Abstract
This study investigates chemical cleaning mechanisms of a tubular ceramic UF membrane. The effect of cleaner type (ozone (O3), 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 (λ) differences in the CIP water and potential differences in cleaning mechanism. The ceramic UF CIP cleaning using O3 (0.50 mg O3/mgC) for 1 h demonstrated higher cleaning efficiency for humic acids and alginate ± Ca+2, (%UMFIcr > 98%), than NaOCl or NaOH alone (%UMFIcr>80%). The O3 CIP was as effective as 4 h cleaning using a sequential NaOH/NaOCl or combined NaOCl + NaOH CIP.
•O3 CIP (0.50 mgO3/mgC) is an effective cleaning method for ceramic membranes.•O3 CIP is effective at removing hydrophilic and hydrophobic NOM fractions.•NaOCl and NaOH are more sensitive to water quality conditions for cleaning than O3.•1 h of O3 CIP is equivalent to 4 h of combined NaOCl and NaOH cleaning.•Measuring the optimal ozonation conditions (time vs. O3 dose) are required.