in sulfur-driven mixotrophic denitrification process. In this model, autotrophic and heterotrophic denitrifiers use their corresponding electron donors (sulfur and organic matter, respectively) to reduce nitrate to nitrogen gas, with each modeled as three-step denitrification (NO 3 − to N 2 via NO 2 − and N 2 O) driven by sulfur or organic matter to describe all potential N 2 O accumulation steps. The developed model, employing model parameters previously reported in literature, was successfully validated using N 2 O and sulfate data from two mixotrophic denitrification systems with different initial conditions. Modeling results revealed substantial N 2 O accumulation due to the relatively low autotrophic N 2 O reduction activity as compared to heterotrophic N 2 O reduction activity, explaining the observation that higher carbon source addition resulted in lower N 2 O accumulation in sulfur-driven mixotrophic denitrifying system. Based on the validated model, optimizations of the overall system performance were carried out. Application of the model to simulate long-term operations of sulfur-driven mixotrophic denitrification process indicates that longer sludge retention time reduces N 2 O emission due to better retention of active biomass. High-level total nitrogen removal with significant N 2 O emission mitigation, appropriate excess sulfate control and maximized COD utilization can be achieved simultaneously through controlling the influent nitrate and COD concentrations. [ABSTRACT FROM AUTHOR]