Biomedical Engineering Reference
In-Depth Information
limited by the external mass transfer rate due to the formation of granules with a lower size
and more active. These authors also observed that internal mass transfer rate was negligible
compared to the external one and attributed this fact to the sudden flow regime change during
the pulse. In fact, several authors have observed experimental evidence of convective fluxes
within biofilms mainly due to pressure gradients (Brito and Melo, 1999; de Ber et al., 1996;
van den Heuvel et al., 1997).
Conclusion
Hydrodynamic conditions are proved to highly influence the properties of the obtained
biomass and the efficiency of the performed process in biological reactors treating
wastewater. Beneficial effects will depend on the values of the input power used up to a limit
value. Higher values over this limit are expected to produce a detrimental effect on the
biomass characteristics and the efficiency of the process, being possible, in some cases, the
complete loss of microbial activity. Shear stress together with the type of reactor and
wastewater composition are the main factors that affect to the performance of the bioreactor
(Figure 5). It has a significant influence on the structure, mass transfer rate, production of
exopolysaccharides, metabolic/genetic behaviour of biofilms, and aerobic and anaerobic
granules. From an engineering point of view, hydrodynamic shear stress can be managed, as a
control parameter, to enhance the operation and efficiency of wastewater treatment systems.
Acknowledgements
This work was funded by the Spanish Government (Biogramem project CTQ2005-
04935/PPQ and NOVEDAR_Consolider project CSD2007-00055).
References
Adav, S.S.; Lee D.J.; Lai, J.Y. (2007). Effects of aeration intensity on formation of phenol-
fed aerobic granules and extracellular polymeric substances.
Applied Microbiology and
Biotechnology,
77
, 175-182.
Alphenaar, P.A.; Pérez, M.C.; van Berkel, W.J.H.; Lettinga, G. (1992). Determination of the
permeability and porosity of anaerobic sludge granules by size exclusion
chromatography.
Applied Microbiology and Biotechnology,
36
(6), 795-799.
Alphenaar, P.A.; Pérez, M.C.; Lettinga, G. (1993). The influence of substrate transport
limitation on porosity and methanogenic activity of anaerobic sludge granules.
Applied
Microbiology and Biotechnology,
39
(2), 276-280.
Arrojo, B.; Mosquera-Corral, A.; Campos, J.L.; Méndez, R. (2006). Effects of mechanical
stress on Anammox granules in a sequencing batch reactor (SBR).
Journal of
Biotechnology,
123
, 453-463.
Arrojo, B.; Figueroa, M.; Mosquera-Corral, A.; Campos, J.L.; Méndez R. (2008). Influence of
gas flow-induced shear stress on the operation of the Anammox process in a SBR.
Chemosphere,
72
(11), 1687-1693.
