BIOAUGMENTATION FOR GROUNDWATER REMEDIATION: AN OVERVIEW - Bioaugmentation for Groundwater Remediation - page 20

criteria, discussed in detail below, include development of bioaugmentation cultures, inoculum
introduction and survival, increasing pollutant and nutrient bioavailability and reducing

unwanted side-effects.

1.5.1 Development of Effective Bioaugmentation Cultures

Perhaps the biggest hurdle for bioaugmentation is to create an inoculum that will survive,
grow and degrade the target pollutant(s) in situ . This chapter deals primarily with the practical
aspects of bioaugmentation implementation and does not discuss the measures necessary to
develop bioaugmentation strains/inocula. However, it is important for practitioners to under-
stand the three basic criteria for a good bioaugmentation culture (Cases and de Lorenzo, 2005 ).
First, the culture has to be able to survive long enough to impact the pollutant concentration in
its new environment, unless it is only being used to transfer genetic material to other organisms.
There are various methods by which its survival can be enhanced, such as the use of a delivery
agent as previously discussed, but bioaugmentation cultures should be selected and cultured to
enhance their in situ survival. Second, the organism needs to have a high degradation activity,
although not necessarily a fast growth rate (Kuiper et al., 2004 ). Finally, control over the
culture's longevity in the system is desirable to ensure the return of the ecosystem to its original
state after treatment is complete. In many cases, it is preferable that the bioaugmented
organism not outlive its usefulness in the system.

1.5.2 Successful Inoculum Delivery and Dispersion

Depending on the polluted site, delivery of the inoculum can vary in difficulty.
In groundwater remediation, the inoculum often has to be injected into a well, where it must
diffuse enough to obtain good coverage of the area but not leave the polluted site.
The hydrogeology of the site can determine whether the inoculum can spread from the
injection point or if injection is even possible. There are a few possibilities for increasing
the dispersivity of cells, like the use of ultramicrobacteria that are more mobile due to their
smaller size, the development of adhesion-deficient bacteria or the addition of surfactants
(Gentry et al., 2004 ).

1.5.3 Inoculum Survival

Once the inoculum is delivered, it needs to survive long enough to perform its function.
The type of inoculum - its robustness and rate of growth - can determine its survival. Some of
the factors that inhibit inoculum survival/growth, such as pH, temperature and nutrient avail-
ability, have already been discussed under “Site Evaluation” in Section 1.4.1 . Lack of nutrient
availability can limit survival and the degradation process. Clay content or organic matter can
limit growth by limiting nutrient availability by diffusion (Vogel, 1996 ). Nutrient or substrate
availability can be enhanced with biostimulation or the use of surfactants. The nutrient issue also
can be ameliorated by using a carrier agent that contains supplements (Gentry et al., 2004 ).
Effective distribution of the inoculum throughout the subsurface will limit the concentration of
organisms in any one area, thus increasing the amount of nutrients available per cell.
The other major factor inhibiting inoculum survival is not abiotic, but rather biotic, in the
form of predation by other organisms (e.g., protozoa) and competition for nutrients. Some
encapsulating agents provide protection against predation, and nutrients also can be included in
the inoculum carrier agent or in a biostimulation process. But these are not necessarily long-
term survival techniques and reinoculation may be necessary (Newcombe and Crowley, 1999 ;