Chemical Engineering Journal Advances (Nov 2020)
Electrochemical ammonia stripping from non-nitrified animal rendering wastewater
Abstract
Electrochemical ammonia stripping (EAS) is a promising technology to remove and recover ammonium (NH4+) from wastewater with high NH4+ concentrations. In this study, we provide the proof of concept for the use of EAS for non-nitrified animal rendering wastewater. To avoid anodic chlorine (Cl2) production, a common side reaction in EAS, we evaluated the effect of electrochemical cell configuration and feeding mode. Cathode-fed operation resulted in higher NH4+ removal (83.5–99.6% removal within 1 h at a current density of 30 A/m2) compared to anode-fed operation (72 ± 2% removal within 1 h at the same current density). NH4+ removal in cathode-fed electrochemical cells that included a cation exchange membrane to separate the anode and cathode chambers had a strong dependence on the anolyte salt concentration. Although NH4+ removal in cathode-fed electrochemical cells that included an anion exchange membrane to separate the anode and the cathode did not show dependence on the anolyte salt concentration, significant anodic Cl2 production was observed (36.0 ± 13.1 mg/L of total Cl2 after 4 h at a current density of 30 A/m2). Anodic Cl2 production was the highest in anode-fed electrochemical cells (53.0 ± 0.25 mg/L of total Cl2 after 4 h at the same current density). In a cathode-fed configuration that included a trap for Cl−, no Cl2 was formed at the anode. This configuration however needed the highest applied voltage. Despite this, treating non-nitrified rendering wastewater in cathode-fed electrochemical cells with a Cl− trap provides several advantages, and presents an opportunity for scale-up of the process.
