FILAMENTOUS ORGANISM BULKING IN NUTRIENT REMOVAL ACTIVATED-SLUDGE SYSTEMS .1. A HISTORICAL OVERVIEW OF CAUSES AND CONTROL

The presence of filamentous organisms in the activated sludge system h as been problematic since early this century and has been noted in sys tems operating as aerobic or incorporating anoxic or anaerobic zones. Early attempts to control bulking in overtly aerobic systems were at b est ad hoc measures, often based on anecdotal evidence and usually wer e unsuccessful. Non-specific control methods such as chlorination have been found successful but these do not remove the causes for bulking. Idenfification of problematic filament types and association of these with specific operating conditions and influent characteristics were the first important steps taken toward establishing specific methods o f control. The kinetic selection approach first proposed by Chudoba et . al. (1973a; b) has provided a basis for developing strategies for sp ecific bulking control in aerobic systems notably selector reactor for control of bulking in low food to micro-organism (low F/M) systems. T he development of systems for the removal of nitrogen (N) and phosphor us (P) resulted in an increase in the occurrence of filament types not associated with bulking sludges in aerobic systems, The majority gf t hese filaments have categorised as low F/M and therefore the kinetic s election approach was adopted as the starting point for developing spe cific control procedures for bulking in nutrient removal plants.