Q-209. Characterization of the Heterotrophic Bacteria in an Industrial Organic Biofilter with Removal of High Load Ammonia Gas

J-F. Vermette1, J. Laperrière2, M. Sirois1;
1Univ. Quebec, Trois-Rivieres, QC, CANADA, 2Norsk Hydro Canada Inc., Becancour, QC, CANADA.

Industrial wastes that contain ammonia are treated by biofilters since many years, mostly by autotrophic nitrifying bacteria. In this work, we studied the biofilter of Norsk Hydro Canada Inc., a magnesium plant located in Becancour QC, Canada. It consists in a fixed peat bed seeded with nitrifying sludge that removes high load of ammonia gas efficiently (up to 20 g N-NH3/m3 filter’s media/h). Since the conditions in the media are unfavourable for nitrifying bacteria, we studied the heterotrophic bacteria that are established in the biofilter to determine if it could play a significant role for ammonia removal. We conducted four sampling campaigns of the biofilter. We inoculated a suspension of the samples on Tryptic Soy Agar plates to count and isolate colonies of easily cultivable heterotrophic bacteria from the biofilter. Those strains were transferred to successive TSA plates to finally obtain pure cultures. We investigated the capacity of these strains to transform nitrogen, using three different liquid organic media, containing NO2-, NO3- and NH4+. We also performed PCR amplifications followed by sequencing of the 16S rRNA gene in attempt to identify the strains minimally to the genus level. The results showed bacterial concentrations of approximately 107 cfu/g filter’s media of heterotrophic bacteria on TSA plates, which was surprisingly high for that type of biofilter (very poor in carbon source). Thirteen strains were isolated in pure cultures: among them, nine strains have shown to metabolize efficiently NO2- or NO3-, which are the sub-products of nitrification. Preliminary molecular identification allowed us to determine that the strains were mostly related to Bacillus species. This study shows that heterotrophic bacteria might play an important role for ammonia removal in biofilters with organic media. A complex network between the different bacteria of a consortium where different forms of nitrogen are produced and consumed should be considered, instead of the “classical” autotrophic nitrification as only responsible for ammonia removal.