A novel electrochemical membrane filtration system operated with periodical polarity reversal for efficient resource recovery from nickel nitrate laden industrial wastewater.

The economical and efficient removal of nickel nitrate from industrial wastewater remains a challenge. Herein, we developed an innovative electrochemical membrane filtration system that used a periodic polarity reversal process to adjust the acid-base environment near membrane interface for the recovery of nickel (II) and ammonia. The Ru based electrocatalytic layer could boost the selective reduction of nitrate to ammonia by generating atomic hydrogen, resulting in the precipitation of Ni by the increasing pH at the membrane interface. Then, the precipitation of Ni(OH) could be effectively stripped and collected under the periodic polarity reversal process. In-situ interfacial measurements demonstrated that the polarity reversal process enabled a reversible transformation between strongly acidic (pH < 2) and alkaline (pH > 13) environments within a 200 µm range at the membrane interface. In continuous flow operation treating real industrial wastewater containing 96.7 mg-N L nitrate and 135.0 mg L Ni, the system demonstrated the capability to achieve 92.5 ± 2.6 % nitrate removal (with a recovery efficiency of 15.1 ± 1.9 g-NH kWh) and 99.7 ± 0.1 % Ni²⁺ removal (with a recovery efficiency of 24.9 ± 2.4 g-Ni kWh). Additionally, the specific treatment cost was approximately $0.17 m, attributed to the recovery of Ni(OH)₂ and ammonia. Furthermore, this system could deliver a significant economic benefit ($1.64 per m) for treating a high concentration real wastewater (331.5 mg-N L nitrate and 1496.3 mg L Ni), outperforming traditional alkali precipitation and biological nitrification/denitrification processes. Overall, our study presents an economical and sustainable method for recovering valuable chemicals from wastewater containing heavy metals and inorganic nitrogen, potentially advancing cost-effective water treatment technologies.