Simultaneous sludge minimization, biological phosphorous removal and membrane fouling mitigation in a novel plant layout for MBR

The integration of one anaerobic reactor in the mainstream (AMSR) of a pre-denitritication-MBR was evaluated with the aim to achieve simultaneous sludge minimization and phosphorous removal. The excess sludge production was reduced by 64% when the AMSR was operated under 8 h of hydraulic retention time (HRT). The highest nutrients removal performances referred to organic carbon (98%), nitrogen (90%) and phosphorous (97%) were obtained under 8 h of HRT. In contrast, prolonged anaerobic-endogenous conditions were found to be detrimental for all nutrients removal performances. Similarly, the lowest membrane fouling tendency (FR = 0.65∙1011 m−1 d−1) was achieved under 8 h of HRT, whereas it significantly increased under higher HRT. The highest polyphosphate accumulating organisms kinetics were achieved under HRT of 8 h, showing very high exogenous P-release (46.67 mgPO4-P gVSS−1 h−1) and P-uptake rates (48.6 mgPO4-P gVSS−1 h−1), as well as a not negligible P-release rate under endogenous conditions at low COD/P ratio (≈1). [Display omitted] •HRT of 8 h in the AMSR enabled the maximum excess sludge minimization (64%).•AMSR (HRT = 8 h) improved phosphorous removal (97%) and reduced the membrane fouling.•P-release was observed under anaerobic/endogenous conditions at low C/P ratio (≈1).•Cryptic growth favored the simultaneous excess sludge minimization and P removal.•Long anaerobic/endogenous HRTs worsen effluent quality and membrane permeability.