Performance deterioration and structural changes of a ceramic membrane bioreactor due to inorganic abrasion

In the present study a pilot-scale ceramic membrane bioreactor (MBR) system was used for the treatment of simulated municipal wastewater. With the int roduction of excess phosphorus to the bioreactor, a gradual deterioration o f the membrane filtration performance and eventual failure of the pilot sys tem was observed. A detailed investigation performed on the mixed liquor sh owed that phosphorus related calcium and magnesium complexes accumulated in the bioreactor. Under excess phosphorus conditions, these crystals caused abrasion of the membrane active filtration layer, leading to higher permeab ility, extensive membrane fouling, and eventual replacement of the membrane unit. A thorough comparison was conducted between the deteriorated membran e and a new module, using X-ray Diffraction (XRD), mercury and gas adsorpti on porosimetry, scanning electron microscopy (SEM), and electron dispersive X-ray (EDX). Porosimetry tests clearly demonstrated that the effective por e size of the deteriorated membrane shifted to higher values. SEM and EDX a nalysis showed that the active filtration layer composed of zirconia was sh eared off entirely. Trace amounts of calcium were detected on the top layer , verifying calcium related abrasion of the filtration surface. (C) 1999 El sevier Science B.V. All rights reserved.