title: Dynamic one-dimensional modeling of secondary settling tanks and design impacts of sizing decisions.
abstract: As one of the most significant components in the activated sludge process (ASP), secondary settling tanks (SSTs) can be investigated with mathematical models to optimize design and operation. This paper takes a new look at the one-dimensional (1-D) SST model by analyzing and considering the impacts of numerical problems, especially the process robustness. An improved SST model with Yee-Roe-Davis technique as the PDE solver is proposed and compared with the widely used Takács model to show its improvement in numerical solution quality. The improved and Takács models are coupled with a bioreactor model to reevaluate ASP design basis and several popular control strategies for economic plausibility, contaminant removal efficiency and system robustness. The time-to-failure due to rising sludge blanket during overloading, as a key robustness indicator, is analyzed to demonstrate the differences caused by numerical issues in SST models. The calculated results indicate that the Takács model significantly underestimates time to failure, thus leading to a conservative design.
authors.affiliation: Civil and Environmental Engineering Department, University of California, 5732 Boelter Hall, Los Angeles 90095-1593, USA.
authors.forename: Ben
authors.initials: B
authors.lastname: Li
authors.affiliation: Civil and Environmental Engineering Department, University of California, 5732 Boelter Hall, Los Angeles 90095-1593, USA. Electronic address: stenstro@seas.ucla.edu.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Stenstrom
mesh_terms: D001673:Biodegradation, Environmental; D018533:Biomass; D019149:Bioreactors / Q000191:economics; D003365:Costs and Cost Analysis; D003657:Decision Making; D004867:Equipment Design / Q000191:economics; D008962:Models, Theoretical; D009716:Numerical Analysis, Computer-Assisted; D015203:Reproducibility of Results; D012722:Sewage / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000191:economics / Q000295:instrumentation* / Q000379:methods*; D018508:Water Purification / Q000191:economics / Q000295:instrumentation*
chemical_list: D012722:Sewage
keywords: Activated sludge; Clarification; Control; Wastewater treatment