Comparison of liquid ferrate and ferric chloride coagulants for humic acid removal in a seawater reverse osmosis desalination plant

This study investigates the removal of humic acid from seawater through coagulation-floccula-tion-sedimentation treatment. Liquid ferrate Fe(VI) and ferric chloride Fe(III) coagulants were used to oxidize humic acids. The experimental results demonstrated that Fe(VI) has a superior per-formance compared to Fe(III) in terms of removal of dissolved organic carbon (DOC), turbidity, and natural organic matter (NOM). DOC removal was up to 95% with Fe(VI) and up to 58% with Fe(III). NOM fractions removal was higher with Fe(VI) compared to Fe(III). Biopolymers removal was up to 80% for Fe(VI) and up to 60% for Fe(III). Humic substances removal was up to 97% for Fe(VI) and up to 68% for Fe(III). The removal of low molecular weight (LMW) compounds showed a different pattern in which Fe(VI) achieved up to 98% removal for LMW neutrals and up to 88% removal of LMW acids while Fe(III) increased the concentration of LMW-neutrals and LMW-acids. The results of this research demonstrates that liquid ferrate can perform better than ferric chloride in the coagulation-flocculation-sedimentation process for treating seawater containing humic acids in terms of removing turbidity, total organic carbon and DOC fractions. Therefore, liquid ferrate is a potential coagulant to enhance seawater treatment during high humic substances conditions.