Environmental Engineering Reference
In-Depth Information
Remediation of Soil PAHs
Traditional
landfarming
Composting
Bioslurry
Nutrient amendments
bioaugmentation
Bulking agents
mixing
ineffective
Too expensive
Incomplete degradation
Modified Land farming
nutrient amendment, bulking agent,
bioaugmentation and limited tilling
Figure 7.1
Project history leading to the selection of land farming as a PAH treatment
technology.
farming. Research in each of these technologies provided insight into areas of
PAH bioremediation useful to the final treatment selection: isolation and char-
acterization of PAH-degrading bacteria and elucidation of the degradation
pathways, surfactant chemistry, bioaugmentation, and microbial carrier tech-
nology. This produced a final treatment with aspects of all three technologies.
For field studies, land farming with bioaugmentation and biostimulation was
selected as the treatment option for PAH-contaminated soils. The treatments
and the technologies that support them are discussed in the following sections.
7.1.3.1 Solid phase treatments
Solid phase treatments, commonly known as land farming and composting,
are two of the most commonly applied technologies for the remediation of
PAH-contaminated soil (Gray et al., 2000; Harmsen, 1991; Mueller et al.,
1991a, 1991b; Mueller-Hurtig et al., 1993; Yare, 1991). Most PAH-contami-
nated soils contain a significant number of PAH degraders that have been
enriched because of the presence of the PAHs, but they are often constrained
in their degradation capability because of some limiting factor. Common
limiting factors include inadequate aeration, poor contact of the microorgan-
isms with the PAHs due to the adherence of the PAHs to surfaces and
nonaqueous phase liquid (NAPL) materials, and the absence of sufficient
nitrogen to sustain extensive mineralization of the contaminant carbon. Any
engineering activity that reduces these limitations brings the native degrad-
ers into action.
Advantages of solid phase treatment are that large quantities of contam-
inated soil can be treated at the same time and that operation and mainte-
nance activities (costs) are minimal. In general, contaminated soil is placed
in aboveground treatment areas that are designed for proper effluent collec-
tion, and then the soil is handled in specific ways to enhance indigenous
microbial activity. Composting usually involves the addition of readily
