Abstract:
In this study, a mathematical biofilm reactor model based on the structure of the Constructed Wetland Model No.1
(CWM1) coupled to AQUASIM’s biofilm reactor compartment has been used to reproduce the sequence of
transformation and degradation of organic matter, nitrogen and sulphur observed in a set of constructed wetland
mesocosms and to elucidate the development over time of microbial species as well as the biofilm thickness of a
multispecies bacterial biofilm in a subsurface constructed wetland. Exper-imental data from 16 wetland mesocosms
operated under greenhouse conditions, planted with three different plant species (Typha latifolia, Carex rostrata,
Schoenoplectus acutus) and an unplanted control were used in the calibration of this mechanistic model. Within the
mesocosms, a thin (predominantly anaerobic) biofilm was simulated with an initial thickness of 49 mm (average)
and in which no con-centration gradients developed. The biofilm density and area, and the distribution of the
microbial species within the biofilm were evaluated to be the most sensitive biofilm properties; while the substrate
diffusion limitations were not significantly sensitive to influence the bulk volume concentrations. The simulated
biofilm density ranging between 105,000 and 153,000 gCOD/m3 in the mesocosms was observed to vary with
temperature, the presence as well as the species of macrophyte. The biofilm modeling was found to be a better tool
than the suspended bacterial modeling approach to show the influence of the rhizosphere configuration on the
performance of the constructed wetlands.
