Impact of Dual Substrate Limitation on Biodenitrification Modeling in Porous Media

In this work, we consider a model of the biodenitrification process taking place in a spatially-distributed bioreactor, and we take into account the limitation of the kinetics by both the carbon source and the oxidized nitrogen. This model concerns a single type of bacteria growing on nitrate, which splits into adherent bacteria or free bacteria in the liquid, taking all interactions into account. The system obtained consists of four diffusion-convection-reaction equations for which we show the existence and uniqueness of a global solution. The system is approximated by a standard finite element method that satisfies an optimal a priori error estimate. We compare the results obtained for three forms of the growth function: single substrate limiting, “multiplicative” form, and “minimum” form. We highlight the limitation of the ‘ single substrate limiting model”, where the dependency of the bacterial growth on the nitrate is neglected, and find that the “minimum” model gives numerical results closer to the experimental results.

Modelling of the Transient Behaviour of a Membrane-Attached Biofilm Reactor under Successive Pulses of a Synthetic Wastewater Substrate

This work deals with the theoretical and experimental study of the transient behaviour of a membrane-attached biofilm reactor (MARB) when it is exposed to a series of pulse injections of concentrated solutions of sodium acetate, used as a synthetic wastewater. The MARB is connected to a reservoir tank with full recirculation containing the synthetic wastewater, and oxygen permeates through the wall membrane to the biofilm attached to it. For the two experiments reported in this work air is also sparged into the residual water in the tank providing an extra source of oxygen that diffuses simultaneously from the membrane and from the liquid into the biofilm. A pseudo-heterogeneous model using Monod kinetics with dual substrate limitation was employed to predict the observed evolution of substrate and dissolved oxygen concentrations in the MABR. The model accounts for the counter-diffusion of substrate and oxygen as well as for the reaction within the biofilm. It also predicts biomass growth and the production of extra cellular polymers, which in turn causes the biofilm to grow. Transport and kinetic parameters previously estimated, are used in the model to predict the growth rates in the biofilm and allow the analysis of the relative contribution of the rates of mass transport by diffusion, convection and growth reaction.