Modeling External Carbon Addition in Biological Nutrient Removal Processes with an Extension of the International Water Association Activated Sludge Model

Abstract

BSTRACT: The aim of this study was to expand the International Water Association Activated Sludge Model No. 2d (ASM2d) to account for a newly defined readiiy biodegradable substrate that can be consumed by polyphosphate-accumulating organisms (PAOs) under anoxic and aerobic conditions, but not under anaerobic conditions. The model change was to add a new substrate component and process terms for its use by PAOs and other heterotrophic bacteria under anoxic and aerobic conditions. The Gdansk (Poland) wastewater treatment plant (WWTP), which has a modified University of Cape Town (MUCT) process for nutrient removal, provided field data and mixed liquor for batch tests for model evaluation. The original ASM2d was first calibrated under dynamic conditions with the results of batch tests with settled wastewater and mixed liquor, in which nitrate-uptake rates, phosphorus-release rates, and anoxic phosphorus uptake rates were followed. Model validation was conducted with data from a 96-hour measurement campaign in the full-scale WWTP. The results of similar batch tests with ethanol and fusel oil as the external carbon sources were used to adjust kinetic and stoichiometric coefficients in the expanded ASM2d. Both models were compared based on their predictions of the effect of adding supplemental carbon to the anoxic zone of an MUCT process. In comparison with the ASM2d, the new model better predicted the anoxic behaviors of carbonaceous oxygen demand, nitrate-nitrogen (NOi-N), and phosphorous (PO4-P) in batch experiments with ethanol and fusel oil. However, when simulating ethanol addition to the anoxic zone of a full-scale biological nutrient removal facility, both models predicted similar effluent NO3-N concentrations (6.6 to 6.9 g N/m^). For the particular application, effective enhanced biological phosphorus removal was predicted by both models with external carbon addition but, for the new model, the effluent PO4-P concentration was approximately onehalf of that found from ASM2d. On a PO4-P removal percentage basis, the difference was small, that is, 94.1 vs 97.1%, respectively, for the ASM2d and expanded ASM2d. Water Environ. Res., 84, 646 (2012).

Computer Simulation in Predicting Biochemical Processes and Energy Balance at WWTPs

“…In this study not only biological part of WWTP was simulated but more complex newly developed model of whole plant Mantis2 (which is extension of well known ASM) was calibrated/validated, behaviors of real date NH 4 -N and NO 3 -N and PO 4 -P in the anoxic/aerobic tank of full-scale MUCT bioreactor, as a sample results presented Figure 2c, were matched accurately by the model predictions in the GPS-x simulator. Moreover full-scale simulations during the validation process revealed that addition of winter scenario in Mantis2 compensate with the temperature parameters resulting in a similar NH 4 -N and NO 3 -N and PO 4 -P behavior compared to the reference case (data not shown) presented earlier by Swinarski et al [3].…”

“…The process calibration in newly developed comprehensive model Mantis2 for simulation study of "virtual" plant layout with the full-scale MUCT bioreactors in GPS-x were started with calibrated results of a series of batch tests with the process biomass (ASM2d) in order to match accurately kinetic/stoichiometric parameters. Then previous model of "Wschód" WWTP [3] as a basepoint of further process calibration was used in conjunction with optimization techniques Nelder-Mead simplex to estimate kinetic/stoichiometric parameters in Mantis2 as was shown in Table 3. The simulations run on the calibrated and validated plant-wide Mantis2 model included scenarios that may influence the WWTP process operation and energy balance.…”

“…volume of 4.0 dm3), control system and computer. This batch experiments results were obtained by Drewnowski and Makinia [4] at a large (600,000 PE) BNR "Wschód" WWTP in Gdansk (Poland) provided the experimental database for comparison of the model predictions as well as additional 96-hour measurement campaign in the full-scale MUCT bioreactor at this plant presented earlier by Swinarski et al [3] was integrated to calibration/validation process. During that time only full-scale MUCT bioreactor was simulated using base model ASM2d.…”

“…This study was based on archives date from real "Wschód" WWTP (presented earlier by Swinarski et al [3]) as a base-point for newly developed "virtual" plant layout, extended in the range of sewage sludge treatment with the following device: -primary sludge thickener, -waste activated sludge dewatering, -anaerobic digester, -digested sludge dewatering (centrifuges).…”

Population balance models: a useful complementary modelling framework for future WWTP modelling

“…Few studies focused specifically on modelling the effects of external carbon addition on PAOs with the ASMs so far. Swinarski et al (2012) developed a new model as an expansion of ASM2d to predict the effect of adding a readily biodegradable substrate to a combined N/P system. The aim of this study was to further modify the ASM2d with regard to the behaviour of PAOs under aerobic conditions in the presence of external carbon (acetate).…”