NITRIFICATION--A POTENTIAL FOR HETEROTROPHIC NITRIFIERS FROM AN ACTIVATED SLUDGE SYSTEM (NITROGEN, SHOCK, LOADING)

Scope of Study. Studies involving the isolation of a heterotrophic nitrifier were undertaken. An enrichment technique was developed for the routine isolation procedures. This technique employed a medium with an organic compound as carbon and energy source and a supplementary substrate. Routine isolations were conducted for a period of 10 months during which time an activated sludge nitrification system was maintained for supplying the nitrifying seeds for isolation. A total of seventy cultures of heterotrophic organisms were isolated with the nitrifying enrichment media. Each isolate was individually tested for ability to form nitrite or nitrate in an acetate broth. Once the heterotrophic nitrifier was isolated, stock cultures of the isolate were maintained in shaken flasks for subsequent studies. Growth rate determinations were made for the culture under both carbon and nitrogen limiting conditions. A range of C:N ratios was selected for study on the substrate removal characteristics in batch systems. The system which promoted nitrification was later used to study the response to a glucose shock load.; Findings and Conclusions. A microorganism capable of utilizing organic carbon as carbon and energy source and capable of nitrifying has been isolated from an activated sludge system. An enrichment medium consisting of minimal salts, sodium acetate and yeast extract was found to enhance heterotrophic nitrification. Kinetic growth constants (mu)(,max) (0.37 hr('-1)) and K(,s) (220 mg/l) obtained under carbon limiting conditions for this microorganism are very typical of heterotrophic bacteria. This microorganism has been confirmed to nitrify heterotrophically by employing N-Serve, a potent inhibitor for the autotrophic nitrifier, Nitrosomonas. The insensitivity of the microorganism to this specific inhibitor and the inability to grow on sodium bicarbonate as sole source of carbon clearly suggests the physiological differences between heterotrophic and autotrophic nitrifiers. Under appropriate conditions of carbon and nitrogen supply especially when nitrogen is in excess of assimilatory needs, heterotrophic nitrification could be the predominant mode of mechanism in a biological nitrification system. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI...