BIOAUGMENTATION FOR GROUNDWATER REMEDIATION: AN OVERVIEW - Bioaugmentation for Groundwater Remediation - page 16

no guarantee that the method will work in the field, prior testing often can save time and
money, and increase the likelihood of success. Care should be taken to ensure that the testing
conditions are representative of field conditions. Unfortunately, this is often a time-consuming
process, as microcosms must be given enough time to demonstrate detectable degradation and
inoculum survival as compared to controls. In some cases, there are methods to accelerate this
testing, such as the use of isotope labeling, where accelerated growth of the bioaugmentation
strain can be detected with greater sensitivity by using isotopically labeled carbon dioxide (CO 2 )
(Hesselsoe et al., 2008 ). Once the microcosm test is successful and/or the treatment has been
approved by the regulatory agencies, full-scale treatment can be implemented.
1.4.3 Implement the Treatment
Site-specific applications of bioaugmentation will naturally depend on the type of bioaug-
mentation strategy chosen and the problems that are foreseen by the site evaluation.
The practitioner must decide on the inoculum type, the inoculum size and the mode of delivery,
all three of which are interdependent. In all cases, the inoculum must first either be acquired or
engineered and grown. Commercially available inocula are appealing because they are easy to
use and readily available in large quantities. For preadapted bacterial inocula or activated soil,
the bacteria/soil must first be obtained from a polluted site and acclimated to the pollutant. Next,
the application rate must be determined, and several interrelated questions must be addressed:
How many bacteria are needed per cubic meter?
Does the inoculum addition need to be done aerobically or anaerobically?
Are there any nutrients that need to be added?
How will adequate distribution of the inoculum be ensured?
The effect of inoculum size on degradation rate or success depends on the site, the pollutant
and the bioaugmenting organism (Vogel and Walter, 2002 ). More is not necessarily better when
it comes to bioaugmentation, as a larger inoculum does not necessarily lead to faster degrada-
tion. Additionally, too much inoculum might overwhelm a system and lead to a loss of available
nutrients. The application of commercially-available inocula depends on the manufacturer, but
the form of the inoculum is tailored for the intended application. For example, for treating
surface oil spills, QM Environmental Services, Ltd. provides Microcat ® -XRC in a powder form
for direct application to the spill. A lake or other body of water might benefit from either a spray
(if the contaminant is on the surface) or addition of a liquid inoculum.
Most groundwater bioaugmentation strategies involve injecting the inoculum, although it is
also possible to convert subsurface irrigation systems (Mehmannavaz et al., 2002 ). Many
commercial inocula come in a liquid form that is ready for direct injection into the ground.
In order to achieve more coverage, it is possible to inject into a strategically placed row of wells
to create a biocurtain or biobarrier through which the groundwater will flow (Dybas et al., 2002 ;
Hunter and Shaner, 2010 ). When injecting inocula into soil or contaminated groundwater, it is
often difficult to ensure that the inoculum will be delivered effectively (so that it will not be
carried away too quickly from the point of injection, for example), or that the inoculum will not
be predated or outcompeted too quickly. One solution may be to use a carrier agent or
encapsulating agent to deliver the inoculum, provide protection and/or nutrition and place
the inoculum where the pollutant is located. Carrier agents tend to be clay or plant-derived
compounds like peat, while encapsulating agents are gels, like alginate or polyacrylamide, that
coat the cell but are flexible enough for injection and can be degraded (van Veen et al., 1997 ).
These agents protect the inoculum against the environment (pH, predation, etc.) but target
compounds can diffuse through (Gentry et al., 2004 ).