Biological nitrogen and phosphorus removal by filamentous bacteria in pure culture

The availability of excess nutrients (phosphorus (P) and nitrogen (N)) in wastewater systems causes many water quality problems. These problems include eutrophication whereby algae grow excessively and lead to depletion of oxygen, death of the aquatic life and bad odours. Biological phosphorus removal has gained attention because the condition of wastewater is manipulated in order to facilitate nutrient removal by the microbial communities in the wastewater. It has been reported that filamentous bacteria are capable of removing P at a similar or higher rate to that of heterotrophic bacteria. It has also been reported that conditions that facilitate biological nitrogen removal promote bulking in a biological nutrient removal system. The aim of the project was therefore to evaluate the role of filamentous bacteria in biological nutrient removal (BNR) processes. For denitrification this was achieved by performing the nitrate reduction preliminary screening test followed by batch tests. Neisser staining was used to locate polyphosphate granules in cells. All Neisser positive isolates were evaluated for P accumulation employing batch tests. The findings of this study demonstrated that 29% of the isolates were true denitrifiers, 3% were sequential denitrifiers, 11% were nitrate respirers, 13% were non-denitrifiers and 45% were nitrate respirers at high concentrations (1 g/. and 0.5 g/.) and true denitrifiers at low concentrations (0.2 g/.). The results of the nitrate reduction batch test demonstrated that up to 18.46 mg/. nitrate was reduced to nitrogen gas. 53% of the isolates reduced nitrite, 33% resulted in nitrite accumulation and 9% did not react to nitrite. Of the 38 isolates 16% were positive for the Neisser stain, 34% were positive for the glycogen stain and 79% were positive for the PHB stain. Batch test results showed phosphate accumulation of up to 17.12 mgP/.. It was demonstrated by this study therefore, that filamentous bacteria have the potential to biologically remove nutrients. These research findings will serve as a basis for further investigations

Isolation and cultivation of filamentous bacteria implicated in activated sludge bulking

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: 405-41