PHYSICAL, CHEMICAL AND BIOLOGICAL PROPERTIES OF SUBMERGED MEMBRANE BIOREACTOR AND CONVENTIONAL ACTIVATED SLUDGES

Abstract

A pilot-scale submerged membrane bioreactor (SMBR) and two bench-scale conventional activated sludge (CAS) reactors were operated on municipal primary effluent over a range of mean cell residence times (MCRTs) from 2-10 d. The reactors had different turbulence levels. The root mean square velocity gradient (G) of the SMBR was 632 s -1 ; for the CAS reactors the G values were 72 s -1 and 250 s -1 . The sludges from all systems were analyzed for particle size distribution (PSD), colloidal material, extracellular polymer substances (EPS) and filamentous microorganisms. Capillary suction time (CST) and time to filter (TTF) analyses were also performed. The SMBR sludges had the highest amount of small particles and higher levels of colloidal material than the CAS sludges. This was attributed to its higher G value and the use of a membrane for solids-liquid separation. The SMBR sludge contained the higher levels of total filamentous organisms attributable largely to its higher nocardioform level. This resulted from more efficient foam trapping by the SMBR. The normalized CST values of the SMBR sludge were lower than for the CAS sludges. This was attributed to its lower EPS content. There was no significant difference between the normalized TTF values of the SMBR and the CAS sludges. This was attributed to the offsetting effects of colloidal material and EPS contents.