Acid Dosing Increases Recoverable Phosphorus during\nDifferent Occupancy Conditions in Full-Scale Urine Diversion System

Phosphorus (P) is a finite resource\nused in fertilizers. Urine\ncontains high concentrations of P that can be recovered using urine\ndiversion (UD), but current UD systems become clogged by P precipitation\nin piping, inhibiting their operations and reducing recoverable P.\nDosing systems with acetic acid can prevent precipitation, resulting\nin more available nutrients for recovery. This study monitored a full-scale\nmultistory UD system and implemented acid dosing to prevent clogging\nand produce urine suitable for P recovery. Both baseline (i.e., no\nacid) and acid dosing conditions were tested during normal and below-normal\noccupancies. In baseline systems, urine collected during below-normal\noccupancy had higher pH and greater nutrient losses compared to during\nnormal occupancy. However, during both occupancies, baseline systems\nhad clogs that decoupled occupancy patterns from urine collection\nin the tank and lowered the mass of recoverable P. During both occupancies,\nacid dosing dissolved pre-existing precipitate, resulting in ∼10×\ngreater recoverable P than in baseline systems, and partially stabilized\nurine (>10%) and lowered pH (<9) until ∼7 days of operation,\nsuggesting that urine can be immediately treated once the storage\ntank is full. The results demonstrate that acid dosing can prevent\noperation challenges in UD, improving UD’s technology readiness.