170 Environmental Biotechnology
Case Study 7.1 Naturalising Phytoremediators (Dyfed and Powys, Wales)
Though necessary for swift clean-up operations where time is limited or the envi-
ronmental risk high, not all examples of the removal of industrial contamination
by biological means involve highly engineered interventions. Many of the most
effective means are those which work with nature.
The combined effects of natural attenuation, phytotechnology and selective
pressures in remediation can be seen at a number of sites throughout Mid-Wales.
Earlier mining of the area’s rich mineral deposits, especially silver and lead, inevitably
brought about significant disturbances to the immediate environment. In some
places, quantities of the relatively metal-enriched ‘spoil’ generated remain as heaps,
while elsewhere it has been spread over the original ground surface in an attempt
to reduce the effects of localised accumulation. While the low concentration, in
absolute terms, makes extraction and refining commercially uneconomic, the level
of contamination is sufficient to pose a challenge to plant growth.
Today, these once barren spoil sites have, in the main, been revegetated and only
a small number remain bare, in areas of the highest residual metal concentration, as
the actions of soil microbes and indigenous plants over the intervening years, have
contributed to a gradual reduction in contamination. Laboratory investigations of the
colonising plant species have revealed high innate tolerances of relatively elevated
metal concentrations, representing an example of selective advantage in response to
environmental pressure. Consequently, particular strains of grasses and other vege-
tation have developed which are able to thrive under these conditions, which has
considerably improved the visual appearance of these old sites. In addition, a number
act as natural phytoremediators, which further assists the wider amelioration process.Case Study 7.2 Engineered Phytoremediation (Billingham, England)
One of the best examples of industrial-scale use of reed beds is the one managed
by Air Products (Chemicals) Teeside Ltd on the old ICI site in Billingham, England
wherePhragmitesare used to clean the effluent from the methylmethacrylate plant
prior to discharge into the river Tees. This wastewater principally contains phenol,
methanol, acetone, chlorinated hydrocarbons and amines.
Although modifying the production process to eliminate much of the problem
would have been possible for a new facility, it was too costly to achieve retro-
spectively and so a variety of biological treatments were explored to ameliorate
the effluent. Although the cheapest capital option was an oxygen activated sludge
system, the phytotechnology approach was eventually selected since its running
costs were very low and, additionally, because sludge disposal was not required.
One of the keys to effective plant-based intervention is ensuring that the right plant
is chosen. It was particularly relevant in this case, since several differentPhragmites
reeds are used in this role around the world. Six varieties were tested for effluent
survival under local environmental conditions. On the basis of this work, three were
selected for use in the pilot trials–Alexander reed from Germany and strains from
two sites in the area, namely Billingham Golf Course and Salt Home Farm.Continued on page 171