Image: Biomass-based model biofilm (apart)
Biofilm, aged 96,000 min (67 days, 9.5 weeks). The contour lines show the oxygen concentration in mg/l. The image was rendered with POV-Ray, showing each biomass brick as a sphere. The biomass of the ammonia oxidisers ("Nitroso") is green; the biomass of the nitrite oxidisers ("Nitro") is red. The grey box at the bottom is the inert substratum. Note the wrapped around boundaries in the horizontal direction.
This Biomass-based model version (apart) does not allow the coexistence of biomasses of the two species in the same grid element. The nitrite oxidisers grew only poorly because the ammonia oxidisers have a kinetic advantage under oxygen limitation. Oxygen limitation is clearly visible from the contour lines, and results from the high concentration of ammonia and nitrite in the bulk liquid.