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.