**6. Conclusion**

In order to clearly depict the impact of every factor on optimum conditions and to determine the optimal parameters for simultaneous removal of nitrate and nitrite by Donnan dialysis with a small number of experiments, RSM according to the Doehlert matrix was used. The RSM is highly efficient and makes it easier to achieve the optimum conditions while accounting for interactions between experimental parameters. These conditions were 82 mg/L for the concentration of nitrite, 406 mg/L for the concentration of nitrate, and 0.412 mol/L for the concentration of chloride, which were the best for the simultaneous removal of nitrates (95.5%) and nitrites (100%) through the AFN membrane. The removal effectiveness of the simultaneous removal of nitrite and nitrate by DD as well as the optimization of process factors for maximal removal were successfully determined by the RSM approach. Finally, the application of the DD for treating real water (from the region of Menzel bouzelfa) to remove nitrate and nitrite allowed us to confirm that AFN is the best membrane and that the elimination rates remain very high and close to those found in the theoretical study.
