Optimization of Culture Conditions for Enhanced Heterotrophic Nitrification by Achromobacter Xylosoxidans Strain SHB CLP Isolated from Eutrophicated Lake Sediment

Heterotrophic nitrifying bacteria (HNB) also convert ammonium to oxidized nitrogen, but they use organic carbon as an energy source, and allow N turnover in nutrient-rich freshwater systems in which classic autotrophic nitrifiers are inhibited. A previous isolated gram-negative heterotrophic nitrifier strain Achromobacter xylosoxidans strain SHB Clp was studied to understand the optimum physico-chemical and nutritional conditions for the nitrifying activity of the organism under all possible combinations of these factors. One factor at a time experiments were used to screen the factors: temperature, pH, carbon source, carbon to nitrogen ratio, initial ammonium-nitrogen concentration, agitation and inoculum size and salinity. The optimal condition for the maximum removal of ammonium was 30 °C, pH 7.5, sodium acetate as the carbon source and C/N = 10. With these optimized conditions, the rate of ammonium-nitrogen removal increased from about 49 % to more than 92 %, the specific growth rate was about doubled and generation of nitrite was significantly reduced. These results suggest that by making few modifications in the culture conditions the nitrogen removal ability of one indigenous nitrifier can be greatly improved, and they justify the use of natural heterotrophic nitrifying bacteria in the biological restoration of eutrophic lakes.