Impact of reverse nutrient diffusion on membrane biofouling in fertilizer-drawn forward osmosis

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Journal Article
Journal of Membrane Science, 2017, 539 pp. 108 - 115
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Impact of reverse diff on biofouling of FDFO JMS_R2_clean.docxAccepted Manuscript Version3.52 MB
© 2017 Elsevier B.V. Biofouling in fertilizer-drawn forward osmosis (FDFO) for water reuse was investigated by spiking pure bacteria species Pseudomonas aeruginosa PAO1+GFP and using three different fertilizers KNO 3 , KCl and KH 2 PO 4 as draw solutions. The performance of FO process for treating synthetic wastewater was assessed and their influence on the membrane fouling and in particular biofouling was evaluated relative to the type of different fertilizers used and their rates of reverse diffusion. FO performances using KNO 3 as draw solute exhibited severer flux decline (63%) than when using KCl (45%) and KH 2 PO 4 (30%). Membrane autopsy indicated that the mass of organic foulants and biomass on fouled membrane surface using KNO 3 as draw solute (947.5 mg/m 2 biopolymers, 72 µm biofilm thickness and 53.3 mg/m 2 adenosine triphosphate) were significantly higher than that using KCl (450 mg/m 2 biopolymers, 33 µm biofilm thickness and 28.2 mg/m 2 ATP) and KH 2 PO 4 (440 mg/m 2 biopolymers, 35 µm biofilm thickness and 33.5 mg/m 2 ATP). This higher flux decline is likely related to the higher reverse diffusion of KNO 3 (19.8 g/m 2 /h) than KCl (5.1 g/m 2 /h) and KH 2 PO 4 (3.7 g/m 2 /h). The reverse diffused potassium could promote the organics and bacterial adhesion on FO membrane via charge screening effect and compression of electrical double layer. Moreover, reverse diffused nitrate provided increased N:P nutrient ratio was favorable for the bacteria to grow on the feed side of the FO membrane.
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