Remediation: Techniques and Cost - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 380

11.3.2 Active and Passive Bioremediation
Active bioremediation involves the introduction of microorganisms, along with additional
nutrients into contaminated soil, to allow natural processes to degrade the contaminants
into harmless substances (USEPA 2001a). Active bioremediation is typically used on soil
where the existing soil bacteria may have been destroyed or overwhelmed by a contami-
nant spill or where time constraints require a more speedy recovery. Active bioremedia-
tion may also be used to target a specific high boiling point hydrocarbon such as fuel oil,
or heavy diesel fuel. Passive bioremediation generally relies on the existing soil bacteria.
This method has often been referred to as landfarming (Figure 11.1), because the contami-
nated soil is spread out to a thickness of no more than a half a meter, and then periodically
tilled to bring the soil in contact with air (see Section 11.3.4). A summary of a form of active
bioremediation using treatment cells is found in Murray and Clark (1993) (Figures 11.2 and
11.3). An unconventional form of passive bioremediation of hydrocarbon contaminated
soil using treatment galleries was successfully demonstrated by Murray et al. (1997). In
either active or passive bioremediation, before the microbes can effectively degrade and
eventually destroy the contaminants, these criteria must be satisfied (USEPA 2001a):
FIGURE 11.1
Example of landfarming in the central valley of California. (Photo by Kent S. Murray.)
FIGURE 11.2
Constructing a treatment cell in San Diego. (Photo by Kent S. Murray.)