BIOAUGMENTATION FOR GROUNDWATER REMEDIATION: AN OVERVIEW - Bioaugmentation for Groundwater Remediation - page 15

Table 1.2. Environmental Factors Influencing Bioaugmentation Success
Type Factor Repercussion

Temperature Affects inoculum growth rate

Physical Type of medium Controls difficulty of inoculum injection

Humidity Affects inoculum growth rate, survival

pH Affects inoculum growth rate, survival

Substrate availability Controls degradation rate

Nutrient availability Affects inoculum growth rate, survival

Chemical

Competing e-acceptors Affects inoculum growth rate, survival

Other pollutants/toxins May require more than one inoculum,

remediation strategy

Competition Affects inoculum growth rate

Biological

Predation Affects inoculum survival

bioaugmentations may be necessary. In some cases, the removal of one pollutant could enhance
the natural attenuation of the remaining pollutants.
A different remediation strategy might be needed in the face of strongly unfavorable site
conditions, such as multiple contaminants or extreme climate and pH. Such conditions are
often the cause of MNA failure and the reason that practitioners turn to biostimulation and
bioaugmentation. Unfortunately, bioaugmentation may not necessarily be an improvement
over MNA - the site parameters might simply be unfavorable for bioremediation. In any
case, each site needs to be carefully examined, as what works at one site is not guaranteed to
work at another. Mixed pollutants can be treated with multiple inocula or multiple remediation
strategies. High pollutant levels might require a more robust inoculum that is able to tolerate
conditions that might kill other microorganisms. It has been noted that dechlorinating microbes
are able to tolerate the high chlorinated solvent levels near a nonaqueous phase liquid (NAPL)
source zone, and the microbes could even aid dissolution of the NAPL (Amos et al., 2008 ).
There is also the possibility of using bacteria adapted to low pH or low temperatures, like
psychrophiles (Margesin, 2007 ). However, commercial use of these bacteria would require
considerable further research and possible genetic modification.

1.4.2 Select and Test Bioaugmentation Strategy

Once the site has been vetted and bioaugmentation is still deemed a feasible remediation
strategy, then the type of bioaugmentation must be chosen. The previous section discussed a
number of bioaugmentation possibilities. The type of pollutant and the site parameters will help
determine the bioaugmentation strategy. For example, if the site is cocontaminated with metals
but near a residential area, rhizoremediation might be appealing both for the efficacy of plants
to accumulate metals and for the aesthetic appeal. Currently, preadapted microbial strains or
commercial organisms have been used in field studies or at actual remediation sites. These
commercial bioaugmentation inocula are being more thoroughly tested, due to past commercial
products failing to meet their promised performance (Simon et al., 2004 ; Mathew et al., 2006 ;
Brooksbank et al., 2007 ).
Even when using a commercial organism, it is generally preferable to test all methods in
microcosms prior to use in the field, although this is infrequently practiced. Although there is