A key to sustainable management of saline organic-rich wastewaters is to precisely fractionate organic components and inorganic salts (NaCl) as individual resources. Conventional nanofiltration and electrodialysis processes suffer from membrane fouling and compromise the fractionation efficacy. Here we develop a thin-film composite nanoporous membrane via co-deposition of dopamine and polyethyleneimine as a highly anion-conducting membrane. Experimental results and molecular dynamics simulations show that co-deposition of dopamine and polyethyleneimine effectively tailors the membrane surface properties, intensifying the charge shielding effect and enabling fast anion transfer for highly efficient electrodialysis. The resulting nanoporous membrane exhibits unprecedented electrodialytic fractionation of organics and NaCl with negligible membrane fouling, dramatically outperforming state-of-the-art anion exchange membranes. Our study sheds light on facile design of high-performance anion-conducting membranes and associated new mass transport mechanisms in electrodialytic separation, paving the way for sustainable management of complex waste streams.