title: Modelling aerobic biodegradation in vertical flow sand filters: impact of operational considerations on oxygen transfer and bacterial activity.
abstract: Oxygen renewal, as a prominent phenomenon for aerobic bacterial activity, deeply impacts Vertical Flow Constructed Wetland (VFCW) treatment efficiency. We introduce a multiphase model able to simulate multi-component transfer in VFCWs. It is based on a two-phase flow module, and a transport module. The flow module can quantify both water and air velocities throughout the filter during operation. The reactive transport module follows dissolved and gaseous oxygen concentrations, and the transport of solutes such as ammonium and readily biodegradable COD (Chemical Oxygen Demand). The consumption of components is governed by Monod-type kinetics. Heterotrophic and autotrophic bacteria, which are responsible for COD and ammonium degradation respectively, are part of the model components. The kinetics are based on the Constructed Wetlands Model 1. The results from the simulation tool were compared with existing experimental data, and two kinds of operation with VFCWs were investigated. The authors show strong interplay between oxygen renewal and bacterial consumption in case of sequential batch feeding with transient flooding of surface. Oxygen renewal is essentially convection mediated in such operation, while convection is not significant in non-flooding operation. Simulated bacterial patterns are impacted by the operation, both quantitatively and spatially. From a modelling point of view, the authors highlight some limitations of the biological model: the description of bacterial lysis processes needs to be enhanced, as well as ammonium adsorption to organic matter.
authors.affiliation: Institut de Mécanique des Fluides et des Solides de Strasbourg UdS/CNRS/ENGEES/INSA, 2 rue Boussingault, 67 000 Strasbourg, France. alain.petitjean@irstea.fr
authors.forename: A
authors.initials: A
authors.lastname: Petitjean
authors.forename: N
authors.initials: N
authors.lastname: Forquet
authors.forename: A
authors.initials: A
authors.lastname: Wanko
authors.forename: J
authors.initials: J
authors.lastname: Laurent
authors.forename: P
authors.initials: P
authors.lastname: Molle
authors.forename: R
authors.initials: R
authors.lastname: Mosé
authors.forename: A
authors.initials: A
authors.lastname: Sadowski
mesh_terms: D001420:Bacteria, Aerobic / Q000378:metabolism*; D001673:Biodegradation, Environmental; D057919:Biological Oxygen Demand Analysis; D005374:Filtration; D007700:Kinetics; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012822:Silicon Dioxide; D053833:Wetlands
chemical_list: D000644:Quaternary Ammonium Compounds; D012822:Silicon Dioxide; D010100:Oxygen