Geoenvironment Impact Mitigation and Management - Sustainable Practices in Geoenvironmental Engineering - page 371

would either be hydrated or would form complexes such as Pb 2+ , PbOH + , and PbCl + . These
would be contained in the left-shaded area of Figure 10.8. When the pH is raised to the pH
levels shown in the right-shaded area of Figure 10.8, one would form complexes such as
PbO 2 H − and PbO 2− that would reside in the right-shaded area.

10.5.2.4 Speciation and Complexation

The processes associated with speciation and complexation apply primarily to inorganic con-
taminants in the liquid waste streams, particularly the heavy metals. The term s peciation refers
to the formation of complexes between heavy metals and ligands in the aqueous phase. Ligands
are deined as anions that can form coordinating compounds with metal ions. Inorganic and
organic ligands include, for example, CO

− − − − − − −
, , , , and humic
and fulvic acids. For the complexes formed between heavy metals and humic and fulvic
acids, these would generally be chelated compounds. From the preceding, we note that the
chemistry of the porewater in the soil-water system is an important factor in mitigation
and control of contaminant transport in the soil-water system—through competition between
the ligands and the soil solids for sorption of the heavy metals.

2 2 2 3

SO Cl NO , OH , Si , PO

3 4 3 3 4

10.5.3 Biological Properties

Biological properties of soils (soil-water systems) are very important factors in the pas-
sive and aggressive treatment and management of organic chemical contaminants in the
subsurface soil regime. These properties are determined by the large variety of microor-
ganisms that reside in the soil-water system. These microorganisms consist of viruses,
bacteria, protozoa, fungi, and algae. Microorganisms are the key to biological treatment
and management of contaminants and contaminants.

10.5.3.1 Protozoa

Protozoa are aerobic, single-celled chemoheterotrophs. They are classiied as eukaryotes
with no cell walls and with sizes that vary from one to a few hundred micrometers. They
include pseudopods, lagellates, amoebas, ciliates, and parasitic protozoa. The four pri-
mary groups of protozoa are (1) Mastigophora—lagellate, (2) Sarcodina—amoeboid,
(3) Ciliophone—ciliated, and (4) Sporozoa—parasites of vertebrates and invertebrates.
Protozoa are found in water and soil and feed on bacteria and need water in order to move.
Although they do not generally biodegrade contaminants, they are useful in reducing bac-
terial numbers near injection wells that become clogged due to excessive growth. Soil pro-
tozoa are heterotrophic, and although their general food source is bacteria, they are known
to feed on soluble and even insoluble organic material. They mineralize nutrients and
release excess nitrogen as NH 4 + , which is beneicial to plants and others on the food web.

10.5.3.2 Fungi

Fungi include slime molds (ilamentous fungus), yeasts, and mushroom and are aerobic,
multicellular, eukaryotes, and chemoheterotrophs that require organic compounds for
energy and carbon. They are larger than bacteria, and do not require as much nitrogen.
They grow more slowly and in a more acidic pH range than bacteria, and are more sensi-
tive to changes in moisture levels. Yeasts are unicellular organisms that are larger than
bacteria, and are shaped like eggs, spheres, or ellipsoids.