Biomedical Engineering Reference
In-Depth Information
Chapter 9
E
FFECT OF
S
HEAR
S
TRESS ON
W
ASTEWATER
T
REATMENT
S
YSTEMS
P
ERFORMANCE
J.L. Campos
a
, B. Arrojo
a
, A. Franco
a
, M. Belmonte
b
,
A. Mosquera-Corral
a
, E. Roca
a
and R. Méndez
a
a
Department of Chemical Engineering. School of Engineering. Rua Lope Gómez de
Marzoa s/n. University of Santiago de Compostela, E-15782,
Santiago de Compostela, Spain
b
Environmental Science Center EULA-Chile, University of Concepción,
Concepción, Chile
Abstract
Wastewater treatment systems must be operated under hydrodynamic conditions that allow
maintaining the biomass in suspension and promoting intimate contact between substrates and
biomass. The systems used to maintain the mixture (mechanical stirring, aeration, etc.) exert
shear stress on the biomass which can affect its physical properties (density and diameter) and
specific activity.
When biomass is subjected to moderate shear stress, stable and dense structures can be
formed, improving its retention, and the substrate transfer rates are also favoured. However,
high shear stress generally leads to the loss of biomass activity and to the formation of
particles with low diameters, which are washed-out of the system. Therefore, it is very
important to control shear stress acting on biomass particles in order to optimize the
performance of wastewater treatment systems.
The effects of impact stress and hydraulic stress by gas or liquid on the efficiency of
different biological systems for carbon and nitrogen removal are discussed in this work.
Keywords:
aeration, biological systems, mechanical agitation, pulsed flow, shear stress,
wastewater
