Electrocatalytic hydrodechlorination system with antiscaling and anti-chlorine poisoning features for salt-laden wastewater treatment

• Scaling and Cl − poisoning decreases the durability of Pd-mediated EHDC reaction • Inclusion of the antiscalant PBTC can prevent both the Cl − poisoning and scaling • PBTC with phosphonic and carboxyl groups stabilizes the scaling ions in water • PBTC with its functional groups can replace the Cl − on Pd surface • PBTC-Pd binding results in more electron-deficient Pd species for an enhanced EHDC The high salinity and coexistence of scaling ions (Ca 2+ , Mg 2+ , HCO 3 − ) in wastewater challenge the efficacy and durability of palladium (Pd)-mediated electrocatalytic hydrodechlorination (EHDC) reaction for chlorinated organic pollutant detoxification, due to the accompanying Cl − poisoning at Pd sites and scaling on electrode. In a concentrated NaCl solution (5.8 g L −1 ) with Ca 2+ (80.0 mg L −1 ), Mg 2+ (30.0 mg L −1 ) and HCO 3 − (180.0 mg L −1 ), the EHDC efficiency of Pd towards 2,4-dichlorophenol decreases significantly from 67.8% to 33.1% in 72.0 h of reaction, and the electrode is covered with layers of fluffy aragonite precipitate. Herein we demonstrate the inclusion of a commercial antiscalant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) can prevent both scale formation and Cl − poisoning, leading to an efficient and steady EHDC process. A mechanistic study reveals that the unique dual function of PBTC primarily originates from the bearing phosphonate and carboxyl groups. With the large affinity of these groups (especially the phosphonate group) for scaling cations and Pd, the PBTC can chelate and stabilize the scaling cations in water and replace Cl − at Pd surface. It can also release protons, and trigger the formation of more electron-deficient Pd δ+ species via PBTC-Pd binding, leading to an enhanced EHDC. This work provides effective solutions to the scaling/poisoning issues that commonly encountered in real wastewater and paves a solid road for EHDC application in pollution abatement.