Trace carbonyls in water reuse: Structure-dependent multi-barrier penetration and enhanced deep mineralization via...

Organics in reclaimed water can penetrate multi-barrier treatments, compromising high-standard reuses including ultrapure water production, while the underlying processes mechanisms remain poorly understood. This study elucidated the mechanisms governing the penetration of carbonyl compounds through representative multi-barrier treatment trains (RO-UV_185/254-ion-exchange resin) and developed targeted dual-radical oxidation solutions. Low-molecular-weight neutral carbonyls, particularly aldehydes and amides, were the dominant RO-permeating and UV_185/254-IER persistent fractions. Their structural features dominated the resistance: strong polarity and H-bonding capacity explained poor RO rejection, exemplified by 19.29 ∼ 66.25% rejection for amides versus >95% rejection for ionized acids, while low HOMO energy explained oxidation resistance under conventional ^•OH. Under ^•OH oxidation, aldehydes were pathway-limited by downstream carboxylic acid accumulation despite facile initial H-atom abstraction, while amides are activation-limited at polar N-H bonds. Spectral matching at UV₂₂₂/peroxydisulfate generated dual-radical (^•OH and SO₄^•-) that synergistically overcome these limitations: SO₄^•- productivity increased 4.6-fold with 2.19∼12.9 times higher amide reactivity and 1.07∼1.86 times higher aldehydes activity, enabling 6.9∼197 folds faster parent degradation and 13.3∼140 folds faster mineralization at μg·L^-1 levels. Combined experimental-computational validation confirmed dual-radical synergism: ^•OH drive oxidative propagation and conjugated structure formation while SO₄^•- reduced activation barriers for conjugated systems disruption. This dual-radical approach enabled >99.5% mineralization at practical fluences, providing reliable high-standard water treatment solutions.