Efficient treatment of nanofiltration concentrate from electroplating wastewater by combined bipolar membrane electrodialysis with UV/H2O2 process

Abstract

The treatment of nanofiltration (NF) concentrate from electroplating wastewater poses challenges for conventional methods due to its high salinity, heavy metal contents, and refractory contaminants. The objective of this study was to investigate the feasibility of treating NF concentrate using bipolar membrane electrodialysis (BMED) combined with the UV/H2O2 process. The results demonstrated that BMED achieved efficient desalination of NF concentrate, while simultaneously generating mixed acid and alkali with concentrations as high as 0.21 ± 0.01 and 0.17 ± 0.01 M at a current density of 150 A/m2. Additionally, the recycled alkali can be directly utilized in both the pretreatment and UV/H2O2 process, resulting in a 39 % reduction in alkali consumption. Within 170 min, the BMED exhibited favorable outcomes with removal rates of nickel (91 ± 1 %), zinc (89 ± 1 %), and calcium (88 ± 1 %), respectively. The energy consumption calculated by acid-production was 5.2 ± 0.1 kWh/kg in BMED. Compared to that without desalination treatment, the combined treatment of BMED and UV/H2O2 process resulted in a total COD removal efficiency of up to 90 ± 8 % for the NF filtrate, which was 1.9 times higher than that achieved by single UV/H2O2 process. The most probable degradation pathway and mechanism are proposed that the refractory organic contaminants were transformed into small molecular weight and efficiently mineralized by the •OH. Therefore, this work provides a promising method for efficiently treating the NF concentrate from electroplating wastewater with low energy consumption and resource recovery.