Pairing Initial and Residual Permeability Loss to Assess Persistent Hydraulic Impairment in Ceramic Nanofiltration

Early permeability decline integrates both recoverable hydraulic effects and persistent membrane impairment, which limits its interpretation as a stand-alone fouling indicator. In this study, we evaluated whether pairing initial permeability loss (IPL) with post-exposure residual permeability loss could distinguish the magnitude and persistence of early hydraulic responses during ceramic nanofiltration. Six water matrices—drinking water, river water, reservoir water, secondary effluent, sodium alginate (SA), and sodium alginate supplemented with calcium (SA+Ca)—were examined using a 60 min early-response window, a defined deionized-water recovery procedure, and 8 h filtration trajectories. Apparent IPL ranged from 2.05% to 76.04%, whereas residual IPL ranged from 1.26% to 41.38%. Across the six matrix means, apparent and residual IPL were strongly associated (R2 = 0.948), while dissolved organic carbon was associated with apparent IPL (R2 = 0.871). Despite nearly identical measured organic carbon concentrations, the SA+Ca formulation showed apparent and residual losses that were 20.28 and 16.34 percentage points higher, respectively, than those of SA. Residual loss also increased progressively with exposure time, indicating that persistent impairment developed within the initial filtration period. Together, paired apparent and residual IPL provide an operational means of comparing early hydraulic-response magnitude and post-recovery persistence across water matrices under fixed membrane and operating conditions.