Treatment of formaldehyde-containing wastewater using membrane bioreactor

Abstract

Performance of a membrane bioreactor (MBR) in removal of formaldehyde from synthetic wastewater was investigated. Batch tests for biodegradation of formaldehyde indicated that bioreactors containing acclimated sludge were able to remove up to 99.9% of the formaldehyde from solution. The 12-L MBR was equipped with a submerged hollow-fiber ultrafiltration (UF) membrane with 0.85-m2 filtration area. The unit was operated at a hydraulic retention time of 10 h in aerobic mode with formaldehyde as the sole carbon source for microbial growth. The results revealed that the MBR reduced formaldehyde concentration from 526±30 to a 1.39±0.73-mg/L, corresponding to a removal efficiency of 99.73±0.14%. Increasing solid retention time (SRT) resulted in an increase in mixed liquor suspended solids (MLSS), leading to improved efficiency in removal of formaldehyde from the MBR. Flux decline during MBR operation was caused by accumulation of MLSS on the membrane surface. SRT did not affect flux decline, but did affect flux recovery after cleaning. Long SRT (60 days) led to greater flux recovery than shorter SRTs (30 and 10 days). © 2012 American Society of Civil Engineers.