Abstract:
The work that we present in this thesis consists of a study of the nitrate degradation reaction
of wastewater by the use of a biological process. Heterotrophic denitrification is one of the
most selective and advanced method for nitrate removal, it is usually inhibited by insufficient
carbon sources. This process requires the use of a final electron acceptor, often it is a hydrocarbon
such as methanol, glucose, fructose .... In our case we tested at 35 ° C in a suitable nutrient medium,
sodium succinate and methanol, in a first step by the use of a mixed culture taken from the
wastewater treatment plant (WWTP) Ibn Ziad, Constantine , Algeria. In a second step by five
bacterial strains that have been isolated but only the N5 and N6 strains that have been identified.
five bacterial strains were isolated but only the strains N5 and N6 were identified. The strains
were preliminarily identified using biochemical, Gram staining and by API 20 E system, tests
and then a method based on the similarity of the PCR-16S rRNA. 16S rRNA gene sequence
analysis indicated that both strains were most closely related to Enterobacter hormaechei with
sequence similarities of 99%. Both strains showed an excellent capability to remove nitrate
and to transform carbon substances namely methanol and sodium-succinate to carbon dioxide.
This process was accompanied by a slight rise in pH with a simultaneous production of
nitrogen gas as the end product at 35°C. Nitrate was removed after 48 h of incubation. Thus,
the anaerobic denitrification ability of strains N5 and N6 has been proved. Sodium-succcinate
is the most favorable carbon source for denitrification by both strains (N5 and N6).
Furthermore, strains N5 and N6 could effectively remove nitrate at low C/N ratios and under
conditions where the temperature is elevated, which would benefit nitrate removal from the
wastewater.
