Consecutive chemical cleaning of fouled PVC membrane using NaOH and ethanol during ultrafiltration of river water

Chemical cleaning of fouled hollow-fiber polyvinyl chloride (PVC) membrane with the consecutive use of NaOH and ethanol during ultrafiltration of river water was investigated in the study. Results showed that through the chemical cleaning with 1% NaOH for 30 min, a negative cleaning efficiency of −14.6% was observed for the PVC membrane. This might be due to the increase of membrane hydrophobicity, which was reflected by the increase of contact angle from 69.7° to 87.6°. On the other hand, the cleaning efficiency of 85.1% was obtained by the consecutive cleaning with 30 min of 1% NaOH and 30 min of ethanol. Individual ethanol cleaning could remove 48.5% of the irreversible resistance, indicating that NaOH cleaning also made its contribution (36.6%) to the removal of membrane foulants. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) analyses demonstrated that both NaOH and ethanol were not only able to eliminate the foulants on membrane surface, but also able to remove the in-pore fouling of the PVC membrane. The synergetic effects for removing membrane foulants were observed between the NaOH and ethanol. Furthermore, ethanol could also restore the hydrophilicity of the membrane by decreasing the contact angle from 87.6° to 71.4°. Considering that ethanol is easy to be used and reclaimed, the consecutive chemical cleaning by alkali and ethanol is recommended for PVC membrane in filtration of surface water.