Impact on sludge inventory and control strategies using the benchmark simulation model no. 1 with the Bürger-Diehl settler model

Abstract

An improved one-dimensional (1-D) model for the secondary clarifier, i.e. the Bürger-Diehl model, was recently presented. The decisive difference to traditional layer models is that every detail of the implementation is in accordance with the theory of partial differential equations. The Bürger-Diehl model allows accounting for hindered and compressive settling as well as inlet dispersion. In this contribution, the impact of specific features of the Bürger-Diehl model on settler underflow concentration predictions, plant sludge inventory and mixed liquor suspended solids based control actions are investigated by using the benchmark simulation model no. 1. The numerical results show that the Bürger-Diehl model allows for more realistic predictions of the underflow sludge concentration, which is essential for more accurate wet weather modelling and sludge waste predictions. The choice of secondary settler model clearly has a profound impact on the operation and control of the entire treatment plant and it is recommended to use the Bürger-Diehl model as of now in any wastewater treatment plant modelling effort.

Fast reliable simulations of secondary settling tanks in wastewater treatment with semi-implicit time discretization

“…For physical reasons, d comp (X) should be a non-negative function (a negative ''diffusion'' coefficient means an ill-posed PDE (1)), which implies that σ e (X) should be non-decreasing. We choose the following particularly simple function [5]:…”

“…Because of the large number of equations in the comprehensive models for entire wastewater treatment plants, the currently most common approach to investigate these models is by simulation. For example, influences of different model assumptions, such as reactions during the sedimentation process were investigated by Flores-Alsina et al [3], the inclusion of dispersion in addition to hindered settling by Ramin et al [4] and the inclusion of compression settling on control strategies by Torfs et al [5]. Further investigations of control strategies for optimal economic operation under effluent constraints were presented by Araujo et al [6,7], Huang et al [8], Nguyen et al [9].…”

“…the one in [19]) in which the modelling is integrated with the development of an ad hoc numerical method. The latter often leads to unreliable simulation models [21,22,5]. A recent simulation model which has a numerical flux connected to PDE theory is the one by Li and Stenstrom [23].…”

Simulations of reactive settling of activated sludge with a reduced biokinetic model

“…Already without reactions, the Takács simulation model is not recommended because of failure of agreement with the solutions of the conservation of mass partial differential equation (PDE) in certain situations (Jeppsson and Diehl, 1996a;Bürger et al, 2011Bürger et al, , 2012a, but also M a n u s c r i p t for other shortcomings during normal operating conditions specifically during wet weather (Torfs et al, 2015).…”

“…Moreover, the Bürger-Diehl model has shown to provide a more realistic representation of the sludge blanket height and thus the sludge accumulation in a secondary clarifier (Torfs et al, 2015) which is an important driving factor for the denitrification process. It is the purpose of this contribution to make a first step towards extending these advances for the numerical treatment of non-reactive settling to the reactive case.…”