Practical parameter identifiability for an activated sludge hindered-transient-compression settling velocity model – assessing data requirements and model structural complexity Borja Valverde-Pérez1, Elena Penkarski-Rodon1, Xueqian Zhang1, Dorottya S. Wágner1, Benedek G. Plósz1 1
Technical University of Denmark (DTU), Department of Environmental Engineering, Miljøvej 113, 2800 Kgs. Lyngby, Denmark (Email:
[email protected],
[email protected])
Abstract: Is there an optimal set of settling column test data to reliably estimate activated sludge hindered, transient and compression settling parameters in full-scale wastewater treatment plants (WWTPs)? To answer this question, the data requirement and the practical identifiability of model structures were assessed in the present study. To model activated sludge settling velocity, calibration methods, notably, for compression settling require non-destructive monitoring of dynamic settling profiles during batch experiments, e.g., radiotracer tests, ultrasonic transducer, which are not simple to do in practice, thus limiting the application of compression settling models (De Clercq et al., 2008; Torfs et al., 2015). Ramin et al., (2014) present the prototype of a simple and robust settling sensor used to infer data for estimating values of the two hindered, one transient and two compression settling parameters. In the present study, we assessed different spatial positions to monitor the temporal variation of total suspended solids (TSS) concentration, thereby providing different datasets to calibrate the settling model developed by Ramin et al. (2014). We used the latin hypercube sampling simplex (LHSS) method presented in Wágner et al. (2016). Since straightforward methodology already exists to estimate both the hindered settling and the maximum transient settling velocity parameter (v0,t), here we focus on developing a parameter estimation methodology for the transient settling velocity parameter, r t (m3/kg) and the compressive solid stress parameters – here we show data for C1 (kg/m3) and C2 (-). Settling data were collected at nine different Danish and Swedish WWTPs. Filamentous bacteria abundance was assessed using quantitative fluorescence in-situ hybridisation (qFISH). Our results – obtained using sludge samples taken from the Fredericia and Ellinge WWTPs, Denmark and Sweden, respectively – suggest that the settling test developed by Ramin et al. (2014) does not provide enough information to properly identify the model parameters, independently of the datasets considered for model calibration. In the oral presentation, we will present an assessment of optimum sets of data required to estimate transient and compression parameters, and an assessment of potential model formulations of the compressive solids stress. Keywords: Hindered, transient, compression settling velocity; settling sensor; practical identifiability
References De Clercq, J., Nopens, I., Defrancq, J., Vanrolleghem, P.A., (2008). Extending and calibrating a mechanistic hindered and compression settling model for activated sludge using in-depth batch experiments. Water Res. 42, 781-791. Ramin, E., Wágner, D.S., Yde, L., Binning, P.J., Rasmussen, M.R., Mikkelsen, P.S., Plósz, B.G., (2014). A new settling velocity model to describe secondary sedimentation. Water Res., 66, 447-458. Torfs, E., Locatelli, F., Balemans, S., Diehl, S., Bürger, R., François, P., Laurent, J., Nopens, I., (2015). Impact of the flocculation state on hindered and compression settling. 9th IWA-Watermatex, June 2015, Gold Coast, Australia. Wágner, D.S., Valverde-Pérez, B., Sæbø, M., Bregua de la Sotilla, M., Van Wagenen, J., Smets, B.F., Plósz, B. Gy., 2016. Towards a consensus-based green microalgal growth model (ASM-A) – uptake and storage of nutrients. Water Res., Accepted with minor revision.
