Permeability and clogging in an immersed hollow fibre membrane bioreactor

A pilot-scale hollow fibre immersed membrane bioreactor (HF iMBR) fed with municipal wastewater was operated under conditions pertaining to those at full-scale to assess the impact of clogging by gross solids on permeability. The study proceeded by operating for ∼22 h periods at two different fluxes with regular backflushing, and the accumulation of solids within the fibre bundle determined through their mechanical removal and gravimetric measurement. Permeability recovery, along with the fouling rate during sludging, from this complete “declogging” was compared with that from conventional maintenance cleaning from chemically enhanced backflushing (CEB).Results revealed declogging to contribute significantly to permeability recovery, but the comparable impact of the CEB alone revealed fouling to also be important. However the rate of transmembrane pressure increase, normally termed the “fouling rate”, was found to strongly correlate with the mass of accumulated solids, suggesting that clogging suppression is important in maintaining permeability overall during HF iMBR operation.

► Relative efficacy of cleaning protocols on permeability recovery of HF iMBR studied.
► Significant heterogeneity of solids accumulation (clogging) between membrane elements.
► Operating pressure increased at 17–25 mbar/h/kg/m2 of clogged solids on average.
► Excessive clogging at higher fluxes associated with decline in absolute permeability.
► Clogging estimated to occlude >20% of available area of most clogged membrane element.