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

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