Sensitivity Analysis of Optimal Operation of an Activated Sludge Process Model for Economic Controlled Variable Selection

Abstract

This paper describes a systematic sensitivity analysis of optimal operation conducted on an activated sludge process model based on the test-bed benchmark simulation model no. 1 (BSM1) and the activated sludge model no. 1 (ASM1). The objective is to search for a control structure that leads to optimal economic operation, while promptly rejecting disturbances at lower layers in the control hierarchy avoiding thus violation of the more important regulation constraints on effluent discharge. We start by optimizing a steady-state nonlinear model of the process. Here, a new steady-state secondary settler mathematical model is developed based on the theory of partial differential equations applied to the conservation law with discontinuous fluxes. The resulting active constraints must be chosen as economic controlled variables. These are the effluent ammonia from the bioreaction section and the final effluent total suspended solids at their respective upper limits, in addition to the internal recycle flow rate at its lower bound. The remaining degrees of freedom need to be fulfilled, and we use several local (linear) sensitivity methods to find a set of unconstrained controlled variables that minimizes the loss between actual and optimal operation; particularly we choose to control linear combinations of readily available measurements so to minimize the effect of disturbances and implementation errors on the optimal static performance of the plant. It is expected that the proposed methodology and results obtained therein can be used in practice as general rules-of-thumb to be tested in actual wastewater treatment plants of the kind discussed in this paper.

Dynamic simulation for wastewater treatment plants management: Case of Souk-Ahras region, north-eastern Algeria

“…BAHGAT [2000] in SOROUR and BAHGAT [2004] developed an expert system called "activated sludge expert" to help inexperienced operators exploiting their activated sludge wastewater treatment plants. Strategies of control of the WWTPs were presented by ARAUJO et al [2013]; HUANG and GOEL [2015] and NGUYEN et al [2013] based on the optimal economic operation. Founded on the techniques of optimization of activated sludge processes, several recent studies were developed to examine a compromise between processing costs and final quality of uncluttered waters.…”

Modeling of multimode anaerobic/anoxic/aerobic wastewater treatment process at low temperature for process optimization

“…The optimization of WWTP operation was required to conform with increasingly stricter discharge standards and at the same time met tight operational budget restrictions [14,15]; therefore, several performance indices, including effluent quality (EQ), effluent violation (EV) and operating costs (OC) must be taken into account for optimization [11,13,[16][17][18][19]. In activated sludge process, temperature is one of the most commonly evaluated influencing factors.…”

Model predictive control for the self-optimized operation in wastewater treatment plants: Analysis of dynamic issues

“…The three active constraints must be controlled to ensure optimal operation. The expression (6) with matrix Q selected as the identity has been considered to obtain the optimal set of five unconstrained selfoptimizing control variables associated with the unconstrained degrees of freedom as a combination of measurements determined by matrix H. The expected range of disturbances for the activated sludge process has been taken from Araujo et al (2013) as representative values for scaling:…”

“…Some of them (Francisco et al, 2011;Rivas et al, 2008) also include plant design, and others are only focused on tanks aeration (Amand and Carlsson, 2012). Only Araujo et al (2011Araujo et al ( , 2013 provides a comprehensive approach, performing a sensitivity analysis of optimal operation for the selection of the best control structure in term of costs and effluent quality. The work of Cadet et al (2004) is similar but without considering the economics of the system.…”