A Unit Process Approach to Nontarget Screening of Organic Contaminants during Urine Treatment

Abstract

Urine treatment has expanded over the past few decades; however, widespread implementation requires rigorous, generalizable comparisons between selective nutrient separation and organic compound mitigation. This study describes and demonstrates an enrichment ratio framework, defined as the relative concentration changes of nutrients (nitrogen or phosphorus) with organic compounds analyzed via high-resolution mass spectrometry. Nontarget analysis enabled comparison of the effects of urine treatment processes (e.g., ion exchange, freeze–thaw, activated carbon, struvite precipitation) on organic compounds. In total, we considered 14 treatment scenarios, including six unit processes for acidified urine and eight for hydrolyzed urine. Acidified and hydrolyzed urine were characterized longitudinally, and each of the two urine types remained stable in terms of the organic compound profile (>79% similarity) over several weeks. Unit processes with mean enrichment ratios (ER) that involved more than a 2-fold concentration change (ER > 2 or ER < 0.5) were considered high priority and were further separated into cases in which organic compounds were concentrated (ER > 2) or removed (ER < 0.5) for various unit processes. Whereas ER values are typically calculated only for compounds present in both the influent and effluent streams, we also analyzed compounds that were detected in only influent or only effluent added. Results from the target analysis of six compounds generally corroborated the nontarget results. Ultimately, our approach to simultaneously characterizing both nutrients and organic compounds through urine processing steps can inform and advance the implementation of urine resource recovery.