Chemical cleaning of nanofiltration membrane filtrating the effluent from a membrane bioreactor

Fouling and decline in membrane performance are inevitable during the application of nanofiltration (NF), and cleaning is a vital and effective way to restore membrane performance. In this study on-line and off-line cleaning were investigated to maintain the performance of NF membrane filtrating the effluent from a membrane bioreactor. X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and contact angle analysis were used to characterize the membrane surface for the purpose of choosing proper cleaning agents and assessing the effects of cleaning agents. NaOH was chosen to be the on-line chemical cleaning agent based on the cleaning efficiency compared to other agents tested. After operated at on-line chemical cleaning mode for 24h membrane was fouled by P, Mg, Fe, Ca from the results obtained by XPS and organic/amino acids from the new absorbance peaks at wave numbers of 2800-3000cm(-1), 1750cm(-1) and 1640cm(-1) obtained by FTIR. Off-line chemical cleaning was performed using citric acid and NaOH in sequence. Acid cleaning was effective for removing P, Mg, Fe, Ca while NaOH cleaning was effective for removing organic/amino acids. The peak strength at wave numbers of 2800-3000cm(-1), 1750cm(-1) and 1640cm(-1), as well as the contact angle, increased after acid cleaning, indicating there might be a coating of inorganic salts on organic foulants, which needed to be removed first so that organic foulant could make good contact with NaOH. (C) 2010 Elsevier B.V. All rights reserved.