RO/MFEDI For High Purity Water Production

Membrane-tree electrodeionization(MFEDI) is a novel deionization technique, in which the exhausted resins can be regenerated using a strong electrical field with neither chemicals nor membranes necessitated. MFEDI will have wide applications due to its high deionization efficiency, quick regeneration, simple structure and easy operation. In this thesis, a RO/MFEDI system for high purity water production was established. The research mainly focused on the performance of MFEDI for desalinating RO permeate.Major works included resin selection, system running performance and operational variables effects. For MFEDI device, weak-acid (D113) resins, strong-acid(650C) resins and strong-base(550A) resins were selected; double-layer resins (the lower layer filled with mixed D113and550A resins; the upper filled with mixed650C and550A resins) were chosen due to its satisfactory adsorption ability, regenerability and conductivity. The performance of RO/MFEDI system was examined in20operational cycles: the conductivity of product water maintained0.055-0.056μs/cm; the resin after regeneration almost recovered its exchange capacity, which layed the foundation of continuous MFEDI; the regeneration concentrate has a pH value around7, thus can be returned directly to RO for water recovery. The optimal operational conditions of MFEDI were:feedwater conductivity7μs/cm, current75A/m2, regeneration flowrate40m/h, service flowrate30m/h and regeneration duration20min. In this condition, the average conductivity of concentrate was48.9μs/cm, the water recovery rate was above85%, and the energy consumption was0.28kWh/m3.