Comparative bench-scale filterability of pilot-scale activated and aerobic granular sludge effluents: Implication for hydraulic performance and scale-up potential for wastewater reuse

This study investigated bench-scale filterability of pilot-scale activated sludge (AS) and aerobic granular sludge (AGS) effluents, highlighting implications for hydraulic performance and scale-up potential in wastewater reuse applications. AGS improved ultrafiltration (UF) hydraulic performance, achieving higher permeate flux (∼150 L/m²/h) compared to AS (∼90 L/m²/h) due to better sludge settleability and reduced solid carryover in the effluent. Optical coherence tomography (OCT) images confirmed a thinner cake layer on AGS-UF. However, the advantage in UF was not sustained in the downstream nanofiltration (NF) stage, where AGS-NF permeate exhibited a severe flux decline exceeding 90 % (decreased to ∼5 L/m²/h) than that observed for AS (maintained at ∼80 L/m²/h). Scanning electron microscopy (SEM) images confirmed a more compact AGS-NF cake layer. Despite comparable NF dissolved organic carbon (DOC) rejection (∼97 %), liquid chromatography – organic carbon detection (LC-OCD) mass balance indicated greater humic associated substances adsorption onto AGS-NF, highlighting the critical role of effluent organic foulant composition on dense membrane fouling. UF-NF scale-up feasibility was assessed using Water Application Value Engine (WAVE, DuPont), calibrated with feedwater parameter values from the effluents used in the bench-scale analysis. However, the model underestimated AS–UF flux decline and AGS–NF fouling severity, overpredicting membrane overall performance. This discrepancy indicates that conventional simulation tools, even when calibrated with feedwater parameters, fail to capture the complex fouling dynamics. These findings highlight that upstream biological treatment selection critically governs downstream membrane fouling, providing practical guidance for optimizing AGS-based hybrid systems. Integrating experimentally validated insights into design and simulation tools will enable more reliable and sustainable scale-up of UF–NF processes for municipal wastewater reuse.