Contaminated Land and Bio-Remediation - Environmental Biotechnology: Theory and Application - page 100

Factors Affecting the Use of Bioremediation
It is possible to divide these into two broad groups; those which relate to the
character of the contamination itself and those which depend on environmental
conditions. The former encompass both the chemical nature of the pollutants and
the physical state in which they are found in a given incident. Thus, in order for a
given substance to be open to bioremediation, clearly it must be both susceptible
to, and readily available for, biological decomposition. Generally it must also
be dissolved, or at the very least, in contact with soil water and typically of a
low - medium toxicity range. The principal environmental factors of significance
are temperature, pH and soil type. As was stated previously, bioremediation tends
to rely on the natural abilities of indigenous soil organisms and so treatment can
occur between 0 and 50 ◦ C, since these temperatures will be tolerated. How-
ever, for greatest efficiency, the ideal range is around 20 - 30 ◦ C, as this tends
to optimise enzyme activity. In much the same way, a pH of 6.5 - 7.5 would be
seen as optimum, though ranges of 5.0 - 9.0 may be acceptable, dependent on the
individual species involved. Generally speaking, sands and gravels are the most
suitable soil types for bioremediation, with heavy clays and those with a high
organic content, like peaty soils, are less well indicated. However, this is not an
absolute restriction, particularly since developments in bioremediation techniques
have removed the one-time industry maxim that clay soils were impossible to
treat biologically.
It should be apparent that these are by no means the only aspects which
influence the use of remediation biotechnologies. Dependent on the circum-
stances, nutrient availability, oxygenation and the presence of other inhibitory
contaminants can all play an important role in determining the suitability of
bioremediation, but these are more specific to the individual application. A num-
ber of general questions are relevant for judging the suitability of biological
treatment. The areas of relevance are the likes of the site character, whether it is
contained or if the groundwater runs off, what contaminants are present, where
they are, in what concentrations and whether they are biodegradable. Other typ-
ical considerations would be the required remediation targets and how long is
available to achieve them, how much soil requires treatment, what alternative
treatment methods are available and at what cost.
Clearly then, there are benefits to the biological approach in terms of
sustainability, contaminant removal or destruction and the fact that it is possible
to treat large areas with low impact or disturbance. However, it is not without
its limitations. For one thing, compared with other technologies, bioremediation
is often relatively slower, especially in situ , and as has been discussed, it is
not equally suitable for all soils. Indeed, soil properties may often be the
largest single influence, in practical terms, on the overall functional character of
pollution, since they are major factors in modifying the empirical contamination
effect. The whole issue may be viewed as hierarchical. The primary influence