Environmental Engineering Reference
In-Depth Information
history. Grathwohl (1990) showed that organic matter in unweathered shales
and high-grade coals enhanced sorption by more than an order of magnitude
when compared to more oxidized organic matter found in recent geologically
young material and highly weathered SOM. Huang and Weber (1997) have
suggested that changes in SOM oxygen-containing functional groups, e.g.,
changes in SOM O/C atomic ratios, can lead to a greater affinity of SOM for
recalcitrant compounds. Gustafsson et al. (1997) differentiated two forms of
SOM — humic acid and soot — for sediment by thermal treatment (Grath-
wohl and Reinhard, 1993).
Currently, there are very few direct observational data revealing the
microscale location or locations in which recalcitrant compounds accumulate
when they associate with soils and sediments (Gillette et al., 1999; Ghosh et
al., 2000). As a result, researchers must rely on inferences from macroscopic
experimental observations that capture overall behavior and provide empir-
ical evidence for deducing sorbent/sorbate mechanistic models (Wu and
Gschwend, 1988; Nkedi-Kizza et al., 1989; Brusseau et al., 1991; Grathwohl
and Reinhard, 1993; Werth and Reinhard, 1997; Huang and Weber, 1997;
Gustafsson et al., 1997). There is no reason to presume that only one sorption
mechanism dominates in any particular case. Indeed, in real systems, more
than one process likely contributes to rate-limited sorption behavior.
Current methods for assessing sorption and sequestration of recalcitrant
compounds on soils and sediments do not provide a basic understanding of
what is attainable by biostabilization or the bioavailability of recalcitrant
compounds, or information to aid interpretation of results of ecotoxicological
testing of residuals after biotreatment. Whether residual recalcitrant com-
pounds remaining after biotreatment represent an acceptable endpoint level
requires understanding of the mechanisms that bind contaminant recalci-
trant compounds within soil or sediment. Research is needed that will assess
the fundamental character of the binding of recalcitrant compounds at the
microscale level in parallel with the development of bioslurry treatment and
ecotoxicological testing, to show how the nature of PAH association with
soils and sediments relates to biostabilization and achievable treatment end-
points.
Research is needed to identify those factors affecting the bioavailability
of recalcitrant compounds on soils and sediments and the development of
the technical basis for enhancing natural recovery processes involved in the
biotreatment of soils and sediments contaminated with recalcitrant
compounds. A special focus is needed on improving the mechanistic under-
standing of sequestration and bioavailability of recalcitrant compounds in
soils and sediments. Such research could result in providing guidelines for
the assessment and prediction of the bioavailability of recalcitrant com-
pounds for
in situ
in situ
biotreatment.
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