Organophosphonate draw solution for produced water treatment with effectively mitigated membrane fouling via forward osmosis

Abstract In this study, an organophosphonate scale inhibitor, ethylenediamine tetra(methylenephosphonic acid) sodium salt (EDTMPA-Na) draw solution, was adopted for alleviating the membrane fouling in the forward osmosis (FO) application of produced water treatment. Compared with the typical NaCl draw solution, the employment of EDTMPA-Na draw solution can alleviate the membrane fouling effectively and therefore achieve a higher water recovery rate (60.6%) after a continuous 48-h test. And the mechanism of membrane fouling control with EDTMPA-Na draw solution has been systemically explored by varying the feed or draw solution compositions. The results turn out that the leakage of EDTMPA-Na draw solute to the feed solution can alleviate the formation of gypsum scales on the membrane surface effectively, ascribed to its excellent scale inhibition ability and the unique diffusion route of the draw solute (resulting in a relative higher concentration of EDTMPA-Na near the membrane surface) in FO process. And the alleviation of membrane scaling can further mitigate the accumulation of organic foulant on the FO membrane. This study may provide an efficient strategy for alleviating the membrane fouling in the FO application of produced water treatment.