Factors affecting the occurrence of filamentous bacteria in activated sludge plants

Abstract

Filamentous bacteria should be considered as normal components of the microbial community of activated sludge plants, although where they come from and how they enter plants is still not known in most cases (Wanner, 1993, 1994a,b). They probably play an important role in the formation of flocs with good settling properties (Jenkins et al., 1993b). However, problems arise when the normal community balance of these systems is upset and the filamentous bacteria proliferate, causing bulking and foaming. Surveys carried out around the world suggest that most, if not all, activated sludge plants will suffer from these operational disorders sooner or later, but certainly from the authors’ experiences in Australia, very few staff bother regularly to examine their plants microscopically, or seem to understand the significance of the presence of filamentous bacteria in them. In addition, insufficient numbers of technical staff are experienced in filament identification, and only recently has the industry shown any interest in acquiring this expertise. Microscopic analysis of activated sludge with practice, is simple cheap and rapid. It can be of enormous benefit in providing information on floc structure and filament composition, as well as in detecting sudden or gradual changes which may pre-warn of changes in plant performance (Seviour et al., 1990b; Jenkins et al., 1993a,b; Wanner, 1994a,b). Microscopy also presents visually the organisms which constitute the activated sludge microflora, bringing operations and management staff closer to the process (see Chapter 10).