Contaminated Land and Bio-Remediation - Environmental Biotechnology: Theory and Application - page 99

Cometabolism , in which the contaminant is again taken up by microbes but
this time is not used as food, being metabolised alongside the organism's food
into a less hazardous chemical. Subsequently, this may in turn be mineralised
by other microbial species.
Immobilisation , which refers to the removal of contaminants, typically met-
als, by means of adsorption or bio-accumulation by various micro-organism or
plant species.
Unsurprisingly, given the expressly biological systems involved, bioremedi-
ation is most suited to organic chemicals, but it can also be effective in the
treatment of certain inorganic substances and some unexpected ones at that. Met-
als and radionuclides are good examples of this. Though, obviously, not directly
biodegradable themselves, under certain circumstances their speciation can be
changed which may ultimately lead to their becoming either more mobile and
accessible or less so. The net result produced in either case can, under the right
conditions, be a very effective functional remediation. A list of typical contam-
inants suitable for bioremediation would include the likes of crude oil and its
derivatives, some varieties of fungicides and herbicides, hydrocarbons, glycols,
phenols, surfactants and even explosives.
Developments in bio-processing continually redefine the definitive catalogue of
what may, and may not, be treated and many chemicals once thought 'impossible'
are now routinely dealt with biologically. Table 5.1 reflects the current state of
the art, though this is clearly subject to change as new approaches are refined.
As a result, it should be obvious that a large number of opportunities exist
for which the application of remediating biotechnologies could have potential
relevance. Even so, there are a number of factors which affect their use,
which will

be considered before moving on to discuss practical treatment

issues themselves.

Table5.1 Potentialforbioremediationofselectedcontaminants
Readily possible

Possible under certain Currently impossible

circumstances

Acids Chlorinated solvents Asbestos

Alcohols Cyanides Asphalt

Aldehydes and ketones Explosives Bitumen

Ammonia PCBs Inorganic acids

Creosote PAHs

Chlorophenols Pesticides, herbicides

Crude oil and petroleum and fungicides

hydrocarbons Tars

Glycols Timber treatments

Phenols
Surfactants