Sustainable recovery of high-saline papermaking wastewater: Optimized separation for salts and organics via membrane-hybrid process

In this work, a novel zero liquid discharge technology combining of electrodialysis (ED), electrochemical catalytic oxidation (ECO), reserve osmosis (RO) and bipolar membrane electrodialysis (BMED) was developed for sustainable recovery of high-saline papermaking wastewater. The effect of membrane type, volume ratio, membrane fouling and voltage were investigated in ED process; subsequently parameter such as electrolyte conductivity was studied in ECO process. The FKB/FAB stack shows good separation performance for the salts and organics, allowing a relatively high COD rejection of 97.80%. Meanwhile, membrane fouling was investigated through a comparison between virgin and fouled membranes. To achieve a high-saline solution with low organics, a second-stage ED process was applied. The concentration factor was increased to 1.799 with a COD rejection of 96.54% at voltage of 12 V. Simultaneously, the ECO process exhibited superior COD removal of 94.99% at the electrolyte conductivity of 4 mS/cm. Through the application of BMED at Vf:Vb:Va (volume ratio of feed, base and acid solution) of 4:1:1, the final acid and base content could approach a high value of 12.30 wt% and 10.60 wt%, respectively. Therefore, this hybrid ED-ECO-RO-BMED combined process demonstrates a strongly technical applicability for sustainable resource recovery from high-saline papermaking wastewater.