| Summary: | Includes bibliography. === Filamentous bulking, which causes deterioration in sludge settleability has been shown, in two nation-wide surveys to be a problem of considerable proportions. Poor sludge settleability in the secondary clarifier limits the daily flow and load that can be treated in activated sludge wastewater treatment plants. Controlling sludge settleability to relatively low levels i.e. Diluted Sludge Volume Index (DSVI < 100 rnl/g) by controlling filamentous organism proliferation would allow increased daily flow and loads by up to 100 on existing activated sludge wastewater treatment plants. From the two surveys, Blackbeard et al. (1986,1988) found that mainly six filamentous organisms tended to dominate in activated sludges in N and N&P removal plants i.e. types 0092, 0041, 0675, 1851, 0914 and Microthrix parvicella. Four of these six filaments are classified by Jenkins et al (1984) as low Food/Micro-organism (low F/M) filaments. At the University of Cape Town and in a 4 year research programme (1986 to 1989) Gabb et al (1989a) investigated specific methods to control low F /M filament proliferation. Traditionally the promoted specific bulking control method was inclusion of either an anoxic or aerobic selector at the head of the wastewater treatment plant. Gabb et al (1989a) found that selectors did not control low F/M filament proliferation but that continuous aeration did. They concluded that the presence of anoxic and aerobic zones in a treatment plant was an important factor in low F/M filament proliferation. In 1989 a second research programme was initiated at the University of Cape Town to identify the factors that influence low F/M filament proliferation. Completed research thus far has established inter alia that fully anoxic and fully aerobic conditions successfully control low F/M filament proliferation but that alternating anoxic-aerobic conditions in single reactor intermittent aeration systems promoted proliferation. The research presented in this thesis focuses on the interchange between anoxic and aerobic conditions in nitrogen removal systems and its effect on low F/M filament proliferation.
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