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Redox‐stratification controlled biofilm (ReSCoBi) for completely autotrophic nitrogen removal: The effect of co‐ versus counter‐diffusion on reactor performance
Author(s) -
Terada Akihiko,
Lackner Susanne,
Tsuneda Satoshi,
Smets Barth F.
Publication year - 2006
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.21213
Subject(s) - biofilm , chemistry , diffusion , oxygen , ammonia , nitrogen , autotroph , diffusion layer , anaerobic exercise , redox , nitrification , chemical engineering , inorganic chemistry , bacteria , thermodynamics , layer (electronics) , organic chemistry , biology , physiology , physics , genetics , engineering
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 µm; 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. Biotechnol. Bioeng. 2007;97:40–51. © 2006 Wiley Periodicals, Inc.