Polyamidoamine and carboxylated cellulose nanocrystal grafted antifouling forward osmosis membranes for efficient leachate treatment via integrated forward osmosis and membrane distillation process

Abstract

Organic fouling remains an intractable challenge for forward osmosis (FO) and integrated FO-membrane distillation (MD) strategy to treat landfill leachate. To address this challenge, polyamidoamine (PAMAM)/polydopamine (PDA) and carboxylated cellulose nanocrystal (CCN) were grafted gradually on the commercial thin film composite (TFC) FO membranes via chemical coupling to achieve excellent antifouling capacity. PAMAM dendrimers, with abundant terminal amines, hyperbranched structure and open interior cavity, served as a unique intermediate platform for chemically covalent attachment of CCN with high water affinity, then cooperated with CCN to form a hydrophilic and robust antifouling layer. Compared to the raw TFC membrane, the PAMAM/PDA-CCN modified TFC membrane exhibited a similar water flux of 30.6 L m−2 h−1 (LMH) accompanied with a decreased reverse salt flux of 6.9 g m−2 h−1 (gMH) by using 1 M NaCl solution as draw solution (DS) and DI water as feed solution (FS). When actual leachate was used as FS, the modified FO membranes possessed significantly enhanced antifouling capacity with a lower flux decline (≤43.7%) and a higher flux recovery rate (≥94.2%) than the raw TFC membrane (flux decline ≤59.4% and flux recovery rate ≥79.0%, respectively). The improved fouling resistance could be further demonstrated by the reduced thickness of the organic fouling layer. Eventually, the employment of the modified FO membranes improved the compatibility of the FO and MD water fluxes and achieved sustained water production. The construction of synergistic dendritic PAMAM and CCN grafted surface paves a new way for the development of high-performance water treatment membranes.