title: Redox-stratification controlled biofilm (ReSCoBi) for completely autotrophic nitrogen removal: the effect of co- versus counter-diffusion on reactor performance.
abstract: A multi-population biofilm model for completely autotrophic nitrogen removal was developed and implemented in the simulation program AQUASIM to corroborate the concept of a redox-stratification controlled biofilm (ReSCoBi). The model considers both counter- and co-diffusion biofilm geometries. In the counter-diffusion biofilm, oxygen is supplied through a gas-permeable membrane that supports the biofilm while ammonia (NH(4)(+)) is supplied from the bulk liquid. On the contrary, in the co-diffusion biofilm, both oxygen and NH(4)(+) are supplied from the bulk liquid. Results of the model revealed a clear stratification of microbial activities in both of the biofilms, the resulting chemical profiles, and the obvious effect of the relative surface loadings of oxygen and NH(4)(+) (J(O(2))/J(NH(4)(+))) on the reactor performances. Steady-state biofilm thickness had a significant but different effect on T-N removal for co- and counter-diffusion biofilms: the removal efficiency in the counter-diffusion biofilm geometry was superior to that in the co-diffusion counterpart, within the range of 450-1,400 microm; however, the efficiency deteriorated with a further increase in biofilm thickness, probably because of diffusion limitation of NH(4)(+). Under conditions of oxygen excess (J(O(2))/J(NH(4)(+)) > 3.98), almost all NH(4)(+) was consumed by aerobic ammonia oxidation in the co-diffusion biofilm, leading to poor performance, while in the counter-diffusion biofilm, T-N removal efficiency was maintained because of the physical location of anaerobic ammonium oxidizers near the bulk liquid. These results clearly reveal that counter-diffusion biofilms have a wider application range for autotrophic T-N removal than co-diffusion biofilms.
authors.affiliation: Department of Chemical Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Terada
authors.forename: Susanne
authors.initials: S
authors.lastname: Lackner
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsuneda
authors.forename: Barth F
authors.initials: BF
authors.lastname: Smets
mesh_terms: D000641:Ammonia / Q000302:isolation & purification / Q000493:pharmacokinetics*; D001420:Bacteria, Aerobic / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D019149:Bioreactors / Q000382:microbiology*; D003198:Computer Simulation; D004058:Diffusion; D008954:Models, Biological; D009584:Nitrogen / Q000302:isolation & purification / Q000493:pharmacokinetics*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification / Q000493:pharmacokinetics; D018508:Water Purification / Q000379:methods*
chemical_list: D014874:Water Pollutants, Chemical; D000641:Ammonia; D009584:Nitrogen