Efficiency of removal by the NF membrane. The concentrations
of SO4
2− and S−2 in produced water were reduced after filtration with
the NF membrane to successfully meet the admissible limit (250 mg/L)
set by WHO and USEPA, wherein the SO4
2− concentration was reduced
from285 to 66 mg/L by the NF membrane. The pre-filtration concentration
of S−2 (0.17 mg/L) in produced water was higher than the allowable
limit (0.05 mg/L) of the WHO standard, and was reduced by
filtration to 0.04 mg/L by the NF membrane. It was observed that
although the pre-filtration concentration of Cl− was lower than the
permissible limits of drinking water standards, the efficiency of the NF
membrane in rejecting Cl− was only 3.03%, which implies that using
such a membrane for highly saline water may not yield a high performance.
Similarly, the percentage of F− rejection was 33.3%. In contrast,
the 76.84% rejection of SO4
2− by the NFmembranewas higher than that
of Cl−