Novel nanocomposites sorbents of superparamagnetic iron oxide nanoparticles (SPION) supported onto electrospun polyacrylonitrile nanofibers were synthesized with a simple and scalable method. The influence of both nanofiber size and SPION loading on As(V) adsorption capacity were studied and optimized. A maximum uptake capacity in batch mode tests of 32.5 mmol As(V)/g SPION while using an extremely low loading of only 2.9 mg of SPION/g of adsorbent was achieved. This represents a remarkable improvement of 36 times compared with SPION in suspension. The optimal material was tested in a continuous flow mode operation reaching to adsorption capacities of 851.7 mg As(V)/g of adsorbent at pH 3.8. It is also demonstrated that the new adsorbents can retain high performance when tested in real conditions with polluted wastewater from a lixiviation dump containing a large amount of competing anions (Cl -, F -) and interfering cations (K + , Na + , Mg 2+ , Ca 2+ ). Furthermore, no release of nanoparticles was observed during operation and the spent porous material can be compressed generating a small amount of solid waste that can be easily treated or stored.