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A methodology for calibration of the activated sludge plant models is proposed on the basis of consolidated engineering experience and a scientific approach. According to the method, the definition of the target(s) plays a crucial role in the selection of the steps incorporated in this so-called 'Biomath-Calibration' protocol. For the activated sludge modelers this protocol tries to combine and link the state of the art methodologies for calibration of different processes in a wastewater treatment plant (hydraulics, biological reactions, sedimentation processes, etc.), and it can thus be used as a complete guideline for extensive model calibration tasks. Finally, an application of the methodology is presented in a case study for a nutrient removing oxidation ditch system.

Hydrolysis mechanism plays a dominant role in the delicate balance of electron donor/ electron acceptor ratios in BNR and EBPR systems as an important carbon source. In this study, the surface-saturation-type hydrolysis kinetics was investigated based on respirometric measurements, within the context of the theoretical and the practical identifiability of mathematical models. The identifiable parameters of a selected model were derived from respirograms. In addition, the information from the experiments was evaluated on the basis of Optimal Experimental Design (OED) methodology for different initial conditions of the batch respirometric experiment.

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A methodology is proposed for the model calibration of nutrient-removing laboratory-scale SBRs under limited aeration. Based on in-process measurements and influent wastewater characterization, the ASM2d model was modified by adding an organic nitrogen module incorporating a hydrolysis mechanism. After calibration, the simulation results showed that enhanced biological nutrient removal occurred during the fill period and under reduced aeration achieving so-called 'simultaneous nutrient removal'. A modelbased systems analysis was performed in terms of the contributions of different processes to overall oxygen, nitrogen and phosphate utilization. In each phase, simultaneously occurring biological reactions were compared using the calibrated model. According to the calibrated model, 61% of all denitrified nitrate is denitrified during the mixing/filling phase. On the other hand, 17% of all denitrified nitrate is consumed by simultaneous nitrification-denitrification during the first aerobic period. The aerobic and anoxic P-removals were quantified as 73% and 12%, respectively.

The effect of settling on mass balance and biodegradation characteristics of domestic wastewater and on denitrification potential was studied primarily using model calibration and evaluation of oxygen uptake rate profiles. Raw domestic wastewater was settled for a period of 30 minutes and a period of 2 hours to assess the effect of primary settling on wastewater characterization and composition. Mass balances in the system were made to evaluate the effect of primary settling on major parameters. Primary settling of the selected raw wastewater for 2 hours resulted in the removal of 32% chemical oxygen demand (COD), 9% total Kjeldahl nitrogen, 9% total phosphorus, and 47% total suspended solids. Respirometric analysis identified COD removed by settling as a new COD fraction, namely settleable slowly biodegradable COD (X SS ), characterized by a hydrolysis rate of 1.0 day 21 and a hydrolysis half-saturation coefficient of 0.08. A model simulation to test the fate and availability of suspended (X S ) and settleable (X SS ) COD fractions as carbon sources for denitrification showed that both particulate COD components were effectively removed aerobically at sludge ages higher than 1.5 to 2.0 days. Under anoxic conditions, the biodegradation of both COD fractions was reduced, especially below an anoxic sludge retention time of 3.0 days. Consequently, modeling results revealed that the settleable COD removed by primary settling could represent up to approximately 40% of the total denitrification potential of the system, depending on the specific configuration selected for the nitrogen removal process. This way, the results showed the significant effect of primary settling on denitrification, indicating that the settleable COD fraction could contribute an additional carbon source in systems where the denitrification potential associated with the influent becomes rate-limiting for the denitrification efficiency. Water Environ. Res., 81, 715 (2009).

This paper explores the merit of the oxygen uptake rate (OUR) profile obtained by means of respirometry as the basic mechanistic instrument for evaluating activated sludge inhibition. Experimental OUR data are generated using the synthetic peptone-based substrate and inhibition is tested with 60 mg/L hexavalent chromium and 33 mg/L nickel additions, corresponding to EC50 levels determined using the standard ISO 8192 procedure. Experimental results are evaluated by model calibration using ASM1 modified for dual hydrolysis and ASM3 modified for simultaneous growth. Model evaluations indicate that inhibition affects not only growth, but also other significant microbial mechanisms such as substrate storage and hydrolysis, leading to conclude that the proposed approach will enable to visualize the overall impact of the inhibitory compound on every stage of substrate biodegradation, through inspection and evaluation of the entire OUR profile.