Survey of filamentous bacteria in activated sludge plants in KwaZulu-Natal

The objective of this investigation was to conduct a survey of filamentous bacteria present in activated sludge plants in Durban and surrounding areas (KwaZulu-Natal, South Africa). A diverse population of filamentous bacteri a was identified. Dominant filamentous bacteria identified from mixed liquo ur samples in descending order fo frequency included: (1) Nocardia spp., (2 ) Type 0041, (3) Type 0675, (4) Type 1851, (5) Type 021N, (6) Nosticola lim icola II, (7) Sphaerotilus natans, (8) Thiothrix I and II and (9) Beggiatoa . Nocardia spp. were the only dominant filamentous bacteria present in foam samples, while Type 0914, Microthrix parvicella and Sphaerotilus natans oc curred incidentally. All filamentous bacteria identified were present throu ghout the year. Nocardia spp. and Microthrix parvicella were found to be do minant during winter months. It can be concluded that filamentous populatio ns are significantly affected by seasonal and influent variations.