WASTE TREATMENT: THE FILAMENTOUS BACTERIA CAUSING BULKING AND FOAMING IN ACTIVATED SLUDGE PLANTS

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...