Isolation and cultivation of filamentous bacteria implicated in activated sludge bulking

Abstract

Filamentous bacteria have long been associated with activated sludge bulking and foaming and are known to be the main cause of this problem. Chemical control methods such as chlorination and the use of hydrogen peroxide have been, and still are, used to cure bulking and foaming but are only effective as interim measures. More detailed understanding of the physiology and biochemistry of filamentous bacteria is still required for effective long-term control of bulking and foaming. Isolation and cultivation of filamentous bacteria in pure culture have shown promise as methods to gaining better understanding of bulking and foaming. The aim of this project was, therefore, to assess different techniques for effective isolation and cultivation of filamentous bacteria in pure culture. Activated sludge samples from Durban and surrounding areas were screened microscopically to identify constituent filamentous bacterial populations. Samples with varieties of different filamentous bacteria were subjected to various floc break-up procedures (nonidet surfactant treatment, sonication and cellulase hydrolysis) in conjunction with physical separation (centrifugation) to separate filamentous bacteria from floc-forming bacteria. Both treated and untreated samples were serially diluted and plated onto a variety of different solid media, whereafter discrete bacterial colonies were isolated and screened microscopically for filamentous morphology. Cellulase hydrolysis proved unsuccessful for filament isolation while direct inoculation, nonidet pretreatment and sonication resulted in the isolation of five different filaments, one via sonication and two each via the other methods. The filaments were provisionally identified as Sphaerotilus natans, Microthrix parvicella, Type 1863, Type 0092 and Haliscomenobacter hydrossis.



WaterSA Vol.29(4) 2003: 405-410