Novel bioelectrochemically assisted in situ pH modulation method for urea stabilization and phosphorus recovery from synthetic urine

Nagy, Kristóf Bence and Meiczinger, Mónika and Bocska, Boglárka and Nemestóthy, Nándor and Koók, László (2025) Novel bioelectrochemically assisted in situ pH modulation method for urea stabilization and phosphorus recovery from synthetic urine. CHEMICAL ENGINEERING JOURNAL, 519. No.-165154. ISSN 1385-8947

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Abstract

Urine is considered as excellent source of N and P. For efficient recovery of these compounds from urine, separate collection and transportation must be managed. However, urease enzyme, highly abundant in nature (and urine-treating systems), rapidly catalyses urea hydrolysis (main N-compound) to ammonia and carbonic acid, causing significant N-loss and odour issues. Thus, the stabilization of urea in urine is crucial for enabling its utilization as resource. In this study, a novel bioelectrochemically assisted pH modulation method in microbial electrolysis cells (MECs) is presented for efficient urea stabilization. Using synthetic urine catholyte in MEC, the cathodic OH− production allowed urease inhibition at a threshold of pH ≥ 11. Experiments in internal cathode chamber MEC revealed reverse linear relationship between cathode surface area to catholyte volume ratio and required operation time to ensure pH = 11. Additional pH modulation experiments with optimized 3D-printed MEC showed that low current density (j = 1.43 A m−2) leads to protracted pH increase (>1000 min), while efficient current generation (j = 4.6 and 5.4 A m−2) led to rapid stabilization in 62 and 55 min, respectively. pH-treated samples remained stable over ~1 month and proved to be effective for urease inhibition in enzyme treatment test. Effective P-recovery achieved 66.7–96.5% of the theoretical maximum (limited by bivalent cations). Aspects of mass transport and pH splitting-related losses were discussed in context of process efficiency. The results highlight the applicability of bioelectrochemically-driven pH modulation as novel strategy for urea stabilization and nutrient recovery from urine.

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