Although the activated sludge system has operated globally to treat
both domestic and industrial wastes for more than 80 years, it is still
treated very much as a "black box" by the engineers. It is a biological
process, and yet until very recently, little understanding of the
microbiology of this huge biotechnological industry has been
forthcoming. There are good reasons for this, most of which are
methodological. Activated sludge is a highly complex ecosystem and,
until quite recently, the methods available for identifying and
characterising the bacteria there were inadequate, even in the unlikely
event that they could be grown in pure culture. The advent of molecular
methods to study natural communities of microbes including those found
in activated sludge has revolutionised our ideas on their composition.
Even so, many engineers (with some justification it has to be said)
would claim that the microbiologists have promised much but in reality
have contributed little to our understanding of how these plants work,
or how their operational efficiencies might be improved. They could
argue that all the microbiologist has achieved is to add to the
confusion by showing that the microbial communities are far more
diverse than were previously thought likely (Amann et al., 1996, 1998;
Snaidr et al., 1997; Seviour & Blackall, 1999), but without
suggesting how this information might be beneficial to the operators
faced with the more mundane daily tasks of running these plants..
