Impact of biomass-decay terms on the simulation of pulsed bioremediation

Abstract

A numerical model is used for simulating the stimulation of biomass growth by injection of alternating pulses of a primary substrate and oxygen. We consider that the substrate sorbs, whereas oxygen does not undergo mass transfer, and mixing of the reacting compounds is dominated by the chromatographic effect. Different mathematical formulations for biomass growth and decay are compared. In models considering biomass decay, a minimal time of joint exposure to both reactants can be determined. This leads to a multimodal distribution of the biomass after multiple injection cycles. In multidimensional heterogeneous domains, the location of the biomass peaks is determined by the advective arrival time. The biomass is much more homogeneously distributed when biomass decay is neglected, because under this condition there is no constraint by a minimal joint exposure time. For the case of oxygen-dependent biomass decay, an injection scheme using shorter pulses of higher oxygen concentrations is shown to be superior to a scheme with equally long pulses of oxygen and the substrate.