Microorganisms commonly used to treat urban wastewater are poorly suited to the treatment of liquid
wastes containing organic compounds and a high concentration of salts.
In response to high salt concentrations gradients bacterial cells will tend to empty their water by
osmosis, and consequently to dry up. This phenomenon is called plasmolysis, causes a decrease in
cellular activity. The presence of salt has an impact on the efficacy of biological treatment.
The salt concentration limit not to exceed in order to have a good biological degradation varies from
one author to another subsequent work (Markez et al. ,1987) , have shown that media containing
less than 1% salt, equivalent to 12 g .l-1 NaCl, are conducive to healthy development of non-halophilic
bacteria. More recent studies (Woolard et al., 1995), made with traditional cultures of bacteria, used in
domestic water treatment (activated sludge), show the difficulty of treatment of effluents containing 0.1 to
5% salt (1.2 to 60 g .l-1 NaCl). Kargi and Dincer (1997) observed that the effluent COD removal
efficiency fell from 85% to 59% when salinity increased from 0 to 5%.
As respirogrammes obtained and the quantity of oxygen consumed before and after addition of
salt it was confirmed that for low salt concentrations up to 5 g / l, the microorganisms was able to adapt
by regulating the gradient osmotic pressure and therefore it was supported that environment for the
degradation of the carbon and nitrogen substrate, no reduction in microbial activity (Table .3) was
detected. On the other side a slight increase in microbial activity is detected due to microbial growth
obtained in the first phase of the experiment (without salt addition) because in this study the substrate is
much more abundant in solution than biomass (high ratio S/X).