BIOAUGMENTATION CONSIDERATIONS - Bioaugmentation for Groundwater Remediation - page 156

Figure 5.4. Photo of an active recirculation bioremediation system.
bioaugmentation culture is low, compared to the capital and operating costs for biostimulation
alone; (2) if bioaugmentation can reduce the time that active recirculation is required, it can
reduce the overall remediation costs significantly; (3) the infrastructure needed for bioaug-
mentation is already present so there is usually little additional cost to inject cultures; and (4) the
active recirculation may act to distribute the bioaugmentation culture.
The use of active recirculation to distribute bacteria and induce complete dechlorination is
well documented at the pilot scale (Ellis et al., 2000 ; Lendvay et al., 2003 ; Major et al., 2002 ;
Hood et al., 2008 ; Schaefer et al., 2010a ), although sufficient sampling was not performed in all
cases in order to provide a full assessment of bacterial growth and distribution. A study at Kelly
AFB, TX (Major et al., 2002 ) was one for which Dehalococcoides transport times could be
reasonably estimated and compared to conservative transport times. Travel times for Dhc were
between 61 and 176 times longer than for conservative transport (i.e., the average groundwater
velocity, based on the average rate of movement of a conservative tracer that is not destroyed
or retarded during transport). The Bachman Road, MI site study suggested that the Dhc
transport time was only about 2.3 times greater than groundwater transport times (Lendvay
et al., 2003 ).
However, performing inoculations can be complicated if the system is already constructed
and operational, and bioaugmentation was not considered in the initial design. For example,
the recirculation system for ESTCP project ER-200513 was constructed and operated to
“pre-condition” the aquifer to establish reducing conditions prior to inoculation. Subsequently,