Treatment of high strength industrial wastewater with membrane bioreactors for water reuse: Effect of pre-treatment with aerobic granular sludge on system performance and fouling tendency

[Display omitted] •Both systems showed excellent organic removal with average efficiency equal to 99%.•The AGS pre-treatment did not produce any significant change of biomass activity.•Worsening of membrane filtration properties with the AGS pre-treatment.•High hydrophobicity of the crushed granules promoted the irreversible cake layer.•Higher irremovable resistance development in the AGS + MBR configuration. In this study, the treatment of citrus wastewater with membrane bioreactors (MBRs) under different configurations was investigated for water reuse. In particular, one MBR and one aerobic granular sludge MBR (AGS + MBR) bench scale plants were operated for 60 days. The experimental campaign was divided into two periods. In Phase I, a conventional hollow fiber MBR was employed for the treatment of the raw high strength wastewater, whereas in Phase II a combination of in-series reactors (AGS + MBR) was adopted for the treatment of the high strength citrus wastewater The results demonstrated that both plant configurations enabled very high COD removal, with average values close to 99%. Respirometric batch tests revealed a considerable high metabolic activity of the biomass in both plant configurations, with higher values in the AGS + MBR. It was speculated that the MBR reactor was enriched in active biomass deriving from the erosion of the external granule layers in the upstream reactor. In terms of fouling tendency, higher resistance to filtration was observed in the AGS + MBR plant, also characterized by higher irremovable resistance increase compared to the MBR plant, that might severely affect the membrane service life.