Phytotechnology and Photosynthesis 171Continued from page 170
Seven beds, amounting to a total of five hectares (12.5acres) were constructed
in 1990, with the design specification of ultimately being able to treat 3000m^3 of
effluent daily.
The system has some noteworthy and unusual features. Reed beds are often
constructed by excavation, but at the Billingham site, one-metre high clay bunds
were created surrounding each of the seven individual beds. The resulting cells were
lined with an impermeable polymer membrane, equipped with drainage pipes and
filled in with soil before planting. The drainage arrangements are also an important
part of the overall process. Unlike many macrophyte beds, where the main prevailing
hydraulic conduction lies effectively in a horizontal direction, at Billingham much
of the treatment takes place during the vertical flow, down through the soil, which
is further enhanced by the provision of outlet pipes at intervals across the bed,
rather than simply at one end. As a result of this somewhat atypical design, it has
been possible to achieve the required level of effluent polishing with a significantly
smaller land requirement than would otherwise have been necessary, which has
important practical and economic implications.
Historically, the environmental record of the chemical industry globally has
not always been a glorious one. However, the successes of commercial projects
like this one, clearly show that the application of biotechnology in general, and
phytotechnology in particular, can bring very real benefits, without compromising
either the local ecology or economy.