Environmental Engineering Reference
In-Depth Information
(b) Contaminant removal by non-chemotactic bacteria
Dispersed
nonchemotatic
strain
Underground
storage tank
Monitoring
wells
Injection
well
Unsaturated
Zone
GW flow
(c) Contaminant removal by chemotactic bacteria
Chemotactic
bacterial band
GW flow
Leaking
contaminant
Injected
bacteria
Contaminant
plume
Saturated
zone
(a) Initial injection
GW flow
time t > 0
Fig. 7.3 Chemotaxis assisted bioaugmentation. Panel (a) represents the initial state of bioaug-
mentation, where bacterial strains are injected for remediation of a contaminant plume. Non-
chemotactic strains (b) remain dispersed and are washed away with ground-water flow,
resulting in a slow removal rate. Chemotactic strains (c) create a chemical gradient as a result
of contaminant consumption and move upgradient and downgradient in the form of con-
centrated bands, resulting in an accelerated contaminant removal rate
chemotactic bacteria may significantly accelerate the degradation rate in con-
taminated aquifers and reduce overall remediation costs. Appropriate bacterial
transport models, including chemotaxis transport parameters, will be helpful in
selecting appropriate injection locations and rates to fully exploit the benefits of
chemotaxis.
7.7.3 Chemotaxis in Monitored Natural Attenuation (MNA)
Natural attenuation of contaminants relies on various naturally occurring in
situ physicochemical and biological processes. A careful evaluation of these
processes to achieve site-specific remediation objectives within a reasonable
timeframe is termed MNA. These in situ processes, under favorable conditions
and without human intervention, may cause stabilization, transformation or
complete destruction of contaminants [55]. Chemotaxis may enhance these
natural processes. Incorporating moving bacterial bands in MNA predictions
for a specific site may significantly reduce the remediation time by overcoming
mass transfer and nutrient limitations.
