Chemical cleaning of ceramic ultrafiltration membranes - Ozone versus conventional cleaning chemicals

This study investigates chemical cleaning mechanisms of a tubular ceramic UF membrane. The effect of cleaner type (ozone (O-3), sodium hypochlorite (NaOCl) and sodium hydroxide (NaOH)), clean in place (CIP) pH (11 vs.12), and cleaning sequence on the removal of irreversible fouling of hydrophobic (humic acids) and hydrophilic (alginate with and without calcium (alginate + Ca(+2 )and alginate - Ca+2, respectively)) NOM fractions were investigated. Results showed that different NOM types responded differently to chemical cleaning. Alginate-Ca+2 and humic acids were equivalently removed by NaOCl or NaOH whereas a lower cleaning efficiency of alginate + Ca+2 was observed. Increasing the pH of NaOCl and NaOH CIP increased the removal of the chemically reversible fouling index (UMFIcr). The efficiency of NaOCl was always lower than that of NaOH at the same pH, which was attributed to surface tension (lambda) differences in the CIP water and potential differences in cleaning mechanism. The ceramic UF CIP cleaning using O-3 (0.50 mg O-3/mgC) for 1 h demonstrated higher cleaning efficiency for humic acids and alginate +/- Ca+2, (%UMFIcr > 98%), than NaOCl or NaOH alone (%UMFcr>80%). The O-3 CIP was as effective as 4 h cleaning using a sequential NaOH/NaOCl or combined NaOCl + NaOH CIP. (C) 2019 Elsevier Ltd. All rights reserved.