Nutrient recovery from urine: Urea adsorption onto biochar integrated with Na-chabazite as urease inhibitor

This study presents an innovative technical integration for concomitant nutrient recovery from source-separated urine. While cation exchange is known for efficient K + recovery, it faces competition due to the high molarity of NH 4 + in hydrolyzed urine. This study proposes inhibiting urease activity to facilitate the recovery of K⁺ and urea from fresh urine. Na-chabazite was first proposed as a urease inhibitor in this study, reducing urease activity by 50 %. Wood biochar, with its high porosity (308.0 m²/g) and polar functional groups, shows a urea adsorption capacity of 25.4 mg/g, which can be further improved by steam activation. The isotherm analysis suggests that urea adsorption onto biochar follows a multi-layer adsorption process. Finally, an integrated process is suggested: "Na-chabazite and Biochar adsorption → urea hydrolysis → struvite precipitation + ammonia stripping-acid scrubbing", ensuring efficient recovery of urea, NH 4 + , PO 4 3- , and K + from source-separated urine.