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 typ-ically of a low – medium toxicity range. The
principal environmental factors of significance are temperature, pH and soil
type. As was stated previously, biore-mediation tends to rely on the natural
abilities of indigenous soil organisms and so treatment can occur between 0 –
50 ◦C, since these temperatures will be tol-erated. However, 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, depen-dent on the
individual species involved. Generally speaking, sands and gravels are the most
suitable soil types for bioremediation, while 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 bioremedi-ation
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 typi-cal
considerations would be the required remediation targets and how much time 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 sus-tainability, 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 sin-gle 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 consists of the contaminants themselves and
actual origin of the contamination, which clearly have a major bearing on the
overall picture. However, edaphic factors such as the soil type, depth,
porosity, texture, moisture content, water-holding capacity, humus content and
biological activity may all interact with the primary influences, and/or with
each other, to modify the contamination effect, for better or worse. Figure 5.3
is a simplified illustration of this relationship.
Hence, it is not enough
simply to consider these elements in isolation; the functional outcome of the
same contaminant may vary markedly, dependent on such site-specific
differences.
After consideration of the
generalised issues of suitability, the decision remains as to which technique
is the most appropriate. This is a site-specific issue, for all of the reasons
discussed, and must be made on the basis of the edaphic matters mentioned
previously, together with proper risk assessment and site surveys.
At the end of all these studies and assessments, the site has been investigated by desk top and practical means, empirical data has been obtained, the
resident con-tamination has been characterised and quantified, its extent
determined, relevant risk factors identified and risk assessment has been
performed. The next stage is the formulation of a remediation action plan,
making use of the data obtained to design a response to the contamination which
is appropriate, responsible and safe. At this point, having obtained the
clearest possible overview, technology selection forms a major part of this
process.
When this has been done, and
approval has been gained from the relevant statu-tory, regulatory or licensing
bodies, as applicable, the last phase is to implement the remediation work
itself.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.