Extracting nitrogen from source-separated urine can eliminate the need for centralized nitrogen removal at wastewater treatment plants and allow for fertilizer production. In this study, we evaluated electrochemical stripping, a novel approach for nitrogen recovery that improves upon conventional ammonia stripping in two ways: (1) pH increase without base addition and (2) internal NH3 stripping without a tower. A cation exchange membrane and gas permeable membrane were used to selectively recover nitrogen based on charge (NH4+) and volatilization (NH3). We investigated ammonia recovery in a three-chamber design comprised of anodic NH4+ migration, cathodic conversion to NH3, and reconversion to NH4+ in a sulfuric acid trap, producing liquid ammonium sulfate concentrate. To identify urine characteristics that influenced nitrogen recovery, efficiencies were determined for ammonium sulfate (99%), synthetic urine (80%), and real urine (94%). Mechanisms contributing to low recovery in synthetic urine were explored, including electrochemical chloride oxidation and chloramination. Cyclic voltammetry was used to confirm the production of HOCl from Cl-. Transmembrane fluxes were calculated to determine the rate-limiting step of the process. Based on full-cell potentials, we calculated energy requirements per kg of nitrogen recovered and compared electrochemical stripping to nitrogen removal technologies like nitrification-denitrification, anammox, and conventional ammonia stripping. Results from this study demonstrate proof-of-concept for a novel nitrogen recovery technology and better characterize the emergent source separation and resource recovery paradigm for urban wastewater management.

Electrochemical stripping to recover nitrogen from source-separated urine

253rd National Meeting (2017)

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